Hsp90 facilitates acquired drug resistance of tumor cells through cholesterol modulation however independent of tumor progression

Acquired multidrug resistance of cancer cells challenges the chemotherapeutic interventions. To understand the role of molecular chaperone, Hsp90 in drug adapted tumor cells, we have used in vitro drug adapted epidermoid tumor cells as a model system. We found that chemotherapeutic drug adaptation of tumor cells is mediated by induced activities of both Hsp90 and P-glycoprotein (P-gp). Although the high-affinity conformation of Hsp90 has correlated with the enhanced drug efflux activity, we did not observe a direct interaction between P-gp and Hsp90. The enrichment of P-gp and Hsp90 at the cholesterol-rich membrane microdomains is found obligatory for enhanced drug efflux activity. Since inhibition of cholesterol biosynthesis is not interfering with the drug efflux activity, it is presumed that the net cholesterol redistribution mediated by Hsp90 regulates the enhanced drug efflux activity. Our in vitro cholesterol and Hsp90 interaction studies have furthered our presumption that Hsp90 facilitates cholesterol redistribution. The drug adapted cells though exhibited anti-proliferative and antitumor effects in response to 17AAG treatment, drug treatment has also enhanced the drug efflux activity. Our findings suggest that drug efflux activity and metastatic potential of tumor cells are independently regulated by Hsp90 by distinct mechanisms. We expose the limitations imposed by Hsp90 inhibitors against multidrug resistant tumor cells.