TPMT and NUDT15 polymorphisms in thiopurine induced leucopenia in inflammatory bowel disease: a prospective study from India

Uphill battle: Innovation of thiopurine therapy in global inflammatory bowel disease care

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract that encompasses two major conditions: Crohn's disease (CD) and ulcerative colitis (UC). Historically, IBD has been primarily reported in western countries, but over the past decades, its prevalence is rapidly increasing, especially in lower and middle-income countries (LMICs) such as India and China and also in Sub-Saharan Africa. The prevalence of IBD in LMICs has been the subject of growing concern due to the impact of access to public healthcare and the burden it places on healthcare resources. The classical thiopurines face significant challenges due to cessation of therapy in approximately half of patients within one year due to side effects or ineffectiveness. In this article, we highlight innovating thiopurine treatment for IBD patients in downregulating side effects and improving efficacy.

ITPA polymorphisms do not predict additional risk beyond TPMT and NUDT15 for thiopurine-induced cytopenia in inflammatory bowel disease

INTRODUCTION AND AIM

Thiopurine-related leukopenia is associated with polymorphisms in the thiopurine methyltransferase (TPMT) and nucleoside diphosphate-linked moiety X type motif 15 (NUDT15) genes. However, those polymorphisms explain only a fraction of thiopurine-related leukopenia. Our aim was to study the role of an inosine triphosphate pyrophosphatase (ITPA) polymorphism in patients with inflammatory bowel disease (IBD) and thiopurine-related leukopenia that was unexplained by the TPMT and NUDT15 polymorphisms.

MATERIAL AND METHODS

We enrolled consecutive IBD patients on thiopurines (azathioprine or 6-mercaptopurine) from January 2019-March 2020, at a tertiary care center in North India. The presence of the ITPA (C.94C > A) polymorphism was evaluated in all patients, along with its association with thiopurine-related leukopenia.

RESULTS

Of the 33 patients (from a total of 119 patients) that developed leukopenia, 8 had the TPMT (n = 1) or NUDT15 (n = 7) polymorphism. Of the remaining 111 patients, their mean age was 36.36 ± 13.54 years and 57 (51.3%) were males. Twenty-five (21.01%) had unexplained leukopenia. The ITPA polymorphism was detected in 4 (16%) patients in the unexplained leukopenia group and 24 (27.9%) patients in the non-leukopenia group (p = 0.228). The odds ratio for predicting leukopenia with the ITPA polymorphism was 0.4921 (95% CI 0.1520-1.5830, p = 0.234).

CONCLUSION

The ITPA (C.94C > A) polymorphism was frequently detected in the study population but was not predictive for leukopenia in patients with IBD on thiopurine therapy.

A Simple, Rapid, and Cost-Effective PCR Procedure for Detection of NUDT15 Gene Variants in Vietnamese Patients with Acute Lymphoblastic Leukemia

Objective  The NUDT15 variants impact thiopurine dose selection in acute lymphoblastic leukemia patients. The ability to rapidly detect variants is important in clinical practice. This study aims to develop a simple polymerase chain reaction (PCR) procedure for detecting NUDT15 variants in Vietnamese patients. Materials and Methods  Sanger sequencing was used to determine NUDT15 variants from 200 patients. We designed primers and optimized the PCR procedure for detection of wild-type and variant alleles and compared with Sanger sequencing results. Results  The inserted variant c.55_56insGAGTCG was detected by differences in size through conventional PCR. The tetra-primer amplification refractory mutation system PCR was successful in detecting two variations, c.52G > A and c.415C > T. The sensitivity and specificity of PCR procedure achieved 100% when compared to 200 Sanger sequencing results. Conclusion  Our PCR procedure is suitable for replacing Sanger sequencing to detect the NUDT15 variants in clinical setting.

Time to incorporate preemptive NUDT15 testing before starting thiopurines in inflammatory bowel disease in Asia and beyond: a review

INTRODUCTION

Thiopurine toxicity is related to genetic polymorphism. Thiopurine methyltransferase (TPMT) variants do not explain thiopurine toxicity in more than half of patients. Asians, despite the low prevalence of TPMT variants, are more susceptible to thiopurine toxicity. Since 2014, studies from many Asian countries have shown a strong association between nucleoside diphosphate-linked moiety X-type motif (NUDT) 15 polymorphism and thiopurine-induced myelotoxicity.

AREAS COVERED

An English language literature search was performed for TPMT and NUDT15 genetic variants in inflammatory bowel disease and other diseases. This article discusses the merits of preemptive NUDT15 and TPMT testing in Asian and non-Asian IBD populations.

