MYC drives temporal evolution of small cell lung cancer subtypes by reprogramming neuroendocrine fate [Single Cell RNA seq on RPM time-series cells and 4 RPM bulk tumors]

Small cell lung cancer (SCLC) is a neuroendocrine tumor treated clinically as a single disease with poor outcomes. Distinct SCLC molecular subtypes have been defined based on expression of lineage-related transcription factors: ASCL1, NEUROD1, POU2F3 or YAP1, but their origins remain unknown. Here, we develop an in vitro model of MYC-driven SCLC tumor cell progression and perform a time-series analysis of single-cell transcriptome profiling to reveal that MYC drives the dynamic evolution of SCLC subtypes. Analyses of these single-cell RNA seq data reveal that MYC promotes a temporal shift from an Ascl1-to-Neurod1-to-Yap1+ state from a neuroendocrine cell of origin. They also support our findings that MYC activates Notch signaling to dedifferentiate tumor cells to non-neuroendocrine fates. Additional single-cell RNA sequencing of 4 bulk Rb1/Trp53/MycT58A (RPM) tumors reveal individual tumors to consist of cells at nearly every stage of RPM tumor evolution modeled in vitro. Together, these single-cell RNA sequencing data place 3 of 4 SCLC subtypes on a defined trajectory and suggest that genetics, cell of origin, and tumor cell plasticity determine SCLC subtype. Overall design: Live RPM time-series transition cells underwent library preparation directly from cell culture at days 4 (n = 2 of the same sample), 7, 11, 14, 17, and 21 post-digestion for a total of 6 distinct transition timepoints. Additionally, we performed single-cell RNA sequencing of 4 bulk RPM tumors.