A novel selective therapeutic targeting heme oxygenase-1 revealed a potent antimetastatic activity in androgen-refractory human prostate cancer models

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Prostate cancer is a highly prevalent disease. Despite a significant improvement in the overall survival attributed in part to early detection and introduction of novel therapeutic modalities, many cancer patients at primary diagnosis present advanced disease or experience recurrence of the cancer. The progression of prostate cancer (PCA) to hormone-refractory phenotype (HRPCA) and to metastasis is an ominous event in patients with advanced PCA. Currently, clinically available drugs for hormone refractory PCA have only marginal efficacy. In this study, we identified heme oxygenase 1 (HO-1) to be significantly upregulated in epithelial PCA cells, but not in surrounding stromal cells, from hormone refractory prostate cancer cases compared to hormone-responsive prostate cancer and to benign tissues. We validated HO-1 as a novel therapeutic target for HRPCA. Specifically, inhibition of HO-1 gene in androgen-independent and highly invasive prostate cancer cells, PC3M, decreased HO-1 activity, oxidative stress, MAPKs activation, cell proliferation, and cell migration and invasion in vitro, as well as inhibition of prostate tumor growth and lymph nodes and lung metastases in vivo. The impact of HO-1 silencing on these oncogenic features was mimicked by exposure of cells to a novel selective small-molecule HO-1 inhibitor referred to as OB-24. OB-24 selectively downregulates HO-1 activity, oxidative stress, and significantly inhibits cell proliferation in vitro and tumor growth and lymph node/lung metastases in vivo. A potent synergistic activity in inhibiting HRPCA metastasis formation was observed when OB-24 was combined with the chemotherapy drug taxol. The molecular and potential clinical impact of OB-24 alone and in combination with taxanes on HRPCA will be discussed.

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