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Published as doi: 10.1096/fj.07-8697rev.
 (The FASEB Journal. 2007;21:3795-3808.)
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Reverse transcription of the HIV-1 pandemic

Aravind Basavapathruni1 and Karen S. Anderson2

Yale University School of Medicine, Department of Pharmacology, New Haven, Connecticut, USA

2Correspondence: Yale University School of Medicine, Department of Pharmacology, SHM B350B, 333 Cedar St., New Haven, CT 06520-8066, USA. E-mail: karen.anderson{at}yale.edu


   ABSTRACT
TOP
 ABSTRACT
HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 
The HIV/AIDS pandemic has existed for >25 years. Extensive work globally has provided avenues to combat viral infection, but the disease continues to rage on in the human population and infected ~4 million people in 2006 alone. In this review, we provide a brief history of HIV/AIDS, followed by analysis of one therapeutic target of HIV-1: its reverse transcriptase (RT). We discuss the biochemical characterization of RT in order to place emphasis on possible avenues of inhibition, which now includes both nucleoside and non-nucleoside modalities. Therapies against RT remain a cornerstone of anti-HIV treatment, but the virus eventually resists inhibition through the selection of drug-resistant RT mutations. Current inhibitors and associated resistance are discussed, with the hopes that new therapeutics can be developed against RT.—Basavapathruni, A., Anderson, K. S. Reverse transcription of the HIV-1 pandemic.


Key Words: resistance • nucleoside • non-nucleoside • AIDS • NRTI removal


   HISTORY AND EPIDEMIOLOGY
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 
THE CLINICAL OCCURRENCE OF AIDS EMERGED between late 1980 and early 1981 when a group of five men inexplicably presented with Pneumocystic carinii pneumonia (PCP) (1) . PCP is a rare opportunistic infection that appeared in people with extremely compromised immune systems attributable to cancer or immunosuppressive drugs. PCP was so rare that treatment consisted of an experimental drug that only the U.S. Centers for Disease Control and Prevention (CDC) could administer. Two of these men died within months; another 10 cases of PCP infection soon developed. Shortly after these cases of PCP infection, another set of men presented with the rare skin cancer Kaposi’s sarcoma (KP) (2) . As with the PCP infections, the root cause of KP infections was unknown.

These cases of PCP and KP infections were not isolated; many more cases of PCP and KP arose (3) , which prompted the CDC to set up a task force to monitor the outbreak of infections (4) . Other infections were soon observed and a pattern of anomalies developed in these infected patients: low CD4+ cell count (which suggested that T cells may be a target of infection), lymphadenopathy (swelling of the lymph nodes), and infection by opportunistic diseases. The condition was soon named acquired immunodeficiency syndrome (AIDS). However, the underlying progression of AIDS was not understood.

Two years later, Gallo et al. discovered that a novel virus may have infected these individuals (5 , 6) . Gallo and his group isolated a virus from the peripheral blood T cells of a patient with AIDS; this virus had a morphology similar to that of human T cell leukemia virus (HTLV) and other type-C retroviruses. Antibodies to viral core proteins p19 and p24 recognized similar proteins from the AIDS virus, which suggested that the AIDS virus belonged to the family of HTLVs; at that time HTLVs consisted of HTLV-1 viruses and the newly discovered HTLV-II. The virus could also be transferred from one mature T cell line to another, and reverse transcriptase (RT) activity was detected in both the donor and recipient cell lines. Gallo would name his isolate HTLV-III. Concomitantly, Montagnier and colleagues isolated a virus from a patient with cervical lymphadenopathy and asthenia, and showed that the core proteins from this virus were not immunologically related to p19 and p24 of HTLV-1 (6) , which contradicted what Gallo et al. had observed. RT activity was observed in Montagnier’s patient sample, and labeling with [3H]uridine illustrated that the new AIDS virus was a retrovirus. Montagnier would call his isolate LAV (lymphadenopathy-associated virus).

Another name was added to the likes of HTLV-III and LAV. Levy et al. established a T cell line from infected individuals in San Francisco (7) . These cultures independently confirmed the findings of Montagnier, but without a direct comparison with LAV, this isolate was further distinguished by its own name: ARV-2 (AIDS-associated retrovirus).

Soon after, phylogenetic studies and replication cycle analysis showed that the AIDS virus was unrelated to HTLV. Rather, it was related to other members of the lentivirus genus of the Retroviridae family of viruses. The isolates of Gallo, Montagnier, and Levy would collectively be named human immunodeficiency virus (HIV) to signify its relationship with other members of its lentivirus family. The focus in this review from here on will concentrate on HIV type 1 (HIV-1), but related strains of HIV, HIV-2 (discovered in Africa), and SIV-1 (simian immunodeficiency virus type 1, which affects nonhuman primates) do exist.

The inception of HIV-1 marked the beginning of the HIV/AIDS pandemic. As of December 2006, the World Health Organization estimated that 40 million adults and children were infected with HIV; 25 million of those infected resided in Africa and >1 million in North America. What is more sad, 3 million deaths occurred globally in 2006 as a result of HIV and AIDS.


   LIFE CYCLE OF HIV-1 AND THERAPEUTIC TARGETS
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 
Attempts to combat the global pandemic begin with understanding viral replication and disease progression. Like other retroviruses, the genome of HIV is single-stranded RNA. The genome is ~10 kb long (8) and codes for 15 proteins (9) . Three coding regions of the genome are the env, pol, and gag genes, each of which provides critical proteins for viral replication. The remaining HIV-1 genes are just as critical for viral replication.

The env gene encodes the envelope proteins that are necessary for viral fusion to host cells. For HIV, the env gene encodes a 160 kDa glycoprotein, and cleavage of this precursor by cellular proteases yields the functional gp120 and gp41 proteins (10 11 12) that noncovalently bind to form a trimer of heterodimers (13) . These critical proteins initiate virus replication, as gp120 binds to the CD4 molecule on the surface of CD4+ T cells. This binding event causes a conformational change in gp120, which exposes a secondary site for binding to a coreceptor on the host cell (either CCR5 or CXCR4). Secondary binding by gp120 causes dissociation of gp41 from the complex, and gp41 subsequently inserts itself into the host membrane and creates the point for viral entry.

Once the virus penetrates the host cell, the protein products of the pol and gag genes exert their control over host-cell machinery. The pol and gag genes encode a gag-pol precursor protein (by overlap of the two open reading frames) that is subsequently cleaved by the viral protease to generate various essential proteins: structural proteins, including the nucleocapsid, capsid, and matrix proteins; and the viral enzymes (protease, reverse transcriptase, and integrase). The structural proteins encapsulate the viral genome and essential proteins during virus maturation and generation; the viral reverse transcriptase copies the single-stranded RNA genome to a double-stranded DNA genome and uses both RNA and DNA as templates for DNA synthesis (14) . Incorporation of this double-stranded viral copy into the host cell’s genome is catalyzed by the viral integrase (15 , 16) . Protein products that result from transcription and translation of the viral genome are processed by the viral protease (17) , which generates a new batch of proteins that will form the new virion. Along with accessory viral proteins, the processes just described hijack the host-cell machinery and initiate pathogenic mechanisms of apoptosis (18) . An abbreviated schematic of the virus’s life cycle is illustrated in Fig. 1 .


Figure 1
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  		Figure 1. The HIV-1 life cycle. HIV fuses to host cells via the CD4+ receptor and coreceptors (see text). Upon fusion, the RNA genome and viral proteins are released into the cell. Reverse transcription occurs to form a double-stranded DNA copy of the genome (step 1), which translocates and integrates into the host genome (step 2). Viral protein expression occurs and precursors are protealytically cleaved by the viral protease (and host proteases) to form functional proteins (step 3). These new proteins are packaged into a new virion, which is subsequently released to infect a new host cell.

During the initial phase of HIV infection, viral load quickly increases and the CD4+ cell count falls from normal levels, which are ~1000 ± 400 cells/mm3 (17) . After this period of acute infection, viral load falls and reaches a set point. The infection of new CD4+ cells and subsequent generation of virus progeny accounts for virus production that can occur at a rate of 1 x 1010 virions per day (19 , 20) . Without treatment, the population of CD4+ cells will slowly decrease; this intermediate phase of infection can last from months to years. Opportunistic infections may surface as host defenses decline. The clinical progression from HIV infection to AIDS occurs when CD4+ levels decline to 200 cells/mm3. The viral load rebounds to the levels observed in the acute phase of infection; without therapeutic intervention, secondary opportunistic infections and death can occur (17) .

The speed with which HIV-infected individuals progress to AIDS and the occurrence of AIDS-associated fatalities have diminished with the advent of anti-HIV therapeutic agents. Inhibitors have not cured the disease but have improved the quality of patient lives and decreased the mortality rate. Thousands of reports have now addressed HIV inhibition, and so far 29 different drug regimens have been approved by the U.S. Food and Drug Administration to treat HIV. Briefly, 11 agents were approved between 1995 and 2006 to inhibit the viral protease. Seventeen agents that target the essential viral RT were approved between 1987 and 2006; these agents are subdivided into nucleoside and non-nucleoside families. Approved in 2003, enfuvirtide (T-20; Fuzeon®) is a peptide derived from amino acids 643–678 of HIV gp160. It prevents viral fusion by interfering with cell penetration by gp41 (21) .


   REVERSE TRANSCRIPTION
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 
Because HIV was found to be a retrovirus, it must encode an enzyme (RT) in order to copy the genomic RNA to integrate into the host’s DNA. The concept of reverse transcription was not initially accepted when RNA-dependent DNA polymerization was discovered (22 23 24) , because it crossed the central dogma that genetic expression progressed from DNA to RNA. The discovery that HIV possessed RT activity (5 , 6) has opened the field of understanding HIV reverse transcription and the development of RT inhibitors.

HIV-1 RT activity and protein expression were first characterized by Rey et al. (25) . Their study established that the enzyme responsible for retroviral replication was capable of using RNA as a substrate, generated DNA as a product, and used Mg2+ as its divalent cation (much like the RT isolated from HTLV I; ref. 26 ). As stated earlier, RT is encoded by an open reading frame that overlaps the gag and pol genes of the viral genome. Although the gene product forms a functional polymerase, immunoblots of sera from HIV-infected patients showed that a full-length construct (66 kDa in size) was repeatedly purified with another peptide 51 kDa in size (27 , 28) . Moreover, the p66 and p51 peptides shared NH2-terminal sequences, which suggested that the shorter p51 peptide arose from C-terminal cleavage. The viral protease was later shown to cleave the p66 peptide, which formed the p51 subunit (29 , 30) . It is the p66/p51 heterodimer that acts as the functional RT (31 , 32) . The viral protease catalyzes the cleavage event, cleaves 50% of the p66 peptide to p51 (33) , and is followed by heterodimer formation. It could be postulated that cleavage would occur on a p66/p66 homodimer. Lowe et al. showed that cleavage on a homodimer molecule occurs only on one subunit, which suggests that one subunit protects the other from cleavage or that both subunits bind asymmetrically (31) . However, the association rate of homodimer formation is slow and occurs with low affinity, while the dissociation constant of heterodimer formation is below 1 nM, which suggests that cleavage occurs before dimer formation (34) . Furthermore, RTs from retroviruses are known to have two catalytic activities: DNA polymerization and an associated RNase H activity (RNA/DNA heteroduplex RNA degradation) (35 36 37) . The formation of a p66/p51 functional heterodimer for HIV-1 RT evoked questions as to whether p66 and/or p51 possessed both DNA polymerase and RNase H activities. Work from Restle et al. and Le Grice et al. showed that p51 alone has little or no polymerase activity (34 , 38) , and others have shown through mutagenesis and antibody detection that RNase H resides at the C terminus, and thus only in the p66 domain (39 , 40) . These data together highlight the functional significance of p51: it is a cleavage product of p66 that loses its RNase H domain and also lacks DNA polymerization catalytic activity. The heterodimerization of p66 and p51 therefore suggests an asymmetric dimer and suggests that p51 may act as an accessory protein for p66. Heterodimerization itself is currently being pursued as a therapeutic target; see Camarasa et al. for a review (41) .

