ESTRO 2024 - Abstract Book

S5253 ESTRO 2024 1 Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSE-SANTE/SERAMED/LRMed, Fontenay-aux-Roses, France. 2 Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSE-SANTE/SERAMED/LRAcc, Fontenay-aux Roses, France. 3 Hôpital Universitaire Pitié-Salpêtrière, Département de Radiothérapie Oncologie, Paris, France Radiobiology - Normal tissue radiobiology

Purpose/Objective:

Chronic Radiation Cystitis (CRC) is a pathology following pelvic irradiation characterized by chronic inflammation occasionally progressing to fibrosis, with symptoms such as pain and bleeding. Mesenchymal stromal cells (MSCs) could be a therapeutic option, thanks to their ability to modulate chronic inflammation and fibrosis after irradiation. Previous studies have shown that MSC therapy is an alternative treatment for interstitial cystitis and hemorrhagic cystitis[1-4]. However, the putative beneficial role of MSCs on CRC remains to be demonstrated. The aim of this study was to set up a rat model of CRC and to evaluate the impact of a MSC-based treatment and their mechanisms of action. We developed a rat model of chronic radiation cystitis using a localised single-dose bladder irradiation using a (Small Animal Radiation Research Platform) SARRP. Intravenous MSC treatment was evaluated for urothelial and vascular damage using physiological, molecular and tissue approaches.

Material/Methods:

The project is divided into two parts, the modeling of radiation-induced cystitis in rats and the effect of MSC treatment on the chronic phase (CRC). Radiation cystitis was generated by localized, single-dose irradiation of the entire bladder. Irradiation was performed using the SARRP from Xstrahl Life Sciences with a voltage of 220 kV, an intensity of 13 mA, a dose rate of 2.4 Gy per minute, a collimator of 10×10 mm2 and a source-sample distance of 35 cm. The dose range was from 20 to 80 Gy, with a follow-up period of 3 to 12 months post-irradiation. For the treatment, we choose the dose of 40 Gy, followed 4 months after irradiation. An intravenous injection of 5 million MSCs, was administered in rats every two weeks (3 injections in all). Physiological, histological, and molecular (at mRNA level) follow-up was carried out for 14 months after irradiation. Hematuria was analyzed using metabolic cages and urine strips. Vascular lesions were analyzed by endoscopy. Incontinence was explored using metabolic cages placing a filter on the metabolic cage floor. The rat stayed in the cage for 4 h, then filters are collected to count the number of spots under UV lamp. [5] Results showed the onset of CRC as early as 6 months after irradiation, with chronic inflammation, hematuria, urothelial disorganization, and fibrosis, increasing with time. mRNA level analysis indicated a profile in favor of chronic inflammation compared to the non-irradiated control, with overexpression of the CCL5 (5-fold; p value<0.05), IL-1β (7-fold; p-value<0.001) and IL-6 (7.5-fold; p-value<0.01) genes, as early as 6 months post irradiation. Urothelial lesions (based on urothelium-free areas with decreased uroplakin III) appeared at 6 months post-irradiation. At 10 months post-irradiation, regeneration of the urothelium appears to be evidenced by overexpression of cytokeratin 14 (a marker for basal stem cells). However, this regeneration appeared to be defective, since at 12 months hyperplasia was confirmed in the irradiated rats (p-value <0.01). In the non irradiated group, the slow renewal of the urothelium is ensured by the division of basal stem cells and their successive differentiation into intermediate cells then into superficial cells which ensure impermeability thanks to the expression of uroplakin 3.[5] At the functional level, we observed that the intensity and frequency of hematuria were proportional to the irradiation dose, with a threshold at 40 Gy and the appearance of bleeding from 60 days post-irradiation. At 12 months post-irradiation, treatment with MSCs appears to reduce vascular lesions. MSC treatment significantly reduces incontinence at 6 months post-irradiation. For control rats, the number of micturition has an average of 3.5±0.38 micturitions which rises to 9.75±1.22 micturitions in irradiated untreated rats (2.79-fold is observed, p value<0 .001). For the MSC treated irradiated group, an average of 3.12±0.51 micturitions is observed showing a Results: