Identification of genes associated with breast cancer micrometastatic disease in bone marrow using a Patient Derived Xenograft mouse model

In this study, using a Patient Derived Xenograft (PDX) system established by transplanting primary tumors from pre-metastatic breast cancer patients we demonstrate that development of distant organ metastases correlates with the presence of Bone Marrow Disseminated Tumor Cells (BM DTCs) in the PDX mice. Comparative gene expression analysis of bone marrow (BM) from tumor bearing PDX mice which developed metastatic disease was carried out with BM from non-tumor bearing controls. In this dataset, BM from seven tumor bearing mice with metastatic tumors, two control mice, a primary tumor and a spleen metastatic tumor from one of the tumor bearing mice were included in this analysis. This study allowed the identification of novel gene expression patterns associated with DTCs present in the BM and supports the concept that DTCs present in the BM undergo epithelial to mesenchymal transition (EMT). Analysis of the gene array data identified several genes which are known oncogenes (ETS1, GNL3), metastatic regulators (MALAT1, ALCAM, CD44), or associated with EMT (SIP 1) expressed at significantly higher levels in the BM of PDX mice as compared to BM from control animals. DTC-enriched BM from seven WHIM17 mice, one primary WHIM17 tumor, and a solid organ metastasis from the WHIM17 mouse was performed to evaluate the molecular differences between primary tumor xenograft cells and their DTC counterparts, as well as to identify unique genes associated with the DTCs themselves using human-based microarrays. Control BM samples from non-tumor bearing NOD-SCID mice with and without humanized mammary fat pads were included to account for cross-hybridization and detection of transcripts emanating from mouse BM cells.