Hormone refractory metastatic prostate cancer is a deadly disease that currently lacks curative treatments. Conditionally replicating adenoviruses (CRAds) are promising new agents against cancer due to their innate capability to cause oncolysis of tumor cells. Their antitumor effect is determined in part by their capacity for infecting cancer cells. However, the respective primary receptor, the coxsackie-adenovirus receptor (CAR), is variably expressed in many cancer types. We created Ad5/3Δ24hCG, a novel CRAd retargeted to the adenovirus serotype 3 receptor, which has been reported to be highly expressed in tumors. Furthermore, we added a transgene for the β-chain of human chorionic gonadotropin (hCGβ), whose expression was tightly coupled to virus replication. Ad5/3Δ24hCG was found effective in killing prostate cancer cells, and oncolysis was seen in concordance with hCGβ production. In a s.c. in vivo model of hormone refractory prostate cancer, Ad5/3Δ24hCG treatment resulted in statistically significant tumor growth inhibition. Moreover, i.v. injection of Ad5/3Δ24hCG prolonged the survival of mice with hormone refractory prostate cancer metastatic to the lung. Detection of hCGβ in serum samples confirmed viral replication in vivo. Infection of human clinical samples of cancerous and normal prostatic tissue resulted in effective hCGβ production in cancer tissue, whereas it remained low in nonmalignant tissue, suggesting cancer-specific replication. These results suggest that Ad5/3Δ24hCG is a potent virus for the treatment of hormone refractory prostate cancer in vitro and in vivo. These preclinical data set the stage for translation into clinical studies. Copyright © 2007 American Association for Cancer Research.