ESTRO 2025 - Abstract Book

S4028

Radiobiology - Tumour radiobiology

ESTRO 2025

4472

Mini-Oral Oesophageal adenocarcinoma radiation resistance is shaped by therapy-associated genomic, epigenetic and transcriptomic evolution Kayli Bolton 1,2 , Daniel Jacobson 1 , Victoria Askinyte 1 , Gunjan Katyal 2 , Ginny Devonshire 1 , Spyridoula Massia 1 , Claire Lim 1 , Adam Freeman 1 , Ahsen Ustaoglu 1 , John L Zhuang 1 , Rebecca C Fitzgerald 1 , Christopher M Jones 1,2 1 Early Cancer Institute, University of Cambridge, Cambridge, United Kingdom. 2 CRUK RadNet Cambridge, University of Cambridge, Cambridge, United Kingdom Purpose/Objective: More than 70% of patients with oesophageal adenocarcinoma (OAC) have residual disease following radiotherapy 1 . To determine the factors underlying this radioresistance and their relationship to therapy, we characterised genomic, epigenetic and transcriptomic evolution in response to fractionated irradiation in a novel radioresistant patient-derived organoid (PDO) model of OAC. Material/Methods: Radiation-naïve OAC PDOs were derived from diagnostic biopsy or surgical resection specimens and their molecular characteristics analysed using RNA sequencing (RNAseq), 30X (PDO)/50X (parent tissue) whole genome sequencing (WGS), 150X whole exome sequencing (WES) and a 123Mb Twist Human Methylome panel. Radiosensitivity was determined by organoid forming efficiency (OFE), viability and γH2AX immunofluorescent staining. Results: Thirty radiation-naïve OAC PDOs were established and confirmed via WGS/RNAseq to match their parent tissue, and to represent known inter-tumoural disease heterogeneity. Analysis of OFE following 0-8Gy exposure of each of the 30 PDOs confirmed a broad spectrum of radiosensitivity. To study therapy-related evolution, a single PDO of intermediate radiosensitivity was exposed in three separate replicates to 30Gy in 15 fractions x-ray irradiation over three consecutive weeks, with WGS, WES, methylomics and RNAseq undertaken at 10Gy intervals. A dose dependent increase in single nucleotide variant (SNV) and insertion/deletion (indel) mutation burden was seen, albeit with no driver mutation acquisition and minimal clonal selection. Differential methylation profiles were apparent at 20Gy and substantial at 30Gy, whilst being generally concordant at lower doses (Fig.1).

Altered regulation of genes related to the extracellular matrix, catabolic processes and TGFβ signalling were seen at all radiation doses but with specific enrichment of metabolic and cell motility genes at 10-20Gy, and host defence