Abstract 455: Hypoxia induced carbonic anhydrase IX is essential for the growth and metastasis of breast tumors

Abstract

Abstract Metastasis of primary malignancies is a multi-step process and remains the principal cause of cancer deaths. Carbonic anhydrase IX (CAIX) is a hypoxia inducible protein and a poor prognostic marker for several types of cancer, including breast cancer. However, the functional role of CAIX in the metastatic progression of breast cancer is unclear. Here, we have investigated its role in the growth and metastasis of breast tumors. Orthotopic mouse mammary tumors derived from metastatic 4T1 and 66cl4 cells or non-metastatic 67NR cells were examined for levels of proliferation (BrdU), hypoxia, (pimonidazole), perfusion (DiOC7), vasculature (CD31), apoptosis (TUNEL) and lymphangiogenesis (LYVE-1). Metastatic 4T1 and 66cl4 tumors expressed a hypoxia gene signature and were characterized as being poorly vascularized, with high levels of hypoxia. Large numbers of apoptotic cells and well developed intratumoral lymphatic vessels were also evident. Inhibition of expression of CAIX in the metastatic 4T1 cells by stable expression of short hairpin RNA (shRNA) resulted in cell death and reversal of extracellular acidosis in hypoxia in vitro, dramatic regression of tumors in vivo, and inhibition of metastasis. These properties were rescued by constitutive expression of human CAIX. Treatment of mice harboring 4T1 tumors with a novel CAIX-specific inhibitor resulted in significant inhibition of tumor growth. Interrogation by immunohistochemistry of a large (3992 patient samples) primary breast tumor tissue microarray showed that CAIX expression was significantly associated with worse distant relapse free survival (p<10−16) and was most prominent in the basal breast cancers (51%). Our data show that CAIX-mediated function is required for the survival and metastasis of hypoxic breast tumors, and suggest that CAIX is a promising therapeutic target for metastatic breast cancer. This work was supported by the Canadian Breast Cancer Research Alliance, with special funding from the Canadian Breast Cancer Foundation. 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 455.