Role of UGT1A1*28 and UGT1A1*6 for irinotecan-induced adverse drug reaction

Irinotecan is widely used in the treatment of colorectal, gastric, and lung cancers. However, adverse drug reactions such as severe diarrhea and neutropenia limit the dose of this drug. Irinotecan is metabolized by carboxylesterase to form an active metabolite, 7-ethyl-10-hydroxycamptothecin(SN-38), which in turn is subsequently conjugated by UGT-glucuronosyltransferase 1A1(UGT1A1)to yield an inactive form, SN-38 glucuronide(SN-38 G). The UGT1A1 gene polymorphisms contribute to the individual variation in adverse events among patients administered irinotecan. However, the distribution of polymorphisms shows large interethnic differences. The distribution of UGT1A1*28 greatly differs between Caucasians and Japanese; the frequency of UGT1A1*28 is high in Caucasians, whereas it is low in Asians including Japanese. Recently, it has been demonstrated that genetic variants of UGT1A1*6 in addition to UGT1A1*28 are associated with the occurrence of adverse events in irinotecan chemotherapy in Asians. This review summarizes recent studies to outline the role of UGT1A1*28 and UGT1A1*6 for irinotecan-induced adverse drug reaction in Japanese cancer patients.     

Clinical and pharmacogenetic factors associated with irinotecan toxicity

Irinotecan is a topo-isomerase-I inhibitor with broad antitumor activity in solid tumors. Its use may lead to severe toxicities, predominantly neutropenia and diarrhea which can be life-threatening. This review discusses clinical determinants and pharmacogenetic factors associated with irinotecan toxicity. Age, performance status, co-medication and elevated transaminases have been associated with increased risk of diarrhea or neutropenia. Also, elevated bilirubin levels, due to liver impairment, conjugation disorders or UGT1A1 *28 genotype, have been associated with increased incidence of grades 3 intestinal toxicity and neutropenia. UGT1A1 *28 homozygosity is strongly associated with irinotecan-induced neutropenia and polymorphisms in the transporting peptides ABCB1 and OATP1B1 have also been associated with gastrointestinal toxicity and irinotecan pharmacokinetics, respectively. In the irinotecan product label, it is advised to reduce the irinotecan starting dose for UGT1A1 *28 homozygotes. However, due to the lack of prospective data, it is yet unknown whether dose reduction leads to reduced toxicity or altered antitumor effect. Combined toxicity analysis reveals that most patients experiencing grade 3-4 diarrhea and/or neutropenia are not homozygous for UGT1A1 *28. Future studies should combine pharmacogenetics with clinical determinants such as performance status and co-medication as to predict irinotecan toxicity and to develop predefined dosing algorithms.     

UGT1A1*28 and Other UGT1A Polymorphisms as Determinants of Irinotecan Toxicity

Abstract

Irinotecan is a drug commonly used for the treatment of cancer patients, both as a single agent or in combination therapy. Neutropenia and diarrhea are the dose-limiting toxicities. Genetic variations of proteins involved in irinotecan metabolism and transport have been considered in the development of irinotecan toxicity. In particular, polymorphisms affecting UDP-glucuronosyltransferase isoform 1A1 (UGT1A1) expression or activity are being investigated. Among these, UGT1A1*28 has been considered as the major predictive pharmacogenetic marker for severe hematological toxicity (neutropenia). However, translation to clinical practice of UGT1A1*28 testing as a predictive marker of adverse effects needs to be further investigated and the available data are not conclusive in defining a precise genotype-based dosage.

Further prospective studies are required to reach a personalization of chemotherapy with irinotecan.     

UGT1A1*28 and other UGT1A polymorphisms as determinants of irinotecan toxicity

Irinotecan is a drug commonly used for the treatment of cancer patients, both as a single agent or in combination therapy. Neutropenia and diarrhea are the dose-limiting toxicities. Genetic variations of proteins involved in irinotecan metabolism and transport have been considered in the development of irinotecan toxicity. In particular, polymorphisms affecting UDP-glucuronosyltransferase isoform 1A1 (UGT1A1) expression or activity are being investigated. Among these, UGT1A1*28 has been considered as the major predictive pharmacogenetic marker for severe hematological toxicity (neutropenia). However, translation to clinical practice of UGT1A1*28 testing as a predictive marker of adverse effects needs to be further investigated and the available data are not conclusive in defining a precise genotype-based dosage. Further prospective studies are required to reach a personalization of chemotherapy with irinotecan.     

