Influence of genetic variants in UGT1A1 and UGT1A9 on the in vivo glucuronidation of SN-38

Dutch pharmacogenetics working group (DPWG) guideline for the gene-drug interaction between UGT1A1 and irinotecan

The Dutch Pharmacogenetics Working Group (DPWG) aims to facilitate PGx implementation by developing evidence-based pharmacogenetics guidelines to optimize pharmacotherapy. This guideline describes the starting dose optimization of the anti-cancer drug irinotecan to decrease the risk of severe toxicity, such as (febrile) neutropenia or diarrhoea. Uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1 encoded by the UGT1A1 gene) enzyme deficiency increases risk of irinotecan-induced toxicity. Gene variants leading to UGT1A1 enzyme deficiency (e.g. UGT1A1*6, *28 and *37) can be used to optimize an individual's starting dose thereby preventing carriers from toxicity. Homozygous or compound heterozygous carriers of these allele variants are defined as UGT1A1 poor metabolisers (PM). DPWG recommends a 70% starting dose in PM patients and no dose reduction in IM patients who start treatment with irinotecan. Based on the DPWG clinical implication score, UGT1A1 genotyping is considered "essential", indicating that UGT1A1 testing must be performed prior to initiating irinotecan treatment.

Characterization of Enzymes Involved in Nintedanib Metabolism in Humans

Nintedanib, which is used to treat idiopathic pulmonary fibrosis and non-small cell lung cancer, is metabolized to a pharmacologically inactive carboxylate derivative, BIBF1202, via hydrolysis and subsequently by glucuronidation to BIBF1202 acyl-glucuronide (BIBF1202-G). Since BIBF1202-G contains an ester bond, it can be hydrolytically cleaved to BIBF1202. In this study, we sought to characterize these metabolic reactions in the human liver and intestine. Nintedanib hydrolysis was detected in human liver microsomes (HLMs) (Clearance [CL int]: 102.8 ± 18.9 µL/min per mg protein) but not in small intestinal preparations. CES1 was suggested to be responsible for nintedanib hydrolysis according to experiments using recombinant hydrolases and hydrolase inhibitors as well as proteomic correlation analysis using 25 individual HLM. BIBF1202 glucuronidation in HLM (3.6 ± 0.3 µL/min per mg protein) was higher than that in human intestinal microsomes (1.5 ± 0.06 µL/min per mg protein). UGT1A1 and gastrointestinal UGT1A7, UGT1A8, and UGT1A10 were able to mediate BIBF1202 glucuronidation. The impact of UGT1A1 on glucuronidation was supported by the finding that liver microsomes from subjects homozygous for the UGT1A1*28 allele showed significantly lower activity than those from subjects carrying the wild-type UGT1A1 allele. Interestingly, BIBF1202-G was converted to BIBF1202 in HLS9 at 70-fold higher rates than the rates of BIBF1202 glucuronidation. An inhibition study and proteomic correlation analysis suggested that β-glucuronidase is responsible for hepatic BIBF1202-G deglucuronidation. In conclusion, the major metabolic reactions of nintedanib in the human liver and intestine were quantitatively and thoroughly elucidated. This information could be helpful to understand the inter- and intraindividual variability in the efficacy of nintedanib. SIGNIFICANCE STATEMENT: To our knowledge, this is the first study to characterize the enzymes responsible for each step of nintedanib metabolism in the human body. This study found that β-glucuronidase may contribute to BIBF1202-G deglucuronidation.

Successful Treatment of Irinotecan-Induced Muscle Twitching: A Case Report

Irinotecan, a topoisomerase I inhibitor, is commonly used in the treatment of advanced colorectal cancer. Its adverse effects include delay diarrhea, severe myelosuppression, and cholinergic-like symptoms. Though 2 cases of irinotecan-induced muscle twitching were reported but the successful treatment of this adverse event still not shown. We present a 24-year-old female patient with advanced colorectal cancer received bevacizumab and FOLFIRI (irinotecan + calcium leucovorin + 5-fluorouracil) treatment. Her right pectoralis major muscle presented with involuntary muscle twitching during the infusion of irinotecan at the sixth cycle of chemotherapy. The muscle twitching was slowly dissipated about 4 hours after the halted of irinotecan infusion. Then lorazepam 2 mg iv was injected before administration of irinotecan in an attempt to prevent the muscle twitching in the seventh cycle of chemotherapy. The patient did not report further muscle twitching. After that, lorazepam was routine administered before each cycle of FOLFIRI regiment. No any muscle twitching was observed after the use of lorazepam. This case provides valuable insight that muscle twitching can occur as rare irinotecan-related adverse effect. Benzodiazepine agonists, such as lorazepam, is the potential treatment of choice.

Effect of UGT1A1, CYP3A and CES Activities on the Pharmacokinetics of Irinotecan and its Metabolites in Patients with UGT1A1 Gene Polymorphisms

BACKGROUND AND OBJECTIVES

Irinotecan (CPT-11) is metabolized to an active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38) by carboxylesterase (CES). SN-38 is then converted to the inactive metabolite SN-38 glucuronide (SN-38G) by glucuronosyltransferase 1A1 (UGT1A1). Genetic polymorphisms in UGT1A1 have been associated with altered SN-38 pharmacokinetics, which increase the risk of toxicity in patients. CPT-11 is also converted to 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC) and 7-ethyl-10-(4-amino-1-piperidino) carbonyloxycamptothecin (NPC) by cytochrome P450 3A (CYP3A), and this route also affects the plasma concentration of SN-38. We evaluated the activities of UGT1A1, CYP3A, and CES and the factors affecting the pharmacokinetics of plasma SN-38 in patients with UGT1A1 gene polymorphisms.

METHODS

Three male patients aged 56, 65, and 49 years were recruited for the analysis. All patients had pancreatic cancer, received FOLFIRINOX, and had UGT1A1*6/*6 (patients 1 and 3) or *6/*28 (patient 2) genetic polymorphisms. The rate constants for evaluating the enzyme activity were determined from the measured plasma concentration of CPT-11 and its metabolites using a two-compartment model by WinNonlin.

RESULTS

The area under the plasma concentration-time curve (AUC) of SN-38 was patient 1 > patient 2 > patient 3. The rate constants obtained from the model analysis indicated the respective enzyme activities of UGT1A1 (k57), CYP3A (k13 + k19), and CES (k15). The order of values for UGT1A1 activity was patient 2 > patient 3 > patient 1. Since UGT1A1 activity was low in patient 1 with a high AUC of SN-38, it can be said that the increase in plasma concentration was due to a decrease in UGT1A1 activity. Conversely, the order of values for CYP3A and CES activities was patient 3 > patient 1 > patient 2 and patient 2 > patient 1 > patient 3, respectively. Patient 3 had the lowest AUC of SN-38, caused by a lower level of CES activity and increased CYP3A activity.

CONCLUSION

In this study, we indicated that the plasma AUC of SN-38 and AUC ratio of SN-38G/SN-38 may depend on changes in the activities of CYP3A, CES, and UGT1A1. Using pharmacokinetic analysis, it is possible to directly evaluate enzyme activity and consider what kind of enzyme variation causes the increase in the AUC of SN-38.

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

The Road so Far in Colorectal Cancer Pharmacogenomics: Are We Closer to Individualised Treatment?

In recent decades, survival rates in colorectal cancer have improved greatly due to pharmacological treatment. However, many patients end up developing adverse drug reactions that can be severe or even life threatening, and that affect their quality of life. These remain a limitation, as they may force dose reduction or treatment discontinuation, diminishing treatment efficacy. From candidate gene approaches to genome-wide analysis, pharmacogenomic knowledge has advanced greatly, yet there is still huge and unexploited potential in the use of novel technologies such as next-generation sequencing strategies. This review summarises the road of colorectal cancer pharmacogenomics so far, presents considerations and directions to be taken for further works and discusses the path towards implementation into clinical practice.

