Impact of CYP3A4 haplotypes on irinotecan pharmacokinetics in Japanese cancer patients

Activation/Inactivation of Anticancer Drugs by CYP3A4: Influencing Factors for Personalized Cancer Therapy

Cytochrome P450 3A4 (CYP3A4), one of the most important members of the cytochrome P450 subfamily, is a crucial catalyst in the metabolism of numerous drugs. As it catalyzes numerous processes for drug activation or inactivation, the pharmacological activities and clinical outcomes of anticancer drugs metabolized by CYP3A4 are highly dependent on the enzyme's activity and expression. Due to the complexity of tumor microenvironments and various influencing factors observed in human in vitro models and clinical studies, the pharmacokinetics of most anticancer drugs are influenced by the extent of induction or inhibition of CYP3A4-mediated metabolism, and these details are not fully recognized and highlighted. Therefore, this interindividual variability due to genetic and nongenetic factors, together with the narrow therapeutic index of most anticancer drugs, contributes to their unique set of exposures and responses, which have important implications for achieving the expected efficacy and minimizing adverse events of chemotherapy for cancer in individuals. To elucidate the mechanisms of CYP3A4-mediated activation/inactivation of anticancer drugs associated with personalized therapy, this review focuses on the underlying determinants that contribute to differences in CYP3A4 metabolic activity and provides a comprehensive and valuable overview of the significance of these factors, which differs from current considerations for dosing regimens in cancer therapy. We also discuss knowledge gaps, challenges, and opportunities to explore optimal dosing regimens for drug metabolic activation/inactivation in individual patients, with particular emphasis on pooling and analyzing clinical information that affects CYP3A4 activity. SIGNIFICANCE STATEMENT: This review focuses on anticancer drugs that are activated/deactivated by CYP3A4 and highlights outstanding factors affecting the interindividual variability of CYP3A4 activity in order to gain a detailed understanding of CYP3A4-mediated drug metabolism mechanisms. A systematic analysis of available information on the underlying genetic and nongenetic determinants leading to variation in CYP3A4 metabolic activity to predict therapeutic response to drug exposure, maximize efficacy, and avoid unpredictable adverse events has clinical implications for the identification and development of CYP3A4-targeted cancer therapeutics.

High hepatic and plasma exposures of atorvastatin in subjects harboring impaired cytochrome P450 3A4∗16 modeled after virtual administrations and possibly associated with statin intolerance found in the Japanese adverse drug event report database

Drug interactions between atorvastatin and cytochrome P450 (P450) 3A substrates/inhibitors lead to an increased incidence of skeletal muscle or hepatic toxicity. However, in this survey, among 483 Japanese subjects administered atorvastatin alone, more than half (258) experienced statin intolerance and were unable to continue using the drug. Although many factors underly atorvastatin toxicity, the intrinsic clearance rate might be a contributing causal factor. The impaired P450 3A4 p.Thr185Ser variant, CYP3A4∗16 (rs12721627), has been identified in East Asians with an allele frequency of 2.2%. Pharmacokinetically modeled plasma concentrations of atorvastatin increased after a virtual oral dose of 40 mg in CYP3A4∗16 homozygotes; the maximum concentration and area under the concentration curve, respectively, were 3.3-fold and 4.2-fold those in subjects homozygous for CYP3A4∗1. In subjects with CYP3A4∗16/∗16, the virtual hepatic concentrations of atorvastatin after daily doses of 10 mg for a week were similar to or higher than the plasma concentrations. These results suggest that the estimated high virtual plasma and hepatic exposures obtained by pharmacokinetic modeling in subjects harboring impaired allele CYP3A4∗16 may be one of the causal factors for statin intolerance in a manner similar to the well-known drug interactions caused by co-administrations of CYP3A inhibitors.

