Abstract 2836: H2S donors as radiosensitizers for glioblastoma multiforme (GBM)

Abstract Glioblastoma multiforme (GBM) is an extremely aggressive CNS cancer in adults. Radiation is a cornerstone therapy but poses high risk of healthy tissue necrosis. Despite maximal treatment, GBM results in death within 15-21 months of diagnosis. These poor statistics suggest the need for a novel therapy. The use of radiosensitizing agents is a novel approach to minimizing radiation mediated healthy tissue necrosis by allowing use of lower doses to achieve comparable cytotoxic effects. Our lab has shown that sodium sulfide (Na2S), a hydrogen sulfide (H2S) donor, selectively kills GBM (T98G) cells while sparing normal human brain endothelial (hCMEC/D3) cells. Na2S also selectively radiosensitizes GBM cells and enhances cell killing with photon or proton radiation. We are currently exploring Diallyl Trisulfide (DATS), another H2S donor, as a radiosensitizing agent and have demonstrated that DATS can kill GBM cells. At a given dose of 2 Gy, radiation alone decreases T98G survival by 10%. With DATS, survival decreases by 70%, suggesting an additive effect. To determine if DATS increases DNA damage mediated cell death, T98G cells were treated with DATS, radiation, or combined DATS + radiation treatment and then analyzed for γH2AX foci, an indicator of double stand breaks (DSB). Our results show that compared to no treatment, DATS increased the number of γH2AX foci per cell by 1.5-fold, by 3-fold with radiation, and by 4-fold with combined DATS + radiation, an additive response. To elucidate the mechanism of increased DNA damage, a novel fluorescence multiplex host cell reactivation (FM-HCR) reporter system was used to assess repair activity of DSBs in live cells. T98G cells pre-treated with DATS were transfected with reporter plasmids containing site-specific lesions, mimicking radiation-like DNA damage. Repair resulted in expression of a fluorescent reporter protein, which was quantitated using flow cytometry. Our results show that DATS did not alter non-homologous end joining (NHEJ) or homologous repair (HR) activity of DSB. However, DATS did alter base excision repair (BER) activity by decreasing repair of abasic lesions and increasing repair 8oxoG lesions. We hypothesize that this attempted BER via simultaneous strand cleavage by AP endonuclease (Ape1) or glycosylase (Ogg1) may lead to build up of repair intermediates, threatening genomic stability and inducing DSB. Pursuing specific DNA repair biochemical assays is required to further understand this effect of DATS on DNA damage and repair inhibition. Citation Format: Morni Modi, Camila Weber, Qinqin Xu, Kuanling Chen, Ana Cheong, Zachery Nagel, Lynn Harrison. H2S donors as radiosensitizers for glioblastoma multiforme (GBM) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2836.