Characterization of Breast Cancer Cell Lines

The epithelial-like human breast adenocarcinoma cell line Michigan Cancer Foundation-7 (MCF- 7, DSMZ no. ACC 115), known to express claudin-3, -4, and -7 (Kominsky et al., 2003 (link); Todd et al., 2015 (link)) was used as claudin positive cells. For controls, we used a breast cancer cell line, MDA-MB-231 with minimal expression of claudin -3, -4, and -7 (Becker et al., 2018 (link)). Between experiments, the cells were kept in an incubator at 37°C with 5% CO₂. Cells were cultured in DMEM/F12 (F4815, Biochrom) supplemented with 10% fetal calf serum (S0615, Biochrom) and 1% penicillin/streptomycin (P06-07050, PAN-Biotech). The confluent culture was split every 3 to 6 days. Cells were detached from the culture plate with trypsin/EDTA (PAN-Biotech) for 3 min at 37°C. Trypsin was subsequently deactivated in the solution by adding a double amount of cell culture medium. An aliquot was then transferred into a new tissue culture dish with fresh culture medium. The remaining cells could be used for experiments.