P2-01-12: Determining the Molecular Signature That Drives Breast Cancer-Induced Brain Metastasis in a Mouse Xenograft Model.
Authors: Mukhopadhyay KD , Elkahloun AG , Yoon K , Cornell JE , Yu L , Liu Z , Sun L-Z 
Published: June 2012

Breast cancer (BCa) is the most common malignant disease in women in U.S. and the mortality in BCa patients is due to the metastasis of the disease from primary site. Brain metastasis accounts for nearly 20% of all metastases in BCa. It is the most feared complication of BCa because of very few effective treatment regimens available, leading to lower survival rate in patients. The exact molecular mechanism for metastases of BCa into brain is unknown. Rodent model systems have been reported for brain metastasis in BCa but the current models for brain metastasis have limitations. Therefore, there is a need of efficient model system that can significantly contribute towards our understanding of different factors from both host and tumor leading to brain metastasis.

Previously we reported isolation and characterization of estrogen independent B6TC cells that are derived from the stable spontaneous fusion of MDA-MB-231/GFP/Neo and ZR-75-1/GFP/puro in mouse bone marrow microenvironment. This chimeric B6TC has propensity to metastasize to brain when inoculated through intracardiac (I.C.) route, and express stem cell-like features. In the present study using B6TC, we have developed an efficient and novel mouse model for studying BCa-induced brain metastasis. We have generated three cell lines from B6TC through three successive rounds of inoculation in mouse and subsequent isolation of brain metastatic cells. Each round of selection enhanced the brain metastatic propensity. An initial microarray analysis identified genes like MMP1, HB-EGF, ST3GAL1, PTGS2, ITGA3, and CXCR4, which showed significant up-regulation in B6TC compared to its parental metastatic MDA-MB-231 or nonaggressive ZR-75-1 cells. These genes are implicated in metastasis regulation. A second round of RNA microarray was performed with three sublines of B6TC with successively enhanced brain metastatic propensity to identify unique potential brain metastatic genes showing gradual up or down-regulation over generations. From analysis of the gene expression profiles, apart from potent brain metastatic genes detected earlier, we also identified some molecular pathways, including TGF beta signaling pathway that are associated with enhanced brain metastasis. The B6TC model is novel for studying the molecular mechanism of brain metastasis, as in this model, apart from experimental metastasis in brain through I.C route, cells show spontaneous metastases to the brain from the primary tumor and this unique feature will enable us to study the mechanisms of the early steps of brain metastasis progression. Further analyses to find out common miRNAs that are over or under-expressed in the sublines over successive generations and determination of gene targets of miRNA are underway. This study will not only provide valuable insight into molecular mechanism of BCa-induced brain metastasis but also lay the foundation to identify novel prognostic and therapeutic markers of brain metastases, leading ultimately to the discovery of novel molecularly targeted drugs to prevent and eradicate BCa metastasis initiation, progression and recurrence.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-01-12.