AP-C5 is a potent and selective inhibitor of the guanosine 3’;,5’;-cyclicmonophosphate (cGMP)-dependent protein kinase II (cGKII)that selectively blocks cGKII dependent phosphorylation of the vasodilator-stimulated phosphoprotein (VASP) in intestinal organoids. AP-C5 mitigates secretory response provoked by the GCC-activating Escherichia coli heat-stable toxin (STa) in mouse small intestinal tissue.