Uridine Diphosphate Glucuronosyltransferase 1A1 Promoter Research Articles

Incidence, Interpretation and Management of Liver Function Abnormalities in Patients with Chronic Myeloid Leukemia (CML) Treated with Tyrosine Kinase Inhibitors (TKI)

Background: Hepatotoxicity is a well-recognised side effect of tyrosine kinase inhibitors (TKI) and in some patients it can be a challenge to find a well-tolerated and effective drug. Isolated hyperbilirubinemia is common but, particularly in the case of nilotinib, is generally attributed to concomitant Gilbert's syndrome, characterized by the reduced expression of uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). We have previously reported hyperbilirubinemia in association with the homozygous Gilbert genotype in patients treated with imatinib, dasatinib and nilotinib and have now extended our studies to more recent TKI. In addition we have analysed the incidence of TKI-associated transaminitis and attempted to identify safer alternative TKI. Methods: From our database of >900 patients presenting with CML CP1 from 2000-2022 and treated with a TKI, we identified 467 individuals who had received only TKI (prior interferon, combination experimental therapy, auto- and allografted patients all excluded), had normal liver function tests (LFT) at TKI start and for whom serial consecutive LFT were available. Variations in dinucleotide repeats in the UGT1A1 promoter region were analyzed by PCR with genotypes: 6/6 (homozygous for (TA) 6 allele; wild-type), 7/7 (homozygous for (TA) 7 allele) and 6/7 (heterozygous). Because individual patients could receive more than one TKI, we defined the period on treatment with each TKI as an ‘episode’ so as to attribute abnormal LFT to a specific drug. Abnormal LFT were graded according to the CTCAE version 4.0 and any occurrence of abnormalities was cross-checked to exclude a confounding reason (e.g. antibiotics, cholecystitis). Patients were censored at last LFT. Results: 229 females and 238 males (median age at diagnosis 47 yrs (range 11-90) had 955 separate TKI episodes: imatinib 406, dasatinib 222, nilotinib 189, bosutinib 87, ponatinib 28 and asciminib 23. The median number of LFT per patient was 47 (range 3-264). 7 UGT1A1 genotypes were identified, of which 45%, 41% and 13% were wild type 6/6, heterozygous 6/7 and homozygous 7/7 respectively (6 patients with other genotypes excluded). With the exception of asciminib, hyperbilirubinemia was more frequent in homozygous patients for all TKI. It was also common in all patients treated with nilotinib but in wild type and heterozygous patients, was frequently associated with concomitant transaminitis. A close temporal relationship between start of TKI and raised bilirubin suggests causality (Fig 1a-d). The incidences of transaminitis of any grade were 44%, 47%, 65%, 66%, 43% and 39%, and of >grade 1 were 7%, 8%, 17%, 32%, 18% and 13% for imatinib, dasatinib, nilotinib, bosutinib, ponatinib and asciminib respectively. Of 202 patients with a transaminitis on first line TKI, 94 were subsequently switched to a 2 nd line TKI, and 27 of those to a 3 rd line TKI. Irrespective of the TKI used, recurrent transaminitis of any grade was common occurring in 60/94 (64%) on 2 nd line and 19/27 (71%) on 3 rd line, although abnormalities >grade 2 were unusual (<1% on 2 nd line, <5% on 3 rd line). 179 patients developed transaminitis on imatinib, 46 and 29 switched (rarely for transaminitis) to dasatinib and nilotinib respectively. 28 (61%) on dasatinib and 23 (79%) on nilotinib had a second transaminitis (dasatinib - 14% >grade 1, nilotinib - 22% >grade 1)). Of 227 patients without transaminitis on imatinib, 63 and 67 switched to dasatinib or nilotinib. 28 (44%) on dasatinib and 38 (57%) on nilotinib developed further transaminitis (dasatinib - 0% >grade 1, nilotinib 19% >grade1). With respect to identifying a ‘safer’ drug we studied in detail 15 patients with grades 3-4 transaminitis on 1 st line therapy; imatininb-10, dasatinib-1, nilotinib-3, bosutinib -1. Four settled on dose reduction, and of the remaining 11, 7 returned to normal or maximum grade 1 on dasatinib. Conclusion: With the exception of asciminib the previous association of TKI, homozygous Gilbert and hyperbilirubinemia was confirmed. Grade 1 transaminitis is common on all TKIs, with higher grades of severity most frequent on bosutinib. Patients experiencing abnormal transaminases on 1 st line TKI are likely to have similar problems on 2 nd and 3 rd line agents, with a trend to higher incidence/severity on nilotinib compared to dasatinib.

