Influence of thiopurine S-methyltransferase polymorphisms in mercaptopurine pharmacokinetics in healthy volunteers

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.

Bioequivalence of Two 6-Mercaptopurine Tablet Formulations in Healthy Fasting Chinese Volunteers

The supply of branded 6-mercaptopurine (6-MP) is limited in China, necessitating the local production and clinical evaluation of generic alternatives. We evaluated the in vivo bioequivalence (BE) of a new generic mercaptopurine tablet (50 mg) formulation by comparing peak plasma concentration and area under the concentration-time curve (AUC) with a branded 6-MP formulation as the reference in 36 healthy fasting Chinese adults. The in vivo BE was evaluated by the average BE test. The safety parameters of the test and reference formulations were also evaluated. The geometric mean ratios for AUC over the dosing interval and AUC from time zero to infinity were 104% and 104%, respectively, of the reference values, while the point estimate of the geometric mean ratio for peak plasma concentration was 104% of the reference value. The test and reference formulations in this study were both deemed safe as only 23 Grade 1 adverse events were observed in 13 of 36 subjects. The test and reference formulations of 6-MP tablets meet the regulatory criteria for BE in healthy fasting Chinese adults.

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

BACKGROUND

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSION

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

Impact of Inflammatory Bowel Disease (IBD) and IBD Medications on Risk of Hyperlipidemia and in vitro Hepatic Lipogenic-Related Gene Expression: A Population-Based Cohort Study

Patients with inflammatory bowel disease (IBD) present a higher risk of developing cardiovascular diseases (CVDs) due to chronic inflammation, which plays an essential role in atherogenesis. Hyperlipidemia is another risk factor for CVDs; however, the association between IBD, IBD medications, and hyperlipidemia remains controversial. We conducted a nationwide, population-based, retrospective, cohort study to examine the effect of IBD and IBD medications on the risk of developing hyperlipidemia. The effects of IBD medications on the expression of lipogenesis-related hepatic genes were also evaluated. We obtained data from the Longitudinal Health Insurance Database of Taiwan from patients with new-onset IBD and a comparison cohort of patients without IBD. A Cox proportional hazards regression model was used to analyze the difference in the risk of developing hyperlipidemia between the two cohorts. We also examined the influence of IBD medications on the expression of lipogenesis-related hepatic genes. After adjusting for comorbidities and confounding factors, the case group (N = 14,524) had a higher risk for hyperlipidemia than the control group (N = 14,524) [adjusted hazards ratio (aHR), 2.18]. Patients with IBD that did not receive IBD medications exhibited a significantly higher risk of hyperlipidemia (aHR, 2.20). In those treated with IBD medications, the risk of developing hyperlipidemia was significantly lowered than those without such medications (all aHR ≤ 0.45). Gene expression analysis indicated that IBD medications downregulated the expression of lipogenesis-related genes. Screening blood lipids in IBD patients is needed to explore the specific role and impact of IBD medications in the development of CVD.

Curing the Curable: Managing Low-Risk Acute Lymphoblastic Leukemia in Resource Limited Countries

Although childhood acute lymphoblastic leukemia (ALL) is curable, global disparities in treatment outcomes remain. To reduce these global disparities in low-middle income countries (LMIC), a paradigm shift is needed: start with curing low-risk ALL. Low-risk ALL, which accounts for >50% of patients, can be cured with low-toxicity therapies already defined by collaborative studies. We reviewed the components of these low-toxicity regimens in recent clinical trials for low-risk ALL and suggest how they can be adopted in LMIC. In treating childhood ALL, the key is risk stratification, which can be resource stratified. NCI standard-risk criteria (age 1–10 years, WBC < 50,000/uL) is simple yet highly effective. Other favorable features such as ETV6-RUNX1, hyperdiploidy, early peripheral blood and bone marrow responses, and simplified flow MRD at the end of induction can be added depending on resources. With limited supportive care in LMIC, more critical than relapse is treatment-related morbidity and mortality. Less intensive induction allows early marrow recovery, reducing the need for intensive supportive care. Other key elements in low-toxicity protocol designs include: induction steroid type; high-dose versus low-dose escalating methotrexate; judicious use of anthracyclines; and steroid pulses during maintenance. In summary, the first effective step in curing ALL in LMIC is to focus on curing low-risk ALL with less intensive therapy and less toxicity.

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.