NOTCH1 reverses immune suppression in small cell lung cancer through reactivation of STING [scRNA-seq]
Downregulation of antigen presentation and lack of immune infiltration are defining features of small cell lung cancer (SCLC) limiting response to immune checkpoint blockade (ICB), While a high MHC Class I, immune-inflamed subset benefits from ICB, underlying mechanisms of immune response in SCLC have yet to be elucidated. Here we show that in the landmark IMpower133 clinical trial high, but not low, NOTCH1 expression is significantly associated with longer survival with the addition of ICB to chemotherapy among ~80% of SCLC patients with neuroendocrine-enriched tumors (ASCL1-enriched, HR 0.39, P=0.0012; NEUROD1-enriched, HR 0.44, P=0.024). Genetic or pharmacologic activation of NOTCH1 in ASCL1 and NEUROD1 SCLC cell lines dramatically up-regulates MHC Class I through epigenetic up-regulation of STING. In syngeneic mouse models, Notch1 activation reprograms SCLC tumors from immune-excluded to immune-inflamed, facilitating durable, complete responses with ICB combined with a STING agonist. STING1 expression is significantly enriched in high compared to low NOTCH1 expressing tumors in IMpower133 thereby validating our proposed mechanism. Our data reveal a previously undiscovered role for NOTCH1 as a critical driver of SCLC immunogenicity and a potential predictive biomarker for ICB in SCLC. NOTCH1 activation may be a therapeutic strategy to unleash anti-tumor immune responses in SCLC and other neuroendocrine cancers in which NOTCH1 is typically suppressed. Overall design: We performed single-cell RNA-seq of a human SCLC cell line (COR-L88) treated ex-vivo with DMSO, LSD1 inhibition or LSD1 inhibition plus GSI (gamma secretase inhibitor).