Cellular and biochemical characterization of VX-710 as a chemosensitizer: Reversal of P-glycoprotein-mediated multidrug resistance in vitro

VX-710 or (S)-N-[2-Oxo-2-(3,4,5-trimethoxyphenyl)a cetyl]-piperidine-2-carboxylic acid 1,7-bis(3-pyridyl)-4-heptyl ester, a novel non-macrocyclic ligand of the FK506-binding protein FKBP12, was evaluated for its ability to reverse P-glycoprotein-mediated multidrug resistance in vitro. VX-710 at 0.5-5 mu M restored sensitivity of a variety of multidrug resistant cells to the cytotoxic action of doxorubicin, vincristine, etoposide or paclitaxel, including drug-selected human myeloma and epithelial carcinoma cells, and human MDR1 cDNA-transfected mouse leukemia and fibroblast cells. Uptake experiments showed that VX-710 at 0.5-2.5 mu M fully restored intracellular accumulation of [C-14]doxorubicin in multidrug resistant cells, suggesting that VX-710 inhibits the drug efflux activity of P-glycoprotein. VX-710 effectively inhibited photoaffinity labeling of P-glycoprotein by [H-3]azidopine or [I-125]iodoaryl azido-prazosin with EC(50) values of 0.75 and 0.55 mu M. Moreover, P-glycoprotein was specifically labeled by a tritiated photoaffinity analog of VX-710 and unlabeled VX-710 inhibited analog binding with an EC(50) of 0.75 mu M. VX-710 also stimulated the vanadate-inhibitable P-glycoprotein ATPase activity 2- to 3-fold in a concentration-dependent manner with an apparent k(a) of 0.1 mu M. These data indicate that a direct, high-affinity interaction of VX-710 with P-glycoprotein prevents efflux of cytotoxic drugs by the MDR1 gene product in multidrug resistant tumor cells.