Pharmacogenomic Assessment of Patients with Colorectal Cancer and Potential Treatments

Evolving intensiveness of colorectal cancer (CRC) treatment, including chemotherapeutics and targeted agents associations, in adjuvant and metastatic CRC (MCRC) settings, increased overall survival (OS) with individual variability of toxicity. Pharmacogenomic guidelines recommended pre-treatment identification of at-risk patients suggesting dose adjustment of fluoropyrimidines based on dihydropyrimidine dehydrogenase (DPYD), and irinotecan on UDP glucuronosyl-transferase 1 family polypeptide A1 (UGT1A1) genetic variants, but they are poorly applied in clinical practice. This review highlighted clinically validated pharmacogenetic markers, to underline the need of their implementation in the multidisciplinary molecular board for individual CRC patients in clinical practice. Five clinically relevant DPYD variants with different prevalence impair enzymatic effectiveness and significantly increase toxicity: c.1236 G>A (c.1129–5923 C>G, HapB3), 4.1–4.8%; c.1679 T>G (DPYD*13), c.1905+1G>A (DPYD*2A), c.2846 A>T, c.2194 A>T (DPYD*6) 1% each. c.1679T>G and c.1905+1G>A are most deleterious on DPD effectiveness, moderately reduced in c.1236/HapB3 and c.2846A>T. Cumulatively, these variants explain approximately half of the estimated 10–15% fluoropyrimidine-related gastrointestinal and hematological toxicities due to DPD. Prevalent UGT1A1 gene [TA]₇TAA promoter allelic variant UGT1A1*28, characterized by an extra TA repeat, is associated with low transcriptional and reduced enzymatic effectiveness, decreased SN38 active irinotecan metabolite glucuronidation, vs wild-type UGT1A1*1 [A(TA)6TAA]. Homozygote UGT1A1*28 alleles patients are exposed to higher hematological and gastrointestinal toxicities, even more than heterozygote, at >150 mg/m² dose. Dose reduction is recommended for homozygote variant. Wild-type UGT1A1*28 alleles patients could tolerate increased doses, potentially affecting favorable outcomes. Implementation of up-front evaluation of the five validated DPYD variants and UGT1A1*28 in the multidisciplinary molecular tumor board, also including CRC genetic characterization, addresses potential treatments with fluoropyrimidines and irinotecan associations at proper doses and schedules, particularly for early CRC, MCRC patients fit for intensive regimens or unfit for conventional regimens, requiring treatment modulations, and also for patients who experience severe, unexpected toxicities. Integration of individual evaluation of toxicity syndromes (TS), specifically limiting TS (LTS), an innovative indicator of toxicity burden in individual patients, may be useful to better evaluate relationships between pharmacogenomic analyses with safety profiles and clinical outcomes.

Human variability in isoform-specific UDP-glucuronosyltransferases: markers of acute and chronic exposure, polymorphisms and uncertainty factors

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro-in vivo extrapolations in chemical risk assessment are discussed.

Irinotecan-Still an Important Player in Cancer Chemotherapy: A Comprehensive Overview

Irinotecan has been used in the treatment of various malignancies for many years. Still, the knowledge regarding this drug is expanding. The pharmacogenetics of the drug is the crucial component of response to irinotecan. Furthermore, new formulations of the drug are introduced in order to better deliver the drug and avoid potentially life-threatening side effects. Here, we give a comprehensive overview on irinotecan’s molecular mode of action, metabolism, pharmacogenetics, and toxicity. Moreover, this article features clinically used combinations of the drug with other anticancer agents and introduces novel formulations of drugs (e.g., liposomal formulations, dendrimers, and nanoparticles). It also outlines crucial mechanisms of tumor cells’ resistance to the active metabolite, ethyl-10-hydroxy-camptothecin (SN-38). We are sure that the article will constitute an important source of information for both new researchers in the field of irinotecan chemotherapy and professionals or clinicians who are interested in the topic.

Association of DNA repair gene polymorphisms with colorectal cancer risk and treatment outcomes

Colorectal cancer (CRC) is the third most common carcinoma worldwide. Despite the progress in screening and treatment, CRC remains a leading cause of cancer-related mortality. Alterations to normal nucleic acid processing may drive neoplastic transformation of colorectal epithelium. DNA repair machinery performs an essential function in the protection of genome by reducing the number of genetic polymorphisms/variations that may drive carcinogenicity. Four essential DNA repair systems are known which include nucleotide excision repair (NER), base excision repair (BER), mismatch repair (MMR), and double-strand break repair (DSBR). Polymorphisms of DNA repair genes have been shown to influence the risk of cancer development as well as outcomes of treatment. Several studies demonstrated the association between genetic polymorphism of DNA repair genes and increased risk of CRC in different populations. In this review, we have summarized the impact of DNA repair gene polymorphisms on risk of CRC development and treatment outcomes. Advancements of the current understanding for the impact of DNA repair gene polymorphisms on the risk and treatment of CRC may support diagnostic and predictive roles in patients with CRC.

Individualization of Irinotecan Treatment: A Review of Pharmacokinetics, Pharmacodynamics, and Pharmacogenetics

Since its clinical introduction in 1998, the topoisomerase I inhibitor irinotecan has been widely used in the treatment of solid tumors, including colorectal, pancreatic, and lung cancer. Irinotecan therapy is characterized by several dose-limiting toxicities and large interindividual pharmacokinetic variability. Irinotecan has a highly complex metabolism, including hydrolyzation by carboxylesterases to its active metabolite SN-38, which is 100- to 1000-fold more active compared with irinotecan itself. Several phase I and II enzymes, including cytochrome P450 (CYP) 3A4 and uridine diphosphate glucuronosyltransferase (UGT) 1A, are involved in the formation of inactive metabolites, making its metabolism prone to environmental and genetic influences. Genetic variants in the DNA of these enzymes and transporters could predict a part of the drug-related toxicity and efficacy of treatment, which has been shown in retrospective and prospective trials and meta-analyses. Patient characteristics, lifestyle and comedication also influence irinotecan pharmacokinetics. Other factors, including dietary restriction, are currently being studied. Meanwhile, a more tailored approach to prevent excessive toxicity and optimize efficacy is warranted. This review provides an updated overview on today’s literature on irinotecan pharmacokinetics, pharmacodynamics, and pharmacogenetics.

Novel targeted strategies to overcome resistance in small-cell lung cancer: focus on PARP inhibitors and rovalpituzumab tesirine

Introduction: Small-cell lung cancer (SCLC) is a highly aggressive neuroendocrine tumour, and its outcome is strongly conditioned by the rapid onset of resistance to conventional chemotherapeutics. First-line treatment with a combination of platinum agents and topoisomerase inhibitors has been the standard of care for over 30 years, with disappointing clinical outcome caused by early-acquired chemoresistance. In this disheartening scenario, novel treatment strategies are being implemented in order to either revert or bypass resistance mechanisms. Areas covered: The general mechanism of action of the standard frontline treatment regimens for SCLC, as well as the known resistance mechanisms to these drugs, is reviewed. Moreover, we focus on the current preclinical and clinical evidence on the potential role of PARP inhibitors and rovalpituzumab tesirine (Rova-T) to tackle chemoresistance in SCLC. Expert opinion: Preliminary evidence supports PARP inhibitors and Rova-T as two promising approaches to either revert or bypass chemoresistance in SCLC, respectively. The identification of potential predictive biomarkers of response to these innovative treatments (SLFN11 and DLL3) has shortened the gap between SCLC and personalized targeted therapy. Further large-scale clinical studies are urgently needed for a better designation of PARP inhibitors and Rova-T in the therapeutic algorithm of SCLC patients.

