Abstract A26: High frequency of Cytosine to Adenine mutations in neuroblastoma correlates with genomic aberrations in 8-Oxo-Guanine repair pathway

Abstract

Abstract Background: Somatic mutations can be grouped into 96 tri-nucleotide patterns, termed mutational signatures. These signatures can provide insights into underlying processes that fuel the evolution of tumor cells, and may expose therapeutic intervention avenues. Here we investigated the mutational signature of 84 whole genome sequenced neuroblastoma cases. Results: Mutational signature analysis revealed an extreme bias towards Cytosine to Adenine (CtoA) mutations in a majority of neuroblastoma tumors. This seems to be a unique feature of neuroblastoma. CtoA mutations are primarily found in high stage tumors and are therefore associated with a poor prognosis. Oxidative stress is known to be a source for such mutations, which can accumulate due to defects in the 8-Oxo-Guanine repair pathway genes OGG1, MUTYH and MTH1. We could show a strong correlation between CtoA mutations and chromosomal loss of MTH1, OGG1 and MUTYH. Besides copy number losses, sequencing also revealed a tumor with a homozygous mutation in OGG1 and this tumor showed a very strong bias towards CtoA mutations. Modified alkaline comet assays were performed for quantification of 8-Oxo-Guanine content present in the DNA of neuroblastoma cell lines. These comet assays showed that neuroblastoma cell lines with loss of either OGG1 or MUTYH, had higher 8-Oxo-Guanine content than cell lines without these losses. 8-Oxo-Guanine content is correlated with CtoA mutation frequency in short term cultured neuroblastoma organoids. Overexpression of OGG1 or MUTYH in neuroblastoma cell lines with losses of OGG1 or MUTYH respectively leads to rescue of the phenotype and a decrease in the amount of 8-Oxo-Guanine in the DNA. We are currently performing a compound screen to test the efficacy of 352 compounds functioning in the DNA damage repair in cell lines with and without MUTYH expression, and were testing compounds that further interfere in this specific branch of DNA damage repair including the newly developed MTH1 inhibitors. Conclusion: We identified a subset of neuroblastoma tumors with a high CtoA mutation frequency, which correlates with losses of glycosylases involved in the repair of CtoA mutations. 8-Oxo-Guanine levels are elevated in cell lines with loss of OGG1 or MUTYH, which can be rescued by overexpression of OGG1 or MUTYH respectively. Citation Format: Anne Hakkert, Marli E. Ebus, Rogier Versteeg, Caron N. Huib, Jan Koster, Jan J. Molenaar. High frequency of Cytosine to Adenine mutations in neuroblastoma correlates with genomic aberrations in 8-Oxo-Guanine repair pathway [abstract]. In: Proceedings of the AACR Special Conference on DNA Repair: Tumor Development and Therapeutic Response; 2016 Nov 2-5; Montreal, QC, Canada. Philadelphia (PA): AACR; Mol Cancer Res 2017;15(4_Suppl):Abstract nr A26.