Clinical pharmacists' knowledge, attitude, perception, and beliefs about the role of pharmacogenetic testing for genes polymorphisms when prescribing mercaptopurine

Background

Single nucleotide polymorphisms in the gene encoding proteins involved in mercaptopurine metabolism can influence drug efficacy and safety. This study aims to assess clinical pharmacists' knowledge about mercaptopurine-related genes and their polymorphisms and investigate their attitudes, perceptions, and beliefs about the need for and importance of pharmacogenetic testing for mercaptopurine.

Methods

A cross-sectional descriptive study was conducted among oncology/hematology clinical pharmacists in Saudi Arabia using an online-questionnaire developed by experts in the field. The questionnaire consists of four-sections exploring clinical pharmacists' knowledge, attitudes, perceptions, and beliefs about the importance of gene testing and genes polymorphism when prescribing mercaptopurine. Descriptive statistics were used to analyze the data in the study.

Results

A total of 41 oncology/hematology clinical pharmacists responded to the survey invitation. Almost half of them had more than 10 years of work experience, but only 17 % of them received formal training in pharmacogenetics. The overall level of knowledge about pharmacogenetics among participants was low, with a mean score of 2.8 points (1.7) out of 8 items. However, around 76 % agreed that it is important to perform pharmacogenetic screening prior to prescribing mercaptopurine, and almost 93 % state that it will influence their dosage recommendation. Most of the participants had a good perception (95.1 %) of their role in genetic testing for medication selection, dosing, and monitoring; however, about 10 % of surveyed pharmacists reported not being completely responsible about recommending pharmacogenetic testing. The surveyed pharmacists had a good belief in the importance of pharmacogenetic testing and their overall attitude was positive toward the use of pharmacogenetic testing, with emphasis on the importance of training on the proper assessment and interpretation of pharmacogenetic tests.

Conclusions

Pharmacists demonstrated good perception and positive attitude toward pharmacogenetic testing, despite the low level of knowledge and limited formal training. Thus, more attention to developing national guidelines on pharmacogenetic testing is warranted to ensure successful pharmacogenetic testing implementation.

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.

Thiopurines exert harmful effects on spermatogenesis in Nudt15R138C knock-in mice

BACKGROUND

The association between thiopurine use and testicular reproductive functions remains unclear. In this study, we investigated whether thiopurines affect testicular functions based on the NUDT15 genotypes using Nudt15R138C knock-in mice.

METHODS

The male Nudt15R138C knock-in mice (9-12 weeks) were treated with mercaptopurine (MP: 0.5 mg/kg/day) for 4 or 12 weeks. To examine reversibility, some mice were maintained for a further 12 weeks under MP-free condition.

RESULTS

After MP treatment for 4 weeks, Nudt15R138C/R138C mice exhibited a significant reduction of testis weight compared to Nudt15+/+ mice and Nudt15+/R138C mice. The epithelial height and diameter of seminiferous tubules were significantly reduced in Nudt15R138C/R138C mice compared to Nudt15+/+ and Nudt15+/R138C mice. Apoptotic cells were significantly increased in Nudt15R138C/R138C mice, and most of apoptotic cells were spermatogonia. There were no significant changes in sperm counts and sperm morphology in MP-treated Nudt15R138C/R138C mice after 4-week MP treatment. On the other hand, after MP treatment for 12 weeks, the Nudt15+/R138C mice, but not Nudt15+/+ mice, exhibited a significant reduction in the testis weight and atrophic changes of seminiferous tubules, but these changes disappeared after 12-week rearing under MP-free condition. Despite a significant increase in abnormal sperm rate, there were no changes in the ability to conceive. No differences in serum levels of follicle-stimulating hormone or testosterone were observed between MP-treated Nudt15+/R138C and Nudt15+/+ mice after 12-week MP treatment.

CONCLUSIONS

Thiopurines exert harmful effects on testicular reproductive function according to host NUDT15 genotypes.

Chemotherapeutic metabolism presenting as a recalcitrant case of hand-foot syndrome and mucositis

INTRODUCTION

Mercaptopurine (6MP) and methotrexate (MTX) are commonly used for maintenance chemotherapy for acute lymphoblastic leukemia (ALL). These medications have been associated with various side effects such as myelosuppression, colitis, and thyroiditis in addition to numerous cutaneous adverse events. Cutaneous side-effects most reported include mucositis, alopecia, xerosis, and pruritus. We report an interesting case of hand-foot syndrome to 6MP in a child on maintenance therapy for B-cell ALL from an alteration in medication metabolism.

CASE

We report a 10-year-old male on maintenance chemotherapy for pre-Bcell ALL who presented to the hospital with worsening oral lesions and erythematous, fissured plaques on the palms and soles. Maintenance therapy consisted of IV vincristine and 5-day pulse of steroids every 12 weeks, daily 6MP, and weekly MTX, which were increased to  ≥ 150% of standard dosing due to persistent absolute neutrophil counts  > 1500. Metabolites obtained on admission demonstrated elevated 6MMP metabolites at 35,761 (normal < 5700). TPMT and NUDT15 enzyme activity were normal and no alterations in genotyping were discovered.

OUTCOME

Patient's oral chemotherapy, including both 6MP and MTX, were stopped and allopurinol 100 mg daily was initiated, which lead to overall improvement.

DISCUSSION

Clinical findings of acute mucositis and worsening of hand-foot syndrome, in the setting of inadequate myelosuppression in a child on maintenance therapy for ALL should raise concerns to consider altered metabolism pathway leading to toxic metabolite buildup. Allopurinol can play in improving cutaneous manifestation and chemotherapeutic dosing in patients with altered metabolism.

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.

Quantification of Thiopurine Metabolites in Human Erythrocytes by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

The thiopurine drugs, azathioprine, mercaptopurine, and thioguanine, are widely used in the treatment of several malignant and nonmalignant diseases. These inactive prodrugs undergo extensive metabolism to form active cytotoxic metabolites, which act mainly by incorporating into DNA and affecting cell replication. Thiopurine methyltransferase is a highly variable cytosolic enzyme that catalyzes the S-methylation of the thiopurine bases-an inactivating pathway. Patients with low-activity variants of TPMT can be affected by pronounced pharmacologic effects when receiving thiopurine medications. Clinical studies have reported significant interpatient variability in intracellular thiopurine metabolite concentrations in patients receiving thiopurine therapy. In this chapter, we present an LC-MS/MS method to monitor the thiopurine metabolites: 6-thioguanine nucleotides and 6-methylmercaptopurine derivatives in human erythrocytes. This method utilizes acid hydrolysis to release the bases and improves upon previously published procedures by utilizing stable isotope internal standards and a more efficient chromatographic separation.

Evaluation of tolerance to mercaptopurine in patients with inflammatory bowel disease and gastrointestinal intolerance to azathioprine

BACKGROUND

Thiopurines such as azathioprine (AZA) and mercaptopurine (MP) are commonly utilized to treat inflammatory bowel disease (IBD). Their use is frequently restricted due to gastrointestinal intolerance (GI). Previous retrospective studies have reported that AZA-intolerant patients may benefit from a switch to MP; yet the effectiveness of this strategy has not been prospectively evaluated.

AIMS

To assess GI tolerance to MP in patients who are intolerant to AZA, and to identify clinical predictors of GI intolerance to AZA or MP.

METHODS

A prospective, observational, single-cohort study was performed in 92 thiopurine-naïve IBD patients. They were started on a 50mg dose of AZA and escalated to 2.5mg/kg per day by week 2. Those with GI intolerance were rechallenged with a 50% dose of AZA, after which another dose escalation attempt was made. If symptoms persisted, they were switched to MP.

RESULTS

Thirty (32.6%) of the recruited patients suffered from GI intolerance to AZA. Of these, 15 did not present recurrence of symptoms after rechallenge with lower doses. Of 15 intolerant patients, 14 were switched to MP. Within the MP cohort, 8 patients (57%) were also intolerant to MP, 5 (36%) had no symptoms, and 1 (7%) was lost to follow-up. Female gender was the only independent predictor of GI intolerance to AZA.

CONCLUSIONS

Up to half of the AZA-intolerant patients tolerated a 50% dose rechallenge that was successfully escalated. A switch to MP was tolerated in over a third of cases whom rechallenge failed. Our strategy (challenge-rechallenge-switch) achieved an overall GI tolerance to thiopurines in most of the patients.

Microbiome changes involves in mercaptopurine mediated anti-inflammatory response in acute lymphoblastic leukemia mice

BACKGROUND

Inflammasome has been reported to play an important role in the pathogenesis and progression of hematologic malignancies. As one of the backbone drugs for treating acute lymphoblastic leukemia (ALL), the anti-inflammatory effect of mercaptopurine (6-MP) and the impact of gut microbiome changes caused by 6-MP on anti-inflammasome remain unclear.

OBJECTIVE

We aimed to explore the association between 6-MP therapeutic effects and microbiome-involved inflammatory responses in ALL mice models.

STUDY DESIGN

ALL murine model was built by i.v. injecting murine L1210 cells into DBA/2 mice (model group). Two weeks after cell injections, 6-MP was orally administrated for 14 days (6-MP group). Fecal samples of mice were collected at different time points. Cecum short-chain fatty acids (SCFAs) concentrations were determined by LC-MS/MS method. Serum cytokines were measured using a cytometric bead array. Gut microbiota composition in mice was explored using 16S rRNA gene sequencing.