Role of UGT1A1*6, UGT1A1*28 and ABCG2 c.421C>A polymorphisms in irinotecan-induced neutropenia in Asian cancer patients

The objectives of the present study were (i) to study the pharmacogenetics of UGT1A1*6, UGT1A1*28 and ABCG2 c.421C>A in three distinct healthy Asian populations (Chinese, Malays and Indians), and (ii) to investigate the polygenic influence of these polymorphic variants in irinotecan-induced neutropenia in Asian cancer patients. Pharmacokinetic and pharmacogenetic analyses were done after administration of irinotecan as a 90-min intravenous infusion of 375 mg/m(2) once every 3 weeks (n = 45). Genotypic-phenotypic correlates showed a non-significant influence of UGT1A1*28 and ABCG2 c.421C>A polymorphisms on the pharmacokinetics of SN-38 (P > 0.05), as well as severity of neutropenia (P > 0.05). Significantly higher exposure levels to SN-38 (P = 0.018), lower relative extent of glucuronidation (REG; P = 0.006) and higher biliary index (BI; P = 0.003) were found in cancer patients homozygous for the UGT1A1*6 allele compared with patients harboring the reference genotype. The mean absolute neutrophil count (ANC) was 85% lower and the prevalence of grade 4 neutropenia (ANC < or = 500/microL) was 27% in patients homozygous for UGT1A1*6 compared with the reference group. Furthermore, the presence of the UGT1A1*6 allele was associated with an approximately 3-fold increased risk of developing severe grade 4 neutropenia compared with patients harboring the reference genotype. These exploratory findings suggest that homozygosity for UGT1A1*6 allele may be associated with altered SN-38 disposition and may increase the risk of severe neutropenia in Asian cancer patients, particularly in the Chinese cancer patients who comprised 80% (n = 36) of the patient population in the present study.     

Life-threatening toxicities in a patient with UGT1A1*6/*28 and SLCO1B1*15/*15 genotypes after irinotecan-based chemotherapy

Introduction  To explore severe toxicities induced by irinotecan-based chemotherapy and UGT1A1*6/*28 and SLCO1B1*15/*15 genotypes. Case report  A 66-year-old Japanese male diagnosed with left pharyngeal carcinoma (T2N2bM0, stage IVA) was treated with irinotecan (70 mg/m²) on days 1, 8 and 15 in combination with docetaxel (60 mg/m²) on day 1 of a 28-day cycle. After the first cycle, he suffered marked toxicities, including grade 4 diarrhea and febrile grade 4 neutropenia. Plasma concentrations of irinotecan, SN-38 and SN-38G were measured, and extensive accumulation of SN-38 was observed. Genotyping of UGT1A1 and OATP1B1 proteins showed UGT1A1*6/*28 and SLCO1B1*15/*15, respectively, which are known to lead to extremely low glucuronidation and transport activities of substrate drugs. Conclusion  The severe toxicities in this patient are attributable to the extensive accumulation of SN-38, which may result from a synergistic or additive effect of low metabolic (UGT1A1*6/*28) and transport (SLCO1B1*15/*15) capabilities.     

Clinical Observations on Associations Between the UGT1A1 Genotype and Severe Toxicity of Irinotecan

Background: Severe toxicity is commonly observed in cancer patients receiving irinotecan (CPT-11)UDPglucuronosyltransferase1A1 (UGT1A1) catalyzes the glucuronidation of the active metabolite SN-38 but therelationship between UGT1A1 and severe toxicity remains unclear. Our study aimed to assess this point to guideclinical use of CPT-11. Materials and Methods: 89 cancer patients with advanced disease received CPT-11-basedchemotherapy for at least two cycles. Toxicity, including GI and hematologic toxicity was recorded in detail andUGT1A1 variants were genotyped. Regression analysis was used to analyse relationships between these variablesand tumor response. Results: The prevalence of grade III-IV diarrhea was 10.1%, this being more common inpatients with the TA 6/7 genotype (5 of 22 patients, 22.7%) (p<0.05). The prevalence of grade III-IV neutropeniawas 13.4%and also highest in patients with the TA 6/7 genotype (4 of 22 patients; 18.2%) but without significance(p>0.05). The retreatment total bilirubin levels were significantly higher in TA6/7 patients (mean, 12.75μmol/L)with compared to TA6/6 (mean, 9.92 μmol/L) with p<0.05. Conclusions: Our study support the conclusion thatpatients with a UGT1A1*28 allele (s) will suffer an increased risk of severe irinotecan-induced diarrhea, whetherwith mid-or low-dosage. However, the UGT1A1*28 allele (s) did not increase severe neutropenia. Higher serumtotal bilirubin is an indication that patients UGT1A1 genotype is not wild-type, with significance for clinic usageof CPT-11.     

Prophylaxis of irinotecan-induced diarrhea with neomycin and potential role for UGT1A1*28 genotype screening: a double-blind, randomized, placebo-controlled study

OBJECTIVE: Delayed-type diarrhea is a common side effect of irinotecan and is associated with a bacterial-mediated formation of the active irinotecan metabolite SN-38 from its glucuronide conjugate in the intestine. Based on a pilot study, we hypothesized that concomitant administration of the antibiotic neomycin would diminish exposure of the gut to SN-38 and ameliorate the incidence and severity of diarrhea. PATIENTS AND METHODS: Patients were treated with irinotecan in a multicenter, double-blind, randomized, placebo-controlled trial. Eligible patients received irinotecan (350 mg/m(2) once every 3 weeks) combined with neomycin (660 mg three times daily for three consecutive days, starting 2 days before chemotherapy) or combined with placebo. Blood samples were obtained for additional pharmacokinetic and pharmacogenetic analyses. RESULTS: Sixty-two patients were evaluable for the toxicity analysis. Baseline patient characteristics, systemic SN-38 exposure, and UGT1A1*28 genotype status (i.e., an additional TA repeat in the promoter region of uridine diphosphate-glucuronosyltransferase isoform 1A1) were similar in both arms. Although distribution, severity, and duration of delayed-type diarrhea did not differ significantly between arms, grade 3 diarrhea tended to be less frequent in the neomycin arm. The presence of at least one UGT1A1*28 allele was strongly related to the incidence of grade 2-3 diarrhea. In the neomycin arm, grade 2 nausea was significantly more common. CONCLUSION: Our results do not suggest a major role for neomycin as prophylaxis for irinotecan-induced delayed-type diarrhea. It is suggested that the UGT1A1*28 genotype status could be used as a screening tool for a priori prevention of irinotecan-induced delayed-type diarrhea.     

Pharmacogenetic impact of polymorphisms in the coding region of the UGT1A1 gene on SN-38 glucuronidation in Japanese patients with cancer

Pharmacogenetic testing for UDP-glucuronosyltransferase (UGT) 1A1*28, a promoter variant of the UGT1A1 gene, is now carried out clinically to estimate the risk of irinotecan-associated toxicity. We studied the clinical significance of UGT1A1*6 and UGT1A1*27, two variants in exon 1 of the UGT1A1 gene that are found mainly in Asians. The study group comprised 46 Japanese patients who received various regimens of chemotherapy including irinotecan at doses from 50 to 180 mg/m(2). Pharmacogenetic relationships were explored between the UGT1A1 genotype and the ratio of the area under the plasma concentration-time curve (AUC) of the active metabolite of irinotecan (SN-38) to that of SN-38 glucuronide (SN-38G), used as a surrogate for UGT1A1 activity (AUC(SN-38)/AUC(SN-38G)). No patient was homozygous for UGT1A1*28, and none had UGT1A1*27. Two were heterozygous for UGT1A1*28. Two were homozygous and 15 heterozygous for UGT1A1*6, all of whom were wild type with respect to UGT1A1*28. Two patients were simultaneously heterozygous for UGT1A1*28 and UGT1A1*6, present on different chromosomes. The other 25 patients had none of the variants studied. The two patients simultaneously heterozygous for UGT1A1*28 and UGT1A1*6 and the two patients homozygous for UGT1A1*6 had significantly higher AUC(SN-38)/AUC(SN-38G) ratios than the others (P = 0.0039). Concurrence of UGT1A1*28 and UGT1A1*6, even when heterozygous, altered the disposition of irinotecan remarkably, potentially increasing susceptibility to toxicity. Patients homozygous for UGT1A1*6 should also be carefully monitored. UGT1A1 polymorphisms in the coding region of the UGT1A1 gene should be genotyped in addition to testing for UGT1A1*28 to more accurately predict irinotecan-related toxicity, at least in Asian patients.     

