We are interested in developing oncolytic adenoviruses for the treatment of prostate cancer (PCa) bone metastases. A key limitation of Adenovirus 5 (Ad5) is that upon systemic administration, it produces major liver and systemic toxicities. To address this issue, a chimaeric Ad5/48 adenovirus mHAd.sTβRFc was created. Seven hypervariable regions of Ad5 hexon present in Ad5-based Ad.sTβRFc expressing soluble transforming growth factor beta receptor II-Fc fusion protein (sTGβRIIFc), were replaced by those of Ad48. mHAd.sTβRFc, like Ad.sTβRFc, was replication competent in the human PCa cells, and produced high levels of sTGβRIIFc expression. Compared to Ad.sTβRFc, the systemic delivery of mHAd.sTβRFc in nude mice resulted in much reduced systemic toxicity, and reduced liver sequestration. Ad.sTβRFc produced significant liver necrosis, and increases in alanine transaminase, aspartate transaminase, lactate dehydrogenase, tumor necrosis factor-α, and interleukin-6 levels, while mHAd.sTβRFc produced much reduced responses of these markers. Intravenous delivery of Ad.sTβRFc or mHAd.sTβRFc (5 × 10(10) viral particles/mouse) in nude mice bearing PC-3-luc PCa bone metastases produced inhibition of bone metastases. Moreover, a larger dose of the mHAd.sTβRFc (4 × 10(11) viral particles /mouse) was also effective in inhibiting bone metastases. Thus, mHAd.sTβRFc could be developed for the treatment of PCa bone metastases.