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An Antibody Targeting the Type I Insulin-like Growth Factor Receptor Enhances the Castration-Induced Response in Androgen-Dependent Prostate Cancer

Authors' Affiliations: Departments of ¹ Medicine and ² Urology and Immunology, University of Washington, ³ Veterans Affairs Puget Sound Health Care System, and ⁴ Fred Hutchinson Cancer Research Center, Seattle, Washington; and ⁵ ImClone Systems, New York, New York

Requests for reprints: Stephen R. Plymate, Box 359625, Department of Medicine, University of Washington, Seattle, WA 98104. Phone: 206-341-4275; Fax: 206-341-5302; E-mail: splymate{at}u.washington.edu.

Purpose: To determine the effect of inhibition of insulin-like growth factor-IR (IGF-IR) signaling with an antibody to the IGF-IR, A12, in conjunction with androgen withdrawal on prostate cancer progression in a human prostate xenograft model, LuCaP 35.

Experimental Design: LuCaP 35 was implanted s.c. in severe combined immunodeficient mice. At the time of castration, mice were randomized to one of three groups. Group 1 was castrate only; group 2 received A12 40 mg/kg i.p. for 2 weeks beginning 1 week after castration; and group 3 received A12 40 mg/kg i.p. for 2 weeks beginning 2 weeks after castration.

Results: In group 1, tumor volume decreased to 60% of the starting volume 4 weeks post-castration. In groups 2 and 3, tumor volumes nadired 6 weeks after castration at <10% of the volume at time of castration (P < 0.01). Tumor regrowth was not seen in groups 2 or 3 until 15 weeks after castration. Androgen receptor (AR) localization in tumors showed a decrease in nuclear staining in groups 2 and 3 compared with group 1 (P < 0.001). Tumor volume correlated with nuclear AR intensity. AR-regulated genes increased early in group 1, but did not increase in groups 2 and 3. Thus, tumor-specific survival was prolonged by the addition of A12 to castration.

Conclusions: This study shows that the inhibition of IGF-IR enhances the effects of castration in prostate cancer. These effects are associated with a decrease in AR signaling and nuclear AR localization, and recurrence is associated with an increase in AR-regulated gene expression.

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				M. M. Chitnis, J. S.P. Yuen, A. S. Protheroe, M. Pollak, and V. M. Macaulay The Type 1 Insulin-Like Growth Factor Receptor Pathway Clin. Cancer Res., October 15, 2008; 14(20): 6364 - 6370. [Abstract] [Full Text] [PDF]