Importance of UDP-glucuronosyltransferase 1A1*6 for irinotecan toxicities in Japanese cancer patients

Recent pharmacogenetic studies on irinotecan have revealed the impact of UDP glucuronosyltransferase (UGT) 1A1*28 on severe irinotecan toxicities. Although the clinical role of UGT1A1*6, which is specifically detected in East Asian patients, in irinotecan toxicities is suggested, clear evidence remains limited. To examine the impact of *6, the association of UGT1A1 genotypes with severe irinotecan toxicities was retrospectively investigated in Japanese cancer patients. A significant *6-dependent increase in the incidence of grade 3 or 4 neutropenia was observed in 49 patients on irinotecan monotherapy (p=0.012). This study further clarifies the clinical importance of *6 in irinotecan therapy in East Asians.     

Integrated pharmacogenetic prediction of irinotecan pharmacokinetics and toxicity in patients with advanced non-small cell lung cancer

To define an integrated pharmacogenetic model for predicting irinotecan pharmacokinetic (PK) and severe toxicity, we evaluated multivariate analysis using 15 polymorphisms within seven genes with putative influence on metabolism and transport of irinotecan. A total of 107 NSCLC patients treated with irinotecan were evaluated for PK and genotyped for the UGT1A1*6, UGT1A1*28, UGT1A9*22, ABCB11236C>T, 2677G>T/A, 3435C>T, ABCC2-24C>T, 1249G>A, 3972C>T, ABCG234G>A, 421C>A, and SLCO1B1 -11187G>A, 388A>G, and 521T>C, and CYP3A5*3 polymorphisms. Multivariate linear and logistic regression analyses including genotypes and clinicopathologic factors were performed. SN-38 AUC was significantly correlated with ANCs (r=-0.3, p=0.009) and grade 4 neutropenia (p=0.01). The UGT1A1*6/*6, UGT1A9*1/*1 or *1/*22, and SLCO1B1 521TC or CC genotypes, and female-gender were predictive for higher AUC(SN-38) in multivariate analysis. Among them, SLCO1B1 521TC or CC and UGT1A1*6/*6 genotypes were independently predictive for grade 4 neutropenia in multivariate analysis (OR=3.8 and 7.4, respectively). Although no significant association was observed between PK parameters and grade 3 diarrhea, UGT1A9*1/*1, ABCC23972CC, and ABCG234GA or AA genotypes were independently predictive for grade 3 diarrhea in multivariate analysis (OR=6.3, 5.6, and 5.1, respectively). Patient selection based on integrated pharmacogenetic model would be helpful for predicting irinotecan-PK and severe toxicities in NSCLC patients.     

Usefulness of one-point plasma SN-38G/SN-38 concentration ratios as a substitute for UGT1A1 genetic information after irinotecan administration

Background

It was recently reported that genetic polymorphisms of UDP glucuronyltransferase-1 polypeptide A1 (UGT1A1), a glucuronidation enzyme, were associated with irinotecan (CPT-11) metabolism. The active metabolite of CPT-11, 7-ethyl-10-hydroxycamptothecin (SN-38) was glucuronidated (SN-38G) by UGT1A1. Genetic polymorphisms of UGT1A1 were associated with potentially serious adverse events, including neutropenia. Several studies have suggested that the dose of CPT-11 should be decreased in patients homozygous for UGT1A1*6 or UGT1A1*28, or double heterozygotes (*6/*28). However, the reference dose for patients with these genetic polymorphisms is unclear.

Methods

We investigated the relationship between the SN-38G/SN-38 concentration ratio and the dose of CPT-11 in 70 patients with colorectal cancer who received FOLFIRI-based regimens, by measuring the plasma concentrations of CPT-11, SN-38, and SN-38G.

