Diuresis and reduced urinary osmolality in rats produced by small‐molecule UT‐A‐selective urea transport inhibitors

Urea transport (UT) proteins of the UT‐A class are expressed in epithelial cells in kidney tubules, where they are required for the formation of a concentrated urine by countercurrent multiplication. Here, using a recently developed high‐throughput assay to identify UT‐A inhibitors, a screen of 50,000 synthetic small molecules identified UT‐A inhibitors of aryl‐thiazole, γ‐sultambenzosulfonamide, aminocarbonitrile butene, and 4‐isoxazolamide chemical classes. Structure‐activity analysis identified compounds that inhibited UT‐A selectively by a noncompetitive mechanism with IC 50 down to ~1 μM. Molecular modeling identified putative inhibitor binding sites on rat UTA. To test compound efficacy in rats, formulations and administration procedures were established to give therapeutic inhibitor concentrations in blood and urine. We found that intravenous administration of an indole thiazole or a γ‐sultambenzosulfonamide at 20 mg/kg increased urine output by 3‐5‐fold and reduced urine osmolality by ~ 2‐fold compared to vehicle control rats, even under conditions of maximum antidiuresis produced by 1‐deamino‐8‐D‐arginine vasopressin (DDAVP). The diuresis was reversible and showed urea > salt excretion. The results provide proof of concept for the diuretic action of UT‐A‐selective inhibitors. UT‐A inhibitors are first in their class salt‐sparing diuretics with potential clinical indications in volume‐overload edemas and high‐vasopressin‐associated hyponatremias.—Esteva‐Font, C., Cil, O., Phuan, P.‐W., Su, T., Lee, S., Anderson, M. O., Verkman, A. S. Diuresis and reduced urinary osmolality in rats produced by small‐molecule UT‐A‐ selective urea transport inhibitors. FASEB J. 28, 3878‐3890 (2014). www.fasebj.org