Structural evidence has similarly offered insight into RT catalysis and has shown that p66 and p51 are not symmetric in the heterodimer (42) . The first crystal structure of HIV-1 RT showed that conformations of p66 and p51 are indeed different, most notably with respect to the active-site aspartic acids: solvent accessible in p66 and buried in p51. This first structure highlighted the structural similarities between the p66 domain and the polymerase domain of the Klenow fragment of Escherichia coli DNA pol I and led to the description of p66 as a "right hand," with domains named accordingly—fingers, palm, and thumb (Fig. 2 ). Structures subsequently solved for a binary complex with DNA (43) and the ternary complex with the liganded enzyme (44) have revealed the conformational changes that RT undergoes. The finger and thumb domains interact in the unliganded enzyme; binding of DNA to unliganded RT results in the "open" state and disrupts the fingers/thumb interaction. dNTP binding causes the fingers domain to close in toward the palm, such that DNA is locked in position and active-site residues (see below) can coordinate the incoming nucleotide. The structure from Huang et al. is most illustrative in structural analysis (44) . The structure of a ternary complex (RT; primer/template; dNTP) was solved through use of a strategy of cross-linking the primer/template to the enzyme via a disulfide bond (45) in order to prevent the enzyme from binding to nonpolymerizable sites on the DNA. Based on similarities between their structure and other known polymerase structures, it was the assertion of Huang et al. that cross-linking did not perturb the complex. In addition to cross-linking, the primer terminus was chain-terminated with a dideoxynucleotide, which prevented nucleophilic attack onto the incoming dNTP. At the polymerase active site, the dNTP (dTTP) is coordinated by many protein residues (Fig. 3 ). The triphosphate is coordinated by Lys65, Arg72, the main-chain amino groups of Asp113 and Ala114, and by the catalytic magnesium ions. The thymine base stacks on the primer terminus and the 3'-hydroxyl group probes a small pocket lined by Asp113, Tyr115, Phe116, and Glu151. It also accepts hydrogen bonding from the main-chain amino group of Tyr115. These interactions with the enzyme highlight potential directions for inhibitor design, but just as important, they demonstrate sites at which RT can simply evade inhibition.


Figure 2
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  		Figure 2. Ternary structure of HIV-1 reverse transcriptase in complex with primer/template and dNTP (using coordinates from Huang et al.) The enzyme consists of two subunits, p66 and p51 (resulting from proteolytic cleavage of p66). The p66 and p51 monomers are shown in green and blue, respectively. Primer/template is indicated in white and dTTP is orange. Domains constructing the "right hand" are indicated. The dotted circle encompasses the binding pocket of non-nucleoside RT inhibitors.


Figure 3
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  		Figure 3. Active site of HIV-1 reverse transcriptase. crystallization of the ternary complex was accomplished by cross-linking DNA to RT via a disulfide linkage. The primer terminus was chain terminated with ddGTP to prevent polymerization. Coordination with Mg2+ ions is observed along with interacting protein residues. From Huang et al., Science, vol. 282, pp. 1669–1875, 1998; reprinted with permission from AAAS.

Resistance to inhibition (discussed in detail later) originates from genome replication by RT. RT replicates the RNA genome to generate an RNA/DNA heteroduplex, and RT’s RNase H degrades the RNA and RT then copies the remaining single-stranded DNA to a double-stranded copy in preparation for host-cell genome integration. The fidelity of polymerization catalyzed by RT is measured at ~1 error every 2000–5000 polymerized nucleotides (46 47 48 49) . A brief comparison illustrates that this fidelity is only 10-fold lower than replication exhibited by spleen necrosis virus and bovine leukemia virus (49) , and is similar to that of avian myeloblastosis virus and DNA polymerase β (46) . It is, however, much lower than DNA polymerases {delta} and {gamma}, each of which has the ability to proofread. However, HIV-1 RT lacks an exonuclease domain and therefore lacks the ability to proofread; mismatched nucleotides are passed over and replication ensues. Considering that RT performs both RNA-directed and DNA-directed DNA synthesis of the viral genome, the error rate translates to ~5–10 mutations per round of replication. Accompanied by the high rate of viral replication of 1 x 1010 virions per day (19 , 20) , the hypermutability of new virions and the notion that "quasispecies" of HIV exist in an infected individual can be well appreciated. One outlook on this "acceptance" of mismatches by RT is the development of nucleotide analogs that would mimic natural nucleotides, incorporate during polymerization, and inhibit viral replication.


   NUCLEOSIDE RT INHIBITORS
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 
Inhibitor development began as characterization of HIV-1 was taking place. With the observation that the virus encoded its own polymerase, RT inhibitor development began and active inhibitors were formulated within a few years of HIV discovery. The first inhibitor that received much attention was AZT (Fig. 4 ), which was approved by the FDA in 1987. In one cell system, it showed antiviral potency at 5 µM with no associated cytotoxicity (50) ; cell supernatants from virus-infected cells treated with AZT showed that RT activity decreased upon drug treatment. Inhibition by AZT could be attenuated by thymidine, which suggested that AZT or a metabolite of AZT competed with thymidine (or a metabolite of thymidine). Furman et al. argued that the triphosphate of AZT exerted its inhibitory potential (51) . Chromatographic analysis of an extract of HIV-infected cells treated with AZT showed that AZT, and its monophosphate, diphosphate, and triphosphate were all present. Thymidine kinase was shown to catalyze the first phosphorylation, and thymidylate kinase phosphorylated the monophosphate. Nucleoside diphosphate kinase would later be shown to catalyze the formation of the triphosphate; the triphosphate inhibited RT activity, which specifically competes with dTMP incorporation (52 , 53) . In comparison, AZTTP inhibited human DNA polymerases {alpha} and β to a lesser extent than HIV RT (51 , 54) . The presence of the azido group in AZT presumably would serve to chain-terminate DNA synthesis catalyzed by RT, and this was supported by findings that the rate of AZTMP incorporation decreased with time (54) . Ensuing work demonstrated this chain termination, and the competition of nucleoside RT inhibitors with natural dNTPs yields their therapeutic value (55) .


Figure 4
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  		Figure 4. Structures of FDA-approved nucleoside RT inhibitors. For comparison, structures of natural deoxynucleosides are shown.

Soon thereafter, activity of dideoxynucleosides (the sugar ring that lacks both 2' and 3'-hydroxyl groups) was studied. A panel of dideoxynucleosides was examined and showed that ddC (Fig. 4) was quite effective in protecting cells from viral killing; in addition, dideoxynucleosides ddA, ddG, ddI (dideoxyinosine, Fig. 4 ) also rescued cells from viral death, but ddT was less protective (56) . The unexpected lack of activity for ddT may be attributed to the phosphorylation of these compounds: different cell lines phosphorylate dideoxynucleosides differently (57 , 58) . Indeed, ddT is phosphorylated poorly relative to ddC (56 , 59) . ddI and ddC were approved in 1991 and 1992, respectively. Further modification of the dideoxy framework led to development of d4T (2',3'-didehydro-3'-deoxythymidine, Fig. 4 ). Activity of d4T was shown to be similar to that of AZT (60 61 62) , although the phosphorylation patterns of d4T and AZT are different (63 , 64) ; the affinity for AZT to thymidine kinase (the enzyme responsible for the first phosphorylation) is similar to that of thymidine, whereas the affinity for d4T is ~700-fold weaker. This results in different distributions of phosphorylated species between AZT and d4T. AZTMP accumulates in the cell (due to a decreased rate of phosphorylation by thymidylate kinase; see ref. 51 ) whereas nucleoside d4T builds up (63) . Thus, the rate-limiting step in activating these thymidine analogs is different. Yet at the final step of RT polymerization, incorporation of AZTTP and d4TTP has been shown to be similar to dTTP incorporation (65 66 67) .

Although the potency of nucleoside analogs rests in their ability to mimic and compete with natural nucleosides, the field of RT inhibition changed course when it was discovered that L-nucleosides could also offer inhibition. Most notably, the inhibitor (–)3T (Fig. 4) was originally developed as a racemic mixture of positive and negative isomers. The racemic mixture showed antiviral activity against both HIV-1 (68) and hepatitis B (69 70 71) . Enantiomeric-selective chemical synthesis and chiral chromatography yielded chirally pure isomers, and it was shown that the (–) isomer of 3TC was not only more potent than the (+) isomer but also less toxic (68 , 72 73 74) . The positive isomer has been shown to be a substrate of deoxycytidine deaminase, and therefore it has a shorter half-life in cells (74 , 75) . Further study into structure-activity relationships of (–)3TC congeners has led to the development and approval of (–)FTC (Fig. 4) . As with its unfluorinated counterpart, (–)FTC is more potent and less toxic than its positive isomer (76) , and shows improved antiviral activity compared to (–)3TC (77) . Furthermore, kinetic studies from our lab have shown that RT incorporates (–)FTCMP more efficiently than (–)3TCMP due to increased affinity for (–)FTCTP (77) .

The last two FDA-approved nucleosides we will briefly discuss here are the carbocyclic abacavir and the acyclic phosphonate of tenofovir (Fig. 4) . Abacavir, by way of its carbocyclic sugar moiety, evades the labile glycosidic bond cleavage that is typical of dideoxynucleosides (78) . After phosphorylation by adenosine phosphotransferase, abacavir is deaminated by a cytosolic deaminase to yield carbovir monophosphate, which is subsequently phosphorylated to the active carbovir triphosphate (79) . The acyclic nucleoside phosphonate tenofovir (also known as PMPA) circumvents the first phosphorylation, which is required by other nucleoside analogs (80 , 81) . A prodrug version of tenofovir has been used to increase oral bioavailability as a result of the negative charges carried by the phosphonyl group (82 , 83) .

The effectiveness of nucleoside analogs rests not only in their potency against RT, but how well they avoid inhibiting host polymerases. Their similarity with natural dNTPs produces undesired toxic effects, which have been demonstrated in enzymatic assays (84 85 86 87) , cell culture, and in the clinic. The accepted hypothesis for host toxicity is that these analogs are incorporated into mitochondrial DNA by mitochondrial DNA polymerase {gamma} (pol {gamma}) (88 89 90) . Pol {gamma} is the sole enzyme for mitochondrial DNA synthesis; therefore, inhibition with NRTIs will have drastic effects. Clinical manifestations include lactic acidosis, peripheral neuropathy, depression, and pancreatitis (88 , 91) . Of note, mitochondrial toxicity due to the nucleoside FIAU (1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodouracil) resulted in severe lactic acidosis and death (92 , 93) . Studies from our lab and others have shown that pol {gamma} incorporates and removes (by way of its exonuclease activity) these analogs (84 , 94 95 96) , and thus NRTI design must weigh in contributions of toxicity from mitochondrial DNA polymerase {gamma}.


   NUCLEOSIDE RT INHIBITOR RESISTANCE
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 
Soon after nucleoside analog therapy was considered and approved for HIV-1 therapy, insensitive viral isolates were collected from patients receiving AZT (97) . This insensitivity to AZT emerged after only 6 months of therapy and was specific to AZT, as these isolates remained susceptible to ddC and d4T. The authors suspected that the insensitivity originated from mutations from RT (98) , but testing of virion-associated RT showed that AZT inhibited wild-type and post-AZT-treated RTs with similar ID50 values. This demonstrated a similar affinity for AZT by wild-type and mutant but did not rule out differential incorporation by mutant isolates. Sequencing of AZT-treated isolates would later show that mutations within RT were indeed enabling HIV to resist AZT inhibition (99) . These mutations were D67N, K70R, T215F/Y, and K219Q. A fifth mutation was added to this complex (M41L), which added to high-level AZT resistance (100) . Initial kinetic experiments designed to quantitate Michaelis-Menten constants for AZTTP incorporation showed that wild-type and AZT-resistant (AZTR) RT incorporated AZTTP equally (99) . Subsequent pre-steady-state experiments in our lab showed only a slight decrease in AZTTP incorporation by the AZTR mutant (65 , 67) . Altogether, these findings point to another mechanism that confers resistance.

