Drug rediscovery in gastroenterology: from off-label to on-label use of thioguanine in inflammatory bowel disease.

Drug rediscovery refers to the principle of using 'old' drugs outside the indications mentioned in the summary of product characteristics. In the past decades, several drugs were rediscovered in a wide variety of medical fields. One of the most recent examples is the unconditional registration of thioguanine (TG), a thiopurine derivative, in patients with inflammatory bowel disease in the Netherlands. In this paper, we aim to visualise potential hurdles that hamper drug rediscovery in general, emphasise the global need for optimal use and development of potentially useful drugs, and provide an overview of the registration process for TG in the Netherlands. With this summary, we aim to guide drug rediscovery trajectories in the near future.

A three-dimensional analysis of the development of cranial nerves in human embryos.

To increase our understanding of the etiology of specific neurological disorders (e.g., Duane syndrome, glossoptosis in Pierre Robin sequence), proper knowledge of anatomy and embryology of cranial nerves is necessary. We investigated cranial nerve development, studied histological sections of human embryos, and quantitatively analyzed the 3D reconstructions. A total of 28 sectioned and histologically stained human embryos (Carnegie stage [CS] 10 to 23 [21-60 days of development]) were completely digitalized by manual annotation using Amira software. Two specimens per stage were analyzed. Moreover, quantitative volume measurements were performed to assess relative growth of the cranial nerves. A chronologic overview of the morphologic development of each of the 12 cranial nerves, from neural tube to target organ, was provided. Most cranial nerves start developing at CS 12 to 13 (26-32 days of development) and will reach their target organ in stage 17 to 18 (41-46 days). In comparison to the rest of the developing brain, a trend could be identified in which relative growth of the cranial nerves increases at early stages, peaks at CS 17 and slowly decreases afterwards. The development of cranial nerves in human embryos is presented in a comprehensive 3D fashion. An interactive 3D-PDF is provided to illuminate the development of the cranial nerves in human embryos for educational purposes. This is the first time that volume measurements of cranial nerves in the human embryonic period have been presented.

Systematic review with meta-analysis: SARS-CoV-2 stool testing and the potential for faecal-oral transmission.

BACKGROUND: Since the start of the COVID-19 pandemic, there have been many scientific reports regarding gastrointestinal manifestations. Several reports indicate the possibility of viral shedding via faeces and the possibility of faecal-oral transmission. AIMS: To critically assess the clinical relevance of testing stool samples and anal swabs and provide an overview of the potential faecal-oral transmission of SARS-CoV-2. METHODS: A systematic literature search with MeSH terms was performed, scrutinising the Embase database, Google scholar, MEDLINE database through PubMed and The Cochrane Library, including articles from December 2019 until July 7 2020. Data were subsequently analysed with descriptive statistics. RESULTS: Ninety-five studies were included in the qualitative analysis. 934/2149 (43%) patients tested positive for SARS-CoV-2 in stool samples or anal swabs, with positive test results up to 70 days after symptom onset. A meta-analysis executed with studies of at least 10 patients revealed a pooled positive proportion of 51.8% (95% CI 43.8 - 59.7%). Positive faecal samples of 282/443 patients (64%) remained positive for SARS-CoV-2 for a mean of 12.5 days, up to 33 days maximum, after respiratory samples became negative for SARS-CoV-2. Viable SARS-CoV-2 was found in 6/17 (35%) patients in whom this was specifically investigated. CONCLUSIONS: Viral shedding of SARS-CoV-2 in stool samples occurs in a substantial proportion of patients, making faecal-oral transmission plausible. Furthermore, detection in stool samples or anal swabs can persist long after negative respiratory testing. Therefore, stool sample or anal swab testing should be (re)considered in relation to decisions for isolating or discharging a patient.

Systematic review with meta-analysis: risk factors for thiopurine-induced leukopenia in IBD.

