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,1
* Intervention Section, Cell and Cancer Biology Department, Medicine Branch, Division of Clinical Science, National Cancer Institute, and
Head and Neck Surgery Branch, National Institute of Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA; and
Procter and Gamble Oral Health Care Technology Division, Cincinnati, Ohio, USA
2Correspondence: Intervention Section, National Cancer Institute, Bldg. 10/12N226, 9000 Rockville Pike, Bethesda, MD 20892, USA. E-mail: mulshinej{at}bprb.nci.nih.gov
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, GM-CSF levels, or in vitro tumor cell
growth. In contrast, ketorolac reduced OPC growth in
vivo. The OPC cell lines used express the IL-6 receptor, and
IL-6 stimulation of these cells causes transduction to occur via STAT3
pathway activation. Coincubation with OPC cell lines with conditioned
medium from a TPA-exposed HL-60 cells stimulated growth proportional to
the IL-6 levels measured in the conditioned medium. This growth effect
was specifically inhibited by anti-IL-6 antibody. These results are
consistent with cytokine products of inflammatory cells having
paracrine growth effects on OPC. If chronic inflammation plays a role
in promoting the development of OPC, this mechanism may also apply to
other epithelial tumor systems modulated by COX activity.—Hong,
S. H., Ondrey, F. G., Avis, I. M., Chen, Z., Loukinova,
E., Cavanaugh, P. F., Jr., Van Waes, C., Mulshine, J. L.
Cyclooxygenase regulates human oropharyngeal carcinomas via the
proinflammatory cytokine IL-6: a general role for inflammation?.
Key Words: colon cancer • arachidonic acid • inflammatory disease • COX inhibitors
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. OPCs have been reported to produce a variety of
eicosanoids that may affect cancer cell proliferation (2
, 3)
, inflammatory cell proliferation (4)
, or inhibit
the immune response (5)
. The prostaglandins are produced
by the catalytic action of two isoforms of prostaglandin endoperoxide
synthase or cyclooxygenase (COX), specifically COX-1 and COX-2, on
arachidonic acid (AA) (6
, 7)
. COX-1 is thought to be
expressed constitutively. In contrast, expression of COX-2 is induced
in response to a variety of physiological stimuli including cytokines,
growth factors, bacterial endotoxins, phorbol esters, chemical
carcinogens, and inflammatory mediators (8
9
10)
. Increased
amounts of COX-2 mRNA and protein have been observed in human tumors of
several lineages (11
12
13
14)
, particularly colon cancer
(15)
. Inhibitors of COX-2 can modulate apoptosis and
suppress carcinogenesis, and suggest that this is the basis for the
favorable effect of aspirin and nonsteroidal antiinflammatory drugs on
reducing colon cancer frequency (16)
. Studies have
suggested that the effects of COX-2 are mediated through the regulation
of cytokine production (17
, 18)
, but controversy exists as
to the precise role of COX activity in the progression of cancer
(19)
. Highly selective COX-2 inhibitors have been
developed to avoid the occurrence of gastrointestinal bleeding
associated with systemic administration of pan-COX inhibitors. To
minimize systemic exposure and maximize delivery to the site of action,
the concept of using an NSAID-containing oral rinse was developed to
treat periodontitis, a chronic infectious inflammatory disease of the
oral cavity (20)
. Ketorolac tromethamine, a pan-COX
inhibitor, was developed for this application due to its demonstrated
potency in the nanomolar range as well as lack of irritation (21
, 22)
. A tailored formulation of the drug allowed for desirable
gingival penetration resulting in favorable tissue residence time
(23)
. Local administration of ketorolac reduces the risk
of gastric toxicity associated with other systemically administered
pan-COX inhibitor. In these periodontal trials, ketorolac was effective
in completely inhibiting pan-COX activity without any significant
subjective side effect. Consequently, in this setting there is no
incentive for narrowing the spectrum of the COX enzyme inhibition.