Elucidating the role of pharmacogenetics in irinotecan efficacy and adverse events in metastatic colorectal cancer patients

INTRODUCTION

Irinotecan is a cytotoxic agent that is widely used in the treatment of several types of solid tumors. However, although it is generally well tolerated, approximately 20% to 35% of patients develop severe toxicity, particularly delayed-type diarrhea and neutropenia. As the incidence of such toxicities is often associated with the UGT1A1 *28/*28, *6/*28 and *6/*6 genotypes, individualized dosing could reduce these adverse events. Furthermore, prospective trials have shown that patients harboring the UGT1A1 *1/*1 and *1/*28 genotypes can tolerate higher doses of irinotecan, which may in turn impact on a better outcome. Upfront UGT1A1 genotyping could therefore be a usefulness strategy in order to individualize irinotecan dosing, but consensus on the recommended dose based on the UGT1A1 genotype is still lacking.

AREAS COVERED

This review summarizes the results of the main pharmacogenetic studies focused on irinotecan. We provide an overview of current evidence and recommendations for individualized dosing of irinotecan in metastatic colorectal cancer patients.

EXPERT OPINION

Implementation of UGT1A1*28 and UGT1A1*6 genotyping in clinical practice is a first step toward personalizing irinotecan therapy. This approach is likely to improve patient care and reduce healthcare costs. Future large and prospective studies will help to clarify the clinical value of other genetic markers in irinotecan treatment personalization.

Relevance of CYP3A4*20, UGT1A1*37 and UGT1A1*28 variants in irinotecan-induced severe toxicity

Severe irinotecan-induced toxicity is associated with UGT1A1 polymorphisms. However, some patients develop side-effects despite harbouring a normal UGT1A1 genotype. As CYP3A4 is also an irinotecan-metabolizing enzyme, our study aimed to elucidate the influence of the CYP3A4*20 loss-of-function allele in the toxicity profile of these patients. Three-hundred and eight metastatic colorectal cancer patients treated with an irinotecan-containing chemotherapy were studied. The presence of CYP3A4*20, UGT1A1*37 and UGT1A1*28 alleles was tested. Associations between these genetic variants and toxicity were evaluated. UGT1A1*28 was significantly associated with severe diarrhoea, neutropenia and asthenia (P = 0.002, P = 0.037 and P = 0.041, respectively). One patient with the UGT1A1*28/*37 genotype presented with grade IV neutropenia and lethal septic shock. One heterozygous UGT1A1 (*1/*28) patient also carried the CYP3A4*20 allele but did not develop toxicity. We confirm that UGT1A1*37 and UGT1A1*28 are associated with severe toxicity and suggest that the CYP3A4*20 allele does not play a role in irinotecan-induced toxicity.

SNPs in predicting clinical efficacy and toxicity of chemotherapy: walking through the quicksand

In the "precision medicine" era, chemotherapy still remains the backbone for the treatment of many cancers, but no affordable predictors of response to the chemodrugs are available in clinical practice. Single nucleotide polymorphisms (SNPs) are gene sequence variations occurring in more than 1% of the full population, and account for approximately 80% of inter-individual genomic heterogeneity. A number of studies have investigated the predictive role of SNPs of genes enrolled in both pharmacodynamics and pharmacokinetics of chemotherapeutics, but the clinical implementation of related results has been modest so far. Among the examined germline polymorphic variants, several SNPs of dihydropyrimidine dehydrogenase (DPYD) and uridine diphosphate glucuronosyltransferases (UGT) have shown a robust role as predictors of toxicity following fluoropyrimidine- and/or irinotecan-based treatments respectively, and a few guidelines are mandatory in their detection before therapy initiation. Contrasting results, however, have been reported on the capability of variants of other genes as MTHFR, TYMS, ERCC1, XRCC1, GSTP1, CYP3A4/3A5 and ABCB1, in predicting either therapy efficacy or toxicity in patients undergoing treatment with pyrimidine antimetabolites, platinum derivatives, irinotecan and taxanes. While formal recommendations for routine testing of these SNPs cannot be drawn at this moment, therapeutic decisions may indeed benefit of germline genomic information, when available. Here, we summarize the clinical impact of germline genomic variants on the efficacy and toxicity of major chemodrugs, with the aim to facilitate the therapeutic expectance of clinicians in the odiern quicksand field of complex molecular biology concepts and controversial trial data interpretation.

