TPMT遗传多态性对硫嘌呤类药物疗效和毒性影响的研究进展

目的:总结硫嘌呤甲基转移酶(TPMT)遗传多态性对硫嘌呤类药物疗效和毒性影响的研究进展,为该药的个体化应用提供参考。方法:通过检索Pub Med和相关专业学术期刊全文数据库近10年来有关TPMT遗传多态性对硫嘌呤类药物疗效和毒性影响的研究文献,对TPMT遗传药理学研究进展作一整理归纳。结果和结论:TPMT是被研究得最早也是最多的一个硫嘌呤类药物代谢酶。TPMT遗传多态性和酶活性的个体差异可以部分解释患者服用硫嘌呤类药物后疗效和不良反应的不同。但目前其与硫嘌呤类药物所致的不良反应之间的关系尚没有统一的结论。对于TPMT遗传多态性对硫嘌呤类药物个体化应用的影响有待于多中心大样本的前瞻性研究以证实。     

次黄苷三磷酸焦磷酸酶遗传多态性对硫嘌呤类药物疗效和不良反应影响的研究进展

硫嘌呤类药物作为一类常用的免疫抑制剂,广泛应用于临床.然而其治疗窗窄,药动学个体差异大一直是困扰该类药物临床应用的难题.尽管硫嘌呤甲基转移酶（thiopurine methyltransferase,TPMT）基因多态性被认为是影响硫嘌呤类药物药动学的主要遗传因素,但研究结论并不统一.而最近的一些研究将焦点集中到了次黄苷三磷酸焦磷酸酶（inosine triphosphate pyrophosphatase,ITPA）的遗传多态性上.因此,本文就ITPA遗传多态性对硫嘌呤类药物疗效和毒性影响的研究进展作一综述,以期为临床个体化应用硫嘌呤类药物提供理论指导.     

硫嘌呤甲基转移酶基因多态性的硫唑嘌呤个体化用药临床研究分析

硫唑嘌呤属于硫嘌呤类药物,是一种免疫抑制药。硫嘌呤甲基转移酶(thiopurine S-methyltransferase, TPMT)是参与硫唑嘌呤代谢的重要酶,TPMT的基因多态性是导致个体间用药差异的重要因素。TPMT基因遗传多态性导致酶活性存在个体差异,从而使接受硫唑嘌呤治疗的人群表现出不同的疗效和药物不良反应。TPMT的遗传多态性能够影响到TPMT酶的活性,而不同TPMT活性的患者在服用硫唑嘌呤后的药效学不同。越来越多的研究证实,在服用硫唑嘌呤之前进行基因型检测,针对不同TPMT活性的患者进行硫唑嘌呤个体化用药指导,可以有效地提高疗效,降低药物不良反应。本研究综述了基于TPMT基因多态性的硫唑嘌呤个体化用药治疗现状,通过讨论TPMT基因型指导下对不同患者服用硫唑嘌呤后的临床结局的影响,以及精准用药的建议,尤其关注了中国人群中TPMT用药的研究现状,以期为不同人群进行硫唑嘌呤治疗提供用药建议。     

影响硫嘌呤类药物个体化应用的主要代谢酶遗传多态性的研究进展

硫嘌呤类药物作为一类常用的免疫抑制药,广泛应用于临床。然而其治疗窗窄,药动学个体差异大一直是困扰该类药物临床应用的难题。许多因素可影响硫嘌呤类药物的代谢及药理效应,但其代谢过程中涉及的代谢酶所具有的遗传药理学方面的个体差异被认为是主要因素。近年来各主要代谢酶的遗传多态性对硫嘌呤类药物药动学和药效学的影响也逐渐成为了关注的焦点。因此本文就相关代谢酶(TPMT,ITPA,GST,HPRT,XO,IMPDH及GMPS)的遗传多态性与硫嘌呤类药物疗效和不良反应的相关性进行综述,以期为临床硫嘌呤类药物个体化应用提供指导。     

硫嘌呤甲基转移酶分子机制研究进展

硫嘌呤甲基转移酶（TPMT）在硫嘌呤类药物的体内代谢中起着关键作用，其活性水平与药物效应及毒副作用密切相关。TPMT活性具有遗传多态性和种族差异。TPMT酶活性降低或缺乏与其基因突变密切相关。对TPMT遗传多态性分子基础的研究具有重要意义。本文综述有关TPMT基因表达调控和TPMT基因突变的分子机制的研究进展。     

