Activation of G551D CFTR channel with MPB-91: regulation by ATPase activity and phosphorylation

We have designed and synthesized benzo[c] quinolizinium derivatives and eva luated their effects on the activity of G551D cystic fibrosis transmembrane conductance regulator (CFTR) expressed in Chinese hamster ovary and Fisher rat thyroid cells. We demonstrated, using iodide efflux, whole cell patch clamp, and short-circuit recordings, that 5-butyl-6- hydroxy-10-chlorobenzo [c] quinolizinium chloride (MPB-91) restored the activity of G551D CFTR (EC 50 = 85 muM) and activated CFTR in Calu-3 cells (EC50 = 47 muM). MPB-91 has no effect on the ATPase activity of wild-type and G551D NBD1/R/GST fusion proteins or on the ATPase, GTPase, and adenylate kinase activities of purif ied NBD2. The activation of CFTR by MPB-91 is independent of phosphorylatio n because 1) kinase inhibitors have no effect and 2) the compound still act ivated CFTR having 10 mutated protein kinase A sites (10SA-CFTR). The new p harmacological agent MPB-91 may be an important candidate drug to ameliorat e the ion transport defect associated with CF and to point out a new pathwa y to modulate CFTR activity.