Furthermore, emerging data suggest that COX-1 activity may contribute
to carcinogenesis, so that maintaining pan-COX inhibition may be
beneficial (24
25
26)
.
An important question is, How general is the contribution of COX
biology to the development of other epithelial cancers? Can the
frequency of other cancers be reduced comparably to what is seen for
colon cancer? To address this question, we have evaluated the potential
contribution of COX activity to the development of OPC. Up-regulation
of the COX-2 isoenzyme in head and neck cancers has been reported
recently (11)
. This paper explores a series of issues
related to the potential mechanism of COX 's role in OPC. Our
hypothesis in these studies is that COX activity is having a comparable
role in OPC to the mechanism of action suggested by Potter for COX
activity in the development of B cell plasmacytomagenesis
(27)
. The essential elements of Potter’s model include
prostaglandin E2 (PGE2)
-dependent recruitment of inflammatory cells, production and local
release of interleukin 6 (IL-6), as well as IL-6-dependent clonal
expansion of initiated B cell populations. In this paper, we
demonstrate that oropharyngeal cancer cell lines also express the
components of the COX pathway previously reported in
plasmacytomagenesis. Further, growth dependence on IL-6 is evaluated to
determine whether the progression of OPC could proceed by the
mechanisms of inflammatory cross stimulation described by Potter
(27)
. Based on these results, we have initiated a Phase
IIB randomized, placebo-controlled chemoprevention trial. NIH Clinical
Center 98-C-0118 evaluates the ability of a general COX inhibitor,
ketorolac rinse, to arrest the progression of oropharyngeal
leukoplakia.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. Squamous carcinoma NA and CA99–2 cells were derived
from oral cavity cancers and were a generous gift of Dr. Toshio Kuroki.
The origin and characterization of metastatic cell line PAM LY-2 have
been described previously (29
30
31)
. These lines were
cultured at 37°C, 5% CO2 as adherent monolayer
cultures in EMEM (minimum essential medium with Earle’s salts) (Life
Technologies, Inc./BRL, Gaithersburg, Md.) with 10% heat-inactivated
fetal calf serum (Life Technologies, Inc./BRL) containing 2 mM
L-glutamine and penicillin (50 µg/ml)/streptomycin (50 µg/ml). All
cell lines were found to be free of mycoplasma. Log-phase cells were
routinely subcultured weekly after trypsinization.
Chemicals
Ketorolac, prostaglandin E2 Enzyme
Immunoassay Kit (PGE2-EIA), anti-COX-1 antibody,
and anti-COX-2 antibody were both purchased from Cayman Chemical Co.
(Ann Arbor, Mich.). MK866 was purchased from Biomol, Inc. (Plymouth
Meeting, Pa.). Anti-IL-6 receptor was purchased from Biosource
International (Camarillo, Calif.). Standard ELISA assay kits for
IL-1, IL-6, IL-8, and granulocyte-macrophage colony-stimulating
factor (GM-CSF) were purchased from R&D Systems (Minneapolis, Minn.).
mRNA expression
The squamous cell carcinoma cell lines were evaluated for a
range of targets involved in AA metabolism including 5-lipoxygenase
(LOX), 12-LOX, 15-LOX, FLAP, COX-1, and COX-2 using the reverse
transcriptase polymerase chain reaction (RT-PCR) as described
previously (32)
. Amplification products for 5-LOX, FLAP,
12-LOX, 15-LOX, COX-1, and COX-2 were determined by ethidium bromide
staining and Southern blot analysis.
Growth studies
We used a modification of the CellTiter 96 (Promega, Madison,
Wis.) semiautomated MTT colorimetric assay, which were performed as
previously published (33)
. Cells were fed with media
containing serum 48 h prior to adding inhibitors, cytokines, or
antibodies. After trypsin treatment and washing, cells were maintained
in serum-free, keratinocyte-SFM media (Life Technologies, Inc., Grand
Island, N.Y.). Seeding densities were 1–2 x
104 cells/well; cells were grown for 3 or 4 days
during the assays.