Relation of Uridine Diphosphate Glucuronosyltransferase 1A1 Promoter Gene Polymorphism (211G>A) With Risk of Hyperbilirubinemia in Neonates

Background: The gene 211G>A variants, that underlie complex disorders, are characteristically common in the neonatal hyperbilirubinemia. However, it is the contribution of multiple different co-expressed susceptibility genes that individually confer a small increase in risk coupled with environmental factors that generate complex disorder phenotypes. Objective: This study aimed to understand the relation of 211G>A promoter polymorphism in UGT1A1 gene and the risk of hyperbilirubinemia in newborns. Patients and Methods: The study included 50 newborns with hyperbilirubinemia with gestation age of ≥ 37weeks and postnatal age of ≤ 2 weeks with normal birth weight. 34 were males and 16 were females. They were divided into two groups; case group consisting of 30 neonates with the peak of total serum bilirubin (TSB) levels ≥ 16 mg /dl and control group consisting of 20 neonates with the peak total serum bilirubin (TSB) levels A genotype can be used as a novel method to detect susceptibility to indirect hyperbilirubinemia in neonates. Conclusion: Our findings added to the understanding of the significance of UGT1A1 in association with neonatal hyperbilirubinemia in East Delta of Egyptian population. Additionally we are in need for other studies to investigate the protective mechanisms.

Relation of Uridine Diphosphate Glucuronosyltransferase 1A1 Promoter Gene Polymorphism (211G>A) With Risk of Hyperbilirubinemia in Neonates

Background: The gene 211G>A variants, that underlie complex disorders, are characteristically common in the neonatal hyperbilirubinemia. However, it is the contribution of multiple different co-expressed susceptibility genes that individually confer a small increase in risk coupled with environmental factors that generate complex disorder phenotypes. Objective: This study aimed to understand the relation of 211G>A promoter polymorphism in UGT1A1 gene and the risk of hyperbilirubinemia in newborns. Patients and Methods: The study included 50 newborns with hyperbilirubinemia with gestation age of ≥ 37weeks and postnatal age of ≤ 2 weeks with normal birth weight. 34 were males and 16 were females. They were divided into two groups; case group consisting of 30 neonates with the peak of total serum bilirubin (TSB) levels ≥ 16 mg /dl and control group consisting of 20 neonates with the peak total serum bilirubin (TSB) levels A genotype can be used as a novel method to detect susceptibility to indirect hyperbilirubinemia in neonates. Conclusion: Our findings added to the understanding of the significance of UGT1A1 in association with neonatal hyperbilirubinemia in East Delta of Egyptian population. Additionally we are in need for other studies to investigate the protective mechanisms.

Prospective analysis of UGT1A1 promoter polymorphism for irinotecan dose escalation in metastatic colorectal cancer patients treated with bevacizumab plus FOLFIRI as the first-line setting: study protocol for a randomized controlled trial.

