Tumor-suppressor effects of anti-p53 IgG on chemically induced colon cancer in rats

Background - We have shown the suppressive effects of rabbit IgG raised against p53 tumor-associated antigen on chemically induced colon cancer in rats. Methods - Rabbit anti-p53 IgG was raised against the p53 antigen isolated in the form of soluble protein from the serum of colon tumor-bearing rats. The induction of colon cancer was achieved by weekly injections of 1,2-dimethylhydrazine (20 mg/kg) for 7 weeks to Sprague Dawley rats. Vaccination of rats started 2 weeks after the end of cancer induction and was performed by 4 subcutaneous injections of IgG (100 μg/rat) at two-week intervals. The results were evaluated 6 months after the start of cancer induction. Results - Vaccination of rats with anti-p53 protein showed clear tumor-suppressor effects. The number of tumor hearing rats in the vaccinated group decreased to 80% compared with 100% in the control group. The number of malignant tumors in vaccinated rats was half that in controls: 52% and 100%, respectively. The number of rats with metastases decreased from 10% in controls to 5% in the vaccinated group. The antitumor effect of vaccination was accompanied by a non significant increase in the serum level of p53 antigen in vaccinated rats compared with non vaccinated controls. Conclusions - We suggest that the anticancer role of a vaccine generated against p53 protein from benign tumor-bearing rats is related to a wild-type p53 protein. Further studies will be performed to confirm this hypothesis.