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

Fecal SN-38 Content as a Surrogate Predictor of Intestinal SN-38 Exposure and Associated Irinotecan-induced Severe Delayed-Onset Diarrhea by a Novel Use of the Spectrofluorimetric Method

BACKGROUND

Irinotecan administration can lead to severe delayed-onset diarrhea (SDOD) in clinical practice. Currently, there is no reliable surrogate predictor of intestinal exposure to SN-38 and subsequent diarrhea incidence.

METHODS

The relationship between fecal 7-ethyl-10-hydroxycamptothecin (SN-38) content and SDOD was investigated in Fisher 344 rats using a novel spectrofluorimetric method. Additionally, a pharmacokinetic study of irinotecan was performed to evaluate the biodistribution of SN-38 to establish the relationship between tissue and fecal SN-38 exposure.

RESULTS

The spectrofluorimetric method was successfully employed to measure fecal SN-38 and CPT-11 content from Day 3 to Day 6 post-irinotecan administration. Only fecal SN-38 content on Day 3 exhibited a significantly positive correlation with SDOD incidence on Days 4 and 5. A cutoff value of SN-38 ≥ 0.066 mg/g in feces was identified, predicting severe diarrhea incidence with 81% accuracy and 80% specificity. The positive correlation between fecal SN-38 content and SN-38 exposure in the ileum on Day 3 was also reflected in the changes of indicators during intestinal injury, such as prostaglandin E2 level and antioxidant activity.

CONCLUSION

Fecal SN-38 content proves to be representative of intestinal exposure to SN-38, indicative of intestinal injury, and predictive of SDOD incidence in rats, while the spectrofluorimetric method demonstrates the translational potential.

Beyond cytotoxic potency: disposition features required to design ADC payload

1. Antibody-drug conjugates (ADCs) have demonstrated impressive clinical usefulness in treating several types of cancer, with the notion of widening of the therapeutic index of the cytotoxic payload through the minimisation of the systemic toxicity. Therefore, choosing the most appropriate payload molecule is a particularly important part of the early design phase of ADC development, especially given the highly competitive environment ADCs find themselves in today.2. The focus of the current review is to describe critical attributes/considerations needed in the discovery and ultimately development of cytotoxic payloads in support of ADC design. In addition to potency, several key dispositional characteristics including solubility, permeability and bystander effect, pharmacokinetics, metabolism, and drug-drug interactions, are described as being an integral part of the integrated activities required in the design of clinically safe and useful ADC therapeutic agents.

Preclinical safety, toxicokinetics and metabolism of BIIB131, a novel prothrombolytic agent for acute stroke

BIIB131, a small molecule, is currently in Phase 2 for the treatment of acute ischemic stroke. Safety and metabolism of BIIB131 were evaluated following intravenous administration to rats and monkeys. Exposure increased dose-proportionally in rats up to 60 mg/kg and more than dose-proportionally in monkeys at greater than 10 mg/kg accompanied by prolonged half-life and safety findings. The BIIB131 was poorly metabolized in microsomes with no inhibition of CYPs. BIIB131-glucuronide, formed by UGT1A1, accounted for 21.5% metabolism in human hepatocytes and 28-40% in rat bile. In rats, excretion was primarily via the bile. BIIB131 inhibited the hERG and Nav1.5 cardiac channels by 39% but showed no effect on cardiovascular parameters in monkeys. Toxicology findings were limited to reversable hematuria, changes in urinary parameters and local effects. A MTD of 30 mg/kg was established in monkeys, the most sensitive species, at total plasma Cmax and AUC of 6- and 14-fold, respectively, greater than the NOAEL. The Phase 1 study started with intravenous 0.05 mg/kg and ascended to 6.0 mg/kg which corresponded to safety margins of 147- to 0.9-fold (for Cmax) within the linear drug exposure. Thus, the preclinical profile of BIIB131 has been appropriately characterized and supports its further clinical development.

Direct Comparative Analysis of a Pharmacogenomics Panel with PacBio Hifi® Long-Read and Illumina Short-Read Sequencing

BACKGROUND

Pharmacogenetics (PGx) aims to determine genetic signatures that can be used in clinical settings to individualize treatment for each patient, including anti-cancer drugs, anti-psychotics, and painkillers. Taken together, a better understanding of the impacts of genetic variants on the corresponding protein function or expression permits the prediction of the pharmacological response: responders, non-responders, and those with adverse drug reactions (ADRs).

OBJECTIVE

This work provides a comparison between innovative long-read sequencing (LRS) and short-read sequencing (SRS) techniques.

METHODS AND MATERIALS

The gene panel captured using PacBio HiFi® sequencing was tested on thirteen clinical samples on GENTYANE's platform. SRS, using a comprehensive pharmacogenetics panel, was performed in routine settings at the Civil Hospitals of Lyon. We focused on complex regions analysis, including copy number variations (CNVs), structural variants, repeated regions, and phasing-haplotyping for three key pharmacogenes: CYP2D6, UGT1A1, and NAT2.

RESULTS

Variants and the corresponding expected star (*) alleles were reported. Although only 38.4% concordance was found for haplotype determination and 61.5% for diplotype, this did not affect the metabolism scoring. A better accuracy of LRS was obtained for the detection of the CYP2D6*5 haplotype in the presence of the duplicated wild-type CYP2D6*2 form. A total concordance was performed for UGT1A1 TA repeat detection. Direct phasing using the LRS approach allowed us to correct certain NAT2 profiles.

CONCLUSIONS

Combining an optimized variant-calling pipeline and with direct phasing analysis, LRS is a robust technique for PGx analysis that can minimize the risk of mis-haplotyping.

Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

Model-Based Prediction of Irinotecan-Induced Grade 4 Neutropenia in Advanced Cancer Patients: Influence of Demographic and Clinical Factors

Severe neutropenia is the major dose-liming toxicity of irinotecan-based chemotherapy. The objective was to assess to what extent a population pharmacokinetic/pharmacodynamic model including patient-specific demographic/clinical characteristics, individual pharmacokinetics, and absolute neutrophil counts (ANCs) can predict irinotecan-induced grade 4 neutropenia. A semimechanistic population pharmacokinetic/pharmacodynamic model was developed to describe neutrophil response over time in 197 patients with cancer receiving irinotecan. For covariate analysis, sex, race, age, pretreatment total bilirubin, and body surface area were evaluated to identify significant covariates on system-related parameters (mean transit time (MTT) and ɣ) and sensitivity to neutropenia effects of irinotecan and SN-38 (SLOPE). The model-based simulation was performed to assess the contribution of the identified covariates, individual pharmacokinetics, and baseline ANC alone or with incremental addition of weekly ANC up to 3 weeks on predicting irinotecan-induced grade 4 neutropenia. The time course of neutrophil response was described using the model assuming that irinotecan and SN-38 have toxic effects on bone marrow proliferating cells. Sex and pretreatment total bilirubin explained 10.5% of interindividual variability in MTT. No covariates were identified for SLOPE and γ. Incorporating sex and pretreatment total bilirubin (area under the receiver operating characteristic curve (AUC-ROC): 50%, 95% CI 50-50%) or with the addition of individual pharmacokinetics (AUC-ROC: 62%, 95% CI 53-71%) in the model did not result in accurate prediction of grade 4 neutropenia. However, incorporating ANC only at baseline and week 1 in the model achieved a good prediction (AUC-ROC: 78%, 95% CI 69-88%). These results demonstrate the potential applicability of a model-based approach to predict irinotecan-induced neutropenia, which ultimately allows for personalized intervention to maximize treatment outcomes.

Prediction of Drug-Drug Interaction Between Dabrafenib and Irinotecan via UGT1A1-Mediated Glucuronidation

BACKGROUND

Dabrafenib and irinotecan are two drugs that can be utilized to treat melanoma. A previous in vivo study has shown that dabrafenib enhances the antitumor activity of irinotecan in a xenograft model with unclear mechanism.

OBJECTIVES

This study aims to investigate the inhibition of dabrafenib on SN-38 (the active metabolite of irinotecan) glucuronidation, trying to elucidate the possible mechanism underlying the synergistic effect and to provide a basis for further development and optimization of this combination in clinical research.

METHODS

Recombinant human uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) and human liver microsomes (HLMs) were employed to catalyze the glucuronidation of SN-38 in vitro. Inhibition kinetic analysis and quantitative prediction study were combined to predict drug-drug interaction (DDI) potential in vivo.

RESULTS

Dabrafenib noncompetitively inhibited SN-38 glucuronidation in pooled HLMs and recombinant UGT1A1 with unbound inhibitor constant (K_i,u) values of 12.43 ± 0.28 and 3.89 ± 0.40 μM, respectively. Based on the in vitro K_i,u value and estimation of kinetic parameters, dabrafenib administered at 150 mg twice daily may result in about a 1-2% increase in the area under the curve (AUC) of SN-38 in vivo. However, the ratios of intra-enterocyte concentration of dabrafenib to K_i,u ([I]_gut/K_i,u) are 2.73 and 8.72 in HLMs and recombinant UGT1A1, respectively, indicating a high risk of intestinal DDI when dabrafenib was used in combination with irinotecan.

CONCLUSION

Dabrafenib is a potent noncompetitive inhibitor of UGT1A1 and may bring potential risk of DDI when combined with irinotecan.

Population pharmacokinetics of liposomal irinotecan in patients with cancer and exposure–safety analyses in patients with metastatic pancreatic cancer

Liposomal irinotecan is a liposomal formulation of irinotecan, which prolongs circulation of irinotecan and its active metabolite SN‐38. A population pharmacokinetic (PK) model was developed based on data from seven studies (N = 440). Adequacy of the model was assessed using multiple methods, including visual predictive check. Associations between PK exposure and the incidence of diarrhea (grade ≥3) and neutropenia adverse events (AEs) (grade ≥3) at first event in patients with metastatic pancreatic ductal adenocarcinoma (mPDAC) were investigated using logistic regression based on data from two studies (the phase III NAPOLI‐1 [N = 260] and phase I/II NCT02551991 [N = 56] trials). The PKs of total irinotecan was described by a two‐compartment model with first‐order elimination, with SN‐38 formed directly by a first‐order constant from the central compartment of irinotecan or after using a transit compartment. Clearance was 17.9 L/week (0.107 L/h) and 19,800 L/week (118 L/h) for total irinotecan and SN‐38, respectively. The UGT1A1*28 7/7 homozygous genotype had no significant impact on SN‐38 clearance. Model evaluation was satisfactory for both irinotecan and SN‐38. The incidence of diarrhea (grade ≥3) at first event was significantly higher with increasing average concentrations of total irinotecan and SN‐38; there was no significant association between an increased risk of neutropenia AEs (grade ≥3) at first event and average SN‐38 concentrations. In summary, the PKs of total irinotecan and SN‐38 after administration of liposomal irinotecan were well‐described by the model. The UGT1A1*28 status had no significant impact on the PKs of liposomal irinotecan.

Integration of DNA sequencing with population pharmacokinetics to improve the prediction of irinotecan exposure in cancer patients

BACKGROUND

Irinotecan (CPT-11) is an anticancer agent widely used to treat adult solid tumours. Large interindividual variability in the clearance of irinotecan and SN-38, its active and toxic metabolite, results in highly unpredictable toxicity.

METHODS

In 217 cancer patients treated with intravenous irinotecan single agent or in combination, germline DNA was used to interrogate the variation in 84 genes by next-generation sequencing. A stepwise analytical framework including a population pharmacokinetic model with SNP- and gene-based testing was used to identify demographic/clinical/genetic factors that influence the clearance of irinotecan and SN-38.

RESULTS

Irinotecan clearance was influenced by rs4149057 in SLCO1B1, body surface area, and co-administration of 5-fluorouracil/leucovorin/bevacizumab. SN-38 clearance was influenced by rs887829 in UGT1A1, pre-treatment total bilirubin, and EGFR rare variant burden. Within each UGT1A1 genotype group, elevated pre-treatment total bilirubin and/or presence of at least one rare variant in EGFR resulted in significantly lower SN-38 clearance. The model reduced the interindividual variability in irinotecan clearance from 38 to 34% and SN-38 clearance from 49 to 32%.

CONCLUSIONS

This new model significantly reduced the interindividual variability in the clearance of irinotecan and SN-38. New genetic factors of variability in clearance have been identified.