AZT mutations would be shown to also confer clinical resistance to d4T (101 102 103 104 105) . These mutations were coined with the name TAMs for thymidine-associated mutations, but have proved to be a considerable roadblock for all currently approved NRTIs (106) . Treatment in cell culture with d4T has also led to development of the V75T mutation, though only low-level resistance is observed (107) .

Resistance to the other nucleoside agents has been observed and is nicely summarized by Johnson et al. (106) . The M184V/I mutation develops within weeks of (–)3TC treatment and causes high-level resistance by way of decreased binding affinity to the triphosphate (108 109 110) . Met184 is part of the YMDD motif common to retroviral RTs (110) , and mutation to valine or isoleucine has also been observed in HBV polymerase (Met204) in response to antiviral treatment (111 , 112) . The Q151M complex of mutations (Q151M, A62V, V75I, F77L, and F116Y) confers high-level resistance to all NRTIs except tenofovir (113 114 115) , and the Q151M mutation itself shows decreased susceptibility to AZT, d4T, and ddC (113 , 116) . Other notable NRTI mutations include K65R, L74V, and L210W (106) .

NRTI mutations have been studied by our lab and others for their effect on nucleoside analog incorporation; our work and that of others have communicated changes in the rate of incorporation and/or binding affinity (as shown above). Work from the lab of Walter Scott has shed new light into resistance mediated by RT. Serendipitously, his lab found that RT could remove chain-terminating analogs (117) . The mechanism was nucleotide dependent and involved attack at the phosphodiester bond between the primer and analog at a site proximal to the active site (Fig. 5 ). Multiple nucleotides were assayed to determine which might be relevant in vivo, and data suggested that ATP may be relevant since the Km of ATP in removal was below the physiological concentration of ATP (117 , 118) . Arion et al. concurrently showed data that support a role for PPi (pyrophosphate, a product of analog incorporation) in mediating removal (119) . Removal occurs only in the presence of enzyme, which illustrates that RT orients and poises ATP or PPi for this nucleophilic attack. Subsequent studies from these labs and others would support a role for PPi and/or ATP in mediating AZT resistance (120) , as AZT -resistant mutants more efficiently removed AZTMP than WT enzyme in the presence of PPi or ATP (119 , 121 122 123 124) . These accumulated data, however, have not quantitatively supported a role for either PPi or ATP in mediating removal and how each may contribute to conferring AZT resistance.


Figure 5
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  		Figure 5. Model for AZTMP removal and effect of next correct dNTP. A) Nucleophilic attack by ATP to the phosphodiester bond (P) liberates the primer from chain termination and allows for continued DNA synthesis by RT. B) Incorporation of AZTTP leads to chain termination of the primer strand (cyan) by AZTMP (Z-N3). Translocation to allow the next correct dNTP (yellow) to bind results in formation of the dead-end complex, as neither incorporation (because AZTMP chain terminates) nor removal can occur (since AZTMP translocating to the "P" site is no longer accessible to removal). Equilibria shifts that allow for AZTMP to occupy the "N" site permit ATP-mediated removal (ATP shown in orange; trisphosphate of ATP shown in blue). Adapted by permission from Macmillan Publishers Ltd: EMBO J., Sarafianos et al. © 2002

Meyer et al. found that although ATP, dATP, GTP, dGTP, CTP, and dCTP could mediate removal, dTTP inhibited removal (117) . In the context of their primer/template, dTTP was the next complementary nucleotide to bind after incorporation of the chain terminator. This finding suggested that after incorporation of the chain terminator, RT translocates to allow the next correct nucleotide to bind at the active site (Fig. 5) and forms what is now deemed the "dead-end complex"; that is, the chain terminator has moved beyond the active site and neither incorporation nor removal can occur. This phenomenon has led to designation of these sites where the primer terminus lies: the P site (priming site) and the N site (nucleotide binding). Removal can only occur if the chain terminator is situated at the N site; thus, the extent to which the next correct dNTP binds will govern when the chain terminator can access the N site and thus the amount of removal.

Therefore, resistance to nucleoside analogs rests not only in how RT modulates their incorporation, but how RT persists in evading inhibition by removing chain termination.


   NON-NUCLEOSIDE RT INHIBITORS
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 
As nucleoside development progressed, the field of non-nucleoside discovery began during the late 1980s and progressed quickly into the 1990s and present-day research. Data on two initial compounds,1-[(2-hydroxyethoxy)methyl]-6-(phenylsulfanyl)thymine (HEPT) and 4,5,6,7-tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-2(1H)-thione (TIBO) (TIBO shown in Fig. 6 ), were published during this initial phase of discovery, and each showed activity against HIV-1 (125 126 127 128) . Surprisingly, these compounds showed selectively against HIV-1, with no activity vs. HIV-2, SIV (simian immunodeficiency virus), FIV (feline immunodeficiency virus), and a host of other viruses. The lack of activity against HIV-2 was surprising since HIV-1 and HIV-2 are related viruses, but solving the 3-dimensional structure of HIV-1 RT with nevirapine, another NNRTI similar in structure, revealed the inhibitory binding site of non-nucleoside inhibitors and offered insight into a fundamental biochemical difference between these two viruses and the lack of inhibition against HIV-2 (the inducible NNRTI pocket does not exist in HIV-2 RT).


Figure 6
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  		Figure 6. Structures of NNRTIs. 8-Cl-TIBO was an early generation inhibitor. Second and third generation inhibitors include UC-781 and the TMC compounds TMC125 and TMC278. Nevirapine, delavirdine, and efavirenz are FDA approved non-nucleosides.

Following these two compounds, Merluzzi et al. used screening methods initially based on muscarinic receptor antagonists to develop BI-RG-587 (129) , which was later approved as the first non-nucleoside inhibitor (Nevirapine, Viramune®, Fig. 6 ). As with HEPT and TIBO, nevirapine inhibited viral RT activity that showed noncompetitive inhibition with respect to dNTP binding. This illustrated that this new class of anti-HIV inhibitors was inhibiting RT activity but not at the active site. Subsequent screening and evolution of many molecules have led to many classes of non-nucleosides, which have been reviewed by De Clerq and Balzarini (130 , 131) .

The first crystal structure of HIV-1 RT was solved with bound nevirapine (42) , and although some preliminary evidence was known about how nevirapine inhibited polymerization, this structure immediately gave insight into a mechanism (or mechanisms) of inhibition. Nevirapine was observed at the pocket between the thumb and palm domains of the enzyme and resided within ~ 10 Å of the active site (Fig. 2) . Based on this binding, two possible mechanisms for nevirapine inhibition were postulated at that time. First, the NNRTI could be locking the enzyme in a conformation that prevented movement of the thumb and palm domains and effectively stopping catalysis. The second possibility was that, by binding in the vicinity of the active site, NNRTI could allosterically affect catalysis by changing the conformation of key residues. A third possible mechanism was soon offered. Ding et al. suggested that NNRTI binding alters the primer grip of the enzyme and repositions the primer within the active site. It is noteworthy that nevirapine, as observed with other RT/NNRTI crystal structures (132 , 133) , resembles a butterfly within the binding pocket. The two aromatic wings of nevirapine conform within the enzyme to resemble the wings of a butterfly. The NNRTI binding pocket is shown in Fig. 7 .


Figure 7
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  		Figure 7. HIV-1 reverse transcriptase non-nucleoside binding pocket. Key residues involved in inhibitor binding are noted. Note the "butterfly" conformation of nevirapine (colored in yellow) within the pocket (using coordinates from Kohlstaedt et al.).

The information that RT/NNRTI structures yielded did not shed absolute light on the mechanism of inhibition by these inhibitors. More detailed kinetic analyses allowed a better understanding of the NNRTI mode of inhibition. Because nevirapine was shown to inhibit polymerase activity, it could conceivably interact with different forms of the enzyme: free RT, RT bound to primer/template, and/or RT bound to primer/template and dNTP. Initial steady-state kinetic analyses suggested that the inhibition occurred in a noncompetitive manner (126 , 129 , 134 135 136 137 138 139) . Subsequent studies with several analogs that are structurally similar to nevirapine implied that all three forms of the enzyme (140) could be inhibited. Furthermore, differential inhibition was suggested to occur with two molecules (UC84 and UC38; Uniroyal Chemical Company, Middlebury, CT, USA) in which these NNRTIs could differentially affect one species of enzyme over another. Specifically, free enzyme and enzyme primer/template could bind UC84 whereas UC38 only bound to the ternary complex. These data implied that perhaps because different steps of catalysis could be modulated, such compounds might be given as a combination treatment for HIV-1 infection. Although similar in structure to UC84 and UC38, UC781 (Fig. 6) , a second-generation NNRTI, inhibited the ternary complex to a further degree (141) . The small variations in chemical structure between these three molecules underscore the variability in NNRTI design and potency (refer to Fletcher et al. and Barnard et al. for structures of these UC compounds; refs. 140 , 141 ). UC781 has shown a good resistance profile and has shown activity against commonly observed mutations in NNRTI treatment: Y181C, K103N, V106A, and L100I (mutations discussed below) (142) . It is a tight inhibitor with a rapid on-rate and a slow off-rate, which indicates it will bind and inhibit RT over a prolonged period (141) . Despite its activity against HIV-1, UC781 is poorly absorbed, and therefore cannot be orally administered. It is, however, being developed as a microbicide to prevent HIV-1 transmission (143) . Additional steady-state kinetic analyses indirectly suggested that NNRTIs efavirenz and sefavirenz (a thiocarbonyl analog of efavirenz) bind to the ternary RT-primer/template-dNTP complex with a higher affinity (144) . These studies offer a preliminary means for characterizing NNRTI inhibition in terms of their effect on steps involved in the binding of substrates. This discussion will now turn to the use of pre-steady-state kinetics to more fully understand mechanisms of NNRTI inhibition, and we refer the reader to Johnson et al. and Kati et al. for background on pre-steady-state kinetics and RT catalysis (145 146 147) .

Pre-steady-state kinetics allows one to define the rate-limiting step of catalysis. RT catalysis of polymerization occurs in a stepwise manner: RT first binds primer/template with high affinity to form a binary complex (also known as the "open" form), followed by binding of the next correct dNTP (to form the "closed" form). This ternary complex then undergoes a conformational change, followed by fast chemistry, and product release occurs after a single incorporation (147) . It has been established that under pre-steady-state conditions (in which primer/template concentration is in ~ 3-fold excess of active enzyme concentration), product formation occurs with two phases. The first phase is a fast phase (also known as the burst phase) that corresponds to the first enzyme turnover of substrate. The second is a slower phase of multiple turnovers in steady-state phase that corresponds to product release. Note that this biphasic product formation occurs only if product release, or some step after chemistry, is the overall rate-limiting step of catalysis. In the case of RT catalysis, this biphasic product formation occurs because elongated primer/template release is the overall rate-limiting step. As the enzyme conformational change is rate-limiting for incorporation, a detailed mechanistic analysis with a pre-steady-state kinetic approach (148 , 149) has shown that the addition of NNRTIs causes the rate-limiting step to be altered from the chemistry step; therefore, chemistry governs the rate of polymerization. It is important to note that this change does not significantly change the rate or equilibrium constant for the conformational change. These studies not only established that the dNTP and NNRTI are simultaneously bound to enzyme, but also that there is communication between the active site and the NNRTI binding pocket. Because the mechanism and binding of NNRTIs is fundamentally different than that of NRTIs, the use of these agents in combination therapy affords multiple routes to inhibit viral replication.