Irinotecan, a key chemotherapeutic drug for metastatic colorectal cancer

Irinotecan hydrochloride is a camptothecin derivative that exerts antitumor activity against a variety of tumors. SN-38 produced in the body by carboxylesterase is the active metabolite of irinotecan. After irinotecan was introduced for the treatment of metastatic colorectal cancer (CRC) at the end of the last century, survival has improved dramatically. Irinotecan is now combined with 5-fluorouracil, oxaliplatin and several molecularly-targeted anticancer drugs, resulting in the extension of overall survival to longer than 30 mo. Severe, occasionally life-threatening toxicity occurs sporadically, even in patients in relatively good condition who have a low risk of chemotherapy-induced toxicity, often causing the failure of irinotecan-based chemotherapy. Clinical pharmacological studies have revealed that such severe toxicity is related to exposure to SN-38 and genetic polymorphisms in UDP-glucuronosyltransferase 1A1 gene. The large inter- and intra-patient variability in systemic exposure to SN-38 is determined not only by genetic factors but also by physiological and environmental factors. This review first summarizes the roles of irinotecan in chemotherapy for metastatic CRC and then discusses the optimal dosing of irinotecan based on the aforementioned factors affecting systemic exposure to SN-38, with the ultimate goal of achieving personalized irinotecan-based chemotherapy.

Application of a combination of a knowledge-based algorithm and 2-stage screening to hypothesis-free genomic data on irinotecan-treated patients for identification of a candidate single nucleotide polymorphism related to an adverse effect

Interindividual variation in a drug response among patients is known to cause serious problems in medicine. Genomic information has been proposed as the basis for “personalized” health care. The genome-wide association study (GWAS) is a powerful technique for examining single nucleotide polymorphisms (SNPs) and their relationship with drug response variation; however, when using only GWAS, it often happens that no useful SNPs are identified due to multiple testing problems. Therefore, in a previous study, we proposed a combined method consisting of a knowledge-based algorithm, 2 stages of screening, and a permutation test for identifying SNPs. In the present study, we applied this method to a pharmacogenomics study where 109,365 SNPs were genotyped using Illumina Human-1 BeadChip in 168 cancer patients treated with irinotecan chemotherapy. We identified the SNP rs9351963 in potassium voltage-gated channel subfamily KQT member 5 (KCNQ5) as a candidate factor related to incidence of irinotecan-induced diarrhea. The p value for rs9351963 was 3.31×10⁻⁵ in Fisher's exact test and 0.0289 in the permutation test (when multiple testing problems were corrected). Additionally, rs9351963 was clearly superior to the clinical parameters and the model involving rs9351963 showed sensitivity of 77.8% and specificity of 57.6% in the evaluation by means of logistic regression. Recent studies showed that KCNQ4 and KCNQ5 genes encode members of the M channel expressed in gastrointestinal smooth muscle and suggested that these genes are associated with irritable bowel syndrome and similar peristalsis diseases. These results suggest that rs9351963 in KCNQ5 is a possible predictive factor of incidence of diarrhea in cancer patients treated with irinotecan chemotherapy and for selecting chemotherapy regimens, such as irinotecan alone or a combination of irinotecan with a KCNQ5 opener. Nonetheless, clinical importance of rs9351963 should be further elucidated.

Pharmacogenetics research on chemotherapy resistance in colorectal cancer over the last 20 years

During the past two decades the first sequencing of the human genome was performed showing its high degree of inter-individual differentiation, as a result of large international research projects (Human Genome Project, the 1000 Genomes Project International HapMap Project, and Programs for Genomic Applications NHLBI-PGA). This period was also a time of intensive development of molecular biology techniques and enormous knowledge growth in the biology of cancer. For clinical use in the treatment of patients with colorectal cancer (CRC), in addition to fluoropyrimidines, another two new cytostatic drugs were allowed: irinotecan and oxaliplatin. Intensive research into new treatment regimens and a new generation of drugs used in targeted therapy has also been conducted. The last 20 years was a time of numerous in vitro and in vivo studies on the molecular basis of drug resistance. One of the most important factors limiting the effectiveness of chemotherapy is the primary and secondary resistance of cancer cells. Understanding the genetic factors and mechanisms that contribute to the lack of or low sensitivity of tumour tissue to cytostatics is a key element in the currently developing trend of personalized medicine. Scientists hope to increase the percentage of positive treatment response in CRC patients due to practical applications of pharmacogenetics/pharmacogenomics. Over the past 20 years the clinical usability of different predictive markers has been tested among which only a few have been confirmed to have high application potential. This review is a synthetic presentation of drug resistance in the context of CRC patient chemotherapy. The multifactorial nature and volume of the issues involved do not allow the author to present a comprehensive study on this subject in one review.

