Determinants of mercaptopurine toxicity in paediatric acute lymphoblastic leukemia maintenance therapy

AIMS

6-mercaptopurine (6-MP) is used in the treatment of childhood acute lymphoblastic leukaemia (ALL). Its red blood cell (RBC) metabolite concentrations (6-thioguanine [6-TGN] and 6-methylmercaptopurine nucleotides [6-MMPN]) are related to drug response. We investigated the impact of non-genetic covariates and pharmacogenetic polymorphisms affecting thiopurine methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) on 6-MP metabolism and response.

METHODS

Sixty-six children with ALL treated according to EORTC 58951 protocol were included in this study. Six patients had a heterozygous genotype for the most common TPMT polymorphisms, nine for ITPA 94 C > A and 17 for ITPA IVS2+21 A > C. 6-MP metabolites concentrations were analyzed by mixed model analysis.

RESULTS

During maintenance, steady-state RBC 6-TGN concentrations were lower in patients aged 6 years or younger (493 pmol/8 × 10⁸RBC) than in older children (600 pmol/8 × 10⁸RBC). 6-MMPN concentrations were low in patients with TPMT variant/wild-type ITPA (1862 pmol/8 × 10⁸RBC), intermediate in wild-type patients and high (16468 pmol/8 × 10⁸RBC) in patients wild-type TPMT/variant ITPA. A 6-MMPN threshold of 5000 pmol/8 × 10⁸RBC was associated with an increased risk of hepatotoxicity.

CONCLUSION

In this study, age and both TPMT and ITPA genotypes influenced 6-MP metabolism. High 6-MMPN was associated with hepatotoxicity. These pharmacological tools should be used to monitor ALL treatment in children.     

Pharmacogenomic studies of the anticancer and immunosuppressive thiopurines mercaptopurine and azathioprine

AIMS

To examine the allelic variation of three enzymes involved in 6-mercaptopurine/azathioprine (6-MP/AZA) metabolism and evaluate the influence of these polymorphisms on toxicity, haematological parameters and metabolite levels in patients with acute lymphoblastic leukaemia (ALL) or inflammatory bowel disease (IBD).

METHODS

Clinical data and blood samples were collected from 19 ALL paediatric patients and 35 IBD patients who were receiving 6-MP/AZA therapy. All patients were screened for seven genetic polymorphisms in three enzymes involved in mercaptopurine metabolism [xanthine oxidase, inosine triphosphatase (C94→A and IVS2+21A→C) and thiopurine methyltransferase]. Erythrocyte and plasma metabolite concentrations were also determined. The associations between the various genotypes and myelotoxicity, haematological parameters and metabolite concentrations were determined.

RESULTS

Thiopurine methyltransferase variant alleles were associated with a preferential metabolism away from 6-methylmercaptopurine nucleotides (P = 0.008 in ALL patients, P = 0.038 in IBD patients) favouring 6-thioguanine nucleotides (6-TGNs) (P = 0.021 in ALL patients). Interestingly, carriers of inosine triphosphatase IVS2+21A→C variants among ALL and IBD patients had significantly higher concentrations of the active cytotoxic metabolites, 6-TGNs (P = 0.008 in ALL patients, P = 0.047 in IBD patients). The study confirmed the association of thiopurine methyltransferaseheterozygosity with leucopenia and neutropenia in ALL patients and reported a significant association between inosine triphosphatase IVS2+21A→C variants with thrombocytopenia (P = 0.012).

CONCLUSIONS

Pharmacogenetic polymorphisms in the 6-MP pathway may help identify patients at risk for associated toxicities and may serve as a guide for dose individualization.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• 6-Mercaptopurine (6-MP) and azathioprine (AZA) are both inactive prodrugs that require intracellular activation into the active 6-thioguanine nucleotides (6-TGNs).
• This metabolic process undergoes three different competitive pathways that are catalysed by three different enzymes; xanthine oxidase (XO), thiopurine methyltransferase (TPMT) and inosine triphosphatase (ITPA), all of which exhibit genetic polymorphisms.
• Although the impact of genetic variation in the TPMT gene on treatment outcome and toxicity has been demonstrated, the role of other polymorphisms remains less well known.

WHAT THIS STUDY ADDS

• New information on the allelic variation of these three enzymes (XO, TPMT and ITPA) and their influence on 6-MP/AZA metabolism and toxicity.
• Confirmation of the association of TPMT polymorphism with haematological toxicity.
• Identified potential genetic characteristics that may contribute to higher risk of adverse events (such as ITPA IVS2+21A→C mutation).

