Inhibition of energy transduction in P‐glycoprotein (974.3)

Abstract

Cancer chemotherapy failures often involve the over‐expression of ABC‐transporters like the MDR1 P‐glycoprotein (P‐gp). These transporters normally protect the cell by pumping toxins and xenobiotics across the plasma membrane. Selection for cells over‐expressing P‐gp during chemotherapy, however, results in populations that are drug resistant. Recently, we used massively parallel in silico drug docking to identify molecules predicted to interact with higher affinity at the energy transducing structures of P‐gp than at the drug transporting structures. In vitro assays verified that the compounds inhibited verapamil‐stimulated ATP hydrolysis and only marginally stimulated basal ATP hydrolysis activities. This indicates that these compounds do not interact with drug binding domains. The effects of the identified compounds on ATP binding was then studied using spin‐labeled ATP analogs and ESR spectroscopy. Results showed that some of the identified compounds decreased ATP binding stoichiometry to P‐gp while others decreased ATP binding affinities. These studies further showed that inhibition by the compounds was reversible. The investigations suggest that the discovered P‐gp inhibitors may make good drug leads. Experiments using ESR spectroscopy and site‐specific spin‐labeling of the drug binding domain are currently underway that may shed further light on the molecular mechanism of inhibition.Grant Funding Source: NIGMS1R15GM094771 ‐ 01A1, Communities Foundations of Texas