Purpose: Medulloblastoma is paediatric tumor of the cerebellum. It represents the most frequent malignant brain tumor in childhood. It can be classified into four disparate molecular subgroups but current therapies are not yet tailored to their specificities. This is particularly important for subgroups with worse prognosis as Group3. Patients who survive often present severe treatment-related morbidity, which can be largely attributed to brain radiation in ages of development. It is therefore important to improve treatment efficacy in more aggressive subgroups as well as reduce treatment-related morbidity across all subgroups. We investigated whether AsiDNATM, a radiosensitizer in clinical trials which works through DNA repair inhibition, could be used to improve radiotherapy efficacy with no additional toxicity allowing radiation dose de-escalation in groups with better prognosis and improved radiotherapy efficacy in those with high-risk disease.

Experimental design: The cytotoxic effect of AsiDNATM was determined in a panel of 4 human medulloblastoma cell lines from different subgroups and different P53 status. We analyzed the ability of AsiDNATM to reach brain tissue and toxicity of treatments with or without irradiation in pups (10 days old mice). Distribution of AsiDNA was estimated by quantification of Cy-5-AsiDNA in brain tissues. Radiation toxicity was estimated by survival to high doses, monitoring of circulating growth hormone (GH), weight loss, bones size at adult age and neuro histology analysis. We assessed the AsiDNATM radio-enhancing efficacy in Group3 xenografted preclinical models using X-RAD 320 (PXI Inc) X-ray irradiator. Local brain irradiation was performed with an image-guided X-ray system (SARPP, Xstrahl Ldt), in which dosimetry and animal setting were controlled at each treatment session.

Results: AsiDNATM treatments exhibit an additive effect to radiation in all cell lines, leading to an approximate 2-fold reduction of the radiation dose to reach 50% survival. Cy5-AsiDNA distributed to pup brain but not to adult brain devoid of tumors. However, in adults AsiDNATM distributed in tumors in brain through permeability of tumor vessels. Irradiation toxicity in pups was confirmed by a significant decrease in GH secretion and associated reduction of bone size. The lethal dose after irradiation was 20 Gy. No increase of irradiation toxicity was observed with AsiDNATM. In vivo, AsiDNATM alone significantly enhances survival rates (p=0.005) and increases radiotherapy efficacy. When combined with radiotherapy, AsiDNATM led to delay in tumor growth and survival improvement as compared to radiotherapy alone.

Conclusion: Overall, our current results show AsiDNATM as an attractive candidate to improve radiation therapy in medulloblastoma in both standard- and high-risk patients with no indication of additional toxicity in healthy developing brain tissues.

Citation Format: Sofia Ferreira, Chloe Foray, Sophie Heinrich, Celio Pouponnot, Marie Dutreix. AsiDNATM, a novel DNA repair inhibitor to sensitize aggressive medulloblastoma subtypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2865.