RESULTS

The anti-tumor effect of 6-MP was proved in ALL mice models. The levels of pro-inflammatory factors IL-6 and TNFα significantly decreased after the administration of 6-MP. Cecum contents' acetate, propionate, and butyrate levels were negatively correlated with IL-6 (correlation coefficient: acetate, -0.24; propionate, -0.26; butyrate, -0.17) and TNFα (correlation coefficient: acetate, -0.45; propionate, -0.42; butyrate, -0.31) changes. Relative abundance changes of f_Lachnospiraceae.g_ASF356 and f_Peptococcaceae.g_uncultured were in accordance with the changes of butyrate levels and opposite to the changes of pro-inflammatory levels.

CONCLUSION

The anti-inflammatory response of 6-MP influenced by intestinal microbiota and its metabolites SCFAs, especially butyrate, played an essential role in improving ALL progression.

Combination Therapy With Immunomodulators Improves the Pharmacokinetics of Infliximab But Not Vedolizumab or Ustekinumab

BACKGROUND AND AIMS

The aim of this study was to assess how 6-thioguanine nucleotide (6-TGN) levels and use of oral methotrexate relate to the pharmacokinetics of biologics.

METHODS

This was a prospective cohort study including patients with inflammatory bowel diseases on maintenance doses of infliximab, vedolizumab, or ustekinumab on monotherapy or combination with a thiopurine or oral methotrexate. We collected 6-TGN concentrations, biomarker levels, and clinical and endoscopic disease activity. The primary outcomes were infliximab, vedolizumab, and ustekinumab concentrations as well as anti-drug antibodies (ADAs).

RESULTS

A total of 369 patients were recruited (113 infliximab, 133 vedolizumab, and 123 ustekinumab). Patients with 6-TGN levels ≥146 pmol per 8 × 108 red blood cells (RBCs), and those receiving combination therapy with thiopurine or oral methotrexate had significantly higher infliximab concentrations when compared with monotherapy (median levels of 17.4 μg/mL on thiopurine with 6-TGN ≥146 pmol per 8 × 108 RBCs, 17.1 on methotrexate, and 3.9 on infliximab monotherapy; P = .001 for both comparisons). However, there was no association between the use of immunomodulators and 6-TGN concentrations with vedolizumab (median levels of 8.8 on thiopurine with 6-TGN ≥152 pmol per 8 × 108 RBCs, 6.8 on methotrexate, and 10.5 on vedolizumab monotherapy; P > .05 for both comparisons) or ustekinumab median concentrations (median levels of 5.0 on thiopurine with 6-TGN ≥154 pmol per 8 × 108 RBCs, 5.2 on methotrexate and 7.0 on ustekinumab monotherapy; P > .05 for both comparisons). Fourteen (12%) patients had anti-infliximab antibodies, while 1 patient had ADAs in each of the other drug cohorts.

CONCLUSIONS

Achieving higher 6-TGN levels or the use of methotrexate improved the pharmacokinetics of infliximab. Conversely, these data do not support the use of combination therapy to augment pharmacokinetics with vedolizumab or ustekinumab.

Theoretical study of the binding mechanism between anticancerous drug mercaptopurine and gold nanoparticles using a cluster model

CONTEXT

Mercaptopurine is an effective anticancer medicine yet known with serious adverse reactions, thus requiring further attempts to enhance its biological targeting. Small gold clusters Aun (n = 2-10) were used as model reactants to simulate the surface of gold nanoparticles. The computed results show that the drug molecules tend to anchor on the gold clusters at the S atom with the associated binding energies varying from -50 to -34 kcal mol-1 (in vacuum) and from -42 to -28 kcal mol-1 (in aqueous solution). Furthermore, the adsorption of the drug onto the gold surface is considered as a reversible process, and the mechanism of drug releasing was found to be triggerable by internal factors, such as a pH change or the concentrated presence of thiol amino acids in cancerous protein structures.

METHOD

Calculations based on density functional theory (DFT) were performed to probe the nature of interactions between the drug and gold nanoparticles. Structural features, thermodynamic parameters, bonding characteristics, and electronic properties of the resulting complexes were investigated at the PBE//cc-pVTZ/cc-pVDZ-PP level.

Azathioprine and 6-mercaptopurine-induced intrahepatic cholestasis of pregnancy: Case report and review of the literature

OBJECTIVE

Azathioprine, a prodrug of 6-mercaptopurine (6-MP), is used in the treatment of inflammatory bowel disease and may be continued during pregnancy. Acute cholestatic liver injury has been reported to occur with azathioprine. We aimed to examine azathioprine related cholestasis effect on pregnancy complications and outcome.

CASE REPORT

We present a unique case of 6-MP-induced severe intrahepatic cholestasis of pregnancy (ICP) that required meticulous combined therapy including plasma exchange. The symptoms resolved following 6-MP withdrawal. A literature review revealed 11 pregnancies complicated by early-induced severe ICP among women treated with azathioprine or 6-MP.

CONCLUSION

We recommend weekly bile acid level tests for pregnant women treated with azathioprine or 6-MP, beginning early in the second trimester of pregnancy, and the prompt discontinuation of treatment upon establishment of an ICP diagnosis.

ITPA Polymorphisms and the Incidence of Toxicities in Children with Acute Lymphoblastic Leukemia

Background

6-Mercaptopurine (6-MP), a thiopurine agent, is a essential medication for treating pediatric acute lymphoblastic leukemia (ALL). However, its side effects of neutropenia and hepatotoxicity might interrupt treatment, resulting in poor outcomes. Inosine triphosphate pyrophosphatase (ITPA), an enzyme in the thiopurine pathway, may prevent the accumulation of toxic thiopurine metabolites. Studies on ITPA and thiopurine-associated toxicities are scarce.

Methods

This study retrospectively investigated 1- to 15-year-old children with ALL who received 6-MP during the maintenance phase of treatment between 2000 and 2020. Toxicity during the first year of maintenance therapy and the mean dose of 6-MP were analyzed.

Results

The 209 patients had a median age of 4.8 (0.3-14.8) years. Of these, 124 patients (59.3%) had wild-type ITPA, 73 patients (34.9%) had heterozygous ITPA 94C>A (hetITPA), and 12 patients (5.7%) had homozygous ITPA 94C>A (homITPA), with an allele frequency of 0.23. The incidence of neutropenia among ITPA polymorphisms did not significantly differ (P = 0.813). In patients harboring homITPA, transaminitis was more frequent than other polymorphisms but without a significant difference (P = 0.063). The mean dose of 6-MP for patients with homITPA was significantly lower than that for patients with hetITPA or wild-type ITPA (P = 0.016).

Conclusions

HomITPA had a higher incidence of transaminitis and required a significantly larger dose reduction of 6-MP than wild-type ITPA. Further study is warranted to elucidate the effects of ITPA polymorphisms on toxicity in patients with ALL treated with 6-MP.

Anti-inflammation and anti-aging mechanisms of mercaptopurine in vivo and in vitro

Skin is the biggest organ of the human body, which easily gets irritated by exposure to the sun. Skin photoaging and acute photodamage are caused by intense UV-B radiation. Therefore, it is imperative to find new compounds to prevent skin damage and aging. Mercaptopurine is an immunologic agent commonly used for treating Acute lymphoblastic leukemia and inflammatory bowel disease. The beneficial effects of mercaptopurine on the skin have not been reported, and its intrinsic mechanism of action is unclear. Therefore, this study was to explore mercaptopurine when exposed to UV-B radiation in HacaT cells and C57BL6 mice aging and damage effects. The model of in vivo UV-B-induced skin damage and skin photoaging was established, and the impact of mercaptopurine on cell and animal skin was studied. The study found that mercaptopurine, on the one hand, inhibits cellular and animal senescence. On the other, it inhibits the expression of mitogen-activated protein kinase (MAPK) and the nuclear factor κB (NF-κB), which are important signaling molecules in the early UV-B reaction signaling pathway. In addition, mercaptopurine downregulates matrix metalloproteinase expression, increases collagen fiber content, and facilitates collagen synthesis. Treatment with mercaptopurine also inhibits the expression of inflammatory factors and reduces inflammatory cell infiltration of the skin. In conclusion, our study elucidates mercaptopurine's anti-photoaging and anti-inflammatory activity in cellular and animal models.

Risk Prediction and Comparative Efficacy of Anti-TNF vs Thiopurines, for Preventing Postoperative Recurrence in Crohn's Disease: A Pooled Analysis of 6 Trials

BACKGROUND & AIMS

The superiority of anti-TNF-α agents to thiopurines for the prevention of postoperative recurrence of Crohn's disease (CD) after ileocolonic resection remains controversial. In this meta-analysis of individual participant data (IPD), the effect of both strategies was compared and assessed after risk stratification.

METHODS

After a systematic literature search, IPD were requested from randomized controlled trials investigating thiopurines and/or anti-TNF-α agents after ileocolonic resection. Primary outcome was endoscopic recurrence (ER) (Rutgeerts score ≥i2) and secondary outcomes were clinical recurrence (Harvey-Bradshaw Index/Crohn's Disease Activity Index score) and severe ER (Rutgeerts score ≥i3). A fixed effect network meta-analysis was performed. Subgroup effects were assessed and a prediction model was established using Poisson regression models, including sex, smoking, Montreal classification, CD duration, history of prior resection and previous exposure to anti-TNF-α or thiopurines.