PGE2 analysis
PGE2 samples were prepared and analyzed by
the prostaglandin E2 Enzyme Immunoassay Kit
according to the manufacturer’s manual. The cells were incubated for
24 h in defined media (keratinocyte-SFM). Data were analyzed using
IBM Software for EIA Data Analysis purchased from Cayman Chemical Co.
Cytokine quantitation
Twelve milliliters of fresh medium were added to tumor cell
lines when 50–70% confluent in 75 cm2 flasks.
After 24 h specimens were collected, aliquoted, and frozen at
-80°C until assayed. Cells were trypsinized and counted, and all
results were standardized for amount of cytokine secreted as
pg/106 cells. Standard ELISA assay kits for
IL-1, IL-6, IL-8, and GM-CSF were used according to the instructions
of the manufacturer (R&D Systems). Standard curves were generated with
recombinant cytokine standards provided with each kit and
concentrations were determined using least square analysis to a zero
order function. Complete medium was used as a blank. Cytokines were
quantitated with an EIA plate reader at 450 nm (Biotek 311, Biotek
Systems, Winooski, Vt.). All samples were assayed in duplicate.
Western blot analysis
Cells were grown 24 h in EMEM with containing 0.5% serum
for 2 days. Cells were then incubated in serum-free media for 2 h,
followed by a 20 min incubation in the presence or absence of 10 mg/ml
of IL-6. Extracts corresponding to 2 x 106
cells were fractionated on 7.5% sodium dodecyl sulfate-polyacrylamide
gels, transferred to nitrocellulose membranes, and incubated with
specific STAT3 antiserum, phospho-specific (tyr-705) anti-STAT3 (New
England Biolabs, Beverly, Mass.). Detection was by enhanced
chemiluminescence (Amersham, Arlington Heights, Ill.).
Immunohistochemistry
Cells prepared by cytospin were fixed using 4% formalin and
incubated with anti-COX-1, anti-COX-2, or anti-IL-6 receptor primary
antibodies (2.5 µg/ml) diluted in phosphate-buffered saline
containing 1 mg/ml bovine serum albumin for 2 h, rinsed with the
same solution for 30 min, and incubated with biotinylated goat
anti-mouse immunoglobulin G (1/200 dilution, Vectastain ABC Elite kit,
Vector Laboratory, Burlingame, Calif.) for 60 min. The samples were
then exposed to avidin-biotin complex (ABC Elite kit, Vector
Laboratory) and reacted with diaminobenzidine according to the
manufacturer’s recommendations and counterstained with hematoxylin.
In vivo treatment of COX inhibitors
All experiments with mice were approved by NINDS Animal Care and
Use Committee under protocol 809–97. PAM LY-2 cell lines were
harvested with trypsin/EDTA, washed three times with EMEM, and
resuspended at a concentration of 5 x 106
cells/200 µl EMEM. Male BALB/c mice, 6–8 wk of age, were inoculated
subcutaneously with 200 µl of cell suspension in the right flank.
Three days after injection of tumor cells, the experimental groups of
animals were given ketorolac 0.6 mg/kg body weight in drinking water
each day for 5 wk. The control group received water without drugs.
Tumor volumes were determined twice a week. Tumor size was calculated
using the formula: tumor size = tumor width x tumor length.
After the tumor area reached ~2 cm2, the mice
were killed by CO2 inhalation. The lungs were
removed and stained in Bouin’s solution for metastases; lung surface
metastatic colonies were counted after 5 days.
