Targeting Apoptosis by Hydroxymethylacylfulvene in Combination with Gamma Radiation in Prostate Tumor Cells

Abstract

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 gamma 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 gamma 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 gamma radiation may have clinical utility for treatments of prostate cancer.

<a name="home"></a>Effects of gamma-radiation on cell growth, cycle arrest, death, and superoxide dismutase expression by DU 145 human prostate cancer cells

“…Thus, IR treatment within a clinically relevant dose range would predominantly express antiproliferative effects rather than cell killing. The significance of the IR-induced antiproliferative effects has been often underestimated compared to cell death (4,(6)(7)(8)(9), but in the present study we showed that a decrease of proliferation is the most prominent effect of γ-IR on DU 145 cells.…”

“…Accordingly, induction of apoptotic cell death plays an important role (4)(5)(6). Radiation biology studies in rat prostate adenocarcinoma have shown that irradiation-induced apoptosis occurred at a higher rate in well-differentiated tumors compared to anaplastic ones (7). Thus, increased radiosensitivity, judged by apoptotic cell death as an end point, was observed for well-differentiated tumors (7).…”

“…Radiation biology studies in rat prostate adenocarcinoma have shown that irradiation-induced apoptosis occurred at a higher rate in well-differentiated tumors compared to anaplastic ones (7). Thus, increased radiosensitivity, judged by apoptotic cell death as an end point, was observed for well-differentiated tumors (7). However, the results obtained for other systems demonstrated that gamma-irradiation (γ-IR) is an inefficient inducer of apoptosis (8,9).…”

Effect of Hypofractionation on Prostate Cancer Radiotherapy

“…However, for less responsive tumor cells (SF 2 (36). However, the uncertainty of SF 2 could be notable (37). Since the uncertainty of SF 2 could be indicative, its impact was studied for SF 2 ranging from 0.3 to 0.9.…”

Irofulven: Resurgence for alkylating therapy in cancer?

“…As Irofulven causes a predominant pre-mitotic form of cell killing, and radiation post-mitotic cell death, it can be envisaged that both therapies empirically will combine to kill cancer cells in at least an additive fashion, as previously noted by this group in prostate cancer cells. 10 Further studies will be required to determine whether Irofulven is a radiosensitizer in multiple other tumor cell types.…”