The objective of the proposed research is to identify the appearance of new or inappropriate cell-surface glycoproteins as well as the deletion or structural modification of normally expressed glycoproteins. Initial studies will focus on further characterization of the basis for the qualitative and quantitative alterations in the expression of dipeptidyl dipeptidase IV (DPPIV) on transplantable hepatocellular carcinomas (THC) and on primary hepatic tumors (PHCC) induced by ethionine, diethylnitrosamine or 2-acetylaminofluorene. Immunochemical and biochemical techniques will be employed to characterize the post translational processing of DPP IV on normal hepatocytes and THC cells and the effect these modifications have on enzymatic activity. In addition, we will attempt to determine whether DDP IV plays a role in the interaction of hepatocytes and THC cells with collagenous substrata. In the proposed studies, we will also examine the expression and structure of a 70 kd glycoprotein which was originally detected using a monoclonal antibody (MAb 324.5) raised against THC cells by a novel immunization protocol. Preliminary results showing that this antigen is not expressed by other normal tissues, suggest that it may be suitable as a target for immunotoxins. To investigate this possibility and the potential use of immunotherapy in hepatocarinogenesis, we will develop an immunotherapy model based on the ability of MAb 324.5 conjugated to an appropriate toxin to arrest the growth of THC cells. Parallel studies will be initiated to examine the effect of spatial configuration and microenvironment on the expression of MAb defined antigens. We will also direct our efforts towards developing MAb which can be used to examine further the structure and expression of gp64, a viral antigen expressed by THC cells and a group of 116 kd tumor associated antigens bound to soybean agglutinin. We will employ heteroantisera raised against normal hepatocytes, THC and PHCC in combination with immunoabsorption on immobilized hepatocyte glycoproteins, two dimensional gel chromatography and peptide mapping techniques to identify and characterize hepatocyte antigens which are expressed in a structurally altered form on tumor cells. Results from the proposed research will thus give insight into the altered processing of normal antigens on tumor cells and will identify tumor associated glycoprotein antigens which have potential for diagnosis and treatment.