BACKGROUND: Thiopurine-induced leukopenia, a frequently observed and potentially life-threatening adverse event, complicates the clinical management of IBD patients. AIM: To assess risk factors for thiopurine-induced leukopenia in IBD. METHODS: MEDLINE, EMBASE, BIOSIS and Cochrane library were searched for studies reporting at least one risk factor for thiopurine-induced leukopenia. Pooled odds ratio (OR) was calculated for each potential risk factor using a random effects model. Studies that were not eligible for meta-analysis were described qualitatively. RESULTS: Seventy articles were included, 34 (11 229 patients) were included in meta-analyses. A significantly higher thiopurine-induced leukopenia risk was found for TPMT (OR 3.9, 95% [CI] 2.5-6.1) and for NUDT15 R139C (OR 6.9, 95% CI 5.2-9.1), G52A (OR 3.2, 95% CI 1.3-7.9) and 36_37ins/delGGAGTC variant carriers (OR 5.6, 95% CI 2.8-11.4). A potential association between high 6-thioguanine nucleotides (6-TGN) or 6-methylmercaptopurine (6-MMP) levels and leukopenia was observed, since most studies reported higher metabolite levels in leukopenic patients (6-TGN: 204-308 (Lennard method) and 397 (Dervieux method), 6-MMP: 4020-10 450 pmol/8 x 108 RBC) compared to controls (6-TGN: 170-212 (Lennard method) and 269 (Dervieux method), 6-MMP: 1025-4550 pmol/8 x 108 RBC). CONCLUSIONS: TPMT and NUDT15 variants predict thiopurine-induced leukopenia. High 6-TGN and 6-MMP levels might induce leukopenia, although exact cut-off values remain unclear. Potential preventive measures to reduce the risk of thiopurine-induced leukopenia include pre-treatment TPMT and NUDT15 genotyping. Routine thiopurine metabolite measurement might be efficient, yet cut-off levels must be validated in advance.

Clinical Course of Nodular Regenerative Hyperplasia in Thiopurine Treated Inflammatory Bowel Disease Patients.

Nodular regenerative hyperplasia (NRH) is a poorly understood liver condition, which is increasingly recognized in thiopurine-treated patients with inflammatory bowel disease (IBD).1 It is difficult to establish an optimal approach to NRH patients, because its manifestations are highly variable (from asymptomatic to symptoms of noncirrhotic portal hypertension [NCPH]) and the prognosis is unknown.2 The aim of this study was to identify NRH cases in IBD patients treated with azathioprine, mercaptopurine, and/or thioguanine, and to describe its clinical course.

High inter-individual variability of serum xanthine oxidoreductase activity in IBD patients.

OBJECTIVES: Thiopurines play an essential role in the management of inflammatory bowel diseases (IBD, i.e. Crohn's disease and ulcerative colitis). Over the past decade, several strategies to optimize treatment with thiopurines have been evaluated, including co-administration of allopurinol, a xanthine-oxidoreductase (XO) inhibitor, to low-dose thiopurine therapy. We aimed to assess the inter-individual variability of XO-activity between IBD-patients. METHODS: We assessed XO activity in serum of IBD-patients of two medical centers in The Netherlands using the Amplex® Red Xanthine/Xanthine Oxidase Assay Kit, which measures the superoxide formation in a coupled reaction to the red-fluorescent oxidation product, resofurine. RESULTS: We observed a high inter-individual variability of XO-activity in 119 patients, with a median activity of 16 µU/ml/hour (range 1-85 µU/ml/hour). The XO-activity was influenced by gender (male 19.5 vs. female 14.0 µU/ml/hour, p < 0.01), patient's age (Pearson's correlation r = 0.21, p = 0.02) and duration of IBD (r = 0.23, p = 0.01). The XO activity was not affected by the type of IBD, smoking status, body mass index or (type of) thiopurine use (p > 0.05). CONCLUSIONS: There is a high inter-individual variability of XO-activity in IBD-patients; XO-activity is positively associated with male gender and patient's age.

Methotrexate and Thioguanine Rescue Therapy for Conventional Thiopurine Failing Ulcerative Colitis Patients: A Multi-center Database Study on Tolerability and Effectiveness.