肾移植受者硫嘌呤甲基转移酶基因多态性与硫唑嘌呤不良反应关系的研究

目的:探讨硫嘌呤甲基转移酶(thiopurine S-methyltransferase,TPMT)表型和基因多态性与硫唑嘌呤(AZA)所致不良反应的关系。方法:应用高效液相色谱法(HPLC)测定150例肾移植患者红细胞TPMT活性,采用等位基因特异性的PCR和限制性片断长度多态性的方法检测TPMT*2、*3A、*3B和*3C四种基因型,分析TPMT活性和基因多态性与AZA所致不良反应的关系。结果:30例(20%)患者由于发生了不良反应而停用AZA或减少了AZA的用量,其中12例患者发生了血液毒性,另外18例发生了肝脏毒性。将未发生不良反应的患者作为对照组,其红细胞TPMT活性范围为16.63~68.25 U,平均为(38.43±11.59)U。发生了血液毒性的患者红细胞TPMT活性平均为(24.16±9.84)U,明显低于未发生不良反应的患者(P=0.0003)。另外18例发生了肝脏毒性的患者TPMT活性离散度较大,与对照组比较差异无统计学意义(P=0.145)。本研究未发现TPMT活性缺乏者。共发现7例(4.7%)TPMT*3C杂合子患者,这7例患者均为TPMT中等活性13.04~19.21 U,平均为(...     

影响硫嘌呤类药物个体化应用的相关转运体遗传多态性的研究状况

硫嘌呤类药物作为一类常用的免疫抑制剂,其疗效和不良反应的差异与转运体的基因多态性的关系已成为研究热点,本文收集并分析了相关转运体的遗传多态性与硫嘌呤类药物疗效和不良反应的相关性报道,以期为临床硫嘌呤类药物个体化应用提供一定参考。     

硫嘌呤甲基转移酶(TPMT)与硫嘌呤类药物的个体化用药

临床上硫嘌呤类药物用于急性白血病、器官移植和一些自身免疫疾病的治疗已近40年,由于此类药物可产生严重的甚至可危及生命的血液毒性,故其合理使用在临床上倍受关注.众多研究表明,硫嘌呤甲基转移酶(TPMT)与这类药物的临床疗效和毒性密切相关,因此,TPMT的研究与监测对硫嘌呤类药物的合理使用有重要意义.     

嘌呤类药物代谢酶和代谢物与药物反应关联及影响因素研究进展

临床上嘌呤类药物作为免疫抑制剂广泛应用于治疗实体器官移植、自身免疫性疾病和炎症性肠病、儿童急性淋巴细胞性白血病等疾病,但该类药物体内处置个体间差异大,治疗窗窄,且所致不良反应（如肾毒性和肝毒性）发生率较高。本文综述近年来嘌呤类药物代谢酶（TPMT、NDPK、ITPA、GST、XO/XDH、HGPRT、IMPDH和NUDT15）和代谢物（6-MMPR、6-TGNs、6-TGTP）对该类药物临床疗效和不良反应的影响,以及患者服药剂量和疗程、性别、年龄、体质量、遗传等多因素对代谢酶和代谢物影响的研究进展。研究表明该类药物临床疗效和不良反应与其体内代谢酶活性和代谢物浓度密切相关,但结论并不完全一致,因此有待大规模临床研究进一步验证以上关联性及影响因素。     

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.     

Clinical pharmacogenomics of thiopurine S-methyltransferase

Thiopurine methyltransferase (TPMT) catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine (6-MP), thioguanine and azathioprine (AZA). These drugs are used to treat conditions such as acute lymphoblastic leukemia, inflammatory bowel disease, rheumatoid arthritis, and organ transplant rejection. This review highlights the polymorphisms of TPMT gene and their clinical impact on the use of thiopurine drugs. To date, there are 18 known mutational TPMT alleles. The three main TPMT alleles, namely TPMT *2, *3A and *3C, account for 80 - 95% of the intermediate and low enzyme activity. The TPMT gene exhibits significant genetic polymorphisms among all ethnic groups studied. Patients who inherited very low levels of TPMT activity are at greatly increased risk for thiopurine-induced toxicity such as myelosuppression, when treated with standard doses of these drugs, while subjects with very high activity may be undertreated. Moreover, clinical drug interactions may occur due to TMPT induction or inhibition. Identification of the TPMT mutant alleles allows physicians to tailor the dosage of the thiopurine drugs to the genotype of the patient or to use alternatives, improving therapeutic outcome.     

