Abstract 132: DNA-PK inhibition to enhance etoposide therapy in neuroblastoma
Authors: Norouzi Mahnaz , Zhu Beibei , Izumi Tadahide , Rellinger Eric J. , Evers B. Mark , Rychahou Piotr G. 
Published: March 2024

Abstract
Introduction. Neuroblastoma is the most common extracranial solid tumor in children and accounts for ~15% of all pediatric cancer deaths. DNA-PK, a key regulator of repair responses to double-strand DNA breakages induced by radiation or induction chemotherapy is used in the treatment of high-risk neuroblastomas. Here, we have demonstrated that high DNA-PK expression is associated with poor overall survival in a patient population, DNA-PK is highly activated in neuroblastoma cell lines, and inhibition of DNA-PK enhances therapeutic effects of DNA damaging therapies.
Methods. DNA double-strand break damage was induced with etoposide, a topoisomerase II inhibitor. DNA-PK activity was inhibited with peposertib or DNA-PK siRNA. DNA-PK Ser2056 phosphorylation was analyzed in MYCN amplified (SK-NDZ, BE(2)-C, LAN-1) and MYCN non-amplified (SK-N-AS, SK-N-SH) cell lines. Clonogenic and proliferation assays were used to evaluate the efficacy of peposertib in combination with etoposide in BE-2-C and SK-N-DZ neuroblastoma cell lines. DSB-induced DNA repair was visualized with confocal laser scanning microscopy using γ-H2AX immunofluorescence. Western blot was used to confirm inhibition of DNA-PKcs (pDNA-PKcs S2056) and analyze cleaved PARP expression in combination groups.
Results. DNA-PK inhibition resulted in enhancement of etoposide cytotoxic therapy (BE-2-C IC50 ET = 2.77 ± 0.2, ET+Pep 0.76 ± 0.04; SK-N-DZ IC50 ET = 0.55 ± 0.06, IC50 ET+Pep = 0.11 ± 0.02) in both BE-2-C and SK-N-DZ cell lines. Immunofluorescence analysis detected γH2AX foci increase in the etoposide and peposertib combination group. DNA-PK inhibition in combination with etoposide treatment significantly increased PARP cleavage in BE-2-C and SK-N-DZ cell lines. The effect of DNA-PK knockdown on neuroblastoma cell survival was even more pronounced compared to DNA-PK inhibition with peposertib. DNA-PK knockdown by siRNA alone increased PARP cleavage to the levels comparable to 2 µM etoposide treatment. The combination of etoposide and DNA-PK knockdown enhanced PARP cleavage even further in neuroblastoma cells.
Conclusions. High DNA repair activity is commonly associated with cancer drug resistance. We have shown that DNA-PK activation is continuously supported in both MYCN amplified and MYCN non-amplified neuroblastoma cell lines. The importance of DNA-PK activity in neuroblastoma cell lines is confirmed with DNA-PK knockdown that leads to apoptosis in MYCN amplifiedneuroblastoma cell lines. In addition, the combination of DNA-PK inhibition or DNA-PK knockdown with DNA-damaging therapies stalled DNA damage response and enhanced neuroblastoma cell apoptosis. These findings demonstrate the significance of high DNA-PK activity in neuroblastoma cells and provide a potent therapeutic strategy to enhance neuroblastoma cell apoptosis with selective DNA-PK inhibition.
Citation Format: Mahnaz Norouzi, Beibei Zhu, Tadahide Izumi, Eric J. Rellinger, B. Mark Evers, Piotr G. Rychahou. DNA-PK inhibition to enhance etoposide therapy in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 132.