Statistics
Significance of difference between samples was determined using
Student’s paired t test. P < 0.05 was regarded
as significant.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Our previous report shows that ~60% of a range of epithelial
cancer cell lines express COX-2 whereas all epithelial cell lines
tested produce COX-1 (32)
. Immunohistochemical analysis
demonstrated that both enzymes are produced in the OPC cell lines
(Fig. 1A, B
). The finding that COX-2 is consistently expressed in
OPC cell lines agree with a previous immunohistochemical study
demonstrating the presence of COX-2 in OPC tumor specimens from
patients (11)
. For comparison, we evaluated the frequency
of mRNA from the expression of several AA metabolizing enzymes and
related protein 5-lipoxygenase activating protein (FLAP) in OPC (Table 1)
.
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Effect of ketorolac on PGE2 production in OPC cells
PGE2 is abundantly produced in
vitro and in vivo by OPC (34
, 35)
. When
cells are stimulated or free AA is added exogenously,
PGE2 is synthesized and released into the
extracellular space. To evaluate the effect of ketorolac on
constitutive PGE2 production,
PGE2 enzyme immunoassays were performed on
unstimulated OPC lines treated with ketorolac. Twenty-four hours after
ketorolac treatment, the production of PGE2 in
UMSCC9 and UMSCC11B cell lines was greatly reduced, with an
IC50 value of 0.8 and 5 µM, respectively
(Fig. 2A
).
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Effect of ketorolac on cell growth of OPC cells
Cellular proliferation was next assessed after cell line treatment
with ketorolac for 3 or 4 days at concentrations ranging from 10 nM to
100 µM. No growth inhibition was observed in any of the five cell
lines for this range of concentrations. Comparable results were also
seen with indomethacin (data not shown). Serum-free medium was used for
these experiments so that serum binding to the inhibitor could be
excluded as a cause for the lack of inhibitory effect. Conversely,
other experiments with the selective LOX inhibitor MK866 demonstrated
marked growth inhibition, suggesting that the other inhibitors of
eicosanoid metabolism inhibition may have anti-proliferative effects
independent of cross talk with the COX pathways (Fig. 2B
).
Effect of ketorolac on production of cytokines in OPC cells
In human and murine squamous tumor systems, proinflammatory
cytokines including IL-1, IL-6, IL-8, and GM-CSF are frequently
produced and are associated with tumor growth and metastatic
progression in vivo (36)
. To study the effect
of ketorolac on the elaboration of proinflammatory cytokines, cells
were cultured with ketorolac under serum-free and serum-containing
conditions and analyzed for the effect of ketorolac on cytokine
production. Cytokines were quantitated from standard curves obtained
with recombinant cytokines and reported as normalized value in
pg/106 cells/24 h. Ketorolac at 10 and 50 µM
inhibited IL-8 production by 50% in UMSCC-9 and 25% in the UMSCC-11B
cell line. There was a 30% decrease in IL-6 production with UMSCC11B.
However, ketorolac at 10 and 50 µM did not significantly affect the
production of IL-1, and GM-CSF in OPC (Fig. 3A
, B
, C
, D
, E
, F
, G
, H
). Negligible effects on cytokine production were
observed in 10% serum-containing media, which are consistent with the
previous observation in vitro (2
, 32)
.
