ESTRO 2024 - Abstract Book

S5210

Radiobiology - Microenvironment

ESTRO 2024

Within the TCMA cohort (n=155), only Fusobacterium (OS: HR=0.42 (95% CI: 0.20-0.89, p=0.02); DSS: 0.28 (0.09 0.89, p=0.03) was significantly associated with OS and DSS. There was a trend for higher OS in patients with a relative abundance (RA) of Fusobacterium above the median RA in the cohort (5.93 years/3.10-NR vs 3.53/2.36 5.81; p=0.1). At a species level, only Fusobacterium nucleatum associated with OS, with its detectability associating with improved OS (5.81 years/4.79-NR vs. 2.34/1.53-3.82; p=0.0003). Patients with an RA of F. nucleatum above the cohort median had better survival outcomes (OS: 5.93/3.29-NR vs. 3.11/2.30-NR, p=0.03; DSS: NR/7.04-NR vs 4.83/3.82-NR, p=0.12). Additionally, Fusobacterium and F. nucleatum detectability strongly associated with OS (p<0.001 for both) and DSS (p<0.001 and p=0.001) when adjusting for confounding factors (disease stage, smoking and HPV status). Within the MicroLearner cohort, patients with a higher abundance of Fusobacterium had a significantly better progression free survival (PFS) (p=0.05; median NR in both groups; 2-year PFS 95% CI 0.73-0.89 vs. 0.59-0.79). Among all salivary Fusobacterium species, Fusobacterium periodonticum conferred a significantly better PFS in patients with an RA above the cohort median (p<0.001), although a non-significant trend for better PFS was also observed in patients with a higher abundance of F. nucleatum. In vitro experiments showed a significant reduction in OSCC viability with the addition of F. nucleatum (p<0.001). OSCC killing rose with MOI. These findings were validated with LDH assays and crystal violet OSCC cell staining. Co-cultures with OSCC and P. oralis (MOIs 100-1000) showed no significant reduction in day 5 OSCC viability. F. nucleatum-mediated cell kill was observed within all OSCC/dysplastic cell lines and with several wild type F. nucleatum strains. F. periodonticum caused OSCC killing comparable to F. nucleatum. F. nucleatum also acts as a radiosensitiser, at 10Gy compared with uninfected, irradiated controls. In irradiation experiments, F. nucleatum caused OSCC radiosensitization if added post-irradiation at MOI 10 (p=0.02) and MOI 100 (p=0.0007). If added pre-irradiation, radiosensitization was only observed at MOI 100 (p=0.0007).

Conclusion:

Fusobacterium detectability is associated with better survival outcomes and response to radiotherapy in HN-SCC. Our in vitro data indicates that Fusobacterium propagates radiotherapy-mediated OSCC killing, but its own radiosensitivity may limit its effect at lower MOIs. Ongoing research will elucidate mechanisms and validate its role as a biomarker in HN-SCC.

Keywords: Microbiome, fusobacterium, radiosensitivity

References:

[1] Sambasivan, K. et al. TNM 8 staging is a better prognosticator than TNM 7 for patients with locally advanced oral cavity squamous cell carcinoma treated with surgery and post-operative radiotherapy. Radiother Oncol 160, 54–60 (2021). [2] Gopalakrishnan, V., Helmink, B. A., Spencer, C. N., Reuben, A. & Wargo, J. A. The Influence of the Gut Microbiome on Cancer, Immunity, and Cancer Immunotherapy. Cancer Cell Preprint at https://doi.org/10.1016/j.ccell.2018.03.015 (2018). [3] Dohlman AB, et al. The cancer microbiome atlas: a pan-cancer comparative analysis to distinguish tissue resident microbiota from contaminants. Cell Host Microbe. 2021 Feb 10;29(2):281-298.e5. doi: 10.1016/j.chom.2020.12.001. Epub 2021 Jan 6. PMID: 33382980; PMCID: PMC7878430.