Adenovirus-mediated restoration of expression of the tumor suppressor gene DLC1 inhibits the proliferation and tumorigenicity of aggressive, androgen-independent human prostate cancer cell lines: Prospects for gene therapy

898 DLC1 encodes a Rho GTPase-activating protein and is a tumor suppressor gene for several major forms of human cancer. The highly recurrent loss of function of DLC1 in primary prostate carcinoma (PCA) implicates this gene in the pathogenesis of this disease. Given the potent oncosuppressive activity of DLC1 in other cancers and the need for improved therapies for aggressive PCA, we investigated the feasibility of DLC1- based gene therapy for PCA. We constructed an adenoviral vector for human DLC1 (Ad-DLC1) and examined the effects of its introduction into the DLC1-deficient, androgen-independent, and aggressive human PCA cell lines PC-3 and C4-2-B2 on cell proliferation, invasion, apoptosis, and anchorage-independent growth in vitro as well as on tumorigenicity in vivo. Adenovirus-mediated restoration of DLC1 expression inhibited the proliferation, invasiveness, and anchorage-independent growth of PC-3 and C4-2-B2 cells in vitro as well as the tumorigenicity of PC-3 cells in nude mice. It also induced cell cycle arrest and inhibited the activation of RhoA as well as the formation of actin stress fibers. Whereas DLC1 induced apoptosis in C4-2-B2 cells, it did not elicit such an effect in PC-3 cells. The abundance of the antiapoptotic protein Bcl-2 was greater in PC-3 cells than in C4-2-B2 cells, and PC-3 cells were rendered sensitive to DLC1-induced apoptosis by treatment with the Bcl-2 inhibitor HA14-1. These results suggest that adenovirus-mediated DLC1 transfer, alone or together with chemical inhibition of Bcl-2 or inhibitors of histone deacetylase might prove effective in the treatment of aggressive, androgen-independent PCA.