Quinazoline-derived 1-Adrenoceptor Antagonists Induce Prostate Cancer Cell Apoptosis Via an 1-Adrenoceptor-independent Action

Recent evidence suggests that the quinazoline-based 1-adrenoceptor antagonists, doxazosin and terazosin, exhibit a potent apoptotic effect against prostate tumor epithelial cells, whereas tamsulosin, a sulfonamide-based 1-adrenoceptor antagonist, was ineffective in inducing a similar apoptotic effect against prostate cells (Cancer Res., 60: 4550–4555, 2000). In this study, to identify the precise molecular mechanism underlying this apoptosis induction, we examined whether doxazosin and terazosin (both piperazinyl quinazolines) affect prostate growth via an 1-adrenoceptor-independent action. Transfection-mediated overexpression of 1-adrenoceptor in human prostate cancer cells, DU-145 (that lack 1-adrenoceptor), did not alter the ability of prostate cancer cells to undergo apoptosis in response to quinazolines. Significantly enough, there was no modification of the apoptotic threshold of the androgen-sensitive prostate cancer cells, LNCaP, to either quinazoline-based 1-agonist by androgens. Furthermore, human normal prostate epithelial cells exhibited a very low sensitivity to the apoptotic effects of doxazosin compared with that observed for the malignant prostate cells. These findings provide the first evidence that the apoptotic activity of the quinazoline-based 1-adrenoceptor antagonists (doxazosin and terazosin) against prostate cancer cells is independent of: (a) their capacity to antagonize 1-adrenoceptors; and (b) the hormone sensitivity status of the cells. This may have potential therapeutic significance in the use of quinazoline-based 1-adrenoceptor antagonists (already in clinical use for the treatment of hypertension and benign prostate hyperplasia) for the treatment of androgen-independent human prostate cancer.