Targeting apoptosis by hydroxymethylacylfulvene in combination with gamma radiation in prostate tumor cells

Hydroxymethylacylfulvene (HMAF) is a novel agent with alkylating activity and is a potent inducer of apoptosis that is currently undergoing Phase II clinical trials for prostate cancer. This study explored the pro-apoptosis and anti-proliferative potential of HMAF in combination with γ radiation in human prostate tumor cell lines. Apoptosis was assessed based on the generation of fragmented DNA, a terminal transferase flow cytometry assay, and cell morphology. In each of the tumor cell lines examined, radiation alone induced a marginal level of apoptosis, even after a prolonged 48-h incubation after exposure. In contrast, HMAF alone was a potent inducer of apoptosis in prostate tumor cells but not in normal cells. Marked levels of apoptosis in tumor cells were also observed for the combination of HMAF with γ radiation. When drug treatment preceded irradiation, at least additive levels of apoptosis were observed in both androgen-responsive and androgen-independent cells. The combined treatment with ionizing radiation and HMAF reduced the radiation dose needed for the same level of clonogenic survival up to 2.5-fold. The potentiation of apoptosis and reduction in the clonogenic survival of tumor cells occurred at HMAF concentrations lower than that which reduced survival to 10% and at doses up to 6 Gy. No potentiation of apoptosis or clonogenic inhibition was noted in normal cells. These results suggest that the combination of HMAF with γ radiation may have clinical utility for treatments of prostate cancer. (C) 2000 by Radiation Research Society.