Loss of Nudt15 thiopurine detoxification increases direct DNA damage in hematopoietic stem cells

Abstract Thiopurines, such as 6-mercaptopurine (6-MP), are widely used as cytotoxic agents and immunosuppressants for leukemia and autoimmune or inflammatory diseases. A nonsynonymous single nucleotide polymorphism (p.Arg139Cys; R139C) of the nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) gene causes the loss of thiopurine detoxification, inducing myelosuppression. To understand such hematotoxicity, we investigate the effects of NUDT15 R139C on hematopoietic stem cells (HSCs) upon thiopurine administration. Using previously established Nudt15 R138C knock-in mice, which mimic myelosuppression in NUDT15 R139C homozygous or heterozygous patients following thiopurine administration, we investigated the numerical changes of HSCs and hematopoietic progenitor cells following 6-MP administration using in vivo flowcytometry and ex vivo HSC expansion. Genes differentially expressed between Nudt15 +/+ HSCs and Nudt15 R138C/R138C HSCs were identified using RNA-sequencing before the emergence of 6-MP-induced HSC-damage. Gene Ontology (GO) and Transcriptional Regulatory Relationships Unraveled by Sentence-based Text Mining (TRRUST) analyses were performed to elucidate the molecular effects of 6-MP on HSCs. In Nudt15 R138C/R138C mice, 6-MP induced exhaustion of HSCs faster than that of multipotent progenitors and as fast as that of myeloid-committed progenitors. Ex vivo-expanded Nudt15 R138C/R138C HSCs were dose- and time-dependently damaged by 6-MP. GO analysis identified the DNA damage response and cell cycle process as the most strongly influenced processes in Nudt15 R138C/R138C HSCs. TRRUST analysis revealed that the Trp53-regulated transcriptional regulatory network is influenced prior to HSC exhaustion in Nudt15 R138C/R138C HSCs. The loss of NUDT15 thiopurine detoxification enhances thiopurine-mediated DNA damage via the Trp53 networks in HSCs. Therefore, caution is required in long-term thiopurine use in patients with NUDT15 R139C in view of its adverse effects on HSCs in the form of DNA damage

Low immunogenicity of vedolizumab determined by a simple drug-tolerant assay in patients with ulcerative colitis.

Vedolizumab is a humanized monoclonal antibody against the α4β7 integrin and is approved for treatment of inflammatory bowel diseases. In this study, we evaluated the immunogenicity of vedolizumab using a simple drug-tolerant assay developed in our laboratory. Serum vedolizumab trough levels and anti-vedolizumab antibody (AVA) levels were measured using new immunoassays in 37 patients with ulcerative colitis (UC) under vedolizumab maintenance therapy. The median vedolizumab trough level at week 30 was 16.0 μg/ml (interquartile range, 7.3-24.4). The vedolizumab trough level of the patients with clinical remission (partial Mayo score ≤1) was significantly higher than that of clinically active patients (16.7 μg/ml vs 6.8). The cut-off value of vedolizumab level predicting clinical remission at week 30 was 7.34 μg/ml. The median AVA level of patients under vedolizumab maintenance therapy was similar to that of healthy controls (n = 20) (0.032 μg/ml-c vs 0.022). One of 37 patients (2.7%) was judged to be AVA positive. There was no significant difference in serum AVA and vedolizumab trough levels between biologics-naïve (n = 19) and biologics-switched (prior anti-TNFα-exposed) patients (n = 18). In conclusion, the simple drug-tolerant assay developed in our laboratory demonstrated low immuno-genicity of vedolizumab. Prior use of anti-TNFα drugs did not affect the immunogenicity of vedolizumab