Revisiting the Role of Thiopurines in Inflammatory Bowel Disease Through Pharmacogenomics and Use of Novel Methods for Therapeutic Drug Monitoring

A personalized network framework reveals predictive axis of anti-TNF response across diseases

Personalized treatment of complex diseases has been mostly predicated on biomarker identification of one drug-disease combination at a time. Here, we use a computational approach termed Disruption Networks to generate a data type, contextualized by cell-centered individual-level networks, that captures biology otherwise overlooked when performing standard statistics. This data type extends beyond the "feature level space", to the "relations space", by quantifying individual-level breaking or rewiring of cross-feature relations. Applying Disruption Networks to dissect high-dimensional blood data, we discover and validate that the RAC1-PAK1 axis is predictive of anti-TNF response in inflammatory bowel disease. Intermediate monocytes, which correlate with the inflammatory state, play a key role in the RAC1-PAK1 responses, supporting their modulation as a therapeutic target. This axis also predicts response in rheumatoid arthritis, validated in three public cohorts. Our findings support blood-based drug response diagnostics across immune-mediated diseases, implicating common mechanisms of non-response.

SERS spectroscopy as a tool for the study of thiopurine drug pharmacokinetics in a model of human B leukemia cells

Thiopurine drugs are immunomodulatory antimetabolites relevant for pediatric patients characterized by dose-dependent adverse effects such as myelosuppression and hepatotoxicity, often related to inter-individual differences, involving the activity of important enzymes at the basis of their biotransformation, such as thiopurine S-methyltransferase (TPMT). Surface Enhanced Raman Scattering (SERS) spectroscopy is emerging as a bioanalytical tool and represents a valid alternative in terms of affordable costs, shorter analysis time and easier sample preparation in comparison to the most employed methods for pharmacokinetic analysis of drugs. The aim of this study is to investigate mercaptopurine and thioguanine pharmacokinetics by SERS in cell lysates of a B-lymphoblastoid cell line (NALM-6), that did (TPMT*1) or did not (MOCK) overexpress the wild-type form of TPMT as an in vitro cellular lymphocyte model to discriminate between cells with different levels of TPMT activity on the base of the amount of thioguanosine nucleotides (TGN) metabolites formed. SERS analysis of the cell lysates was carried out using SERS substrates constituted by Ag nanoparticles deposited on paper and parallel samples were used for quantification of thiopurine nucleotides with liquid chromatography-tandem mass spectrometry (LC-MS/MS). A direct SERS detection method has been set up that could be a tool to study thiopurine drug pharmacokinetics in in vitro cellular models to qualitatively discriminate between cells that do and do not overexpress the TPMT enzyme, as an alternative to other more laborious techniques. Results underlined decreased levels of TGN and increased levels of methylated metabolites when TPMT was overexpressed, both after mercaptopurine and thioguanine treatments. A strong positive correlation (Spearman's rank correlation coefficient rho = 0.96) exists between absolute quantification of TGMP (pmol/1 x 106 cells), obtained by LC-MS/MS, and SERS signal (intensity of TGN at 915 cm-1). In future studies, we aim to apply this method to investigate TPMT activity in pediatric patients' leukocytes.

Recent developments in the assessment and management of inflammatory bowel disease in childhood: a narrative review

Background and Objective

The landscape of paediatric inflammatory bowel disease (pIBD) continues to evolve in an era of increasing incidence. There have been rapid developments in understanding, as we begin to perceive IBD as a spectrum of conditions, alongside advancements in monitoring and treatment. The objective of this article was to provide an overview of recent advances and challenges in the management of pIBD, with a focus on sustainable healthcare, personalised therapy, genomics, new drugs and avenues for future optimisation.

Methods

We present a narrative review that synthesises and summarises recent research (2017-2022) related to pIBD. We undertook a structured search of the literature (PubMed and Medline) and additional articles were identified through manual searches of reference lists. Evidence tables were compiled for disease outcomes.

Key Content and Findings

In this review we outline current practice, integrating clinical guidelines and contemporary research. We discuss initial investigations (including suggested threshold for paediatric faecal calprotectin), specialist investigations for disease monitoring [with reference to video capsule endoscopy (VCE) and therapeutic drug levels] and outline new and established treatment options. Biomarkers and genomic testing are examined as important tools for individualising care and identifying potential therapeutic targets, including for top-down therapy. Despite these advances, significant challenges remain, including the need for further research to understand the mechanisms of disease and the translation of these advances into real-world improvements in practice.

Conclusions

Recent advances in understanding of the pathogenesis of pIBD, alongside genomic and pharmacological developments have added more tools to the armamentarium for the treatment of these conditions and highlighted ongoing areas of research need.

A Review of Therapeutic Drug Monitoring in Patients with Inflammatory Bowel Disease Receiving Combination Therapy

Background: Inflammatory Bowel Disease (IBD) impacts millions worldwide, presenting a major challenge to healthcare providers and patients. The advent of biologic therapies has enhanced the prognosis, but many patients exhibit primary or secondary non-response, underscoring the need for rigorous monitoring and therapy optimization to improve outcomes. Objective: This narrative review seeks to understand the role of therapeutic drug monitoring (TDM) in optimizing treatment for IBD patients, especially for those on combination therapies of biologics and immunomodulators. Methods: A comprehensive synthesis of the current literature was undertaken, focusing on the application, benefits, limitations, and future directions of TDM in patients receiving a combination of biologic therapies and immunomodulators. Results: While biological therapies have improved outcomes, rigorous monitoring and therapy optimization are needed. TDM has emerged as a pivotal strategy, enhancing outcomes cost-effectively while reducing adverse events. While most data pertain to monotherapies, TDM's applicability also extends to combination therapy. Conclusion: TDM plays a crucial role in the treatment optimization of IBD patients on combination therapies. Further research is needed to fully understand its potential and limitations in the broader context of IBD management.

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.

