Transforming growth factor-β-stimulated clone-22 is an androgen-regulated gene that enhances apoptosis in prostate cancer following insulin-like growth factor-I receptor inhibition

Abstract

Purpose: Inhibition of insulin-like growth factor (IGF) signaling using the human IGF-I receptor monoclonal antibody A12 is most effective at inducing apoptosis in prostate cancer xenografts in the presence of androgen. We undertook this study to determine mechanisms for increased apoptosis by A12 in the presence of androgens. Experimental Methods: The castrate-resistant human xenograft LuCaP 35 V was implanted into intact or castrate severe combined immunodeficient mice and treated with A12 weekly. After 6 weeks of tumor growth, animals were sacrificed and tumors were removed and analyzed for cell cycle distribution/apoptosis and cDNA arrays were done. Results: In castrate mice, the tumors were delayed in G2 with no apoptosis; in contrast, tumors from intact mice underwent apoptosis with either G1 or G2 delay. Transforming growth factor-β-stimulated clone-22 (TSC-22) was significantly elevated in tumors from the intact mice compared with castrate mice, especially in those tumors with the highest levels of apoptosis. To further determine the function of TSC-22, we transfected various human prostate cancer cell lines with a plasmid expressing TSC-22. Cell lines overexpressing TSC-22 showed an increase in apoptosis and a delay in G1. When these cell lines were placed subcutaneously in athymic nude mice, a decreased number of animals formed tumors and the rate of tumor growth was decreased compared with control tumors. Conclusions: These data indicate that IGF-I receptor inhibition in the presence of androgen has an enhanced effect on decreasing tumor growth, in part, through increased expression of the tumor suppressor gene TSC-22. © 2009 American Association for Cancer Research.