Abstract 365: Autocrine vascular endothelial growth factor signaling mediates survival and chemoresistance of human colorectal cancer cells

Abstract

Abstract Introduction. Although the effects of VEGF on angiogenesis and vascular function are well known, the autocrine effects of VEGF on tumor cell function remain to be elucidated. We studied phenotypic changes in human colorectal cancer (CRC) cells with homologous deletion of VEGF alleles to determine any potential autocrine/intracrine role of VEGF on tumor cell function. Methods. The human CRC cell lines HCT116 and LS174T with homologous recombination-mediated deletion of VEGF alleles were generated previously (Dang et al, Can Res 2006). To exclude the effect of exogenous VEGF, the cells were grown in low serum condition for all assays. MTT assay was used to detect changes in cell growth. Migration and invasion were determined using modified Boyden chamber assays. Cell death and apoptosis were assessed by FACS analysis following PI and Annexin V/PI staining respectively. Changes in protein levels of VEGF signaling intermediates and mediators of apoptosis were evaluated by Western blotting. Chemosensitivity was determined by FACS analysis following 5-FU treatment and PI staining of cells. Results. Loss of VEGF expression decreased cell growth and increased spontaneous apoptosis in CRC cells. Cells null for VEGF demonstrated increases in migration and invasion. Loss of VEGF expression also increased the sensitivity of cells to the cytotoxic effects of the chemotherapeutic drug, 5-FU, as shown by increased cell death and apoptosis. These effects are mediated via upregulation of the pro-apoptotic mediators cleaved caspase-3 and PARP and, downregulation of the anti-apoptotic mediator survivin. In addition, loss of VEGF led to increased levels of PlGF, SDF-1 and phosphorylated VEGFR-1 in CRC cells. Conclusion. Loss of autocrine/intracrine VEGF signaling leads to an increase in spontaneous apoptosis and chemosensitivity of colon cancer cells. In addition, loss of VEGF signaling led to increases in PlGF and SDF-1, suggesting that loss of VEGF signaling can lead to induction of compensatory pathways that may be mediated by numerous cell types in the tumor microenvironment. These findings have implications for a better understanding of mechanisms of action for VEGF targeted therapies when combined with chemotherapy in patients with metastatic CRC. 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 365.