Abstract 538: Targeting the tumor premetastatic microenvironment to prevent and inhibit cancer metastasis

Abstract

Abstract Tumor metastasis is the leading cause of death for most cancer patients. Recent studies reveal a sequence of events involving the recruitment of bone marrow-derived cells and activation of proinflammatory cytokines in the tissue parenchyma at future sites of metastasis, which provide a hospitable microenvironment for later arriving tumor cells. In this study, we explore the potential of targeting the premetastatic microenvironment by using pharmacologic inhibitors to prevent and inhibit cancer metastasis. 4T1 mouse breast cancer and MDA-MB-231 human breast cancer cells were orthotopically implanted in mouse mammary fat pads to develop lung and liver metastases. Treatment with Brivanib (BMS-582664), a novel small molecule kinase inhibitor of VEGFRs and FGFRs, significantly inhibited primary tumor growth and metastasis development in lung and liver in both models. Primary tumors induced an inflammation response in premetastatic lungs, and to a lesser extent, livers, characterized by intensive influx of Gr1+ neutrophils and upregulation of proinflammatory cytokines/enzymes such as TNF-α, IL-1β, IL-6 and iNOS. Brief treatment (3 – 4 days) with Brivanib (100 mg/kg/d) completely blocked the recruitment of Gr1+ neutrophils and upregulation of the proinflammatory cytokines/enzymes, associated with inhibition of the MAPK and Stat3 signaling pathways induced in premetastatic lungs/livers. Our results further demonstrate that Brivanib significantly inhibits tumor cell conditioned medium (TCCM)-stimulated pulmonary accumulation of Gr1+ neutrophils and seeding of tumor cells injected i.v. in the absence of primary tumors, suggesting a direct inhibitory impact of Brivanib on formation of the premetastatic microenvironment. Using flow cytometry analyses, we demonstrated that only a minority of circulating Gr1+ neutrophils (<10%) from the peripheral blood of tumor-bearing mice express surface VEGFR1/2 in our models. Moreover, in an in vitro chemotaxis assay, we detected no enhanced migration of freshly-isolated circulating Gr1+ cells towards VEGF or PlGF, two ligands for VEGFR1. By contrast, we found that resident alveolar macrophages (AMs) express relatively higher level (>5 fold) of VEGFR1/2 proteins compared to incoming Gr1+ neutrophils. Addition of exogenous TCCM to in vitro culture of freshly-isolated AMs induced the expression of proinflammatory cytokines that facilitate the recruitment of Gr1+ neutrophils. Brivanib treatment significantly inhibited TCCM-induced upregulation of proinflammatory cytokines in cultured AMs. Our findings suggest a critical role of the VEGF/VEGFR axis in resident pulmonary cells like AMs to initiate formation of the premetastatic microenvironment and support targeting the VEGF/VEGFR signaling pathway for the treatment and prevention of metastatic disease. 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 538. doi:10.1158/1538-7445.AM2011-538