Antiandrogen Therapy Radiosensitizes Androgen Receptor-Positive Cancers to F-18-FDG

A subset (35%) of triple-negative breast cancers (TNBCs) expresses androgen receptor (AR) activity. However, clinical trials with antiandrogen drugs have shown limited efficacy, with about a 19% clinical benefit rate. We investigated the therapeutic enhancement of antiandrogens as radiosensitizers in combination with F-18-FDG in TNBC. Methods: We screened 5 candidate drugs to evaluate shared toxicity when combined with either F-18-FDG, x-rays, or ultraviolet radiation, at doses below their respective half-maximal inhibitory concentrations. Cytotoxic enhancement of antiandrogen in combination with F-18-FDG was evaluated using cell proliferation and DNA damage assays. Finally, the therapeutic efficacy of the combination treatment was evaluated in mouse tumor models of TNBC and prostate cancer. Results: Bicalutamide, an antiandrogen drug, was found to share similar toxicity in combination with either F-18-FDG or x-rays, indicating its sensitivity as a radiosensitizer to F-18-FDG. Cell proliferation assays demonstrated selective toxicity of combination bicalutamide-F-18-FDG in AR-positive 22RV1 and MDA-MB-231 cells in comparison to AR-negative PC3 cells. Quantitative DNA damage and cell cycle arrest assays further confirmed radiation-induced damage to cells, suggesting the role of bicalutamide as a radiosensitizer to F-18-FDG-mediated radiation damage. Animal studies in MDA-MB-231, 22RV1, and PC3 mouse tumor models demonstrated significant attenuation of tumor growth through combination of bicalutamide and F-18-FDG in the AR-positive model in comparison to the AR-negative model. Histopathologic examination corroborated the in vitro and in vivo data and confirmed the absence of off-target toxicity to vital organs. Conclusion: These data provide evidence that F-18-FDG in conjunction with antiandrogens serving as radiosensitizers has utility as a radiotherapeutic agent in the ablation of AR-positive cancers.