We describe the discovery of an agonist of the nuclear receptor NR2F1 that specifically activates dormancy programs in malignant cells. The agonist led to a self-regulated increase in NR2F1 mRNA and protein and downstream transcription of a novel dormancy program. This program led to growth arrest of an HNSCC PDX line, human cell lines, and patient-derived organoids in 3D cultures and in vivo. This effect was lost when NR2F1 was knocked out by CRISPR-Cas9. RNA sequencing revealed that agonist treatment induces transcriptional changes associated with inhibition of cell cycle progression and mTOR signaling, metastasis suppression, and induction of a neural crest lineage program. In mice, agonist treatment resulted in inhibition of lung HNSCC metastasis, even after cessation of the treatment, where disseminated tumor cells displayed an NR2F1hi/p27hi/Ki-67lo/p-S6lo phenotype and remained in a dormant single-cell state. Our work provides proof of principle supporting the use of NR2F1 agonists to induce dormancy as a therapeutic strategy to prevent metastasis.

Cancer cells can disseminate during very early and sometimes asymptomatic stages of tumor progression. Though biological barriers to tumorigenesis have been identified and characterized, the mechanisms that limit early dissemination remain largely unknown. We report here that the orphan nuclear receptor nuclear receptor subfamily 2, group F, member 1 (NR2F1)/COUP-TF1 serves as a barrier to early dissemination. NR2F1 expression was decreased in patient ductal carcinoma in situ (DCIS) samples. High-resolution intravital imaging of HER2+ early-stage cancer cells revealed that loss of function of NR2F1 increased in vivo dissemination and was accompanied by decreased E-cadherin expression, activation of wingless-type MMTV integration site family, member 1 (WNT)-dependent β-catenin signaling, disorganized laminin 5 deposition, and increased expression of epithelial–mesenchymal transition (EMT) genes such as twist basic helix-loop-helix transcription factor 1 (TWIST1), zinc finger E-box binding homeobox 1 (ZEB1), and paired related homeobox 1 (PRRX1). Furthermore, downregulation of NR2F1 promoted a hybrid luminal/basal phenotype. NR2F1 expression was positively regulated by p38α signaling and repressed by HER2 and WNT4 pathways. Finally, early cancer cells with NR2F1LOW/PRRX1HIGH staining were observed in DCIS samples. Together, these findings reveal the existence of an inhibitory mechanism of dissemination regulated by NR2F1 in early-stage breast cancer cells. Significance: During early stages of breast cancer progression, HER2-mediated suppression of NR2F1 promotes dissemination by inducing EMT and a hybrid luminal/basal-like program.

Metastasis is the systemic manifestation of cancer and the main cause of death from breast cancer. In mouse models of lung metastases, recruitment of classical monocytes from blood to the lung and their differentiation to metastasis-associated macrophages (MAMs) facilitate cancer cell extravasation, survival and growth. Ablation of MAMs or their monocytic progenitors inhibits metastasis. We hypothesized that factors controlling macrophage polarization modulate tumor cell extravasation in the lung. We evaluated whether signaling by Th1 or Th2 cytokines in macrophages affected transendothelial migration of tumor cells in vitro. Interferon gamma and LPS inhibited macrophage-dependent tumor cell extravasation while the Th2 cytokine interleukin-4 (IL4) enhanced this process. We demonstrated that IL4 receptor (IL4rα)-null mice developed fewer and smaller lung metastasis in E0771-LG mammary cancer models of this disease. Adoptive transfer of wild-type monocytes to IL4rα-deficient mice partially rescued this phenotype. IL4 signaling in macrophages controlled the expression of the chemokine receptor CXCR2, necessary for IL4-mediated tumor cell extravasation in vitro. Furthermore, IL4 signaling in macrophages regulated the transcript abundance of several other genes already causally associated with mammary cancer lung metastasis including Ccl2, Csf1, Ccr1, Hgf and Flt1. The central role of IL4 signaling in MAMs was confirmed by high-resolution intravital imaging of the lung in mice at the time of metastatic seeding, which showed reduced physical interaction between tumor cells and IL4rα-deficient macrophages. This interaction with wild-type MAMs enhanced tumor cell survival and seeding, which was lost in the IL4rα mice. These data indicate that IL4 signaling in monocytes and macrophages is key during seeding and growth of breast metastasis in the lung, as it regulates pro-tumoral paracrine signaling between cancer cells and macrophages.

