Characterizing a murine breast cancer mouse model reveals chromosomal abnormalities in structure and number of single-cell clones and the presence of rare cancer stem cell-like phenotypes

Realistic models for cancer research representing disease progression that commensurately respond to therapeutics consistent with clinical observation are the holy grail for pre-clinical research and screening. Although such an ideal is elusive, well-characterized in vivo models facilitate our understanding of disease, progression, and therapeutic opportunities. Here, we characterize a commonly used syngeneic BALB/c mouse model of triple negative breast cancer (4T1) after establishing tumors in their flanks. Tumors developed at the subcutaneous injection site for all experimental mice and their volumes were monitored. We quantified a rare subset of breast cancer stem-like cells (CSCs), classified as CD44⁺/CD24⁻ phenotypes in in vitro and ex vivo cell populations. Chromosome numbers in ex vivo metaphase cells were greater than cells cultured in vitro (89.4 ± 3.4, range of 70–132 and 82.6 ± 1.1, range of 70–128; respectively). Further, we observed different types of chromosome aberrations, including gap, deletion, exchange, interstitial deletion, terminal deletion, ring, dicentric, and Robertsonian translocations. For both sources of cells, the number of aberrations was dominated by deletions, terminal deletions, and Robertsonian translocations. Ex vivo cells exhibited greater prevalence of deletions and terminal deletions, whereas in vitro cells displayed more ring aberrations and Robertsonian translocations. In conclusion, we successfully characterized cancer cells from a syngeneic mouse model of breast cancer in terms of rare CSC proportion and a variety of chromosomal aberrations, which is useful for understanding tumor traits associated with cancer development and therapeutic action. The data act as a valuable resource for other studies using the 4T1 BALB/c model.