(a) Purpose: We recently reported that an angiotensin II (AII) type 1 receptor (AT1R) antagonist could prevent metastasis of murine renal cancer by inhibiting tumor angiogenesis. In this study, we sought to determine whether AT1R antagonist affects tumor angiogenesis and growth in prostate cancer. (b) Procedures: Two prostate cancer cell lines (LNCap and C4-2) were used. Athymic nude BALB/C mice were castrated by scrotal incision under local anesthesia, and mice were subcutaneously inoculated with 5×106 C4-2 cells. The volume of the tumors was examined in a time-dependant manner. When the tumor volume reached 80-100 mm3, the animals were killed and the subcutaneous tumors were harvested. By using this model,we orally administered candesartan(10mg/kg) every day. The treatment was started on day 1. We further evaluated the expression of endothelial growth factor(VEGF), tumor microvessel density(MVD) by immunocytochemistry. To investigate the effects of AII or an AT1R antagonist (CV11974) on cell proliferation, a 3H-thymidine incorporation assay was performed. To assess VEGF production by cancer cells, supernatant was collected after incubation for 24 h under various conditions and ELISA was performed. The expression of AT1R was investigated by flow cytometric analysis(FCM) and immunocytochemistry. (c) Results: Mice without candesartan had large nodules (830.6 ± 147.6 mm3,n=9), while candesartan treatment caused a significant decrease in the subcutaneous tumor nodules(235.8 ± 37.4 mm3, n=8, p<0.001). MVD of subcutaneous tumors in the control group was 14.0 ± 4.8(n=9). Candesartan significantly decreased tumor MVD (5.9 ± 0.8, p<0.001, n= 8). Tumors treated with candesartan had significantly lower VEGF expression (1.6 ± 0.4, n=9) than tumors treated without candesartan (2.3 ± 0.5, p<0.01, n=8). In vitro proliferation assay with clinically achievable concentraion of AII and AT1R antagonist didn‘t show any effects on tumor growth. C4-2 cells showed significantly higher production of VEGF (9.7 ± 1.2 pg/103 cells, p<0.01) than LNCaP cells (2.2 ± 0.4 pg/103 cells) after serum deprivation for 24 hr. While AII treatment (10nM) significantly increased VEGF production by C4-2 cells (12.6 ± 1.6/103 cells, p<0.001), addition of CV11974 (10nM) significantly reduced AII-induced VEGF production (10.0 ± 1.4/103 cells, p=0.01). FCM analysis and immunocytochemistry revealed that C4-2 cells showed higher levels of AT1R expression than LNCaP cells. (d) Conclusions: These results demonstrated that specific AT1R blockade suppressed VEGF production in hormone independent prostate cancer and tumor growth, suggesting that the AT1R may be a key molecule for targeting tumor angiogenesis.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]