High tumor-preventive effects of polyclonal IgG generated against p53 tumor-associated protein obtained from benign-tumor bearing rats

We have shown the different effects of rabbit IgG generated against various types of p53 tumor-associated protein on chemically induced colon cancer in rats. p53 protein was isolated in the form of cytoplasmic, soluble, protein from sera obtained from: a) rats with colon cancer and b) rats with benign colon tumors. The isolation was performed using the affinity chromatography columns with,eel fiberglass membranes. Anti-p53 IgG were obtained from rabbits vaccinated with the above mentioned types of p53. Sprague Dawley rats were vaccinated with anti-p53 IgG (100 mu g/rat) at two-week intervals for 2 months and then monthly for 3 months. The induction of colon cancer was caused by weekly injections with 1,2-dimethylhydrazine (20 mg/kg) for 7 weeks and was initiated 8 weeks after the start of the vaccination. Results of experiments were evaluated 6 months after the start of cancer induction. It was found that vaccination of rats with IgG generated against the p53 protein isolated from cancer-bearing rats did not exhibit significant protective effect. Only IgG generated against p53 protein from benign tumor-bearing rats significantly prevented the carcinogenic effect of DMH. The number of tumor-bearing rats in vaccinated group decreased to 44% as compared with 93% in the control group. In vaccinated rats, the number of tumors/rat was 0.8 as compared to 9.3 in controls. The number of malignant tumors in vaccinated rats was half that in controls: 29% and 58%, respectively. In the controls, metastases were found in 6 of 45 rats (13%). Anti-p53 IgG not only has an anti-tumor effect but also prevented benign tumors from becoming malignant. 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 clarify this hypothesis.