Pharmacogenetics of thiopurine therapy in paediatric IBD patients

BACKGROUND: Azathioprine is widely used in the treatment of children with inflammatory bowel disease. The occurrence and type of adverse events to azathioprine may be related to thiopurine S-methyltransferase (TPMT) enzyme activity and to inosine triphophate pyrophosphatase (ITPase) deficiency. AIM: Investigate frequencies of functional TPMT polymorphisms and ITPA polymorphisms and their association with the occurrence of adverse events during azathioprine therapy in a paediatric inflammatory bowel disease population. METHODS: Seventy-two azathioprine treated paediatric inflammatory bowel disease patients, 47% girls, mean age 12.5 years (range 6.5-17.5), were assessed for TPMT and ITPA polymorphisms and for adverse events. The relation between polymorphisms and adverse events is evaluated. RESULTS: Of all azathioprine treated patients, 11 experienced an adverse event for which azathioprine was stopped: pancreatitis (n = 4), leucopenia (n = 2) and 'general malaise' (n = 5). Of the 11 patients who stopped azathioprine because of adverse events, 10 had wild-type alleles for all investigated genotypes. Genotyping of ITPA 94C>A polymorphisms showed that two patients were homozygous, both tolerated azathioprine well. CONCLUSIONS: No association of functional ITPA and TPMT polymorphisms and the occurrence of azathioprine related adverse events could be detected. Pharmacogenetic assessment prior to thiopurine therapy does not seem warranted.     

Clinical Utility of Thiopurine S-Methyltransferase Genotyping

Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme that plays a major role in the metabolism of thiopurine drugs such as mercaptopurine and azathioprine. The interindividual differences in response to thiopurine administration is in part due to the presence of genetic polymorphisms in the gene that regulates TPMT activity. TPMT genotype correlates well with the in vivo enzyme activity within erythrocytes. Patients with genetically determined decreased TPMT activity develop severe myelosuppression when treated with standard doses of thiopurine drugs because an excess of thioguanine nucleotides accumulates in hematopoietic tissues. TPMT genotyping provides clinicians with a reliable method for identifying TPMT-deficient patients who can benefit from low doses of thiopurine drugs in order to reduce the risk of developing adverse effects. Moreover, the administration of higher doses of the drug could improve therapeutic response in patients in whom the TPMT genotyping demonstrates the absence of mutated alleles.     

Detection assay of rare variants of the thiopurine methyltransferase gene by PCR-RFLP using a mismatch primer in a Japanese population

Thiopurine methyltransferase (TPMT) catalyzes the metabolism of important drugs such as 6-mercaptopurine, 6-thioguanine, and azathioprine. The identification and frequency distributions of several variant TPMT alleles (TPMT*2--*8) have been described recently in many ethnic groups. We have recently demonstrated that TPMT*3C is the most common allele in Japanese subjects; however, it remains to be elucidated whether TPMT*4--*8 variants also exist in Japanese subjects. To detect polymorphisms in the TPMT gene (TPMT*4--*8), we have developed a mismatch polymerase chain reaction and restriction fragment length polymorphism method and conducted a population study of Japanese subjects. Genotyping of these variant forms was carried out in 192 Japanese healthy volunteers. The TPMT*4, TPMT*5, TPMT*6, TPMT*7, and TPMT*8 variants were not detected in any of the samples analyzed. This study provides the first analysis of the TPMT*4--*8 variants in a sample of the Japanese population and indicates that TPMT*4--*8 variants do not occur or are rare alleles in this population.     

Adverse drug reactions to azathioprine therapy are associated with polymorphism in the gene encoding inosine triphosphate pyrophosphatase (ITPase)

Adverse drug reactions to azathioprine (AZA), the pro-drug of 6-mercaptopurine (6-MP), occur in 15% to 28% of patients and the majority are not explained by thiopurine methyltransferase (TPMT) deficiency. Inosine triphosphate pyrophosphatase (ITPase) deficiency results in the benign accumulation of the inosine nucleotide ITP. 6-MP is activated through a 6-thio-IMP intermediate and, in ITPase deficient patients, potentially toxic 6-thio-ITP is predicted to accumulate. The association between polymorphism in the ITPA gene and adverse drug reactions to AZA therapy was studied in patients treated for inflammatory bowel disease. Sixty-two patients with inflammatory bowel disease suffering adverse drug reactions to AZA therapy were genotyped for ITPA 94C>A and IVS2 + 21A>C polymorphisms, and TPMT*3A, *3C, *2 polymorphisms. Genotype frequencies were compared to a consecutive series of 68 controls treated with AZA for a minimum of 3 months without adverse effect. The ITPA 94C>A deficiency-associated allele was significantly associated with adverse drug reactions [odds ratio (OR) 4.2, 95% confidence interval (CI) 1.6-11.5, P = 0.0034]. Significant associations were found for flu-like symptoms (OR 4.7, 95% CI 1.2-18.1, P = 0.0308), rash (OR 10.3, 95% CI 4.7-62.9, P = 0.0213) and pancreatitis (OR 6.2,CI 1.1-32.6, P = 0.0485). Overall, heterozygous TPMT genotypes did not predict adverse drug reactions but were significantly associated with a subgroup of patients experiencing nausea and vomiting as the predominant adverse reaction to AZA therapy (OR 5.5, 95% CI 1.4-21.3, P = 0.0206). Polymorphism in the ITPA gene predicts AZA intolerance. Alternative immunosuppressive drugs, particularly 6-thioguanine, should be considered for AZA-intolerant patients with ITPase deficiency.     