BackgroundIrinotecan is approved and widely administered to metastatic colorectal cancer (mCRC) patients; however, it can cause severe toxicities including neutropenia and diarrhea. The polymorphisms of genes encoding drug-metabolizing enzymes can play a crucial role in the increased susceptibility of cancer patients to chemotherapy toxicity. Therefore, we plan to explore the effect of the genetic polymorphism of uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) for irinotecan detoxification in mCRC patients. This trial will compare the clinical outcomes and side effects observed in mCRC patients treated with bevacizumab plus 5-fluorouracil/leucovorin/irinotecan (FOLFIRI) with and without UGT1A1 genotyping and irinotecan dose escalation. A total of 400 mCRC patients were randomized into a study group and a control group.Methods/DesignThis trial is a prospective, multicenter, randomized clinical trial comparing UGT1A1 promoter polymorphism for irinotecan dose escalation in mCRC patients administered with bevacizumab plus FOLFIRI as the first-line setting. The enrolled patients were randomly assigned to one of two groups, a study group and a control group, on the basis of receiving UGT1A1 genotyping or not. The study group receive a biweekly FOLFIRI regimen, with irinotecan dose escalation based on UGT1A1 genotyping; whereas the control group receive the conventional biweekly FOLFIRI regimen without UGT1A1 genotyping. The clinicopathological features, response rates, toxicity, and progression-free survival or overall survival will be compared between the two groups.DiscussionPatients with mCRC undergoing UGT1A1 genotyping may receive escalated doses of irinotecan for a potentially more favorable clinical response and outcome, in addition to comparable toxicities. Such personalized medicine based on genotyping may be feasible for clinical practice.Trial registrationNCT02256800. Date of registration: 3 October 2014. Date of first patient randomized: 16 January 2015

The Association of Gilbert's Syndrome with Hyperbilirubinaemia Occurring on Any of Imatinib, Dasatinib and Nilotinib in Patients with Chronic Myeloid Leukaemia (CML)

Background: Individuals with Gilbert's syndrome present with mild, unconjugated hyperbilirubinaemia, resulting from impaired glucuronidation by reduced uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) expression. The A(TA)7TAA polymorphism responsible for the syndrome has been associated with nilotinib-induced hyperbilirubinaemia in patients with chronic myeloid leukaemia (CML). Our study extends UGT1A1 molecular analysis to a larger cohort of CML patients receiving other tyrosine kinase inhibitors (TKIs) and explores the relationship with other abnormalities of liver function.Methods: We interrogated our database of 832 patients treated with a TKI for CML at our center and identified 467 individuals who presented in first chronic phase, who had received only a TKI (prior interferon, combination experimental therapy, autologous and allogeneic transplant patients were all excluded) and for whom serial liver function results were available. We then performed PCR to identify variations in dinucleotide repeats in the UGT1A1 promoter region. Genotypes were assigned as follows: 6/6 (homozygous for (TA)6 allele; wild-type), 7/7 (homozygous for (TA)7allele) and 6/7 (heterozygous). Because individual patients may have received more than one TKI, we defined the period on treatment with each TKI as an 'episode' in order to be able to attribute abnormalities of liver function to a specific drug. Hyperbilirubinaemia was graded according to the Common Terminology Criteria for Adverse Events (CTCAE), version 4.0. Both ALT and ALP were defined as increased if they were above the upper limit of normal. To date we have completed the analysis for 340 patients comprising a total of 568 episodes of TKI therapy (imatinib 313, dasatinib 125, nilotinib 130).Results: The UGT1A1 genotype analysis showed six variants. The majority of patients displayed one of 6/6 (149 patients), 6/7 (138 patients) or 7/7 (48 patients) genotypes. Small numbers of patients with the 5/6, 5/7 and 6/8 genotypes were excluded from further analysis. Hyperbilirubinaemia was seen in patients with all three genotypes, but was more frequent in patients on nilotinib (44%), compared to imatinib (14%) and dasatinib (8%). The incidence of hyperbilirubinaemia in individuals with the 6/6 genotype was 6%, 0% and 22% for imatinib, dasatinib and nilotinib respectively, and 10%, 6% and 56% for patients with the 6/7 genotype. The frequency of hyperbilirubinaemia in those with the 7/7 genotype was significantly higher compared to the occurrence of such events in any other genotype, irrespective of treatment. However, it occurred more often in patients on nilotinib (80%), followed by imatinib (61%) and dasatinib (44%). A significantly higher number of patients with the 7/7 genotype on nilotinib reported Grade 3 hyperbilirubinaemia (25%), with no grade 3 events on imatinib and only one on dasatinib. Hyperbilirubinaemia on any single drug did not predict for this event on any subsequent drug.Further analysis of liver function tests (LFTs) and bilirubin levels divided episodes into four groups: 1. Episodes with normal bilirubin and normal LFTs (n = 273), 2. Episodes with isolated raised LFTs but normal bilirubin (n = 179), 3. Episodes with isolated hyperbilirubinaemia (n = 27) but normal LFTs and 4. Episodes with raised bilirubin and raised LFTs (n = 84). Abnormal LFTs with or without hyperbilirubinaemia were most commonly seen on nilotinib (65%) compared to imatinib (40%) and dasatinib (46%), confirming previous reports of the frequencies of transaminitis on the various TKIs. Isolated hyperbilirubnaemia was uncommon (<6%) on any of the drugs, but was more frequent in the 7/7 than the 6/6 or 6/7 genotypes for imatinib or dasatinib. Interestingly it was not seen in patients with the 7/7 genotype on nilotinib, as 80% of the 7/7 patients with hyperblirubinaemia on nilotinib had other abnormalities of liver function.Conclusion. We confirmed the increased risk of hyperbilirubinaemia in individuals with the A(TA)7TAA polymorphism when treated with nilotinib. In contrast to other reports, we found that all patients with the 7/7 genotype are susceptible to increases in bilirubin when treated with any of imatinib, dasatinib or nilotinib. Hyperbilirubinaemia most commonly occurs alongside elevations in LFTs on nilotinib, indicating a nilotinib-induced hepatotoxicity that is compounded by the additional UGT1A1 inhibition. DisclosuresMilojkovic:ARIAD Pharmaceuticals Inc.: Honoraria; Pfizer: Honoraria; BMS: Honoraria; Novartis: Honoraria. Apperley:Pfizer: Honoraria; Bristol Myers Squibb: Honoraria; Ariad: Honoraria; Novartis: Honoraria. Foroni:Bristol Myers Squibb: Research Funding; Novartis: Research Funding; Ariad: Research Funding.