DNA-Thioguanine Nucleotides as a Marker for Thiopurine Induced Late Leukopenia after Dose Optimizing by NUDT15 C415T in Chinese Patients with IBD

Thiopurine dose optimization by thiopurine-S-methyltransferase (TPMT) or nudix hydrolase-15 (NUDT15) significantly reduced early leucopenia in Asia. However, it fails to avoid the late incidence (> 2 months). Although laboratory monitoring of 6-thioguanine nucleotides (6TGN) to optimize thiopurine dose was suggested in White patients the exact association between leucopenia and 6TGN was controversial in Asian patients. In the present study, we aimed to explore whether DNA-thioguanine nucleotides (DNA-TGs) in leukocytes, compared with 6TGN in erythrocytes, can be a better biomarker for late leucopenia. This was a prospective, observational study. Patients with inflammatory bowel disease (IBD) prescribed thiopurine from February 2019 to December 2019 were recruited. Thiopurine dose was optimized by NUDT15 C415T (rs116855232). DNA-TG and 6TGN levels were determined at the time of late leucopenia or 2 months after the stable dose was obtained. A total of 308 patients were included. Thiopurine induced late leucopenia (white blood cells < 3.5 × 10⁹ /L) were observed in 43 patients (14.0%), who had significantly higher DNA-TG concentration than those without leucopenia (P = 4.1 × 10^-9 , 423.3 (~ 342.2 to 565.7) vs. 270.5 (~ 188.1 to 394.3) fmol/μg DNA). No difference in 6TGN concentrations between leucopenia and non-leucopenia was found. With a DNA-TG threshold of 340.1 fmol/μg DNA, 83.7% of leucopenia cases could be identified. Multivariate analysis showed that DNA-TG was an independent risk factor for late leucopenia. Quantification of DNA-TG, rather than 6TGN, can be applied to gauge thiopurine therapy after NUDT15 screening in Chinese patients with IBD.

The Intersection of Human and Veterinary Medicine-A Possible Direction towards the Improvement of Cell Therapy Protocols in the Treatment of Perianal Fistulas

The effective treatment of perianal fistulizing Crohn's disease is still a challenge. Local administration of mesenchymal stromal cells (MSCs) is becoming a part of accepted treatment options. However, as a fledgling technique, it still can be optimized. A new trend in translational research, which is in line with "One Health" approach, bases on exploiting parallels between naturally occurring diseases affecting humans and companion animals. Canine anal furunculosis (AF) has been indicated as condition analogous to human perianal Crohn's disease (pCD). This narrative review provides the first comprehensive comparative analysis of these two diseases based on the published data. The paper also outlines the molecular mechanisms of action of MSCs which are likely to have a role in modulating the perianal fistula niche in humans, and refers them to the current knowledge on the immunomodulatory properties of canine MSCs. Generally, the pathogenesis of both diseases shares main determinants such as the presence of genetic predispositions, dysregulation of immune response and the relation to intestine microbiota. However, we also identified many aspects which should be further specified, such as determining the frequency of true fistulas formation in AF patients, elucidating the role of TNF and Th17 pathway in the pathogenesis of AF, or clarifying the role of epithelial-to-mesenchymal transition phenomenon in the formation of canine fistulae. Nevertheless, the available data support the hypothesis that the results from testing cell therapies in dogs with anal furunculosis have a significant translational value in optimizing MSC transplants procedures in pCD patients.

Drug-Induced Liver Injury Used in the Treatment of Inflammatory Bowel Disease

Therapeutic options for the management of inflammatory bowel disease [IBD] have been expanding in recent decades. New biological and small molecule therapies have been incorporated into the pharmacological arsenal, allowing a more personalized management, and seeking increasingly strict remission goals. However, the fear of developing adverse events represents one of the most important limitations in deciding its use by patients and by a multidisciplinary team. Despite the risk of hepatotoxicity of thiopurines and methotrexate, these drugs are still used either as monotherapy or as combined therapy with anti-tumour necrosis factor [anti-TNF] biological agents. Although drug-induced liver injury [DILI] appears to be less frequent with anti-TNF agents, newer biologics and small molecules, liver tests should be considered in the follow-up of these patients, especially regarding future combined therapy of biologics or of these drugs with small molecules. The objective of this review is to show data on the risk of developing DILI in patients with IBD who are undergoing treatment with traditional therapy or new drugs, whether biological or small molecules.

Inosine Triphosphate Pyrophosphatase and NUDT15 are Good Predictors of Clinical Outcomes in Thiopurine-Treated Chinese Patients with Inflammatory Bowel Disease

BACKGROUND

Although the relationship between NUDT15 and thiopurine-induced leukopenia has been proven in previous studies, no prominent factors explaining interindividual variations in its active metabolite, 6-thioguanine nucleotide (6-TGN), and clinical efficacy have been identified. In this study, the correlation between genotypes (thiopurine S-methyltransferase, NUDT15, and ITPA polymorphisms), 6-TGN concentrations, and clinical outcomes (efficacy and side effects) in patients with inflammatory bowel disease were investigated.

METHODS

In total, 160 patients with inflammatory bowel disease were included, and the 3 genotyped genes and 6-TGN levels were measured by high-performance liquid chromatography. Statistical analyses and calculations were performed to determine their relationships.

RESULTS

ITPA genotypes and 6-TGN concentration were both associated with the clinical effectiveness of azathioprine (P = 0.036 and P = 4.6 × 10-7), with a significant correlation also detected between them (P = 0.042). Patients with ITPA variant alleles exhibited higher 6-TGN levels than those with the wild-type allele. In addition, the relationship between NUDT15 and leukopenia and neutropenia was confirmed (P = 1.79 × 10-7 and 0.002).

CONCLUSIONS

In summary, it is recommended that both ITPA and NUDT15 genotyping should be performed before azathioprine initiation. Moreover, the 6-TGN concentration should be routinely monitored during the later period of treatment.

