Patient-derived breast and melanoma circulating tumor cell (CTC) in vitro models as encouraging new tools for cancer research

Circulating Tumor Cells (CTCs) have emerged as powerful tools for understanding the mechanisms behind cancer biology, particularly in context of metastatic disease. Although rare, CTCs are increasingly recognized for their potential in the early diagnosis, monitoring, and progression of tumors. These cells can detach from a primary cancer tumor and enter the bloodstream, facilitating metastasis at distant tissue sites. As research into CTCs advances, new opportunities will continue to emerge to better manage therapeutic targets, especially for metastatic disease. Despite progress in CTC isolation techniques, detecting CTCs remains challenging due to their rarity in the bloodstream. Furthermore, long-term and scalable in vitro culture of CTCs has not been previously achieved. As a result, there is a significant lack of widely available CTC models for studying cancer biology, metastatic progression and development of new treatment strategies. ATCC is actively collaborating with various institutions to make CTCs widely available for cancer research, focusing on the development of standardized expansion and characterization protocols for CTCs isolated from clinical patient samples. In this study, we present the successful propagation and characterization of six well-established breast and melanoma CTC models originating from metastatic breast and melanoma disease: Brx50 (ATCC® CRL-3648™), Brx61 (ATCC® CRL-3649™), Brx142 (ATCC® CRL-3650™), MEL167 (ATCC® CRL-3651™), MEL182 (ATCC® CRL-3652™) and PEM78 (ATCC® CRL-3653™). We evaluated the genomic, proteomic, and functional characteristics of both the breast cancer and melanoma CTC models. Genetic profiling via sequencing revealed key oncogenic drivers potentially linked to metastatic behavior. Gene expression profiles were compared with commonly used breast and melanoma cell lines to highlight distinct molecular signatures. Immunofluorescence staining was performed to assess the distinct presence of breast cancer or melanoma molecular biomarker panels. Drug response assays were conducted to evaluate the sensitivity of the breast models to estrogen receptor (ER) inhibitors and melanoma models to BRAF inhibitors. Additionally, drug response profiles of the breast CTC models were compared to those of commonly used triple-positive and triple-negative breast cancer cell lines, while melanoma CTC models were compared to the A375 melanoma cell line and CRISPR-engineered drug-resistant variants. In conclusion, metastatic disease remains difficult to treat due to reduced therapeutic response rates and increased disease relapse potential. The six new widely available CTC lines-Brx50, Brx61, Brx142, MEL167, MEL182 and PEM78-represent robust and versatile models for investigating the role of CTCs in pre-clinical diagnostics, disease monitoring, and the progression of metastatic breast cancer and melanoma.