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Effect of exogenous cytokines on cell growth of OPC cells
It has been hypothesized that proinflammatory cytokines (including
IL-6 and IL-8) from tumor cells or their inflammatory infiltrates
confer a growth advantage to tumors (30
, 36)
. To test this
hypothesis, cell proliferation experiments were performed with IL-6 or
IL-8 added exogenously to the OPC cell lines. When IL-6 (1 ng/ml) was
added to serum-free medium, proliferation of three of the oropharyngeal
cancer cells increased by 30% to 50% (Fig. 4A
, B
, C
). Exogenously added IL-8 (1 µg/ml) increased the
growth of UMSCC9 cells by 30% (Fig. 4D
), but did not
increase the growth of UMSCC11B (Fig. 4E
) or UMSCC38 (Fig. 4F
). To test the specificity of IL-6 stimulation, we added
IL-6 receptor antagonist (IL-6 RA) and IL-6 neutralizing antibody
(anti-IL-6 Ab) to the culture medium to neutralize endogenous
extracellular IL-6-induced proliferation. Neutralizing IL-6 RA at 10
µg/ml blocked the activity of IL-6 on UMSCC38 cells (Fig. 5A
), which suggests an IL-6 receptor-specific proliferative
effect. Antibody to IL-6 also blocked the activity of IL-6 on UMSCC38
in a dose-dependent manner (Fig. 5B
). These results are
consistent with IL-6 stimulating OPC growth in a paracrine fashion; as
suggested in Fig. 4
, these cell lines also produce variable amounts of
IL-6 in defined media without additional IL-6. The addition of
neutralizing antibody to IL-6 or IL-6 receptor had no significant
effect on the growth of UMSCC9, which produces small amounts of IL-6
(Fig. 5C
). In contrast, UMSCC11B, which produces large
amounts of IL-6, displayed marked growth inhibition when exposed to
neutralizing antibody to IL-6 or IL-6 receptor (Fig. 5D
).
These results suggest both autocrine and paracrine roles for IL-6 on
OPC cell lines.
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IL-6 induces STAT signaling in OPC cells
IL-6 receptor is present in the membrane as well as the cytoplasm.
This receptor is thought to signal through the phosphorylation of
STAT3. To further evaluate the specific nature of this stimulation, we
monitored STAT3 phosphorylation in IL-6 receptor-positive UMSCC9 cells
(Fig. 1D
) after IL-6 exposure. After 20 min exposure to
IL-6, levels of phosphorylated-STAT3 were greatly increased compared to
unexposed cells (Fig. 1E
), suggesting that functional IL-6
receptors were present in the OPC cell lines.
COX inhibitors reduce tumor growth in vivo
Although ketorolac did not reduce in vitro OPC growth,
we determined whether it could exert an anti-proliferative effect by
disrupting paracrine effects of IL-6 producing cell populations
in vivo. To evaluate this possibility, we used the
aggressive in vivo, syngeneic murine squamous cell cancer
model LY-2. This model was selected because it has been extensively
characterized with regard to its cytokine production of IL-6 (29
, 30)
. Treatment of tumor-bearing mice daily with ketorolac for 3
wk produced a statistically significant reduction in tumor size
(P<0.01) (Fig. 6
). Also metastatic dissemination of LY-2 was detected in three of five
(60%) control mice compared to only two of eight (25%) ketorolac
treated mice. Comparable results were also seen with indomethacin (data
not shown).
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Effect of HL-60 conditioned medium (CM) on growth of OPC cells
To test the hypothesis that inflammatory cells (including
tumor-associated monocytes) may elaborate growth-conferring substances
to the tumor milieu, we used CM from promyelocytic HL-60 cells.
Treatment of HL-60 cells with phorbol esters (TPA) induces
macrophage-like differentiation (37)
. Differentiated HL-60
cells have enhanced ability to produce varieties of growth factors and
cytokines. The amount of IL-6 produced by HL-60 cells increased from
100 ng/ml to 160 ng/ml after TPA stimulation. In proliferation
experiments, we observed that CM from TPA-stimulated HL-60 cells
increased the proliferation of UMSCC9 cells by 100% over CM from
non-TPA-exposed HL-60 cells (Fig. 7
). Neutralizing antibody to IL-6 receptor shows that CM-induced growth
stimulation was blocked in a dose-dependent manner (Fig. 8
). These data suggest that differentiated HL-60 CM mediates growth
stimulation via IL-6 receptor activation.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. In the current report,
both COX-1 and COX-2 isoforms were found to be expressed by all five
OPC lines compared to a frequency of 60% for COX-2 expression that we
reported for other types of epithelial cancer cell lines
(32)
. Dannenberg and co-workers (11)
recently
reported abundant expression of COX-2 mRNA and protein in tumor
specimens from patients with head and neck cancer contrasted with low
expression in adjacent normal tissue. Taken together, these data are
consistent with COX activity having an important role in oropharyngeal
carcinogenesis.