Evaluation of the maternal and developmental toxicity of 6-methylmercaptopurine riboside in rats

Thiopurine prodrugs (azathioprine, AZA, and 6-mercaptopurine, 6MP) are embryotoxic to rodents and rabbits. Little is known about the developmental toxicity of 6-methylmercaptopurine riboside (6MMPr), a thiopurine drug metabolite that is thought to mediate its liver toxicity. A limb bud assay found that 6MMPr impairs the in vitro morphogenetic differentiation of mouse limb extremities, being more potent than 6MP in the assay. This study evaluated the embryotoxicity of 6MMPr (0, 7.5, 15, 30mg/kg bw sc) in rats after single-dose exposure in mid organogenesis (GD10). One group of pregnant rats was similarly treated with 6MP (15mg/kg bw sc). After C-section (GD21), fetuses were weighed, and examined for external abnormalities. One third of each litter was examined for soft-tissue abnormalities while the remaining fetuses were cleared and stained for skeleton evaluation. 6MMPr caused a dose-dependent maternal weight loss followed by recovery before term pregnancy. Except for a nonsignificant increase in embryolethality and slight reduction in fetal weight at 30mg/kg bw, no indication of embryotoxicity was noted at this dose or at lower doses of 6MMPr. In contrast, 6MP led to nearly 98% of post-implantation losses in the presence of slight-to-mild maternal toxicity. These results are consistent with the notion that maternal treatment with 6MMPr affects embryo development, causing a nonsignificant increase in embryolethality and a slight reduction in fetal weight at 30mg/kg bw. However, there was no increase in abnormalities at this dose, which was severely toxic to the dams, as reflected in the maternal weight gain data.

Gut Microbiota Metabolism of Azathioprine: A New Hallmark for Personalized Drug-Targeted Therapy of Chronic Inflammatory Bowel Disease

Despite the growing number of new drugs approved for the treatment of inflammatory bowel disease (IBD), the long-term clinical use of thiopurine therapy and the well-known properties of conventional drugs including azathioprine have made their place in IBD therapy extremely valuable. Despite the fact that thiopurine S-methyltransferase (TPMT) polymorphism has been recognized as a major cause of the interindividual variability in the azathioprine response, recent evidence suggests that there might be some yet unknown causes which complicate dosing strategies causing either failure of therapy or toxicity. Increasing evidence suggests that gut microbiota, with its ability to release microbial enzymes, affects the pharmacokinetics of numerous drugs and subsequently drastically alters clinical effectiveness. Azathioprine, as an orally administered drug which has a complex metabolic pathway, is the prime illustrative candidate for such microbial metabolism of drugs. Comprehensive databases on microbial drug-metabolizing enzymes have not yet been generated. This study provides insights into the current evidence on microbiota-mediated metabolism of azathioprine and systematically accumulates findings of bacteria that possess enzymes required for the azathioprine biotransformation. Additionally, it proposes concepts for the identification of gut bacteria species responsible for the metabolism of azathioprine that could aid in the prediction of dose-response effects, complementing pharmacogenetic approaches already applied in the optimization of thiopurine therapy of IBD. It would be of great importance to elucidate to what extent microbiota-mediated metabolism of azathioprine contributes to the drug outcomes in IBD patients which could facilitate the clinical implementation of novel tools for personalized thiopurine treatment of IBD.

Cytotoxicity of Thiopurine Drugs in Patients with Inflammatory Bowel Disease

The effectiveness of thiopurine drugs in inflammatory bowel disease (IBD) was confirmed more than a half-century ago. It was proven that these can be essential immunomodulatory medications. Since then, they have been used routinely to maintain remission of Crohn’s disease (CD) and ulcerative colitis (UC). The cytotoxic properties of thiopurines and the numerous adverse effects of the treatment are controversial. However, the research subject of their pharmacology, therapy monitoring, and the search for predictive markers are still very relevant. In this article, we provide an overview of the current knowledge and findings in the field of thiopurines in IBD, focusing on the aspect of their cytotoxicity. Due to thiopurines’ benefits in IBD therapy, it is expected that they will still constitute an essential part of the CD and UC treatment algorithm. More studies are still required on the modulation of the action of thiopurines in combination therapy and their interaction with the gut microbiota.

Hepatobiliary manifestations in inflammatory bowel disease: A practical approach

Inflammatory bowel diseases (IBD) are associated with various hepatobiliary disorders. They can occur at any moment in the course of the disease or associated with the treatment. The prevalence of liver dysfunction can reach up to 50% in different studies. Nonalcoholic fatty liver disease is considered the most common hepatobiliary complication in IBD, while primary sclerosing cholangitis is the most specific. Management of hepatic manifestations in IBD involves a multidisciplinary approach that includes a high index of suspicion and joint management with hepatologists. The medical confrontation with abnormal liver tests must include an exhaustive study to determine if these patterns can be related to IBD, associated diseases or to the therapies used.

Insights into the cellular pharmacokinetics and pharmacodynamics of thiopurine antimetabolites in a model of human intestinal cells

Thiopurines, immunomodulating drugs used in the management of different chronic autoimmune conditions and as anti-leukemic agents, may exert in some cases gastrointestinal toxicity. Moreover, since these agents are administered orally, they are absorbed across the gastrointestinal tract epithelium. On these premises, cellular and molecular events occurring in intestinal cells may be important to understand thiopurine effects. However, quantitative information on the biotransformation of thiopurines in intestinal tissues is still limited. To shed light on biotransformation processes specific of the intestinal tissue, in this study thiopurine metabolites concentrations were analyzed by an in vitro model of human healthy colon, the HCEC cell line, upon exposure to cytotoxic concentrations of azathioprine or mercaptopurine; the investigation was carried out using an innovative mass spectrometry method, that allowed the simultaneous quantification of 11 mono-, di-, and triphosphate thionucleotides. Among the 11 metabolites evaluated, TIMP, TGMP, TGDP, TGTP, MeTIMP, MeTIDP and MeTITP were detectable in HCEC cells treated with azathioprine or mercaptopurine, considering two different incubation times before the addition of the drugs (4 and 48 h). Different associations between metabolites concentrations and cytotoxicity were detected. In particular, the cytotoxicity was dependent on the TGMP, TGDP, TGTP and MeTITP concentrations after the 4 h incubation before the addition of thiopurines. This may be an indication that, to study the association between thiopurine metabolite concentrations and the cytotoxicity activity in vitro, short growth times before treatment should be used. Moreover, for the first time our findings highlight the strong correlation between cytotoxicity and thiopurine pharmacokinetics in HCEC intestinal cells in vitro suggesting that these cells could be a suitable in vitro model for studying thiopurine intestinal cytotoxicity.

