Lonidamine and analogue AF2785 block the cyclic adenosine 3 ',5 '-monophosphate-activated chloride current and chloride secretion in the rat epididymis

The cystic fibrosis transmembrane conductance regulator (CFTR) or the small conductance cAMP-activated chloride channel encoded by the CFTR gene has b een shown to play an important role in the formation of the epididymal flui d microenvironment. Mutation of the gene has led to widespread effects on m ale reproduction. Like other ion channels, CFTR is amenable to pharmacologi cal intervention. Blocking CFTR in the epididymis could in principle lead t o disruption of the epididymal fluid environment. We report for the first t ime two indazole compounds: lonidamine and 1-(2,4-dichlorobenzyl) -indazole -3-acrylic acid (AF2785) are potent blockers of CFTR in the epididymis. Whe n added to the external solution under whole-cell patch clamp conditions, A F2785 and lonidamine inhibited the cAMP-activated chloride current in rat e pididymal cells with apparent IC50 values of 170.6 and 631.5 mu M, respecti vely; by comparison the IC50 Value for diphenylamine-2-carboxylate, a well- known chloride channel blocker was 1294 mu M. In cultured rat epididymal ep ithelia mounted in a Ussing chamber, AF2785 and lonidamine inhibited the cA MP-stimulated short-circuit current (a measure of chloride secretion) when added to the apical bathing solution with potency greater than any known ch loride channel studied. It is proposed that in view of the important role C FTR plays in male reproduction, further study with these and other new inda zole compounds for their CFTR blocking actions can provide a new avenue of research into the development of novel male contraceptives.