To date, three NNRTI compounds have been approved by the U.S. FDA for the treatment of HIV-1 infection. Nevirapine (Viramune®) was approved in 1996, delavirdine (Rescriptor®) in 1997, and efavirenz (Sustiva®, Stocrin®) in 1998 (Fig. 6) . The three structures themselves depict the wide array of rings, substituents, and bond attachments that afford activity against HIV-1 RT. This diversity offers insight into why so many non-nucleosides have been synthesized, but does not address why, with such diversity, only three inhibitors have been approved. The answer lies in the potency of new compounds and their utility against the predominant underlying obstacle facing anti-HIV medications: resistance.


   NON-NUCLEOSIDE RT INHIBITOR RESISTANCE
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
CONCLUSIONS
 REFERENCES
 
Non-nucleoside inhibitors bind to an inactive site of RT. How might it circumvent inhibition by these molecules? This question becomes more relevant since RT has no proofreading activity, which leads to "quasispecies" of virus that encompass many genetic variants of HIV-1; these quasispecies may hold different genetic codes for each and every protein within the viral genome. It is estimated that production of virus occurs at a rate of ~1 x 1010 virions per day (19 , 20) , and with expression of quasispecies constantly occurring, it can be understood that effective anti-HIV-1 treatment is not trivial. Some of these quasispecies are lethal (i.e., mutations render the virus noninfectious) and die off, but treatment with inhibitors can select for drug-resistant mutations that impart an advantage over wild-type virus.

Although non-nucleosides are highly selective against HIV-1, two papers in the early 1990s first described the appearance of a mutation within RT that mediated resistance to nevirapine in cell culture (150 , 151) . Richman et al. described a population of virus that became less susceptible (~250-fold) to nevirapine after a few passages, which suggests that the virus was averting inhibition. Sequencing of the virus indicated a single mutation at RT residue 181(Y 224 C mutation). This mutation was stable under nevirapine pressure and showed decreased binding affinity (~8-fold) for a photoaffinity analog of nevirapine. In addition, Y181C showed cross resistance for TIBO analogs, which illustrated a common binding site for non-nucleosides. During the same time, data from Mellors et al. showed the same mutation on nevirapine treatment, with a corresponding change in IC50 values of 100-fold. Cross resistance was again observed; surprisingly, however, the mutation was observed after only one viral passage. This phenomenon is surprising and yet might be explained by the mere nature of the NNRTI binding pocket. Because this pocket is an inactive site pocket with no known endogenous ligands, one can argue that mutations might easily arise because these residues are not critical for RT’s catalytic cycle. The fates for delavirdine and efavirenz are no less negative. For delavirdine, a first-generation inhibitor like nevirapine, resistance was initially shown with the Y181C and K103N mutations, individually changing the IC50 value for delavirdine by 30-fold (152) . Another study showed that K103N was the predominant mutation against delavirdine, followed by Y181C and P236L (131) . For the second-generation inhibitor efavirenz, IC50 changes by the K103N mutation range between 20- and 100-fold, though efavirenz remains potent against the Y181C mutant (131 , 153 , 154) . Double and triple mutations are also observed; thus, NNRTI design dictates that new therapeutics be formulated with resistance in mind. For further analysis, we suggest reviews by Balzarini and De Clerq (131 , 155) .

At the biochemical level, mutations to NNRTIs have been well characterized with the goal of using mechanistic information to improve drug design. Structural studies have suggested that the aromatic ring of tyrosine 181 lies on a plane with the methyl pyridine ring of nevirapine generating favorable {pi}-{pi} interactions between the two ring systems (Fig. 7) . Mutation of tyrosine to cysteine causes loss of these hydrophobic interactions and a subsequent decrease in binding affinity of nevirapine (156 , 157) . This loss does not affect the activity of efavirenz due to its smaller propynylcyclopropyl moiety (153 , 156 , 158 159 160) . The predominant mutation, K103N, selected by efavirenz, lies at the entrance to the NNRTI binding pocket and is thought to prevent binding of NNRTIs. It has been shown to decrease the association rate of nevirapine (161) and decrease the binding affinity of efavirenz by 6-fold (153) . Other common, but less predominant, mutations include L100I, V106A, Y188C, G190A, and P236L. These mutations all confer resistance to the FDA-approved non-nucleosides, with the noted exception that little or no resistance is observed for P236L to efavirenz (106 , 158 , 160) .

The onset of resistance to current non-nucleoside therapies calls for novel inhibitors. A wealth of data from cell culture and structural studies have illustrated that an essential consideration in formulating a novel NNRTI is molecular flexibility (158 , 162 , 163) ; that is, early generation inhibitors (e.g., nevirapine) display activity against wild-type HIV but fail to retain activity against mutations generated in the NNRTI binding pocket. Thus, flexibility has been implemented into NNRTI design in an effort to afford activity against mutations by enabling inhibitor(s) to adapt to pocket alterations. This adaptation results from the inhibitor’s ability to reposition and change conformations within the pocket. Prime examples of utilizing flexibility include TMC125 (etravirine in phase III trials) and TMC278 (rilpivirine, phase IIb) (Fig. 6) , which have shown good clinical activity. As mentioned earlier, novel angles on RT activity are currently being pursued: dimerization of p66/p51 can be inhibited by TSAO derivatives (41) and a novel class of indolopyridone compounds can bind to the active site and prevent dNTP incorporation despite being structurally inequivalent to common NRTIs (164) .


   CONCLUSIONS
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
REFERENCES
 
The discovery of HIV-1 as the etiological agent of AIDS has spawned much research into therapeutic treatments. Bypassing the notion that HIV/AIDS was limited to certain populations was a large hurdle in accepting this disease; but when the severity of the pandemic was realized, robust work in designing therapeutics emerged. The nucleoside and non-nucleoside RT inhibitors are prime examples of this effort. Over a span of 17 years, 14 different NRTI formulations have been approved by the FDA. They comprise a wide class of functionalities and strategies to improve their effectiveness (Fig. 4) . The non-nucleoside inhibitors, first developed through screening methods, show good selectivity against RT by targeting a pocket that does not exist in the apoenzyme. Three were approved between 1996 and 1998. They bind by an induced-fit mechanism, and effective inhibitors show nanomolar potency against viral replication.

Although toxicity, pharmacokinetics, drug clearance, dosing, cost, and drug adherence can affect viral load and patient well being, the development of viral resistance is the principal force preventing any of these anti-HIV agents from maximizing their potential. Resistance has been observed for all anti-HIV agents and results from the error-prone replication provided by reverse transcription. The lack of RT proofreading produces many different populations of virus, the so-called quasispecies. Therapeutic targeting of quasispecies of virus is difficult, but when the virus can select for a population that is insensitive to one or more agents, one can realize how HIV/AIDS has resulted in a catastrophic number of deaths despite therapeutic interventions. Further advances in education, vaccines, prophylactics, and therapeutics will, with luck, lessen this pandemic.


   ACKNOWLEDGMENTS
 
This work was supported by National Institutes of Health grant GM49551 to K.S.A.


   FOOTNOTES
 
1 Current address: Beth Israel Deaconess Medical Center, 41 Ave. Louis Pasteur, Boston, MA 02215, USA.

Received for publication March 30, 2007. Accepted for publication June 7, 2007.


   REFERENCES
TOP
 ABSTRACT
 HISTORY AND EPIDEMIOLOGY
 LIFE CYCLE OF HIV-1...
 REVERSE TRANSCRIPTION
 NUCLEOSIDE RT INHIBITORS
 NUCLEOSIDE RT INHIBITOR...
 NON-NUCLEOSIDE RT INHIBITORS
 NON-NUCLEOSIDE RT INHIBITOR...
 CONCLUSIONS
 REFERENCES
 