In vitro inhibition of human UDP-glucuronosyltransferase (UGT) 1A1 by osimertinib, and prediction of in vivo drug-drug interactions

Osimertinib is the only third-generation epidermal growth factor receptor tyrosine-kinase inhibitor (EGFR-TKI) approved by Food and Drug Administration (FDA). This study aimed to know the inhibitory effect of osimertinib on human UDP-glucosyltransferases (UGTs) and human liver microsomes (HLMs), as well as to identify its potential to cause drug-drug interaction (DDI) arising from the modulation of UGT activity. High inhibitory effect of osimertinib was shown towards UGT1A1, 1A3, 1A6, 1A7, 1A8, 1A10, 2B7 and 2B15. Especially, osimertinib exhibited competitive inhibition against UGT1A1 with a K_i,u of 0.87 ± 0.12 μM. It also noncompetitively inhibited SN-38 glucuronidation in pooled HLMs with a K_i,u of 3.32 ± 0.25 μM. Results from quantitative prediction study indicated that osimertinib administered at 80 mg/day may result in a 4.83 % increase in the AUC of drugs mainly metabolized by UGT1A1, implying low risk of DDI via liver metabolism. However, the ratios of [I]_gut/K_i,u are much higher than 11 in HLMs and recombinant UGT1A1, indicating a risk for interaction in intestine. The effects of osimertinib on intestinal UGT should be paid more attention on to avoid unnecessary clinical DDI risks.

Influence of UGT1A1 *6/*28 Polymorphisms on Irinotecan-Related Toxicity and Survival in Pediatric Patients with Relapsed/Refractory Solid Tumors Treated with the VIT Regimen

Objective

The association between UGT1A1*6/*28 polymorphisms and treatment outcomes of irinotecan in children remains unknown. This retrospective study investigated the influence of UGT1A1*6/*28 polymorphisms on irinotecan toxicity and survival of pediatric patients with relapsed/refractory solid tumors.

Methods

The present study enrolled a total of 44 patients aged younger than 18 years at Sun Yat-sen University Cancer Center between 2014 and 2017.

Results

There were 26 boys and 18 girls; the median age at first VIT course was six years (range: 1-18 years). The tumor types included neuroblastoma (n = 25), rhabdomyosarcoma (n = 11), Wilm's tumor (n = 4), medulloblastoma (n = 2), and desmoplastic small round cell tumor (n = 2). Overall, 203 courses of VIT regimens were prescribed. Neither UGT1A1*6 nor *28 polymorphisms were associated with the incidence rates of severe (grade III-IV) irinotecan-related toxicities, but tended to reduce the patient overall survival (UGT1A1*6, P = 0.146; UGT1A1*28, P = 0.195). Moreover, patients with mutant UGT1A1*6 genotypes were more likely to develop grade I-IV irinotecan-related diarrhea (P = 0.043) and anemia (P = 0.002). Overall, the UGT1A1*28 polymorphism may play a protective role against irinotecan-related diarrhea and abdominal pain.

Conclusion

In relapsed/refractory pediatric solid tumors, the UGT1A1*6 polymorphism was a risk factor of irinotecan-related diarrhea and anemia. The UGT1A1*28 polymorphism may serve a protective role in irinotecan-related abdominal pain and diarrhea. Both mutations had a tendency to be risk factors for survival. Nevertheless, prospective studies are required to verify such conclusions.

Pharmacokinetic and Pharmacogenetic Markers of Irinotecan Toxicity

BACKGROUND

Irinotecan (IRI) is a widely used chemotherapeutic drug, mostly used for first-line treatment of colorectal and pancreatic cancer. IRI doses are usually established based on patient's body surface area, an approach associated with large inter-individual variability in drug exposure and high incidence of severe toxicity. Toxic and therapeutic effects of IRI are also due to its active metabolite SN-38, reported to be up to 100 times more cytotoxic than IRI. SN-38 is detoxified by the formation of SN-38 glucuronide, through UGT1A1. Genetic polymorphisms in the UGT1A1 gene are associated to higher exposures to SN-38 and severe toxicity. Pharmacokinetic models to describe IRI and SN-38 kinetic profiles are available, with few studies exploring pharmacokinetic and pharmacogenetic-based dose individualization. The aim of this manuscript is to review the available evidence supporting pharmacogenetic and pharmacokinetic dose individualization of IRI in order to reduce the occurrence of severe toxicity during cancer treatment.

METHODS

The PubMed database was searched, considering papers published in the period from 1995-2017, using the keywords irinotecan, pharmacogenetics, metabolic genotyping, dose individualization, therapeutic drug monitoring, pharmacokinetics and pharmacodynamics, either alone or in combination, with original papers being selected based on the presence of relevant data.

CONCLUSION

The findings of this review confirm the importance of considering individual patient characteristics to select IRI doses. Currently, the most straightforward approach for IRI dose individualization is UGT1A1 genotyping. However, this strategy is sub-optimal due to several other genetic and environmental contributions to the variable pharmacokinetics of IRI and its active metabolite. The use of dried blood spot sampling could allow the clinical application of limited sampling and population pharmacokinetic models for IRI doses individualization.

Prediction of irinotecan toxicity in metastatic colorectal cancer patients based on machine learning models with pharmacokinetic parameters

Irinotecan (CPT-11) is a drug used against a wide variety of tumors, which can cause severe toxicity, possibly leading to the delay or suspension of the cycle, with the consequent impact on the prognosis of survival. The main goal of this work is to predict the toxicities derived from CPT-11 using artificial intelligence methods. The data for this study is conformed of 53 cycles of FOLFIRINOX, corresponding to patients with metastatic colorectal cancer. Supported by several demographic data, blood markers and pharmacokinetic parameters resulting from a non-compartmental pharmacokinetic study of CPT-11 and its metabolites (SN-38 and SN-38-G), we use machine learning techniques to predict high degrees of different toxicities (leukopenia, neutropenia and diarrhea) in new patients. We predict high degree of leukopenia with an accuracy of 76%, neutropenia with 75% and diarrhea with 91%. Among other variables, this study shows that the areas under the curve of CPT-11, SN-38 and SN-38-G play a relevant role in the prediction of the studied toxicities. The presented models allow to predict the degree of toxicity for each cycle of treatment according to the particularities of each patient.