     

Population pharmacokinetic and pharmacogenetic analysis of 6-mercaptopurine in paediatric patients with acute lymphoblastic leukaemia

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• The cytotoxic effects of 6-mercaptopurine (6-MP) were found to be due to drug-derived intracellular metabolites (mainly 6-thioguanine nucleotides and to some extent 6-methylmercaptopurine nucleotides) rather than the drug itself.
• Current empirical dosing methods for oral 6-MP result in highly variable drug and metabolite concentrations and hence variability in treatment outcome.

WHAT THIS STUDY ADDS

• The first population pharmacokinetic model has been developed for 6-MP active metabolites in paediatric patients with acute lymphoblastic leukaemia and the potential demographic and genetically controlled factors that could lead to interpatient pharmacokinetic variability among this population have been assessed.
• The model shows a large reduction in interindividual variability of pharmacokinetic parameters when body surface area and thiopurine methyltransferase polymorphism are incorporated into the model as covariates.
• The developed model offers a more rational dosing approach for 6-MP than the traditional empirical method (based on body surface area) through combining it with pharmacogenetically guided dosing based on thiopurine methyltransferase genotype.

AIMS

To investigate the population pharmacokinetics of 6-mercaptopurine (6-MP) active metabolites in paediatric patients with acute lymphoblastic leukaemia (ALL) and examine the effects of various genetic polymorphisms on the disposition of these metabolites.

METHODS

Data were collected prospectively from 19 paediatric patients with ALL (n = 75 samples, 150 concentrations) who received 6-MP maintenance chemotherapy (titrated to a target dose of 75 mg m⁻² day⁻¹). All patients were genotyped for polymorphisms in three enzymes involved in 6-MP metabolism. Population pharmacokinetic analysis was performed with the nonlinear mixed effects modelling program (nonmem) to determine the population mean parameter estimate of clearance for the active metabolites.

RESULTS

The developed model revealed considerable interindividual variability (IIV) in the clearance of 6-MP active metabolites [6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-mMPNs)]. Body surface area explained a significant part of 6-TGNs clearance IIV when incorporated in the model (IIV reduced from 69.9 to 29.3%). The most influential covariate examined, however, was thiopurine methyltransferase (TPMT) genotype, which resulted in the greatest reduction in the model''s objective function (P < 0.005) when incorporated as a covariate affecting the fractional metabolic transformation of 6-MP into 6-TGNs. The other genetic covariates tested were not statistically significant and therefore were not included in the final model.

CONCLUSIONS

The developed pharmacokinetic model (if successful at external validation) would offer a more rational dosing approach for 6-MP than the traditional empirical method since it combines the current practice of using body surface area in 6-MP dosing with a pharmacogenetically guided dosing based on TPMT genotype.     

NUDT15c.415C>T和TPMT*3C基因多态性检测方法的比较与临床应用

目的 建立准确、快速、经济的方法,检测NUDT15 c.415C>T和TPMT*3C基因多态性,探讨临床应用价值。方法 收集2017年5月-2018年5月期间福建汉族患者服用硫唑嘌呤2周以上的血清样本,提取DNA或白细胞后分别采用PCR-RFLP法、PCR-Sanger测序法和荧光定量PCR法对NUDT15 c.415C>T和TPMT*3C进行基因多态性分型,比较这3种方法的准确性、简便性及经济性。根据白细胞值分组,结合临床资料,探讨基因多态性等因素与硫唑嘌呤致白细胞减少的相关性。结果 共纳入129例患者,其中硫唑嘌呤致白细胞减少15例（11.6%）。3种方法的基因多态性检测结果一致,TPMT*3C未发现突变纯合子。携带NUDT15c.415C>T突变等位基因者服用硫唑嘌呤致白细胞减少的风险高于携带野生等位基因者（OR=6.2,95%CI：2.5~15.4,P=0.000 054）,而携带TPMT*3C突变等位基因者与野生等位基因者出现白细胞减少比例并无显著性差异（P=0.393）。NUDT15c.415C>T基因多态性预测白细胞减少敏感度为53.3%,特异度为85.1%,ROC曲线AUC为0.69。结论 3种方法都可用于临床检测NUDT15 c.415C>T和TPMT*3C基因多态性。PCR-RFLP法不需要专用试剂盒,也不需要昂贵的仪器设备,成本较低,过程简单,易于操作,特别适合条件有限的单位开展工作。福建汉族患者在服用硫唑嘌呤前进行NUDT15c.415C>T基因多态性检测比TPMT*3C更具临床价值。     

