Phase separation of RXRγ drives tumor chemoresistance and represents a therapeutic target for small-cell lung cancer.

Small-cell lung cancer (SCLC) is the most lethal type of lung cancer, characterized by rapid evolution from chemosensitivity to chemoresistance and limited treatment options. However, the mechanisms underlying this evolution remain poorly understood. Here, we show that Retinoid X receptor γ (RXRγ) is uniquely overexpressed in chemo-resistant SCLC tumors, and that RXRγ serves as an essential factor driving chemoresistance in SCLC. RXRγ forms phase-separated droplets with LSD1 in the nucleus, which enhances RXRγ-mediated gene transcription activity and reprograms gene expression, promoting tumor stemness and metastasis, and eventually driving SCLC chemoresistance. In turn, RXRγ antagonist disrupts RXRγ-LSD1 interaction, reducing their binding to the target gene locus, markedly suppressing the expression of the RXRγ target gene network. Finally, RXRγ antagonists strongly suppress tumor growth and metastasis and restore SCLC vulnerability to chemotherapy in multiple preclinical SCLC models, resulting in a substantial extension of survival in mouse models. Thus, these results establish RXRγ as a key player in SCLC by phase separation and as a potential therapeutic target for this deadly disease.