Thiopurines in Inflammatory Bowel Disease. How to Optimize Thiopurines in the Biologic Era?

Thiopurines have been a cornerstone in the treatment of inflammatory bowel disease (IBD). Although they have been used for more than 50 years, there are still some unsolved issues about their efficacy and, also, some safety concerns, mainly the risk of myelosuppression and life-threatening lymphoproliferative disorders. Furthermore, the development of biological therapy raises the question whether there is still a role for thiopurines in the IBD treatment algorithm. On the other hand, limited cost and wide availability make thiopurines a reasonable option in settings of limited resources and increasing prevalence of IBD. In fact, there is a growing interest in optimizing thiopurine therapy, since pharmacogenomic findings suggest that a personalized approach based on the genotyping of some molecules involved in its metabolism could be useful to prevent side effects. Polymorphisms of thiopurine methyltransferase enzyme (TPMT) that result in low enzymatic activity have been associated with an increased risk of myelotoxicity, especially in Caucasians; however, in Asians it is assumed that the variants of nudix hydrolase 15 (NUDT15) are more relevant in the development of toxicity. Age is also important, since in elderly patients the risk of complications seems to be increased. Moreover, the primo-infection of Epstein Barr virus and cytomegalovirus under thiopurine treatment has been associated with severe lymphoproliferative disorders. In addition to assessing individual characteristics that may influence thiopurines treatment outcomes, this review also discusses other strategies to optimize the therapy. Low-dose thiopurines combined with allopurinol can be used in hypermethylators and in thiopurine-related hepatotoxicity. The measurement of metabolites could be useful to assess compliance, identify patients at risk of adverse events and also facilitating the management of refractory patients. Thioguanine is also a rescue therapy in patients with toxicity related to conventional thiopurine therapy. Finally, the current indications for thiopurines in monotherapy or in combination with biologics, as well as the optimal duration of treatment, are also reviewed.

Association of genetic variants in TPMT, ITPA, and NUDT15 with azathioprine-induced myelosuppression in southwest china patients with autoimmune hepatitis

This study aimed to investigate the influence of TPMT*3C, ITPA, NUDT15, and 6-thioguanine nucleotides (6-TGN) on azathioprine (AZA)-induced myelosuppression in Southwest China patients with autoimmune hepatitis (AIH). A total of 113 Chinese patients with AIH receiving AZA maintenance treatment were evaluated. The relevant clinical data of the patients were collected from the hospital information system. Genotyping of TPMT*3C(rs1142345), ITPA (rs1127354) and NUDT15(rs116855232) was conducted using a TaqMan double fluorescent probe. The concentration of 6-TGN was determined using UPLC-MS/MS. Among AIH patients treated with AZA, 40 (35.4%) exhibited different degrees of myelosuppression. The NUDT15 variant was associated with leukopenia (P = 8.26 × 10^–7; OR = 7.5; 95% CI 3.08–18.3) and neutropenia (P = 3.54 × 10^–6; OR = 8.05; 95% CI 2.96–21.9); however, no significant association with myelosuppression was observed for TPMT*3C and ITPA variants (P > 0.05). There was no significant difference in 6-TGN concentration between AIH patients with or without myelosuppression (P = 0.556), nor was there a significant difference between patients with variant alleles of TPMT*3C, ITPA, or NUDT15 and wild-type patients (P > 0.05). Interestingly, it was found that patients with a lower BMI had higher adjusted 6-TGN levels and a higher incidence of myelosuppression (P = 0.026 and 0.003). This study confirmed that NUDT15 variants are a potential independent risk predictor for AZA-induced leukopenia and neutropenia. BMI may be a crucial non-genetic factor that affects the concentration of AZA metabolites and myelosuppression. In addition, the 6-TGN concentration in red blood cells does not reflect the toxicity of AZA treatment, and new biomarkers for AZA therapeutic drug monitoring need further research.

Comprehensive molecular, probiotic, and quorum-sensing characterization of anti-listerial lactic acid bacteria, and application as bioprotective in a food (milk) model

Listeria monocytogenes is a major foodborne pathogen that adversely affects the food industry. In this study, 6 anti-listerial lactic acid bacteria (LAB) isolates were screened. These anti-listerial LAB isolates were identified via 16S rRNA gene sequencing and analyzed via repetitive extragenic palindromic-PCR. Probiotic assessment of these isolates, comprising an evaluation of the antibiotic susceptibility, tolerance to lysozyme, simulated gastric and intestinal juices, and gut conditions (low pH, bile salts, and 0.4% phenol), was carried out. Most of the isolates were resistant to streptomycin, vancomycin, gentamycin, kanamycin, and ciprofloxacin. All of the isolates were negative for virulence genes, including agg, ccf, cylA, cylB, cylLL, cylLS, cylM, esp, and gelE, and hemolytic activity. Furthermore, autoinducer-2 (a quorum-sensing molecule) was detected and quantified via HPLC with fluorescence detection after derivatization with 2,3-diaminonaphthalene. Metabolites profiles of the Lactobacillus sakei D.7 and Lactobacillus plantarum I.60 were observed and presented various organic acids linked with antibacterial activity. Moreover, freeze-dried cell-free supernatants from Lb. sakei (55 mg/mL) and Lb. plantarum (40 mg/mL) showed different minimum effective concentration (MEC) against L. monocytogenes in the food model (whole milk). In summary, these anti-listerial LAB isolates do not pose a risk to consumer health, are eco-friendly, and may be promising candidates for future use as bioprotective cultures and new probiotics to control contamination by L. monocytogenes in the food and dairy industries.

Clinical Genomics for the Diagnosis of Monogenic Forms of Inflammatory Bowel Disease: A Position Paper From the Paediatric IBD Porto Group of European Society of Paediatric Gastroenterology, Hepatology and Nutrition

BACKGROUND

It is important to identify patients with monogenic IBD as management may differ from classical IBD. In this position statement we formulate recommendations for the use of genomics in evaluating potential monogenic causes of IBD across age groups.

METHODS

The consensus included paediatric IBD specialists from the Paediatric IBD Porto group of the European Society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) and specialists from several monogenic IBD research consortia. We defined key topics and performed a systematic literature review to cover indications, technologies (targeted panel, exome and genome sequencing), gene panel setup, cost-effectiveness of genetic screening, and requirements for the clinical care setting. We developed recommendations that were voted upon by all authors and Porto group members (32 voting specialists).

RESULTS

We recommend next-generation DNA-sequencing technologies to diagnose monogenic causes of IBD in routine clinical practice embedded in a setting of multidisciplinary patient care. Routine genetic screening is not recommended for all IBD patients. Genetic testing should be considered depending on age of IBD-onset (infantile IBD, very early-onset IBD, paediatric or young adult IBD), and further criteria, such as family history, relevant comorbidities, and extraintestinal manifestations. Genetic testing is also recommended in advance of hematopoietic stem cell transplantation. We developed a diagnostic algorithm that includes a gene panel of 75 monogenic IBD genes. Considerations are provided also for low resource countries.

CONCLUSIONS

Genomic technologies should be considered an integral part of patient care to investigate patients at risk for monogenic forms of IBD.

Microbiota and Drug Response in Inflammatory Bowel Disease

A mutualistic relationship between the composition, function and activity of the gut microbiota (GM) and the host exists, and the alteration of GM, sometimes referred as dysbiosis, is involved in various immune-mediated diseases, including inflammatory bowel disease (IBD). Accumulating evidence suggests that the GM is able to influence the efficacy of the pharmacological therapy of IBD and to predict whether individuals will respond to treatment. Additionally, the drugs used to treat IBD can modualate the microbial composition. The review aims to investigate the impact of the GM on the pharmacological therapy of IBD and vice versa. The GM resulted in an increase or decrease in therapeutic responses to treatment, but also to biotransform drugs to toxic metabolites. In particular, the baseline GM composition can help to predict if patients will respond to the IBD treatment with biologic drugs. On the other hand, drugs can affect the GM by incrementing or reducing its diversity and richness. Therefore, the relationship between the GM and drugs used in the treatment of IBD can be either beneficial or disadvantageous.

NUDT15 genotyping during azathioprine treatment in patients with inflammatory bowel disease: implications for a dose-optimization strategy

Background

NUDT15 R139C is an Asian-prevalent genetic variant related to azathioprine (AZA) intolerance in patients with inflammatory bowel disease (IBD). However, it remains unclear how to utilize the genotyping results to improve the step-up dosing strategy with an already low starting dose in Asian practice.

Methods

Clinical data of eligible IBD patients who received AZA therapy and NUDT15 R139C testing were retrospectively collected. The relationship between NUDT15 genotype, AZA doses, and AZA-induced toxicity and efficacy were comprehensively analysed.

Results

A total of 159 patients were included for toxicity analysis. Compared with the wild genotype, patients heterozygous for R139C are more prone to developing myelotoxicity and alopecia (P = 0.007; P = 0.042). In particular, they had a 5.4-fold risk of developing myelotoxicity when AZA dosage was increased from 25 mg/d to 50 mg/d (P < 0.001). Regarding efficacy, 115 patients who had received AZA for >4 months and maintained clinical remission on AZA monotherapy were included for further analysis. R139C heterozygotes were finally titrated to a significantly lower dose than the wild genotype [median (interquartile range): 0.83 (0.75-0.96) vs 1.04 (0.89-1.33) mg/kg/d, P = 0.001], whereas the clinical remission rates did not differ between groups (P = 0.88).

Conclusions

IBD patients with R139C heterozygote are highly susceptible to AZA-induced myelotoxicity at an escalated dose of 50 mg/d. Thus, they may require a smaller dose increase after a starting dose of 25 mg/d. The final target dose of these patients could be set lower than that of the wild genotypes without compromising efficacy.

Effect of Thiopurine on Potential Surgical Intervention in Crohn’s Disease in Korea: Results from the CONNECT Study

Objectives: The incidence of Crohn's disease and the number of associated surgeries are increasing in Korea. This study investigated the effect of azathioprine/6-mercaptopurine (6-MP) and TNF-α antagonists on abdominal and perianal surgery in Korean patients with Crohn's disease. Design: A retrospective cohort study. Setting: Data from the Crohn's Disease Clinical Network and Cohort (CONNECT) were used. Patients with confirmed Crohn's disease between 1982 and 2008 from 32 hospitals in the Republic of Korea were enrolled. The effect of azathioprine/6-MP on abdominal and perianal surgery was analysed using logistic regression analysis adjusting for age and sex. Participants: In total, 1161 Crohn's disease patients were included in the Republic of Korea in the surgery (n = 462, male = 339, female = 123) and control groups (n = 699, male = 484, female = 215). Results: In total, 1161 patients were selected, with 462 patients who underwent abdominal (n = 245) or perianal surgery (n = 217). The preoperative usage rates of azathioprine/6-MP were 18.8% and 65.1% (p < 0.0001) in the surgery and control groups, respectively. The preoperative usage rates of TNF-α antagonists were 7.1% and 23.3% (p < 0.0001) in the surgery and control groups, respectively. A multivariate analysis revealed that the preoperative use of azathioprine/6-MP had an odds ratio of 0.094 for all surgeries (95% confidence interval [CI]: 0.070-0.127, p < 0.0001), 0.131 for abdominal surgery (95% CI: 397-1.599, p < 0.0001), and 0.059 for perianal surgery (95% CI: 0.038-0.091, p < 0.0001). The preoperative use of TNF-α antagonists had an odds ratio of 0.225 for all surgeries (95% CI: 0.151-0.335, p < 0.0001), 0.403 for abdominal surgery (95% CI: 0.261-0.623, p < 0.0001), and 0.064 for perianal surgery (95% CI: 0.026-0.160, p < 0.001). Strengths of this study: The study presents new evidence of the reduced risk of surgery following azathioprine use in Crohn's disease patients. Limitations of this study (1) This was not a controlled prospective study. (2) There was a selection bias specific to the CONNECT cohort. (3) The combination or sequential use of azathioprine/6-MP and TNF-α antagonists was not excluded. Conclusion: Azathioprine/6-MP is significantly associated with a reduced risk of abdominal and perianal surgery in Korean patients with Crohn's disease.

Thiopurine Drugs in the Treatment of Ulcerative Colitis: Identification of a Novel Deleterious Mutation in TPMT

Chronic inflammatory bowel disease (IBD) includes Crohn’s disease and ulcerative colitis. Both are characterized by inflammation of part of the digestive tract lining. Azathioprine (AZA) is a well-known immunosuppressant that has been known for many years for its ability to provide long-term disease remission in IBDs, but has important side effects, most of which are related to a single nucleotide polymorphism in the gene for thiopurine methyltransferase (TPMT), which ensures the degradation and efficacy of AZA. Since a direct correlation between TPMT gene polymorphisms and the haematological toxicity of the AZA treatment has been widely demonstrated, TPMT genotyping has been made necessary prior to any introduction of AZA. The monitoring of thiopurine metabolites presents one of the factors that limit wide adaptation of these thiopurines in clinical practice. Thus, identifying patients with asymmetric metabolism could help clinicians provide an ideal treatment recommendation to improve response and reduce adverse effects. Here, we review the role of AZA in the treatment of IBD and discuss the usefulness of TPMT genotyping to guide clinical decision-making. In addition, we report the identification of a new molecular alteration, never described, TPMT mutation affecting the TPMT activity and responsible for deleterious side effects in a clinical case of a 20-year-old woman patient.

Efficacy, safety and drug survival of thioguanine as maintenance treatment for inflammatory bowel disease: a retrospective multi-centre study in the United Kingdom

BACKGROUND

Thioguanine (TG) is a thiopurine which has been used for patients with inflammatory bowel disease (IBD), who have failed azathioprine (AZA) or mercaptopurine (MP) due to adverse events or suboptimal response. Its widespread use has been hampered due to concerns about nodular regenerative hyperplasia (NRH) of the liver. The aim of this study was to investigate the long-term efficacy and safety of low-dose TG therapy in IBD patients failing AZA and MP.

METHODS

A retrospective multicentre study was performed in IBD patients who failed prior treatment with conventional thiopurines with or without following immunomodulation (thiopurine-allopurinol, biologicals, methotrexate, tacrolimus) and were subsequently treated with TG as rescue monotherapy between 2003 and 2019 at three hospitals in the United Kingdom. Clinical response, adverse events, laboratory results, imaging and liver biopsies were retrospectively collected.

RESULTS

A total of 193 patients (57% female and 64% Crohn's disease) were included, with a median daily TG dose of 20 mg (range: 20-40 mg), a median treatment duration of 23 months (IQR 10-47) and a median follow-up of 36 months (IQR 22-53). The clinical response rate at 12 months was 65 and 54% remained on TG until the end of follow-up. Adverse events consisted primarily of elevated liver tests (6%), myelotoxicity (7%) and rash (5%). NRH was histologically diagnosed in two patients and two other patients (1%) developed non-cirrhotic portal hypertension. The median 6-TGN and TPMT levels were 953 pmol/8 × 10⁵ RBC (IQR 145-1761) and 47 mu/L (IQR 34.5-96).

CONCLUSIONS

Long-term follow-up suggests that TG can be an effective and well-tolerated therapy in more than half of difficult-to-treat and multi-therapy failing IBD patients. Findings of this study indicate that TG can be used safely and the occurrence of hepatotoxicity was low. The incidence rate of NRH was within the background incidence.

Development of a chemical probe against NUDT15

The NUDIX hydrolase NUDT15 was originally implicated in sanitizing oxidized nucleotides but was later shown to hydrolyze the active thiopurine metabolites, 6-thio-(d)GTP, thereby dictating the clinical response of this standard-of-care treatment for leukemia and inflammatory diseases. Nonetheless, its physiological roles remain elusive. Here, we sought to develop the first small-molecule NUDT15 inhibitors to elucidate its biological functions, and potentially for improving NUDT15-dependent chemotherapeutics. Lead compound TH1760, demonstrated low-nanomolar biochemical potency through direct and specific binding into the NUDT15 catalytic pocket and engaged cellular NUDT15 in the low-micromolar range. We further employed thiopurine potentiation as a proxy functional read-out and demonstrated that TH1760 sensitized cells to 6-thioguanine through enhanced accumulation of 6-thio-(d)GTP in nucleic acids. A biochemically validated, inactive structural analog, TH7285, confirmed that increased thiopurine toxicity is via direct NUDT15 inhibition. In conclusion, TH1760 represents the first chemical probe for interrogating NUDT15 biology and potential therapeutic avenues.

Thiopurines' Metabolites and Drug Toxicity: A Meta-Analysis

Many questions remain unanswered regarding therapeutic drug monitoring (TDM) utility with thiopurines. This study aims to establish a relationship between thiopurines' metabolites and drug toxicity. We performed a systematic review with inclusion of studies evaluating the relationship between thiopurines' metabolites and drug toxicity. Meta-analysis of mean difference (MD), correlations and odds ratio (OR) was performed. We identified 21,240 records, 72 of which were eligible for meta-analysis. Levels of 6-thioguanine nucleotides (6-TGN) were higher in patients with leukopenia (MD 127.06 pmol/8 × 10⁸ RBC) and gastrointestinal intolerance (MD 201.46 pmol/8 × 10⁸ RBC), and lower in patients with hepatotoxicity (MD -40.6 pmol × 10⁸ RBC). We established a significant correlation between 6-TGN and leukocytes (r = -0.21), neutrophils (r = -0.24) and alanine aminotransferase levels (r = -0.24). OR for leukopenia in patients with elevated 6-TGN was 4.63 (95%CI 2.24; 9.57). An optimal cut-off of 135 pmol/8 × 10⁸ RBC for leukopenia was calculated (sensitivity 75.4%; specificity 46.4%). 6-methylmercaptopurine ribonucleotides (6-MMPR) were significantly associated with hepatotoxicity (MD 3241.2 pmol/8 × 10⁸ RBC; OR 4.28; 95%CI 3.20; 5.71). Levels of 6-MMPR measured in the first 8 weeks of treatment were associated with leukopenia. We conclude that TDM could be used to prevent thiopurines' toxicity. As optimal metabolites level may vary according to indication, physicians may adapt posology to decrease toxicity without compromising efficacy.