Population pharmacokinetic analysis of AR-67, a lactone stable camptothecin analogue, in cancer patients with solid tumors

Background AR-67 is a novel camptothecin analogue at early stages of drug development. The phase 1 clinical trial in cancer patients with solid tumors was completed and a population pharmacokinetic model (POP PK) was developed to facilitate further development of this investigational agent. Methods Pharmacokinetic data collected in the phase 1 clinical trial were utilized for the development of a population POP PK by implementing the non-linear mixed effects approach. Patient characteristics at study entry were evaluated as covariates in the model. Subjects (N = 26) were treated at nine dosage levels (1.2-12.4 mg/m²/day) on a daily × 5 schedule. Hematological toxicity data were modeled against exposure metrics. Results A two-compartment POP PK model best described the disposition of AR-67 by fitting a total of 328 PK observations from 25 subjects. Following covariate model selection, age remained as a significant covariate on central volume. The final model provided a good fit for the concentration versus time data and PK parameters were estimated with good precision. Clearance, inter-compartmental clearance, central volume and peripheral volume were estimated to be 32.2 L/h, 28.6 L/h, 6.83 L and 25.0 L, respectively. Finally, exposure-pharmacodynamic analysis using E_max models showed that plasma drug concentration versus time profiles are better predictors of AR-67-related hematologic toxicity were better predictors of leukopenia and thrombocytopenia, as compared to total dose. Conclusions A POP PK model was developed to characterize AR-67 pharmacokinetics and identified age as a significant covariate. Exposure PK metrics C_max and AUC were shown to predict hematological toxicity. Further efforts to identify clinically relevant determinants of AR-67 disposition and effects in a larger patient population are warranted.

Influence of UGT1A1 polymorphisms on the outcome of acute myeloid leukemia patients treated with cytarabine-base regimens

BACKGROUNDS

UDP-glucuronosyltransferase 1A subfamily (UGT1A) enzymes can inactivate cytarabine (Ara-C) by glucuronidation, and thus serves as candidate genes for interindividual difference in Ara-C response. UGT1A1 is a major UGT1A isoform expressed in human liver.

METHODS

UGT1A1*6 and *28 polymorphisms resulting in reduced UGT1A1 activity were genotyped in 726 adult acute myeloid leukemia (AML) patients treated with Ara-C based regimens. Influences of both polymorphisms on chemosensitivity and disease prognosis of the patients were evaluated.

RESULTS

After one or two courses of Ara-C based induction chemotherapy, the complete remission (CR) rate was significantly higher in patients carrying the UGT1A1*6 (77.0%) or the UGT1A1*28 (76.4%) alleles as compared with corresponding wild-type homozygotes (66.9 and 68.5%, respectively). Carriers of the UGT1A1*6 or *28 alleles showed significantly decreased risk of non-CR (OR = 0.528, 95% CI 0.379-0.737, P = 1.7 × 10^-4) and better overall survival (HR = 0.787, 95% CI 0.627-0.990, P = 0.040) as compared with homozygotes for both polymorphisms.

CONCLUSION

Our results suggest that UGT1A1*28 and UGT1A1*6 are associated with improved clinical outcomes in Chinese AML patients treated with Ara-C.

Contribution of UGT1A1 genetic polymorphisms related to axitinib pharmacokinetics to safety and efficacy in patients with renal cell carcinoma

Axitinib is a potent second-line molecular-targeted agent for metastatic renal cell carcinoma (mRCC). Axitinib pharmacokinetics and its relation with genetic polymorphisms were evaluated to predict the adverse events (AEs) and efficacy of axitinib. We analyzed 46 patients with mRCC who were treated with axitinib. The plasma axitinib level was measured at 0, 2, 4, 8, and 12 h after administration (C₀, C₂, C₄, C₈, and C₁₂; ng/mL) on day 7 of the treatment. Genetic polymorphisms related to axitinib pharmacokinetics, including SLCO1B1, SLCO1B3, SLCO2B1, ABCB1, ABCG2, CYP2C19, CYP3A5, and UGT1A1, were analyzed. Axitinib C₀ and AUC_0-12 in patients with UGT1A1 poor metabolisers (*6/*6, *6/*28, and *28/*28; n = 10) were significantly higher than those in patients with UGT1A1 extensive metabolisers (*1/*1, *1/*6,*1/*28, and *27/*28; n = 36) (23.6 vs. 7.8 ng/mL, p = 0.030, and 441.3 vs. 217.1 ng h/mL, p = 0.007). The cutoff levels of C₀ to predict ≥ G2 hypothyroidism and ≥ G2 anorexia were 6.6 and 7.1 ng/mL, respectively (p = 0.005 and p = 0.035). The overall survival (OS) in patients with C₀ > 5 ng/mL was significantly better than that in patients with C₀ < 5 ng/mL (p = 0.022). Genetic polymorphisms in UGT1A1 were significantly associated with the plasma axitinib level. The plasma axitinib level was significantly associated with the frequency of AEs and OS in patients with mRCC. No direct relationship was observed between UGT1A1 genotypes and the frequency of AEs or OS.

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.

Distribution of uridine diphosphate glucuronosyltransferase 1A polymorphisms and their role in irinotecan-induced toxicity in patients with cancer

Uridine diphosphate glucuronosyltransferase 1A (UGT1A1), which affects irinotecan metabolism, has been associated with severe adverse reactions in patients with cancer treated with irinotecan. However, neither large-scale analysis of the distribution of UGT1A1 polymorphisms, nor standardized assessment of how UGT1A1 polymorphisms affect irinotecan treatment has been performed in China. The aim of the present study was to investigate the distribution of UGT1A1 polymorphisms (*28 and *6) in 2,093 Chinese patients with cancer who were treated with irinotecan from more than 15 hospitals in Shandong, to examine how the coexistence of UGT1A1*6 and UGT1A1*28 alleles may be able to predict toxicities induced by irinotecan in 105 of the patients, and to search for other relevant risk factors. The distribution of the genotypes was as follows: TA₆/TA₆ (1,601, 76.5%), TA₆/TA₇ (463, 22.1%) and TA₇/TA₇ (29, 1.4%) for UGT1A1*28 (n=2,093); and G/G (286, 66.4%), G/A (124, 28.8%) and A/A (21, 4.9%) for UGT1A1*6 (n=431). The most frequent severe hematological toxicity was neutropenia, and the predominant non-hematological toxicities were diarrhea and cholinergic syndrome. In toxicity comparisons, grade 3–4 leukopenia and neutropenia were significantly higher in TA₆/TA₇ compared with TA₆/TA₆ (P<0.05). The UGT1A1*6 polymorphism was associated with a higher risk of severe diarrhea and total adverse drug reactions (P<0.05). Logistic regression showed that the UGT1A1*6 genotype was an independent predictor of severe diarrhea. These findings suggested that the UGT1A1*28 and UGT1A1*6 genotypes may be associated with irinotecan-induced severe toxicity, and clarified the clinical importance of UGT1A1 polymorphisms, particularly UGT1A1*6, regarding irinotecan therapy in Chinese patients.

Clarithromycin co-administration does not increase irinotecan (CPT-11) toxicity in colorectal cancer patients

PURPOSE

Irinotecan (CPT-11) is used to treat advanced colorectal cancer. The drug is activated by carboxylesterases and rendered inactive by CYP3A4. Recently, the efficacy of combining CPT-11 and anti-epidermal growth factor receptor (EGFR) agents was confirmed in patients with KRAS wild-type metastatic colorectal cancer. Clarithromycin (CAM) is a strong CYP3A inhibitor often used to prevent rash associated with anti-EGFR therapy. The objective of this study was to evaluate the risk of increased neutropenia and diarrhea in combining CPT-11 and CAM.

METHODS

Retrospective analyses were conducted at Osaka National Hospital (Osaka, Japan) on the records of colorectal cancer patients treated with a CPT-11-containing regimen between November 2006 and January 2014. The incidence of neutropenia and diarrhea was compared between patients who received CPT-11 and CAM and patients who received CPT-11 without CAM.

RESULTS

One-hundred and twenty-eight patients were included in this study, of whom 21 were concomitantly treated with CAM and 107 were not. There was no difference in the incidence of grade 3-4 neutropenia between the CAM co-administration group (10%) and the non-CAM group (16%) [Odds ratio: 0.56 (95% confidence interval: 0.12-2.62), p = 0.45]. No difference in the incidence of grade 3-4 diarrhea was found between the CAM co-administration group (0%) and the non-CAM group (4%) (p = 0.37).

CONCLUSIONS

This study did not identify an increase in CPT-11 toxicity by co-administration with CAM.

Non-alcoholic fatty liver disease fibrosis score predicts hematological toxicity of chemotherapy including irinotecan for colorectal cancer

Liver dysfunction that may affect drug metabolism is a major concern in patients treated with chemotherapy. Thus, assessment of the degree of liver dysfunction is crucial for predicting the adverse events of chemotherapy. The non-alcoholic fatty liver disease fibrosis score (NFS) is a non-invasive clinical scoring system constructed from routine clinical and laboratory variables. The aim of this study was to evaluate whether NFS was useful for predicting the adverse events of chemotherapy including irinotecan (CPT-11) for colorectal cancer. Between January, 2007 and May, 2013, a total of 87 patients with unresectable/recurrent colorectal cancer who received first-line chemotherapy including CPT-11 were reviewed. Demographic variables, including pretreatment NFS, were retrospectively collected from medical records. The primary outcome was the association between pretreatment NFS and adverse events, such as hematological and non-hematological toxicity, of chemotherapy including CPT-11. The median pretreatment NFS was 1.302 (range, 5.158-2.620). Pretreatment NFS was an independent risk factor for hematological toxicity in a multivariate analysis (coefficient=0.932, 95% CI: 0.083-1.781; P=0.031). Receiver operating characteristic curve analysis identified 0.347 as the optimal cut-off value associated with hematological toxicity. Using this cut-off, high NFS was found to be a significant risk factor for hematological toxicity (coefficient=2.019, 95% CI: 0.239-3.798, P=0.026), but not for non-hematological toxicity (P=0.546). Therefore, based on these results, NFS appears to be a significant predictor of hematological adverse events in chemotherapy including CPT-11 for colorectal cancer and it is a non-invasive, useful tool that may be used for determining regimens or doses of chemotherapy including CPT-11.

ABC transporter polymorphisms are associated with irinotecan pharmacokinetics and neutropenia

Neutropenia is a common dose-limiting toxicity associated with irinotecan treatment. Although UGT1A1 variants have been associated with neutropenia, a fraction of neutropenia risk remains unaccounted for. To identify additional genetic markers contributing to variability in irinotecan pharmacokinetics and neutropenia, a regression analysis was performed in 78 irinotecan-treated patients to analyze comprehensively three hepatic efflux transporter genes (ABCB1, ABCC1 and ABCG2). rs6498588 (ABCC1) and rs12720066 (ABCB1) were associated with increased SN-38 exposure, and rs17501331 (ABCC1) and rs12720066 were associated with lower absolute neutrophil count nadir. rs6498588 and a variant in high linkage disequilibrium are located in transcriptionally active regions or are predicted to alter transcription factor binding sites. While enhancer activity was not evident in vitro for genomic regions containing these single-nucleotide polymorphisms, rs6498588 was significantly associated with ABCC1 expression in human liver. These results suggest that genetic variation in ABCC1 and ABCB1 may contribute to irinotecan-induced neutropenia by altering expression of transporters involved in irinotecan metabolite disposition.

Fasting protects against the side effects of irinotecan treatment but does not affect anti-tumour activity in mice

BACKGROUND

The main limitation to the use of irinotecan in the treatment of colorectal cancer is the severity of side effects, including neutropaenia and diarrhoea. Here, we explored the effects of 3 days of fasting on irinotecan-induced toxicities, on plasma, liver and tumour pharmacokinetics and on anti-tumour activity in mice.

EXPERIMENTAL APPROACH

Male BALB/c mice received C26 colon carcinoma cells subcutaneously. They were randomized 1:1 into equally sized ad libitum fed and fasted groups after which they were treated with irinotecan. Weight and adverse side effects were recorded daily. At the end of the experiment, tumours were resected and weighed, and concentrations of irinotecan and its active metabolite SN-38 were determined in plasma and tumour.

