Inhibition of heat-stable toxin–induced intestinal salt and water secretion by a novel class of guanylyl cyclase C inhibitors

Background. Many enterotoxigenic Escherichia coli strains produce the heat-stable toxin, STa, which, by activa- tion of the intestinal receptor-enzyme guanylyl cyclase (GC) C, triggers an acute, watery diarrhea. We set out to identify GCC inhibitors that may be of benefit for the treatment of infectious diarrheal disease. Methods. Compounds that inhibit STa-induced cyclic guanosine 3′,5′-monophosphate (cGMP) production were selected by performing cyclase assays on cells and membranes containing GCC, or the related GCA. The effect of leads on STa/GCC-dependent activation of the cystic fibrosis transmembrane conductance regulator anion chan- nel was investigated in T84 cells, and in porcine and human intestinal tissue. Their effect on STa-provoked fluid transport was assessed in ligated intestinal loops in piglets. Results. Four N-2-(propylamino)-6-phenylpyrimidin-4-one–substituted piperidines were shown to inhibit GCC-mediated cellular cGMP production. The half maximal inhibitory concentrations were ≤5 × 10−7 mol/L, whereas they were >10 times higher for GCA. In T84 monolayers, these leads blocked STa/GCC-dependent, but not forskolin/adenylyl cyclase-dependent, cystic fibrosis transmembrane conductance regulator activity. GCC inhi- bition reduced STa-provoked anion secretion in pig jejunal tissue, and fluid retention and cGMP levels in STa- exposed loops. These GCC inhibitors blocked STa-provoked anion secretion in rectal biopsy specimens. Conclusions. We have identified a novel class of GCC inhibitors that may form the basis for development of future therapeutics for (infectious) diarrheal disease