Shengjiang Xiexin Decoction Alters Pharmacokinetics of Irinotecan by Regulating Metabolic Enzymes and Transporters: A Multi-Target Therapy for Alleviating the Gastrointestinal Toxicity

Shengjiang Xiexin decoction (SXD), a classic traditional Chinese medical formula chronicled in Shang Han Lun, is used in modern clinical practice to decrease gastrointestinal toxicity induced by the chemotherapeutic drug irinotecan (CPT-11). In this study, the effect of SXD on the pharmacokinetics of CPT-11 and its active metabolites (SN-38 and SN-38G), and the underlying mechanisms were further examined. An ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated for the simultaneous quantification of CPT-11, SN-38, and SN-38G in the plasma, bile, liver, intestine, and intestinal contents of control and SXD-pre-treated rats after intravenous administration of CPT-11. SXD pretreatment increased the area under the curve (AUC) and the initial plasma concentration (C₀) of CPT-11 but decreased the plasma clearance (CL). The AUC and the maximum plasma concentration (C_max) of SN-38 decreased, whereas the C_max of SN-38G increased. Compared with that of the control group, the biliary excretion of CPT-11, SN-38, and SN-38G was inhibited. The CPT-11, SN-38, and SN-38G concentrations in the liver, intestine, and intestinal contents were different between the two groups. Furthermore, the hepatic expression of multidrug resistance-associated protein-2 (Mrp-2), P-glycoprotein (P-gp), and carboxylesterase 2 (CES2) was significantly down-regulated by SXD, while the hepatic and jejunal uridine diphosphate (UDP)-glucuronosyltransferase 1A1 (UGT1A1) expression was elevated. The hydrolysis of CPT-11 to SN-38 by CES and the glucuronidation of SN-38 to SN-38G by UGT were affected by liver and jejunum S9 fractions from rats pre-treated with SXD. Therefore, this study demonstrated for the first time that SXD could alter the pharmacokinetics of CPT-11 and its metabolites to alleviate CPT-11-induced diarrhea. And the underlying mechanism of drug interaction between CPT-11 and SXD involves decreasing hepatic Mrp-2 and P-gp expression and altering the activities of CES and UGT.

Germline genetic variants with implications for disease risk and therapeutic outcomes

Genetic testing has multiple clinical applications including disease risk assessment, diagnosis, and pharmacogenomics. Pharmacogenomics can be utilized to predict whether a pharmacologic therapy will be effective or to identify patients at risk for treatment-related toxicity. Although genetic tests are typically ordered for a distinct clinical purpose, the genetic variants that are found may have additional implications for either disease or pharmacology. This review will address multiple examples of germline genetic variants that are informative for both disease and pharmacogenomics. The discussed relationships are diverse. Some of the agents are targeted for the disease-causing genetic variant, while others, although not targeted therapies, have implications for the disease they are used to treat. It is also possible that the disease implications of a genetic variant are unrelated to the pharmacogenomic implications. Some of these examples are considered clinically actionable pharmacogenes, with evidence-based, pharmacologic treatment recommendations, while others are still investigative as areas for additional research. It is important that clinicians are aware of both the disease and pharmacogenomic associations of these germline genetic variants to ensure patients are receiving comprehensive personalized care.

α-Synuclein Aggregates with β-Amyloid or Tau in Human Red Blood Cells: Correlation with Antioxidant Capability and Physical Exercise in Human Healthy Subjects

Neurodegenerative disorders (NDs) are characterized by abnormal accumulation/misfolding of specific proteins, primarily α-synuclein (α-syn), β-amyloid_1-42 (Aβ), and tau, in both brain and peripheral tissue. In addition to homo-oligomers, the role of α-syn interactions with Aβ or tau has gradually emerged. The altered protein accumulation has been related to both oxidative stress and physical activity; nevertheless, no correlation among the presence of peripheral α-syn hetero-aggregates, antioxidant capacity, and physical exercise has been discovered as of yet. Herein, the content of α-syn, Aβ, tau, and of their heterocomplexes was determined in red blood cells (RBCs) of healthy subjects (sedentary and athletes). Such parameters were related to the extent of the antioxidant capability (AOC), a key marker of oxidative stress in aging-related pathologies, and to physical exercise, which is known to play an important preventive role in NDs and to modulate oxidative stress. Tau content and plasma AOC toward hydroxyl radicals were both reduced in older or sedentary subjects; in contrast, α-syn and Aβ accumulated in elderly subjects and showed an inverse correlation with both hydroxyl AOC and the level of physical activity. For the first time, α-syn heterocomplexes with Aβ or tau were quantified and demonstrated to be inversely related to hydroxyl AOC. Furthermore, α-syn/Aβ aggregates were significantly reduced in athletes and inversely correlated with physical activity level, independent of age. The positive correlation between antioxidant capability/physical activity and reduced protein accumulation was confirmed by these data and suggested that peripheral α-syn heterocomplexes may represent new indicators of ND-related protein misfolding.

Correlative analysis of plasma SN-38 levels and DPD activity with outcomes of FOLFIRI regimen for metastatic colorectal cancer with UGT1A1 *28 and *6 wild type and its implication for individualized chemotherapy

It remains uncertain whether there is an correlation between clinical pharmacokinetic parameters and outcomes for metastatic colorectal cancer especially with UGT1A1 *28 and *6 wild type (*1/*1-*1/*1) for serious events associated with Irinotecan are largely excluded. This study retrospectively analyzed the relationship between Irinotecan metabolite levels and outcomes of UGT1A1 *1/*1-*1/*1 genotype arrangement. Blood samples (n = 244) were collected for analysis of plasma DPD activity (before first chemotherapy) and SN-38 levels (1.5 and 49 hour after CPT-11 administration). Clinical variables such as toxicity and outcomes were then assessed. Of the *1/*1 -*1/*1 genotype combination, the median progression free survival of the C_{SN-38 1.5 h} > 50.24 ng/ml subset was remarkably longer than that of the C_{SN-38 1.5 h} ≤ 50.24 ng/ml subset. However, there were no differences between the C_{SN-38 49 h} > 15.25 ng/ml subgroup and the ≤ 15.25 ng/ml group. It was lower DPD activity that responsible for the relatively higher incidence of bone marrow hypocellular, diarrhea, and oral mucositis in the C_{SN-38 1.5 h} > 50.24 ng/ml and C_{SN-38 49 h} > 15.25 ng/ml subsets. Therefore, plasma SN-38 levels is related to outcomes for UGT1A1 *1/*1-*1/*1 genotype, to improve efficacy, patients with C_{SN-38 1.5 h} lower than 50.24 ng/ml, CPT-11 dosage could be added in next chemmotherapy on SN-38 plasma level monitoring. Additionally, in patients with DPD activity below 3.18 before treatment, appropriate reduction of 5-FU dose could be considered to minimize the incidence of adverse events.

In vitro metabolism of canagliflozin in human liver, kidney, intestine microsomes, and recombinant uridine diphosphate glucuronosyltransferases (UGT) and the effect of genetic variability of UGT enzymes on the pharmacokinetics of canagliflozin in humans

O-glucuronidation is the major metabolic elimination pathway for canagliflozin. The objective was to identify enzymes and tissues involved in the formation of 2 major glucuronidated metabolites (M7 and M5) of canagliflozin and subsequently to assess the impact of genetic variations in these uridine diphosphate glucuronosyltransferases (UGTs) on in vivo pharmacokinetics in humans. In vitro incubations with recombinant UGTs revealed involvement of UGT1A9 and UGT2B4 in the formation of M7 and M5, respectively. Although M7 and M5 were formed in liver microsomes, only M7 was formed in kidney microsomes. Participants from 7 phase 1 studies were pooled for pharmacogenomic analyses. A total of 134 participants (mean age, 41 years; men, 63%; white, 84%) were included in the analysis. In UGT1A9*3 carriers, exposure of plasma canagliflozin (Cmax,ss , 11%; AUCτ,ss , 45%) increased relative to the wild type. An increase in exposure of plasma canagliflozin (Cmax,ss , 21%; AUCt,ss , 18%) was observed in participants with UGT2B4*2 genotype compared with UGT2B4*2 noncarriers. Metabolites further delineate the role of both enzymes. The pharmacokinetic findings in participants carrying the UGT1A9*3 and UGT2B4*2 allele implicate that UGT1A9 and UGT2B4 are involved in the metabolism of canagliflozin to M7 and M5, respectively.

