Abstract 5913: ECO nanoparticle delivery of siRNA targeting DNA repair to enhance the radiation response of glioblastoma

Background: Glioblastoma (GBM) is among the most lethal of human cancers with a median survival of ~15 months. Novel treatment strategies targeting DNA damage response proteins such as ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNApk) are being investigated for the radiosensitization of GBM. Previously, (1-aminoethyl)iminobis[N-(oleicylcysteinyl-1-amino-ethyl)-propionamide (ECO) nanoparticles (NPs) were shown to effectively deliver siRNA targeting tumor growth and metastasis. Here we investigate the ability of these NPs to deliver siRNA targeting ATM and DNApk to enhance the radiation response of glioma and glioma stem cell populations. Methods: Normal astrocytes, glioma (U251), and glioma stem cells (NSC11, GBMJ1) were used. Protein analysis revealed the degree of silencing using ECO NPs with siRNA targeting ATM or DNApk. The effects of each siRNA alone (40nM) and in combination (20nM each) on radiation response was evaluated using clonogenic cell survival and γH2AX foci assays. A cranial guide screw model was used to assess the effectiveness of NPs in vivo. U251 tumor cells expressing luciferase were orthotopically implanted in nude mice and NPs targeting luciferase or DNApk were injected intratumorally. The efficacy of siRNA delivery was assessed via bioluminescence signaling and immunohistochemical staining. Results: ECO NPs effectively silenced both target genes in all tumor cells. The effect of this silencing on double strand break (DSB) repair varied with each cell line. γH2AX studies showed significantly impaired DSB repair in U251 cells with DNApk and ATM/DNApk combination treatment and in GBMJ1 stem cells with combination treatment. Treatment of NSC11 stem cells resulted in trends towards impaired DSB repair however the results were not statistically significant. Importantly, each treatment had no significant effect on DSB repair in normal astrocytes. Evaluation of radiation response in the long term using clonogenic assays resulted in dose enhancement factors for ATM, DNApkcs, and combination treatments of 1.24, 1.43, and 1.34 for U251, 1.34, 1.35, and 1.48 for NSC11, and 1.35, 1.36, and 1.51 for GBMJ1. In vivo studies showed evidence that ECO NPs were able to deliver siRNA targeting luciferase and reduce the bioluminescence signal output in vivo. Conclusions: The use of ECO NPs in normal astrocytes resulted in no significant effect on DSB repair demonstrating a potential therapeutic advantage to ECO NP/siRNA therapies. In contrast, NPs effectively delivered siRNA targeting ATM and DNApk to glioma and glioma stem cells showing the ability to target and treat a heterogeneous GBM cell population. The subsequent enhancement of radiation response in vitro coupled with in vivo observations of bioluminescence silencing provide the basis for future investigation into the use of ECO/siRNA complexes to enhance the radiation response of GBM in vivo. Citation Format: Jennifer A. Lee, Nadia Ayat, Zhanhu Sun, Tatsuya Kawai, Zheng-Rong Lu, Kevin Camphausen. ECO nanoparticle delivery of siRNA targeting DNA repair to enhance the radiation response of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5913.