KEY RESULTS

Fasting prevented the diarrhoea and visible signs of discomfort induced by irinotecan. Ad libitum fed animals developed leucopenia compared with untreated controls, whereas fasted mice did not. Irinotecan suppressed tumour growth equally in both treated groups, compared with untreated controls. Levels of the active irinotecan metabolite SN-38 9 (calculated as AUC values) were significantly lower in fasted mice in both plasma and liver, but not in tumour tissue.

CONCLUSIONS AND IMPLICATIONS

Fasting protected against irinotecan-induced side effects without interfering with its anti-tumour efficacy. Fasting induced a lower systemic exposure to SN-38, which may explain the absence of adverse side effects, while tumour levels of SN-38 remained unchanged. These data offer important new approaches to improve treatment with irinotecan in patients.

UGT1A1 genotype-dependent dose adjustment of belinostat in patients with advanced cancers using population pharmacokinetic modeling and simulation

Belinostat is a second-generation zinc-binding histone deacetylase inhibitor that is approved for peripheral T-cell lymphoma and is currently being studied in small cell lung cancer and other advanced carcinomas as a 48-hour continuous intravenous infusion. Belinostat is predominantly metabolized by UGT1A1, which is polymorphic. Preliminary analyses revealed a difference in belinostat clearance based on UGT1A1 genotype. A 2-compartment population pharmacokinetic (PK) model was developed and validated that incorporated the UGT1A1 genotype, albumin, and creatinine clearance on the clearance parameter; body weight was a significant covariate on volume. Simulated doses of 600 and 400 mg/m(2) /24 h given to patients considered extensive or impaired metabolizers, respectively, provided equivalent AUCs. This model and subsequent simulations supported additional PK/toxicity and pharmacogenomics/toxicity analyses to suggest a UGT1A1 genotype-based dose adjustment to normalize belinostat exposure and allow for more tolerable therapy. In addition, global protein lysine acetylation was modeled with PK and demonstrated a reversible belinostat exposure/response relationship, consistent with previous reports.

The cost-effectiveness of UGT1A1 genotyping before colorectal cancer treatment with irinotecan from the perspective of the German statutory health insurance

BACKGROUND

The evidence concerning the cost-effectiveness of UGT1A1*28 genotyping is ambiguous and does not allow drawing valid conclusions for Germany. This study evaluates the cost-effectiveness of UGT1A1 genotyping in patients with metastatic colorectal cancer undergoing irinotecan-based chemotherapy compared to no testing from the perspective of the German statutory health insurance.

MATERIAL AND METHODS

A decision-analytic Markov model with a life time horizon was developed. No testing was compared to two genotype-dependent therapy strategies: 1) dose reduction by 25%; and 2) administration of a prophylactic G-CSF growth factor analog for homozygous and heterozygous patients. Probability, quality of life and cost parameters used in this study were based on published literature. Deterministic and probabilistic sensitivity analyses were performed to account for parameter uncertainties.

RESULTS

Strategy 1 dominated all remaining strategies. Compared to no testing, it resulted in only marginal QALY increases (0.0002) but a cost reduction of €580 per patient. Strategy 2 resulted in the same health gains but increased costs by €10 773. In the probabilistic analysis, genotyping and dose reduction was the optimal strategy in approximately 100% of simulations at a threshold of €50 000 per QALY. Deterministic sensitivity analysis shows that uncertainty for this strategy originated primarily from costs for irinotecan-based chemotherapy, from the prevalence of neutropenia among heterozygous patients, and from whether dose reduction is applied to both homozygotes and heterozygotes or only to the former.

CONCLUSION

This model-based synthesis of the most recent evidence suggests that pharmacogenetic UGT1A1 testing prior to irinotecan-based chemotherapy dominates non-personalized colon cancer care in Germany. However, as structural uncertainty remains high, these results require validation in clinical practice, e.g. based on a managed-entry agreement.

Application of molecular profiling in clinical trials for advanced metastatic cancers

There is growing interest in the application of molecular profiling, including sequencing, genotyping, and/or mRNA expression profiling, to the analysis of patient tumors with the objective of applying these data to inform therapeutic choices for patients with advanced cancers. Multiple clinical trials that are attempting to validate this personalized or precision medicine approach are in various stages of development and execution. Although preliminary data from some of these efforts have fueled excitement about the value and utility of these studies, their execution has also provoked many questions about the best way to approach complicating factors such as tumor heterogeneity and the choice of which genetic mutations to target. This commentary highlights some of the challenges confronting the clinical application of molecular tumor profiling and the various trial designs being utilized to address these challenges. Randomized trials that rigorously test patient response to molecularly targeted agents assigned based on the presence of a defined set of mutations in putative cancer-driving pathways are required to address some of the current challenges and to identify patients likely to benefit from this approach.

Pre-treatment serum total bilirubin level as an indicator of optimal CPT-11 dosage

BACKGROUND

Irinotecan (CPT-11), a highly effective chemotherapeutic agent, can cause severe neutropenia and diarrhea. The area under the curve of plasma levels over time of SN-38, an active metabolite of CPT-11, was previously reported to correlate with the pre-treatment serum total bilirubin level (PTB). However, there are no established criteria for selecting CPT-11 dose on the basis of PTB. Therefore, we evaluated PTB as an indicator for the optimal CPT-11 dose.

METHODS

Retrospective analyses were conducted in patients administered CPT-11 as a single agent at the Osaka National Hospital from June 2006 to July 2013. Data obtained during the first 28 days following CPT-11 administration were analyzed to compare PTB between patients with and without grade 3-4 neutropenia and grade 3-4 diarrhea. Receiver operating characteristics (ROC) curve analysis was performed to determine the optimal PTB cutoff value for PTB-associated toxicity. Subgroup analysis was performed comparing the incidence of toxicity in patients with PTB values below or above the cutoff value.

