Mechanism Based Inhibition of P‐glycoprotein

Multidrug resistances (MDR) pose a significant obstacle in the treatment of cancer and other diseases by decreasing the efficacy of therapeutics. MDR is often associated with the overexpression of ABC transporters like P‐glycoprotein (P‐gp) and has been linked to poor outcome in the treatment of cancers. Inhibiting these transporters could reverse the MDR phenotype, but so far clinical trials of inhibitors of P‐gp have only been moderately successful. We are employing a novel mechanism‐based approach in our search for P‐gp inhibitors to identify lead compounds that are specifically targeted at the energy transduction processes of the transporters. Using computational simulations of the catalytic transport cycle, drug docking and biochemical analyses, we identified four compounds capable of inhibiting ATP hydrolysis through interactions with the energy transducing structures in P‐gp. Three of these compounds reversed MDR phenotype in cancer cell culture models. The molecular mechanisms of P‐gp inhibition by these compounds was evaluated using biochemical and biophysical techniques. Kinetic analyses examined the modalities of inhibition and their drug‐like properties. Electron spin resonance spectroscopy using spin‐labeled nucleotides and site‐directed spin labeling evaluated the binding interactions of the inhibitors. Experiments designed to evaluate where in the catalytic mechanism the inhibitors block P‐gp's action are under way. This work is supported by NIH NIGMS [Grant 1R15‐GM094771‐01A1] to PDV and JGW, SMU Research Council, SMU Dean's Research Council, the SMU Center for Drug Discovery, Design and Delivery, and the Communities Foundation of Texas, Dallas.