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In cancer metastasis, single circulating tumor cells (CTCs) in the blood and disseminated tumor cells (DTCs) in the bone marrow mediate cancer metastasis. Because suitable biomarker proteins are lacking, CTCs and DTCs with mesenchymal attributes are difficult to isolate from the bulk of normal blood cells. To establish a procedure allowing the isolation of such cells, we analyzed the cell line BC-M1 established from DTCs in the bone marrow of a breast cancer patient by stable isotope labeling by amino acids in cell culture (SILAC) and mass spectrometry. We found high levels of the transmembrane protein CUB domain-containing protein 1 (CDCP1) in breast cancer cell lines with mesenchymal attributes. Peripheral blood mononuclear cells were virtually negative for CDCP1. Confirmation in vivo by CellSearch revealed CDCP1-positive CTCs in 8 of 30 analyzed breast cancer patients. Only EpCam-positive CTCs were enriched by CellSearch. Using the extracellular domain of CDCP1, we established a magnetic-activated cell sorting (MACS) approach enabling also the enrichment of EpCam-negative CTCs. Thus, our approach is particularly suited for the isolation of mesenchymal CTCs with downregulated epithelial cancer that occur, for example, in triple-negative breast cancer patients who are prone to therapy failure.

Functional studies giving insight into the biology of circulating tumor cells (CTCs) remain scarce due to the low frequency of CTCs and lack of appropriate models. Here, we describe the characterization of a novel CTC-derived breast cancer cell line, designated CTC-ITB-01, established from a patient with metastatic estrogen receptor-positive (ER + ) breast cancer, resistant to endocrine therapy. CTC-ITB-01 remained ER + in culture, and copy number alteration (CNA) profiling showed high concordance between CTC-ITB-01 and CTCs originally present in the patient with cancer at the time point of blood draw. RNA-sequencing data indicate that CTC-ITB-01 has a predominantly epithelial expression signature. Primary tumor and metastasis formation in an intraductal PDX mouse model mirrored the clinical progression of ER + breast cancer. Downstream ER signaling was constitutively active in CTC-ITB-01 independent of ligand availability, and the CDK4/6 inhibitor Palbociclib strongly inhibited CTC-ITB-01 growth. Thus, we established a functional model that opens a new avenue to study CTC biology., (© 2020 The Authors. Published under the terms of the CC BY 4.0 license.)

Protein Tyrosin Kinase 7 (PTK7) is upregulated in several human cancers; however, its clinical implication in breast cancer (BC) and lymph node (LN) is still unclear. In order to investigate the function of PTK7 in mediating BC cell motility and invasivity, PTK7 expression in BC cell lines was determined. PTK7 signaling in highly invasive breast cancer cells was inhibited by a dominant-negative PTK7 mutant, an antibody against the extracellular domain of PTK7, and siRNA knockdown of PTK7. This resulted in decreased motility and invasivity of BC cells. We further examined PTK7 expression in BC and LN tissue of 128 BC patients by RT-PCR and its correlation with BC related genes like HER2, HER3, PAI1, MMP1, K19, and CD44. Expression profiling in BC cell lines and primary tumors showed association of PTK7 with ER/PR/HER2-negative (TNBC-triple negative BC) cancer. Oncomine data analysis confirmed this observation and classified PTK7 in a cluster with genes associated with agressive behavior of primary BC. Furthermore PTK7 expression was significantly different with respect to tumor size (ANOVA, p = 0.033) in BC and nodal involvement (ANOVA, p = 0.007) in LN. PTK7 expression in metastatic LN was related to shorter DFS (Cox Regression, p = 0.041). Our observations confirmed the transforming potential of PTK7, as well as its involvement in motility and invasivity of BC cells. PTK7 is highly expressed in TNBC cell lines. It represents a novel prognostic marker for BC patients and has potential therapeutic significance.

Expression analysis of genes encoding components of the phosphotyrosine signaling system by cDNA array hybridization revealed elevated levels of FGFR4 transcripts in several mammary carcinoma cell lines. In the FGFR4 gene transcript from MDA-MB-453 mammary carcinoma cells, a G to A conversion was discovered that results in the substitution of glycine by arginine at position 388 in the transmembrane domain of the receptor. The Arg(388) allele was also found in cell lines derived from a variety of other tumor types as well as in the germ-line of cancer patients and healthy individuals. Analysis of three geographically separated groups indicated that it occurs in approximately 50% of the human population. Investigation of the clinical data of 84 breast cancer patients revealed that homo- or heterozygous carriers of the Arg(388) allele had a significantly reduced disease-free survival time (P = 0.01) within a median follow-up of 62 months. Moreover, the FGFR4 Arg(388) allele was associated with early lymph node metastasis and advanced tumor-node-metastasis (TNM) stage in 82 colon cancer patients. Consistent with this finding, MDA-MB-231 mammary tumor cells expressing FGFR4 Arg(388) exhibited increased motility relative to cells expressing the FGFR4 Gly(388) isotype. Our results support the conclusion that the FGFR4 Arg(388) allele represents a determinant that is innocuous in healthy individuals but predisposes cancer patients for significantly accelerated disease progression.

Fourteen patients with metastatic breast cancer previously treated with one chemotherapy regimen received Pirarubicin at a dose of 70 mg/m2 at 3-week intervals. In 7 patients the dose had to be reduced, in 1 patient to 40 mg/m2 and in 6 patients to 50-60 mg/m2. There were 1 complete and 2 partial remissions. These objective responses were observed in soft tissue, lung and pleural areas and lasted 1+; 4+ and 5+ months. Grade 3 and 4 leukopenia was found in 42%, grade 3 thrombocytopenia in 2%, grade 3 nausea/vomiting in 29% of the cycles. Grade 1 and 2 alopecia occurred in 64% of the patients, the remaining 36% of the patients did not suffer from any alopecia. No cardiotoxic side effects were observed in 13 patients. In 1 patient with severe coronary heart disease extrasystoles and reduction in left ventricular ejection fraction occurred. Pirarubicin has antitumor activity in previously treated metastatic breast cancer patients.