Drug-induced Apoptosis Is Not Necessarily Dependent on Macromolecular Synthesis or Proliferation in the p53-negative Human Prostate Cancer Cell Line PC-3¹

The propensity of a cell to undergo apoptosis has been proposed to be a determinant for chemotherapy sensitivity that is not directly dependent on specific drug-target interactions. Androgen-independent prostate cancer is typically refractory to cytotoxic drugs, and we tested whether this is due to a loss of the ability to undergo apoptosis. Exposure of the hormone-insensitive and p53-negative human prostate carcinoma cell line PC-3 to 22 µm cisplatin, 1 µm camptothecin, 10 µm tenoposide, 135 nm vincristine, or 10 µm lovastatin for 72 h caused cell death, internucleosomal DNA fragmentation, and morphological changes typical for apoptosis. One µm cycloheximide prevented anticancer drug-induced apoptosis, whereas high concentration (1 mm) of cycloheximide alone induced apoptosis, indicating that protein synthesis was not needed for these cells to undergo apoptosis. Since cycloheximide affected DNA synthesis and proliferation of PC-3 cells, we tested whether the DNA polymerase inhibitor aphidicolin could also suppress drug-induced apoptosis. In contrast to cycloheximide, aphidicolin inhibited only vincristine-induced apoptosis. Cycloheximide prevented drug-induced changes in cell cycle distribution except for vincristine, while aphidicolin led to an accumulation of cells at the G₁-S border independent of the drug used. These data indicate that macromolecular synthesis, active cell cycling, and p53 expression are not required for apoptosis to proceed in this system.