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.

Pharmacogenetic markers of toxicity for chemotherapy in colorectal cancer patients

Chemotherapeutic agents used in colorectal cancer are frequently associated with severe adverse reactions that compromise the efficacy of treatment. Predicting toxicity could enable therapy to be tailored. Genetic variations have been associated with toxicity in patients treated with fluoropyrimidines (5-fluorouracil, capecitabine and tegafur), oxaliplatin, irinotecan and cetuximab. Complexity of treatment and variability in toxicity classifications make it difficult to compare studies. This article analyzes the association between toxicity and polymorphisms in DPYD, TYMS, MTHFR, ABCB1, UGT1A1, ERCC1, ERCC2, XRCC1, GSTT1 and GSTM1. In addition, the state-of-the-art and future perspectives are discussed.

Ethnic differences in the metabolism, toxicology and efficacy of three anticancer drugs

INTRODUCTION

Large inter-individual and inter-ethnic differences are observed in efficacies and toxicities of medical drugs. To improve the predictability of these differences, pharmacogenetic information has been applied to clinical situations. Expanding pharmacogenetic information would be a valuable tool to the medical community as well as the patient to fulfill the promise of personalized anticancer drug therapy.

AREAS COVERED

This review highlights genetic polymorphisms and ethnic differences of genes, UGT1As, CYP3A4, CES1As, ABCB1, ABCC2, ABCG2, SLCO1B1, CDA and CYP2D6, involved in metabolism and disposition of three anticancer drugs: irinotecan, gemcitabine and tamoxifen.

EXPERT OPINION

Recent pharmacogenetic studies have successfully identified distinct ethnic differences in genetic polymorphisms that are potentially involved in efficacies and toxicities of anticancer drugs. This achievement has led to personalized irinotecan therapy, reflecting ethnic differences in UGT1A1 genotypes, and possible benefits of genetic testing have also been suggested for gemcitabine and tamoxifen therapy, which still requires further validation. The ultimate goal for patients is a high rate or even perfect prediction of efficacies and toxicities of anticancer drugs in each ethnic population. For this challenge, more clinical studies combined with comprehensive omics approaches are necessary to further advance the field.

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.

Association of carboxylesterase 1A genotypes with irinotecan pharmacokinetics in Japanese cancer patients

