S2594
Radiobiology - Preclinical biomarkers
ESTRO 2026
pre-operative radiosurgery, distinguishing between individuals achieving or not clinical downstaging. CCDC97 is a poorly characterized gene, that might contribute to pre-mRNA splicing by interacting with the splicing complex SF3B, known to be involved in DNA damage response (DDR). Recently, SF3B3 has been reported to support lipid metabolic reprogramming, that in turn affects RT sensitivity. Thus, this study aims to investigate CCDC97 role in BC, elucidating its molecular functions and involvement in RT response. Material/Methods: ER+/HER2- BC cancer cell lines (MCF7, T47D) were transiently silenced for CCDC97 and treated with ionizing radiation (2Gy, 8Gy). Functional assays were performed, including the evaluation of cell survival, reactive oxygen species (ROS) production (DCFDA staining), and apoptosis (Annexin V/PI assay and apoptosis/necrosis inhibitor treatment). Western blot analysis allowed the assessment of the protein expression of DDR, apoptosis, cell cycle, and lipid metabolism markers. Results: To explore CCDC97 role in affecting BC cells RT-sensitivity, we performed its transient silencing in MCF7 and T47D cells. First, we found that CCDC97-silencing led to a strong reduction in cell survival, that was further enhanced following RT treatment. RT exerts its cytotoxic effects by causing physical DNA-damage and enhancing ROS levels. CCDC97-silenced BC cells exhibited a strong increase in ROS production and γ H2AX levels, accompanied by a downregulation of DDR-related proteins (RAD51, PARP1, Ku70), effects that were amplified by RT administration. These findings suggest that CCDC97 expression is involved in ER+/HER2- BC cells sensitivity to RT. Then, we investigated CCDC97 role in mediating cell death mechanisms. Specifically, we observed an increase of apoptosis and an absence of necrosis induction, validated by cell survival rescue in presence of the pan-caspase inhibitor ZVAD-Fmk. Accordingly, apoptosis and cell cycle markers were downregulated upon CCDC97 silencing. Moreover, CCDC97-silencing was associated with decreased SF3B3 expression, suggesting that their interaction may regulate DDR. Consistent with SF3B3 reported role in lipid metabolism, we also pointed out a lipid metabolic reshaping upon CCDC97 silencing. Conclusion: Overall, our findings suggest that CCDC97 dysregulation potentiates RT-induced damage in BC cells, ultimately leading to apoptosis, and warrant further investigation as potential therapeutic target to improve RT efficacy in BC. Keywords: breast cancer, radiosensitivity, CCDC97 Digital Poster Highlight 2830 Impact of rare genetic variants in muscle repair genes on post- radiotherapy toxicities in patients with breast, lung, and prostate cancers Miguel E Aguado-Barrera 1,2 , Olivia Fuentes-Rios 1,2 , Patricia Calvo- Crespo 3,1 , Ana M Carballo-Castro 3 , Paula Peleteiro-Higuero 3,1 , Begoña Taboada-Valladares 3,1 , Antonio Gómez-Caamaño 4 , David Azria 5 , Jenny Chang-Claude 6,7 , Ananya Choudhury 8 , Dirk de Ruysscher 9 , Alison Dunning 10 , Sara Gutierrez-Enriquez 11 , Sarah Kerns 12 , Maarten Lambrecht 13 , Tiziana Rancati 14 , Tim Rattay 15 , Barry S Rosenstein 16,17 , Petra Seibold 6 , Elena Sperk 18 , Christopher J Talbot 19 , Liv Veldeman 20 , Adam Webb 19 , Catharine M.L. West 21 , Ana Vega 22,23 1 Genetics in Cancer and Rare Disease Group, Instituto de Investigación Sanitaria de Santiago, Santiago de Compostela, Spain. 2 Genetics in Cancer and Rare Disease Group, Fundación Pública Galega de Medicina Xenómica, Santiago de Compostela, Spain. 3 Radiation Oncology, Complexo Hospitalario Universitario de
overexpression. Expression levels of ALDH1A1, ALDH1A3, and MMP11 and their association with pathological parameters and clinical outcomes were analyzed in several patient datasets. The levels of MMP11 protein in plasma were examined by ELISA in independent cohorts of patients. Results: We found that ALDH1A1 positively regulates tumor cell survival in circulation, extravasation, and metastatic dissemination, whereas ALDH1A3 plays the opposite role1. Expression of ALDH1A1 is increased while ALDH1A3 decreased in metastatic PCa, and their expression levels oppositely correlate with clinical outcomes. PCa progression is associated with the increasing interplay of ALDH1A1 with androgen receptor (AR) and retinoid receptor (RAR) transcriptional programs. Mechanistically, the ALDH1A1 gene positively regulates TGFB1 expression in a RAR- and AR-dependent manner2. The TGF- β 1 pathway further contributes to the regulation of the MMP11 expression in PCa cells. Genetic silencing of MMP11 in a panel of PCa cell lines increased cell radiosensitivity. The 3D hydrogel-based microcapsules, generating a stiff microenvironment and anchorage-free conditions, induced the MMP11 and TGFB1 expression. Cells depleted for Mmp11 formed fewer metastatic nodules than the control in the syngeneic immunocompetent mouse model. To analyze tumor control in vivo, we assess the number of metastatic nodules formed by ALDH wild-type or ALDH- depleted cells in combination with 2x5 Gy conventional RT; the results are currently being analyzed. The plasma MMP11 levels have the potential to differentiate between mPCa and non-metastatic PCa with high specificity (0.93) and sensitivity (0.9). MMP11 plasma level had a significant association with PSA increase in patients with mPCa treated with local ablative EBRT.A hypothetical ALDH1A1/MMP11-related plasma proteome-based prognostic signature was identified. Conclusion: ALDH/TGFB1/MMP11 signalling contributes to both PCa metastases and radioresistance. MMP11 is a promising blood-based prognostic biomarker in patients with mPCa receiving RT. References: 1. Gorodetska et al., Theranostics. 2024. doi: 10.7150/thno.88057. 2. Gorodetska et al., J Exp Clin Cancer Res. 2025. doi: 10.1186/s13046- 025-03299-6. Keywords: prostate cancer, metastases, biomarkers Digital Poster 2752 Uncovering CCDC97 role in radiotherapy response of ER+ breast cancer cells Assia Duatti 1 , Ylenia Martinini 1 , Elisa Pardella 1 , Cinzia Talamonti 1 , Chiara Mattioli 2 , Mauro Loi 2 , Marianna Valzano 3 , Luca Visani 2 , Viola Salvestrini 2 , Carlotta Becherini 3 , Andrea Rampini 3 , Icro Meattini 2 , Monica Mangoni 2 , Lorenzo Livi 2 1 Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, University of Florence, Florence, Italy. 2 Department of Experimental and Clinical Biomedical Sciences “Mario Serio”; Radiation Oncology Unit, Department of Oncology, University of Florence; Careggi, Florence, Italy. 3 Department Radiation Oncology Unit, Department of Oncology, Careggi, Florence, Italy Purpose/Objective: Radiotherapy (RT) represents an essential therapeutic approach for breast cancer (BC). As acquired/intrinsic resistance poses major clinical challenges, identifying molecular mechanisms and predictive biomarkers of RT response stand as fundamental clinical needs. CCDC97 has emerged as the main differentially expressed gene in a translational study involving ER+/HER2- BC patients that received
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