Abstract 2692: Novel chemotherapy stable subpopulations are conserved across multiple small cell lung carcinoma patient derived xenograft models

Introduction: Small cell lung cancer (SCLC) is an aggressive neuroendocrine carcinoma of the lung responsible for up to 25% of lung cancer deaths and the 6th leading cause of cancer death. SCLC initially responds well to chemotherapy, but inevitably recurs even after initial complete responses. The etiology of this relapse is likely secondary to tumor heterogeneity and/or chemotherapy resistance subpopulations reconstituting tumor. Characterization of these resistant subpopulations could yield novel therapeutic targets for SCLC treatment. Mass cytometry uses metal labeled antibodies to profile expression and phosphorylation of multiple proteins in a single cell and offers the opportunity to identify new subpopulations as targets for novel therapies in SCLC. Methods: Nude mice with SCLC patient derived xenografts (PDXs) were treated with a single cycle of carboplatin/etoposide or saline injection. PDX samples were stained with a 26-35 marker panel and an intercalator dye to identify nucleated cells. This panel measured phospho-signaling, neuroendocrine, immune, and mesenchymal cell markers, and functional markers including ki67 and cleaved caspase 3. Mouse cells, including leukocytes, were excluded using mouse MHC1 gating and Histone H3 was used to identify nucleated cells Single cell protein expression and phosphorylation was analyzed using viSNE, manual gating, as well as unsupervised clustering approaches with SPADE to identified multiple subpopulations with neuroendocrine and non-neuroendocrine features. Subpopulations were compared across multiple patient derived xenograft (PDX) models with and without chemotherapy treatment. Results: Patient derived Xenograft (PDX) tumors across 3 distinct models including with and without a single cycle of chemotherapy treatment released viable tumor and stromal cells suitable for cryopreservation and mass cytometry. Chemotherapy treated tumors had dramatic changes in subpopulation distribution compared to matched mock treated tumor. This included enrichment in EPCAM+, CD24+, CD44- progenitor like subpopulations. Similar patterns of population shift were observed in multiple models. Of note, chemotherapy stable subpopulations were conserved across 5 different PDX models including SOX2+ and Oct ¾+ tumor populations. These subpopulations sorted similarly in multidimensional space in multiple PDX models suggesting conserved origins. Conclusions: Mass cytometry was able to identify multiple NE and non-neuroendocrine cell populations from SCLC PDXs and characterize their signaling include rare subpopulations with stem like signaling factors of interest. Chemotherapy treated PDX had differential subpopulation distribution with enrichment of progenitor like cells with chemotherapy treatment similar to previous work in mouse genetic SCLC. However, rare conserved chemotherapy stable subpopulations enriched in stem-like signaling factors were identified across 5 PDX models including those with and without chemotherapy treatment. This work raises the possibility that chemotherapy stable subpopulations may contribute to progenitor populations which lead to relapse. Future work in this lab will focus on characterizing the stem like features of these subpopulations and their phenotypic dynamics and signaling. Citation Format: Jonathan M. Lehman, Jeremy Staub, Yong Zou, Jonathan Irish, Pierre Massion. Novel chemotherapy stable subpopulations are conserved across multiple small cell lung carcinoma patient derived xenograft models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2692.