Combination bromo- and extraterminal domain and poly (ADP-ribose) polymerase inhibition synergistically enhances DNA damage and inhibits neuroblastoma tumorigenesis

Abstract

Purpose JQ1 is a bromo- and extraterminal (BET) domain inhibitor that downregulates MYC expression and impairs the DNA damage response. Poly (ADP-ribose) polymerase (PARP) inhibitors prevent DNA damage sensing and repair. We hypothesized that JQ1 would promote a DNA repair-deficient phenotype that sensitizes neuroblastoma cells to PARP inhibition. Methods Four human neuroblastoma cell lines were examined: two MYCN-amplified (BE(2)-C and IMR-32), and two non-MYCN-amplified (SK-N-SH and SH-SY5Y). Cells were treated with JQ1 (BET inhibitor), Olaparib (PARP inhibitor), or in combination to assess for therapeutic synergy of JQ1 and Olaparib. Treated cells were harvested and analyzed. Quantitative assessment of combination treatment synergy was performed using the median effect principle of Chou and Talalay. Results Combination treatment with Olaparib decreased the IC50 of JQ1 by 19.9-fold, 2.0-fold, 12.1-fold, and 2.0-fold in the BE(2)-C, IMR-32, SK-N-SH, and SH-SY5Y cell lines, respectively. In the MYCN-amplified cell lines, BE(2)-C and IMR-32, combination treatment decreased gene expression of MYCN relative to single-drug treatment alone or control. Combination treatment decreased protein expression of DNA repair proteins Ku80 and RAD51, led to accumulation of DNA damage marker phospho-histone H2A.X, and increased caspase activity. In the non-MYCN-amplified cell lines, SK-N-SH and SH-SY5Y, combination treatment induced G0/G1 cell cycle arrest. Conclusions Combination BET and PARP inhibition synergistically inhibited neuroblastoma tumorigenesis in vitro. In MYCN-amplified neuroblastoma cells, this effect may be induced by downregulation of MYCN transcription, defects in DNA repair, accumulation of DNA damage, and apoptosis. In non-MYCN-amplified cell lines, combination treatment induced cell cycle arrest.

Clinical Response to a PARP Inhibitor and Chemotherapy in a Child with BARD1-Mutated Refractory Neuroblastoma: A Case Report

“…In our cohort of 59 NBLs, we found 3 cases with P/LP germline mutations in HRR genes (Figure 1 D), consistent with recent genomic profiling of HR-NBL germline and tumor samples, which showed multiple defective DNA repair mechanisms (ATRX, 11q LOH, ATM, H2AFX, CHK1, CEP131 and MRE11) [41][42][43][44][45] . Published studies of drug exposure experiments using in vitro cell line models and in vivo zebrafish models also suggest that patients with such defects may benefit from a similar therapeutic strategy [46][47][48][49][50][51][52][53][54][55][56] .…”