Sources of interindividual variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in other individuals. A major source of this variability in drug response is drug metabolism, where differences in pre-systemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C max, and/or C min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is well recognized that both intrinsic (such as genetics, age, sex, and disease states) and extrinsic (such as diet, chemical exposures from the environment, and even sunlight) factors play a significant role. For the family of cytochrome P450 enzymes, the most critical of the drug metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, up- and down-regulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less reliably predictable and time-dependent manner. Understanding the mechanistic basis for drug disposition and response variability is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that brings with it true improvements in health outcomes in the therapeutic treatment of disease.

Relevance of UDP-glucuronosyltransferase polymorphisms for drug dosing: A quantitative systematic review

UDP-glucuronosyltransferases (UGT) catalyze the biotransformation of many endobiotics and xenobiotics, and are coded by polymorphic genes. However, knowledge about the effects of these polymorphisms is rarely used for the individualization of drug therapy. Here, we present a quantitative systematic review of clinical studies on the impact of UGT variants on drug metabolism to clarify the potential for genotype-adjusted therapy recommendations. Data on UGT polymorphisms and dose-related pharmacokinetic parameters in man were retrieved by a systematic search in public databases. Mean estimates of pharmacokinetic parameters were extracted for each group of carriers of UGT variants to assess their effect size. Pooled estimates and relative confidence bounds were computed with a random-effects meta-analytic approach whenever multiple studies on the same variant, ethnic group, and substrate were available. Information was retrieved on 30 polymorphic metabolic pathways involving 10 UGT enzymes. For irinotecan and mycophenolic acid a wealth of data was available for assessing the impact of genetic polymorphisms on pharmacokinetics under different dosages, between ethnicities, under comedication, and under toxicity. Evidence for effects of potential clinical relevance exists for 19 drugs, but the data are not sufficient to assess effect size with the precision required to issue dose recommendations. In conclusion, compared to other drug metabolizing enzymes much less systematic research has been conducted on the polymorphisms of UGT enzymes. However, there is evidence of the existence of large monogenetic functional polymorphisms affecting pharmacokinetics and suggesting a potential use of UGT polymorphisms for the individualization of drug therapy.

Analysis of UGT1A1*28 genotype and SN-38 pharmacokinetics for irinotecan-based chemotherapy in patients with advanced colorectal cancer: results from a multicenter, retrospective study in Shanghai

BACKGROUND

The UGT1A1*28 polymorphism, although closely linked with CPT-11-related adverse effects, cannot be used alone to guide individualized treatment decisions. However, CPT-11 dosage can be adjusted according to measured SN-38 pharmacokinetics. Our study is designed to investigate whether there is a relationship between SN-38 peak or valley concentrations and efficacy or adverse effects of CPT-11-based chemotherapy. We retrospectively studied 98 patients treated with advanced colorectal cancer in various UGT1A1*28 genotype groups (mainly (TA)6/(TA)6 and (TA)6/(TA)7 genotypes) treated with CPT-11 as first-line chemotherapy in Shanghai.

METHODS

One hundred and sixty-four advanced colorectal cancer patients were enrolled. To understand differences in genotype expression, the frequency of UGT1A1*28 thymine-adenine (TA) repeats in TATA box arrangement was assessed by PCR with genomic DNA extracted from peripheral blood. For ninety-eight cases with the (TA)6/(TA)6 and (TA)6/(TA)7 genotypes treated with CPT-11 as first-line chemotherapy, the plasma concentration of SN-38 was detected by HPLC 1.5 and 49 h after CPT-11 infusion. Efficacy and adverse effects were observed subsequently, and the relationship between SN-38 plasma concentration and efficacy or adverse effects within genotype groups, as well as differences in efficacy and adverse effects between (TA)6/(TA)6 and (TA)6/(TA)7 genotypes were analyzed statistically.

RESULTS

One hundred and fourteen patients (69.51 %) were identified with the (TA)6/(TA)6 genotype, forty-eight patients (29.27 %) with the (TA)6/(TA)7 genotype, and two patients (1.22 %) with the (TA)7/(TA)7 genotype. The average peak and valley concentrations of SN-38 after CPT-11 infusion and plasma bilirubin average levels before and after CPT-11 treatment in the (TA)6/(TA)7 genotype group were all higher than those in (TA)6/(TA)6 group, and the difference was statistically significant (p = 0.00). Stepwise regression analysis showed that SN-38 peak and valley concentration was correlated with PFS in the (TA)6/(TA)6 genotype. In the (TA)6/(TA)7 group, SN-38 peak concentration was correlated with CPT-11 starting dose and OS, valley concentration correlated with plasma bilirubin levels before CPT-11 treatment, delayed diarrhea, and OS. For the (TA)6/(TA)6 genotype, mPFS of the SN-38 peak concentration >43.2 ng/ml subgroup was significantly longer than that of ≤43.2 ng/ml subgroup (8.0 ± 0.35 vs. 6.5 ± 0.79 months, χ (2) = 17.18, p = 0.00) with a relatively high incidence of Grade I/II° myelosuppression; for the (TA)6/(TA)7 genotype, there was no significant difference in mOS between the SN-38 valley concentration >16.83 ng/ml and ≤16.83 subgroups (17.3 ± 0.45 vs. 18.8 ± 0.50 months, χ (2) = 1.38, p = 0.24), but the former had a higher incidence of Grade III/IV° mucositis and delayed diarrhea. For 2 (TA)7/(TA)7 cases, although 25 % dose reduction of CPT-11, which is calculated according to body surface area, Grade IV° bone marrow suppression and Grade III° delayed diarrhea still occurred after CPT-11 treatment, though both adverse effects resolved and did not recur again after a 50 % dose reduction.

CONCLUSION

The (TA)6/(TA)6 genotype and (TA)6/(TA)7 genotype accounted for the most, and (TA)7/(TA)7 genotype only account for a very small portion of advanced colorectal cancer patients in Shanghai. For the (TA)6/(TA)6 genotype, CPT-11 dosage can be increased gradually to improve efficacy for patients with SN-38 peak concentration ≤43.2 ng/ml after CPT-11 infusion; and for (TA)6/(TA)7 genotype patients, CPT-11 dosage may be lowered appropriately to reduce serious adverse effects such as bone marrow suppression and delayed diarrhea without affecting the efficacy for those with SN-38 valley concentration >16.83 ng/ml. For (TA)7/(TA)7 genotype patients, adverse effects should be closely observed after treatment even if CPT-11 dosage has been reduced.

Use of pharmacogenetics for predicting cancer prognosis and treatment exposure, response and toxicity

Cancer treatment is complicated because of a multitude of treatment options and little patient-specific information to help clinicians choose appropriate therapy. There are two genomes relevant in cancer treatment: the tumor (somatic) and the patient (germline). Together, these two genomes dictate treatment outcome through four processes: the somatic genome primarily determines tumor prognosis and response while the germline genome modulates treatment exposure and toxicity. In this review, we describe the influence of these genomes on treatment outcomes by highlighting examples of genetic variation that are predictors of each of these four factors, prognosis, response, toxicity and exposure, and discuss the translation and clinical implementation of each. Use of pre-treatment pharmacogenetic testing will someday enable clinicians to make individualized therapy decisions about aggressiveness, drug selection and dose, improving treatment outcomes for cancer patients.