NUDT15 gene variants and thiopurine-induced leukopenia in patients with inflammatory bowel disease

Thiopurine has been used to maintain remission and to reduce antidrug antibody formation in monoclonal antibody therapy in patients with inflammatory bowel disease (IBD). The use of thiopurine is limited by side effects such as leukopenia. Thiopurine S-methyltransferase (TPMT) variants are associated with thiopurine-induced leukopenia in Westerners, but the frequency of the risk alleles is low in Asians. Recently, a variant in the nudix hydrolase 15 (NUDT15) gene (R139C, c.415C > T) was reported to be associated with early severe leukopenia in Asians. NUDT15 is an enzyme that converts 6-thio-(deoxy)guanosine triphosphate (6-T(d)GTP) to 6-thio-(deoxy)guanosine monophosphate (6-T(d)GMTP). The R139C variant impairs the stability of the protein and increases incorporation of 6-TGTP and 6-TdGTP into RNA and DNA, respectively, resulting in leukopenia. The frequency of C/C, C/T, and T/T are approximately 80%, 20%, and 1%, respectively in East Asians. Early leukopenia occurred in less than 3% of patients with C/C and in around 20% of those with C/T, whereas it occurred in almost all patients with T/T. Patients homozygous for this variant also develop severe hair loss. The measurement of NUDT15 R139C can increase the safety of thiopurine dramatically and is a successful example of personalized medicine in the field of IBD.

Mycophenolate mofetil, azathioprine and tacrolimus: mechanisms in rheumatology

The introduction of biologic DMARDs into rheumatology has resulted in a substantial reduction of the burden of many rheumatic diseases. In the slipstream of the success achieved with these biologic DMARDs, some conventional immunosuppressive drugs have also found use in new indications. Notably, mycophenolate mofetil, azathioprine and tacrolimus have made their way from solid organ transplantation drugs to become useful assets in rheumatology practice. Mycophenolate mofetil and azathioprine inhibit the purine pathway and subsequently diminish cell proliferation. Both drugs have a pivotal role in the treatment of various rheumatic diseases, including lupus nephritis. Tacrolimus inhibits lymphocyte activation by inhibiting the calcineurin pathway. Mycophenolate mofetil and tacrolimus are, among other indications, increasingly being recognized as useful drugs in the treatment of interstitial lung disease in systemic rheumatic diseases and skin fibrosis in systemic sclerosis. A broad array of trials with mycophenolate mofetil, azathioprine and/or tacrolimus are ongoing within the field of rheumatology that might provide further novel avenues for the use of these drugs. In this Review, we discuss the historical perspective, pharmacodynamics, clinical indications and novel avenues for mycophenolate mofetil, azathioprine and tacrolimus in rheumatology.

Biomarkers Predictive of Response to Thiopurine Therapy in Inflammatory Bowel Disease

The complex nature of inflammatory bowel disease (IBD) often results in treatment failure for many patients. With some patients cycling through multiple therapies before achieving a sustained period of remission, the ability to predict a patient's response to therapeutics could decrease the time from active disease to clinical remission and mucosal healing. The prospect of such individualized treatment of IBD would be aided by accurate biomarkers, both fecal and serological, which have to date shown value as indicators of IBD activity. Here we review the utility of generic biomarkers for inflammation or mucosal healing, such as calprotectin, C-reactive protein (CRP), and fecal hemoglobin (fHb) as predictors of response to treatment of IBD. We further provide a deeper insight into the utility of monitoring the thiopurine treatment by thiopurine metabolites or alternative hematologic parameters. In light of multiple recent publications of biomarkers and biological therapy, our focus in this review is predicting response to thiopurine treatment only, that is, Azathioprine and 6-Mercaptopurine.

An intronic FTO variant rs16952570 confers protection against thiopurine-induced myelotoxicities in multiethnic Asian IBD patients

Thiopurines are used in the treatment of inflammatory bowel disease (IBD) but remain clinically challenging to manage due to wide interpatient variability in clinical outcomes and adverse events. Apart from genetic variants in thiopurine S-methyltransferase (TPMT) and nudix hydrolase 15 (NUDT15) genes, polymorphisms in FTO alpha-ketoglutarate dependent dioxygenase (FTO) were found predictive of thiopurine-induced leukopenia, albeit with conflicting results. To clarify the role of FTO variants in a multiethnic Asian IBD cohort, we recruited 149 patients on thiopurine-based therapy and genotyped two FTO variants p.Ala134Thr (rs79206939) and rs16952570 T > C using Sanger sequencing. FTO p.Ala134Thr (rs79206939) was non-polymorphic and absent whereas intronic rs16952570 T > C was equally prevalent in Chinese (22%) and Indians (18%) and higher in Malays (28%). Higher nadir white blood cell (WBC) and absolute neutrophil count (ANC) levels were observed in patients harboring FTO rs16952570 CC genotypes compared with TT carriers at 4, 8, and 12 weeks after start of thiopurine therapy (P < 0.05). A similar trend was observed in patients carrying the previously well-characterized NUDT15 rs116855232 wild-type CC genotypes. Further in silico analysis suggests that FTO variants linked to rs16952570, particularly rs74018601, may play a regulatory role in altering the FTO expression. The findings from this study indicate a novel protective association with the FTO variant rs16952570 CC genotype and hematological parameters.

Nucleoside diphosphate-linked moiety X-type motif 15 R139C genotypes impact 6-thioguanine nucleotide cut-off levels to predict thiopurine-induced leukopenia in Crohn’s disease patients

BACKGROUND

Thiopurine-induced leukopenia (TIL) is a life-threatening toxicity and occurs with a high frequency in the Asian population. Although nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) variants significantly improve the predictive sensitivity of TIL, more than 50% of cases of this toxicity cannot be predicted by this mutation. The potential use of the 6-thioguanine nucleotide (6TGN) level to predict TIL has been explored, but no decisive conclusion has been reached. Can we increase the predictive sensitivity based on 6TGN by subgrouping patients according to their NUDT15 R139C genotypes?

