NUDT15 Hydrolyzes 6-Thio-DeoxyGTP to Mediate the Anticancer Efficacy of 6-Thioguanine

Abstract

Thiopurines are a standard treatment for childhood leukemia, but like all chemotherapeutics, their use is limited by inherent or acquired resistance in patients. Recently, the nucleoside diphosphate hydrolase NUDT15 has received attention on the basis of its ability to hydrolyze the thiopurine effector metabolites 6-thio-deoxyGTP (6-thio-dGTP) and 6-thio-GTP, thereby limiting the efficacy of thiopurines. In particular, increasing evidence suggests an association between the NUDT15 missense variant, R139C, and thiopurine sensitivity. In this study, we elucidated the role of NUDT15 and NUDT15 R139C in thiopurine metabolism. In vitro and cellular results argued that 6-thio-dGTP and 6-thio-GTP are favored substrates for NUDT15, a finding supported by a crystallographic determination of NUDT15 in complex with 6-thio-GMP. We found that NUDT15 R139C mutation did not affect enzymatic activity but instead negatively influenced protein stability, likely due to a loss of supportive intramolecular bonds that caused rapid proteasomal degradation in cells. Mechanistic investigations in cells indicated that NUDT15 ablation potentiated induction of the DNA damage checkpoint and cancer cell death by 6-thioguanine. Taken together, our results defined how NUDT15 limits thiopurine efficacy and how genetic ablation via the R139C missense mutation confers sensitivity to thiopurine treatment in patients. Cancer Res; 76(18); 5501-11. Ó2016 AACR.

NUDT15,FTO, andRUNX1genetic variants and thiopurine intolerance among Japanese patients with inflammatory bowel diseases

“…Substitution of arginine with cysteine at this position may affect the enzyme's structure, and thereby, reduce cellular TGTP hydrolysis 24. One study has shown that NUDT15 proteins harboring the Arg139Cys mutation demonstrate enzyme activity comparable to that of the wild-type form, but are degraded rapidly in cells 25. Therefore, NUDT15 protein level may be implicated in the cytotoxicity of and sensitivity to thiopurines.…”

SAMHD1 protects cancer cells from various nucleoside-based antimetabolites

“…Hence, inhibitors of dUTPase can increase the efficacy of 5-FU 79,80 . A more recent target to improve cytotoxic therapies with thiopurines has emerged by discovering that the nudix enzyme family member NUDT15 can hydrolyse triphosphates of 6-thioguanine and mercaptopurine 81,82 . Hence, also in this case, combining these drugs with a NUDT15 inhibitor might improve therapy outcomes.…”

Severe thiopurine‐induced leukocytopenia and hair loss in Japanese patients with defective NUDT15 variant: Retrospective case–control study

“…The enzyme has a protective effect against endogenous oxygen radicals. NUDT15 missense variant R139C influences protein stability, leading to reduced or absence of enzyme activity and thiopurine intolerance . The variant frequency is relatively higher in East Asians and Hispanics, but lower in Europeans, which can explain why the Asian population is highly thiopurine intolerant compared with the Western population …”

“…NUDT15 missense variant R139C influences protein stability, leading to reduced or absence of enzyme activity and thiopurine intolerance. 26 The variant frequency is relatively higher in East Asians and Hispanics, but lower in Europeans, which can explain why the Asian population is highly thiopurine intolerant compared with the Western population. 19,25 In this study, the relationship between thiopurine-susceptible gene polymorphisms and thiopurine-induced adverse effects was assessed in adult patients with dermatological diseases.…”