The Role of SN-38 Exposure,UGT1A1*28Polymorphism, and Baseline Bilirubin Level in Predicting Severe Irinotecan Toxicity

Irinotecan, an anticancer drug, is associated with severe and potentially fatal diarrhea and neutropenia. The objective of this analysis was to evaluate the role of SN-38 exposure, the active metabolite of irinotecan, UGT1A1 genotypes, and baseline bilirubin on the maximum decrease (nadir) in absolute neutrophil counts following irinotecan. This analysis extended the work of a previous study that examined the effect of UGT1A1 genotypes on the incidence of severe neutropenia in 86 advanced cancer patients following irinotecan treatment. Regression analysis showed that the absolute neutrophil count nadir depended on SN-38 exposure (AUC) and UGT1A1*28 homozygous 7/7 genotype. An increased SN-38 AUC and the 7/7 genotype were significantly associated with a lower absolute neutrophil count nadir (R2 = .49). An alternate model suggested that higher baseline bilirubin and the 7/7 genotype were also significantly associated with a lower absolute neutrophil count nadir, although with a lower coefficient of determination (R2 = .31). Based on these findings and other reports, the irinotecan label was modified to indicate the role of UGT1A1*28 polymorphism in the metabolism of irinotecan and the associated increased risk of severe neutropenia. The label modifications also included recommendations for lower starting doses of irinotecan in patients homozygous for the UGT1A1*28 (7/7) polymorphism.

Functional impact and prevalence of polymorphisms involved in the hepatic glucuronidation of valproic acid

Metabolism of valproic acid, a widely used drug, is only partially understood. It is mainly metabolized through glucuronidation and acts as a substrate for various UDP-glucuronosyltransferases (UGTs). UGTs metabolizing valproic acid in the liver are UGT1A3, UGT1A4, UGT1A6, UGT1A9 and UGT2B7, with UGT1A6 and UGT2B7 being the most prominent. Polymorphisms in genes expressing these enzymes may have clinical consequences, regarding dosing, blood levels of the drug and adverse reactions. Not all genes are well studied and studies, where they exist, report conflicting results. Prevalence of polymorphisms and various haplotypes is also of great importance, as it may suggest different therapeutic approaches in various populations. Presented here is a review of currently known polymorphisms, their functional impact, when known, and their prevalence in different populations, highlighting the current state of understanding and areas where there is a lack of data and suggesting new perspectives for further research.

UDP-glucuronosyltransferase (UGT) 1A9-overexpressing HeLa cells is an appropriate tool to delineate the kinetic interplay between breast cancer resistance protein (BRCP) and UGT and to rapidly identify the glucuronide substrates of BCRP

The interplay between phase II enzymes and efflux transporters leads to extensive metabolism and low bioavailability for flavonoids. To investigate the simplest interplay between one UDP-glucuronosyltransferase isoform and one efflux transporter in flavonoid disposition, engineered HeLa cells stably overexpressing UGT1A9 were developed, characterized, and further applied to investigate the metabolism of two model flavonoids (genistein and apigenin) and excretion of their glucuronides. The results indicated that the engineered HeLa cells overexpressing UGT1A9 rapidly excreted the glucuronides of genistein and apigenin. The kinetic characteristics of genistein or apigenin glucuronidation were similar with the use of UGT1A9 overexpressed in HeLa cells or the commercially available UGT1A9. Small interfering (siRNA)-mediated UGT1A9 silencing resulted in a substantial decrease in glucuronide excretion (>75%, p < 0.01). Furthermore, a potent inhibitor of breast cancer resistance protein (BCRP), 3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6,7,12,12a-octahydropyrazino[1',2':1,6]pyrido[3,4-b]indol-3-yl)-propionic acid tert-butyl ester (Ko143), caused, in a dose-dependent manner, a substantial and marked reduction of the clearance (74-94%, p < 0.01), and a substantial increase in the intracellular glucuronide levels (4-8-fold, p < 0.01), resulting in a moderate decrease in glucuronide excretion (19-59%, p < 0.01). In addition, a significant, albeit moderate, reduction in the fraction of genistein metabolized (f(met)) in the presence of Ko143 was observed. In contrast, leukotriene C₄ and siRNA against multidrug resistance protein (MRP) 2 and MRP3 did not affect excretion of flavonoid glucuronides. In conclusion, the engineered HeLa cells overexpressing UGT1A9 is an appropriate model to study the kinetic interplay between UGT1A9 and BCRP in the phase II disposition of flavonoids. This simple cell model should also be very useful to rapidly identify whether a phase II metabolite is the substrate of BCRP.

Ugt1a is required for the protective effect of selenium against irinotecan-induced toxicity

PURPOSE

Irinotecan (CPT-11) is widely used for the treatment of patients with colorectal cancer. However, the adverse effects associated with the treatment have hindered the efficacies of irinotecan. We have shown that organic selenium compounds could significantly attenuate irinotecan-associated toxicity and enhance antitumor activity in xenograft tumor models. The objective of this study is to determine the role of a specific group of uridine diphosphate glucuronosyltransferases, which is coded by UGT1A, in detoxification process of irinotecan as well as selenium-associated protective effect against irinotecan-induced toxicity.

METHODS

In this study, the toxicities of irinotecan, docetaxel and cisplatin in the Ugta1 mutant rats and their wild-type controls were compared. The plasma concentrations of irinotecan and SN-38 were measured. The modulatory effect of a selenium compound on irinotecan-induced toxicity was analyzed in these rats.

RESULTS

We demonstrated that the maximum tolerated doses of irinotecan in the homozygous mutant rats were significantly lower than those in wild-type rats, 25 mg/kg × 1 versus 200 mg/kg × 1 and 3 mg/kg/day × 3 versus 100 mg/kg/day × 3, respectively. The enhanced sensitivity was specific to irinotecan and was not observed with other chemotherapeutic agents, such as docetaxel and cisplatin, where Ugt1a is not required for their metabolism. Our results also showed that selective protection against irinotecan-induced toxicity by 5-methylselenocysteine was achieved in the wild-type rats but not in the Ugt1a null rats.

CONCLUSION

These data support the hypothesis that expression of UGT1A is critical for 5-methylselenocysteine to exert its protective effect against irinotecan-induced toxicity.

Population pharmacokinetic analysis of sorafenib in patients with solid tumours

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Sorafenib is a multikinase inhibitor with activity against B-raf, C-raf, VEGFR2, PDGFRβ and FGFR1. Sorafenib is clinically approved for the treatment of renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC). The pharmacokinetics (PK) of sorafenib are highly variable between subjects. Sorafenib exposure increases less than dose proportionally (likely due to limited solubility). Sorafenib undergoes enterohepatic recycling (EHC).

WHAT THIS STUDY ADDS

This is the first study to characterize the PK of sorafenib using a model based on sorafenib's known disposition characteristics such as delayed/solubility-limited GI absorption and EHC. The parameterization of the EHC model used a square wave function to describe the gall bladder emptying. This study evaluated the effect of baseline bodyweight, BSA, age, gender, liver function parameters, kidney function parameters and genotype with respect to CYP3A4*1B, CYP3A5*3C, UGT1A9*3 and UGT1A9*5 on sorafenib PK. No clinically important covariates were identified. This model can be used to simulate and explore alternative dosing regimens and to develop exposure-response relationships for sorafenib.

AIMS

To characterize the pharmacokinetics (PK) of sorafenib in patients with solid tumours and to evaluate the possible effects of demographic, clinical and pharmacogenetic (CYP3A4*1B, CYP3A5*3C, UGT1A9*3 and UGT1A9*5) covariates on the disposition of sorafenib.

METHODS

PK were assessed in 111 patients enrolled in five phase I and II clinical trials, where sorafenib 200 or 400 mg was administered twice daily as a single agent or in combination therapy. All patients were genotyped for polymorphisms in metabolic enzymes for sorafenib. Population PK analysis was performed by using nonlinear mixed effects modelling (NONMEM). The final model was validated using visual predictive checks and nonparametric bootstrap analysis.

RESULTS

A one compartment model with four transit absorption compartments and enterohepatic circulation (EHC) adequately described sorafenib disposition. Baseline bodyweight was a statistically significant covariate for distributional volume, accounting for 4% of inter-individual variability (IIV). PK model parameter estimates (range) for an 80 kg patient were clearance 8.13 l h(-1) (3.6-22.3 l h(-1) ), volume 213 l (50-1000 l), mean absorption transit time 1.98 h (0.5-13 h), fraction undergoing EHC 50% and average time to gall bladder emptying 6.13 h.

