PARENT SESSION
3:45 PM to 5:15 PM
Tuesday, April 23, 2002
Mini-Symposium 12
Cell Cycle and Apoptosis
Room: Nevada 4-5
, Co-Chair: Muschel, Ruth¹; Haimovitz-Friedman, Adriana²¹University of Pennsylvania, Philadelphia, PA²Memorial Sloan-Kettering Cancer Center, New York, NY

(MS12-9) Didox overcomes bcl-2 mediated radiation resistance in prostate tumor cell line PC-3.

Inayat, Mohammed^*,1,2, Chendil, Damodaran³, Tonning, Nina⁴, Dey, Swatee³, Mohiuddin, Mohammed³, Elford, Howard⁵, Gallicchio, Vincent², Ahmed, Mansoor³, ¹ Department of Biological Sciences, Westminster, London² Departments of Clinical Sciences, Lexington, KY³ Radiation Medicine, Lexington, KY⁴ College of Aalesund, Norway⁵ Molecules for Health Inc, Richmond, VA

ABSTRACT-
In this study, we investigated the influence of bcl-2 overexpression on the radiosensitizing potential of Didox (DX; 3,4-Dihdroxybenzohydroxamic acid), a second generation RRI, in p53-null prostate cancer cell line PC-3 . The PC-3 cells were transfected with vector alone or ectopically overexpressed with CMV-bcl-2 construct. The effect of radiation (IR) or DX alone and in combination (pre and post IR exposure of DX) on cell survival was determined by colony-forming assay. The impact of these two treatments on the cell cycle was determined by flow cytometry. To further understand the molecular mechanism of DX mediated radiosensitization, induction of pro-survival and pro-apoptotic factors were determined by Western blot and gel-shift assays respectively. When compared to PC-3/ bcl-2 cells (SF2=0.84; D0=437cGy), uhe PC-3/vector cells (SF2=0.4; D0=235cGy) were significantly sensitive to ionizing radiation (p<0.001). Exposure of DX at IC50 dose prior or post to radiation in both PC-3/vector and PC-3/ bcl-2 transfectants caused an increase in radiation enhancement ratios. A significant reduction in G2M phase was observed in cells exposed to DX post IR when compared to cells exposed to IR alone. Exposure to DX after radiation in PC-3/vector significantly abrogated radiation-induced bcl-2 upregulation, with a concomitant induction of bax protein. In PC-3/bcl-2 transfectants, DX exposure after IR caused an induction of bax protein. Gel shift assays indicated that in PC-3/vector cells when exposed to IR caused an induction of NFk-B activity however, DX down regulated the NFk-B activity. Radiationinduced NFk-B activity was abrogated in pre and post DX exposure in combination with IR. These findings strongly indicate that DX mediates a potent radiosensitizing effect in p53 null prostate cancer cells by overcoming either bcl-2 overexpression or radiation-induced pro-survival factor NFk-B.

KEYWORDS: radiosensitization, didox, prostate cancer, bcl-2