Abstract 5828: Distinct immunosuppressive tumor microenvironment modulates small cell lung carcinoma neuroendocrine phenotypic plasticity and heterogeneity

Abstract Small cell lung carcinoma (SCLC) is prototypical of cancers with exceptional chemoresistance, and metastatic capabilities fueled by remarkable heterogeneity. The cell-extrinsic factors that govern SCLC heterogeneity are poorly understood especially since non-genetic mechanisms are thought to be major contributors to its intratumoral heterogeneity and plasticity. In order to answer the above question, we sought to inquire about the role of tumor microenvironment (TME) in SCLC heterogeneity which is challenged universally by a lack of patient-derived adequate tumor biopsies. Leveraging large tumor sampling performed at rapid autopsies done on 10 different patients who died from SCLC metastatic disease, we developed a multi-omics approach involving spatial transcriptomics (ST) (Whole transcriptomic atlas), bulk whole genome sequencing, and multiplex immunofluorescence (IF) and standard immunohistochemistry (IHC) to better characterize spatially proximate tumor (36 segments), TME (32 segments) and 4 normal segments. Genomically, SCLC characteristic alterations like TP53 (70%) and RB1 (80%) inactivation and MYC (50%)/MYCL (80%) were evident. ST profiling reveals three distinct tumor subtypes corresponding to the known high-Neuroendocrine (NE) and low-NE SCLC subtypes as well as a novel hybrid-NE state with multiple elevated cancer hallmark capabilities and morphological evidence of nesting and budding. High-NE and hybrid-NE subtypes appear to be driven by ASCL1 and the low-NE subtype resembles the SCLC- inflamed subtype. ST profiling of proximate TMEs reveals similar heterogeneity that is closely linked with SCLC-NE heterogeneity at inter-patient and intra-tumoral levels with distinct features and cellular compositions. Specifically, low-NE TME is marked by increased pro and anti-tumor features including B cells, NK cells, M1-macrophages, and evidence of more checkpoint molecules. High-NE TMEs are predominated by a distinct absence of adaptive immune cells and a strong presence of M2 macrophages. Most strikingly the hybrid-NE TME shows a significant enrichment of immunosuppressive cancer-associated fibroblasts with the absence of T and other adaptive immune cells confirmed using IHC and IF. Next, we attempt to narrow down the fibroblast growth factor receptor (FGF) axis as one of the unique TME-driven factor(s) that could groom non-NE features in SCLC fueling their plasticity and heterogeneity. Subsequently using various SCLC cell lines, we demonstrate that in-vitro modulation of FGFR in SCLC may constrain their plasticity by downregulation of NOTCH signaling, MYC, and its downstream effector REST. We describe the remarkable phenotypic heterogeneity of SCLC tumor and TME and demonstrate their interlinking as well as potential translational avenues of leveraging the cellular crosstalk in order to constrain SCLC heterogeneity. Citation Format: Parth Anil Desai, Nobuyuki Takahashi, Yingying Cao, Christopher Schultz, Darryl Nousome, Desiree Tillo, Lakshya Chauhan, Mayank tandon, Rajesh kumar Bhardwaj, Delphine Lissa, Vinodh Rajapakse, Suresh kumar, Yang Zhang, Elmeskini Rajaa, Donna Butcher, Linda Scuito, Jingjing Gong, Brett Schroder, Andrew Warner, Samantha Nichols, Jordan Kimberly, Alejandro Schaffer, Mohit kumar Jolly, Stephen Hewitt, Anish Thomas. Distinct immunosuppressive tumor microenvironment modulates small cell lung carcinoma neuroendocrine phenotypic plasticity and heterogeneity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5828.