RESULTS

Although PTB incidence was significantly higher in patients who developed grade 3-4 neutropenia than in those who did not, PTB was not associated with grade 3-4 diarrhea. The PTB cutoff value for association with grade 3-4 neutropenia occurrence was set at 0.8 mg/dL. The incidence of febrile neutropenia (FN) significantly elevated to 21% in patients with PTB ≥0.8 mg/dL, whereas that of patients with PTB <0.8 mg/dL was 4%. In the subgroup analysis, no difference was found in the neutropenia incidence between patients treated with a dose below 80 mg/m(2) and those treated on a weekly schedule.

CONCLUSIONS

PTB can be used as a predictive marker of CPT-11-induced severe neutropenia and FN. In patients with PTB ≥0.8 mg/dL, the CPT-11 dose should be reduced to less than 80 mg/m(2) with weekly dosing.

Dose-finding and pharmacokinetic study to optimize the dosing of irinotecan according to the UGT1A1 genotype of patients with cancer

PURPOSE

The risk of severe neutropenia from treatment with irinotecan is related in part to UGT1A1*28, a variant that reduces the elimination of SN-38, the active metabolite of irinotecan. We aimed to identify the maximum-tolerated dose (MTD) and dose-limiting toxicity (DLT) of irinotecan in patients with advanced solid tumors stratified by the *1/*1, *1/*28, and *28/*28 genotypes.

PATIENTS AND METHODS

Sixty-eight patients received an intravenous flat dose of irinotecan every 3 weeks. Forty-six percent of the patients had the *1/*1 genotype, 41% had the *1/*28 genotype, and 13% had the *28/*28 genotype. The starting dose of irinotecan was 700 mg in patients with the *1/*1 and *1/*28 genotypes and 500 mg in patients with the *28/*28 genotype. Pharmacokinetic evaluation was performed at cycle 1.

RESULTS

In patients with the *1/*1 genotype, the MTD was 850 mg (four DLTs per 16 patients), and 1,000 mg was not tolerated (two DLTs per six patients). In patients with the *1/*28 genotype, the MTD was 700 mg (five DLTs per 22 patients), and 850 mg was not tolerated (four DLTs per six patients). In patients with the *28/*28 genotype, the MTD was 400 mg (one DLT per six patients), and 500 mg was not tolerated (three DLTs per three patients). The DLTs were mainly myelosuppression and diarrhea. Irinotecan clearance followed linear kinetics. At the MTD for each genotype, dosing by genotype resulted in similar SN-38 areas under the curve (AUCs; r(2) = 0.0003; P = .97), but the irinotecan AUC was correlated with the actual dose (r(2) = 0.39; P < .001). Four of 48 patients with disease known to be responsive to irinotecan achieved partial response.

CONCLUSION

The UGT1A1*28 genotype can be used to individualize dosing of irinotecan. Additional studies should evaluate the effect of genotype-guided dosing on efficacy in patients receiving irinotecan.

Pharmacogenetic biomarkers for predicting drug response

Drug response shows significant interpatient variability and evidence that genetics influences outcome of drug therapy has been known for more than five decades. However, the translation of this knowledge to clinical practice remains slow. Using examples from clinical practice six considerations about the implementation of pharmacogenetics (PGx) into routine care are discussed: the need for PGx biomarkers; the sources of genetic variability in drug response; the amount of variability explained by PGx; whether PGx test results are actionable; the level of evidence needed for implementation of PGx and the sources of information regarding interpretation of PGx data.

Extended mathematical model for "in vivo" quantification of the interaction betweeen atazanavir and bilirubin

The objective of the present work was to conduct an "in vivo" analysis of the atazanavir-bilirubin interaction. We developed a new mathematical approach to PK/PDPK models for competitive interaction based on the Michaelis-Menten equation, which was applied to patients with polymorphisms in the gene for UDP-glucuronosyltransferase 1A1 (UGT1A1). Atazanavir is known to induce concentration-dependent increases in bilirubin plasma levels. Thus, we employed our mathematical model to analyse rises in steady state atazanavir and bilirubin concentrations, ultimately plotting a nomogram for detection of suboptimal atazanavir exposure. Application of our model revealed that an absolute value or a steady state increase in bilirubin falling below 3.8Φ µmol/L (where Φ is a correction factor, =1 for UGT1A1 wild type and ≠1 for UGT1A1 variants) could be used to predict suboptimal atazanavir exposure and treatment failure. Thus, we have successfully established a new mathematical approach for pharmacodynamic-pharmacokinetic modelling of the interaction between atazanavir and bilirubin, as it relates to genetic variants of UGT1A1. Taken together, our findings indicate that bilirubin plasma levels represent a valuable marker of atazanavir exposure.

Polymorphisms in the UGT1A1 gene predict adverse effects of irinotecan in the treatment of gynecologic cancer in Japanese patients

Irinotecan is a key chemotherapeutic drug used to treat many tumors, including cervical and ovarian cancers; however, irinotecan can cause toxicity, particularly in the presence of uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene polymorphisms, which are associated with reduced enzyme activity. Here, we investigated the prevalence of three different variants of UGT1A1 (UGT1A1*6, UGT1A1*27 and UGT1A1*28) and their relationships with irinotecan-induced adverse events in patients with gynecologic cancer, who are treated with lower doses of irinotecan than patients with other types of solid tumors. Fifty-three female patients treated with irinotecan and 362 female patients not treated with irinotecan were screened for UGT1A1*6, UGT1A1*27 and UGT1A1*28. Homozygosity for UGT1A1*6 or heterozygosity for UGT1A1*6/*28 was associated with a high risk of severe absolute neutrophil count decrease or diarrhea (odds ratios: 16.03 and 31.33, respectively). In contrast, serum bilirubin levels were not associated with irinotecan toxicity. Homozygosity for UGT1A1*6/*6 and heterozygosity for UGT1A1*6/*28 were associated with an increased risk of absolute neutrophil count and/or diarrhea in Japanese gynecologic cancer patients, despite the lower doses of irinotecan used in these patients. UGT1A1*6 and UGT1A1*28 are potential predictors of severe absolute neutrophil decrease and diarrhea caused by low-dose irinotecan in gynecologic cancer patients.

