Phenotypic characteristics of cell lines derived from disseminated cancer cells in bone marrow of patients with solid epithelial tumors: Establishment of working models for human micrometastases

Bone marrow (BM) is a clinically relevant site of micrometastatic disease i n patients with solid epithelial tumors. It is, therefore, important to est ablish suitable models that allow the in-depth characterization of dissemin ated tumor cells present at low frequencies of 10(-5)-10(-6) nucleated BM c ells. The aim of this study was to assess common phenotypic features of nin e tumor cell lines established from BM of patients with cancer of the prost ate (four cell lines), breast (two cell lines), lung (two cell lines), and colon (one cell line) using immunocytochemistry, flow cytometry, and revers e transcription-PCR, All cell lines stained positive for both cytokeratins, the epithelial intermediate filaments, and the epithelial cell adhesion mo lecule E-cadherin, and they lacked markers of BM-derived cells. The tumor o rigin of the cell lines was supported by the expression of the ErbB2 oncoge ne (seven of nine) and MAGE mRNA (eight of eight). All cell lines coexpress ed cytokeratin and vimentin, the mesenchymal intermediate filament, indicat ing an epithelial-mesenchymal transition of micrometastatic cells. The inva sive phenotype of the immortalized cells was also reflected by the consiste nt expression of several metastasis-associated adhesion molecules, includin g alpha 5 (eight of nine), alpha 6 (five of nine), alpha V (nine of nine), beta 1 (nine of nine), and beta 3 (nine of nine) integrin subunits and the M-r 67,000 laminin receptor (seven of nine). Contrary to our expectations, metastasis-promoting CD44 variant isoforms were only detected on two lines, whereas all cell lines expressed MUC18/melanoma cell adhesion molecule and intercellular adhesion molecule-1, two members of the immunoglobulin super family of adhesion molecules that are not frequently found on primary carci noma cells. The consistent expression of various epithelial and tumor-assoc iated antigens provides evidence that the established cell lines are derive d from disseminated cancer cells present in the BM. The invasive phenotype of the immortalized cells was mirrored by their epithelial-mesenchymal tran sition and the expression of several metastasis-associated molecules, which might be potential candidates for novel therapeutic targets.