Characterization of a novel breast cancer cell line derived from a metastatic bone lesion of a breast cancer patient.

PURPOSE: We aimed to generate and characterize a novel cell line from a breast cancer bone metastasis to better study the progression of the disease. METHODS: The cell line, P7731, was derived from a metastatic bone lesion of a breast cancer patient and assessed for marker expression. P7731 was analyzed for DNA copy number variation, somatic mutations, and gene expression and was compared with the primary tumor. RESULTS: P7731 cells are negative for estrogen receptor alpha (ERα), progesterone receptor (PR), and HER2 (triple-negative); strongly express vimentin (100% of cells positive) and also express cytokeratins 8/18 and 19 but at lower frequencies. Flow cytometry indicates P7731 cells are predominantly CD44+/CD49f+/EpCAM-, consistent with a primitive, mesenchymal-like phenotype. The cell line is tumorigenic in immunocompromised mice. Exome sequencing identified a total of 45 and 76 somatic mutations in the primary tumor and cell line, respectively, of which 32 were identified in both samples and included mutations in known driver genes PIK3CA, TP53, and ARID1A. P7731 retains the DNA copy number alterations present in the matching primary tumor. Homozygous deletions detected in the cell line and in the primary tumor were found in regions containing three known (CDKN2A, CDKN2B, and CDKN1B) and 23 putative tumor suppressor genes. Cell line-specific gene amplification coupled with mRNA expression analysis revealed genes and pathways with potential pro-metastatic functions. CONCLUSION: This novel human breast cancer-bone metastasis cell line will be a useful model to study aspects of breast cancer biology, particularly metastasis-related changes from breast to bone.