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Urearetics: a small molecule screen yields nanomolar potency inhibitors of urea transporter UT-B

Departments of Medicine and Physiology, Cardiovascular Research Institute, Graduate Group in Biophysics, University of California, San Francisco, California, USA

¹Correspondence: 1246 Health Sciences East Tower, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA 94143-0521, USA. E-mail: verkman{at}itsa.ucsf.edu

Functional studies in knockout mice indicate a critical role for urea transporters (UTs) in the urinary concentrating mechanism and in renal urea clearance. However, potent and specific urea transport blockers have not been available. Here, we used high-throughput screening to discover high-affinity, small molecule inhibitors of the UT-B urea transporter. A collection of 50,000 diverse, drug-like compounds was screened using a human erythrocyte lysis assay based on UT-B-facilitated acetamide transport. Primary screening yielded 30 UT-B inhibitors belonging to the phenylsulfoxyoxazole, benzenesulfonanilide, phthalazinamine, and aminobenzimidazole chemical classes. Screening of 700 structurally similar analogs gave many active compounds, the most potent of which inhibited UT-B urea transport with an EC₅₀ of 10 nM, and 100% inhibition at higher concentrations. Phenylsulfoxyoxazoles and phthalazinamines also blocked rodent UT-B and had good UT-B vs. UT-A specificity. The UT-B inhibitors did not reduce aquaporin-1 (AQP1)-facilitated water transport. In AQP1-null erythrocytes, "chemical UT-B knockout" by UT-B inhibitors reduced by 3-fold UT-B-mediated water transport, supporting an aqueous pore pathway through UT-B. UT-B inhibitors represent a new class of diuretics, "urearetics," which are predicted to increase renal water and solute clearance in water-retaining states.—Levin, M. H., de la Fuente, R., Verkman, A. S. Urearetics: a small molecule screen yields nanomolar potency inhibitors of urea transporter UT-B.

Key Words: urea transport • UT-B • kidney • diuretic • drug discovery • small-molecule discovery • aquaporin