Background: Patients with active ulcerative colitis (UC) failing conventional therapies are in need of rescue strategies. Due to the fact that accepted step-up therapy with biologicals is expensive and sometimes unavailable, alternative therapies are warranted. Methotrexate (MTX) and thioguanine (TG) have both been suggested as alternative maintenance strategies in conventional thiopurine failing UC patients. In this multicenter database study, we compared safety and effectiveness (drug-survival) of MTX and TG in UC patients. Methods: We collected data from the Parelsnoer database, a prospective Dutch national database consisting of inflammatory bowel disease patients from all university hospitals in The Netherlands. Additional data were collected from detailed chart review. Results: In total, 99 UC patients were included, of which 48 used TG, 43 used MTX, and 8 patients had a history of both TG and MTX use. In 12% of the patients, biological therapy had failed. Roughly 70% of the patients in both groups were able to continue therapy for over 1 year. Adverse events were noted in 33% of all the patients and were mainly elevated liver enzymes or gastrointestinal complaints. Twenty-eight patients (28%) continued therapy (15 TG, 13 MTX) without the need of escalation therapy (eg, corticosteroids, biologicals, or surgery). Drug survival curves of both drugs were comparable, just as the number of patients with sustained clinical benefit of therapy (P > 0.05). Conclusion: Both MTX and TG may be used and maintained as rescue therapy with sustained clinical benefit in one-third of the UC patients failing conventional therapies.

Thiopurines in Inflammatory Bowel Disease: New Findings and Perspectives.

Thiopurines, available as azathioprine, mercaptopurine, and thioguanine, are immunomodulating agents primarily used to maintain corticosteroid-free remission in patients with inflammatory bowel disease. To provide a state-of-the-art overview of thiopurine treatment in inflammatory bowel disease, this clinical review critically summarises the available literature, as assessed by several experts in the field of thiopurine treatment and research in inflammatory bowel disease.

Transient elastography to assess liver stiffness in patients with inflammatory bowel disease.

BACKGROUND: Liver injury during inflammatory bowel disease (IBD) is primarily diagnosed by liver biopsy, which has a small but serious risk of severe complications. The aim of this study was to assess liver stiffness, and subsequently the prevalence and associations of liver fibrosis in IBD patients with thiopurine therapy and other clinical factors, by using transient elastography (TE). METHODS: In this prospective, international two-center study, included IBD-patients underwent TE measurements. Laboratory results and medication reports, radiology results and historical liver biopsy results were extracted from the patient charts. RESULTS: Transient elastography results of 168 patients were presented. Moderate and severe fibrosis were detected in 4% (7/168) and 1% (1/168) of the cohort, respectively. Factors contributing to lower liver stiffness were female gender and (historical) exposure to azathioprine. Further, there was a statistical trend towards lower liver stiffness in patients using thiopurines overall (4.7 vs. 5.2kPa, p=0.07). Liver stiffness correlated positively with waist circumference, liver enzyme tests, hemoglobin and 6-methylmercaptopurine concentration and negatively with platelet count. CONCLUSION: Exposure to thiopurine therapy was not associated with higher liver stiffness, although no clinical difference in severity of fibrosis was detected. Further research should robustly determine the accuracy of TE as an evaluation of liver fibrosis in IBD patients.

Finding hidden treasures in old drugs: the challenges and importance of licensing generics.

Identifying new indications for existing drugs creates new therapeutic options while bypassing much of the costs and time involved with bringing a new drug to market. The rediscovery of a generic drug, however, is a challenging pursuit because there is no formal regulatory approach and a lack of economic interest by pharmaceutical companies. This played a part in the re-registration of thioguanine as a rescue drug for the treatment of patients with inflammatory bowel disease in The Netherlands. In this article, we aim to underline the importance of drug rediscovery, the difficulties of this procedure in Europe and we attempt to suggest conceivable solutions.

Analytical Pitfalls of Therapeutic Drug Monitoring of Thiopurines in Patients With Inflammatory Bowel Disease.