NUDT 15基因多态性与巯嘌呤类药物耐受性及其所致白细胞减少的研究进展

目的 综述NUDT 15基因多态性与巯嘌呤类药物耐受性及其所致白细胞减少的研究,以期为巯嘌呤类药物在临床中的应用提供参考。方法 检索国内外相关文献,进行整理和综合分析。结果 研究人群主要集中在亚洲,大多为韩国和日本人,在中国儿童急性淋巴细胞白血病患者中仅有2个人群的研究,在中国炎症性肠病患者中有3个相关研究。大多数研究显示在亚洲人群中NUDT 15 c.415 C>T位点突变与巯嘌呤类药物的耐受性及相关白细胞减少有关,此外多个在炎症性肠患者群中的研究发现c.415 C>T纯合突变可能与严重脱发有关。结论 大多数研究显示亚洲人群NUDT 15 c.415 C>T位点突变与巯嘌呤类药物的耐受性及相关白细胞减少有关,该位点的测定可能会优化巯嘌呤类药物在临床中的应用,但其他NUDT 15基因位点突变相关的研究较少,还需要进一步探究。     

TPMT基因多态性与儿童ALL的6-MP个体化治疗

6-巯基嘌呤(6-MP)是儿童急性淋巴细胞白血病(ALL)维持治疗阶段的关键化疗药物.巯嘌呤甲基转移酶(TPMT)作为巯嘌呤类药物在体内代谢过程中的关键酶之一,其基因多态性及酶活性与急性淋巴细胞白血病患儿对6-巯基嘌呤的剂量耐受性有一定的相关性,从而进一步影响急性淋巴细胞白血病患儿服用6-巯基嘌呤后不良反应的发生程度和远期预后.此外,巯嘌呤甲基转移酶基因型也可能与继发恶性肿瘤有关.因此,检测巯嘌呤甲基转移酶活性或基因型,有助于预测巯嘌呤类药物不良反应的严重程度,及时调整给药剂量,制订安全合理的个体化用药方案.     

ABCC4 is regulated by microRNA-124a and microRNA-506

Multidrug resistance protein 4 (MRP4, ABCC4) is an efflux membrane transporter expressed in renal tubules, hepatocytes, brain capillaries, prostate and blood cells. MRP4 drives energy dependent efflux of important physiological and pharmacological compounds. MRP4 expression and function is highly variable but cannot be fully attributed to known mechanisms. The goal of this study was to characterize ABCC4 regulation by miRNAs and to assess the influence of ABCC4 3′-UTR polymorphisms on ABCC4 regulation by miRNAs. miR-124a and miR-506 decreased MRP4 protein levels in HEK293T/17 cells 20–30% and MRP4 function by 50%. These miRNAs did not affect ABCC4 mRNA expression. Moreover, miR-124a and miR-506 expression was negatively correlated with MRP4 protein expression in 26 human kidney samples (Spearman r = −0.62, P = 0.007 and r = −0.41, P = 0.03 for miR-124a and miR-506, respectively). To assess the effect of ABCC4 3′-UTR polymorphisms, six common 3′-UTR haplotypes were inferred in Caucasians, African Americans and Asians and tested in luciferase reporter assays. Multiple ABCC4 3′-UTR haplotypes caused significant reductions in luciferase activity; in the presence of miR-124a or miR-506 mimics the luciferase activity of all six ABCC4 3′-UTR haplotypes was further reduced. Mutation of the putative binding site for miR-124a and miR-506 in the ABCC4 3′-UTR eliminated the effect of these miRNAs. In conclusion, ABCC4 is directly regulated by miR-124a and miR-506 but polymorphisms in the ABCC4 3′-UTR have no significant effect on this miRNA regulation. Regulation of ABCC4 by miRNAs represents a novel mechanism for regulation of MRP4 function.     