Results

The SN-38G/SN-38 concentration ratio was lower in patients who were homozygous for UGT1A1*6, heterozygous for UGT1A1*6 or UGT1A1*28, or were double heterozygotes compared with patients with wild-type genes. The relative decreases in the SN-38G/SN-38 concentration ratio in patients homozygous for UGT1A1*6 and in double heterozygotes were greater than in patients heterozygous for UGT1A1*6 or UGT1A1*28. Interestingly, decreases in the SN-38G/SN-38 concentration ratio were associated with decreases in the neutrophil count and the final infusion dose of CPT-11.

Conclusion

Our results suggest that the SN-38G/SN-38 concentration ratio is an important factor for guiding dose adjustments, even in patients with wild-type genes. Therefore, the SN-38G/SN-38 concentration ratio, as an index of the patient’s metabolic capacity, is useful for assessing dose adjustments of CPT-11.     

Genotype-directed, dose-finding study of irinotecan in cancer patients with UGT1A1*28 and/or UGT1A1*6 polymorphisms

Irinotecan-induced severe neutropenia is associated with homozygosity for the UGT1A1*28 or UGT1A1*6 alleles. In this study, we determined the maximum-tolerated dose (MTD) of irinotecan in patients with UGT1A1 polymorphisms. Patients who had received chemotherapy other than irinotecan for metastatic gastrointestinal cancer were enrolled. Patients were divided into three groups according to UGT1A1 genotypes: wild-type (*1/*1); heterozygous (*28/*1, *6/*1); or homozygous (*28/*28, *6/*6, *28/*6). Irinotecan was given every 2 weeks for two cycles. The wild-type group received a fixed dose of irinotecan (150 mg/m(2)) to serve as a reference. The MTD was guided from 75 to 150 mg/m(2) by the continual reassessment method in the heterozygous and homozygous groups. Dose-limiting toxicity (DLT) and pharmacokinetics were evaluated during cycle 1. Of 82 patients enrolled, DLT was assessable in 79 patients (wild-type, 40; heterozygous, 20; and homozygous, 19). Dose-limiting toxicity occurred in one patient in the wild-type group, none in the heterozygous group, and six patients (grade 4 neutropenia) in the homozygous group. In the homozygous group, the MTD was 150 mg/m(2) and the probability of DLT was 37.4%. The second cycle was delayed because of neutropenia in 56.3% of the patients given the MTD. The AUC(0-24 h) of SN-38 was significantly greater (P < 0.001) and more widely distributed in the homozygous group. Patients homozygous for the UGT1A1*28 or UGT1A1*6 allele can receive irinotecan in a starting dose of 150 mg/m(2), but many required dose reductions or delayed treatment in subsequent cycles. UMIN Clinical Trial Registration number: UMIN000000618.     

Associations between UGT1A1*6 or UGT1A1*6/*28 polymorphisms and irinotecan-induced neutropenia in Asian cancer patients

Purpose

Neutropenia is a life-threatening side effect of irinotecan, and uridine diphosphate glucuronosyltransferases (UGTs) gene polymorphisms are considered to be one of the predictive markers of irinotecan-related toxicities. Many studies have demonstrated that patients bearing UGT1A1*28 have a higher risk of severe neutropenia on toxicity of irinotecan. However, UGT1A1 (TA7/TA7) was very rare in Asian populations. Some researches reported that UGT1A1*28 and/or UGT1A1*6 could predict irinotecan-induced toxicities in Asian populations, but controversial conclusions still remained. This study aims to investigate the association between UGT1A1 gene polymorphisms *6, *6/*28 and irinotecan-related neutropenia in Asian cancer patients receiving irinotecan regimen chemotherapy.

Experimental design

Meta-analyses were done to assess the relationship between UGT1A1*6 or UGT1A1*6/*28 and irinotecan-induced neutropenia.

