Induction of anoikis by doxazosin in prostate cancer cells is associated with activation of caspase-3 and a reduction of focal adhesion kinase

The quinazoline family of α₁-blockers (prazosin, doxazosin, and terazosin) induce apoptosis of prostate cells through an α₁-adrenoceptor–independent mechanism. The objective of this study was to gain insight into the non-adrenergic, apoptotic mechanism of action of doxazosin in the prostate and the induction of anoikis by doxazosin. Primary cultures of benign prostate stromal and epithelial cells and the LNCaP (androgen sensitive) and PC-3 (androgen insensitive) prostate carcinoma cell lines were treated with doxazosin (0–50 μM). The effects of doxazosin on cell morphology, caspase-3 activity, and the expression levels of focal adhesion kinase (FAK) and integrin-linked kinase (ILK) were examined. Doxazosin induced changes in morphology consistent with anoikis in both benign and cancerous prostatic cells and increased caspase-3 activity. The effects were similar comparing benign cells (which express α₁-adrenoceptors ) and cancer cells (which do not express α₁-adrenoceptors ), but were more robust in benign cells. Norepinephrine had no effect on doxazosin-induced cell morphology or caspase-3 activity. Treatment of PC-3 cells with doxazosin significantly reduced the protein levels of FAK but did not significantly affect the levels of ILK. These findings suggest that doxazosin induces apoptosis and anoikis of prostate cancer cells by a mechanism of action that is α₁-adrenoceptor independent. The apoptosis of cancer cells induced by doxazosin counteracts cell proliferation and may have the potential of retarding or reversing prostate cancer cell growth.