Universität zu Köln

Bebber, Christina M. (2021). Characterisation of ferroptosis response in small cell lung cancer neuroendocrine subtypes. PhD thesis, Universität zu Köln.

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Abstract

Small cell lung cancer (SCLC) treatment has remained a major clinical challenge with very few newly approved treatment strategies in the last 30 years. After initial chemotherapy response SCLC almost invariably relapses presenting with intratumoural neuroendocrine (NE) subtype heterogeneity as a result of different cells-of-origin and subtype plasticity. SCLC is defined by loss of function mutations in tumour suppressor genes TP53 and RB1 as well as a significant tumour mutational burden (TMB), suggesting selective pressure to inactivate cell death pathways prior to therapy. However, a comprehensive analysis of cell death pathway availability in SCLC has not been pursued yet. In this study, through systematic characterisation of regulated cell death pathway availability in RNA-sequencing data of human treatment-naïve SCLC patient tissue, we find broad inactivation of the extrinsic apoptosis and necroptosis pathway components and high expression of genes preventing from ferroptosis. Ferroptosis is a recently described form of regulated cell death induced by iron-dependent accumulation of fatal lipid-peroxides resulting in destabilisation of the lipid bilayer and membrane rupture. In this study, we identified that non-NE mouse and human SCLC cells marked by low Achaete-Scute Homolog 1 (ASCL1) expression are uniquely primed for ferroptosis, while NE SCLC cells instead are highly vulnerable to thioredoxin (TRX) pathway inhibition. Non-NE SCLC presents with an elevated oxygenated lipidome and is selectively vulnerable to genetic or pharmacological induction of ferroptosis. We identified NE-differentiation marked by the NE lineage-defining transcription factor ASCL1 expression to determine ferroptosis resistance. ASCL1 suppresses glutathione synthesis in the NE SCLC subtype which acquires addiction to the thioredoxin (TRX) anti-oxidant pathway. Co-cultures replicating non-NE/NE intratumoural heterogeneity selectively deplete non-NE populations upon ferroptosis induction, while only TRX pathway inhibition eliminates NE cell populations. Importantly, single redox-pathway targeting induces NE/non-NE plasticity enabling treatment escape in SCLC. Hence, combined ferroptosis induction and inhibition of the TRX pathway kills established non-NE and NE tumours in xenografts, genetically engineered mouse models of SCLC and patient-derived treatment-naïve and refractory NE SCLC models. In SCLC but not lung adenocarcinoma, combined low expression of GPX4 and TRX reductase 1 (TXNRD1) identified a patient subset with significantly improved overall survival. Taken together, these findings reveal that informed cell death pathway mining in treatment-naïve SCLC can identify rational combination therapies which address SCLC NE/non-NE heterogeneity and plasticity under treatment.