Prostaglandins are mediators of a wide variety of pathophysiological
processes; increased levels of prostaglandins have been reported with
human OPC as well as with other epithelial cancer cells (34
, 35)
. OPC cells can express a range of proinflammatory cytokines
such as IL-1, IL-6, IL-8, and GM-CSF at variable concentrations.
These cell products can partake in a complex set of autocrine,
paracrine, and/or endocrine interactions (36)
. Our results
with COX inhibition by ketorolac were similar to a parallel experiment
with indomethacin in regard to the production of
PGE2, cytokines as well as in vitro
and in vivo growth (data not shown). Ketorolac was
specifically formulated for local delivery and mucosal penetration in
the oral cavity to control the infectious inflammatory disease,
periodontitis (39)
. In randomized, double-blind,
placebo-controlled clinical trials, ketorolac administered twice daily
has been shown to consistently arrest the progression of periodontal
disease and significantly decrease the oral mucosal levels of
PGE2 (40)
. Using OPC cell lines,
ELISA analysis showed that ketorolac significantly reduced the in
vitro production of IL-6 and IL-8, but did not directly affect the
production of IL-1 and GM-CSF. Despite this marked effect on
reduction of specific cytokine levels, the pan-COX inhibitor ketorolac
did not inhibit in vitro proliferation of any of the
oropharyngeal cancer cell lines at 72–96 h. This is the same situation
described by Potter (27)
for the in vitro
response of B cell populations to another pan-COX inhibitor,
indomethacin. In contrast to the in vitro situation,
ketorolac was effective in significantly reducing the in
vivo tumor growth of OPC. This finding is also consistent
with Potter’s finding of indomethacin causing in vivo
inhibition of plasmacytomagenesis in BALB/c mice (27)
.
This result with in vivo COX inhibition was the basis for
Potter’s mechanistic proposal, which suggests a pivotal role for
chronic prostaglandin-dependent inflammation in promoting
plasmacytomagenesis. The presence of cytokine-producing inflammatory
cells for the in vivo experiments but not for the in
vitro assay may be the basis for the differential sensitivity to
the COX inhibitors. Stimulated macrophage populations produce a variety
of inflammatory mediators that could potentially exert growth-promoting
effects on clonal populations of epithelial cells. Our working model
involving interaction of COX and inflammatory mediator is presented in
Fig. 9
. Other exogenously added proinflammatory cytokines such as IL-8
can also increase the growth of OPC, so we suspect that these cross
feeding effects are a general phenomenon.
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The presence of IL-6-responsive signaling circuits in OPC is a recent
observation, but the ability of epithelial cells to respond to immune
cell products is well supported (41)
. Proinflammatory and
proangiogenic cytokines produced by squamous cancer cells have been
suggested to play an important role in promotion of tumor progression,
highlighting the importance of the interaction between malignant cells
and surrounding inflammatory cells (27
, 29
, 30
, 36
, 42)
.
The cross feeding of the OPC cells with the conditioned media from
TPA-exposed HL-60 cells was an attempt to model the type of community
interactions mediated by COX activation that are relevant to in
vivo carcinogenesis. Such proposed paracrine interactions are
similar to the type of community interactions found in prokaryotic
systems such as bacterial biofilm (43)
. Short-term
cultures of activated macrophages could have been used as an
alternative source of IL-6, but it is difficult to standardize
reproducible experimental conditions. Whereas there are good sources of
mouse macrophage lines, the availability of human macrophage lines is
much more limited. We used UMSCC9 for the cross feeding experiments
because the amount of autocrine IL-6 produced by this cell line was
minimal and not required for growth as was the case with UMSCC11B as
shown in Fig. 5C, D
. The in vitro production of
proinflammatory cytokines is heterogeneous both quantitatively and
qualitatively (30
, 36)
. We speculate that this repertoire
of cytokine production is more frequent in cell lines established from
advanced cancers. Early clonal population of initiated cells in the
oral cavity may be more consistently dependent on the cytokines
produced locally by the non-cancer cell population. This possibility is
supported by the epidemiological data, which suggest chronic COX
inhibition results in reduced risk for colon cancer development
(44)
.
