title: Nanoparticle mediated silencing of DNA repair sensitizes pediatric brain tumor cells to γ-irradiation.
abstract: Medulloblastoma (MB) and ependymoma (EP) are the most common pediatric brain tumors, afflicting 3000 children annually. Radiotherapy (RT) is an integral component in the treatment of these tumors; however, the improvement in survival is often accompanied by radiation-induced adverse developmental and psychosocial sequelae. Therefore, there is an urgent need to develop strategies that can increase the sensitivity of brain tumors cells to RT while sparing adjacent healthy brain tissue. Apurinic endonuclease 1 (Ape1), an enzyme in the base excision repair pathway, has been implicated in radiation resistance in cancer. Pharmacological and specificity limitations inherent to small molecule inhibitors of Ape1 have hindered their clinical development. Here we report on a nanoparticle (NP) based siRNA delivery vehicle for knocking down Ape1 expression and sensitizing pediatric brain tumor cells to RT. The NP comprises a superparamagnetic iron oxide core coated with a biocompatible, biodegradable coating of chitosan, polyethylene glycol (PEG), and polyethyleneimine (PEI) that is able to bind and protect siRNA from degradation and to deliver siRNA to the perinuclear region of target cells. NPs loaded with siRNA against Ape1 (NP:siApe1) knocked down Ape1 expression over 75% in MB and EP cells, and reduced Ape1 activity by 80%. This reduction in Ape1 activity correlated with increased DNA damage post-irradiation, which resulted in decreased cell survival in clonogenic assays. The sensitization was specific to therapies generating abasic lesions as evidenced by NP:siRNA not increasing sensitivity to paclitaxel, a microtubule disrupting agent. Our results indicate NP-mediated delivery of siApe1 is a promising strategy for circumventing pediatric brain tumor resistance to RT.
authors: Department of Neurological Surgery, University of Washington, Seattle, WA 98195, USA.
authors: Forrest M
authors: FM
authors: Kievit
authors: Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
authors: Zachary R
authors: ZR
authors: Stephen
authors: Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
authors: Kui
authors: K
authors: Wang
authors: Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
authors: Christopher J
authors: CJ
authors: Dayringer
authors: Department of Surgery, University of Washington, Seattle, WA 98195, USA.
authors: Jonathan G
authors: JG
authors: Sham
authors: Department of Neurological Surgery, University of Washington, Seattle, WA 98195, USA; Department of Radiology, University of Washington, Seattle, WA 98195, USA. Electronic address: rge@uw.edu.
authors: Richard G
authors: RG
authors: Ellenbogen
authors: Department of Neurological Surgery, University of Washington, Seattle, WA 98195, USA.
authors: John R
authors: JR
authors: Silber
authors: Department of Neurological Surgery, University of Washington, Seattle, WA 98195, USA; Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA; Department of Radiology, University of Washington, Seattle, WA 98195, USA. Electronic address: mzhang@uw.edu.
authors: Miqin
authors: M
authors: Zhang
mesh_terms: D001932:Brain Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D045744:Cell Line, Tumor; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000096:biosynthesis; D004806:Ependymoma / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D005720:Gamma Rays; D006801:Humans; D008527:Medulloblastoma / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D053758:Nanoparticles; D009363:Neoplasm Proteins / Q000096:biosynthesis; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: D009363:Neoplasm Proteins; D011838:Radiation-Sensitizing Agents; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase
keywords: Ape1; Base excision repair; Ependymoma; Medulloblastoma; Nanomedicine; siRNA