Abstract PR09: Alterations in cell junctions and neuroendocrine differentiation are key early steps in Crebbp/Ep300 mutation-driven SCLC development

Abstract

Abstract The abundance and heterogeneity of somatic alterations in small cell lung cancer (SCLC) present immense challenges in identifying key mechanisms of tumor development. Functional characterization of recurrent mutations is an essential step towards understanding the early stages of SCLC development, but this remains extremely difficult due to the scarcity of relevant and tractable models for defining oncogenic drivers and molecular pathways. In a previous study, we derived precancerous cells (preSCs) from the Rb/p53/Rbl2-mutant mouse model of SCLC and developed an engineered preSC-based model of early tumor development. In this model, activation of oncogenic drivers transforms preSCs into tumorigenic cells that form spheroid clusters characteristic of SCLC in culture and subcutaneous tumors in athymic nude mice. Using this streamlined approach, we found that both retroviral amplification of the Myc family members and CRISPR/Cas9-mediated mutation of Crebbp/Ep300 were sufficient to cause transformation of preSCs into SCLC cells. Notably, both sets of mutant preSC underwent a similar phenotypic change from adherent monolayers to spheroid aggregates, suggesting that the two different types of alterations interact with or converge on common molecular pathways. Comparative profiling of control preSCs and mutant preSCs carrying either a Myc family amplification or Crebbp/Ep300 mutation revealed that alterations in cell junctions and neuroendocrine differentiation are the most significant molecular changes during cellular transformation. The transformed preSCs exhibited decreased expression of adhesion-related genes, including Cdh1 and Dsp, but increased expression of mesenchymal genes Vim and Twist1. The transformed cells also showed reduced expression of neuroendocrine (NE) differentiation genes, including Ascl1, Chga, and Syp. Furthermore, these changes coincided with increased expression of Notch receptors and decreased expression of their ligands Dlls and Jags. Taken together, these novel findings suggest that a phenotypic switch from Dll/Jag-expressing NE cells to Notch-expressing non-NE cells is a key event in early SCLC development. This study also demonstrated that the preSC-based model can facilitate functional validation of recurrent mutations in SCLC and molecular pathways that will be further explored for mechanistic elucidation and development of targeted therapies. This abstract is also being presented as Poster A09. Citation Format: Dong-Wook Kim, Keebeom Kim, Colin T. Dunn, Kwon-Sik Park. Alterations in cell junctions and neuroendocrine differentiation are key early steps in Crebbp/Ep300 mutation-driven SCLC development [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr PR09.