  1. Centers for Disease Control (1981) Pneumocystis pneumonia—Los Angeles. MMWR Morb. Mortal. Wkly. Rep. 30,250-252[Medline]
  2. Centers for Disease Control (1981) Kaposi’s sarcoma and Pneumocystis pneumonia among homosexual men—New York City and California. MMWR Morb. Mortal. Wkly. Rep. 30,305-308[Medline]
  3. Hanrahan, J. P., Wormser, G. P., Maguire, G. P., Delorenzo, L. J., Gavis, G. (1982) Opportunistic infections in prisoners. N. Engl. J. Med. 307,498[Medline]
  4. Epidemiologic aspects of the current outbreak of Kaposi’s sarcoma and opportunistic infections. N. Engl. J. Med. 1982;306,248-252[Medline]
  5. Gallo, R. C., Sarin, P. S., Gelmann, E. P., Robert-Guroff, M., Richardson, E., Kalyanaraman, V. S., Mann, D., Sidhu, G. D., Stahl, R. E., Zolla-Pazner, S., Leibowitch, J., Popovic, M. (1983) Isolation of human T-cell leukemia virus in acquired immune deficiency syndrome (AIDS). Science 220,865-867[Abstract/Free Full Text]
  6. Barre-Sinoussi, F., Chermann, J. C., Rey, F., Nugeyre, M. T., Chamaret, S., Gruest, J., Dauguet, C., Axler-Blin, C., Vezinet-Brun, F., Rouzioux, C., Rozenbaum, W., Montagnier, L. (1983) Isolation of a T-lymphotropic retrovirus from a patient at risk for acquired immune deficiency syndrome (AIDS). Science 220,868-871[Abstract/Free Full Text]
  7. Levy, J. A., Hoffman, A. D., Kramer, S. M., Landis, J. A., Shimabukuro, J. M., Oshiro, L. S. (1984) Isolation of lymphocytopathic retroviruses from San Francisco patients with AIDS. Science 225,840-842[Abstract/Free Full Text]
  8. Hahn, B. H., Shaw, G. M., Arya, S. K., Popovic, M., Gallo, R. C., Wong-Staal, F. (1984) Molecular cloning and characterization of the HTLV-III virus associated with AIDS. Nature 312,166-169[CrossRef][Medline]
  9. Sierra, S., Kupfer, B., Kaiser, R. (2005) Basics of the virology of HIV-1 and its replication. J. Clin. Virol. 34,233-244[CrossRef][Medline]
  10. Allan, J. S., Coligan, J. E., Barin, F., McLane, M. F., Sodroski, J. G., Rosen, C. A., Haseltine, W. A., Lee, T. H., Essex, M. (1985) Major glycoprotein antigens that induce antibodies in AIDS patients are encoded by HTLV-III. Science 228,1091-1094[Abstract/Free Full Text]
  11. Veronese, F. D., DeVico, A. L., Copeland, T. D., Oroszlan, S., Gallo, R. C., Sarngadharan, M. G. (1985) Characterization of gp41 as the transmembrane protein coded by the HTLV-III/LAV envelope gene. Science 229,1402-1405[Abstract/Free Full Text]
  12. Robey, W. G., Safai, B., Oroszlan, S., Arthur, L. O., Gonda, M. A., Gallo, R. C., Fischinger, P. J. (1985) Characterization of envelope and core structural gene products of HTLV-III with sera from AIDS patients. Science 228,593-595[Abstract/Free Full Text]
  13. Earl, P. L., Doms, R. W., Moss, B. (1990) Oligomeric structure of the human immunodeficiency virus type 1 envelope glycoprotein. Proc. Natl. Acad. Sci. U. S. A. 87,648-652[Abstract/Free Full Text]
  14. Goff, S. P. (1990) Retroviral reverse transcriptase: synthesis, structure, and function. J. Acquir. Immune Defic. Syndr. 3,817-831[Medline]
  15. Buchow, H. D., Tschachler, E., Gallo, R. C., Reitz, M., Jr (1989) HIV-I replication requires an intact integrase reading frame. Haematol. Blood Transfus. 32,402-405[Medline]
  16. LaFemina, R. L., Schneider, C. L., Robbins, H. L., Callahan, P. L., LeGrow, K., Roth, E., Schleif, W. A., Emini, E. A. (1992) Requirement of active human immunodeficiency virus type 1 integrase enzyme for productive infection of human T-lymphoid cells. J. Virol. 66,7414-7419[Abstract/Free Full Text]
  17. Richman, D. D. (2003) Human Immunodeficiency Virus International Medical Press London, UK.
  18. Stevenson, M. (2003) HIV-1 pathogenesis. Nat. Med. 9,853-860[CrossRef][Medline]
  19. Sallie, R. (2005) Replicative homeostasis: a fundamental mechanism mediating selective viral replication and escape mutation. Virol. J. 2,10[CrossRef][Medline]
  20. Perelson, A. S., Neumann, A. U., Markowitz, M., Leonard, J. M., Ho, D. D. (1996) HIV-1 dynamics in vivo: virion clearance rate, infected cell life-span, and viral generation time. Science 271,1582-1586[Abstract]
  21. Matthews, T., Salgo, M., Greenberg, M., Chung, J., DeMasi, R., Bolognesi, D. (2004) Enfuvirtide: the first therapy to inhibit the entry of HIV-1 into host CD4 lymphocytes. Nat. Rev. Drug Discov. 3,215-225[CrossRef][Medline]
  22. Baltimore, D. (1970) RNA-dependent DNA polymerase in virions of RNA tumour viruses. Nature 226,1209-1211[CrossRef][Medline]
  23. Temin, H. M., Mizutani, S. (1970) RNA-dependent DNA polymerase in virions of Rous sarcoma virus. Nature 226,1211-1213[CrossRef][Medline]
  24. Raju, T. N. (1999) The Nobel chronicles. 1975: Renato Dulbecco (b. 1914), David Baltimore (b. 1938), and Howard Martin Temin (1934–1994). Lancet 354,1308[CrossRef][Medline]
  25. Rey, M. A., Spire, B., Dormont, D., Barre-Sinoussi, F., Montagnier, L., Chermann, J. C. (1984) Characterization of the RNA dependent DNA polymerase of a new human T-lymphotropic retrovirus (lymphadenopathy associated virus). Biochem. Biophys. Res. Commun. 121,126-133[Medline]
  26. Rho, H. M., Poiesz, B., Ruscetti, F. W., Gallo, R. C. (1981) Characterization of the reverse transcriptase from a new retrovirus (HTLV) produced by a human cutaneous T-cell lymphoma cell line. Virology 112,355-360[CrossRef][Medline]
  27. di Marzo Veronese, F., Copeland, T. D., DeVico, A. L., Rahman, R., Oroszlan, S., Gallo, R. C., Sarngadharan, M. G. (1986) Characterization of highly immunogenic p66/p51 as the reverse transcriptase of HTLV-III/LAV. Science 231,1289-1291[Abstract/Free Full Text]
  28. Lightfoote, M. M., Coligan, J. E., Folks, T. M., Fauci, A. S., Martin, M. A., Venkatesan, S. (1986) Structural characterization of reverse transcriptase and endonuclease polypeptides of the acquired immunodeficiency syndrome retrovirus. J. Virol. 60,771-775[Abstract/Free Full Text]
  29. Farmerie, W. G., Loeb, D. D., Casavant, N. C., Hutchison, C. A., 3rd, Edgell, M. H., Swanstrom, R. (1987) Expression and processing of the AIDS virus reverse transcriptase in Escherichia coli. Science 236,305-308[Abstract/Free Full Text]
  30. Mous, J., Heimer, E. P., Le Grice, S. F. (1988) Processing protease and reverse transcriptase from human immunodeficiency virus type I polyprotein in Escherichia coli. J. Virol. 62,1433-1436[Abstract/Free Full Text]
  31. Lowe, D. M., Aitken, A., Bradley, C., Darby, G. K., Larder, B. A., Powell, K. L., Purifoy, D. J., Tisdale, M., Stammers, D. K. (1988) HIV-1 reverse transcriptase: crystallization and analysis of domain structure by limited proteolysis. Biochemistry 27,8884-8889[CrossRef][Medline]
  32. Muller, B., Restle, T., Weiss, S., Gautel, M., Sczakiel, G., Goody, R. S. (1989) Co-expression of the subunits of the heterodimer of HIV-1 reverse transcriptase in Escherichia coli. J. Biol. Chem. 264,13975-13978[Abstract/Free Full Text]
  33. Le Grice, S. F., Gruninger-Leitch, F. (1990) Rapid purification of homodimer and heterodimer HIV-1 reverse transcriptase by metal chelate affinity chromatography. Eur. J. Biochem. 187,307-314[Medline]
  34. Restle, T., Muller, B., Goody, R. S. (1990) Dimerization of human immunodeficiency virus type 1 reverse transcriptase. A target for chemotherapeutic intervention. J. Biol. Chem. 265,8986-8988[Abstract/Free Full Text]
  35. Verma, I. M. (1975) Studies on reverse transcriptase of RNA tumor viruses III. Properties of purified Moloney murine leukemia virus DNA polymerase and associated RNase H. J. Virol. 15,843-854[Abstract/Free Full Text]
  36. Gerard, G. F., Grandgenett, D. P. (1975) Purification and characterization of the DNA polymerase and RNase H activities in Moloney murine sarcoma-leukemia virus. J. Virol. 15,785-797[Abstract/Free Full Text]
  37. Molling, K., Bolognesi, D. P., Bauer, H., Busen, W., Plassmann, H. W., Hausen, P. (1971) Association of viral reverse transcriptase with an enzyme degrading the RNA moiety of RNA-DNA hybrids. Nat. New. Biol. 234,240-243[CrossRef][Medline]
  38. Le Grice, S. F., Naas, T., Wohlgensinger, B., Schatz, O. (1991) Subunit-selective mutagenesis indicates minimal polymerase activity in heterodimer-associated p51 HIV-1 reverse transcriptase. EMBO J. 10,3905-3911[Medline]
  39. Hansen, J., Schulze, T., Mellert, W., Moelling, K. (1988) Identification and characterization of HIV-specific RNase H by monoclonal antibody. EMBO J. 7,239-243[Medline]
  40. Schatz, O., Cromme, F. V., Gruninger-Leitch, F., Le Grice, S. F. (1989) Point mutations in conserved amino acid residues within the C-terminal domain of HIV-1 reverse transcriptase specifically repress RNase H function. FEBS Lett. 257,311-314[CrossRef][Medline]
  41. Camarasa, M. J., San-Felix, A., Velazquez, S., Perez-Perez, M. J., Gago, F., Balzarini, J. (2004) TSAO compounds: the comprehensive story of a unique family of HIV-1 specific inhibitors of reverse transcriptase. Curr. Top. Med. Chem. 4,945-963[CrossRef][Medline]
  42. Kohlstaedt, L. A., Wang, J., Friedman, J. M., Rice, P. A., Steitz, T. A. (1992) Crystal structure at 3.5 A resolution of HIV-1 reverse transcriptase complexed with an inhibitor. Science 256,1783-1790[Abstract/Free Full Text]
  43. Jacobo-Molina, A., Ding, J., Nanni, R. G., Clark, A. D., Jr, Lu, X., Tantillo, C., Williams, R. L., Kamer, G., Ferris, A. L., Clark, P., et al (1993) Crystal structure of human immunodeficiency virus type 1 reverse transcriptase complexed with double-stranded DNA at 3.0 A resolution shows bent DNA. Proc. Natl. Acad. Sci. U. S. A. 90,6320-6324[Abstract/Free Full Text]
  44. Huang, H., Chopra, R., Verdine, G. L., Harrison, S. C. (1998) Structure of a covalently trapped catalytic complex of HIV-1 reverse transcriptase: implications for drug resistance. Science 282,1669-1675[Abstract/Free Full Text]
  45. Huang, H., Harrison, S. C., Verdine, G. L. (2000) Trapping of a catalytic HIV reverse transcriptase*template: primer complex through a disulfide bond. Chem. Biol. 7,355-364[CrossRef][Medline]
  46. Roberts, J. D., Bebenek, K., Kunkel, T. A. (1988) The accuracy of reverse transcriptase from HIV-1. Science 242,1171-1173[Abstract/Free Full Text]
  47. Preston, B. D., Poiesz, B. J., Loeb, L. A. (1988) Fidelity of HIV-1 reverse transcriptase. Science 242,1168-1171[Abstract/Free Full Text]
  48. Ricchetti, M., Buc, H. (1990) Reverse transcriptases and genomic variability: the accuracy of DNA replication is enzyme specific and sequence dependent. EMBO J. 9,1583-1593[Medline]
