Analysis of Peoxisome Proliferator-Induced Rat Tumour Cell Antigens Using Monoclonal Antibodies.

Abstract

In this thesis a study of peroxisome proliferator-induced rat liver tumours was performed, and the antigenic characteristics of the tumour cells examined. Peroxisome proliferators are non-genotoxic, non-mutagenic carcinogens which produce tumours in rodents, notably hepatocellular carcinomas. These tumours are similar in histology to hepatocellular carcinomas of other etiology. 1. The ciprofibrate-induced rat liver tumour cells exhibited a significantly longer survival time in vitro as compared to their normal counterparts. They also exhibited a potential for cell proliferation in vitro. The tumour cells were clearly transformed showing characteristically higher agglutinibility with plant lectins (wheat germ agglutinin and concanavalin-A) and a potential for growth and colony formation in semisolid media such as soft agar and methylcellulose. 2. Monoclonal antibodies (MoAbs) were raised against the tumour cells using two different schedules of immunization. The schedule of prolonged and multiple immunization was found to be more efficient for the production of tumour-specific MoAbs. A number of clones were obtained showing reactivity with either tumour cells, normal cells or both. A total of 23 MoAbs were obtained showing preferential or selective reactivity with the tumour cells. On further characterization, five of these (M-19, M-23, M-28, M-54 and M-56) did not react with any other normal or fetal rat tissues. 3. Some of the MoAbs also reacted with pre-neoplastic and peri-neoplastic tissues from the ciprofibrate-treated rat livers, and most of the MoAbs were reactive with liver tumours induced by ciprofibrate in other rats. 4. The antigens identified by these MoAbs were mainly cytoplasmic, as observed by immunocytochemical methods. The MoAbs were also tested in a cross-species system, but showed no reactivity with normal human tissues and little reactivity with non-hepatic human tumours. Two of the MoAbs (M-23 and M-28) reacted strongly with human hepatocellular carcinoma. 5. Immunoblotting was used to study further the antigens identified by the MoAbs. The antigens demonstrated a size range between 45 kd and 159 kd. While some of these molecular weights may correspond to cellular enzymes induced by peroxisome proliferators (e. g. cytochrome P-450), several of them appear to be new antigens not previously described. The elucidation of their structure and function, and their examination as specific tumour markers may help in the diagnosis or treatment of human hepatocellular carcinoma