PTC124 is a inhibitor of Firefly luciferase (FLuc) with IC50 of 7 nM, but PTC124 can also increase cellular FLuc activity levels by posttranslational stabilization. FLuc inhibition and stabilization is the result of an inhibitory product formed during the FLuc-catalyzed reaction between its natural substrate, ATP, and PTC124. And the inhibitory activity of PTC124-AMP is relieved by free coenzyme A. PTC124 can effectively suppress the hCFTR-G542X nonsense mutation in vivo. Oral administration of PTC124 to Cftr-/- mice expressing a human CFTR-G542X transgene suppressed the G542X nonsense mutation and restored a significant amount of human (h)CFTR protein and function.