The use of thiopurines in the treatment of inflammatory bowel disease (IBD) can be optimized by the application of therapeutic drug monitoring. In this procedure, 6-thioguanine nucleotides (6-TGN) and 6-methylmercaptopurine (6-MMP) metabolites are monitored and related to therapeutic response and adverse events, respectively. Therapeutic drug monitoring of thiopurines, however, is hampered by several analytical limitations resulting in an impaired translation of metabolite levels to clinical outcome in IBD. Thiopurine metabolism is cell specific and requires nucleated cells and particular enzymes for 6-TGN formation. In the current therapeutic drug monitoring, metabolite levels are assessed in erythrocytes, whereas leukocytes are considered the main target cells of these drugs. Furthermore, currently used methods do not distinguish between active nucleotides and their unwanted residual products. Last, there is a lack of a standardized laboratorial procedure for metabolite assessment regarding the substantial instability of erythrocyte 6-TGN. To improve thiopurine therapy in patients with IBD, it is necessary to understand these limitations and recognize the general misconceptions in this procedure.

Nodular regenerative hyperplasia rarely leads to liver transplantation: A 20-year cohort study in all Dutch liver transplant units.

BACKGROUND: Nodular regenerative hyperplasia is an uncommon liver condition associated with several autoimmune disorders and drugs. The clinical symptoms of nodular regenerative hyperplasia vary from asymptomatic to severe complications of portal hypertension (nodular regenerative hyperplasia-syndrome). OBJECTIVE: The purpose of this study was to identify the prognosis and optimal management, as well as the role of liver transplantation, in nodular regenerative hyperplasia. METHODS: The pathology databases of all three Dutch liver transplant units were retrospectively scrutinised for explanted livers diagnosed with nodular regenerative hyperplasia or without clear diagnosis. Pre- and post-transplantation clinical, biochemical, radiological and histological information was obtained from electronic and paper records. RESULTS: In total, 1886 patients received a liver transplant. In 255 patients, nodular regenerative hyperplasia could not be excluded. After detailed chart review, the native livers of 11 patients (0.6%) (82% male, median age: 44 years) displayed nodular regenerative hyperplasia. Seven patients (64%) had underlying disorders or drug exposure which possibly caused nodular regenerative hyperplasia. Laboratory and imaging abnormalities were present in all patients but did not contribute to the diagnosis of nodular regenerative hyperplasia. Five-year survival was 73% (median follow-up: four years, range: 2-248 months). CONCLUSION: Nodular regenerative hyperplasia is a rare finding in patients, predominantly young males, transplanted for end-stage liver disease with unknown aetiology. Nonetheless, liver transplantation may have an important role in end-stage nodular regenerative hyperplasia-syndrome.

Optimizing Thiopurine Therapy in Inflammatory Bowel Disease Among 2 Real-life Intercept Cohorts: Effect of Allopurinol Comedication?

BACKGROUND: Thiopurines (azathioprine and mercaptopurine) are frequently used immunosuppressive drugs to maintain remission in patients with inflammatory bowel disease. Half of the conventional thiopurine-derivative users have to discontinue treatment within 5 years, mainly because of intolerable adverse events. Over recent years, different strategies to optimize thiopurine treatment were suggested, yet, studies describing the clinical effectiveness of these strategies remain scarce. The aims of this study were to compare tolerability and sustained clinical benefit of conventional thiopurine derivatives therapy among two 5-year real-life intercept cohorts and to assess the clinical value of specifically allopurinol cotherapy. METHODS: In this retrospective single-center cohort study, we analyzed data from patients in whom weight-based thiopurine monotherapy was initiated between 2005 and 2009 (cohort 1) or between 2010 and 2014 (cohort 2). The initiation of the second cohort was synchronic to the start of allopurinol-based optimization in our center. Optimization strategies were extracted from patient charts. RESULTS: In total, 105 patients were included (60 in cohort 1, and 45 in cohort 2). Metabolite measurement was performed in 37% versus 84% of the patients (P < 0.001). Subsequent optimization strategies were applied in 33% versus 58% of the patients because of inadequate metabolite concentrations, intolerance, or ineffectiveness (P = 0.01). Allopurinol was coadministered to therapy in 18 patients (40%) in the second cohort. Therapy was switched to thioguanine in 11 versus 6 patients (P > 0.05). Overall, total duration was longer in the second cohort (10.8 versus 34.1 months, P < 0.001). The number of ongoing thiopurine users (20% versus 49%) and sustained clinical benefit (13% versus 38%) were higher in the second cohort (both P < 0.05). This was mainly because of a decrease in hepatotoxicity after optimization (P < 0.01). CONCLUSIONS: Optimization of thiopurine therapy by the use of therapeutic drug monitoring with subsequent administration of allopurinol cotherapy successfully enhanced sustained clinical benefit and tolerability in patients with inflammatory bowel disease.

