Induction of apoptosis in malignant and camptothecin-resistant human cells.

Flow cytometry studies demonstrate that androgen-independent human prostate carcinoma DU-145 cells are arrested at the G1-phase of the cell cycle in the presence of suramin, but they die by apoptosis in the presence of 9-nitrocamptothecin (9NC). The addition of cytostatic concentrations of suramin increases the apoptotic action of 9NC on DU-145 cells, and induces apoptosis in 9NC-resistant DU-145/RC cells that were derived from the parental DU-145 cells by continuous exposure to progressively increased concentrations of 9NC. In addition, the topoisomerase II-directed drug etoposide exerts more extensive apoptotic action on DU-145/RC than DU-145 cells. Increased resistance of DU-145 cells to 9 NC and collaterally increased sensitivity to etoposide and suramin appear to correlate with alterations in the structure rather than synthesis of topoisomerases and possibly with specific cellular proteins that regulate apoptosis. The results suggest that etoposide and suramin may be successful alternative treatments for 9NC-resistant androgen-independent prostate cancer.