Anti‐Tumor Effect of Adenovirus‐Mediated P53 Gene Therapy on the Growth of Canine Osteosarcoma Transplanted into Nude Mice

Introduction:  It has been reported that 40–50% of canine osteosarcoma cases have p53 mutations. The p53 tumor supressor gene plays a central role in cell cycle regulation and induction of apoptosis. We previously showed that adenoviral vector expressing canine P53 (AxCA-cp53) inhibited growth of cultured canine osteosarcoma cell lines. Here, we evaluated anti-tumor effect of adenovirus-mediated p53 gene therapy on the growth of canine osteosarcomas transplanted into nude mice. Methods:  Nine nude mice were subcutaneously injected with cells of a canine osteosarcoma cell line (POS) having p53 gene mutation. The transplanted tumors formed into nude mice were injected with AxCA-cp53, AxCA-LacZ (adenovirus vector expressing LacZ) or PBS (3 mice each) 7 times during 15 days. Tumor sizes were measured every 3 days for 27 days after injection with the adenovirus vectors. Expression efficiency of the adenovirus-mediated gene transfer was examined by X-gal staining and P53 immunostaining. Effects of the P53 expression on cell cycle control were examined by RT-PCR for expression of p21 gene downstream of P53. Results:  Significant differences in the tumor size was observed between the transplanted osteosarcoma tissues injected with AxCA-cp53 and those injected with AxCA-LacZ or PBS. Expressions of LacZ and P53 were confirmed at the injection sites of the tumors. Moreover, p21 mRNA expression was shown to be induced in the AxCA-cp53-injected tumors, indicating the funciton of P53 to induce cell cycle arrest. Conclusions:  Adenoviral vector expressing canine P53 inhibited the growth of canine ostersarcoma transplanted into nude mice.