The impact of thiopurine s-methyltransferase polymorphism on azathioprine-induced myelotoxicity in renal transplant recipients

Thiopurine S-methyltransferase (TPMT) is an enzyme that catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathioprine. TPMT activity exhibits an interindividual variability, mainly as a result of genetic polymorphism. Patients with intermediate or deficient TMPT activity are at risk for toxicity after receiving standard doses of thiopurine drugs. It has previously been reported that 3 variant alleles: TPMT*2, *3A, and *3C are responsible for over 95% cases of low enzyme activity. The purpose of this study was to explore the association between these polymorphisms and the occurrence of azathioprine adverse effects in 112 renal transplant recipients undergoing triple immunosuppressive therapy including azathioprine, cyclosporine, and prednisone. TPMT genetic polymorphism was determined using PCR-RFLP and allele-specific PCR methods. Azathioprine dose, leukocyte, erythrocyte, and platelet counts, graft rejection episodes, as well as cyclosporine levels were analyzed throughout the first year after organ transplantation. We found the frequency of leukopenia episodes (WBC < 4.0 x 10(9)/L) significantly higher in heterozygous patients (53.8%) compared with those with TPMT wild-type genotype (23.5%). One patient, who was a compound homozygote (3A/*3C), experienced severe azathioprine-related myelotoxicity each time after receiving the standard drug dose. Our results suggest that polymorphisms in TPMT gene may be responsible for approximately 12.5% of all leukopenia episodes in renal transplant recipients treated with azathioprine. Genotyping for the major TPMT variant alleles may be a valuable tool in preventing AZA toxicity and optimization of immunosuppressive therapy.     

Lack of association between the ITPA 94C>A polymorphism and adverse effects from azathioprine

A 94C>A missense mutation in the ITPA gene which encodes inosine triphosphate pyrophosphatase has been associated with adverse effects from azathioprine, specifically flu-like symptoms, pancreatitis and rash. We hypothesized that this association may also be present in a larger, population-based group of inflammatory bowel disease patients intolerant of thiopurine drugs. We performed genotyping for this polymorphism and TPMT*2 and TPMT*3 in 73 such patients and 74 patients with inflammatory bowel disease who have tolerated azathioprine. We could not demonstrate a significant association between the ITPA94C>A genotype and any adverse effects (Odds ratio (OR) 1.015, 95% confidence interval (CI) 0.360-2.867, P = 0.593), flu-like symptoms (OR 1.547, 95%CI 0.368-6.496, P = 0.398), rash (no ITPA 94C>A polymorphism identified) or pancreatitis (no ITPA 94C>A polymorphism identified). We found no significant association between the ITPA 94C>A polymorphism and adverse effects to thiopurine drugs.     

Explaining TPMT genotype/phenotype discrepancy by haplotyping of TPMT*3A and identification of a novel sequence variant, TPMT*23

Thiopurine methyltransferase (TPMT) is a polymorphic enzyme involved in the metabolism of thiopurine drugs. Owing to polymorphisms in the TPMT gene (TPMT*2-*22), the enzyme activity varies interindividually. Patients with reduced TPMT activity may develop adverse reactions when treated with standard doses of thiopurines. This work focuses on a TPMT genotype/phenotype discrepancy found in a patient during routine testing. The patient displayed very low TPMT enzyme activity and she was genotyped by pyrosequencing as being heterozygous for the 460G>A and 719A>G polymorphisms (TPMT*3A). Complete sequencing in combination with haplotyping of the TPMT gene revealed a novel sequence variant, 500C>G, on one allele and TPMT*3A on the other allele, giving rise to the novel genotype TPMT*3A/*23. When investigating the patient's relatives, they too had the TPMT*3A/*23 genotype in combination with low enzyme activity. We conclude that this novel variant allele affects enzyme activity, as the individuals carrying it had almost undetectable TPMT activity.