Quinazoline-based α1-adrenoceptor antagonists induce prostate cancer cell apoptosis via TGF-β signalling and IκBα induction

Previous studies documented the ability of quinazoline-based alpha1-adrenoceptor antagonists to induce apoptosis in prostate cancer cells via an alpha1-adrenoceptor-independent mechanism. In this study we investigated the molecular events initiating this apoptotic effect. Since transforming growth factor-beta1 (TGF-beta1) mediates prostate epithelial cell apoptosis, we hypothesised that the activation of the TGF-beta1 pathway underlies the quinazoline-based apoptotic effect in prostate cancer cells. Treatment of the androgen-independent human prostate cancer cells PC-3 with doxazosin resulted in a strong caspase-3 activation within 24 h, whereas tamsulosin, a sulphonamide-based alpha1-adrenoceptor antagonist, had no significant apoptotic effect against prostate cancer cells. To identify the molecular components involved in this quinazoline-mediated apoptosis, cDNA microarray analysis of PC-3 prostate cancer cells treated with doxazosin ( 3 h) was performed. Induced expression of several genes was observed including p21(WAF-1) and IkappaBalpha (inhibitor of NF-kappaB alpha). Relative quantitative reverse transcription - polymerase chain reaction analysis revealed induction of several TGF-beta1 signalling effectors: Induction of mRNA for Smad4 and the TGF-beta1-regulated apoptosis-inducing transcription factor TGF-beta1-inducible early gene (TIEG1) was detected within the first 6 h of doxazosin treatment. Upregulation of IkappaBalpha at both the mRNA and protein level was also detected after 6 h of treatment. Furthermore, doxazosin resulted in a considerable elevation in Smad4 and TIEG protein expression ( 6 h). A 'latent' increase in TGF-beta mRNA expression was detected after 48 h of treatment. These findings suggest that the quinazoline-based doxazosin mediates prostate cancer apoptosis by initially inducing the expression of TGF-beta1 signalling effectors and subsequently IkappaBalpha. The present study provides an initial insight into the molecular targets of the apoptotic action of quinazolines against prostate cancer cells.