EXPERT OPINION

The NUDT polymorphism occurs in up to 27% of the Asian and Hispanic population. Hematological toxicity occurs in up to one-third of patients with this genetic variant. Given this, preemptive testing for NUDT15 variant is worthwhile and is probably more cost-effective than TPMT testing in these groups. Prevalence of NUDT15 variants is low in non-Finnish European population, but NUDT15 variants have been linked to myelotoxicity along with TPMT genetic variants. NUDT15 preemptive testing should be considered in the migrant Asian population in Europe and North America and in Caucasian populations who develop myelotoxicity.

Safety and efficacy of personalized versus standard initial dosing of thiopurines: Systematic review and meta-analysis of randomized trials

BACKGROUND

Pretherapy assessment of specific genetic polymorphism (TPMT, NUDT15, FTO, RUNX1, etc) or enzyme levels (for TPMT) may help personalize the dose of thiopurines and avoid adverse effects.

RESEARCH DESIGN AND METHODS

A systematic review of randomized controlled trials (RCTs) comparing personalized versus standard strategy for initial thiopurine dosing was performed. The electronic databases were searched on 27 September 2022. The outcomes were overall adverse effects, myelotoxicity, drug interruptions, and therapeutic efficacy with either strategy. The certainty of evidence was assessed using GRADE methodology.

RESULTS

We included six randomized trials, done dominantly in patients with inflammatory bowel disease (IBD). The personalized strategies were genotype testing in 4 trials (TPMT in three trials, NUDT15 in two) and enzyme levels for TPMT in two trials. The pooled risk of myelotoxicity in personalized dosing was lower [RR = 0.72 (95%CI, 0.55-0.94, I2 = 0%)]. The pooled risk of pancreatitis (RR = 1.10I, 0.78-1.56, I2 = 0%), hepatotoxicity (RR = 1.13, 0.69-1.88, I2 = 45), and GI intolerance (RR = 1.01, 0.92-1.10, I2 = 0) were similar in two groups. The pooled risk of drug interruption in individualized dosing was similar to the standard dosing group (RR = 0.97, I2 = 68%).

CONCLUSION

Personalized testing-based initial thiopurine dosing is protective against myelotoxicity as compared to standard weight-based dosing.

Thiopurine therapy in inflammatory bowel disease in the pandemic era: Safe or unsafe?

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract. Crohn's disease (CD) and Ulcerative colitis (UC) are the two major types affecting millions across the globe. Various immunomodulatory drugs consisting of small molecules (thiopurines, methotrexate and tofacitinib) and biologics are used to treat IBD. Thiopurines (TP) are widely used in the treatment of IBD and it plays an important role both alone and in combination with anti-TNF agents as IBD maintenance therapy. Although the advent of biologics therapy has significantly advanced the management of IBD, TP remains the mainstay of treatment in resource-limited and low economic settings. However, the recently commenced pandemic has raised uncertainty over the safety of the use of immunosuppressant drugs such as TP among healthcare care providers and patients, as there is a scarcity of data on whether IBD patients are at higher risk of COVID-19 infection or more prone to its severe outcomes.

AIM

This review aims to encapsulate evidence on the risk of COVID-19 infection and its severe prognosis in IBD patients on TP. Additionally, it also evaluates the role of TP in inhibiting the viral protease, a potential drug target, essential for the replication and pathogenesis of the virus.

CONCLUSION

Emerging evidence suggests that TP therapy is safe during the current pandemic and does not carry an elevated risk when used as monotherapy or in combination with other IBD drugs. In-vitro studies demonstrate that TP is a potential therapeutic for present and future betacoronavirus pandemics.

Positioning of tofacitinib in treatment of ulcerative colitis: a global perspective

INTRODUCTION

Tofacitinib has emerged as a useful drug for the treatment of ulcerative colitis (UC).

AREAS COVERED

There is an unmet need for cost-effective, non-immunogenic drugs with a safe adverse effect profile to treat patients with ulcerative colitis. In the present review, we evaluate the available literature to inform the appropriate positioning of tofacitinib in the current drug landscape and identify subsets where its use should be done with caution.

EXPERT OPINION

Tofacitinib is helpful in the treatment of patients where the standard conventional or biological therapies have failed or were not tolerated. With lower costs of the generic drug than the biologicals (or biosimilars), it could be an important therapy in low- to middle-income countries. The risk of infections, especially Herpes Zoster and tuberculosis, needs to be addressed before initiation. Tofacitinib should be avoided in patients with venous thromboembolism and cardiovascular disease risk factors. Due to limited evidence, the use is not recommended in pregnancy, while it should be used with caution in elderly citizens. Future trials should look into the head-to-head comparison of tofacitinib with biologicals. The role of tofacitinib in acute severe colitis needs evaluation with comparative trials with current standards of care.