We recently demonstrated that silodosin, a selective α1-blocker often prescribed for the symptomatic treatment of benign prostatic hyperplasia (BPH), could inactivate a c-fos proto-oncogene regulator ELK1 in bladder cancer cells possessing a functional androgen receptor (AR). However, the clinical impact of α1-blockers on the development and progression of bladder cancer remained poorly understood. In the present study, we investigated if α1-blockers clinically used, including silodosin, tamsulosin, and naftopidil, could prevent the neoplastic/malignant transformation and cell growth, using non-neoplastic urothelial SVHUC sublines with carcinogen/MCA challenge and bladder cancer lines, respectively. Bladder cancers in men treated with silodosin, tamsulosin, or naftopidil for their BPH were then compared. Silodosin at 1-10 µM significantly inhibited the neoplastic transformation of MCA-SVHUC-AR cells, but not that of AR-negative MCA-SVHUC-control cells. In MCA-SVHUC-AR, silodosin significantly reduced the expression levels of oncogenes (c-fos/NF-κB1) and induced those of tumor suppressors (p27/PTEN). However, tamsulosin (up to 1 µM) or naftopidil (up to 10 µM) failed to significantly inhibit the neoplastic transformation of AR-positive or AR-negative urothelial cells. Similarly, cell proliferation/migration of AR-positive bladder cancer lines was considerably inhibited only by silodosin. Meanwhile, the incidence of bladder cancer in patients with silodosin [49/540 (9.1%)] was marginally lower, compared to those with tamsulosin [64/523 (12.2%); P=0.094] or tamsulosin or naftopidil [64+28/523+236 (12.1%); P=0.082]. There were no significant differences in tumor grade/stage among the 3 cohorts. Outcome analysis revealed lower risks for disease progression of non-muscle-invasive bladder tumors in the silodosin group than in the naftopidil group (P=0.011) or tamsulosin+naftopidil groups (P=0.035). Similarly, silodosin patients with muscle-invasive tumor had lower risks for disease progression, compared with tamsulosin (P=0.006) or tamsulosin+naftopidil (P=0.028) patients. Multivariate analysis further showed that silodosin treatment in those with non-muscle-invasive tumor was associated with improved progression-free survival, compared with naftopidil (hazard ratio=0.086; 95% confidence interval=0.008-0.905; P=0.041) or tamsulosin/naftopidil (hazard ratio=0.128; 95% confidence interval=0.016-1.036; P=0.054) treatment. Our in vitro studies thus indicate that both urothelial tumorigenesis and tumor growth are inhibited by silodosin, but not by tamsulosin or naftopidil. Clinical data further suggest that even pharmacological doses (e.g. 0.1 µM) of silodosin contribute to preventing bladder cancer progression.
Keywords: androgen receptor; bladder cancer; naftopidil; silodosin; tamsulosin; α1-blocker.
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