AIM

To determine the 6TGN cut-off levels after dividing patients into subgroups according to their NUDT15 R139C genotypes.

METHODS

Patients’ clinical and epidemiological characteristics were collected from medical records from July 2014 to February 2017. NUDT15 R139C, thiopurine S-methyltransferase, and 6TGN concentrations were measured.

RESULTS

A total of 411 Crohn’s disease patients were included. TIL was observed in 72 individuals with a median 6TGN level of 323.4 pmol/8 × 10⁸ red blood cells (RBC), which was not different from that of patients without TIL (P = 0.071). Then, we compared the 6TGN levels based on NUDT15 R139C. For CC (n = 342) and CT (n = 65) genotypes, the median 6TGN level in patients with TIL was significantly higher than that in patients without (474.8 vs 306.0 pmol/8 × 10⁸ RBC, P = 9.4 × 10^-5; 291.7 vs 217.6 pmol/8 × 10⁸ RBC, P = 0.039, respectively). The four TT carriers developed TIL, with a median 6TGN concentration of 135.8 pmol/8 × 10⁸ RBC. The 6TGN cut-off levels were 411.5 and 319.2 pmol/8 × 10⁸ RBC for the CC and CT groups, respectively.

CONCLUSION

The predictive sensitivity of TIL based on 6TGN is dramatically increased after subgrouping according to NUDT15 R139C genotypes. Applying 6TGN cut-off levels to adjust thiopurine therapies based on NUDT15 is strongly recommended.

Highly sensitive and rapid determination of azathioprine metabolites in whole blood lysate by liquid chromatography-tandem mass spectrometry

Individualized therapy involves genetic test of drug metabolism, which provides information about the initial dose and therapeutic drug monitoring for adjusting the subsequent dose. Consequently, toxic side effects are expected to be minimized and therapeutic effects to be maximized. In this study, an ultra-performance liquid chromatography tandem mass spectrometry method that was specific, accurate and sensitive was developed to simultaneously determine azathioprine two metabolites, 6-thioguanine nucleotides (6-TGN) and 6-methyl-mercaptopurine riboside (6-MMPr) in the whole blood lysate. We precipitated the sample by trifluoroacetic acid under the protection of dithiothreitol, with 6-MMPr and 6-TGN being hydrolyzed to produce 6-methymercaptopurine and 6-thioguanine. In the chromatographic separation, Waters ACQUITY BEH C18 (2.1 × 100 mm, 1.7 μm) chromatographic column was applied and gradient elution was conducted with 0.02 mol/L ammonium acetate buffer (which contains 0.3% formic acid) and acetonitrile at a flow rate of 0.4 ml/min. Tandem mass spectrometry in multiple reaction monitoring mode was applied for detection via electrospray ionization source in positive ionization mode. The analyzing process lasted for no more than 2 min. The calibration curve for each metabolite fitted a least squares model (weighed 1/X) from 1.25 to 5000 ng/ml (r² > 0.99). The ion pairs were detected as 6-MMP m/z 167.07 → 152.15, 6-TG m/z 168.06 → 134.13, and internal standard m/z 171.07 → 137.14. Under the guidance of FDA guidelines for bioanalytical method validation, we carried out validation and obtained satisfactory results. The method was successfully utilized for monitoring the concentrations of each metabolite from 65 affected patients who had received azathioprine maintenance therapy and achieved optimal results.

Thiopurine Therapy in Patients With Inflammatory Bowel Disease: A Focus on Metabolism and Pharmacogenetics

Thiopurines have been widely used for the maintenance of remission or steroid sparing in patients with inflammatory bowel disease. However, potential drug-related adverse events frequently interfere with their use. Indeed, drug withdrawals associated with adverse reactions have been reported in approximately 25% of patients. To balance the efficacy, safety, and tolerability of thiopurines, regular monitoring of biomarkers (complete blood cell count, liver function test, and metabolic profiles), steady dose escalation, and pretreatment thiopurine S-methyltransferase (TPMT) genotype screening have been routinely recommended. However, the complex thiopurine metabolic pathway and individual differences attributed to pharmacogenetic diversity limit the effectiveness of these strategies in the optimization of thiopurine therapy. Recently, in an effort to facilitate more accurate and personalized prediction of thiopurine response or toxicity, novel genetic markers including NUDT15 and FTO genes were discovered. These discoveries are remarkable because TPMT screening has minimal efficacy for predicting myelosuppression especially in Asian populations, despite the fact that thee populations have a higher frequency of myelosuppression than Western populations. This review focuses on the current understanding of the metabolic pathway and the pharmacogenetics of thiopurines and suggests a personalized preventive strategy against potential adverse drug reactions to optimize their therapeutic application.

Pharmacogenetics of treatments for inflammatory bowel disease

INTRODUCTION

Inflammatory bowel disease is a chronic inflammation of the gut whose pathogenesis is still unclear. Although no curative therapy is currently available, a number of drugs are used in induction and maintenance therapy; however, for most of these drugs, a high inter-individual variability in response is observed. Among the factors of this variability, genetics plays an important role. Areas covered: This review summarizes the results of pharmacogenetic studies, considering the most important drugs used and in particular aminosalycilates, glucocorticoids, thiopurines, monoclonal antibodies and thalidomide. Most studies used a candidate gene approach, even if significant breakthroughs have been obtained recently from applying genome-wide studies. When available, also investigations considering epigenetics and pharmacogenetic dosing guidelines have been included. Expert opinion: Only for thiopurines, genetic markers identified as predictors of efficacy or adverse events have allowed the development of dosing guidelines. For the other drugs, encouraging results are available and great expectations rely on the study of epigenetics and integration with pharmacokinetic information, especially useful for biologics. However, to improve therapy of IBD patients with these drugs, for implementation in the clinics of pharmacogenetics, informatic clinical decision support systems and training about pharmacogenetics of health providers are needed.