Small-molecule inhibitor of intestinal anion exchanger SLC26A3 for treatment of hyperoxaluria and nephrolithiasis

Nephrolithiasis is a common and recurrent disease affecting 9% of the US population. Hyperoxaluria is major risk factor for calcium oxalate kidney stones, which constitute two-thirds of all kidney stones. SLC26A3 (DRA, downregulated in adenoma) is an anion exchanger of chloride, bicarbonate, and oxalate thought to facilitate intestinal oxalate absorption, as evidenced by approximately 70% reduced urine oxalate excretion in knockout mice. We previously identified a small-molecule SLC26A3 inhibitor (DRA(inh)-A270) that selectively inhibited SLC26A3-mediated chloride/bicarbonate exchange (IC(50) ~ 35 nM) and, as found here, oxalate/chloride exchange (IC(50) ~ 60 nM). In colonic closed loops in mice, luminal DRA(inh)-A270 inhibited oxalate absorption by 70%. Following oral sodium oxalate loading in mice, DRA(inh)-A270 largely prevented the 2.5-fold increase in urine oxalate/creatinine ratio. In a mouse model of oxalate nephropathy produced by a high-oxalate low-calcium diet, vehicle-treated mice developed marked hyperoxaluria with elevated serum creatinine, renal calcium oxalate crystal deposition, and renal injury, which were largely prevented by DRA(inh)-A270 (10 mg/kg twice daily). DRA(inh)-A270 administered over 7 days to healthy mice did not show significant toxicity. Our findings support a major role of SLC26A3 in intestinal oxalate absorption and suggest the therapeutic utility of SLC26A3 inhibition for treatment of hyperoxaluria and prevention of calcium oxalate nephrolithiasis.