RESULTS

In the meta-analysis of IPD, 645 participants from 6 studies were included. In the total population, a superior effect was demonstrated for anti-TNF-α compared with thiopurine prophylaxis for ER (relative risk [RR], 0.52; 95% confidence interval [CI], 0.33-0.80), clinical recurrence (RR, 0.50; 95% CI, 0.26-0.96), and severe ER (RR, 0.41; 95% CI, 0.21-0.79). No differential subgroup effects were found for ER. In Poisson regression analysis, previous exposure to anti-TNF-α and penetrating disease behavior were associated with ER risk. The advantage of anti-TNF-α agents as compared with thiopurines was observed in low- and high-risk groups.

CONCLUSIONS

Anti-TNF-α is superior to thiopurine prophylaxis for the prevention of endoscopic and clinical postoperative CD recurrence after ileocolonic resection. The advantage of anti-TNF-α agents was confirmed in subgroup analysis and after risk stratification.

Theoretical evaluation of poly(amidoamine) dendrimers with different peripheral groups as a purinethol drug delivery system in aqueous medium

In this work, density functional theory calculations were used to study the association of PUR with amine- and acetyl-terminated PAMAM dendrimers considering implicit solvent effect at neutral and low pH conditions. Frontier molecular orbitals' analysis indicates that the electronic properties of dendrimers are extremely sensitive to the presence of PUR molecule at both neutral and low pH conditions. Encapsulation of PUR molecule into the both amine- and acetyl-terminated PAMAM dendrimers leads to a Gibbs free energy of (ΔG) - 20.25 kcal.mol^-1 at physiological pH. The corresponding ΔG values reduce to the - 1.45 and - 0.91 kcal.mol^-1 at low pH, indicating that the drug molecule is released easily at low pH. The calculated recovery times for amine- (3.87 ×10² and 3.87 ×10², at neutral and low pH, respectively) and acetyl-terminated (5.34 ×10¹⁰ and 1.81 ×10^-1, at neutral and low pH, respectively) dendrimers suggest that acetylation can improve the release pattern of drug molecule.

Adsorption of a thione derivative on carbon, AlN, and BN nanotubes: a detailed DFT and MD investigation

The performance of nanotubes (NT) of carbon (CC), aluminium-nitrogen (AlN), and boron-nitrogen (BN) as a sensor and nanocarrier for mercaptopurine (MCP) was investigated by means of a theoretical approach. The calculated negative values of adsorption energy showed the interaction and adsorption of MCP. Highest-occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO) distributions were only found on the NT counter portion of the drug-nanotube not on MCP for AlN-NT and BN-NT while HOMO is over MCP and LUMO is over NT for CC-NT. The polarizability of MCP-NTs is greater than that of MCP. Raman wavenumbers of MCP are enhanced in NTs, and hence, NTs can act as a sensor for the detection of MCP. Solvent dependency on adsorption behaviour is also presented in the manuscript, where we found that the AlN nanotube showed exceptionally high free energy of adsorption over other nanotubes in all solvent mediums. Solvation-free energies were also reported. Noncovalent interaction scattered plot also showed significant intermolecular interaction between AlN nanotubes and the mercaptopurine when compared to other nanotubes under study. To find the antiviral activity of MCP and MCP-NTs against antiviral activities, docking and molecular dynamics simulations were performed with 1HMP PDB. Recovery times show that MCP desorption occurs quickly. The MD simulations and docking results show that BN and CC-NTs with MCP show good activity as drug carriers.

Analysis of mono-, di-, and triphosphates of thioguanosine and methylthioinosine in children with acute lymphoblastic leukemia by LC-MS/MS

Mercaptopurine (6-MP) is an indispensable, first-line, drug in the treatment of pediatric acute lymphoblastic leukemia (ALL). However, 6-MP has several intrinsic drawbacks, such as large individual variability in the drug response, undesirable adverse reactions, and drug resistance in patients with release ALL, which requires therapeutic drug monitoring (TDM). Several studies analyzed the total concentration of thiopurine nucleotides in red blood cells (RBCs) after hydrolysis, and two studies detected them separately and accurately by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this study, we developed a rapid and robust LC-MS/MS method for simultaneous quantitation of mono-, di-, and triphosphates of thioguanosine and methylthioinosine. Not only EDTA and DTT were added, but also EHT1864, a new Rac family small GTPases inhibitor, was innovatively added to ensure the stability of the analytes. Commercial availability and relatively low cost compound methotrexate-D3 was selected as internal standards. The linearity, accuracy, precision, recovery, matrix effect and stability of the method were all in line with the guidelines. This method provide an accurate and robust new solution for the determination of 6 metabolites of MP in RBCs from ALL patients with maintenance therapy.

[Pharmacogenomics in hematological malignancy]

Therapeutic response and drug-induced toxicity have been reported to be associated with genetic variants of drug-metabolizing enzymes and transporters. Recently, new causative variants associated with drug response have been reported by genome-wide association studies (GWASs). Additionally, therapeutic response has been predicted using a model of multiple single-nucleotide polymorphisms. In acute lymphoblastic leukemia (ALL), the genetic variants of NUDT15 associated with therapeutic response to 6-mercaptopurine (6-MP) have been reported by GWASs, and the frequency of NUDT15 variants was higher in Asians. Then, several reports on NUDT15 genetic variants associated with 6-MP-induced toxicities and the tolerable doses and outcomes of 6-MP therapy for ALL have been published in Asian countries. The drugs used in treating hematological malignancies have reported new genetic variants associated with its therapeutic response. However, the association between these genetic variants has not been validated in other populations. Here, we reviewed recent reports on the association between the genetic variants and response to drugs used in treating hematological malignancies, such as 6-MP, cytarabine, methotrexate, and vincristine.

The association between pre-colectomy thiopurine use and risk of neoplasia after ileal pouch anal anastomosis in patients with ulcerative colitis or indeterminate colitis: a propensity score analysis

BACKGROUND

The risk of neoplasia of the pouch or residual rectum in patients with ulcerative colitis (UC) who undergo total proctocolectomy (TPC) with ileal pouch anal anastomosis (IPAA) is incompletely investigated. Thiopurine use is associated with a reduced risk of colorectal neoplasia in patients with UC. We tested the hypothesis that thiopurine use prior to TPC may be associated with a reduced risk of primary neoplasia after IPAA.

METHODS

We conducted a retrospective cohort analysis of patients from a tertiary referral center from January 2008 to December 2017. Eligible patients with UC or IC underwent TPC with IPAA and had at least two pouchoscopies with biopsies ≥ 6 months after surgery. Propensity score analysis was conducted to match thiopurine exposed vs unexposed groups based on clinical covariates. Multivariable Cox regression analysis estimated the risk of neoplasia.

RESULTS

A total of 284 patients with UC or IC (57.4% male, median age 35.6 years) were analyzed. Ninety-seven patients (34.2%) were confirmed to have thiopurine exposure ≥ 12 weeks immediately prior to TPC ("exposed") and 187 (65.8%) were confirmed to have no thiopurine exposure for at least 365 days prior to TPC ("non-exposed"). Compared to non-exposed patients, patients with thiopurine exposure less often had dysplasia (7.2% vs 23.0%, p = 0.001) and had lower grades of dysplasia before colectomy. After IPAA, patients with neoplasia were older (44.0 vs 34.8 years, p = 0.03), more likely to have had dysplasia as colectomy indication (44.4% vs 15.4%, p = 0.007), and more likely to require pouch excision (55.6% vs 10.2%, p < 0.0001), compared to patients without neoplasia. On propensity-matched cohort analysis, no factors were significantly associated with risk of primary neoplasia.

CONCLUSION

Thiopurine exposure for at least the 12 weeks prior to TPC in patients with UC or IC does not appear to be independently associated with risk of primary neoplasia following IPAA.

Adsorption behavior of mercaptopurine and 6-thioguanine drugs on the B12N12, AlB11N12 and GaB11N12 nanoclusters, a comparative DFT study

Lately, drug delivery systems established on nanostructures have become the most proficient to be studied. There are different studies suggested that the BN nanoclusters can be used as drug carriers and transport drugs in the target cell. Therefore, the interactions and adsorption behavior of Mercaptopurine (MC) and 6-thioguanine (TG) as anti-cancer drugs on the B₁₂N₁₂ (BN), AlB₁₁N₁₂ (AlBN) and GaB₁₁N₁₂ (GaBN) nanoclusters were studied by density functional theory (DFT) and quantum mechanics atoms in molecules (QMAIM) methods to find a new drug delivery system. Our results showed strong adsorption obtained in BN-MC/TG and AlBN-MC/TG complexes can be decomposed by the BN and AlBN indicating that these nanostructures are not suitable in drug efficiency of MC and TG drugs. Unlike the BN and AlBN nanoclusters, GaBN significantly makes the MC and TG drugs adsorption energetically favorable. The high solvation energy of GaBN when interacting with MC and TG drugs led it to applicability as nanocarriers for these drugs in the drug delivery systems. Furthermore, GaBN has a short recovery time for MC, and TG drugs desorption compared to BN and AlBN nanoclusters. It is predicted that the MC, and TG drugs over GaBN can be used as a drug delivery system.Communicated by Ramaswamy H. Sarma.