Several alternatives have been proposed for the mechanism by which COX
has an effect on epithelial cell growth (26
, 45
, 46)
.
Kinzler and co-workers have suggested a role for the buildup of
ceramide in response to COX inhibition as triggering apoptosis and
accounting for the anti-proliferative effect of these compounds
(47)
. The induction of apoptosis by ceramide is well
established, but the relative contribution of this mechanism to the
inhibition of carcinogenesis in this context is unclear
(48)
. Although the mechanisms are not mutually exclusive,
further analysis of the relative importance of these two mechanisms is
warranted.
We used ketorolac as a pan-COX inhibitor in this study since it was
developed as a rinse for use in the oral cavity to block prostanoid
activity without incurring gastrointestinal adverse effect
(39)
. Though this favorable therapeutic index makes direct
delivery of ketorolac attractive as a chemoprevention candidate, there
is another benefit of being able to use a pan-COX inhibitor to arrest
the progression of OPC. Emerging data suggest that COX-1 activity
overlap with COX-2 in the carcinogenic process (24
25
26
, 39
, 49)
, implying that pan-COX inhibition may be required for
effective long-term treatment and/or prevention of OPC.
In conclusion, our initial experiments suggest a pivotal role for IL-6
as an autocrine or paracrine product in oropharyngeal cancer cell
regulation. This type of cross feeding mechanism could involve other
cytokines as well. Indirect regulation of inflammatory cytokines by COX
in non-neoplastic cells may drive cancer cell growth in a paracrine
fashion, providing a direct link between the biology of cancer and
inflammation. We also recognize that sources of cytokine production may
not originate solely from inflammatory cells, but from other local
cells such as the epithelium and stromal cells (50)
or the
tumor itself, as shown in this report. There is a growing awareness of
the complex contribution of the microenvironment to the induction of a
cancer. Examples of this include the relationship of epithelial cell
interaction with the stroma (51)
. A more complete
understanding of such issues is critical, especially with regard to
developing more relevant models for drug discovery. The contribution of
proinflammatory cytokines to other chronic diseases is emerging
(19)
. Our report suggests that the cytokine-rich oral
environment of an individual with periodontal disease could contribute
to accelerating carcinogenesis. Recent data also suggest a contributory
role of gram-negative periodontal pathogens being associated with
increased levels of circulating cytokines and elevated risk of
cardiovascular disease (52
, 53)
. Taken together, these
results may force a reconsideration of the significance of an unbridled
chronic inflammatory condition such as periodontal disease relative to
its contribution to other more ominous health conditions. Local
inhibition of COX may be of particular strategic importance in this
context.
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FOOTNOTES |
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Received for publication August 31, 1999.
Revision received January 3, 2000.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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of nuclear factor—KB in human head and neck cancer inhibits survival, proinflammatory cytokine expression, and tumor growth in vivo. Cancer Res 59,3468-3474This article has been cited by other articles:
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G. Dong, Z. Chen, Z.-Y. Li, N. T. Yeh, C. C. Bancroft, and C. Van Waes Hepatocyte Growth Factor/Scatter Factor-induced Activation of MEK and PI3K Signal Pathways Contributes to Expression of Proangiogenic Cytokines Interleukin-8 and Vascular Endothelial Growth Factor in Head and Neck Squamous Cell Carcinoma Cancer Res., August 1, 2001; 61(15): 5911 - 5918. [Abstract] [Full Text] [PDF]
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