  49. Mansky, L. M., Temin, H. M. (1995) Lower in vivo mutation rate of human immunodeficiency virus type 1 than that predicted from the fidelity of purified reverse transcriptase. J. Virol. 69,5087-5094[Abstract]
  50. Mitsuya, H., Weinhold, K. J., Furman, P. A., St Clair, M. H., Lehrman, S. N., Gallo, R. C., Bolognesi, D., Barry, D. W., Broder, S. (1985) 3'-Azido-3'-deoxythymidine (BW A509U): an antiviral agent that inhibits the infectivity and cytopathic effect of human T-lymphotropic virus type III/lymphadenopathy-associated virus in vitro. Proc. Natl. Acad. Sci. U. S. A. 82,7096-7100[Abstract/Free Full Text]
  51. Furman, P. A., Fyfe, J. A., St. Clair, M. H., Weinhold, K., Rideout, J. L., Freeman, G. A., Nusinoff-Lehrman, S., Bolognesi, D. P., Broder, S., Mitsuya, H., Barry, D. W. (1986) Phosphorylation of 3'-azido-3'-deoxythymidine and selective interaction of the 5'-triphosphate with human immunodeficiency virus reverse transcriptase. Proc. Natl. Acad. Sci. U. S. A. 83,8333-8337[Abstract/Free Full Text]
  52. Schneider, B., Biondi, R., Sarfati, R., Agou, F., Guerreiro, C., Deville-Bonne, D., Veron, M. (2000) The mechanism of phosphorylation of anti-HIV D4T by nucleoside diphosphate kinase. Mol. Pharmacol. 57,948-953[Abstract/Free Full Text]
  53. Heidenreich, O., Kruhoffer, M., Grosse, F., Eckstein, F. (1990) Inhibition of human immunodeficiency virus 1 reverse transcriptase by 3'-azidothymidine triphosphate. Eur. J. Biochem. 192,621-625[Medline]
  54. St Clair, M. H., Richards, C. A., Spector, T., Weinhold, K. J., Miller, W. H., Langlois, A. J., Furman, P. A. (1987) 3'-Azido-3'-deoxythymidine triphosphate as an inhibitor and substrate of purified human immunodeficiency virus reverse transcriptase. Antimicrob. Agents Chemother. 31,1972-1977[Abstract/Free Full Text]
  55. Goody, R. S., Muller, B., Restle, T. (1991) Factors contributing to the inhibition of HIV reverse transcriptase by chain-terminating nucleotides in vitro and in vivo. FEBS Lett. 291,1-5[CrossRef][Medline]
  56. Mitsuya, H., Broder, S. (1986) Inhibition of the in vitro infectivity and cytopathic effect of human T-lymphotrophic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV) by 2',3'-dideoxynucleosides. Proc. Natl. Acad. Sci. U. S. A. 83,1911-1915[Abstract/Free Full Text]
  57. Kim, C. H., Marquez, V. E., Broder, S., Mitsuya, H., Driscoll, J. S. (1987) Potential anti-AIDS drugs. 2',3'-Dideoxycytidine analogues. J. Med. Chem. 30,862-866[CrossRef][Medline]
  58. Mitsuya, H., Yarchoan, R., Broder, S. (1990) Molecular targets for AIDS therapy. Science 249,1533-1544[Abstract/Free Full Text]
  59. Hao, Z., Cooney, D. A., Hartman, N. R., Perno, C. F., Fridland, A., DeVico, A. L., Sarngadharan, M. G., Broder, S., Johns, D. G. (1988) Factors determining the activity of 2',3'-dideoxynucleosides in suppressing human immunodeficiency virus in vitro. Mol. Pharmacol. 34,431-435[Abstract]
  60. Balzarini, J., Kang, G. J., Dalal, M., Herdewijn, P., De Clercq, E., Broder, S., Johns, D. G. (1987) The anti-HTLV-III (anti-HIV) and cytotoxic activity of 2',3'-didehydro-2',3'-dideoxyribonucleosides: a comparison with their parental 2',3'-dideoxyribonucleosides. Mol. Pharmacol. 32,162-167[Abstract]
  61. Lin, T. S., Schinazi, R. F., Prusoff, W. H. (1987) Potent and selective in vitro activity of 3'-deoxythymidin-2'-ene (3'-deoxy-2',3'-didehydrothymidine) against human immunodeficiency virus. Biochem. Pharmacol. 36,2713-2718[CrossRef][Medline]
  62. Baba, M., Pauwels, R., Herdewijn, P., De Clercq, E., Desmyter, J., Vandeputte, M. (1987) Both 2',3'-dideoxythymidine and its 2',3'-unsaturated derivative (2',3'-dideoxythymidinene) are potent and selective inhibitors of human immunodeficiency virus replication in vitro. Biochem. Biophys. Res. Commun. 142,128-134[CrossRef][Medline]
  63. Ho, H. T., Hitchcock, M. J. (1989) Cellular pharmacology of 2',3'-dideoxy-2',3'-didehydrothymidine, a nucleoside analog active against human immunodeficiency virus. Antimicrob. Agents Chemother. 33,844-849[Abstract/Free Full Text]
  64. August, E. M., Marongiu, M. E., Lin, T. S., Prusoff, W. H. (1988) Initial studies on the cellular pharmacology of 3'-deoxythymidin-2'-ene (d4T): a potent and selective inhibitor of human immunodeficiency virus. Biochem. Pharmacol. 37,4419-4422[CrossRef][Medline]
  65. Vaccaro, J. A., Anderson, K. S. (1998) Implication of the tRNA initiation step for human immunodeficiency virus type 1 reverse transcriptase in the mechanism of 3'-azido-3'-deoxythymidine (AZT) resistance. Biochemistry 37,14189-14194[CrossRef][Medline]
  66. Vaccaro, J. A., Parnell, K. M., Terezakis, S. A., Anderson, K. S. (2000) Mechanism of inhibition of the human immunodeficiency virus type 1 reverse transcriptase by d4TTP: an equivalent incorporation efficiency relative to the natural substrate dTTP. Antimicrob. Agents Chemother. 44,217-221[Abstract/Free Full Text]
  67. Kerr, S. G., Anderson, K. S. (1997) Pre-steady-state kinetic characterization of wild-type and 3'-azido-3'-deoxythymidine (AZT) resistant human immunodeficiency virus type 1 reverse transcriptase: implication of RNA directed DNA polymerization in the mechanism of AZT resistance. Biochemistry 36,14064-14070[CrossRef][Medline]
  68. Schinazi, R. F., Chu, C. K., Peck, A., McMillan, A., Mathis, R., Cannon, D., Jeong, L. S., Beach, J. W., Choi, W. B., Yeola, S., Liotta, D. C. (1992) Activities of the four optical isomers of 2',3'-dideoxy-3'-thiacytidine (BCH-189) against human immunodeficiency virus type 1 in human lymphocytes. Antimicrob. Agents. Chemother. 36,672-676[Abstract/Free Full Text]
  69. Doong, S. L., Tsai, C. H., Schinazi, R. F., Liotta, D. C., Cheng, Y. C. (1991) Inhibition of the replication of hepatitis B virus in vitro by 2',3'-dideoxy-3'-thiacytidine and related analogues. Proc. Natl. Acad. Sci. U. S. A. 88,8495-8499[Abstract/Free Full Text]
  70. Honkoop, P., de Man, R. A., Zondervan, P. E., Schalm, S. W. (1997) Histological improvement in patients with chronic hepatitis B virus infection treated with lamivudine. Liver 17,103-106[Medline]
  71. Dienstag, J. L., Perrillo, R. P., Schiff, E. R., Bartholomew, M., Vicary, C., Rubin, M. (1995) A preliminary trial of lamivudine for chronic hepatitis B infection. N. Engl. J. Med. 333,1657-1661[Abstract/Free Full Text]
  72. Coates, J. A., Cammack, N., Jenkinson, H. J., Mutton, I. M., Pearson, B. A., Storer, R., Cameron, J. M., Penn, C. R. (1992) The separated enantiomers of 2'-deoxy-3'-thiacytidine (BCH 189) both inhibit human immunodeficiency virus replication in vitro. Antimicrob. Agents Chemother. 36,202-205[Abstract/Free Full Text]
  73. Skalski, V., Chang, C. N., Dutschman, G., Cheng, Y. C. (1993) The biochemical basis for the differential anti-human immunodeficiency virus activity of two cis enantiomers of 2',3'-dideoxy-3'-thiacytidine. J. Biol. Chem. 268,23234-23238[Abstract/Free Full Text]
  74. Chang, C. N., Doong, S. L., Zhou, J. H., Beach, J. W., Jeong, L. S., Chu, C. K., Tsai, C. H., Cheng, Y. C., Liotta, D., Schinazi, R. (1992) Deoxycytidine deaminase-resistant stereoisomer is the active form of (±)-2',3'-dideoxy-3'-thiacytidine in the inhibition of hepatitis B virus replication. J. Biol. Chem. 267,13938-13942[Abstract/Free Full Text]
  75. Cammack, N., Rouse, P., Marr, C. L. P., Reid, P. J., Boehme, R. E., Coates, J. A. V., Penn, C. R., Cameron, J. M. (1992) Cellular metabolism of (–) enatiomeric 2'-deoxy-3'-thiacytidine. Biochem. Pharmacol. 43,2059-2064[CrossRef][Medline]
  76. Schinazi, R. F., McMillan, A., Cannon, D., Mathis, R., Lloyd, R. M., Peck, A., Sommadossi, J. P., St Clair, M., Wilson, J., Furman, P. A., Painter, G. R., Choi, W.-B., Liotta, C. (1992) Selective inhibition of human immunodeficiency viruses by racemates and enantiomers of cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine. Antimicrob. Agents Chemother. 36,2423-2431[Abstract/Free Full Text]
  77. Ray, A. S., Schinazi, R. F., Murakami, E., Basavapathruni, A., Shi, J., Zorca, S. M., Chu, C. K., Anderson, K. S. (2003) Probing the mechanistic consequences of 5-fluorine substitution on cytidine nucleotide analogue incorporation by HIV-1 reverse transcriptase. Antivir. Chem. Chemother. 14,115-125[Medline]
  78. Daluge, S. M., Good, S. S., Faletto, M. B., Miller, W. H., St. Clair, M. H., Boone, L. R., Tisdale, M., Parry, N. R., Reardon, J. E., Dornsife, R. E., et al (1997) 1592U89, a novel carbocyclic nucleoside analog with potent, selective, anti-human immunodeficiency virus activity. Antimicrob. Agents Chemother. 41,1082-1093[Abstract]
  79. Faletto, M. B., Miller, W. H., Garvey, E. P., St Clair, M. H., Daluge, S. M., Good, S. S. (1997) Unique intracellular activation of the potent anti-human immunodeficiency virus agent 1592U89. Antimicrob. Agents Chemother. 41,1099-1107[Abstract]
  80. Balzarini, J., De Clercq, E. (1991) 5-Phosphoribosyl 1-pyrophosphate synthetase converts the acyclic nucleoside phosphonates 9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine and 9-(2-phosphonylmethoxyethyl)adenine directly to their antivirally active diphosphate derivatives. J. Biol. Chem. 266,8686-8689[Abstract/Free Full Text]
  81. Robbins, B. L., Greenhaw, J., Connelly, M. C., Fridland, A. (1995) Metabolic pathways for activation of the antiviral agent 9-(2-phosphonylmethoxyethyl)adenine in human lymphoid cells. Antimicrob. Agents Chemother. 39,2304-2308[Abstract]
  82. Robbins, B. L., Srinivas, R. V., Kim, C., Bischofberger, N., Fridland, A. (1998) Anti-human immunodeficiency virus activity and cellular metabolism of a potential prodrug of the acyclic nucleoside phosphonate 9-R-(2-phosphonomethoxypropyl)adenine (PMPA), bis(isopropyloxymethylcarbonyl)PMPA. Antimicrob. Agents Chemother. 42,612-617[Abstract/Free Full Text]
  83. De Clercq, E., Holy, A. (2005) Acyclic nucleoside phosphonates: a key class of antiviral drugs. Nat. Rev. Drug Discov. 4,928-940[CrossRef][Medline]
  84. Feng, J. Y., Johnson, A. A., Johnson, K. A., Anderson, K. S. (2001) Insights into the molecular mechanism of mitochondrial toxicity by AIDS drugs. J. Biol. Chem. 276,23832-23837[Abstract/Free Full Text]
  85. Anderson, K. S. (2001) The molecular basis of inhibition and toxicity of modified cytosine analogues targetting HIV-1 reverse transcriptase. Antivir. Chem. Chemother. 12(Suppl. 1),13-17[Medline]
  86. Anderson, K. S. (2002) Perspectives on the molecular mechanism of inhibition and toxicity of nucleoside analogs that target HIV-1 reverse transcriptase. Biochim. Biophys. Acta 1587,296-299[Medline]
