ESTRO 2024 - Abstract Book

S5209

Radiobiology - Microenvironment

ESTRO 2024

1 King's College London, Centre for Host-Microbiome Interactions, London, United Kingdom. 2 Guy's and St Thomas' NHS Foundation Trust, Clinical Oncology, London, United Kingdom. 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Data Science Unit, Milan, Italy. 4 Guy's and St Thomas' NHS Foundation Trust, Medical Physics, London, United Kingdom. 5 King's College London, Cancer Bioinformatics, London, United Kingdom. 6 Fondazione IRCCS Istituto Nazionale dei Tumori, Radiation Oncology Unit, Milan, Italy. 7 National Center for Oncological Hadrontherapy (CNAO), Radiation Oncology Clinical Department, Pavia, Italy. 8 Fondazione IRCCS Istituto Nazionale dei Tumori, Molecular Mechanisms Unit, Milan, Italy. 9 Weill Cornell Medicine, Department of Medicine, Division of Haematology-Oncology, New York, USA. 10 King's College London, Comprehensive Cancer Centre, London, United Kingdom. 11 The Hebrew University - Hadassah, The Institute of Biomedical and Oral Research, Jerusalem, Israel. 12 Johns Hopkins University, School of Medicine, Baltimore, USA

Purpose/Objective:

Head and neck squamous cell carcinoma (HN-SCC) is often diagnosed at advanced stages, with curative treatments yielding poor survival outcomes (5-year rates: 28-67%)[1].

Previous research suggests that the microbiota affects cancer therapy outcomes[2]. Shifts in the oral microbiome are associated with inflammatory oral conditions such as periodontitis. The role of oral bacteria in HN-SCC treatment outcomes remains underexplored. We analysed microbiome data from two independent cohorts to explore and validate associations between oral bacteria and HN-SCC treatment efficacy. Clinical observations were validated using in vitro models investigating mechanistic relationships and the impact on radiotherapy-mediated HN-SCC cell killing.

Material/Methods:

Tumour-associated microbiome data from HN-SCC patients was obtained from the cancer microbiome atlas database (TCMA). Survival data was obtained from TCMA and the cancer genome atlas databases[3,4].

The MicroLearner observational study enrolled patients with HN-SCC over a 3-year period, treated with high-dose volumetric modulated arc radiotherapy with curative intent (primary or post-operative radiotherapy). Survival data was prospectively collected until 5 years post-treatment. Pre-treatment salivary bacterial communities were characterised with 16S rRNA gene sequencing. Linear regression, Cox proportional hazards regression, and Kaplan Meier models were used to identify bacteria associating with overall (OS) and disease-specific survival (DSS). An in vitro 2D co-culture model consisting of oral cavity SCC (OSCC; TR146, HN5 and HSC3 cell lines) or dysplastic oral keratinocytes (DOK cell line),+/- Fusobacterium nucleatum (F. nucleatum; ATCC 23726 or ATCC 25586 strains) was developed and optimised. The effect of infection with F. nucleatum (single infection at day 0 or daily infection on days 0-4) was assessed. Ratios of bacteria-to-OSCC (termed multiplicity of infection, MOI) from 0.5 to 10 were used. OSCC viability was assessed at day 5 with an ATP-based assay, LDH and crystal violet assays. The effect of infection with Prevotella oralis (P. oralis; NCTC 11459), which is also a Gram-negative commensal anaerobic bacterium of the oral cavity, and Fusobacterium peridonticum (F. periodonticum; ATCC 33693), a different species within the Fusobacterium genus, were also assessed as comparators. A previously developed in vitro co-culture irradiation model was used to assess whether F. nucleatum is an effective radiosensitiser[5]. Co-cultures were irradiated using a clinical linear accelerator to 10Gy (single fraction). F. nucleatum was added either before or after irradiation. Significance was assessed with Student’s t-test.

Results: