Development of novel nuclease inhibitors as potential anticancer agents

Thesis

SNM1A and SNM1B are 5' to 3' exonucleases that are involved in the repair of DNA interstrand crosslinks (ICLs); the endonuclease SNM1C is involved in the repair of DNA double strand breaks via non-homologous end-joining. Cells depleted in SNM1A and SNM1B show increased sensitivity toward clinically used ICL inducing drugs, such as cisplatin or mitomycin C and those cells depleted in SNM1C display increased sensitivity towards ionising radiation. Inhibitors of SNM1A, SNM1B, and SNM1C could potentiate the effects of these commonly used cancer drugs or prevent the development of resistance to them.

A high-throughput screen was carried out to identify SNM1 hits for use as a foundation for the development of new inhibitors. Building on these hits, sets of structural analogues were synthesised to investigate structure-activity relationships (SAR). The developed compounds were initially tested using a fluorescence-based assay, with activity for apparent inhibitors being validated by radioactive gel-based assays.

The hydroxamic acid group was identified as a pharmacophore targeting the active site of SNM1 nucleases. Initial sets of hydroxamate-based compounds inhibited all three SNM1 nucleases, demonstrating no selectivity. By application of iterative rounds of SAR analysis informed by crystallographic data, improved hydroxamate-based inhibitors were developed. The work culminated in a series of compounds that selectively inhibits SNM1B with IC50s in the low nanomolar range. Although potent inhibition was observed against purified, recombinant SNM1B, achieving a similar result in human cell lines was more challenging despite the use of a prodrug strategy.

Overall, the work reveals that potent and selective inhibition of human SNM1 nuclease isoforms is viable. Future work can focus on optimising the cellular potency of SNM1 inhibitors.

Authors: Bielinski, M

• DOI: 10.5287/ora-ozm0pkwg9
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: DNA repair; nuclease