Maintenance therapy and risk of osteonecrosis in children and young adults with acute lymphoblastic leukemia: a NOPHO ALL2008 sub-study

PURPOSE

Osteonecrosis is a burdensome treatment-related toxicity that is mostly diagnosed during or soon after 6-mercaptopurine (6MP)/methotrexate (MTX) maintenance therapy for acute lymphoblastic leukemia (ALL), possibly indicating a pathogenic role of these drugs.

METHODS

We prospectively registered symptomatic osteonecrosis during treatment of 1234 patients aged 1.0-45.9 years treated according to the Nordic Society of Hematology and Oncology (NOPHO) ALL2008 protocol. MTX/6MP metabolites were measured as part of the NOPHO ALL2008 maintenance therapy study.

RESULTS

After a median follow-up of 5.6 years [interquartile range (IQR) 3.6-7.5], 68 patients had been diagnosed with symptomatic osteonecrosis. The cumulative incidence was 2.7% [95% confidence interval (CI) 1.6-3.8%] for patients aged < 10 years, 14.9% (95% CI 9.7-20.2%) for patients aged 10.0-17.9 years, and 14.4% (95% CI 8.0-20.8%) for patients aged ≥ 18 years. The median time from diagnosis of ALL to diagnosis of osteonecrosis in these age groups was 1.0 year (IQR 0.7-2.0), 2.0 years (IQR 1.1-2.4), and 2.2 years (IQR 1.8-2.8), respectively (p = 0.001). With 17,854 blood samples available for MTX and 6MP metabolite analysis, neither erythrocyte levels of 6-thioguanine (TG) nucleotides (p > 0.99), methylated 6MP metabolites (p = 0.37), MTX polyglutamates (p = 0.98) nor DNA-TG (p = 0.53) were significantly associated with the hazard of osteonecrosis in Cox models stratified by the three age groups and adjusted for sex.

CONCLUSION

Maintenance therapy intensity determined by 6MP and MTX metabolites was not associated with the risk of developing osteonecrosis in the NOPHO ALL2008 cohort.

Use of thiopurines in inflammatory bowel disease: an update

Inflammatory bowel disease (IBD), once considered a disease of the Western hemisphere, has emerged as a global disease. As the disease prevalence is on a steady rise, management of IBD has come under the spotlight. 5-Aminosalicylates, corticosteroids, immunosuppressive agents and biologics are the backbone of treatment of IBD. With the advent of biologics and small molecules, the need for surgery and hospitalization has decreased. However, economic viability and acceptability is an important determinant of local prescription patterns. Nearly one-third of the patients in West receive biologics as the first/initial therapy. The scenario is different in developing countries where biologics are used only in a small proportion of patients with IBD. Increased risk of reactivation of tuberculosis and high cost of the therapy are limitations to their use. Thiopurines hence become critical for optimal management of patients with IBD in these regions. However, approximately one-third of patients are intolerant or develop adverse effects with their use. This has led to suboptimal use of thiopurines in clinical practice. This review article discusses the clinical aspects of thiopurine use in patients with IBD with the aim of optimizing their use to full therapeutic potential.

Dynamics of leucocyte DNA thioguanine nucleotide levels during maintenance therapy of childhood acute lymphoblastic leukemia

PURPOSE

Methotrexate (MTX)/6-Mercaptopurine (6MP)-based maintenance therapy is crucial to cure childhood acute lymphoblastic leukemia (ALL). Cytotoxicity is mediated by incorporation of thioguanine nucleotides (TGN) into DNA (DNA-TG) with higher levels in leucocytes being associated with reduced relapse risk. To further understand the dynamics of DNA-TG formation, we measured DNA-TG levels in leucocyte subsets during maintenance therapy and in the months following its discontinuation.

METHODS

DNA-TG levels were measured in leucocytes (DNA-TG_Total), polymorph nucleated granulocytes (neutrophils, eosinophils, basophils [DNA-TG_PMN]) and mononucleated cells (lymphocytes, monocytes [DNA-TG_MNC]) in 1013 samples from 52 patients on ALL maintenance therapy (951 samples during therapy and 62 samples after therapy discontinuation, respectively).

RESULTS

Median DNA-TG_Total, DNA-TG_PMN and DNA-TG_MNC during maintenance therapy were 539, 563 and 384 fmol/µg DNA, respectively. DNA-TG_PMN displayed more pronounced fluctuation than DNA-TG_MNC (range 0-3084 [interquartile range IQR 271-881] versus 30-1411 [IQR 270-509] fmol/µg DNA). DNA-TG_Total was more strongly correlated with DNA-TG_PMN (r_S = 0.95, p < 0.0001) than DNA-TG_MNC (r_S = 0.73, p < 0.0001). DNA-TG_PMN correlated less with DNA-TG_MNC (r_S = 0.64, p < 0.0001) and to a much lesser extent with absolute neutrophil count (r_S = 0.35, p < 0.0001). Following discontinuation of therapy, DNA-TG_PMN was rapidly eliminated, and not measurable beyond day 22 after discontinuation, whereas DNA-TG_MNC was slowly eliminated, and five patients demonstrated a measurable DNA-TG_MNC more than 365 days after therapy discontinuation.

CONCLUSION

Fluctuations in DNA-TG_Total are predominantly caused by corresponding fluctuations in DNA-TG_PMN, thus DNA-TG_Total measures recent TGN incorporation in these short-lived cells. Measurement of DNA-TG_Total at 2-4 weeks intervals provides a reliable profile of DNA-TG levels.

Nonbiologic Immune Suppression in Ulcerative Colitis

This article reviews nonbiologic immunosuppressive agents in the induction and maintenance of remission of ulcerative colitis. Based on meta-analyses and North American guidelines, azathioprine, mercaptopurine, and methotrexate monotherapy are not recommended for induction therapy. Thiopurines are recommended in combination with infliximab. Tofacitinib has been shown to be an effective induction agent. Cyclosporine or tacrolimus are calcineurin inhibitors that can be used as induction therapy. Thiopurine monotherapy is suggested or recommended as maintenance therapy for patients who have achieved steroid-induced remission. Methotrexate monotherapy is not recommended. Tofacitinib has been shown to be an effective maintenance agent in moderate to severe disease.

An exploration of mercaptopurine/methotrexate tolerance during maintenance therapy in children with acute lymphoblastic leukemia

PURPOSE

Mercaptopurine (6MP) and methotrexate (MTX) cause myelosuppression and interruptions in therapy in children with lymphoblastic leukemia (ALL). Length of time off of therapy is related to poorer outcomes. To date the dose at which most children tolerate these agents without drops in blood counts has not been identified. This study attempts to determine the maximum tolerated dose of both 6MP/MTX.

METHODS

A retrospective chart review of 77 ALL children, median age 4.5 years. Time to first interruption and dose, along with total number of interruptions were collected. Absolute neutrophil and platelet counts recorded at time of interruption. Subgroup analysis of age, sex, diagnosis and risk stratification were also completed. REB approval was gained.

RESULTS

Of the 77 patients that were studied, 9 of them had no treatment interruptions. Descriptive statistics are reported using Strata software. The mean number of interruptions during maintenance was 3.2, the mean time to first interruption was 149.8 days. The mean dose percent of MTX and 6MP at first interruption was 94.4% and 106% respectively. Maintenance therapy was interrupted independent of age, sex, diagnosis or disease risk stratification.

CONCLUSION

Few patients complete maintenance therapy without interruptions at the current dose escalation schedules outlined by the Children's Oncology Group protocols. The interruptions are due in part to intolerance of dose escalations of MTX and 6 MP above 100%. Future research should investigate doses of 6MP and MTX in maintenance therapy in relation to leukemia outcomes.

Phosphorene and Na-, Ca-, and Fe-doped phosphorene as candidates for delivery of mercaptopurine and fluorouracil anticancer drugs

Phosphorene ability for delivery of mercaptopurine and fluorouracil was investigated by the density functional theory (DFT) method. However, the effects of Na, Ca, and Fe as dopants on phosphorene electronic properties such as HOMO and LUMO energies, density of states, chemical potential, electrophilicity index, softness, hardness, and its ability for drug delivery were studied. Natural bond orbital (NBO) analysis was performed. Our findings indicate that metallic dopants can improve the ability of phosphorene. Calcium-doped phosphorene has the greatest adsorption energy.

Simultaneous UPLC-MS/MS Determination of 6-mercaptopurine, 6-methylmercaptopurine and 6-thioguanine in Plasma: Application to the Pharmacokinetic Evaluation of Novel Dosage forms in Beagle Dogs

BACKGROUND

6-Mercaptopurine (6-MP) is widely used to treat pediatric acute lymphoblastic leukemia (ALL). Mini-tablets of 5 mg per tablet were developed for precision individual therapy for children and individuals with poor thiopurine S-methyltransferase (TPMT) or nucleoside diphophate-linked moiety X-type motif 15 (NUDT15) metabolism. This study investigated the pharmacokinetic profiles of mini-tablets and conventional tablets with an improved ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method.

