ESTRO 2020 Abstract book

S266 ESTRO 2020

associated cytokine production. Clinical relevance was validated using gene expression analyses of in silico data (The Cancer Genome Atlas) and a retrospective HNSCC cohort (LMU-KKG). Results In the HNSCC cell line panel a significant positive correlation was observed for inherent radioresistance with radiation-induced senescence and an associated cytokine release (CXCR2 ligands). The functional relevance of the cytokines for the development of radioresistance, was demonstrated via medium-transfer and inhibition of cytokine release in vitro . In vivo , irradiation-induced release of CCL5, CXCL12, CXCL1, IL1a, IL1b and IL6 dominated in HPV-negative tumors, while CXCL10 and CXCL11 were induced in HPV-positive tumors. Pharmacological inhibition of cytokine production affected tumor growth upon radiotherapy. Retrospective clinical analyses confirmed an association of expression of CXCR2 and its ligands with overall- and disease-specific survival. Conclusion Our study identifies irradiation-induced senescence and the associated production of cytokines as critical drivers of radioresistance in HNSCC. Therapeutic targeting of these mechanisms may open new treatment perspectives for a stratified subgroup of patients as shown in retrospective clinical analyses. Further experiments are under way to validate the clinical relevance of these findings. Acknowledgments : The project was funded by BMBF, ZiSStrans (NUK047) OC-0447 ATP Citrate Lyase is associated with radiosensitivity in head and neck squamous cell carcinoma E. Göttgens 1 , C. Van den Heuvel 2 , M. De Jong 3 , J. Kaanders 1 , W. Leenders 2 , M. Ansems 1 , J. Bussink 1 , P. Span 1 1 Radboud university medical center, Radiotherapy and OncoImmunology Laboratory- Department of Radiation Oncology, Nijmegen, The Netherlands ; 2 Radboud university medical center, Department of Biochemistry, Nijmegen, The Netherlands ; 3 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Radiotherapy is an important treatment modality of head and neck squamous cell carcinomas (HNSCC). Tumour metabolism might influence radiosensitivity, and a relationship between metabolism and clinical outcome has been reported. Here we probed a large number of genes involved in metabolism for their role in radiosensitivity both in vitro and in patient cohorts. Material and Methods Radiosensitivity of 14 human HNSCC cell lines was determined using colony forming assays and the expression profiles of approximately 200 metabolic and targetable tyrosine kinase genes were generated using targeted RNA sequencing by single molecule Molecular Inversion Probes. The effect of pharmacological inhibition of candidate genes on DNA repair (53BP1 foci and homologous recombination assays) and radiosensitivity (colony forming assays) was established in vitro. The predictive value was assessed in patients in silico (n=445) and validated in a separate cohort (n=91). The subcellular localisation was established using immunohistochemistry in HNSCCs and also related to outcome. Results

Correlation between radiosensitivity data and expression profiles yielded 18 genes associated with radiosensitivity or -resistance. Pharmacological inhibition of ATP citrate lyase (ACLY) ACLY caused an impairment of DNA damage repair, specifically homologous recombination (HR), and lead to radiosensitisation in several HNSCC cell lines. This did not occur after inhibition of fatty acid synthase (FASN), suggesting that ACLY inhibited HR via histone acetylation as reported earlier (1). In silico examination of a TCGA cohort of HNSCC patients revealed that high expression ACLY was predictive for radiotherapy response, as it was only associated with poor overall survival in patients who received radiotherapy (hazard ratio (HR) = 2.00, 95% CI: 1.12 – 3.55; P = 0.0184). These data were further validated in an independent cohort of HNSCC patients treated with chemoradiation (HR = 4.17; 95% CI 1.35-12.86; P = 0.0130). Furthermore, patients with poor locoregional control after radiotherapy has significantly higher nuclear ACLY protein levels, again in line with its reputed role in attenuating HR via histone acetylation.

Figure: patients with poor locoregional control (locoregional event within 8 months) had significantly higher levels of ACLY in the nucleus (left, P = 0.037). In patients with good locoregional control (no event within 3 years after primary treatment), ACLY was almost unequivocally expressed in the cytoplasm, but not the nucleus (right). Conclusion ACLY affects DNA damage repair, and is a predictive factor for radiotherapy treatment outcome in HNSCC. Patients treated with (chemo)irradiation may benefit from pharmacological inhibition of ACLY.

1.

Nuclear Acetyl-CoA Production by ACLY Promotes Homologous Recombination. Mol Cell, 2017. 67 (2): p. 252-265 e6.