WITHDRAWN: The Effect of Iodine-131 Beta-particles in Combination With A-966492 and Topotecan on Radio-sensitization of Glioblastoma

Abstract

Glioblastoma tumors are resistant to radiotherapy, and the need for drugs to induce radio-sensitization in tumor cells has always been a challenge. Besides, radiotherapy using targeted radionuclide is effective even for resistant tumors. Poly (ADP-ribose) polymerase (PARP) and topoisomerase I enzymes have critical roles in the repairmen of DNA damage in cells. Thus, the inhibition of the activity of these enzymes can prevent the process of DNA repair and lead to the accumulation of damaged DNA in cells, resulting in the induction of cell death in tumors. In the current study, we investigated the effect of beta-particles of iodine-131 in combination with Topotecan (TPT), as the inhibitor of topoisomerase I, and A-966492, as the inhibitor of the PARP enzyme to increase radio-sensitivity of glioblastoma cells.The U87MG cell line (a human glioblastoma cell line) were cultured in Poly-Hema-coated flasks to reach 300μm-diameter spheroids. Then, the cells were treated with non-toxic concentrations of A-966492 and TPT. The viability of the cells treated with iodine131 in combination with A-966492 and TPT was determined by the clonogenic assay. The expression level of the gamma-H2AX protein, as a biomarker of DNA double-strand breaks, was measured by the immunofluorescence staining method to examine the impact of A-966492 (1μM), TPT, and radiation on the induction cell death.The combination of A-966492 and TPT with radiation resulted in the enhanced cell death, and sensitizer enhancement ratios at 50% survival (SER50) were 1.25 and 1.45, respectively. Radio- and chemo-sensitization were promoted when iodine-131 was combined with A-966492 and TPT, with the SER50 of 1.68. Also, the expression of γ-H2AX was significantly increased in cells treated with A-966492 and TPT combined with radiation.The results demonstrated that iodine-131, in combination with A-966492 and TPT, had marked effects on radio-sensitizing and can be used as a targeted radionuclide for targeting radiotherapy in combination with PARP and topoisomerase I inhibitors to improve radiotherapy in clinics.