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Cancer Res. 1997 Jun 15;57(12):2493-500.

Quiescence in R3327-G rat prostate tumors after androgen ablation.

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  • 1Department of Clinical Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.


Androgen ablation is frequently used in conjunction with radiotherapy in the treatment of high-risk prostate cancer. Androgen ablation-induced cell kinetic changes could result in sub-additive (increased quiescence) or supra-additive (reduction in repopulation) interactions with radiotherapy. The cell kinetic changes were studied in R3327-G Dunning rat prostate tumors grown in vivo using double thymidine analogue labeling and flow cytometry, the terminal deoxynucleotidyl transferase-mediated nick end labeling assay for apoptosis, and measurements of tumor cell numbers. Tumors grown in intact and castrate male rats were continuously labeled for various periods of time with chlorodeoxyuridine and pulse-labeled with iododeoxyuridine 8 h before tumor removal. Androgen ablation resulted in a maximal reduction in labeling index (10 to 1.6%) and an increase in potential doubling time (Tpot; 6-42 days) within 3 days, which was related to a reduction in growth fraction (65% to <10%). In contrast, the length of S-phase was minimally altered (19 to 23 h). The response to androgen ablation involved little apoptosis and no necrosis, and Tpot was approximately the same as the tumor volume doubling time. Hence, the increase in Tpot was mainly the result of a shift to quiescence, and this shift occurred with minimal cell loss. Because quiescence is usually associated with radioresistance, these cell kinetic changes suggest that a sub-additive interaction may occur for some prostate cancers when androgen ablation and irradiation are given together.

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