ESTRO 2024 - Abstract Book

S5230

Radiobiology - Microenvironment

ESTRO 2024

Interpatient microbial heterogeneity is greater than dynamic microbiome shifts through treatment in this study. Certain microbiome constituents may be associated with more favourable radiation responses. The absence of significant microbial variation during treatment suggests baseline microbiome features could be further explored as a predictive biomarker. Gene expression data suggests an increase in immune activity at resection compared to baseline and is potentially associated with a virus-specific reaction.

Keywords: Rectal, Microbiome, Translational sampling

3237

Digital Poster

Pulsatile exposure to acid and radiation response in cells resembling oesophageal adenocarcinoma

Wee Han Ng 1 , Rebecca C Fitzgerald 2 , Christopher Mark Jones 2,3

1 University of Bristol, Medical School, Bristol, United Kingdom. 2 University of Cambridge, Department of Oncology, Cambridge, United Kingdom. 3 Cambridge University Hospitals NHS Foundation Trust, Department of Clinical Oncology, Cambridge, United Kingdom

Purpose/Objective:

Radiotherapy is an important treatment for patients diagnosed with oesophageal adenocarcinoma (OAC). Response rates are nevertheless disappointing, with for instance a pathological complete response achieved in around 30% of patients managed with neoadjuvant chemoradiotherapy. The drivers of this radiation resistance are uncertain. One underexplored area is the impact of the lower oesophageal microenvironment in which OAC arises, which is characterised by frequent exposure to pulsatile acidic gastric refluxate. Previous studies have suggested that pH may modulate radiation response but there has been no specific analysis of the impact of an acidic environment on OAC radiation response. We sought to evaluate this in vitro using a cell line resembling OAC.

Material/Methods:

An authenticated FLO-1 OAC cell line was maintained in DMEM supplemented with 10% foetal bovine serum (FBS) in a humidified atmosphere consisting of 5% CO2/95% air at 37°C. The impact of an acidic microenvironment prior to (pre-), during (intra-) and following (post-) exposure to ionising radiation (IR) was simulated using 10-minute pulses of media acidified to a pH of 4.0 using hydrochloric acid. In each instance, a total of 10,000 cells were seeded and cells maintained in proliferative media for 24 hours prior to experimentation. X-ray irradiation was delivered at 2Gy intervals between 0 (control) – 8 Gy using a 225kV cabinet irradiator. Pre-IR acid exposure was modelled through the 10 minute addition of acidified media to cells immediately followed by a wash step and subsequent irradiation in phosphate buffered saline (PBS). Cells for post-IR acid exposure were irradiated in PBS and then immediately exposed to a 10 minute pulse of acidified media. Cells for intra-IR acid exposure were irradiated in acidified media and then washed in PBS. A separate control group was irradiated at neutral (7.4) pH. Cells were subsequently allowed to grow in proliferative DMEM media and, after 7 days of incubation, cell viability and activity was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and clonogenic assay. Three biological replicates, each comprising of three technical replicates, were obtained for each experimental condition unless otherwise stated. Data are shown as mean +/- standard error of the mean.