Pharmacology of Thiopurine Therapy in Inflammatory Bowel Disease and Complete Blood Cell Count Outcomes: A 5-Year Database Study.

BACKGROUND: Thiopurines are the prerequisite for immunomodulation in inflammatory bowel disease (IBD) therapy. When administered in high (oncological) dose, thiopurine metabolites act as purine antagonists, causing DNA-strand breakage and myelotoxicity. In lower IBD dosages, the mode of action is primarily restricted to anti-inflammatory effects. Then, myelosuppression and hepatotoxicity are the most common adverse events of thiopurines. The aim of this study was to assess the effect of thiopurine metabolites on hematologic and hepatic parameters and to determine which patient characteristics are related to generation of thiopurine metabolites. METHODS: The authors scrutinized the therapeutic drug monitoring database of the VU University medical center and subsequently merged this database with the Clinical Laboratory database of our hospital covering the same time period (2010-2015). RESULTS: The authors included 940 laboratory findings of 424 unique patients in this study. Concentrations of 6-thioguanine nucleotides (6-TGN) correlated negatively with red blood cell count, white blood cell count, and neutrophil count in both azathioprine (AZA) and mercaptopurine users. There was a positive correlation with mean corpuscular volume. In patients using 6-thioguanine, 6-TGN concentrations correlated positively with white blood cell count. Furthermore, there was an inverse correlation between patient's age and 6-TGN concentrations in patients using AZA or 6-thioguanine, and we observed an inverse correlation between body mass index and 6-TGN concentrations in patients using AZA or mercaptopurine. No relations were observed with liver test abnormalities. CONCLUSIONS: Thiopurine derivative therapy influenced bone marrow production and the size of red blood cells. Age and body mass index were important pharmacokinetic factors in the generation of 6-TGN.

6-methylmercaptopurine-induced leukocytopenia during thiopurine therapy in inflammatory bowel disease patients.

BACKGROUND AND AIM: Thiopurines have a favorable benefit-risk ratio in the treatment of inflammatory bowel disease. A feared adverse event of thiopurine therapy is myelotoxicity, mostly occurring due to toxic concentrations of the pharmacologically active metabolites 6-thioguaninenucleotides. In oncology, myelosuppression has also been associated with elevated 6-methylmercaptopurine (6-MMP). In this case series, we provide a detailed overview of 6-MMP-induced myelotoxicity in inflammatory bowel disease patients. METHODS: We retrospectively scrutinized pharmacological laboratory databases of five participating centers over a 5-year period. Patients with leukocytopenia at time of elevated 6-MMP levels (>5700 pmol/8 × 108 red blood cells) were included for detailed chart review. RESULTS: In this case series, we describe demographic, clinical, and pharmacological aspects of 24 cases of 6-MMP-induced myelotoxicity on weight-based thiopurine therapy with a median steady-state 6-MMP level of 14 500 pmol/8 × 108 red blood cells (range 6600-48 000). All patients developed leukocytopenia (white blood cell count 2.7 ± 0.9 × 109 /L) after a median period of 11 weeks after initiation of thiopurine therapy (interquartile range 6-46 weeks). Eighteen patients (75%) developed concurrent anemia (median hemoglobin concentration 6.9 × 109 /L), and four patients developed concurrent thrombocytopenia (median platelet count 104 × 109 /L). Leukocytopenia resolved in 20 patients (83%) within 4 weeks upon altered thiopurine treatment regimen, and white blood cell count was increasing, but not yet normalized, in the remaining four patients. CONCLUSION: We observed that thiopurine-induced myelotoxicity also occurs because of (extremely) high 6-MMP concentrations in patients with a skewed thiopurine metabolism. Continued treatment with adapted thiopurine therapy was successful in almost all patients.