  87. Bridges, E. G., Jiang, Z., Cheng, Y. C. (1999) Characterization of a dCTP transport activity reconstituted from human mitochondria. J. Biol. Chem. 274,4620-4625[Abstract/Free Full Text]
  88. Brinkman, K., ter Hofstede, H. J., Burger, D. M., Smeitink, J. A., Koopmans, P. P. (1998) Adverse effects of reverse transcriptase inhibitors: mitochondrial toxicity as common pathway. AIDS 12,1735-1744[Medline]
  89. Martin, J. L., Brown, C. E., Matthews-Davis, N., Reardon, J. E. (1994) Effects of antiviral nucleoside analogs on human DNA polymerases and mitochondrial DNA synthesis. Antimicrob. Agents Chemother. 38,2743-2749[Abstract/Free Full Text]
  90. Parker, W. B., Cheng, Y. C. (1994) Mitochondrial Toxicity of Antiviral Nucleoside Analogs. J. NIH Res. 6,57-61[Medline]
  91. Brinkman, K., Kakuda, T. N. (2000) Mitochondrial toxicity of nucleoside analogue reverse transcriptase inhibitors: a looming obstacle for long-term antiretroviral therapy?. Curr. Opin. Infect. Dis. 13,5-11[Medline]
  92. Honkoop, P., Scholte, H. R., de Man, R. A., Schalm, S. W. (1997) Mitochondrial injury. Lessons from the fialuridine trial. Drug Safety 17,1-7[Medline]
  93. McKenzie, R., Fried, M. W., Sallie, R., Conjeevaram, H., Di Bisceglie, A. M., Park, Y., Savarese, B., Kleiner, D., Tsokos, M., Luciano, C., et al (1995) Hepatic failure and lactic acidosis due to fialuridine (FIAU), an investigational nucleoside analogue for chronic hepatitis B. N. Engl. J. Med. 333,1099-1105[Abstract/Free Full Text]
  94. Johnson, A. A., Ray, A. S., Hanes, J., Suo, Z., Colacino, J. M., Anderson, K. S., Johnson, K. A. (2001) Toxicity of antiviral nucleoside analogs and the human mitochondrial DNA polymerase. J. Biol. Chem. 276,40847-40857[Abstract/Free Full Text]
  95. Johnson, A. A., Johnson, K. A. (2001) Exonuclease proofreading by human mitochondrial DNA polymerase. J. Biol. Chem. 276,38097-38107[Abstract/Free Full Text]
  96. Murakami, E., Ray, A. S., Schinazi, R. F., Anderson, K. S. (2004) Investigating the effects of stereochemistry on incorporation and removal of 5-fluorocytidine analogs by mitochondrial DNA polymerase gamma: comparison of D- and L-D4FC-TP. Antiviral Res. 62,57-64[CrossRef][Medline]
  97. Larder, B. A., Darby, G., Richman, D. D. (1989) HIV with reduced sensitivity to zidovudine (AZT) isolated during prolonged therapy. Science 243,1731-1734[Abstract/Free Full Text]
  98. Larder, B. A., Purifoy, D. J., Powell, K. L., Darby, G. (1987) Site-specific mutagenesis of AIDS virus reverse transcriptase. Nature 327,716-717[CrossRef][Medline]
  99. Larder, B. A., Kemp, S. D. (1989) Multiple mutations in HIV-1 reverse transcriptase confer high-level resistance to zidovudine (AZT). Science 246,1155-1158[Abstract/Free Full Text]
  100. Kellam, P., Boucher, C. A., Larder, B. A. (1992) Fifth mutation in human immunodeficiency virus type 1 reverse transcriptase contributes to the development of high-level resistance to zidovudine. Proc. Natl. Acad. Sci. U. S. A. 89,1934-1938[Abstract/Free Full Text]
  101. Coakley, E. P., Gillis, J. M., Hammer, S. M. (2000) Phenotypic and genotypic resistance patterns of HIV-1 isolates derived from individuals treated with didanosine and stavudine. AIDS 14,F9-F15[CrossRef][Medline]
  102. Izopet, J., Bicart-See, A., Pasquier, C., Sandres, K., Bonnet, E., Marchou, B., Puel, J., Massip, P. (1999) Mutations conferring resistance to zidovudine diminish the antiviral effect of stavudine plus didanosine. J. Med. Virol. 59,507-511[CrossRef][Medline]
  103. Lin, P. F., Samanta, H., Rose, R. E., Patick, A. K., Trimble, J., Bechtold, C. M., Revie, D. R., Khan, N. C., Federici, M. E., Li, H., et al (1994) Genotypic and phenotypic analysis of human immunodeficiency virus type 1 isolates from patients on prolonged stavudine therapy. J. Infect. Dis. 170,1157-1164[Medline]
  104. Pellegrin, I., Izopet, J., Reynes, J., Denayrolles, M., Montes, B., Pellegrin, J. L., Massip, P., Puel, J., Fleury, H., Segondy, M. (1999) Emergence of zidovudine and multidrug-resistance mutations in the HIV-1 reverse transcriptase gene in therapy-naive patients receiving stavudine plus didanosine combination therapy. STADI Group. AIDS 13,1705-1709[CrossRef][Medline]
  105. De Ronde, A., van Dooren, M., de Rooij, E., van Gemen, B., Lange, J., Goudsmit, J. (2000) Infection by zidovudine-resistant HIV-1 compromises the virological response to stavudine in a drug-naive patient. AIDS 14,2632-2633[CrossRef][Medline]
  106. Johnson, V. A., Brun-Vezinet, F., Clotet, B., Conway, B., Kuritzkes, D. R., Pillay, D., Schapiro, J. M., Telenti, A., Richman, D. D. (2005) Update of the drug resistance mutations in HIV-1: Fall 2005. Top. HIV Med. 13,125-131[Medline]
  107. Lacey, S. F., Larder, B. A. (1994) Novel mutation (V75T) in human immunodeficiency virus type 1 reverse transcriptase confers resistance to 2',3'-didehydro-2',3'-dideoxythymidine in cell culture. Antimicrob. Agents Chemother. 38,1428-1432[Abstract/Free Full Text]
  108. Schinazi, R. F., Lloyd, R. M., Jr, Nguyen, M. H., Cannon, D. L., McMillan, A., Ilksoy, N., Chu, C. K., Liotta, D. C., Bazmi, H. Z., Mellors, J. W. (1993) Characterization of human immunodeficiency viruses resistant to oxathiolane-cytosine nucleosides. Antimicrob. Agents Chemother. 37,875-881[Abstract/Free Full Text]
  109. Schuurman, R., Nijhuis, M., van Leeuwen, R., Schipper, P., de Jong, D., Collis, P., Danner, S. A., Mulder, J., Loveday, C., Christopherson, C., et al (1995) Rapid changes in human immunodeficiency virus type 1 RNA load and appearance of drug-resistant virus populations in persons treated with lamivudine (3TC). J. Infect. Dis. 171,1411-1419[Medline]
  110. Feng, J. Y., Anderson, K. S. (1999) Mechanistic studies examining the efficiency and fidelity of DNA synthesis by the 3TC-resistant mutant (184V) of HIV-1 reverse transcriptase. Biochemistry 38,9440-9448[CrossRef][Medline]
  111. Fu, L., Cheng, Y. C. (1998) Role of additional mutations outside the YMDD motif of hepatitis B virus polymerase in L(–)SddC (3TC) resistance. Biochem. Pharmacol. 55,1567-1572[CrossRef][Medline]
  112. Ling, R., Mutimer, D., Ahmed, M., Boxall, E. H., Elias, E., Dusheiko, G. M., Harrison, T. J. (1996) Selection of mutations in the hepatitis B virus polymerase during therapy of transplant recipients with lamivudine. Hepatology 24,711-713[Medline]
  113. Maeda, Y., Venzon, D. J., Mitsuya, H. (1998) Altered drug sensitivity, fitness, and evolution of human immunodeficiency virus type 1 with pol gene mutations conferring multi-dideoxynucleoside resistance. J. Infect. Dis. 177,1207-1213[Medline]
  114. Kosalaraksa, P., Kavlick, M. F., Maroun, V., Le, R., Mitsuya, H. (1999) Comparative fitness of multi-dideoxynucleoside-resistant human immunodeficiency virus type 1 (HIV-1) in an In vitro competitive HIV-1 replication assay. J. Virol. 73,5356-5363[Abstract/Free Full Text]
  115. Miller, M. D., Margot, N. A., Hertogs, K., Larder, B., Miller, V. (2001) Antiviral activity of tenofovir (PMPA) against nucleoside-resistant clinical HIV samples. Nucleosides Nucleotides Nucleic Acids 20,1025-1028[CrossRef][Medline]
  116. Lennerstrand, J., Stammers, D. K., Larder, B. A. (2001) Biochemical mechanism of human immunodeficiency virus type 1 reverse transcriptase resistance to stavudine. Antimicrob. Agents. Chemother. 45,2144-2146[Abstract/Free Full Text]
  117. Meyer, P. R., Matsuura, S. E., So, A. G., Scott, W. A. (1998) Unblocking of chain-terminated primer by HIV-1 reverse transcriptase through a nucleotide-dependent mechanism. Proc. Natl. Acad. Sci. U. S. A. 95,13471-13476[Abstract/Free Full Text]
  118. Traut, T. (1994) Physiological concentrations of purines and pyrimidines. Mol. Cell Biochem. 140,1-22[CrossRef][Medline]
  119. Arion, D., Kaushik, N., McCormick, S., Borkow, G., Parniak, M. A. (1998) Phenotypic mechanism of HIV-1 resistance to 3'-azido-3'-deoxythymidine (AZT): increased polymerization processivity and enhanced sensitivity to pyrophosphate of the mutant viral reverse transcriptase. Biochemistry 37,15908-15917[CrossRef][Medline]
  120. Sarafianos, S. G., Clark, A. D., Jr, Das, K., Tuske, S., Birktoft, J. J., Ilankumaran, P., Ramesha, A. R., Sayer, J. M., Jerina, D. M., Boyer, P. L., et al (2002) Structures of HIV-1 reverse transcriptase with pre- and post-translocation AZTMP-terminated DNA. EMBO J. 21,6614-6624[CrossRef][Medline]
  121. Borkow, G., Arion, D., Wainberg, M. A., Parniak, M. A. (1999) The thiocarboxanilide nonnucleoside inhibitor UC781 restores antiviral activity of 3'-azido-3'-deoxythymidine (AZT) against AZT-resistant human immunodeficiency virus type 1. Antimicrob. Agents Chemother. 43,259-263[Abstract/Free Full Text]
  122. Meyer, P. R., Matsuura, S. E., Mian, A. M., So, A. G., Scott, W. A. (1999) A mechanism of AZT resistance: an increase in nucleotide-dependent primer unblocking by mutant HIV-1 reverse transcriptase. Mol. Cell 4,35-43[CrossRef][Medline]
  123. Meyer, P. R., Matsuura, S. E., Schinazi, R. F., So, A. G., Scott, W. A. (2000) Differential removal of thymidine nucleotide analogues from blocked DNA chains by human immunodeficiency virus reverse transcriptase in the presence of physiological concentrations of 2'-deoxynucleoside triphosphates. Antimicrob. Agents Chemother. 44,3465-3472[Abstract/Free Full Text]
  124. Meyer, P. R., Matsuura, S. E., Tolun, A. A., Pfeifer, I., So, A. G., Mellors, J. W., Scott, W. A. (2002) Effects of specific zidovudine resistance mutations and substrate structure on nucleotide-dependent primer unblocking by human immunodeficiency virus type 1 reverse transcriptase. Antimicrob. Agents Chemother. 46,1540-1545[Abstract/Free Full Text]
  125. Baba, M., Tanaka, H., De Clercq, E., Pauwels, R., Balzarini, J., Schols, D., Nakashima, H., Perno, C. F., Walker, R. T., Miyasaka, T. (1989) Highly specific inhibition of human immunodeficiency virus type 1 by a novel 6-substituted acyclouridine derivative. Biochem. Biophys. Res. Commun. 165,1375-1381[CrossRef][Medline]
  126. Debyser, Z., Pauwels, R., Andries, K., Desmyter, J., Kukla, M., Janssen, P. A., De Clercq, E. (1991) An antiviral target on reverse transcriptase of human immunodeficiency virus type 1 revealed by tetrahydroimidazo-[4,5,1-jk] [1,4]benzodiazepin-2 (1H)-one and -thione derivatives. Proc. Natl. Acad. Sci. U. S. A. 88,1451-1455[Abstract/Free Full Text]