Distinct Associations Between UGT1A1 Gene Promoter Polymorphism and Hyperbilirubinemia in Korean CML Patients Treated with Nilotinib and Radotinib

Background: Second-generation BCR-ABL tyrosine kinase inhibitors (2nd generation TKIs) including nilotinib (NIL) and radotinib (RAD) are approved for the treatment of newly diagnosed and other TKI failed chronic myeloid leukemia (CML). Uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene promoter polymorphism, distinct number of TA repeats in promoter, has been reported for an association with hyperbilirubinemia on nilotinib therapy (Singer et al. Leukemia (2007) 21, 2311–2315). However, the distribution of UGT1A1 (TA)7 repeat polymorphism differs greatly between Caucasians and Japanese, namely, the frequency of UGT1A1(TA)7 repeat polymorphism is high in Caucasians, whereas it is low in Asians (Beutler et al. Proc. Natl. Acad. Sci. USA 95 (1998) 95, 8170–8174 ).Aims: The aim of this study was to investigate the association between UGT1A1 gene promoter polymorphism and hyperbilirubinemia in Korean CML patients treated with NIL and RAD as a frontline therapy.Methods: A total of 88 newly diagnosed chronic phase CML patients who treated with frontline NIL (n=39) and RAD (n=49) was screened for UGT1A1 promoter polymorphism genotype analysis. We used the High Pure PCR Template Preparation Kit (Roche, Germany) to prepare genomic DNA from whole blood and genotyped by direct sequencing of the 253- to 255-bp fragments produced by PCR.Results: The (TA)6/(TA)6 homozygote and (TA)6/(TA)7 heterozygote were seen in all genotyped population and frequency of (TA)6/(TA)6 homozygote was 79.5% (70/88) in our patients. (TA)6/(TA)6 homozygote predominated with 81.6% of the alleles in the RAD group and 76.9% in the NIL group. Relative riskfor each genotype presented in Table 1, with hyperbilirubinemia defined as CTCAE grade 2 or greater observed at any post-baseline point. The relative risks for 6/6 genotype versus 6/7 genotype was 3.5 with 95% CIs of (0.6, 18.9) in the RAD group compared with 8.1 (1.5, 43.8) in the NIL group and NIL group showed significantly high association with UGT1A1 gene promoter polymorphism (P<0.05).Conclusions: This finding suggests that UGT1A1 gene promoter polymorphism may be an important determinant of hyperbilirubinemia in CML patients with NIL therapy, but not in RAD. However other mechanisms should be explored in patients who have significant hyperbilirubinemia with RAD therapy. Updated data with longer follow-up duration will be presented in the meeting.Table 1Relative risk calculations for prevalence of hyperbilirubinemiaRadotinibNilotinibMax grade=,<1Max grade>,=2TotalMax grade=,<1Max grade>,=2Total(TA)6/(TA)6202040(TA)6/(TA)62643050.00%50.00%65.00%10.00%(TA)6/(TA)7279(TA)6/(TA)745922.22%77.78%44.44%55.56%Total222749Total30939Relative risk=3.5, 95% CI of (0.6, 18.9)Relative risk=8.1, 95% CI of (1.5, 43.8)Abbreviation: CI, confidence interval. DisclosuresNo relevant conflicts of interest to declare.

Prospective analysis of UGT1A1 promoter polymorphism for irinotecan dose escalation in metastatic colorectal cancer patients treated with bevacizumab combined with FOLFIRI as the first-line setting.

491 Background: Infusional fluorouracil/leucovorin plus irinotecan-based regimen (FOLFIRI) with bevacizumab has been widely used as first-line treatment for patients with metastatic colorectal cancer (mCRC). We prospectively analyzed the influence of uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) genotyping for irinotecan dose escalation in mCRC patients treated with combination of FOLFIRI and bevacizumab as the first-line setting. Methods: A total of 65 mCRC patients undergoing first-line treatment with FOLFIRI combined with bevacizumab were analyzed. Genotypes were performed by analyzing the sequence of TATA box of UGT1A1 of genomic DNA from the patients. Genotype and clinical parameters were compared by univariate analysis. The irinotecan dose is escalating form 180 mg/m2 to 260 mg/m2 in UGT1A1 6/6 or 6/7, and from 120 mg/m2 to 210 mg/m2 in UGT1A17/7. Results: The response rate was observed in 44 of 60 UGT1A1 6/6 or 6/7 (73.3%) in comparison to 1 of 5 UGT1A1 7/7 (20%) patients (p=0.013). The grade III-IV adverse events (AE) was observed in 4 of 60 UGT1A1 6/6 or 6/7 (6.7%) in comparison to 3 of 5 UGT1A1 7/7 (60%) patients (p&lt;0.001), but it was not different between age of ≥ 70 and &lt; 70 (p=0.559). Fifteen of 60 (20%) patients with UGT1A1 6/6 or 6/7 could be performed with liver or lung metastaectomy in comparison to none of 5 patients with UGT1A1 7/7. In addition, the disease control rate was significantly higher in irinotecan dose of ≥ 210 mg/m2 than irinotecan dose of &lt; 210 mg/m2(p=0.015). Conclusions: UGT1A1 promoter polymorphism was found to be predictive of toxicity and efficacy in mCRC patients with first-line treatment of FOLFIRI combined with bevacizumab. The higher dose of irinotecan (≥ 210 mg/m2) may achieve a better disease control rate but do not increase the incidence of GR III-IV AE in mCRC patients of age ≥ 70 years.

