Preliminary evaluation of caspases-dependent apoptosis signaling pathways of free and HPMA copolymer-bound doxorubicin in human ovarian carcinoma cells.

The purpose of the study was to examine the role of caspases in signaling pathways of apoptosis induced by free doxorubicin (DOX) and HPMA copolymer-bound DOX (P(GFLG)-DOX) in human ovarian carcinoma cells. Sensitive A2780 and DOX resistant A2780/AD cells were exposed to different doses of drugs within 12, 18, 24 and 36 h. Caspase activity, expression of genes encoding human caspases 1-10, Apaf-1 and bcl-2 proteins and apoptosis were studied. In sensitive cells both free and P(GFLG)-DOX activated caspases 3, 7 and 9. In addition, P(GFLG)-DOX activated caspases 6 and 8. In resistant cells apoptosis induced by free DOX depended on the activation of caspases 2, 7 and 9, while caspase 3 was not involved; this explains the low degree of apoptosis induced by free DOX in resistant cells. P(GFLG)-DOX triggered the additional caspases 3, 6 and 8. A more pronounced degree of caspase activation and apoptosis after the action of P(GFLG)-DOX depended on the inhibition of bcl-2-encoded cellular defensive mechanisms and a more significant activation of Apaf-1. It was concluded that HPMA copolymer-bound DOX induced additional caspase-dependent apoptosis signaling pathways and the degree of the induction was higher, which led to more pronounced apoptosis when compared to free DOX.