Methylation of 6-mercaptopurine and 6-thioguanine by thiopurine S-methyltransferase A comparison of activity in red blood cell samples of 199 blood donors

Objectives: To compare 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) as substrates for the methylation reaction catalysed by the enzyme thiopurine S-methyltransferase (TPMT). Methods: TPMT activity in haemolysed red blood cells of healthy blood donors was determined twice, using the same experimental setting and equal molar concentrations of 6-TG and 6-MP as substrates. After extraction, the reaction products 6-methyl-TG and 6-methyl-MP were quantified using specific high-performance liquid chromatography procedures. Results: The medians of the TPMT activities from 199 blood donors were 54.4 nmol 6-MTG g⁻¹Hb h⁻¹ when measured with 6-TG as the substrate and 35.8 nmol 6-MMP g⁻¹ Hb h⁻¹ when measured with 6-MP. The correlation coefficient for the 199 pairs of values was 0.8695. On average, TPMT activity was 34% lower with 6-MP as substrate than with 6-TG as substrate. Received: 4 October 1999 / Accepted in revised form: 15 March 2000     

NUDT15 c.415C>T和TPMT*3C基因多态性与汉族人群服用硫唑嘌呤致白细胞减少关联性研究

目的：探讨NUDT15 c.415C>T和TPMT*3C基因多态性与汉族人群服用硫唑嘌呤致白细胞减少的关联性。方法：选取2017年5月-2018年5月在福建医科大学附属第一医院就诊,接受硫唑嘌呤治疗2周以上的汉族患者,PCR-RFLP法检测患者NUDT15 c.415C>T和TPMT*3C基因型,HPLC法测定患者红细胞内6-硫鸟嘌呤核苷酸谷浓度。根据白细胞值分组,结合临床资料,分析2种基因多态性与硫唑嘌呤致白细胞减少的相关性。结果：共纳入患者129例,白细胞减少组15例（11.6%）,白细胞正常组114例（88.4%）,2组在性别、年龄、日剂量、是否联合使用美沙拉秦或柳氮磺吡啶、沙利度胺、英夫利西及TPMT*3C基因多态性等均无显著性差异（P>0.05）。白细胞减少组53.3%（8/15）携带NUDT15 c.415>T突变基因,与白细胞正常组14.9%（17/114）差异有显著性（P=0.000 372）。携带该等位基因突变型患者出现白细胞减少风险高于携带野生型患者（OR=6.2,95%CI：2.5~15.4,P=0.000 054）,更易发生Ⅲ度以上严重的白细胞减少（P=0.000 022）。同一剂量范围野生型患者与突变型患者的6-硫鸟嘌呤核苷酸谷浓度并没有显著性差异（P>0.05）。NUDT15 c.415>T预测白细胞减少特异度为85.1%,敏感度为53.3%,ROC曲线AUC为0.69。结论：NUDT15c.415C>T基因多态性检测对降低汉族人群服用硫唑嘌呤致白细胞减少的风险具有较好的临床价值。     

NUDT15基因多态性与巯嘌呤类药物所致白细胞减少的研究进展

硫唑嘌呤（azathioprine,AZA）和6-巯基嘌呤（6-mercaptopurine,6-MP）被广泛用于炎症性肠病、急性淋巴细胞白血病的治疗,但以白细胞减少为主的不良反应一直是困扰临床安全用药的难题。研究发现个体间的基因差异与该不良反应密切相关,美国食品药品监督管理局早在2005年就推荐服药前进行巯嘌呤类药物代谢相关的巯基嘌呤甲基转移酶（TPMT）的基因型检测以评估白细胞减少不良反应的发生,但该位点不能很好地预防亚洲人群中该不良反应的频发。新近研究提示NUDT15基因位点与亚洲人群的白细胞减少更密切,本文将综述NUDT15位点与亚洲人群服用AZA/6-MP后出现的白细胞减少之间的相关性研究。     

Genetic polymorphism of inosine-triphosphate-pyrophosphatase influences mercaptopurine metabolism and toxicity during treatment of acute lymphoblastic leukemia individualized for thiopurine-S-methyl-transferase status

Importance of the field: Although genetic polymorphisms in the gene encoding human thiopurine methyltransferase (TPMT) are known to have a marked effect on mercaptopurine metabolism and toxicity, there are many patients with wild-type TPMT who develop toxicity. Furthermore, when mercaptopurine dosages are adjusted in patients who are heterozygous at the TPMT locus, there are still some patients who develop toxicity for reasons that are not fully understood. Therefore, we recently studied the effects of a common polymorphism in another gene encoding an enzyme involved in mercaptopurine metabolism (SNP rs1127354 in inosine-triphospate-pyrophosphatase, ITPA), showing that genetic polymorphism of ITPA is a significant determinant of mercaptopurine metabolism and of febrile neutropenia following combination chemotherapy of acute lymphoblastic leukemia (ALL) in which mercaptopurine doses are individualized based on TPMT genotype.