Study of irinotecan-induced toxicity and its correlation to UGT1A1 gene promoter polymorphisms

To investigate the distribution of uridine diphosphate-glucuronosyltransferase 1A1 (UGT1A1) gene promoter polymorphism and its relation to the toxicities caused by irinotecan in Chinese patients with cervical cancer and ovarian cancer. Sixty-four blood samples were taken from the patients with ovarian cancer and cervical cancer. The DNA was extracted and amplified with PCR. Then, the sequences of UGT1A1 gene promoter were detected by capillary electrophoresis allele fragment analysis (size-based analysis) methods. The relationship between UGT1A1 gene promoter polymorphism and the toxicity caused by irinotecan was analyzed. In all the patients, TA 6/6 was the most common genotype of UGT1A1 gene promoter (44 cases), accounting for 69% (44/64), followed by genotype of TA 6/7 (17 cases, 27%, 17/64), while genotype TA 7/7 was rare (3 cases, 5%, 3/64). The genotypes of UGT1A1 gene promoter was an independent factor for the occurrence of delayed diarrhea (P = 0.040, OR = 4.228, 95%CI: 1.065 - 16.785) but not for neutropenia (P = 0.068, OR = 3.659, 95%CI: 0.911 - 14.700). The patients with both genotype TA 6/7 and TA 7/7 presented much higher risk of delayed diarrhea and neutropenia than those with TA 6/6 (all P = 0.001). UGT1A1 gene promoter polymorphism may be a significant influencing factor for delayed diarrhea. The patients with both genotype TA 6/7 and TA 7/7 could present much higher risk for delayed diarrhea than those with TA 6/6, while genotype TA 6/6 may be the most common UGT1A1 promoter type in Chinese patients with cervical or ovarian cancer.

Uridine diphosphate glucuronosyl transferase 1A1 promoter polymorphism is associated with choledocholithiasis in Taiwanese patients

The gene product of the uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) is crucial to bilirubin metabolism. Mutations in this gene subsequently result in disease presented with unconjugated hyperbilirubinemia. A previous study showed that a TA-repeat polymorphism in the promoter region of this gene might play a role in the metabolism of bilirubin. Whether this polymorphism might predispose choledocholithiasis is unclear. We recruited 32 patients who were diagnosed with pigment choledocholithiasis (common bile duct stones) by endoscopic retrograde cholangiopancreatography (ERCP) morphology and 107 population controls. The TA-repeat in the UGT1A1 promoter was genotyped. We found that among the 32 patients, 15 (46.9%) were wild type (A[TA](6)TAA homozygous); 15 (46.9%) were a heterozygous variation (A[TA[(6)TAA/A[TA](7)TAA) and 2 (6.2%) were a homozygous variation (A[TA](7)TAA). Among the controls, 81 (75.7%) were wild type, 23 (21.5%) were a heterozygous variation and 3 (2.8%) were a homozygous variation. The genotype distribution was significantly different between patients and controls. The results suggest that the UGT1A1 promoter TA-repeat polymorphism is associated with choledocholithiasis in Taiwanese patients.

Irinotecan and uridine diphosphate glucuronosyltransferase 1A1 pharmacogenetics

Pharmacogenetic research indicates a relationship between a polymorphism in the gene encoding uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) and irinotecan inactivation, in that degradation of SN-38, the active metabolite of irinotecan, correlates inversely with the number of TA repeats in the TATA element of the UGT1A1 promoter region. Individuals who are homozygous for the UGT1A1*28 allele (7 repeats) may exhibit reduced degradation of SN-38 and increased probability of severe toxicities. Clinical study results, as reported in the literature, have not been uniform, however, in showing a relation between genotype and the development of toxicities. Even when correlations are statistically significant, confidence intervals are wide, rendering assessment of individual risk difficult at best. Irinotecan labeling recommends testing for the UGT1A1*28 allele and reducing irinotecan dosing in patients who are positive to reduce the likelihood of dose-limiting neutropenia only, but not diarrhea. Importantly, both dose-limiting neutropenia and diarrhea are dependent on numerous known and unknown factors, such as the specific regimen used, duration of therapy, doses, cycle of treatment, and complexities of irinotecan pharmacodynamics and pharmacokinetics, including other key enzymes and drug transporters. Guidance on how to modify irinotecan dosing or how to incorporate the impact of multiple variables into clinical decision-making does not exist. Furthermore, pharmacogenomic test results at this time can only provide an estimate of risk for subsets of populations rather than a risk-benefit estimate for an individual. Consequently, these test results are supplementary to clinical judgment, which requires assessing multiple variables that contribute to phenotype to arrive at individual dosing decisions.

