Abstract 5278: Suppression of angiogenic potential of breast cancer by the inhibition of SAF-1 transcription factor activity

Abstract

Abstract Angiogenesis plays an important role in the tumor growth and metastasis by facilitating increased blood supply and thus fueling unwanted growth factors and nutrients to the growing tumor. Vascular endothelial growth factor (VEGF) is recognized as a multifunctional angiogenic stimulator that stimulates blood vessel formation and endothelial cell survival. Recent therapeutic trials with anti-VEGF antibody bevacizumab (Avastin), although produced beneficial effects on some cancers including colorectal and lung cancers, had very limited beneficial outcome in breast cancer. The diverse response of avastin raised questions about the efficacy of anti-VEGF antibody approach for breast cancer therapy. Despite the disappointing outcome, it cannot be ignored that regulation of angiogenesis plays a critical role in breast cancer. We hypothesized that angiogenesis may be better controlled by blocking the synthesis of VEGF protein as opposed to the present approach that attempts to block the functions of VEGF by using antibodies. Induction of VEGF by a plethora of physiological and environmental stimuli strongly suggests the presence of multiple routes of VEGF synthesis, which are incompletely understood. We present evidence for a novel mode of transcriptional induction of VEGF, regulated by an inflammation-responsive transcription factor, SAF-1. Incidentally, inflammatory breast cancer exhibits increased angiogenesis and has a higher metastatic potential than noninflammatory breast cancer, supporting the notion that chronic inflammation plays a strong role in angiogenesis and in the progression of cancer. SAF-1 is present in high abundance in human breast cancer tissues. We show that inhibition of endogenous SAF-1 by antisense shRNA can markedly inhibit VEGF expression and block cancer cell-supported vascular endothelial cell function and angiogenesis. Furthermore, SAF-1 inhibition by shRNA reduces tumor growth in mouse tumor model. We provide evidence that SAF-1-mediated induction of VEGF remains suppressed by KLF-4 transcription factor which is abundantly present in normal breast epithelial cells but absent in breast cancer cells. Mutually exclusive interaction of KLF-4 and SAF-1 at the VEGF promoter provides a mechanism for regulation of low-expression of VEGF in normal breast tissues. In correlation, lack of KLF-4 in breast cancer cells appears to be linked to un-restricted interaction of SAF-1 leading to the induction of VEGF expression. Together, our studies provide a new insight into the molecular mechanisms of VEGF expression regulated by SAF-1 and its impact in angiogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5278. doi:1538-7445.AM2012-5278