Abstract 2949: The VEGF quadruplex-forming sequence inhibits cell growth of lung cancer

Abstract

Abstract Vascular endothelial growth factor (VEGF), commonly overexpressed in a variety of malignancies including lung cancer, is a key regulator of angiogenesis promoting tumor survival, growth, and metastasis. The promoters of several cancer-related genes, including VEGF, contain disproportionate sequences within nuclease hypersensitivity regions capable of forming quadruplex (four-stranded) DNA. The VEGF quadruplex-forming sequence (VEGFq), a polyG/polyC tract located in the proximal promoter region upstream of the transcription initiation site, has been implicated in the regulation of both basal and inducible VEGF expression. However, the biological role of this sequence remains unclear. We hypothesize that treatment of A549 non-small lung cancer cells with VEGFq induces cell death by inhibiting gene expression. To determine the biological role of VEGF on lung cancer cell proliferation, A549 cells were treated with VEGFq or the corresponding mutant sequence (MutVEGF), which lacks runs of two or more guanines. Changes in cell proliferation were compared to levels of VEGF protein expression. Quadruplex formation was confirmed by circular dichroism spectroscopy. Our results demonstrate that VEGFq formed a stable parallel quadruplex structure, while the MutVEGF sequence did not form a quadruplex. Treatment of A549 cells with VEGFq caused a significant dose and time-dependent decrease in cell proliferation after 3 and 6 days (IC50<5µM) as determined by MTT assay. No change in the growth of nontransformed fibroblast cells occurred in response to VEGFq indicating the effect is specific for malignant cells. Confocal and flow cytometry analysis of cells treated with FITC-labeled VEGFq or MutVEGF showed prominent uptake and nuclear localization of VEGFq not MutVEGF after 72 h. Inhibition of cell proliferation corresponded with decreased VEGF protein expression. No specific change in the cell cycle was measured after 72 h. These results demonstrate striking growth inhibition of A549 cells in response to the VEGF quadruplex-forming sequence related to inhibition of VEGF expression and suggest significant therapeutic implications for the treatment of non-small cell lung cancer. 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 2949.