Combination of carmustine and selenite effectively inhibits tumor growth by targeting androgen receptor, androgen receptor-variants, and Akt in preclinical models: New hope for patients with castration resistant prostate cancer

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Despite established androgen receptor (AR) antagonists, AR/AR-variants signaling remain a major obstacle for the successful treatment of castration resistant prostate cancer (CRPC). In addition, CRPC cells adapt to survive via AR-independent pathways to escape next generation therapies. Therefore, there is an urgent need for drugs that can target these signaling pathways in CRPC. In this study, we sought to determine whether carmustine and selenite in combination could induce apoptosis and inhibit growth of CRPC in-vitro and in-vivo. CRPC (22Rv1, VCaP, and PC-3) cell lines in culture and xenograft mouse were used. Combination of carmustine and selenite treatment significantly increased reactive oxygen species, apoptosis and growth inhibition in CRPC cells with down regulation of anti-apoptotic (Bcl-2 and Mcl-1) and proliferative proteins (c-Myc and cyclin-D1). This effect was associated with complete reduction of AR/AR-variants, AR-V7, PSA and significant induction of p27Kip1. Combination treatment substantially abolished phospho-Akt, phospho-GSK-3β, and anchorage-independent growth in AR-positive and AR-negative cells. Consistent with in-vitro results, combination treatment effectively induced apoptosis and completely inhibited xenograft tumor growth and markedly reduced AR/AR-variants, AR-V7, PSA, and Bcl-2 in xenograft tumors without causing genotoxicity in host mice. Individual agent treatment showed only partial effect. The combination treatment showed a significant synergistic effect. The present study is the first to demonstrate that the combination of carmustine and selenite treatment completely suppressed CRPC tumor growth by reducing AR/AR-variants and Akt signaling. Our findings suggest that the combination of carmustine and selenite could constitute a promising next-generation therapy for successful treatment of patients with CRPC.

What's new?

Androgen deprivation therapy remains a leading prostate cancer treatment. Nonetheless, androgen receptor (AR) antagonists ultimately are undermined by AR variants, which drive progression to castration-resistant prostate cancer (CRPC). CRPC escape from next-generation AR-targeted therapies and survive through AR-independent signaling pathways. This study demonstrates that the combination of selenite and carmustine, an alkylating agent, completely inhibits CRPC tumor growth both in vitro and in vivo by targeting AR/AR-variants and AR-independent signaling. The findings build on earlier observations in which the two agents together induced apoptosis in prostate cancer cells via oxidative stress. The new results indicate clinical promise for carmustine and selenite combination therapy.

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