P2.21 Targeting Chaperone Activity and Chaperone Expression for Cancer Cell Sensitization to Chemo-, Radio- and Thermotherapy

Abstract

ABSTRACT Development of clinically applicable methods for selective elimination of malignant cells is the important task of anticancer therapy. For this purpose we used inhibitors of the chaperone activity and chaperone expression to selectively sensitize tumor cells to the cytotoxic action of chemo-, radio- and thermo-therapy (hyperthermia). Our approach was based on three known facts: (i) cancer cells are “addicted” to inducible chaperones (or heat-shock proteins: Hsp90, Hsp70 and Hsp27) whose expression is often enhanced in tumors and correlated with poor outcome for patients, (ii) inhibitors of the Hsp90 chaperone activity (e.g. 17AAG) may have much more higher (~100-fold) affinity toward Hsp90 in cancer cells than in normal cells, and (iii) inhibitors of the Hsp90 chaperone activity cause undesirable induction of Hsp70 and Hsp27 that impair the antitumor effects of the Hsp90 inhibition. Hyperthermia (42-43 C, 60 min) or gamma-irradiation (2-6 Gy), or paxlitaxel(10-50 nM) were used as mono-treatments or with 17AAG and inhibitors of the Hsp induction such as quercetin, triptolide or NZ28 to kill cancer cells derived from human breast and cervical tumors. It was found that 10-100 nM 17AAG significantly enhanced apoptosis and impaired clonogenicity in the cancer cells subjected to hyperthermia or gamma-radiation, or paclitaxel. This enhancement of cytotoxicity correlated with a degree of inhibition of the Hsp90 chaperone activity. As biomarkers of the Hsp90 activity inhibition, the specific depletion of Akt and Raf-1 and up-regulation of Hsp70 and Hsp27 were revealed in the samples of 17AAG-treated tumor cells. Addition of either 10-30 uM quercetin or 2-5 nM triptolide, or 0·3-1 uM NZ28 fully prevented the Hsp accumulation in the 17AAG-treated cancer cells and rendered them much more sensitive to hyperthermia, radiation and paclitaxel. In contrast, almost no enhanced cytotoxicity was observed in normal human fibroblasts and epithelial cells treated by the same way. The achieved chemo-, radio- and thermo-sensitization of tumor cells appears to be due to blockade of the Hsp90-dependent antiapoptotic pathways, and blockade of the 17AAG-induced up-regulation of cytoprotective Hsp70 and Hsp27. The achieved selectivity toward cancer cells allows to expect the enhancement of therapy-associated cytotoxicity just within target tumor area.