Area covered in this review: In this review, we summarize the knowledge available about the effect and clinical relevance of TPMT and ITPA on mercaptopurine pharmacogenomics, with a particular focus on the use of this medication in pediatric patients with ALL.

What the reader will gain: Reader will gain insights into: i) the effects of pharmacogenomic traits on mercaptopurine toxicity and efficacy for the treatment of ALL and ii) individualization strategies that can be used to mitigate toxicity without compromising efficacy in pediatric patients with ALL.

Take home message: Mercaptopurine dose can be adjusted on the basis of TPMT genotype to mitigate toxicity in pediatric patients with ALL. As treatment is individualized in this way for the most relevant genetic determinant of drug response (i.e., for mercaptopurine, TPMT), the importance of other genetic polymorphisms emerges (e.g., ITPA).     

Renal function in HIV/HBV co‐infected and HBV mono‐infected patients on a long‐term treatment with tenofovir in real life setting

The human immunodeficiency virus (HIV)/hepatitis B virus (HBV) co‐infection is likely to be associated with an increased risk of kidney disease, due to the additional factors that may affect renal function in the HIV population. We aimed to evaluate renal toxicity in HIV/HBV and HBV mono‐infected patients on long‐term therapy with tenofovir (TDF) and to explore the association of polymorphisms in ATP‐binding cassette (ABCC)2, ABCC4, ABCC10 with the development of renal dysfunction. From September 2006 to November 2014, 44 HIV/HBV co‐infected and 34 HBV mono‐infected patients were commenced on TDF. Data of renal safety were retrospectively collected and analyzed. ABCC2, ABCC4 and ABCC10 genotypes were identified by real‐time PCR. Over 60 months of observation, there was a significant increase in mean creatinine levels from baseline (P<.01) that was not significantly different between the two study groups. Moreover, a significant decline in estimated glomerular filtration rate (eGFR) was observed from baseline (P<.01), and it was significantly greater in HBV mono‐infected than co‐infected patients (P=.03). The distribution of ABCC2, ABCC4 and ABCC10 genotypes among a subgroup of 34 patients did not show significant association with eGFR decline <90 mL/min per 1.73 m². Although our findings showed a statistically significant decrease in eGFR with long‐term use of TDF, its clinical impact seems to be modest. The role of genetic factors to identify patients at greater risk for developing tenofovir‐induced renal toxicity needs to be further investigated.     

CYP2B6 (c.516G→T) and CYP2A6 (*9B and/or *17) polymorphisms are independent predictors of efavirenz plasma concentrations in HIV-infected patients

AIMS

Interindividual variability in efavirenz pharmacokinetics is not entirely explained by the well-recognized CYP2B6 516G→T single nucleotide polymorphism. The aim of this study was to determine whether polymorphisms in the CYP2A6 gene can be used to enhance the predictability of efavirenz concentrations in human immunodeficiency virus (HIV)-infected native African patients.

METHODS

Mid-dose efavirenz plasma concentrations were determined at 4 and 8 weeks following initiation of antiretroviral therapy in 65 HIV-infected Ghanaian patients. Selected CYP2B6 and CYP2A6 genotypes were determined by commercial 5′-nuclease assays. Relationships between averaged 4- and 8-week mid-dose efavirenz concentrations, demographic variables and genotypes were evaluated by univariate and multivariate statistical approaches including gene–gene interactions.

RESULTS

CYP2B6 c.516G→T, CYP2B6 c.983T→C, CYP2A6*9B and CYP2A6*17 allele frequencies were 45, 4, 5 and 12%, respectively. Rifampicin therapy, gender, age and body mass index had no significant influence on efavirenz mid-dose concentrations. Median efavirenz concentrations were more than five times higher (P < 0.001) in patients with CYP2B6 c.516TT genotype compared with GG and GT genotypes. Although none of the CYP2A6 genotypes was associated with altered efavirenz concentrations individually, CYP2A6*9B and/or CYP2A6*17 carriers showed a 1.8 times higher median efavirenz concentration (P= 0.017) compared with noncarriers. Multiple linear regression analysis indicated that the CYP2B6 c.516G→T polymorphism and CYP2A6 slow-metabolizing variants accounted for as much as 36 and 12% of the total variance in efavirenz concentrations, respectively.

