Activating cystic fibrosis transmembrane conductance regulator channels with pore blocker analogs

Cystic fibrosis (CF) is caused by mutations that disrupt the surface localization and/or gating of the CF transmembrane conductance regulator ( CFTR) chloride channel. The most common CF mutant is Delta F508-CFTR, which inefficiently traffics to the surfaces of most cells. The Delta F508 mutation may also disrupt the opening of CFTR channels once they reach the cell surface, but the extent of this gating defect is unclear. Here, we describe potent activators of wild-type and Delta F508-CFTR channels that are structurally related to 5-nitro-2-(3-phenylpropylamino) benzoate (NPPB), a negatively charged pore blocker that we show to have mixed agonistic activity ( channel activation plus voltage-dependent pore block). These CFTR agonists include 1) an uncharged NPPB analog that stimulates channel opening at submicromolar concentrations without blocking the pore and 2) curcumin, a dietary compound recently reported to augment Delta F508-CFTR function in mice by an unknown mechanism. The uncharged NPPB analog enhanced the activities of wild-type and Delta F508-CFTR channels both in excised membrane patches and in intact epithelial monolayers. This compound increased the open probabilities of Delta F508-CFTR channels in excised membrane patches by 10-15-fold under conditions in which wildtype channels were already maximally active. Our results support the emerging view that CFTR channel activity is substantially reduced by the Delta F508 mutation and that effective CF therapies may require the use of channel openers to activate mutant CFTR channels at the cell surface.