NR2F1 underlies persistence of residual disease in BRAF-mutant melanoma
Despite the clinical success of targeted therapy inhibitors, tumor responses are transient, and a subpopulation of residual drug-tolerant cells may seed resistance. Understanding minimal residual disease (MRD) mechanisms and the connection with dormancy-like traits may guide strategies to target drug-tolerant persister cells and optimize target therapies. Here, we studied the relationship between persister cell tolerance to BRAF and MEK inhibitors (BRAFi + MEKi) and expression of nuclear receptor subfamily 2 group F member 1 (NR2F1), which has been linked to tumor dormancy in the context of cutaneous melanoma. In previously published RNA-seq datasets, NR2F1 expression was enriched in melanoma samples following BRAF inhibitor and MEK inhibitor (BRAFi + MEKi) treatment compared to pre-treatment patient-matched samples. We also found that NR2F1 is highly expressed in the residual drug-tolerant cell state following BRAFi + MEKi treatment in patient-derived and cell line-derived melanoma xenografts. Additionally, xenografts overexpressing NR2F1 displayed higher tumor growth and poorer animal survival following BRAFi + MEKi treatment compared to control xenografts expressing basal levels of NR2F1. In vitro, NR2F1-overexpressing cells showed increased tumor proliferation and higher expression of cell cycle and survival-related proteins on targeted therapy, such as phosphorylation of both RB and S6K proteins. In addition, NR2F1, highly expressed in invasive melanoma cells, was sufficient to promote invasiveness following BRAFi + MEKi in 3D tumor spheroid assays. Furthermore, when compared to young mice, NR2F1 was overexpressed in tumor xenografts in an old microenvironment. The use of shRNA NR2F1 in older mice led to slower tumor growth and the highest survival in animals on BRAFi + MEKi treatment. We also tested a pharmacological approach to target drug-tolerant persister cells that overexpress NR2F1 on BRAFi + MEKi treatment. The inhibition of mTORC1 delayed NR2F1-overexpressing cell proliferation compared to non-NR2F1-overexpressing cells on targeted therapy. Altogether, our findings suggest that NR2F1 plays a role in the persistence of MRD in melanoma, indicating that targeting NR2F1 expression could improve targeted therapy outcomes in melanoma patients. Overall design: RNA was obtained from 1205LuTR-NR2F1, WM793TR-NR2F1, and A375TR-NR2F1 cell lines treated with DMSO (control) -/+ BRAF plus MEK inhibitors (Combo), -/+ doxycycline (DOX). Comparison of doxycycline(DOX)-inducible NR2F1 overexpression melanoma cells lines treated with BRAF and MEK inhibitors (Combo) with or without DOX for 72 hours.