SLC26A6-selective inhibitor identified in a small-molecule screen blocks fluid absorption in small intestine

SLC26A6 (also known as putative anion transporter 1 [PAT1]) is a Cl(–)/HCO(3)(–) exchanger expressed at the luminal membrane of enterocytes where it facilitates intestinal Cl(–) and fluid absorption. Here, high-throughput screening of 50,000 synthetic small molecules in cells expressing PAT1 and a halide-sensing fluorescent protein identified several classes of inhibitors. The most potent compound, the pyrazolo-pyrido-pyrimidinone PAT1(inh)-B01, fully inhibited PAT1-mediated anion exchange (IC(50) ~350 nM), without inhibition of the related intestinal transporter SLC26A3 (also known as DRA). In closed midjejunal loops in mice, PAT1(inh)-B01 inhibited fluid absorption by 50%, which increased to >90% when coadministered with DRA inhibitor DRA(inh)-A270. In ileal loops, PAT1(inh)-B01 blocked fluid absorption by >80%, whereas DRA(inh)-A270 was without effect. In colonic loops, PAT1(inh)-B01 was without effect, whereas DRA(inh)-A270 completely blocked fluid absorption. In a loperamide constipation model, coadministration of PAT1(inh)-B01 with DRA(inh)-A270 increased stool output compared with DRA(inh)-A270 alone. These results provide functional evidence for complementary and region-specific roles of PAT1 and DRA in intestinal fluid absorption, with PAT1 as the predominant anion exchanger in mouse ileum. We believe that PAT1(inh)-B01 is a novel tool to study intestinal ion and fluid transport and perhaps a drug candidate for small intestinal hyposecretory disorders such as cystic fibrosis–related meconium ileus and distal intestinal obstruction syndrome.