Objective: Overexpression of the oncogene erbB-2 contributes to chemoresistance in various malignant tumors including lung cancer. The aim of this study was to investigate whether depletion of the erbB-2 gene product (p185) by 17-allylamino 17-demethoxygeldanamycin would sensitize lung cancer cells to paclitaxel (Taxol) in vitro.
Methods: Paclitaxel cytotoxicity was evaluated in a panel of non-small cell lung cancer cell lines that expressed varying levels of p185 by means in vitro proliferation assays and 2 drug combination schedules. Cell cycle kinetics and apoptosis after exposure to paclitaxel or paclitaxel plus 17-allylamino 17-demethoxygeldanamycin were analyzed by flow cytometry.
Results: The 17-allylamino 17-demethoxygeldanamycin treatment efficiently depleted p185 expression in lung cancer cells. Concurrent exposure of these cells to paclitaxel and 17-allylamino 17-demethoxygeldanamycin significantly enhanced paclitaxel-mediated cytotoxicity, particularly in cells which overexpressed p185. There was a 1.3 to more than 20-fold reduction of paclitaxel 50% inhibitory concentration values in those cells that were responding positively to the drug combination. Significant induction of apoptosis was observed after treatment of cells with the combination of paclitaxel and 17-allylamino 17-demethoxygeldanamycin. The combination cytotoxic effect was only additive in cells expressing low levels of p185. In contrast, of lung cancer cells with exposure to 17-allylamino 17-demethoxygeldanamycin before combined paclitaxel and 17-allylamino 17-demethoxygeldanamycin exposure actually rendered the cells refractory to paclitaxel cytotoxicity.
Conclusion: The compound 17-allylamino 17-demethoxygeldanamycin sensitizes non-small cell lung cancer cells expressing high levels of p185 to paclitaxel-mediated growth arrest and apoptosis. These preclinical data support the evaluation of the combination of paclitaxel and 17-allylamino 17-demethoxygeldanamycin in the treatment of patients with lung cancer whose tumors exhibit p185 overexpression.