CONCLUSIONS

Our findings support previous work showing efavirenz oxidation by CYP2A6, and suggest that both CYP2A6 and CYP2B6 genotyping may be useful for predicting efavirenz plasma concentrations.     

小样本探讨黄嘌呤脱氢酶和鸟苷酸合成酶基因多态性对硫唑嘌呤所致骨髓抑制和脱发的影响

摘要：目的 研究黄嘌呤脱氢酶(Xanthine dehydrogenase,XDH)和鸟苷酸合成酶(Guanosine monophosphate synthetase,GMPS)基因多态性对硫唑嘌呤(Azathioprine,AZA)所致骨髓抑制和脱发的影响,探讨上述位点联合NUDT15 rs116855232检测对预测AZA所致骨髓抑制的价值。方法 回顾性分析曾经服用或正在服用AZA治疗自身免疫性疾病患者,收集静脉血采用直接测序法测定GMPS rs61750368、rs61750369,XDH rs2295475、rs1884725、rs17011368、rs566362和NUDT15 rs116855232基因型。依据不良反应进行分组,分析上述基因型与AZA所致骨髓抑制和脱发的相关性,NUDT15 rs116855232作为对照位点。结果 共纳入80例患者,2组在年龄、日剂量、疗程、BMI以及6-硫鸟嘌呤核苷酸浓度均无显著性差异(P＞0.05)。Logistic回归分析表明,AZA所致骨髓抑制与XDH rs229547突变相关(P=0.003, OR=3.10, 95% CI: 1.45~6.25),该基因预测骨髓抑制敏感度为69.6%,特异度为63.2%,ROC曲线AUC为0.66;NUDT15 rs116855232突变也和AZA所致骨髓抑制相关(P=0.008, OR=3.46, 95% CI: 1.21~9.93);其余位点基因型暂未发现与骨髓抑制和脱发相关。rs116855232野生型且rs2295475突变型的患者对比两位点野生型的患者,其骨髓抑制的危险值升高(OR=6.53, P=0.004),而两位点同时突变者骨髓抑制的危险值更高(OR=51.67, P＜0.001)。结论 在中国自身免疫性疾病患者中XDH rs2295475突变可能为AZA诱导骨髓抑制的独立危险因素,尽管预测准确度较低但仍有预测价值。尤其XDH联合NUDT15 rs116855232监测,可能会弥补NUDT15 野生型者对骨髓抑制预测不足的风险,提高NUDT15突变型对骨髓抑制预测的准确性,但以上结果还更多临床研究验证。     

巯嘌呤甲基转移酶基因检测用于指导6-巯基嘌呤在中国儿童急性淋巴细胞白血病中个体化治疗的循证评价

目的　系统评价6-巯基嘌呤(6-mercaptopurine, 6-MP)治疗亚洲儿童急性淋巴细胞白血病(acute lymphoblastic leukemia, ALL)出现骨髓抑制与巯嘌呤甲基转移酶(thiopurine methyltransferase, TPMT)基因多态性的相关性,并分析中国ALL患儿TPMT基因检测的经济性。方法　采用循证医学方法搜集6-MP治疗亚洲儿童ALL相关骨髓抑制与TPMT基因多态性相关的随机对照试验或观察性研究进行Meta分析。借助决策树模型针对中国ALL患儿,对两种6-MP初始给药剂量方案,进行成本效果分析。结果　最终纳入6个观察性研究,共577例亚洲患儿。Meta分析结果显示：TPMT基因多态性与骨髓毒性［OR=5.61,95%CI（2.05,15.34）,P=0.0008］发生有关。在基础数据分析中,针对中国ALL患儿,以上两个方案以严重骨髓抑制发生率为效果指标,增量成本-效果比为10403.83,敏感性分析显示结果稳定。结论　亚洲ALL患儿的TPMT基因多态性与6-MP的骨髓毒性显著相关。决策树模型结果显示,在中国,ALL患儿通过TPMT基因检测调整6-MP初始剂量并不优于标准剂量给药。     

Simple pharmacokinetic models accounting for drug monitoring results of atomoxetine and its 4-hydroxylated metabolites in Japanese pediatric patients genotyped for cytochrome P450 2D6