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Association of UDP-glucuronosyltransferase 1A1 (UGT1A1) genetic polymorphisms *6 and *28 with reduced clearance of SN-38 and severe neutropenia in irinotecan therapy was demonstrated in Japanese cancer patients. * The detailed gene structure of CES1 has been characterized. * Possible functional SNPs in the promoter region have been reported. WHAT THIS STUDY ADDS * Association of functional CES1 gene number with AUC ratio [(SN-38 + SN-38G)/irinotecan], an in vivo index of CES activity, was observed in patients with irinotecan monotherapy. * No significant effects of major CES1 SNPs on irinotecan PK were detected. AIMS Human carboxylesterase 1 (CES1) hydrolyzes irinotecan to produce an active metabolite SN-38 in the liver. The human CES1 gene family consists of two functional genes, CES1A1 (1A1) and CES1A2 (1A2), which are located tail-to-tail on chromosome 16q13-q22.1 (CES1A2-1A1). The pseudogene CES1A3 (1A3) and a chimeric CES1A1 variant (var1A1) are also found as polymorphic isoforms of 1A2 and 1A1, respectively. In this study, roles of CES1 genotypes and major SNPs in irinotecan pharmacokinetics were investigated in Japanese cancer patients. METHODS CES1A diplotypes [combinations of haplotypes A (1A3-1A1), B (1A2-1A1), C (1A3-var1A1) and D (1A2-var1A1)] and the major SNPs (-75T>G and -30G>A in 1A1, and -816A>C in 1A2 and 1A3) were determined in 177 Japanese cancer patients. Associations of CES1 genotypes, number of functional CES1 genes (1A1, 1A2 and var1A1) and major SNPs, with the AUC ratio of (SN-38 + SN-38G)/irinotecan, a parameter of in vivo CES activity, were analyzed for 58 patients treated with irinotecan monotherapy. RESULTS The median AUC ratio of patients having three or four functional CES1 genes (diplotypes A/B, A/D or B/C, C/D, B/B and B/D; n= 35) was 1.24-fold of that in patients with two functional CES1 genes (diplotypes A/A, A/C and C/C; n= 23) [median (25th-75th percentiles): 0.31 (0.25-0.38) vs. 0.25 (0.20-0.32), P= 0.0134]. No significant effects of var1A1 and the major SNPs examined were observed. CONCLUSION This study suggests a gene-dose effect of functional CES1A genes on SN-38 formation in irinotecan-treated Japanese cancer patients.

CYP3A4*16 and CYP3A4*18 alleles found in East Asians exhibit differential catalytic activities for seven CYP3A4 substrate drugs

CYP3A4, the major form of cytochrome P450 (P450) expressed in the adult human liver, is involved in the metabolism of approximately 50% of commonly prescribed drugs. Several genetic polymorphisms in CYP3A4 are known to affect its catalytic activity and to contribute in part to interindividual differences in the pharmacokinetics and pharmacodynamics of CYP3A4 substrate drugs. In this study, catalytic activities of the two alleles found in East Asians, CYP3A4*16 (T185S) and CYP3A4*18 (L293P), were assessed using the following seven substrates: midazolam, carbamazepine, atorvastatin, paclitaxel, docetaxel, irinotecan, and terfenadine. The holoprotein levels of CYP3A4.16 and CYP3A4.18 were significantly higher and lower, respectively, than that of CYP3A4.1 when expressed in Sf21 insect cell microsomes together with human NADPH-P450 reductase. CYP3A4.16 exhibited intrinsic clearances (V(max)/K(m)) that were lowered considerably (by 84-60%) for metabolism of midazolam, carbamazepine, atorvastatin, paclitaxel, and irinotecan compared with CYP3A4.1 due to increased K(m) with or without decreased V(max) values, whereas no apparent decrease in intrinsic clearance was observed for docetaxel. On the other hand, K(m) values for CYP3A4.18 were comparable to those for CYP3A4.1 for all substrates except terfenadine; but V(max) values were lower for midazolam, paclitaxel, docetaxel, and irinotecan, resulting in partially reduced intrinsic clearance values (by 34-52%). These results demonstrated that the impacts of both alleles on CYP3A4 catalytic activities depend on the substrates used. Thus, to evaluate the influences of both alleles on the pharmacokinetics of CYP3A4-metabolized drugs and their drug-drug interactions, substrate drug-dependent characteristics should be considered for each drug.

An overview of the recent progress in irinotecan pharmacogenetics

Recent developments in a number of molecular profiling technologies, including genomic/genetic testing, proteomic profiling and metabolomic analysis have allowed the development of 'personalized medicine'. Irinotecan is one of the models for personalized medicine based on pharmacogenetics, and a number of clinical studies have revealed significant associations between UGT1A1*28 and irinotecan toxicity. Based on this cumulative evidence, the US FDA and pharmaceutical companies revised the irinotecan label in June 2005. However, a recommended strategy for irinotecan-dose adjustments based on individual genetic factors has not yet been fully established. This article provides an overview of recent progress in irinotecan pharmacogenetics and discusses the clinical significance of the UGT1A1 genotype/haplotype with regard to severe irinotecan toxicity.

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.