CONCLUSIONS

Overall, population PK analysis was consistent with known biopharmaceutical/PK characteristics of oral sorafenib. No clinically important PK covariates were identified.

Genetic polymorphism in metabolism and host defense enzymes: implications for human health risk assessment

Genetic polymorphisms in xenobiotic metabolizing enzymes can have profound influence on enzyme function, with implications for chemical clearance and internal dose. The effects of polymorphisms have been evaluated for certain therapeutic drugs but there has been relatively little investigation with environmental toxicants. Polymorphisms can also affect the function of host defense mechanisms and thus modify the pharmacodynamic response. This review and analysis explores the feasibility of using polymorphism data in human health risk assessment for four enzymes, two involved in conjugation (uridine diphosphoglucuronosyltransferases [UGTs], sulfotransferases [SULTs]), and two involved in detoxification (microsomal epoxide hydrolase [EPHX1], NADPH quinone oxidoreductase I [NQO1]). This set of evaluations complements our previous analyses with oxidative and conjugating enzymes. Of the numerous UGT and SULT enzymes, the greatest likelihood for polymorphism effect on conjugation function are for SULT1A1 (*2 polymorphism), UGT1A1 (*6, *7, *28 polymorphisms), UGT1A7 (*3 polymorphism), UGT2B15 (*2 polymorphism), and UGT2B17 (null polymorphism). The null polymorphism in NQO1 has the potential to impair host defense. These highlighted polymorphisms are of sufficient frequency to be prioritized for consideration in chemical risk assessments. In contrast, SNPs in EPHX1 are not sufficiently influential or defined for inclusion in risk models. The current analysis is an important first step in bringing the highlighted polymorphisms into a physiologically based pharmacokinetic (PBPK) modeling framework.

Do pharmacokinetic polymorphisms explain treatment failure in high-risk patients with neuroblastoma?

PURPOSE

Neuroblastoma is the most common extracranial solid tumour in childhood. It accounts for 15% of all paediatric oncology deaths. In the last few decades, improvement in treatment outcome for high-risk patients has not occurred, with an overall survival rate <30-40%. Many reasons may account for such a low survival rate. The aim of this review is to evaluate whether pharmacogenetic factors can explain treatment failure in neuroblastoma.

METHODS

A literature search based on PubMed's database Medical Subject Headings (MeSH) was performed to retrieve all pertinent publications on current treatment options and new classes of drugs under investigation. One hundred and fifty-eight articles wer reviewed, and relevant data were extracted and summarised.

RESULTS AND CONCLUSIONS

Few of the large number of polymorphisms identified thus far showed an effect on pharmacokinetics that could be considered clinically relevant. Despite their clinical relevance, none of the single nucleotide polymorphisms (SNPs) investigated can explain treatment failure. These findings seem to reflect the clinical context in which anti-tumour drugs are used, i.e. in combination with multimodal therapy. In addition, many pharmacogenetic studies did not assess (differences in) drug exposure, which could contribute to explaining pharmacogenetic associations. Furthermore, it remains unclear whether the significant activity of new drugs on different neuroblastoma cell lines translates into clinical efficacy, irrespective of resistance or myelocytomatosis viral related oncogene, neuroblastoma derived (MYCN) amplification. Elucidation of the clinical role of pharmacogenetic factors in the treatment of neuroblastoma demands an integrated pharmacokinetic-pharmacodynamic approach to the analysis of treatment response data.

Dose-dependent association between UGT1A1*28 genotype and irinotecan-induced neutropenia: low doses also increase risk

PURPOSE

A previous meta-analysis showed that the association between the UGT1A1*28 genotype and irinotecan-induced neutropenia was influenced by irinotecan dose and that the risk of neutropenia was similar at low doses for patients with all genotypes. However, the sample sizes for the low- and high-dose groups were small. Because additional studies have now been reported, an updated and refined meta-analysis is needed.

EXPERIMENTAL DESIGN

Meta-analyses were done to assess the relationship between UGT1A1*28 and neutropenia. The association between UGT1A1*28 and the relative extent of glucuronidation (REG) of SN-38 was also examined. The studies included were stratified into different dose groups.

RESULTS

A total of 1,998 patients were included for the analysis of neutropenia and 581 patients were included for REG. The risk of neutropenia at low doses was significantly higher among patients with a UGT1A1*28/*28 genotype than among those carrying the UGT1A1*1 allele(s) [relative risk (RR), 2.43; 95% confidence interval, 1.34-4.39; P = 0.003]. In addition, the RR of neutropenia at low doses was comparable with that at medium doses (2.43 versus 2.00). The RR of neutropenia at high doses was significantly higher than that at low and medium doses (7.22 versus 2.04). We found the weighted mean difference of REG (UGT1A1*1/*1 or UGT1A1*1/*28 versus UGT1A1*28/*28) increased with increasing dose of irinotecan.

CONCLUSIONS

In conclusion, the UGT1A1*28/*28 genotype was associated with an increased risk of neutropenia not only at medium or high doses of irinotecan but also at low doses. The dose-dependent manner of SN-38 glucuronidation explained why the association between UGT1A1*28 and neutropenia was dose dependent.

Uridine 5'-diphospho-glucuronosyltransferase genetic polymorphisms and response to cancer chemotherapy

Pharmacogenetics aims to elucidate how genetic variation affects the efficacy and side effects of drugs, with the ultimate goal of personalizing medicine. Clinical studies of the genetic variation in the uridine 5'-diphosphoglucuronosyltransferase gene have demonstrated how reduced-function allele variants can predict the risk of severe toxicity and help identify cancer patients who could benefit from reduced-dose schedules or alternative chemotherapy. Candidate polymorphisms have also been identified in vitro, although the functional consequences of these variants still need to be tested in the clinical setting. Future approaches in uridine 5'-diphosphoglucuronosyltransferase pharmacogenetics include genetic testing prior to drug treatment, genotype-directed dose-escalation studies, study of genetic variation at the haplotype level and genome-wide studies.

Pharmacodynamic genes do not influence risk of neutropenia in cancer patients treated with moderately high-dose irinotecan

AIMS

A recent study found that variation in camptothecin pharmacodynamic genes (TOP1, PARP1, TDP1 and XRCC1) correlated with efficacy and risk of neutropenia in irinotecan-treated cancer patients (median dose: 180 mg/m2), which suggests that these genes might predict outcomes to irinotecan-based therapies. The present study was conducted to evaluate previous gene associations using an independent sample of patients receiving irinotecan.

MATERIALS & METHODS

DNA was isolated from 85 advanced cancer patients treated with 300 or 350 mg/m2 irinotecan and genotyped for haplotype-tag polymorphisms across TOP1, PARP1, TDP1 and XRCC1. Associations between genotypes and haplotypes and log(absolute neutrophil count nadirs) were assessed by linear regression.

RESULTS

No associations were observed.

CONCLUSION

Our findings suggest that the genes we tested do not influence toxicity of irinotecan when adminstered at 300-350 mg/m2.

Dose-dependent association between UGT1A1*28 polymorphism and irinotecan-induced diarrhoea: a meta-analysis

Life-threatening diarrhoea is observed in up to 25% of cancer patients receiving irinotecan. The associations between the UGT1A1*28 polymorphism and irinotecan-induced diarrhoea remains controversial because of conflicting data in the literature. Meta-analyses were performed on published data in terms of relationships between UGT1A1*28 and severe diarrhoea. We searched databases for relevant studies that were published in English or Chinese. Two reviewers extracted data and assessed methodological quality. UGT1A1*28 related odds ratios (ORs) were pooled by use of a fixed-effects model. The studies included were stratified into subgroups representing different races and irinotecan doses, and meta-regression analyses were performed to investigate the effect of study characteristics on the association between UGT1A1*28 and diarrhoea. Twenty trials including a total of 1760 cancer patients were included. The risk of severe diarrhoea at medium and high irinotecan doses was higher among patients with a UGT1A1*28/*28 genotype than among those with a UGT1A1*1/*1 genotype (OR=3.69, 95% confidence interval [CI]=2.00-6.83; P<0.001). Considering the patients with a UGT1A1*1/*28 genotype, the risk of toxicity was also higher than among those with a wild-type genotype at medium and high doses (OR=1.92, 95% CI=1.31-2.82; P=0.001). No association was observed between UGT1A1*28 and severe diarrhoea at low doses (<125 mg/m(2)). In conclusion, patients carrying UGT1A1*28 allele(s) are at an increased risk of irinotecan-induced severe diarrhoea. This increased risk is only apparent in those who are administrated with medium or high irinotecan doses.