Cancer cells can leave their primary sites and travel through the circulation to distant sites, where they lodge as disseminated cancer cells (DCCs), even during the early and asymptomatic stages of tumor progression. In experimental models and clinical samples, DCCs can be detected in a non-proliferative state, defined as cellular dormancy. This state can persist for extended periods until DCCs reawaken, usually in response to niche-derived reactivation signals. Therefore, their clinical detection in sites like lymph nodes and bone marrow is linked to poor survival. Current cancer therapy designs are based on the biology of the primary tumor and do not target the biology of the dormant DCC population and thus fail to eradicate the initial or subsequent waves of metastasis. In this brief review, we discuss the current methods for detecting DCCs and highlight new strategies that aim to target DCCs that constitute minimal residual disease to reduce or prevent metastasis formation. Furthermore, we present current evidence on the relevance of DCCs derived from early stages of tumor progression in metastatic disease and describe the animal models available for their study. We also discuss our current understanding of the dissemination mechanisms utilized by genetically less- and more-advanced cancer cells, which include the functional analysis of intermediate or hybrid states of epithelial–mesenchymal transition (EMT). Finally, we raise some intriguing questions regarding the clinical impact of studying the crosstalk between evolutionary waves of DCCs and the initiation of metastatic disease.

A bstract: Disseminated tumor cells (DTCs) in secondary organs often remain dormant for a long period of time before re-awakening and growing into overt metastases. We have previously identified NR2F1/COUP-TF1, an orphan nuclear receptor, as a master regulator of tumor cell dormancy in head and neck squamous cell carcinoma (HNSCC) and other cancer types. Here we describe the identification and function of a novel NR2F1 agonist herein referred to as compound 26 (C26). C26 was found to specifically activate NR2F1 in HNSCC cells, leading to increased NR2F1 transcription and nuclear protein accumulation. C26-mediated activation of NR2F1 induced growth arrest of HNSCC PDX line and cell lines in 3D cultures in vitro and on chicken embryo chorioallantoic membrane (CAM) in vivo . The effect of C26 on growth arrest was lost when NR2F1 was knocked out by CRISPR/Cas9. C26-induced growth arrest was mediated by activation of an NR2F1-regulated dormancy program, including upregulation of cyclin-dependent kinase (CDK) inhibitor p27 and the transcription factors retinoic acid receptor β (RARβ) and Sox9. In mice bearing HNSCC PDX tumors, combined adjuvant and neo-adjuvant treatment with C26 resulted in complete inhibition of lethal lung metastasis. Mechanistic analysis showed that lung DTCs in C26-treated mice displayed an NR2F1 ^hi /p27 ^hi /Ki-67 ^lo phenotype, which kept them dormant in a single-cell state preventing their outgrowth into overt metastases. Our work reveals a novel NR2F1 agonist and provides a proof of principle strategy supporting that inducing DTC dormancy using NR2F1 agonists could be used as a therapeutic strategy to prevent metastasis.

A major challenge in melanoma treatment is the emergence of aggressive metastases from previously dormant disseminated cancer cells (DCCs). Here we identify Midkine (MDK) as a key factor that disrupts melanoma DCC dormancy by triggering an autocrine signal that suppresses the dormancy inducer NR2F1 and alters the p-p38/p-ERK ratio, via ALK signaling. Dormant melanoma DCCs in lymph nodes and visceral tissues exhibit an MDK ^LOW /NR2F1 ^HIGH phenotype. Transient NR2F1 activation for one month with a potent agonist counteracts MDK-driven mTORC1 activity and suppresses lung metastasis in mice bearing human melanoma DCCs. Dual targeting of MDK (genetic blockade) and NR2F1 (activation) markedly limits metastatic outgrowth and extends survival for 6 months in mouse models independent of BRAF status. These findings support the MDK-NR2F1 axis as a promising therapeutic target to sustain dormancy and prevent melanoma recurrence. Statement of Significance: This work identifies Midkine as a key disruptor of tumor dormancy in melanoma, driving metastatic awakening via NR2F1 suppression. Dual targeting of Midkine (inhibition) and NR2F1 (activation) prolongs survival in preclinical models.