Abstract 2323: Inhibition of in vitro growth of human mesothelioma cells by CSPG4-specific monoclonal antibodies

Abstract The membrane bound chondroitin sulphate protidoglycan 4 (CSPG4), also known as high molecular weight-melanoma associated antigen (HMW-MAA), plays a role in tumor cell proliferation, growth and differentiation, as well as in angiogenesis and extracellular matrix remodeling. Contrary to the early reports which had described CSPG4 expression restricted to melanoma cells, this molecule is expressed by various types of malignant tumors. Because of its high expression on tumor cells, including cancer stem cells, and its restricted distribution in normal tissues, CSPG4 represents an attractive target for immunotherapy. The lack of effective conventional therapy and the paucity of suitable targets for immunotherapy in mesothelioma have prompted us to test whether CSPG4 is expressed by mesothelioma cells and mediates the anti-tumor activity of CSPG4-specific monoclonal antibodies (mAb). Immunohistochemical staining with mAb showed that CSPG4 was expressed on mesothelioma cells in 24 out of 40 MM biopsies with minimal expression on surrounding normal cells. Furthermore FACS analysis and western blots detected CSPG4 in all the 9 human MM cell lines tested and that the expression was induced on MM cells by their interactions with the extracellular matrix (ECM). To test the sensitivity of MM cells to the anti-tumor activity of CSPG4-specific mAb, 3 MM cell lines were incubated with mAb TP41.2 (final concentration 10ug/ml) for up to 72hrs. Cell proliferation was determined by MTT assay. Cells incubated with normal mouse IgG antibodies were used as controls. Addition of mAb TP41.2 to cells already attached to plates had no detectable effect on their proliferation. On the other hand incubation of MM cells with mAb TP41.2 before seeding in plates markedly inhibited their growth. The effect was time-dependent. These results were observed in all 3 cell lines and each cell lines was tested 3 times. The data suggest that CSPG4 promotes MM cell growth by mediating their interactions with ECM. This conclusion is corroborated by the growth of CSPG4-positive MM cells in serum-free medium in plates coated with collagen I, collagen IV or fibronectin. Furthermore CSPG4-specific mAb decreased the expression of the angiogenic growth factors VEGF and HEY1, as determined by RT-PCR, in MM cells. These results suggest that it may be worthwhile to test the hypothesis that CSPG4-specific mAb-based immunotherapy may represent a viable approach for the treatment of MM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2323.