Crystal structures of NUDT15 variants enabled by a potent inhibitor reveal the structural basis for thiopurine sensitivity
Introduction: The enzyme NUDT15 efficiently hydrolyzes the active metabolites of thiopurine drugs, commonly used to treat cancer and inflammatory diseases. Loss-of-function variants in NUDT15 are strongly associated with thiopurine intolerance, such as leukopenia, and preemptive NUDT15 genotyping has been clinically implemented to personalize thiopurine dosing. However, understanding the molecular consequences of these variants has been challenging due to the inherent instability of NUDT15 proteins encoded by clinically actionable pharmacogenetic variants, which prevented structural analysis.
Recent Advances: Recently, the small molecule NUDT15 inhibitor TH1760 was shown to sensitize cells to thiopurines by enhancing the accumulation of 6-thio-guanine in DNA. Building on this, we report the development of a potent and specific NUDT15 inhibitor, TH7755. TH7755 exhibits significantly improved cellular target engagement and potentiation of 6-thioguanine compared to TH1760, without showing any cytotoxicity on its own.
Structural Insights: The potent inhibitor TH7755 also stabilized NUDT15, allowing analysis via X-ray crystallography. We determined high-resolution structures of clinically relevant NUDT15 variants, including Arg139Cys, Arg139His, Val18Ile, and V18_V19insGlyVal. These structures provide clear insights into the structural basis for thiopurine intolerance observed in patients carrying these pharmacogenetic variants.
Conclusion: These findings will aid in predicting the effects of new NUDT15 sequence variations yet to be discovered in the clinic, enhancing our ability to personalize thiopurine therapy and manage thiopurine intolerance.