Atomoxetine is an approved medicine for attention-deficit/hyperactivity disorder and a cytochrome P450 2D6 (CYP2D6) probe substrate. Simple physiologically based pharmacokinetic (PBPK) models and compartment models were set up to account for drug monitoring results of 33 Japanese patients (6–15 years of age) to help establish the correct dosage for the evaluation of clinical outcomes. The steady-state one-point drug monitoring data for the most participants indicated the extensive biotransformation of atomoxetine to 4-hydroxyatomoxetine under individually prescribed doses of atomoxetine. However, 5 participants (with impaired CYP2D6 activity scores based on the CYP2D6 genotypes) showed high plasma concentrations of atomoxetine (0.53–1.5 μM) compared with those of total 4-hydroxyatomoxetine (0.49–1.4 μM). Results from full PBPK models using the in-built Japanese pediatric system of software Simcyp, one-compartment models, and new simple PBPK models (using parameters that reflected the subjects' small body size and normal/reduced CYP2D6-dependent clearance) could overlay one-point measured drug/metabolite plasma concentrations from almost common 28 participants within threefold ranges. Validated one-compartment or simple PBPK models can be used to predict steady-state plasma concentrations of atomoxetine and/or its primary metabolites in Japanese pediatric patients (>6 years) who took a variety of individualized doses in a clinical setting.     

Rectal bioavailability of 6-mercaptopurine in children with acute lymphoblastic leukaemia: partial avoidance of “first-pass” metabolism

Summary Plasma levels and the area under the plasma concentration-time curve (AUC) values of 6-mercaptopurine (6-MP) were determined in a balanced crossover study of oral (powder) and rectal (macrogol suppository) administration to 5 children with acute lymphoblastic leukaemia (ALL). The AUC (538.6 ng · h · ml^–1) after the rectal dose of 30 mg/m² was approximately 1.5-times of that (365.5 ng · h · ml^–1) after the oral dose of 87.5 mg/m². The coefficients of variation of interindividual variability of the AUCs were 21.5% and 32.3%, respectively. The relative bioavailability of the macrogol suppository compared to the powder was approximately 4.39. These findings indicate that rectal administration of 6-MP could avoid the first-pass effect of this drug in the alimentary canal and/or liver, resulting in a large AUC of 6-MP, and so could reduce interindividual variability in plasma 6-MP concentrations. Rectal administration of 6-MP may be more effective than empirical oral dosing for the treatment of children with ALL, especially for patients with nausea and/or vomiting.A preliminary account of this work was presented at the 19th Annual Meeting International Society for Experimental Haematology, Seattle, Washington, 26–30 August 1990     

The impact of cytokines on the expression of drug transporters,cytochrome P450 enzymes and chemokine receptors in human PBMC

Background and purpose:

The function of transporters in peripheral blood mononuclear cells (PBMC) has been characterized, but less is known about cytochrome P450 (CYP) enzyme function in these cells. Given that cytokines are dysregulated in many diseases, the purpose of this work was to assess the impact of cytokines on the expression of CYPs, transporters and chemokine receptors in PBMC.

Experimental approach:

Human PBMC were incubated with cytokines for 48 h. ATP-binding cassette (ABC)B1, ABCC1, ABCC2, CYP2B6, CYP3A4, CXCR4 and CCR5 expression were measured by quantitative polymerase chain reaction and flow cytometry at 0, 4, 8, 24 and 48 h. Enzyme activity was assessed using fluorescent probes.

Key results:

We show here functional activity of CYP3A4 and CYP2B6 in PBMC. Furthermore, cytokines had a significant impact on the mRNA and protein expression of all proteins. For example, interleukin-2 (IL-2) had a marked impact on ABCB1 mRNA (% control 4745 ± 11961) and protein (% control 200 ± 57). Increases in drug efflux transporter expression, in response to cytokines, resulted in reduced cellular accumulation of digoxin [decrease of 17% and 26% for IL-2 and interferon-γ (IFNγ) respectively] and saquinavir (decrease of 28% and 30% for IL-2 and IFNγ respectively). The degree to which drug transporter and chemokine receptor expression changed in response to cytokines was positively correlated (e.g. ABCB1 and CXCR4, r² = 0.545).

Conclusions and implications:

These data have important implications for diseases in which cytokines are dysregulated and for which pharmacological intervention targets immune cells.