Effect of combination inhibition of vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGF-R) on ovarian cancer cell lines

Abstract

13112 Background: Bevacizumab, a VEGF inhibitor, and cetuximab, an EGF-R inhibitor, have shown promising results in the treatment of solid tumors. The combination of these two antibodies and combinations with platinum chemotherapy is of interest for the treatment of ovarian cancer. Our objective is evaluate the mechanism of action and to determine the direct effect on tumor proliferation, the role of antibody dependent cell cytotoxicity (ADCC) with immune effector cells and the outcome in nude mouse xenografts with antibody treatment combinations. Methods: Five ovarian cancer cell lines were studied; SKOV3, SKOV8, OVCAR3, A2780, and CaOV3. VEGF secretion levels were determined for each cell line by standard ELISA. EGF-R, VEGF-R and VEGF surface expression was determined by flow cytometry. Cytotoxicity alamar blue 96-well plate assays were performed and cells were plated and exposed to bevacizumab or cetuximab alone, in combination and with cisplatin. Standard 51chromium release assays were performed to determine if bevacizumab and cetuximab have a role in ADCC when combined with peripheral blood mononuclear cells (PBMC). Results: All ovarian cancer cell lines secreted VEGF ranging from 210 to 1,849 pg/ml. Flow cytometry studies demonstrated varying degrees of expression of VEGF-R and minimal surface expression of VEGF ligand. EGF-R was present on all cell lines. Five day alamar blue cytotoxicity assays using varying concentrations of single agent bevacizumab (0.1–10 μM) or single agent cetuximab (0.01–1.0 μM) had minimal to no cytotoxic effect on ovarian cancer cell lines. The IC50 for cisplatin in these cell lines was obtained and ranged from 1–5 μM and was not altered by the addition of antibodies. In 51chromium release assays, the combination of bevacizumab and cetuximab caused a trend toward increased SKOV3 cell lysis by PBMC. Conclusion: Bevacizumab or cetuximab alone or in combination with each other in vitro had minimal direct cytotoxic effect. ADCC may be a mechanism of cell lysis when these antibodies are combined with effector cells (PBMC) and further studies are underway. In vivo studies with nude mouse SKOV3 xenografts are being performed to evaluate the effect on combination antibody therapy on established tumors. No significant financial relationships to disclose.