Prediction of irinotecan and 5-fluorouracil toxicity and response in patients with advanced colorectal cancer

Irinotecan and 5-fluorouracil (5-FU) are used to treat metastatic colorectal cancer. Irinotecan's active metabolite is inactivated by UDP-glucuronosyltransferase 1A1 (UGT1A1), which is deficient in Gilbert's syndrome. Irinotecan and metabolites are transported by P-glycoprotein, encoded by ABCB1. 5-FU targets folate metabolism through inhibition of thymidylate synthase (TYMS). Methylenetetrahydrofolate reductase (MTHFR) generates active folate necessary for haematopoiesis. We retrospectively genotyped 140 Swedish and Norwegian irinotecan and 5-FU-treated colorectal cancer patients from the Nordic VI clinical trial for selected variants of UGT1A1, ABCB1, TYMS and MTHFR. We found an increased risk of clinically relevant early toxicity in patients carrying the ABCB1 3435 T/T genotype, Odds ratio (OR)=3.79 (95% confidence interval (CI)=1.09–13.2), and in patients carrying the UGT1A1^*28/^*28 genotype, OR=4.43 (95% CI=1.30–15.2). Patients with UGT1A1^*28/^*28 had an especially high risk of neutropenia, OR=6.87 (95% CI=1.70–27.7). Patients who had reacted with toxicity during the first two cycles were in total treated with fewer cycles (P<0.001), and less often responded to treatment (P<0.001). Genetic variation in ABCB1 was associated with both early toxicity and lower response to treatment. Carriers of the ABCB1 1236T-2677T-3435T haplotype responded to treatment less frequently (43 vs 67%, P=0.027), and survived shorter time, OR=1.56 (95% CI=1.01–2.45).

UGT1A1 genotyping: a predictor of irinotecan-associated side effects and drug efficacy?

Irinotecan [Camptosar (CPT-11), Pfizer Pharmaceuticals, New York, USA] is one of the most effective chemotherapeutic agents in the treatment of metastatic colorectal cancer. In vivo, the prodrug CPT-11 is biotransformed by carboxylesterase into its active metabolite SN-38. SN-38 is inactivated by uridine disphosphate glucuronosyl transferase 1 (UGT1A1) into the inactive compound SN-38G, which is excreted with the bile.This review concentrates on a critical evaluation of UGT1A1 gene polymorphism as a predictor of toxicity and treatment efficacy in patients who received irinotecan for metastatic colorectal cancer. Irinotecan is explained with its main toxicities as well as the underlying mechanisms. The enzyme UGT1A1 is shown in the context of other metabolic pathways and different UGT enzymes involved. We will review in detail the controversy of the current literature with regard to the significance of identifying patients carrying the homozygous genotype UGT1A1 28. Racial differences concerning UGT enzymes have to be considered when discussing a pragmatic approach to determine gene polymorphisms as a predictor of treatment efficacy and outcome in patients receiving irinotecan-based chemotherapy. Dose dependency of toxicity and the clinical relevance of various UGT1 enzymes and single nucleotide polymorphisms in different alternative metabolic pathways are clarified to put UGT1A1 genotyping in a broad context with additional and competing strategies of patient-tailored therapy.

Pharmacogenetics of solid tumors: directed therapy in breast, lung, and colorectal cancer: a paper from the 2008 william beaumont hospital symposium on molecular pathology

Genetic variability in drug-metabolizing enzymes and signaling pathways affects chemotherapy-related toxicity and treatment outcome in cancer. In breast and colorectal cancer, polymorphisms in metabolic enzymes involved in tamoxifen and irinotecan therapies has led the U.S. Food and Drug Administration to address genetic factors relevant to patient consideration of treatment with these compounds. Tamoxifen therapeutic failure in breast cancer has been associated with reduced CYP2D6 activity due to inefficient activation of tamoxifen. Irinotecan toxicity in colorectal cancer is more common in patients with reduced-activity UGT1A alleles, resulting in excessive exposure to the potent SN-38 metabolite. In colorectal and lung cancers, somatic mutations in the epidermal growth factor receptor and downstream signaling molecules have been associated with the therapeutic outcome of epidermal growth factor receptor-directed therapies. This review discusses the current knowledge regarding the utility of single gene-UGT1A1, CYP2D6, EGFR, and KRAS-or multigene analysis, for optimizing breast, colorectal, and lung cancer therapy. Current advances in these areas highlight how pharmacogenetics help personalized decision-making for patient management.

Disposition of flavonoids via enteric recycling: UDP-glucuronosyltransferase (UGT) 1As deficiency in Gunn rats is compensated by increases in UGT2Bs activities

Flavonoids have poor bioavailabilities largely because of metabolism via UDP-glucuronosyltransferases (UGTs). This study aims to further understand the functions of UGT in metabolizing genistein and apigenin, two compounds metabolized more extensively in the gut than in the liver. Because Gunn rats are deficient in UGT1As, we determined whether this deficiency would result in less flavonoid glucuronidation, using rat intestinal perfusion model and microsomes prepared from rat liver and intestine. In yeast-expressed rat UGT isoforms, rat UGT1A isoforms (especially UGT1A7) were mainly responsible for flavonoid metabolism. In perfusion studies, the two flavonoids were rapidly absorbed at comparable rates, but the intestinal excretions of glucuronides in Gunn rats compared with Wistar rats were not only comparable for genistein but also were higher (p < 0.05) for apigenin, suggesting up-regulation of UGT isoforms in Gunn rats. To determine the possible compensatory UGT isoforms, we first verified that UGT1A activities were significantly lower (p < 0.05) in Gunn rats by using UGT1A-specific probes 7-ethyl-10-hydroxycamptothecin (SN-38) and prunetin. We then demonstrated using UGT2B probes testosterone, ezetimibe, and indomethacin that UGT2B activities were usually significantly higher in Gunn rats. In addition, testosterone was metabolized much faster in liver microsomes than in intestinal microsomes, and in microsomes prepared from Gunn rats compared with Wistar rats. In conclusion, flavonoids are efficiently metabolized by UGT1A-deficient Gunn rats because of compensatory up-regulation of intestinal UGT2Bs and hepatic anion efflux transporters, which increases their disposition and limits their oral bioavailabilities.

Pharmacogenetics in chemotherapy of colorectal cancer

Although in recent years, chemotherapeutic options for colorectal carcinoma have expanded, overall response rates are still too low, with high rates of toxicity. Pharmacogenetics aim at predicting both treatment response and adverse effects in individual patients. This review describes the current knowledge of pharmacogenetic markers in the systemic treatment of colorectal cancer. UGT1A1*28 leads to reduced conjugation of SN-38, the active metabolite of irinotecan, resulting in an increased rate of adverse effects, especially neutropenia. To a lesser extent, increased 5-FU toxicity is predicted by DPYD*2A. A variable number of tandem repeats polymorphism in the thymidylate synthase enhancer region, in combination with a single nucleotide polymorphism C>G, may predict poorer response to 5-FU. Efficacy of oxaliplatin is influenced by polymorphisms in components of DNA repair systems, such as ERCC1 and XRCC1. Polymorphic changes in the endothelial growth factor receptor probably predict cetuximab efficacy. Furthermore, the antibody-depended cell-mediated cytotoxic effect of cetuximab may be reduced by polymorphisms in the immunoglobin G fragment C receptors. Bevacizumab efficacy is suspected to be influenced by polymorphisms in the VEGF gene and the hypoxia inducible factor 1alpha gene. Although the interpretation of pharmacogenetic studies is complicated, results imply a promising way of pretreatment prediction of chemotherapy efficacy and toxicity.

