Abstract 6326: A comparative study of C3H and C57Bl/6 murine models of radiation-induced fibrosis

Introduction: Approximately 50% of cancer patients are treated with radiation therapy; ∼60% of whom will experience significant radiation-induced fibrosis (RF) caused by excessive collagen accumulation. RF reduces tissue function and flexibility, increasing surgical complications during disease recurrence. Accurate and reproducible in vivo models are required to elucidate the mechanisms of this condition and to facilitate the development of effective therapeutic strategies. Although there have been comprehensive studies related to model development for other forms of fibrosis, the characterization and comparison of murine RF models remains limited in the literature. This work aims to assess and contrast C3H and C57Bl/6 mice as models for RF. Methods: RF was assessed in two mouse strains, C3H and C57BL/6. Mice were irradiated using the Precision SmART+ irradiator. C3H mice received 40 Gy, while C57BL/6 mice received 10 Gy, 15 Gy, or 20 Gy. Following irradiation, the tibiofemoral joint angle was measured using X-ray images acquired weekly. At 4-, 8-, 12-, and 16-weeks post-irradiation, skin samples were collected, and collagen deposition was analyzed. Collagen was measured using: a) picrosirius red staining and polarized light microscopy; b) pro-collagen ELISA; and c) the hydroxyproline assay. Results: The pattern of RF development was unique to each mouse strain. In C3H mice, three phases were observed: an acute response with increased limb stiffness, a recovery phase with reduced stiffness, and a fibrotic phase correlating with collagen accumulation, evidenced by histology and biochemical analyses. At 16 weeks post-irradiation, collagen deposition was observed to increase by 1.48- (p<0.05), 1.62- (p<0.05), and 1.32-fold via picrosirius, ELISA, and hydroxyproline assays, respectively. In C57BL/6 mice, 20 Gy induced RF without a recovery phase, 10 Gy did not induce fibrosis, while 15 Gy induced RF in 50% of cases, revealing unexpected variability despite genetic uniformity. At 16 weeks post-20 Gy irradiation, collagen deposition was observed to increase by 4.2- (p<0.01), 1.55-, and 2.69-fold (p<0.05) via picrosirius, ELISA, and hydroxyproline assays, respectively. Skin thickness following irradiation increased by 1.66-fold (p<0.05) in C3H mice, and by 2.35-fold (p<0.01) in C57BL/6 mice, compared to non-irradiated controls. Conclusions: Measuring the tibiofemoral joint angle using weekly X-ray is non-invasive approach in assessing murine RF. The data reveal mouse strain-specific differences in RF. C3H mice may more accurately recapitulate the development of RF in humans. However, due to many more gain- and loss-of-function genetic models, C57BL/6 mice remain essential for investigating RF. Citation Format: Pierre-Antoine Bissey, Justin Williams, Wei Shi, Madison Hossack, Ken W. Yip, Fei-Fei Liu. A comparative study of C3H and C57Bl/6 murine models of radiation-induced fibrosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6326.