METHODS

After giving 8 healthy beagle dogs 50 mg 6-MP in different dosage forms, plasma samples collected at different time points were analyzed for pharmacokinetic evaluation. The samples were precipitated by methanol with 0.05% formic acid and separated on a Waters Atlantis T3 column (2.1 × 150 mm, 3 μm particles) using 0.1% formic acid in water and methanol at a flow rate of 0.4 mL/min in 4 min.

RESULTS

This method showed good linearity, accuracy, precision and stability with a detection range of 5.0-500.0 ng/mL for 6-MP, 6-methylmercaptopurine (6-MMP) and 6-thioguanine (6-TG). The main parameters, half-life of apparent terminal disposition, maximum observed plasma concentration, total AUC extrapolated to infinity, AUC since initiation of the experiment, mean residence time, distribution volume and clearance were 1.62 ± 0.87 hours, 90.58 ± 60.43 ng/mL, 151.20 ± 94.18 ng·h/mL, 292.06 ± 184.02 ng·h2/mL, 1.90 ± 0.92 hours, 864.08 ± 538.52 L, and 432.75 ± 360.64 L/h for conventional tablets and 1.70 ± 1.10 hours, 84.15 ± 39.50 ng/mL, 147.70 ± 51.80 ng·h/mL, 300.92 ± 124.48 ng·h2/mL, 2.07 ± 0.50 hours, 756.90 ± 324.00 L, and 340.75 ± 125.81 L/h for minitablets, respectively. Paired t-tests showed no significant difference in any of the evaluated pharmacokinetic parameters between the two types tablets (P > 0.05).

CONCLUSION

Two dosage forms showed the same pharmacokinetic characteristics. This developing, novel formulation will help to provide a more accurate and optimal dosing regimen of 6-MP for humans in the future.

Pharmacokinetics of tablet and liquid formulations of oral 6-mercaptopurine in children with acute lymphoblastic leukemia

PURPOSE

Mercaptopurine (6MP) is essential to cure childhood acute lymphoblastic leukemia (ALL). A liquid 6MP formulation was recently introduced to facilitate oral 6MP administration, especially to children. Its approval and bioequivalence with 6MP tablet were based on comparative pharmacokinetics in 60 healthy adults. Due to potential pharmacokinetic differences between healthy adults and children with ALL, we compared pharmacokinetics of tablet and liquid 6MP formulations in children with ALL.

METHODS

Pharmacokinetics of 50 mg 6MP tablet (Puri-Nethol^®) and 20 mg/ml 6MP liquid suspension (Xaluprine^®) were compared in a non-blinded, random order, single-dose, cross-over study in 16 children with ALL (eight males). 6MP was administered after a 12 h fast, and 6MP plasma concentrations measured consecutively over seven hours post-dose. Pharmacokinetic outcomes were as follows: Area under the curve (AUC), maximum plasma concentration (C_max), time to maximum plasma concentration (T_max), and terminal half-life (T_½).

RESULTS

Liquid 6MP formulation resulted in a 26% lower AUC (p = 0.02) compared with tablet (median 1215 vs. 1805 h × nmol/l). No significant differences were observed for C_max,T_max and T_½ (p = 0.28, p = 0.09, p = 0.41, respectively). Based on criteria declared by the World Health Organization the results did not establish non-inferiority of liquid 6MP formulation compared with 6MP tablet.

CONCLUSION

Non-inferiority of liquid 6MP formulation compared with 6MP tablet was not demonstrated. Yet, maintenance therapy doses are adjusted by degree of myelosuppression and not by 6MP dose. Thus, in spite of a lower bioavailability, a liquid 6MP formulation is still desirable in a clinical setting, especially for children. However, if shifting between 6MP formulation is indicated, dose adjustments should be anticipated to maintain equivalent treatment intensity in children with ALL. The study is registered on clinicaltrials.gov (NCT01906671). Date of registration: 24.07.13.

Magnetite Fe3O4 surface as an effective drug delivery system for cancer treatment drugs: density functional theory study

In this paper, the magnetite Fe₃O₄ surface was studied as a drug delivery system for the two commercially famous cancer treatment drugs, including Cisplatin and Mercaptopurine, using the density functional theory (DFT) computations. Adsorption properties, magnetic and electronic properties were calculated. Results indicate that the adsorptions are thermodynamically favorable and binding energies were decreased by increasing the concentration of the ligands adsorption on the Fe₃O₄ surface. Our spin-polarized calculations determine that the magnetization of all systems is greater than the pristine magnetite Fe₃O₄ surface witch is vital for drug delivery and magnetic hyperthermia. This study provides a deep understanding of the interaction mechanism at the atomistic scale and proposed that magnetite Fe₃O₄ could be employed as an efficient drug carrier.Communicated by Ramaswamy H. Sarma.

Higher Mucosal Healing with Tumor Necrosis Factor Inhibitors in Combination with Thiopurines Compared to Methotrexate in Crohn's Disease

BACKGROUND

The differential impact of anti-tumor necrosis factor (anti-TNF) therapy with methotrexate versus thiopurine co-therapy on endoscopic remission remains uncertain.

AIMS

To compare rates of endoscopic remission based on methotrexate or thiopurine co-therapy used with anti-TNF therapy in Crohn's disease.

METHODS

A retrospective observational study at two tertiary centers between 2010 and 2016 compared endoscopic remission rates and persistence on anti-TNF therapy in combination with methotrexate versus thiopurines for at least 3 months.

RESULTS

Of 412 patients on anti-TNF therapy, 278 (67%) received immunomodulator co-therapy for ≥ 3 months and 269 (65%) had complete data for analysis. Methotrexate was used in 77 (29%) and thiopurines in 192 (71%) patients plus either infliximab (156, 58%) or adalimumab (113, 42%), with median follow-up of 2.8 years. The methotrexate group had greater prior immunomodulator intolerance (62% vs 20%, p < 0.01). Endoscopic remission rates were higher in those treated with thiopurine compared to methotrexate co-therapy at 12 m (58% vs 17%, p < 0.01) and at last review (59% vs 40%, p = 0.03). Endoscopic remission rates were higher with thiopurines than methotrexate when combined with adalimumab (49% vs 6%, p < 0.01) but not with infliximab (65% vs 54%, p = 0.09). In multivariate analysis, thiopurine co-therapy, elevated baseline CRP, and therapeutic anti-TNF drug levels were each associated with longer persistence of co-therapy (each p < 0.05). There were no significant differences in adverse events, malignancy or infection rates.

CONCLUSION

In this cohort, anti-TNF and thiopurine co-therapy resulted in higher rates of mucosal healing than methotrexate, the difference is most pronounced with adalimumab and conversely with low-dose methotrexate.

Aminosalicylates, thiopurines and methotrexate in inflammatory bowel disease: Is it possible to discontinue the treatment?

The current goals of treatment in inflammatory bowel disease, both Crohn's disease and ulcerative colitis, are to achieve clinical, endoscopic and ideally histological remission and improve the quality of life of these patients. Current therapies are effective in achieving remission in most cases, but there is a lack of clear guidelines on their optimal duration. This review aims to evaluate the current evidence on the withdrawal of therapy with 5-aminosalicylates, thiopurines and methotrexate. We also aim to identify which specific group of patients, while in remission and in the absence of risk factors, may be able to discontinue therapy without a significant risk of relapse.

Low-dose thiopurine with allopurinol co-therapy overcomes thiopurine intolerance and allows thiopurine continuation in inflammatory bowel disease

AIMS

To assess the utility and tolerability of thiopurine-allopurinol co-therapy in inflammatory bowel disease (IBD) patients with intolerance to thiopurine monotherapy.

METHODS

A retrospective observational study assessed cases of thiopurine intolerance then switched to thiopurine allopurinol co-therapy between 2011 and 2015 at two centres. Indications for switch, dosing and subsequent clinical outcomes (including thiopurine persistence) were recorded.

RESULTS

Of 767 patients on thiopurines for IBD, 89 (12%) were switched to co-therapy for intolerance. 64/89 (72%) had Crohn's disease, 38 (43%) were males, median age at switch was 40y (range 17-78), median IBD duration 6y (0-29). Median follow-up was 1.9y (0-5). Reasons for switching to co-therapy included fatigue (37%), hepatotoxicity (23%), nausea (23%), arthralgia (10%), headache (12%) and hypersensitivity reaction (4%). Overall, 66 (74%) patients remained on co-therapy until most recent review and achieved a clinical response. High rates of overcoming intolerance (62-100%) occurred with co-therapy for all reasons above, although fatigue was less amenable to switching than non-fatigue indications (62% vs 91%, p = <0.001). Of 34 patients not escalated to biologics with endoscopic data, 15 were in remission (44%) at most recent review.

CONCLUSION

Low-dose thiopurine combined with allopurinol appears safe and effective in overcoming intolerances to thiopurine monotherapy in many cases.

