Evaluation of FOXC1 as a therapeutic target for basal-like breast cancer.

Basal-like breast cancer (BLBC) is a malignant carcinoma with aggressive motility and rapid growth. Accounting for 15% of breast cancers, BLBC often exhibits a poor prognosis and tends to metastasize to the brain and lungs. Because most BLBC display a triple-negative phenotype (ER-, PR-, and HER2-), conventional cytotoxic chemotherapy remains the only treatment option despite poor success and high rate of relapse. The overexpression of the forkhead-box transcription factor C1 (FOXC1) was recently identified as a biomarker of BLBC. Increased expression of FOXC1 was linked to excessive mobility and growth of BLBC cell lines, suggesting FOXC1 as a therapeutic target. In this study, siRNA-mediated knockdown of FOXC1 was confirmed to decrease the proliferation rate, migration, and invasion in a model BLBC-like cell line (4T1). 4T1 and 4T1-∆FOXC1 cells lacking FOXC1 expression (generated by CRISPR/Cas9) were used to evaluate the effects of FOXC1 expression in an orthotopic murine model of BLBC. No statistically significant difference in tumor volume was observed between 4T1 and 4T1-∆FOXC1 tumors. Furthermore, tumors metastasized to the liver and lungs to a similar degree regardless of FOXC1 expression. These data suggest that, despite positive results in vitro, FOXC1 may not be a promising therapeutic target for BLBC.