SUMMARY Loss of the tumor suppressors RB1 and TP53 and MYC amplification are frequent oncogenic events in small cell lung cancer (SCLC). We show that Myc expression cooperates with Rb1 and Trp53 loss in the mouse lung to promote aggressive, highly metastatic tumors, that are initially sensitive to chemotherapy followed by relapse, similar to human SCLC. Importantly, MYC drives a neuroendocrine-low “variant” subset of SCLC with high NEUROD1 expression corresponding to transcriptional profiles of human SCLC. Targeted drug screening reveals that SCLC with high MYC expression is vulnerable to Aurora kinase inhibition, which combined with chemotherapy strongly suppresses tumor progression and increases survival. These data identify molecular features for patient stratification and uncover a potential targeted treatment approach for MYC-driven SCLC.

SUMMARY The major types of non-small cell lung cancer (NSCLC) - squamous cell carcinoma and adenocarcinoma - have distinct immune microenvironments. We developed a genetic model of squamous NSCLC based on overexpression of the transcription factor Sox2, which specifies lung basal cell fate, and loss of the tumor suppressor Lkb1 (SL mice). SL tumors recapitulated gene expression and immune infiltrate features of human squamous NSCLC, including enrichment of tumor-associated neutrophils (TANs) and decreased expression of NKX2–1, a transcriptional regulator that specifies alveolar cell fate. In Kras-driven adenocarcinomas, mis-expression of Sox2 or loss of Nkx2–1, led to TAN recruitment. TAN recruitment involved SOX2-mediated production of the chemokine CXCL5. Deletion of Nkx2–1 in SL mice (SNL) revealed that NKX2–1 suppresses SOX2-driven squamous tumorigenesis by repressing adeno-to-squamous transdifferentiation. Depletion of TANs in SNL mice reduced squamous tumors, suggesting that TANs foster squamous cell fate. Thus, lineage defining transcription factors determine the tumor immune microenvironment, which in turn may impact the nature of the tumor.

Purpose: Small-cell lung cancer (SCLC) has been treated clinically as a homogeneous disease, but recent discoveries suggest that SCLC is heterogeneous. Whether metabolic differences exist among SCLC subtypes is largely unexplored. In this study, we aimed to determine whether metabolic vulnerabilities exist between SCLC subtypes that can be therapeutically exploited.Experimental Design: We performed steady state metabolomics on tumors isolated from distinct genetically engineered mouse models (GEMM) representing the MYC-and MYCLdriven subtypes of SCLC. Using genetic and pharmacologic approaches, we validated our findings in chemo-na€ ve and -resistant human SCLC cell lines, multiple GEMMs, four human cell line xenografts, and four newly derived PDX models.Results: We discover that SCLC subtypes driven by different MYC family members have distinct metabolic pro-files. MYC-driven SCLC preferentially depends on arginineregulated pathways including polyamine biosynthesis and mTOR pathway activation. Chemo-resistant SCLC cells exhibit increased MYC expression and similar metabolic liabilities as chemo-na€ ve MYC-driven cells. Arginine depletion with pegylated arginine deiminase (ADI-PEG 20) dramatically suppresses tumor growth and promotes survival of mice specifically with MYC-driven tumors, including in GEMMs, human cell line xenografts, and a patient-derived xenograft from a relapsed patient. Finally, ADI-PEG 20 is significantly more effective than the standard-of-care chemotherapy.Conclusions: These data identify metabolic heterogeneity within SCLC and suggest arginine deprivation as a subtype-specific therapeutic vulnerability for MYC-driven SCLC. DiscussionDespite numerous clinical trials and years of research, therapeutic options for SCLC remain limited. However, recent studies suggest that molecular subtypes of SCLC exist with distinct