ESTRO 2024 - Abstract Book

S5319

Radiobiology - Tumour biology

ESTRO 2024

Ayşe Sedef Köseer 1 , Mareike Gruhn 2 , Jacqueline Nathansen 2 , Mechthild Krause 1,2,3 , Annett Linge 1,2,3 , Claudia Arndt 4,5 , Anna Dubrovska 1,2,3 1 National Center for Tumor Diseases (NCT), German Cancer Research Center (DKFZ), Heidelberg, Faculty of Medicine and University Hospital Carl Gustav Carus, Dresden, Germany. 2 OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Dresden, Germany. 3 German Cancer Consortium (DKTK), partner site Dresden and German Cancer Research Center (DKFZ), Heidelberg, Germany. 4 Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmaceutical Cancer Research, Dresden, Germany. 5 Mildred Scheel Early Career Center, Faculty of Medicine Carl Gustav Carus, Dresden, Germany Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide, with primary and postoperative radiochemotherapy being the standard of care for patients with locally advanced disease. The standard therapy is based on population-based clinical studies, whereas individual tumor biology remains unconsidered. CD98hc protein, encoded by the SLC3A2 gene, together with the light subunits LAT1, LAT2, and xCT, constitutes a heterodimeric transmembrane amino acid transporter (AAT) and serves as a key regulator of the stress response and stemness. CRISPR/Cas9-mediated knockout of SLC3A2 expression is associated with a decreased level of reduced glutathione, induction of oxidative stress, and less efficient DNA double-strand break repair (1). Therefore, CD98hc driven signaling is a promising biomarker for radiotherapy and a potential target for tumor radiosensitization. This study aims to validate CD98hc-associated AATs LAT1, LAT2, and xCT as biomarkers of HNSCC radioresistance and investigate the associated, potentially druggable molecular mechanism of action. We used immunohistochemical analysis to assess the expression levels of CD98hc and CD98hc-related AATs LAT1, LAT2, and xCT in patients with locally advanced HNSCC treated with postoperative radiochemotherapy (n = 197). We performed CRISPR/Cas9 or siRNA-mediated knockdown of CD98hc-related AATs in a panel of HNSCC cell lines to investigate their influence on HNSCC radioresistance and stemness. We investigated the radioresistance properties and cancer stem cells (CSC) phenotype of HNSCC cell lines upon genetic depletion or chemical inhibition of CD98hc AATs. The mechanism of the reciprocal regulation between CD98hc-related AATs and CSCs was deciphered with RT qPCR, flow cytometry analysis of aldehyde dehydrogenase activity (ALDH), and chromatin immunoprecipitation assay (ChIP) to validate CSC-specific AAT transcription regulation. To validate CD98hc as a potential target for tumor radiosensitization, we combined fractionated irradiation and CD98hc-targeted immune therapy with a switchable universal CAR (UniCAR) system against radioresistant HNSCC cells in 3D tumor spheroid cultures. Purpose/Objective: Material/Methods:

Results:

Our data show a significant correlation between the high expression levels of CD98hc, LAT1, xCT, and locoregional control and a statistical trend for this association for LAT2 protein. A large-scale analysis of the potential association of CD98hc-associated transporters and locoregional control in patients with locally advanced HNSCC is currently ongoing. Genetic knockout or knockdown of CD98hc, LAT1, LAT2, and xCT expression in a panel of HNSCC cell lines decreased stemness, clonogenic cell survival, and DNA repair efficiency. We also found a mechanism of the reciprocal regulation between CD98hc-related AATs and CSC phenotype. CD98hc-redirected UniCAR T cells showed a high infiltration into 3D spheroids and efficient targeting of radioresistant HNSCC cells. The combination of fractionated