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 α1-adrenoceptor antagonists to induce apoptosis in prostate cancer cells via an α1-adrenoceptor-independent mechanism. In this study we investigated the molecular events initiating this apoptotic effect. Since transforming growth factor-β1 (TGF-β1) mediates prostate epithelial cell apoptosis, we hypothesised that the activation of the TGF-β1 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 24h, whereas tamsulosin, a sulphonamide-based α1-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 IκBα (inhibitor of NF-κB alpha). Relative quantitative reverse transcription-polymerase chain reaction analysis revealed induction of several TGF-β1 signalling effectors: Induction of mRNA for Smad4 and the TGF-β1-regulated apoptosis-inducing transcription factor TGF-β1-inducible early gene (TIEGI) was detected within the first 6h of doxazosin treatment. Upregulation of IκBα at both the mRNA and protein level was also detected after 6h of treatment. Furthermore, doxazosin resulted in a considerable elevation in Smad4 and TIEG protein expression (6 h). A 'latent' increase in TGF-β 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-β1 signalling effectors and subsequently IκBα. The present study provides an initial insight into the molecular targets of the apoptotic action of quinazolines against prostate cancer cells.