Can UGT1A1 genotyping reduce morbidity and mortality in patients with metastatic colorectal cancer treated with irinotecan? An evidence-based review

This evidence-based review addresses the question of whether testing for UGT1A1 mutations in patients with metastatic colorectal cancer treated with irinotecan leads to improvement in outcomes (e.g., irinotecan toxicity, response to treatment, morbidity, and mortality), when compared with no testing. No studies were identified that addressed this question directly. The quality of evidence on the analytic validity of current UGT1A1 genetic testing methods is adequate (scale: convincing, adequate, inadequate), with available data indicating that both analytic sensitivity and specificity for the common genotypes are high. For clinical validity, the quality of evidence is adequate for studies reporting concentration of the active form of irinotecan (SN-38), presence of severe diarrhea, and presence of severe neutropenia stratified by UGT1A1 common genotypes. The strongest association for a clinical endpoint is for severe neutropenia. Patients homozygous for the *28 allele are 3.5 times more likely to develop severe neutropenia compared with individuals with the wild genotype (risk ratio 3.51; 95% confidence interval 2.03-6.07). The proposed clinical utility of UGT1A1 genotyping would be derived from a reduction in drug-related adverse reactions (benefits) while at the same time avoiding declines in tumor response rate and increases in morbidity/mortality (harms). At least three treatment options for reducing this increased risk have been suggested: modification of the irinotecan regime (e.g., reduce initial dose), use of other drugs, and/or pretreatment with colony-stimulating factors. However, we found no prospective studies that examined these options, particularly whether a reduced dose of irinotecan results in a reduced rate of adverse drug events. This is a major gap in knowledge. Although the quality of evidence on clinical utility is inadequate, two of three reviewed studies (and one published since our initial selection of studies for review) found that individuals homozygous for the *28 allele had improved survival. Three reviewed studies found statistically significant higher tumor response rates among individuals homozygous for the *28 allele. We found little or no direct evidence to assess the benefits and harms of modifying irinotecan regimens for patients with colorectal cancer based on their UGT1A1 genotype; however, results of our preliminary modeling of prevalence, acceptance, and effectiveness indicate that reducing the dose would need to be highly effective to have benefits outweigh harms. An alternative is to increase irinotecan dose among wild-type individuals to improve tumor response with minimal increases in adverse drug events. Given the large number of colorectal cancer cases diagnosed each year, a randomized controlled trial of the effects of irinotecan dose modifications in patients with colorectal cancer based on their UGT1A1 genotype is feasible and could clarify the tradeoffs between possible reductions in severe neutropenia and improved tumor response and/or survival in patients with various UGT1A1 genotypes.

Characterization of UGTs active against SAHA and association between SAHA glucuronidation activity phenotype with UGT genotype

Suberoylanilide hydroxamic acid (SAHA) is a histone deacetylase inhibitor used in the treatment of cutaneous T-cell lymphoma and in clinical trials for treatment of multiple other cancers. A major mode of SAHA metabolism is by glucuronidation via the UDP-glucuronosyltransferase (UGT) family of enzymes. To characterize the UGTs active against SAHA, homogenates from HEK293 cell lines overexpressing UGT wild-type or variant UGT were used. The hepatic UGTs 2B17 and 1A9 and the extrahepatic UGTs 1A8 and 1A10 exhibited the highest overall activity against SAHA as determined by V(max)/K(M) (16+/-6.5, 7.1+/-2.2, 33+/-6.3, and 24+/-2.4 nL x min(-1) x microg UGT protein(-1), respectively), with UGT2B17 exhibiting the lowest K(M) (300 micromol/L) against SAHA of any UGT in vitro. Whereas the UGT1A8p.Ala173Gly variant exhibited a 3-fold (P<0.005) decrease in glucuronidation activity against SAHA compared with wild-type UGT1A8, the UGT1A8p.Cys277Tyr variant exhibited no detectable glucuronidation activity; a similar lack of detectable glucuronidation activity was observed for the UGT1A10p.Gly139Lys variant. To analyze the effects of the UGT2B17 gene deletion variant (UGT2B17*2) on SAHA glucuronidation phenotype, human liver microsomes (HLM) were analyzed for glucuronidation activity against SAHA and compared with UGT2B17 genotype. HLM from subjects homozygous for UGT2B17*2 exhibited a 45% (P<0.01) decrease in glucuronidation activity and a 75% (P<0.002) increase in K(M) compared with HLMs from subjects homozygous for the wild-type UGT2B17*1 allele. Overall, these results suggest that several UGTs play an important role in the metabolism of SAHA and that UGT2B17-null individuals could potentially exhibit altered SAHA clearance rates with differences in overall response.

Acute and long-term gastrointestinal consequences of chemotherapy

There are many anti-neoplastic agents in cancer treatment. Combination regimens are often the main standard treatment, particularly for gastrointestinal malignancies. The introduction of new regimens that combine fluoropyrimidines with irinotecan or oxaliplatin and recently also with antibodies against the Epidermal Growth Factor Receptor (EGFR) (cetuximab and panitumumab) and against the Vascular Endothelial Growth Factor (VEGF) (bevacizumab) pathways, has dramatically improved the progression free survival and survival of patients with metastatic colorectal cancer. This rapid extension of available anti-neoplastic drugs has, however, also highlighted the urgent need for clinicians to better understand and identify the spectrum of acute and late toxicities of these drugs. Acute and long-term adverse effects are inherent to non-surgical cancer treatment using chemotherapy and/or radiation therapy, which can profoundly affect the gastrointestinal tract leading to a wide spectrum of acute and late toxicities. An improved knowledge of the aetiology, incidence, supportive measures and of the prevention of these toxicities is warranted to improve patient care. We herein review and discuss the main acute and late gastrointestinal toxicities of chemotherapy and/or radiotherapy for patients with gastrointestinal malignancies.

Pharmacogenetic testing for uridine diphosphate glucuronosyltransferase 1A1 polymorphisms: are we there yet?

Recent changes to the labels of three prescription drugs--irinotecan, 6-mercaptopurine, and warfarin--include recommendations for pharmacogenetic testing in patients. Thus, clinicians are faced with determining the utility and practicality of pharmacogenetic testing in clinical practice. We illustrate the clinical implications that this testing may have using irinotecan, an agent approved for the treatment of metastatic colorectal cancer, as an example. A clinical association between the drug's active metabolite and toxicity has been found. By performing uridine diphosphate glucuronosyltransferase (UGT) 1A1 genetic testing, some studies have been able to predict which patients receiving irinotecan will experience the toxicity. Thus, irinotecan's package insert was revised to include a recommendation for such testing. In addition, the United States Food and Drug Administration approved a clinical test for the UGT1A1*28 allele. These events demonstrate that pharmacogenetics has entered the realm of clinical practice. However, the transition from bench to bedside of these tests has distinct challenges such as population differences, test sensitivity, and the role of other genetic and nongenetic factors that influence drug toxicity. In addition, ethical and logistic implications of pharmacogenetic testing exist.

Use of genome-wide high-throughput technologies in biomarker development

In recent years, the usage of high-throughput technologies in the fields of genomics, transcriptomics, proteomics and metabolomics for biomarker discovery has expanded enormously. Biomarkers can be applied for many purposes, including diagnosis, prognosis, staging and selecting appropriate patient therapy. In addition, biomarkers can provide information on disease mechanism or progression. Biomarker development for clinical application encompasses phases for their discovery and characterization, assay development and, finally, implementation using automated platforms employed in clinical laboratories. However, translation from bench to bedside outside a research-oriented environment has proven to be more difficult. This is reflected by only few new biomarkers being integrated into clinical application in the last years. This article reviews currently used high-throughput technologies for the identification of biomarkers, as well as present approaches to increase the percentage of biomarkers that pass the barriers for clinical application.