3668 - Characterizing Neuroendocrine Lineage Plasticity Following Radiotherapy in Small Cell Lung Cancer
Presenter(s)
Y. Wu1, B. Wang2, R. Zhang1, and J. Xue3; 1West China Hospital, Sichuan University, Chengdu, Sichuan, China, 2State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan, China, 3Laboratory of Clinical Cell Therapy, West China Hospital, Sichuan University, Chengdu, Sichuan, China
Purpose/Objective(s):
Small cell lung cancer (SCLC) is characterized by robust neuroendocrine (NE) features, yet clinical progression is frequently associated with a shift toward a non-NE phenotype. Although radiotherapy (RT) is a standard-of-care, whether ionizing radiation actively promotes this lineage transformation remains elusive. This study aims to characterize the RT-induced NE-to-non-NE transition and identify the molecular drivers underlying this phenotypic evolution.
Materials/Methods:
An orthotopic SCLC model was established using mouse-derived organoids and subjected to fractionated RT, with lineage markers (ASCL1 and YAP1) dynamically assessed. Bulk RNA sequencing of irradiated tumors was integrated with public datasets (CCLE, cBioPortal) to identify key regulatory pathways. CRISPR/Cas9-mediated knockout of Lats1 or Ccnd1, along with pharmacologic CDK4/6 inhibition using Trilaciclib, was employed for functional validation and pathway interrogation.
Results:
Fractionated radiotherapy significantly promoted lineage remodeling in SCLC. Following irradiation, tumors transitioned from an NE-high state toward a non-NE phenotype, characterized by ASCL1 downregulation and activation of the YAP1–CCND1 signaling axis. Mechanistically, radiation triggered YAP1 nuclear translocation and enhanced its interaction with TEAD1, leading to increased transcriptional activation of Ccnd1.
Transcriptomic analysis of patient datasets further revealed that, in the context of RB1 loss, CCND1 upregulation was not only associated with canonical cell cycle regulation but was also significantly enriched in epithelial–mesenchymal transition (EMT)–related pathways, suggesting a non-canonical role in promoting mesenchymal-like features. Histological and immunofluorescence analyses of repeatedly irradiated tumor samples confirmed sustained upregulation of EMT markers, revealing that RT-induced lineage transition is coupled with the activation of a mesenchymal program.
Functionally, Lats1 deletion enhanced YAP1 activity and accelerated the non-NE transition and EMT progression. Conversely, genetic deletion of Ccnd1 or pharmacologic inhibition of the CCND1–CDK4/6 axis with Trilaciclib markedly suppressed EMT-associated gene expression, reduced tumor recurrence, and decreased metastatic burden, highlighting the critical role of this axis in radiation-driven tumor adaptive evolution.
Conclusion:
Radiotherapy promotes neuroendocrine lineage plasticity in SCLC via the Hippo–YAP1–CCND1–EMT axis, driving evolution toward a non-NE, mesenchymal state and contributing to recurrence and metastasis. Targeting this pathway may restrain post-RT tumor progression.