156P - Simultaneous Inhibition of Chaperone Activity and Chaperone Expression in Human Cancer Cells Sensitizes Them to Chemotherapy and Radiotherapy

Abstract

ABSTRACT Aim: We propose to combine inhibitors of chaperone activity with inhibitors of chaperone expression for better targeting tumors because (i) cancer cells are addicted to the chaperone activity of heat-shock protein 90 (Hsp90), (ii) the Hsp90 chaperone activity inhibitors (e.g. 17AAG) may have a 100-fold higher affinity to Hsp90 in malignant cells than in normal cells, (iii) these Hsp90 inhibitors cause induction of cytoprotective chaperones Hsp70 and Hsp27 that impairs antitumor effects of the Hsp90 inhibition. Methods: MCF-7 and HeLa cell lines derived from human breast and cervical tumors and human normal epithelium or fibroblasts were subjected to 17AAG and inhibitors of the Hsp induction (quercetin, triptolide, NZ28), and conventional drugs (doxorubicin, paclitaxel) or clinically relevant doses of gamma-photon radiation. The cell death/survival was assessed in annexin V-staining and clonogenic assays. The expression of certain cellular proteins was analyzed by western blotting. Results: It was found that 10–100 nM 17AAG significantly retarded proliferation in both the cancer cell lines. As markers of the Hsp90 activity inhibition, the specific depletion of Akt, survivin and HIF-1alpha as well as up-regulation of Hsp70 and Hsp27 were revealed in those cell samples. Co-treatment with 10–30 µM quercetin or 2–4 nM triptolide, or 0.3–1 µM NZ28 prevented the Hsp up-regulation in the 17AAG-treated cancer cells and sensitized them to doxorubicin and paclitaxel, and gamma-radiation. Importantly, no enhanced cytotoxicity was observed in normal human fibroblasts and epithelial cells co-treated by the same way. The enhanced chemo- and radiosensitization of cancer cells appears to be due to simultaneous blockade of both the Hsp90-dependent antiapoptotic pathways and the 17AAG-induced up-regulation of Hsp70 and Hsp27. Conclusions: Combined administration of inhibitors of the Hsp90 chaperone activity and blockers of the concomitant induction of Hsp70 and Hsp27 enables us to selectively sensitize tumors to chemo- and radiotherapy. In perspective, such an approach may be developed into an effectual pharmacological strategy for cancer treatment. Disclosure: All authors have declared no conflicts of interest.