Magnetic molecularly imprinted polymer nanoparticles for simultaneous extraction and determination of 6-mercaptopurine and its active metabolite thioguanine in human plasma

Cytotoxic drugs used in cancer chemotherapy require the continuous monitoring of their plasma concentration levels for dose adjustment purposes. Such condition necessitates the presence of a sensitive technique for accurate extraction and determination of these drugs together with their active metabolites. In this study a novel solid phase extraction technique using magnetic molecularly imprinted nanoparticles (MMI-SPE) is combined with liquid chromatography tandem mass spectrometry (LC-MS/MS) to extract and determine the anti-leukemic agent; 6-mercaptopurine (6-MP) and its active metabolite thioguanine (TG) in human plasma. The magnetic molecularly imprinted nanoparticles (Fe₃O₄@MIP NPs) were synthesized via precipitation polymerization technique and were characterized using different characterization methods A computational approach was adopted to help in the choice of the monomer used in the fabrication process. The Fe₃O₄@MIPs NPs possessed a highly improved imprinting efficiency, fast adsorption kinetics following 2nd order kinetics and good adsorption capacity of 1.0 mg/g. The presented MMI-SPE provided the optimum approach in comparison to other reported ones to achieve good extraction recovery and matrix effect of trace levels of 6-MP and TG from plasma. Chromatographic separation was carried out using a validated LC-MS/MS assay and recovery, matrix effect and process efficiency were evaluated. Recovery of 6-MP and TG was in the range of 85.94-103.03%, while, matrix effect showed a mean percentage recovery of 85.94-97.62% and process efficiency of 85.54-96.18%. The proposed extraction technique is simple, effective and can be applicable to the extraction and analysis of other pharmaceutical compounds in complex matrices for therapeutic drug monitoring applications.

Recommendations of the Spanish Working Group on Crohn's Disease and Ulcerative Colitis (GETECCU) on the use of thiopurines in inflammatory bowel disease

Thiopurines (azathioprine and mercaptopurine) are widely used in patients with inflammatory bowel disease. In this paper, we review the main indications for their use, as well as practical aspects on efficacy, safety and method of administration. They are mainly used to maintain remission in steroid-dependent disease or with ciclosporin to control a severe ulcerative colitis flare-up, as well as to prevent postoperative Crohn's disease recurrence, and also in combination therapy with biologics. About 30-40% of patients will not respond to treatment and 10-20% will not tolerate it due to adverse effects. Before they are prescribed, immunisation status against certain infections should be checked. Determination of thiopurine methyltransferase activity (TPMT) is not mandatory but it increases initial safety. The appropriate dose is 2.5mg/kg/day for azathioprine and 1.5mg/kg/day for mercaptopurine. Some adverse effects are idiosyncratic (digestive intolerance, pancreatitis, fever, arthromyalgia, rash and some forms of hepatotoxicity). Others are dose-dependent (myelotoxicity and other types of hepatotoxicity), and their surveillance should never be interrupted during treatment. If therapy fails or adverse effects develop, management can include switching from one thiopurine to the other, reducing the dose, combining low doses of azathioprine with allopurinol and assessing metabolites, before their use is ruled out. Non-melanoma skin cancer, lymphomas and urinary tract tumours have been linked to thiopurine therapy. Thiopurine use is safe during conception, pregnancy and breastfeeding.

A combined molecular dynamics simulation and quantum mechanics study on mercaptopurine interaction with the cucurbit [6,7] urils: Analysis of electronic structure

In the current study, the probability of complex formation between mercaptopurine drug with cucurbit[6]urils and cucurbit[7]urils has been investigated. The calculations for geometry optimization of complexes have been carried out by means of DFT (B3LYP), DFT-D (B3LYP-D) and M06-2X methods. The Atoms In Molecules (AIM), Natural Bond Orbital (NBO), NMR, the density of states (DOSs) and frontier molecular orbital (MO) analyses have been done on the inclusion complexes. In addition, the UV-Vis spectra of the first eight states have been obtained by CAM-B3LYP/TD-DFT calculation. The obtained results of the complexation process reveal that CB[7]-DRG complexes are more favorable than that of CB[6]-DRG interactions. Furthermore, our theoretical results show that configurations III and I are the most stable configurations related to the CB[6]/DRG and CB[7]/DRG interactions, respectively. The positive ∇²_ρ(r) and HC values at the bond critical points indicate that exist the weak H-bonds between CB[6] and CB[7] with H atoms of the drug molecule. The obtained negative binding energy values of CB[7]-DRG interaction in solution phase show the stability of these complexes in the aqueous medium. Also, all of the observed parameters of molecular dynamics simulation such as the number of contacts, hydrogen bonding, center-of-mass distance and van der Waals energy values confirm the encapsulation of mercaptopurine molecule inside the cucurbit[7]urils cavity at about 3.2ns.

Role of Anomalous Water Constraints in the Efficacy of Pharmaceuticals Probed by 1H Solid-State NMR

Water plays a complex and central role in determining the structural and reactive properties in numerous chemical systems. In crystalline materials with structural water, the primary focus is often to relate hydrogen bonding motifs to functional properties such as solubility, which is highly relevant in pharmaceutical applications. Nevertheless, understanding the full electrostatic landscape is necessary for a complete structure-function picture. Herein, a combination of tools including ¹H magic angle spinning NMR and X-ray crystallography are employed to evaluate the local landscape of water in crystalline hydrates. Two hydrates of an anti-leukemia drug mercaptopurine, which exhibit dramatically different dehydration temperatures (by 90°C) and a three-fold difference in the in vivo bioavailability, are compared. The results identify an electrosteric caging mechanism for a kinetically trapped water in the hemihydrate form, which is responsible for the dramatic differences in properties.

Pharmacokinetics and pharmacodynamics of thiopurines in an in vitro model of human hepatocytes: Insights from an innovative mass spectrometry assay

AIM

To apply an innovative LC-MS/MS method to quantify thiopurine metabolites in human hepatocytes and to associate them to cytotoxicity.

METHODS

Immortalized human hepatocytes (IHH cells) were treated for 48 and 96 h, with 1.4 × 10^-4 M azathioprine and 1.1 × 10^-3 M mercaptopurine, concentrations corresponding to the IC₅₀ values calculated after 96 h exposure in previous cytotoxicity analysis. After treatments, cells were collected for LC-MS/MS analysis to quantify 11 thiopurine metabolites with different level of phosphorylation and viable cells were counted by trypan blue exclusion assay to determine thiopurines in vitro effect on cell growth and survival. Statistical significance was determined by analysis of variance (ANOVA).

RESULTS

Azathioprine and mercaptopurine had a significant time-dependent cytotoxic effect (p-value ANOVA = 0.012), with a viable cell count compared to controls of 55.5% and 67.5% respectively after 48 h and 23.7% and 36.1% after 96 h; no significant difference could be observed between the two drugs. Quantification of thiopurine metabolites evidenced that the most abundant metabolite was TIMP, representing 57.1% and 40.3% of total metabolites after 48 and 96 h. Total thiopurine metabolites absolute concentrations decreased over time: total mean content decreased from 469.9 pmol/million cells to 83.6 pmol/million cells (p-value ANOVA = 0.0070). However, considering the relative amount of thiopurine metabolites, TGMP content significantly increased from 11.4% cells to 26.4% (p-value ANOVA = 0.017). A significant association between thiopurine effects and viable cell counts could be detected only for MeTIMP: lower MeTIMP concentrations were associated with lower cell survival (p-value ANOVA = 0.011). Moreover, the ratio between MeTIMP and TGMP metabolites directly correlated with cell survival (p-value ANOVA = 0.037).

CONCLUSION

Detailed quantification of thiopurine metabolites in a human hepatocytes model provided useful insights on the association between thioguanine and methyl-thioinosine nucleotides with cell viability.

Differential effects of thiopurine methyltransferase (TPMT) and multidrug resistance-associated protein gene 4 (MRP4) on mercaptopurine toxicity

PURPOSE

Mercaptopurine plays a pivotal role in treatment of acute lymphoblastic leukemia (ALL) and autoimmune diseases, and inter-individual variability in mercaptopurine tolerance can influence treatment outcome. Thiopurine methyltransferase (TPMT) and multi-drug resistant Protein 4 (MRP4) have both been associated with mercaptopurine toxicity in clinical studies, but their relative contributions remain unclear.

METHODS

We studied the metabolism of and tolerance to mercaptopurine in murine knockout models of Tpmt, Mrp4, and both genes simultaneously.

RESULTS

Upon mercaptopurine treatment, Tpmt ^-/- Mrp4 ^-/- mice had the highest concentration of bone marrow thioguanine nucleotides (8.5 pmol/5 × 10⁶ cells, P = 7.8 × 10^-4 compared with 2.7 pmol/5 × 10⁶ cells in wild-types), followed by those with Mrp4 or Tpmt deficiency alone (6.1 and 4.3 pmol/5 × 10⁶ cells, respectively). Mrp4-deficient mice accumulated higher concentrations of methylmercaptopurine metabolites compared with wild-type (76.5 vs. 23.2 pmol/5 × 10⁶ cells, P = 0.027). Mice exposed to a clinically relevant mercaptopurine dosing regimen displayed differences in toxicity and survival among the genotypes. The double knock-out of both genes experienced greater toxicity and shorter survival compared to the single knockout of either Tpmt (P = 1.7 × 10^-6) or Mrp4 (P = 7.4 × 10^-10).

CONCLUSIONS

We showed that both Tpmt and Mrp4 influence mercaptopurine disposition and toxicity.

Thiopurine use associated with reduced B and natural killer cells in inflammatory bowel disease

AIM

To identify which blood and mucosal lymphocyte populations are specifically depleted by thiopurine use in vivo.