Results

The risk of neutropenia was significantly higher among patients with a UGT1A1*6 genotype than among those carrying the UGT1A1*1 allele(s) [odds ratio (OR) 3.276; 95 % confidence interval (CI) 1.887–5.688; P = 0.000 (*6/*6 vs. *1/*6 or *1/*1)], [OR 1.542; 95 % CI 1.180–2.041; P = 0.001 (*6/*6 or *1/*6 vs. *1/*1)]. Also, the risk was significantly higher among patients with a UGT1A1*6/*28 than among those carrying the UGT1A1*1 allele(s) [OR 3.275; 95 % CI 2.152–4.983; P = 0.000 (*6/*6 or *28/*28 or *6/*28 vs. *1/*6 or *1/*28 or *1/*1)].

Conclusions

In conclusion, the UGT1A1*6 and UGT1A1*6/*28 genotypes were associated with an increased risk of irinotecan-induced neutropenia in Asian cancer patients.     

川东北地区人群结直肠癌患者UGT1A1*28基因多态性与伊立替康所致毒副反应的相关性

目的:观察结直肠癌患者UGT1A1*28基因多态性的分布频率,了解UGT1A1*28基因多态性与结直肠癌患者应用伊立替康联合5-氟尿嘧啶化疗毒副反应的相关性。方法:从384例接受伊立替康联合氟尿嘧啶一线化疗的晚期结直肠癌病例中采外周血提取DNA。采用PCR 法扩增目的基因片段,直接测序法分析UGT1A1*28基因多态性。临床观察并评价患者化疗毒副反应分级,统计分析UGT1A1*28基因表型与化疗毒副反应相关性。结果:全部 384例患者 UGT1A1*28基因多态性分布情况:TA6/6野生基因型287例(74.7％),TA6/7杂合基因型73例（19.0％）,TA7/7纯合基因型24例（6.3％）。化疗毒副反应和UGT1A1*28基因多态性进行临床单因素分析显示UGT1A1*28基因纯合型TA7/7、杂合型TA6/7与3-4度白细胞减少、中性粒细胞减少、腹泻、胆红素升高具有明显相关性（P<0.01）,UGT1A1*28基因纯合型TA7/7及杂合型TA6/7患者发生中性粒细胞减少的风险较UGT1A1*28基因野生型TA6/6患者高5.625倍（OR=5.625）。UGT1A1*28基因纯合型TA7/7和UGT1A1*28基因杂合型TA6/7患者发生腹泻的风险较UGT1A1*28基因野生型TA6/6患者高6.778倍（OR=6.778）。结论:UGT1A1*28基因纯合型TA7/7及杂合型TA6/7患者应用伊立替康化疗后发生重度中性粒细胞减少、重度腹泻的风险高于UGT1A1*28基因野生型TA6/6,为临床伊立替康用药选择、剂量调整、毒副反应的提前干预提供理论依据。     

UGT1A1基因多态性与伊立替康临床用药安全性及疗效的关系

目的：研究 UGT1A1基因多态性与伊立替康治疗结直肠癌患者的不良反应及疗效之间的关系。方法：自外周血中抽提基因组 DNA,进行 PCR 扩增,应用直接测序法分析2012年3月至2013年3月,于我院行基因检测的65例结直肠癌患者 UGT1A1*28和 UGT1A1*6基因多态性的分布情况。并对这65例应用含伊立替康方案化疗的患者出现的不良反应及化疗疗效,进行观察记录,比较不同基因型间的差异。结果：65例患者中,UGT1A1*28野生型 TA6／6有49例（75．4％）,杂合突变型 TA6／7有14例（21．5％）,纯合突变型TA7／7有2例（3．1％）。UGT1A1*6野生型 G／G 有47例（72．3％）,杂合突变型 G／A 有15例（23．1％）,纯合突变型 A ／A 有3例（4．6％）。在以上65例结直肠癌患者中,UGT1A1基因启动子区28位点,TA6／6、TA6／7和TA7／7型,发生3级以上腹泻者分别为8．2％、37．5％;发生3级以上中性粒细胞减少者分别为28．6％、62．5％。UGT1A1基因启动子区6位点,G／G、G／A 和 A ／A 型,发生3级以上腹泻者分别为12．8％、44．4％;发生3级以上中性粒细胞减少者分别为14．9％、22．2％。各组之间疗效无统计学差异。结论：患者 UGT1A1*28和UGT1A1*6多态性分布基本一致,UGT1A1*28突变型可以使应用含伊立替康化疗患者发生3级以上腹泻和中性粒细胞减少的风险增加。UGT1A1*6突变型可增加3级以上腹泻的发生风险。因此,UGT1A1基因型的检测对伊立替康相关的不良反应有一定的预测作用,可提高用药安全性,在临床用药中起到了指导作用。     

