Abstract 3481: The SDF-1α/PDGF-B pathway plays a critical role in bone marrow cell – derived pericyte differentiation during vasculogenesis of Ewing's sarcoma

The purpose of this study was to investigate the role of the SDF-1α/PDGF-B pathway in bone marrow cell (BMC) differentiation into pericytes during Ewing9s sarcoma growth. Previous findings form our group demonstrated that BMCs migrate to TC71 and A4573 tumors, differentiate into endothelial cells and pericytes and, participate in the development of the tumor vasculature. Vascular endothelial growth factor VEGF165 is the chemotactic stimulus for BMCs. Introducing stromal derived growth factor SDF-1α into VEGF165-inhibited tumors induced chemotaxis of BMCs to a perivascular area where they differentiated into pericytes and up-regulated platelet derived growth factor PDGF-B mRNA levels. These observations prompted us to further investigate the correlation between SDF-1α and PDGF-B and the role of this pathway in BMC differentiation into pericytes. We found that SDF-1α regulates PDGF-B expression through the ELK-1transcription factor and that the SDF-1α/PDGF-B pathway is critical for BMC differentiation into pericytes in vitro. Here, we used AMD3100 to specifically inhibit SDF-1α in both TC71 and A4573 Ewing9s tumors and analyzed the effect of SDF-1α inhibition on PDGF-B expression and BMC differentiation into pericytes in vivo. We performed a BM transplant from GFP+ transgenic mice into nude mice in order to track BMC migration to the tumor site. Following engraftment, the mice were injected with either TC71 or A4573 Ewing9s sarcoma cells. Once the tumors became palpable, the mice received daily subcutaneous injections of either PBS or AMD3100 for the duration of the experiment. Tumor sections were analyzed by immunohistochemistry (IHC). We found that inhibiting SDF-1α led to smaller vessels with smaller lumens and to a decrease in the microvessel density. We intravenously injected the mice with Hoechst prior to sacrificing and found that AMD3100 decreased tumor blood vessel perfusion. TUNEL staining also showed an increase in tumor apoptosis. To elucidate the effect of SDF-1α on vasculogenesis of Ewing9s sarcoma, we stained tumor sections for GFP, CD31, desmin and NG2. Although AMD3100 did not inhibit BMCs from migrating to the tumor site, it decreased BMC differentiation into desmin and NG2 pericytes. We also stained the tumor sections for PDGF-B and confirmed that inhibiting SDF-1α also inhibited PDGF-B. These findings support our previous data that SDF-1α regulates PDGF-B and that this pathway is critical for the differentiation of BMCs into pericytes. All together, our data demonstrates the role of SDF-1α as a signaling molecule which regulates the expression of angiogenic factors such as PDGF-B that are critical for pericyte maturation during tumor growth. Understanding these pathways will allow us to devise new therapeutic approaches for targeting tumor neo-vascularization which may be applied not only to Ewing9s sarcoma but to other tumor models. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3481. doi:10.1158/1538-7445.AM2011-3481