METHODS

The thiopurines azathioprine and 6-mercaptopurine have been a mainstay of inflammatory bowel disease (IBD) therapy for decades, but their mechanism of action in vivo remains obscure. Although thiopurines are lymphotoxic at high doses, and have been reported to cause T cell apoptosis in vitro, their ability to control IBD at lower doses suggests that they may selectively deplete particular lymphocyte populations. Blood cells from 19 IBD patients on a thiopurine, 19 IBD patients not on a thiopurine, and 38 matched healthy control subjects were analyzed by multiple multi-color flow cytometry panels to quantify the immune cell subsets contained therein, both as a percent of cells, and as an absolute cell count. Similar analyses were performed on colon biopsies from 17 IBD patients on a thiopurine, 17 IBD patients not on a thiopurine, and 49 healthy screening colonoscopy recipients.

RESULTS

Complete blood counts revealed lower lymphocyte, but not monocyte or granulocyte, counts in IBD patients who were taking thiopurines at the time of sampling. This reduction was restricted to CD3-negative lymphocytes, wherein both natural killer (NK) and B cells were significantly reduced among thiopurine recipients. Among CD19+ B cells, the transitional B cells were particularly depleted, being nearly absent in both blood and colon biopsies of thiopurine recipients. No differences were associated with thiopurine use in CD8+ T cells, mucosa-associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells, gamma/delta T cells, Th1, Th17, regulatory T cells (Tregs) or naïve CD4+ T cells. However, patients with IBD had significantly more circulating FOXP3+, Helios+ Tregs and fewer iNKT and MAIT cells than healthy controls.

CONCLUSION

Thiopurine use is associated with reduced B and NK cell, but not T cell, subpopulations in the blood of IBD patients.

Rate and Predictors of Mucosal Healing in Ulcerative Colitis Treated with Thiopurines: Results of a Multicentric Cohort Study

BACKGROUND AND AIMS

Mucosal healing (MH) with thiopurines has been poorly investigated in ulcerative colitis (UC). We aimed to assess MH rate in UC patients treated with thiopurine monotherapy.

PATIENTS AND METHODS

We retrospectively collected all UC patients treated with thiopurines more than 6 months who have undergone colonoscopy at baseline and after at least 6 months of treatment. Patients were recruited from January 2005 to May 2015 through a personal database and/or standardized hospital inpatient diagnostic dataset. Patients were excluded in case of any use of other immunomodulator or biological agent. MH was defined as a Mayo endoscopic subscore ≤1 and UCEIS ≤ 2. Histological healing (HH) was defined by the absence of epithelial polynuclear infiltrate, cryptic abscesses, or ulcerations.

RESULTS

Eighty patients (31 women, median age 43 [IQR 32-58]) were included. Median disease duration was 10.5 [6-16] years. At baseline, median full Mayo score, endoscopic subscore, and UCEIS were 8 [6.8-10], 3 [2-3], and 5 [3-6], respectively. MH was first assessed after a mean follow-up of 38 ± 31 months. Median full Mayo score, endoscopic subscore, and UCEIS decreased to 3.5 [1-6], 2 [0-2.2], and 2 [0-4], respectively. MH was achieved in 43.7%, HH in 38%. In multivariate analysis, predictors of MH were thiopurine exposure duration ≥2 years [odds ratio (OR) 2.9, CI 95% (1.1-7.6), p = 0.03] and a prior acute severe colitis [OR 5.9, CI 95% (1.1-32), p = 0.04]. Factors associated with MH during treatment were partial Mayo score ≤2 (NPV = 100%), BMI ≥ 25 kg/m² (NPV = 75%), and MCV ≥ 95 fL (NPV = 73%).

CONCLUSIONS

In UC, thiopurine monotherapy is associated with MH in 43.7% and HH in 38%.

Thiopurines and inflammatory bowel disease: Current evidence and a historical perspective

The use of thiopurines in inflammatory bowel disease (IBD) has been examined in numerous prospective, controlled trials, with a majority demonstrating a clinical benefit. We conducted this review to describe the historical and current evidence in the use of thiopurines in IBD. A systematic search was performed on MEDLINE between 1965 and 2016 to identify studies on thiopurines in IBD. The most robust evidence for thiopurines in IBD includes induction of remission in combination with anti-tumor necrosis factor (anti-TNF) agents, and maintenance of remission and post-operative maintenance in Crohn’s disease. Less evidence exists for thiopurine monotherapy in induction of remission, maintenance of ulcerative colitis, chemoprevention of colorectal cancer, and in preventing immunogenicity to anti-TNF. Evidence was often limited by trial design. Overall, thiopurines have demonstrated efficacy in a broad range of presentations of IBD. With more efficacious novel therapeutic agents, the positioning of thiopurines in the management of IBD will change and future studies will analyze the benefit of thiopurines alone and in conjunction with these new medications.

How I treat my inflammatory bowel disease-patients with thiopurines?

Thiopurines are essential drugs to maintain remission in patients with inflammatory bowel disease (IBD). Thiopurines used in IBD are azathioprine (2.0-2.5 mg/kg), mercaptopurine (1.0-1.5 mg/kg) and thioguanine (0.2-0.3 mg/kg). However, mainly due to numerous adverse events associated with thiopurine use, almost 50% of the patients have to discontinue conventional thiopurine treatment. Extensive monitoring and the application of several treatment strategies, such as split-dose administration, co-administration with allopurinol or dose reduction/increase, may increase the chance of successful therapy. With this review, we provide practical information on how thiopurines are initiated and maintained in two thiopurine research centers in The Netherlands. We provide clinical information concerning safety issues, indications and management of therapy that may serve as a guide for the administration of thiopurines in IBD patients in daily practice.

Microbial metabolism of thiopurines: A method to measure thioguanine nucleotides

Thiopurines are anti-inflammatory prodrugs. We hypothesised that bacteria may contribute to conversion to active drug. Escherichia coli strain DH5α was evaluated to determine whether it could metabolise the thiopurine drugs, thioguanine or mercaptopurine, to thioguanine nucleotides. A rapid and reliable high performance liquid chromatography (ultraviolet detection) method was developed to quantify indirectly thioguanine nucleotides, by measuring thioguanine nucleoside.

Clinical predictors of thiopurine-related adverse events in Crohn's disease

AIM: To determine the incidence and predictors of thiopurine-related adverse events.

METHODS: Subjects with Crohn’s disease who were followed in the Alberta Inflammatory Bowel Disease Consortium patient database registry were identified. Retrospective chart review was conducted between August 5^th, 2010 and June 1^st, 2012. We collected data on: age at diagnosis; sex; disease location and behaviour at time of prescribing thiopurine; perianal fistulising disease at or prior to thiopurine prescription; smoking status at time of thiopurine prescription, use of corticosteroid within 6 mo of diagnosis; dosage, age at onset, and cessation of 5-aminosalicyclic acid (5-ASA); anti-tumour necrosis factor medication exposure and intestinal resection before thiopurine prescription. The primary outcome of interest was the first adverse event that led to discontinuation of the first thiopurine medication used. Logistic regression models were used to associate clinical characteristics with outcomes after adjusting for potential confounders. Risk estimates were presented as odds ratios (OR) with 95% CI. Effect modification by age and sex were explored.

RESULTS: Our cohort had a median follow-up duration of 5.8 years [interquartile range (IQR 25^th-75^th) 2.7-9.1]. Thiopurine therapy was discontinued in 31.3% of patients because of: hypersensitivity reactions (7.1%), acute pancreatitis (6.2%), gastrointestinal intolerance (5.4%), leucopenia (3.7%), hepatotoxicity (3.4%), infection (1.1%) and other reasons (4.3%). A higher incidence of thiopurine withdrawal was observed in patients over the age of 40 (39.4%, P = 0.007). A sex-by-age interaction (P = 0.04) was observed. Females older than 40 years of age had an increased risk of thiopurine discontinuation due to an adverse event (age above 40 vs age below 40, adjusted OR = 2.8; 95%CI: 1.4-5.6). In contrast, age did not influence thiopurine withdrawal in males (age above 40 vs below 40, adjusted OR = 0.9; 95%CI: 0.4-2.1). Other clinical variables (disease location and phenotype, perianal disease, smoking history, history of intestinal resection and prior 5-ASA or corticosteroid use) were not associated with an increased risk an adverse event leading to therapy cessation.

CONCLUSION: Thiopurine withdrawal due to adverse events is commoner in women over the age of 40 at prescription. These findings need to be replicated in other cohorts.

Concentrations of 6-thioguanine nucleotide correlate with trough levels of infliximab in patients with inflammatory bowel disease on combination therapy

BACKGROUND & AIMS

In patients with inflammatory bowel diseases, the combination of infliximab and thiopurines (such as 6-thioguanine) is more effective treatment than monotherapy. We assessed the correlation between serum levels of 6-thioguanine (6-TGN) and infliximab levels or antibodies to infliximab (ATI).

METHODS

We performed a cross-sectional study of 72 patients receiving maintenance therapy with infliximab and a thiopurine for inflammatory bowel disease at the Crohn's and Colitis Center of the University of Miami, FL. We collected clinical, endoscopic, and biochemical data, and levels of thiopurine metabolites. The primary outcomes were trough level of infliximab and the presence of ATI.