  127. Miyasaka, T., Tanaka, H., Baba, M., Hayakawa, H., Walker, R. T., Balzarini, J., De Clercq, E. (1989) A novel lead for specific anti-HIV-1 agents: 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine. J. Med. Chem. 32,2507-2509[CrossRef][Medline]
  128. Pauwels, R., Andries, K., Desmyter, J., Schols, D., Kukla, M. J., Breslin, H. J., Raeymaeckers, A., Van Gelder, J., Woestenborghs, R., Heykants, J., et al (1990) Potent and selective inhibition of HIV-1 replication in vitro by a novel series of TIBO derivatives. Nature 343,470-474[CrossRef][Medline]
  129. Merluzzi, V. J., Hargrave, K. D., Labadia, M., Grozinger, K., Skoog, M., Wu, J. C., Shih, C. K., Eckner, K., Hattox, S., Adams, J., et al (1990) Inhibition of HIV-1 replication by a nonnucleoside reverse transcriptase inhibitor. Science 250,1411-1413[Abstract/Free Full Text]
  130. De Clerc, Q. E. (2004) Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs): past, present, and future. Chem. Biodivers. 1,44-64[CrossRef][Medline]
  131. Balzarini, J. (2004) Current status of the non-nucleoside reverse transcriptase inhibitors of human immunodeficiency virus type 1. Curr. Top. Med. Chem. 4,921-944[CrossRef][Medline]
  132. Ren, J., Esnouf, R., Garman, E., Somers, D., Ross, C., Kirby, I., Keeling, J., Darby, G., Jones, Y., Stuart, D., et al (1995) High resolution structures of HIV-1 RT from four RT-inhibitor complexes. Nat. Struct. Biol. 2,293-302[CrossRef][Medline]
  133. Ding, J., Das, K., Moereels, H., Koymans, L., Andries, K., Janssen, P. A., Hughes, S. H., Arnold, E. (1995) Structure of HIV-1 RT/TIBO R 86183 complex reveals similarity in the binding of diverse nonnucleoside inhibitors. Nat. Struct. Biol. 2,407-415[CrossRef][Medline]
  134. Carroll, S. S., Olsen, D. B., Bennett, C. D., Gotlib, L., Graham, D. J., Condra, J. H., Stern, A. M., Shafer, J. A., Kuo, L. C. (1993) Inhibition of HIV-1 reverse transcriptase by pyridinone derivatives. Potency, binding characteristics, and effect of template sequence. J. Biol. Chem. 268,276-281[Abstract/Free Full Text]
  135. Althaus, I. W., Chou, J. J., Gonzales, A. J., Deibel, M. R., Chou, K. C., Kezdy, F. J., Romero, D. L., Aristoff, P. A., Tarpley, W. G., Reusser, F. (1993) Steady-state kinetic studies with the non-nucleoside HIV-1 reverse transcriptase inhibitor U-87201E. J. Biol. Chem. 268,6119-6124[Abstract/Free Full Text]
  136. Frank, K. B., Noll, G. J., Connell, E. V., Sim, I. S. (1991) Kinetic interaction of human immunodeficiency virus type 1 reverse transcriptase with the antiviral tetrahydroimidazo[4,5,1-jk]-[1,4]-benzodiazepine-2-(1H)-thione compound, R82150. J. Biol. Chem. 266,14232-14236[Abstract/Free Full Text]
  137. Goldman, M. E., Nunberg, J. H., O’Brien, J. A., Quintero, J. C., Schleif, W. A., Freund, K. F., Gaul, S. L., Saari, W. S., Wai, J. S., Hoffman, J. M., et al (1991) Pyridinone derivatives: specific human immunodeficiency virus type 1 reverse transcriptase inhibitors with antiviral activity. Proc. Natl. Acad. Sci. U. S. A. 88,6863-6867[Abstract/Free Full Text]
  138. Taylor, P. B., Culp, J. S., Debouck, C., Johnson, R. K., Patil, A. D., Woolf, D. J., Brooks, I., Hertzberg, R. P. (1994) Kinetic and mutational analysis of human immunodeficiency virus type 1 reverse transcriptase inhibition by inophyllums, a novel class of non-nucleoside inhibitors. J. Biol. Chem. 269,6325-6331[Abstract/Free Full Text]
  139. Tramontano, E., Cheng, Y. C. (1992) HIV-1 reverse transcriptase inhibition by a dipyridodiazepinone derivative: BI-RG-587. Biochem. Pharmacol. 43,1371-1376[CrossRef][Medline]
  140. Fletcher, R. S., Syed, K., Mithani, S., Dmitrienko, G. I., Parniak, M. A. (1995) Carboxanilide derivative non-nucleoside inhibitors of HIV-1 reverse transcriptase interact with different mechanistic forms of the enzyme. Biochemistry 34,4346-4353[CrossRef][Medline]
  141. Barnard, J., Borkow, G., Parniak, M. A. (1997) The thiocarboxanilide nonnucleoside UC781 is a tight-binding inhibitor of HIV-1 reverse transcriptase. Biochemistry 36,7786-7792[CrossRef][Medline]
  142. Balzarini, J., Pelemans, H., Aquaro, S., Perno, C. F., Witvrouw, M., Schols, D., De Clercq, E., Karlsson, A. (1996) Highly favorable antiviral activity and resistance profile of the novel thiocarboxanilide pentenyloxy ether derivatives UC-781 and UC-82 as inhibitors of human immunodeficiency virus type 1 replication. Mol. Pharmacol. 50,394-401[Abstract]
  143. Stone, A. (2002) Microbicides: a new approach to preventing HIV and other sexually transmitted infections. Nat. Rev. Drug Discov. 1,977-985[CrossRef][Medline]
  144. Maga, G., Ubiali, D., Salvetti, R., Pregnolato, M., Spadari, S. (2000) Selective interaction of the human immunodeficiency virus type 1 reverse transcriptase nonnucleoside inhibitor efavirenz and its thio-substituted analog with different enzyme-substrate complexes. Antimicrob. Agents Chemother. 44,1186-1194[Abstract/Free Full Text]
  145. Johnson, K. A. (1995) Rapid quench kinetic analysis of polymerases, adenosinetriphosphatases, and enzyme intermediates. Methods Enzymol. 249,38-61[Medline]
  146. Johnson, K. A. (1992) The Enzymes XX Academic Press Orlando, Florida.
  147. Kati, W. M., Johnson, K. A., Jerva, L. F., Anderson, K. S. (1992) Mechanism and fidelity of HIV reverse transcriptase. J. Biol. Chem. 267,25988-25997[Abstract/Free Full Text]
  148. Spence, R. A., Kati, W. M., Anderson, K. S., Johnson, K. A. (1995) Mechanism of inhibition of HIV-1 reverse transcriptase by nonnucleoside inhibitors. Science 267,988-993[Abstract/Free Full Text]
  149. Rittinger, K., Divita, G., Goody, R. S. (1995) Human immunodeficiency virus reverse transcriptase substrate-induced conformational changes and the mechanism of inhibition by nonnucleoside inhibitors. Proc. Natl. Acad. Sci. U. S. A. 92,8046-8049[Abstract/Free Full Text]
  150. Mellors, J. W., Dutschman, G. E., Im, G. J., Tramontano, E., Winkler, S. R., Cheng, Y. C. (1992) In vitro selection and molecular characterization of human immunodeficiency virus-1 resistant to non-nucleoside inhibitors of reverse transcriptase. Mol. Pharmacol. 41,446-451[Abstract]
  151. Richman, D., Shih, C. K., Lowy, I., Rose, J., Prodanovich, P., Goff, S., Griffin, J. (1991) Human immunodeficiency virus type 1 mutants resistant to nonnucleoside inhibitors of reverse transcriptase arise in tissue culture. Proc. Natl. Acad. Sci. U. S. A. 88,11241-11245[Abstract/Free Full Text]
  152. Dueweke, T. J., Poppe, S. M., Romero, D. L., Swaney, S. M., So, A. G., Downey, K. M., Althaus, I. W., Reusser, F., Busso, M., Resnick, L., et al (1993) U-90152, a potent inhibitor of human immunodeficiency virus type 1 replication. Antimicrob. Agents Chemother. 37,1127-1131[Abstract/Free Full Text]
  153. Young, S. D., Britcher, S. F., Tran, L. O., Payne, L. S., Lumma, W. C., Lyle, T. A., Huff, J. R., Anderson, P. S., Olsen, D. B., Carroll, S. S., et al (1995) L-743, 726 (DMP-266): a novel, highly potent nonnucleoside inhibitor of the human immunodeficiency virus type 1 reverse transcriptase. Antimicrob. Agents Chemother. 39,2602-2605[Abstract]
  154. Balzarini, J., De Clercq, E., Carbonez, A., Burt, V., Kleim, J. P. (2000) Long-term exposure of HIV type 1-infected cell cultures to combinations of the novel quinoxaline GW420867X with lamivudine, abacavir, and a variety of nonnucleoside reverse transcriptase inhibitors. AIDS Res. Hum. Retroviruses 16,517-528[CrossRef][Medline]
  155. De Clercq, E. (1998) The role of non-nucleoside reverse transcriptase inhibitors (NNRTIs) in the therapy of HIV-1 infection. Antiviral Res. 38,153-179[CrossRef][Medline]
  156. Ren, J., Nichols, C., Bird, L., Chamberlain, P., Weaver, K., Short, S., Stuart, D. I., Stammers, D. K. (2001) Structural mechanisms of drug resistance for mutations at codons 181 and 188 in HIV-1 reverse transcriptase and the improved resilience of second generation non-nucleoside inhibitors. J. Mol. Biol. 312,795-805[CrossRef][Medline]
  157. Spence, R. A., Anderson, K. S., Johnson, K. A. (1996) HIV-1 reverse transcriptase resistance to non-nucleoside inhibitors. Biochemistry 35,1054-1063[CrossRef][Medline]
  158. Das, K., Clark, A. D., Jr, Lewi, P. J., Heeres, J., De Jonge, M. R., Koymans, L. M., Vinkers, H. M., Daeyaert, F., Ludovici, D. W., Kukla, M. J., et al (2004) Roles of conformational and positional adaptability in structure-based design of TMC125–R165335 (etravirine) and related non-nucleoside reverse transcriptase inhibitors that are highly potent and effective against wild-type and drug-resistant HIV-1 variants. J. Med. Chem. 47,2550-2560[CrossRef][Medline]
  159. Delaugerre, C., Rohban, R., Simon, A., Mouroux, M., Tricot, C., Agher, R., Huraux, J. M., Katlama, C., Calvez, V. (2001) Resistance profile and cross-resistance of HIV-1 among patients failing a non-nucleoside reverse transcriptase inhibitor-containing regimen. J. Med. Virol. 65,445-448[CrossRef][Medline]
  160. Bacheler, L., Jeffrey, S., Hanna, G., D’Aquila, R., Wallace, L., Logue, K., Cordova, B., Hertogs, K., Larder, B., Buckery, R., et al (2001) Genotypic correlates of phenotypic resistance to efavirenz in virus isolates from patients failing nonnucleoside reverse transcriptase inhibitor therapy. J. Virol. 75,4999-5008[Abstract/Free Full Text]
  161. Maga, G., Amacker, M., Ruel, N., Hubscher, U., Spadari, S. (1997) Resistance to nevirapine of HIV-1 reverse transcriptase mutants: loss of stabilizing interactions and thermodynamic or steric barriers are induced by different single amino acid substitutions. J. Mol. Biol. 274,738-747[CrossRef][Medline]
  162. Wang, D. P., Rizzo, R. C., Tirado-Rives, J., Jorgensen, W. L. (2001) Antiviral drug design: computational analyses of the effects of the L100I mutation for HIV-RT on the binding of NNRTIs. Bioorg. Med. Chem. Lett. 11,2799-2802[CrossRef][Medline]
  163. Das, K., Lewi, P. J., Hughes, S. H., Arnold, E. (2005) Crystallography and the design of anti-AIDS drugs: conformational flexibility and positional adaptability are important in the design of non-nucleoside HIV-1 reverse transcriptase inhibitors. Prog. Biophys. Mol. Biol. 88,209-231[CrossRef][Medline]
  164. Jochmans, D., Deval, J., Kesteleyn, B., Van Marck, H., Bettens, E., De Baere, I., Dehertogh, P., Ivens, T., Van Ginderen, M., Van Schoubroeck, B., et al (2006) Indolopyridones inhibit human immunodeficiency virus reverse transcriptase with a novel mechanism of action. J. Virol. 80,12283-12292[Abstract/Free Full Text]



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