Abstract 1521: Hypoxia inducible factor is an important regulator of metastatic niche formation

Abstract An increasing number of studies have reported that primary tumors facilitate metastasis by directing bone marrow cells (BMC) to prime metastatic sites. Intratumoral hypoxia promotes metastasis through the stabilization of hypoxia-inducible factors (HIF1α and HIF2α), which upregulate a variety of genes crucial to cancer progression. It has been recently reported that hypoxic tumors induce lysyl oxidase (LOX), an amine oxidase that cross-links collagen and elastin in extracellular matrices, which is fundamental to metastatic niche formation. There are 4 other highly conserved members of the LOX family: lysyl oxidase like 1-4 (LOXL1-4). We found that different LOX members were induced by hypoxia in different human breast cancer cell lines, consistent with the unique expression pattern of LOX members in individual breast cancer patients. LOX and LOXL4 were markedly upregulated by hypoxia in MDA-MB-231 cells whereas LOXL2 was upregulated by hypoxia in MDA-MB-435 cells at the mRNA and protein levels. Hypoxic induction of various LOX members was abolished when HIF is genetically silenced or pharmacologically inhibited by HIF inhibitors acriflavine or digoxin (DIG). By microrheology and confocal imaging of collagen, we found that conditioned medium from hypoxic breast cancer cells increased collagen crosslinking compared to non-hypoxic conditioned medium. This effect was lost when HIF is knocked down. Also, we found an increase of BMC invasion through matrigel pretreated with conditioned medium from hypoxic MDA-MB-231 and MDA-MB-435 cells as compared to non-hypoxic cells. This induction was abrogated when HIF was genetically or pharmacologically inhibited. Importantly, pharmacologic (daily DIG intraperitoneal injection) or genetic inhibition of HIF in breast cancer cells significantly reduced lung metastasis and recruitment of CD11b+ BMCs to the lungs in an orthotopic implantation model. Fewer cross-linked collagen fibers were observed in the lungs of tumor-bearing mice when HIF was inhibited. Knockdown of LOX or LOXL4 in MDA-MB-231 and knockdown of LOXL2 in MDA-MB-435 cells recapitulated the results from HIF inhibition. Knockdown of LOX members in the cell lines suppressed hypoxia-induced collagen remodeling, BMC invasion in vitro, and CD11b+ recruitment to lungs in vivo. In conclusion, HIF induced secretion of multiple LOX members by primary breast cancers induces collagen remodeling and facilitates BMC recruitment to the lungs, leading to increased metastasis. Antibodies or small molecule inhibitors of LOX do not inhibit all family members. In contrast, HIF, the key determinant of LOX family expression, serves as an attractive chemotherapeutic target to inhibit niche formation and subsequent metastasis. 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 1521. doi:10.1158/1538-7445.AM2011-1521