RESULTS

Levels of 6-TGN correlated with those of infliximab (ρ, 0.53; P < .0001). The cut-off point of 6-TGN that best predicted a higher level of infliximab was 125 pmol/8 × 10(8) red blood cells (RBCs) (area under receiver operating characteristic, 0.86; P < .001). Patients in the lowest quartile of 6-TGN had infliximab levels that were similar to patients on no thiopurines (4.3 vs. 4.8 mcg/mL, respectively; P = .8). An infliximab level of 8.3 mcg/mL or greater was associated with mucosal healing. Only 8 patients (11%) had detectable ATI. Patients with 6-TGN levels less than 125 pmol/8 × 10(8) RBCs were significantly more likely to have ATI (odds ratio, 1.3; 95% confidence interval, 2.3-72.5; P < .01).

CONCLUSIONS

Although 6-TGN levels of greater than 230 pmol/8 × 10(8) RBCs have been associated with improved outcomes in patients on monotherapy, a level of 6-thioguanine of 125 pmol/8 × 10(8) RBCs or greater may be adequate to achieve therapeutic levels of infliximab. In the long term, this may minimize the toxicity for patients on combination therapy.

Assessment of mercaptopurine (6MP) metabolites and 6MP metabolic key-enzymes in childhood acute lymphoblastic leukemia

Pediatric acute lymphoblastic leukemia (ALL) is treated with combination chemotherapy including mercaptopurine (6MP) as an important component. Upon its uptake, 6MP undergoes a complex metabolism involving many enzymes and active products. The prognostic value of all the factors engaged in this pathway still remains unclear. This study attempted to determine which components of 6MP metabolism in leukemic blasts and red blood cells are important for 6MP's sensitivity and toxicity. In addition, changes in the enzymatic activities and metabolite levels during the treatment were analyzed. In a cohort (N=236) of pediatric ALL patients enrolled in the Dutch ALL-9 protocol, we studied the enzymes inosine-5'-monophosphate dehydrogenase (IMPDH), thiopurine S-methyltransferase (TPMT), hypoxanthine guanine phosphoribosyl transferase (HGPRT), and purine nucleoside phosphorylase (PNP) as well as thioguanine nucleotides (TGN) and methylthioinosine nucleotides (meTINs). Activities of selected enzymes and levels of 6MP derivatives were measured at various time points during the course of therapy. The data obtained and the toxicity related parameters available for these patients were correlated with each other. We found several interesting relations, including high concentrations of two active forms of 6MP--TGN and meTIN--showing a trend toward association with better in vitro antileukemic effect of 6MP. High concentrations of TGN and elevated activity of HGPRT were found to be significantly associated with grade III/IV leucopenia. However, a lot of data of enzymatic activities and metabolite concentrations as well as clinical toxicity were missing, thereby limiting the number of assessed relations. Therefore, although a complex study of 6MP metabolism in ALL patients is feasible, it warrants more robust and strict data collection in order to be able to draw more reliable conclusions.

[Aquagenic palmoplantar keratoderma during treatment of Langerhans cell histiocytosis]

BACKGROUND

Aquagenic palmoplantar keratoderma (APPK) is characterised by whitish oedematous papules, sometimes itchy or painful of rapid onset following immersion of the palms and/or soles in water. We report a case that was atypical in terms of the secondary appearance of persistent fine desquamation.

PATIENTS AND METHODS

A 6-year-old girl presented with typical APPK, present for three months and characterised by swelling, skin wrinkling, hyperhidrosis and secondary desquamation of the palms and soles, and which occurred after bathing. The patient had been treated with vinblastine, mercaptopurine and oral corticosteroids for Langerhans cell histiocytosis ongoing for six months. Physical examination revealed persistent fine desquamation of the palms and soles, occurring some time after immersion in water. There was no mutation of the CFTR gene. No similar cases could be found in the pharmacovigilance database. Topical therapy with an emollient provided some relief. Symptoms had partially resolved two months after discontinuation of chemotherapy and oral corticosteroids.

DISCUSSION

Cases of unilateral palmar damage involving unusual sites have been reported. Neither secondary desquamation nor association with Langerhans cell histiocytosis have been described. Hyperhidrosis and association with 1 or 2 CFTR mutations appear to constitute predisposing factors. There are cases of APPK related to anti-inflammatory intake. In view of the clinical course, an iatrogenic origin cannot be excluded in this case.

CONCLUSION

Persistent fine palmoplantar desquamation may be a manifestation of APPK.

Routine use of thiopurines in maintaining remission in pediatric Crohn’s disease

AIM: To evaluate the effectiveness of thiopurines in maintaining steroid-free remission in routine clinical practice.

METHODS: The multi-center Pediatric Inflammatory Bowel Disease Network (PIBDNet) cohort study prospectively collected data on thiopurine naïve patients initiating mercaptopurine (6MP) or azathioprine. Patients with a diagnosis of Crohn’s disease (CD) were included in our study upon entering remission as determined by physician global assessment (PGA) within 365 d of initiation of thiopurines. The primary outcome of the study was maintenance of steroid-free remission (SFR) at each follow up visit. Patients were considered treatment failures if there had been a change in PGA from remission to mild, moderate or severe disease; disease relapse between visits; need for rescue therapy (biologic therapy, methotrexate, steroids); thiopurine discontinuation, hospitalization or surgical intervention. A secondary outcome defined treatment failure as a change from remission to moderate or severe (not mild) in addition to the previously defined criteria.

RESULTS: Sixty-five of 182 patients in the PIBDNet registry met criteria for inclusion in this study. Forty-five of 65 (69%) of included patients achieved remission within 180 d of thiopurine initiation. For the primary outcome, 47% and 23% of patients remained in SFR at 6 and 12 mo. The mean thiopurine dose at initiation for the 65 included patients was 0.89 ± 0.31 mg/kg per day. Metabolite levels were obtained in 48% (31/65) of the included patients with a mean 6TG level of 258 pmole/8 × 10⁸ RBC ± 147. For the secondary outcome, 65% and 42% of patients remained in SFR at 6 and 12 mo.

CONCLUSION: Thiopurines were less effective in maintaining remission for pediatric CD in this “real world” cohort than has been previously described. Variation in thiopurine dosing and metabolite measurement was found among practitioners.

Use of thiopurines in inflammatory bowel disease: Safety issues

Thiopurines are widely used for maintenance treatment of inflammatory bowel disease. Inter-individual variability in clinical response to thiopurines may be attributed to several factors including genetic polymorphisms, severity and chronicity of disease, comorbidities, duration of administration, compliance issues and use of concomitant medication, environmental factors and clinician and patient preferences. The purpose of this review is to summarise the current evidence on thiopurine safety and toxicity, to describe adverse drug events and emphasise the significance of drug interactions, and to discuss the relative safety of thiopurine use in adults, elderly patients, children and pregnant women. Thiopurines are safe to use and well tolerated, however dose adjustment or discontinuation of treatment must be considered in cases of non-response, poor compliance or toxicity. Drug safety, clinical response to treatment and short to long term risks and benefits must be balanced throughout treatment duration for different categories of patients. Treatment should be individualised and stratified according to patient requirements. Enzymatic testing prior to treatment commencement is advised. Surveillance with regular clinic follow-up and monitoring of laboratory markers is important. Data on long term efficacy, safety of thiopurine use and interaction with other disease modifying drugs are lacking, especially in paediatric inflammatory bowel disease. High quality, collaborative clinical research is required so as to inform clinical practice in the future.

The pharmacokinetic effect of adalimumab on thiopurine metabolism in Crohn's disease patients

BACKGROUND AND AIMS

A drug interaction between infliximab and azathioprine has previously been reported in Crohn's disease patients: the concentration of the main active thiopurine metabolites, the 6-thioguanine nucleotides (6-TGN), increased 1-3 weeks after the first infliximab infusion by 50% compared to baseline. The aim of this prospective study was to determine the effect of adalimumab on thiopurine metabolism in Crohn's disease patients, evaluated by 6-TGN and 6-methylmercaptopurine ribonucleotides (6-MMPR) concentration measurement.

METHODS

Crohn's disease patients on azathioprine or mercaptopurine maintenance therapy starting with concomitant adalimumab treatment were included. 6-TGN and 6-MMPR concentrations were determined before initiation of adalimumab and after 2, 4, 6 and 12 weeks of combination therapy. The activity of three essential enzymes involving thiopurine metabolism, thiopurine S-methyltransferase (TPMT), hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and inosine-triphosphate pyrophosphatase (ITPase), was evaluated at baseline and week 4. Clinical outcome was evaluated by the Crohn's disease activity index and C-reactive protein concentrations at baseline, week 4 and week 12.

RESULTS

Twelve Crohn's disease patients were analyzed. During the follow-up period of 12 weeks the median 6-TGN and 6-MMPR concentrations did not significantly change compared to baseline. TPMT, ITPase and HGPRT enzyme activity did not change either after 4 weeks. In two patients (17%) myelotoxicity was observed within 2-4 weeks, in whom both low therapeutic 6-TGN and 6-MMPR concentrations were found.

CONCLUSIONS

In this study in Crohn's disease patients no pharmacokinetic interaction was shown between adalimumab and the conventional thiopurines, azathioprine and mercaptopurine.