Eradication of LIG4-deficient glioblastoma cells by the combination of PARP inhibitor and alkylating agent

// Monika Toma 1 , Monika Witusik-Perkowska 2 , Marzena Szwed 3 , Robert Stawski 4 , Janusz Szemraj 2 , Malgorzata Drzewiecka 1 , Margaret Nieborowska-Skorska 5 , Maciej Radek 6 , Pawel Kolasa 7, 8 , Ksenia Matlawska-Wasowska 9 , Tomasz Sliwinski 1 and Tomasz Skorski 5 1 Laboratory of Medical Genetics, Faculty of Biology and Environmental Protection, University of Lodz, Lodz, Poland 2 Department of Medical Biochemistry, Medical University of Lodz, Lodz, Poland 3 Department of Medical Biophysics, University of Lodz, Lodz, Poland 4 Department of Clinical Physiology, Medical University of Lodz, Lodz, Poland 5 Department of Microbiology and Immunology, Fels Institute for Cancer Research and Molecular Biology, Temple University Lewis Katz School of Medicine, Philadelphia, PA, USA 6 Department of Neurosurgery, Surgery of Spine and Peripheral Nerves, Medical University of Lodz, University Hospital WAM-CSW, Lodz, Poland 7 Department of Neurosurgery, Medical University of Lodz, Copernicus Memorial Hospital, Lodz, Poland 8 Social Sciences Academy in Lodz, Lodz, Poland 9 Division of Pediatric Research, Department of Pediatrics, University of New Mexico Health Sciences Center, Albuquerque, NM, USA Correspondence to: Tomasz Sliwinski, email: tomasz.sliwinski@biol.uni.lodz.pl Tomasz Skorski, email: tskorski@temple.edu Keywords: glioblastoma; PARP inhibitor; LIG4; alkylating agent; synthetic lethality Received: June 30, 2018      Accepted: November 16, 2018      Published: December 07, 2018 ABSTRACT Cancer cells often accumulate spontaneous and treatment-induced DNA damage i.e. potentially lethal DNA double strand breaks (DSBs). Targeting DSB repair mechanisms with specific inhibitors could potentially sensitize cancer cells to the toxic effect of DSBs. Current treatment for glioblastoma includes tumor resection followed by radiotherapy and/or temozolomide (TMZ) – an alkylating agent inducing DNA damage. We hypothesize that combination of PARP inhibitor (PARPi) with TMZ in glioblastoma cells displaying downregulation of DSB repair genes could trigger synthetic lethality. In our study, we observed that PARP inhibitor (BMN673) was able to specifically sensitize DNA ligase 4 (LIG4)-deprived glioblastoma cells to TMZ while normal astrocytes were not affected. LIG4 downregulation resulting in low effectiveness of DNA-PK–mediated non-homologous end-joining (D-NHEJ), which in combination with BMN673 and TMZ resulted in accumulation of lethal DSBs and specific eradication of glioblastoma cells. Restoration of the LIG4 expression caused loss of sensitivity to BMN673+TMZ. In conclusion, PARP inhibitor combined with DNA damage inducing agents can be utilized in patients with glioblastoma displaying defects in D-NHEJ.