ESTRO 2024 - Abstract Book

S5228

Radiobiology - Microenvironment

ESTRO 2024

3061

Digital Poster

Gut microbiome and gene expression changes during a Phase 1 trial of enadenotucirev and radiotherapy

Lily V Hillson 1 , Jethro Johnson 2 , Rui Ru Ji 3 , Oliver Rosen 3 , Yu Qiao 4 , Alex Ooms 4 , Timothy S Maughan 5 , Campbell S Roxburgh 1 , Maria Hawkins 6 , Sean M O'Cathail 1 1 University of Glasgow, School of Cancer Sciences, Glasgow, United Kingdom. 2 University of Oxford, Kennedy Institute of Rheumatology, Glasgow, United Kingdom. 3 Akamis Bio, Akamis Bio, Cambridge, USA. 4 University of Oxford, Centre for Statistical Medicine, Oxford Clinical Trials Research Unit, Oxford, United Kingdom. 5 University of Oxford, Oxford Institute of Radiation Oncology, Glasgow, United Kingdom. 6 University College London, Medical Physics and Biomedical Engineering, London, United Kingdom

Purpose/Objective:

The CEDAR trial was a multi-centre phase 1 clinical trial (NCT03916510) in locally advanced rectal cancer patients which combined 25x2Gy chemoradiation with concurrent capecitabine and Enadenotucirev (EnAd), a tumour selective intravenous oncolytic adenovirus. Increasing evidence suggests that tumour immunogenicity partly explains the heterogeneity in response to radiotherapy and provides a rationale for combining standard-of-care with immunomodulatory agents. Here, we aim to elucidate patient and tumour biological responses within the CEDAR trial from translational (tumour tissue and microbiome) samples.

Material/Methods:

Patients with histologically confirmed adenocarcinoma of the rectum and staged at cT3< with threatened involvement of the resection margin determined by pelvic MRI were enrolled. Enadenotucirev was administered intravenously in 3 doses of 1x10 12 -3x10 12 viral particles the week before and after a course of 50 Gy in 25 fractions irradiation with concurrent oral capecitabine. Treatment response was assessed 13 weeks after starting treatment using MRI Tumour Regression Grade. Paired formalin-fixed paraffin-embedded pre-treatment biopsy and post treatment resection tumour samples were collected from n=9 patients. Gene expression in tumour samples was measured using the Nanostring NCounter® PanCancer Immune Profiling Panel. Stool samples were collected from n=7 patients pre-treatment, during and after radiotherapy and subject to whole genome sequencing (WGS). The raw WGS data was processed to taxa by MetaPhlan3, visualised in R Studio version 4.1.2.

Results:

The relative abundance of bacterial species within individual patients changed considerably through treatment. By principal component analysis (PCA), matched individuals' samples clustered while the pre-, during- and post treatment samples completely overlapped. This is reflected in Figure 1, which shows the relative abundance of the top 10 most abundant species is visually similar among samples from the same patient. We did not observe an overall change in alpha diversity through treatment, whilst individual patients maintained their microbiome diversity throughout treatment. As shown in Figure 2, we identified differences in the relative abundance of bacterial families ( f_Bacteroidaceae, f_Enterobacteriaceae, f_Oscillospiraceae, f_Prevotellaceae ) between samples of responders and non-responders. Gene expression in tumour samples was measured using the NCounter® PanCancer Immune Profiling Panel. PCA demonstrated more significant variance in the post-treatment samples than the pre-treatment samples. Six genes were differentially expressed between the pre-treatment and post-