Abstract 6925: Integrative single-cell tracking of genome evolution and tumor cell plasticity in small cell lung cancer (SCLC)
Authors: Schmiel Marcel , Kaiser Laura , Cartolano Maria , Peifer Martin , Thomas Roman K. , George Julie 
Published: March 2024

Abstract
SCLC is the deadliest type of lung cancer, which is mostly diagnosed at late stages and accounts for 15% of pulmonary tumors. Even though chemotherapy is initially effective, patients with SCLC relapse quickly and develop resistant tumors. Genome studies revealed a universal loss of TP53 and RB1; recent transcriptional studies categorized SCLC based on the expression of 4 lineage transcription factors (TFs). We aimed to dissect how genomic cues impact transcriptional phenotypes, tumor cell plasticity and the dynamics of tumor and immune cell interactions, to thus decipher molecular mechanisms of phenotypic divergence and therapy resistance in SCLC. We performed genome sequencing and single cell transcriptome profiling of 55 tumors from patients with SCLC, including primary tumors, local and distant metastases and of paired relapsing tumors acquired after chemotherapy. Single cell sequencing was performed with the 10x Genomics platform and yielded &gt; 200.000 cells. Transcriptome profiles at single cell levels revealed co-expression of at least two of the lineage TFs ASCL1, NEUROD1 or POU2F3 in each tumor. Copy number (cn) estimation for transcriptome data pointed to genomic events impacting transcriptional heterogeneity within the tumor. Furthermore, our data pointed to a marked intra- and interpatient, as well as to inter-metastatic heterogeneity. To specifically investigate how underlying genetic alterations affect molecular phenotypes, integrative studies across all patients were performed. This revealed shared transcriptional programs in tumors with amplifications of MYC family members; trajectory inference for cases with low and high-level copy gains of MYCN pointed to distinct transcriptional states. We performed multi-regional and longitudinal studies of matched patient cases to reconstruct the genomic patterns of clonal evolution, and projected genomic subsets to transcriptional profiles at single cell level, thus analyzing the effect of genome diversity on the transcriptional landscape. Additionally, tumor intrinsic profiles of heterogeneity were mapped to single cell data of patient tumors to elucidate the effects on tumor-immune cell interactions.
All together our data points to a concerted regulation of a multitude of lineage factors and transcriptional programs in each SCLC tumor and provides a first comprehensive framework for the study of underlying genetic alterations that shape the transcriptional landscape and phenotypic plasticity in SCLC.
Citation Format: Marcel Schmiel, Laura Kaiser, Maria Cartolano, Martin Peifer, Roman K. Thomas, Julie George. Integrative single-cell tracking of genome evolution and tumor cell plasticity in small cell lung cancer (SCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6925.