UGT1A1*28 genotype and irinotecan-induced neutropenia: dose matters

The Food and Drug Administration and Pfizer changed the package insert for irinotecan to include a patient's UGT1A1*28 genotype as a risk factor for severe neutropenia on the basis of the findings of four pharmacogenetic studies, which found that irinotecan-treated patients who were homozygous for the UGT1A1*28 allele had a greater risk of hematologic toxic effects than patients who had one or two copies of the wild-type allele (UGT1A1*1). Findings of subsequent irinotecan pharmacogenetic studies have been inconsistent. In a meta-analysis, we reviewed data presented in nine studies that included a total of 10 sets of patients (for a total of 821 patients) and assessed the association of irinotecan dose with the risk of irinotecan-related hematologic toxicities (grade III-IV) for patients with a UGT1A1*28/*28 genotype. The risk of toxicity was higher among patients with a UGT1A1*28/*28 genotype than among those with a UGT1A1*1/*1 or UGT1A1*1/*28 genotype at both medium (odds ratio [OR] = 3.22, 95% confidence interval [CI] = 1.52 to 6.81; P = .008) and high (OR = 27.8, 95% CI = 4.0 to 195; P = .005) doses of irinotecan. However, risk was similar at lower doses (OR = 1.80, 95% CI = 0.37 to 8.84; P = .41). Low doses of irinotecan (100-125 mg/m2) are in the commonly used therapeutic range. The risk of experiencing irinotecan-induced hematologic toxicity for patients with a UGT1A1*28/*28 genotype thus appears to be a function of the dose of irinotecan administered.     

Polymorphisms of UDP-glucuronosyltransferase gene and irinotecan toxicity: a pharmacogenetic analysis

Irinotecan unexpectedly causes severe toxicity of leukopenia or diarrhea. Irinotecan is metabolized to form active SN-38, which is further conjugated and detoxified by UDP-glucuronosyltransferase (UGT) 1A1 enzyme. Genetic polymorphisms of the UGT1A1 would affect an interindividual variation of the toxicity by irinotecan via the alternation of bioavailability of SN-38. In this case-control study, retrospective review of clinical records and determination of UGT1A1 polymorphisms were performed to investigate whether a patient with the variant UGT1A1 genotypes would be at higher risk for severe toxicity by irinotecan. All patients previously received irinotecan against cancer in university hospitals, cancer centers, or large urban hospitals in Japan. We identified 26 patients who experienced severe toxicity and 92 patients who did not. The relationship was studied between the multiple variant genotypes (UGT1A1*28 in the promoter and UGT1A1*6, UGT1A1*27, UGT1A1*29, and UGT1A1*7 in the coding region) and the severe toxicity of grade 4 leukopenia (< or =0.9 x 10(9)/liter) and/or grade 3 (watery for 5 days or more) or grade 4 (hemorrhagic or dehydration) diarrhea. Of the 26 patients with the severe toxicity, the genotypes of UGT1A1*28 were homozygous in 4 (15%) and heterozygous in 8 (31%), whereas 3 (3%) homozygous and 10 (11%) heterozygous were found among the 92 patients without the severe toxicity. Multivariate analysis suggested that the genotype either heterozygous or homozygous for UGT1A1*28 would be a significant risk factor for severe toxicity by irinotecan (P < 0.001; odds ratio, 7.23; 95% confidence interval, 2.52-22.3). All 3 patients heterozygous for UGT1A1*27 encountered severe toxicity. No statistical association of UGT1A1*6 with the occurrence of severe toxicity was observed. None had UGT1A1*29 or UGT1A1*7. We suggest that determination of the UGT1A1 genotypes might be clinically useful for predicting severe toxicity by irinotecan in cancer patients. This research warrants a prospective trial to corroborate the usefulness of gene diagnosis of UGT1A1 polymorphisms prior tb irinotecan chemotherapy.