Establishment and Characterization of a Brca1−/−, p53−/− Mouse Mammary Tumor Cell Line

Abstract

Breast cancer is the most commonly occurring cancer in women and the second most common cancer overall. By the age of 80, the estimated risk for breast cancer for women with germline BRCA1 or BRCA2 mutations is around 80%. Genetically engineered BRCA1-deficient mouse models offer a unique opportunity to study the pathogenesis and therapy of triple negative breast cancer. Here we present a newly established Brca1 −/− , p53 −/− mouse mammary tumor cell line, designated as CST. CST shows prominent features of BRCA1-mutated triple-negative breast cancers including increased motility, high proliferation rate, genome instability and sensitivity to platinum chemotherapy and PARP inhibitors (olaparib, veliparib, rucaparib and talazoparib). Genomic instability of CST cells was confirmed by whole genome sequencing, which also revealed the presence of COSMIC (Catalogue of Somatic Mutations in Cancer) mutation signatures 3 and 8 associated with homologous recombination (HR) deficiency. In vitro sensitivity of CST cells was tested against 11 chemotherapy agents. Tumors derived from orthotopically injected CST-mCherry cells in FVB-GFP mice showed sensitivity to cisplatin, providing a new model to study the cooperation of BRCA1-KO, mCherry-positive tumor cells and the GFP-expressing stromal compartment in therapy resistance and metastasis formation. In summary, we have established CST cells as a new model recapitulating major characteristics of BRCA1-negative breast cancers.Germline mutations in BRCA1 are responsible for a large proportion of inherited predispositions to breast and ovarian cancer. Women who carry mutations in BRCA1 or BRCA2 face 60% to 80% elevated lifetime risk to develop breast cancer by the age of 80 [6][7][8][9]. Germline mutations in BRCA1/2 occur in approximately 10% of TNBC patients [7], and mutations in further genes involved in the maintenance of genomic integrity and DNA repair, such as ATM (ataxia-telangiectasia), CHEK2 (Checkpoint kinase 2), and TP53 are also common [10,11]. BRCA-related mammary tumors are considered a distinct subtype due to their unique mutation profile ("BRCAness") [12,13]. Breast cancers with BRCA1 or BRCA2 mutations are characterized by different gene expression patterns, highlighting the influence of heritable mutations on the phenotype and chemosensitivity of cancer [14,15].In lack of targeted therapeutic options, chemotherapy remains the most effective treatment for TNBC. Neoadjuvant chemotherapy regimens containing taxanes and anthracyclines achieve complete response (CR) in 30% to 50% of patients with TNBC [16,17]. Unfortunately, TNBC patients with mutated BRCA1 are resistant to taxane therapy [18][19][20]. Conversely, drugs that induce DNA double-strand breaks and thereby increase genomic instability, represent a promising strategy for the treatment of TNBC with BRCA1/2 mutations [16,21,22]. Clinical studies have shown that platinum-based neoadjuvant chemotherapy is highly effective in TNBC patients with BRCA1 gene mutations [23,24]. Since 2018, patients relapsing after p...

BRCA1/Trp53 heterozygosity and replication stress drive esophageal cancer development in a mouse model

“…There was no accumulation of signature 3 in any of the tumor samples, including Brca1 mutant tumors (BPM). Previous studies with Brca1 mutant mouse tumors also have failed to detect the strong accumulation of an HRD signature unlike what was detected in human BRCA1 mutant tumors (53)(54)(55).…”

“…This observation is similar to what has been reported previously for tumor lines derived from mice where both Brca1 alleles were conditionally deleted in the mammary gland. There too, only minor enrichment of signature 3 in the Brca1-deleted tumors was found (53)(54)(55).…”

Experimental Closed‐Loop Control of Breast Cancer in Mice

“…Moreover, these tumors respond to chemotherapy very similarly, as initial treatment with doxorubicin, docetaxel, or cisplatin significantly reduces tumor size and induces remission. Nevertheless, long-term therapy often fails due to the emergence of drug resistance [19,20], and most of the novel therapeutic approaches to tackle it are in the early developmental phase [21][22][23]. Although we showed previously that pegylated liposomal doxorubicin (PLD) increases relapse-free and overall survival by 6 and 3-fold, respectively, these tumors cannot be cured using conventional chemotherapy regimens [15].…”

Establishment and characterization of novel highly aggressive HER2‑positive and triple‑negative breast cancer cell lines

“…The trastuzumab-resistant HER2-positive MDA-MB-453 cell line has an abnormal gene expression profile, in particular, the upregulation of transforming growth factor (TGF)-β1 and epidermal growth factor (EGF), and insulin-liked growth factor binding protein-3 (IGFBP3) (9). Although, novel breast cancer cell lines have been established (10)(11)(12), no recent cell models of TN and HER2-positive subtypes have been reported for mechanistic investigation of metastasis and drug resistance.…”