Abstract 2978:In vivoprofiling of migratory tumor cells identifies novel mediators for invasion and dissemination in human breast cancer.

Breast cancer is one of the most frequent malignant neoplasms occurring in women in developed countries and metastasis of breast cancer is the main cause of death in these patients. Molecular profiling has led to the identification of gene sets, or “signatures,” the expression of which in primary tumors is associated with metastatic risk and poor outcome for the patients. Early such signatures were derived from whole pieces of tumor tissue. We now know that tumors are highly heterogeneous, that not all cells within a tumor are migratory and invasive, and that the tumor microenvironment gives spatial-temporal cues to tumor cells for invasion and metastasis. Therefore, despite having prognostic value in patients, early signatures have given little insight on the specific mechanisms of metastasis and especially the crucial early steps of the metastatic cascade: migration, invasion and entry of tumor cells into the systemic circulation. Using an in vivo invasion assay, we isolated the migratory tumor cell subpopulation from MDA-MB-231 derived orthotopic tumors and compared their molecular profile to the average primary tumor cells, thus deriving a gene expression profile specific for invasion and dissemination of breast cancer. Unsupervised bioinformatics analysis of this human invasion signature (HIS) shows that the most significant upregulated gene networks in the migratory breast tumor cells include genes regulating DNA repair, embryonic development and cell movement, with TGFβ acting as a central regulator of the migratory phenotype. Importantly, we developed a panel of patient-derived breast tumor xenografts in mice by orthotopic engraftment of tumor tissue from surgical resections, which we have used to directly validate our findings from the MDA-MB-231 xenografts. Indeed, in both MDA-MB-231 and patient-derived xenografts, we found a significant increase of nuclear γH2AX staining as well as increased nuclear accumulation of phospho-ATM and Smad2/3 in the migratory tumor cells compared to the average primary tumor cells. These findings confirm a novel link between activated DNA repair pathways and tumor cell invasion in vivo, as well as identify specifically the migratory subpopulation of a primary tumor to have a gene pattern similar to embryonic development. In addition, we verified that the function of selected genes from the HIS was required for in vivo invasion and hematogenous dissemination in the MDA-MB-231 and the patient-derived xenografts by use of specific inhibitors. Finally, the HIS significantly predicts risk of metastasis in public breast cancer databases independent of other clinical parameters. Overall, our data suggests a molecular basis for the invasive properties of tumor cells in human breast tumors in vivo and a rationale for new prognostic and therapeutic target design. 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 2978. doi:1538-7445.AM2012-2978