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-macroc yclic ligand of the FK506-binding protein FKBP12, was evaluated for it s ability to reverse P-glycoprotein-mediated multidrug resistance in v itro. VX-710 at 0.5-5 mu M restored sensitivity of a variety of multid rug resistant cells to the cytotoxic action of doxorubicin, vincristin e, etoposide or paclitaxel, including drug-selected human myeloma and epithelial carcinoma cells, and human MDR1 cDNA-transfected mouse leuk emia and fibroblast cells. Uptake experiments showed that VX-710 at 0. 5-2.5 mu M fully restored intracellular accumulation of [C-14]doxorubi cin in multidrug resistant cells, suggesting that VX-710 inhibits the drug efflux activity of P-glycoprotein. VX-710 effectively inhibited p hotoaffinity labeling of P-glycoprotein by [H-3]azidopine or [I-125]io doaryl azido-prazosin with EC(50) values of 0.75 and 0.55 mu M. Moreov er, P-glycoprotein was specifically labeled by a tritiated photoaffini ty 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-inhibitab le P-glycoprotein ATPase activity 2- to 3-fold in a concentration-depe ndent manner with an apparent k(a) of 0.1 mu M. These data indicate th at a direct, high-affinity interaction of VX-710 with P-glycoprotein p revents efflux of cytotoxic drugs by the MDR1 gene product in multidru g resistant tumor cells.