UGT1A1 promoter polymorphism increases risk of nilotinib-induced hyperbilirubinemia

Nilotinib is a novel BCR-ABL inhibitor with significantly improved potency and selectivity over imatinib. In Phase I and Phase II clinical studies of nilotinib in patients with a variety of leukemias, infrequent instances of reversible, benign elevation of bilirubin were observed. Uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) glucuronidates bilirubin in humans, and a polymorphism in the promoter of the gene that encodes it has been associated with hyperbilirubinemia during treatment with a number of drugs. Pharmacogenetic analysis of that TA-repeat polymorphism found an association between the (TA)7/(TA)7 genotype and risk of hyperbilirubinemia in Phase I patients with imatinib-resistant/intolerant chronic myeloid leukemia (CML) or relapsed/refractory Ph+ acute lymphoblastic leukemia (ALL); this result was replicated in two separate analyses of the chronic phase (CP) and accelerated phase (AP) CML arms of a Phase II study. As nilotinib is not known to be glucuronidated by UGT1A1, the combined impact of inhibition of UGT1A1 activity by nilotinib and genetic polymorphism is the most likely cause of the increased rate of hyperbilirubinemia.

Irinogenetics: What Is the Right Star?

Irinogenetics: What Is the Right Star?

UGT1A1 promoter genotype and toxicity in patients with advanced colorectal cancer treated with irinotecan-containing chemotherapy

2016 Background: Inherited variation in the activity of enzymes involved in drug metabolism are likely to be responsible for most inter-individual variability in the toxicity and the efficacy of the drugs themselves. The topoisomerase-I inhibitor irinotecan may have unpredictable severe toxicity: mainly diarrhea and myelosuppression. Its active metabolite, SN38, is inactivated through glucuronidation by uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). The UGT1A1 promoter includes, in the TATA box region, a well known polymorphism containing either 7 or, more commonly, 6 TA repeats. The (TA)7 allele has been associated with a reduced rate of SN-38 glucuronidation and more severe toxicity in patients treated with irinotecan. Methods: UGT1A1 was genotyped by PCR on samples obtained under an institutional review board-approved protocol from 66 patients with advanced colorectal cancer treated, 24 in first and 42 in second line, with irinotecan-containing chemotherapy. Toxicity has been graded accordin...

Variability at the uridine diphosphate glucuronosyltransferase 1A1 promoter in human populations and primates

Variation at the UDP-glucuronosyltransferase (UGT) 1A1 gene promoter is present in humans. Variable numbers of TA repeats in the TATA box of this gene are found which are inversely related to levels of gene expression. We investigated this polymorphism in 658 individuals from a worldwide sample of 15 aboriginal and two admixed human populations. This study shows that there is a great deal of variability across ethnic groups with regard to UGT1A1 allele frequencies, with the most common allele varying in frequency from 33% to 91%. Populations of African origin harbor four different alleles while non-African populations appear to have only two alleles. In addition, alleles associated with lower gene expression levels reach the highest frequencies in populations of African origin and lowest among Asians and Amerindians. Thus, more variability in the metabolism of drugs eliminated by UGT1A1 glucuronidation should be expected in populations of Sub-Saharan African origin. The sequence analysis of nine primate species shows that the number of TA repeats has increased during primate evolution achieving the largest number in humans. We suggest that the UGT1A1 promoter variability does not reflect historical relationships between populations and that it may be maintained by natural selection. Our findings are consistent with the proposal that the TA repeat variation is a balanced polymorphism.

Variability at the uridine diphosphate glucuronosyltransferase 1A1 promoter in human populations and primates

Variability at the uridine diphosphate glucuronosyltransferase 1A1 promoter in human populations and primates