The effect of 17-allylamino-17-demethoxygeldanamycin alone or in combination with paclitaxel on anaplastic thyroid carcinoma cells

The effect of 17-allylamino-17-demethoxygeldanamycin (17-AAG), an hsp90 inhibitor, alone or in combination with paclitaxel on survival of anaplastic thyroid carcinoma (ATC) was evaluated. In 8505C and CAL62 cells, after treatment of 17-AAG, cell viability decreased, and the percentage of dead cells increased. 17-AAG did not cause cleavage of caspase-3 protein, and change expression of IAPs. Pretreatment of z-VAD-fmk did not alter cell viability and the percentage of dead cells. In 17-AAG-treated cells, knockdown of p53 rescued growth inhibition, while cycloheximide attenuated cell death. When cells were treated with both 17-AAG and paclitaxel, all of the combination index values were higher than 1, indicating antagonism between 17-AAG and paclitaxel. In 17-AAG- and paclitaxel-treated cells, compared with paclitaxel alone-treated cells, the protein levels of hsp90, hsp70, and hsc70 increased. In conclusion, our results suggest that 17-AAG induces non-apoptotic cell death requiring de novo protein synthesis in ATC cells. Moreover, these results demonstrate that 17-AAG antagonizes paclitaxel with concomitant alterations in hsp90 client proteins in ATC cells.