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 UGT1A1*28 polymorphism correlates with erlotinib's effect on SN-38 glucuronidation

The combination of irinotecan and erlotinib has been evaluated in clinical trials, although toxicity has been significant. We aimed to investigate the effect of erlotinib on SN-38 glucuronidation and the association between UGT1A polymorphisms and SN-38 glucuronidation activity in the presence of erlotinib. The inhibitory effect of erlotinib on SN-38 glucuronidation was determined by measuring the formation rates for SN-38 glucuronide, using recombinant human UGT1A1, pooled human liver microsomes (HLMs) and 52 Caucasian liver microsomes in the absence or presence of erlotinib. Inhibition kinetic studies were conducted. AUC ratios were used to predict the risk of potential drug-drug interactions (DDI) in vivo. Our data showed that erlotinib exhibited potent non-competitive inhibition against SN-38 glucuronidation in pooled HLMs and UGT1A1. Using the physiological and pharmacokinetic parameters obtained from the literature, we estimated the in vivo concentrations of unbound erlotinib available for UGT1A1 active site and thus the AUC ratios of SN-38 were also quantitatively predicted. It is estimated that erlotinib administered at 50mg/day or higher doses may result in at least a 24% increase in SN-38 AUC. Significant correlations were observed between SN-38 glucuronidation activity in the presence of erlotinib and UGT1A1*28 in 52 Caucasian liver microsomes. Our results suggest that erlotinib is a potent inhibitor of SN-38 glucuronidation via UGT1A1 inhibition. The coadministration of erlotinib with irinotecan may result in clinically significant DDI. UGT1A1*28 polymorphism correlates with erlotinib's effect on SN-38 glucuronidation. The present findings shed light on the development and optimisation of combinations involving irinotecan and erlotinib.

Interindividual variability in hepatic drug glucuronidation: studies into the role of age, sex, enzyme inducers, and genetic polymorphism using the human liver bank as a model system

The human liver bank has provided an invaluable model system for the study of interindividual variability in expression and activity of the major hepatic UGTs, including UGT1A1, 1A4, 1A6, 1A9, 2B7, and 2B15. Based on studies using UGT-isoform-selective probes, the rank order of activity variability is UGT 1A1>1A6>2B15>1A4 = 1A9>2B7, with coefficient of variation values ranging from 92 to 45%. Liver donor age, sex, enzyme inducers, and genetic polymorphism are factors that have been implicated as sources of this variability in UGT activity. The expression of UGTs prior to, and immediately following, birth is quite limited, explaining the susceptibility of neonates to certain drug toxicities. Old age appears to have minimal effect on UGT function. Sex differences in UGT activity are relatively small and are confined to several UGTs, including UGT2B15, which shows higher activity in males, compared with females. Enzyme inducers, including coadministered drugs, smoking, and alcohol, may increase hepatic UGT levels. Human liver bank phenotype-genotype studies, using UGT-isoform-selective probes have identified common genetic polymorphisms that are predictive of glucuronidation activity in vitro and that were subsequently verified as predictors of probe-drug clearance by glucuronidation in vivo.

Phase I trial of two schedules of vincristine, oral irinotecan, and temozolomide (VOIT) for children with relapsed or refractory solid tumors: a Children's Oncology Group phase I consortium study

BACKGROUND

In preclinical models, temozolomide, and vincristine are additive or synergistic with irinotecan. We examined this three-drug combination in children with relapsed solid tumors. Patients received orally administered irinotecan together with temozolomide and vincristine on two different schedules, using cefixime to reduce irinotecan-associated diarrhea.

METHODS

Oral irinotecan was given daily on days 1-5 and 8-12 (Schedule A), or on days 1-5 (Schedule B). Temozolomide was given on days 1-5, with vincristine 1.5 mg/m(2) administered on days 1 and 8 (Schedule A) or day 1 (Schedule B) in 21-day courses.

RESULTS

On Schedule A, the maximum tolerated dose of oral irinotecan was 35 mg/m(2)/day combined with temozolomide 100 mg/m(2)/day and vincristine on days 1 and 8. Dose-limiting toxicities in 4 of 12 patients included hepatotoxicity, abdominal pain, anorexia, hypokalemia, and thrombocytopenia at 50 mg/m(2)/day. Using Schedule B, 0 of 6 patients experienced dose-limiting toxicity (DLT) at the highest doses studied of oral irinotecan 90 mg/m(2)/day, temozolomide 150 mg/m(2)/day x 5, and vincristine on day 1. First-course and cumulative toxicity was greater with Schedule A. UGT1A1*28 genotype did not correlate with DLT. At the irinotecan dose of 90 mg/m(2)/day, the mean SN-38 AUC(inf) was 63 ng/ml hr. Activity was seen in sarcoma patients, and overall eight patients received >or=6 courses.

CONCLUSIONS

The 5-day schedule of VOIT was well tolerated and provided SN-38 exposures similar to those achieved with intravenous IRN. Activity on this and prior studies suggests a potential role for VOIT in a spectrum of childhood solid tumors.

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.

UGT1A1*6 polymorphism is most predictive of severe neutropenia induced by irinotecan in Japanese cancer patients

BACKGROUND

Gene polymorphisms of the UDP-glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) contribute to individual variations in adverse events among patients administered irinotecan, and the distribution of the polymorphisms shows large interethnic differences. Variation in the solute carrier organic anion-transporter family, member 1B1 (SLCO1B1) gene also has a significant effect on the disposition of irinotecan in Asian cancer patients. In the present study, we evaluated the association of genetic polymorphisms of UGT1A1 and SLCO1B1 with irinotecanrelated neutropenia in Japanese cancer patients.

METHODS

One hundred and thirty-five consecutive patients treated with irinotecan were enrolled. Genotypes of UGT1A1 (*60, *28, *6, and *27) and SLCO1B1 (*1b, *5, and haplotype *15) were determined by direct sequencing. Severe neutropenia refers to events observed during the first cycle of irinotecan treatment.

RESULTS

Severe neutropenia was observed in 29 patients (22%). Six patients were homozygous and 48 heterozygous for UGT1A1*6. Only 1 patient was homozygous for UGT1A1*28. Homozygosity for UGT1A1*6 was associated with a high risk of severe neutropenia (odds ratio [OR], 7.78; 95% confidence interval [CI], 1.36 to 44.51). No significant association was found between severe neutropenia and other UGT1A1 polymorphisms or SLCO1B1 polymorphisms.

CONCLUSION

These findings suggest that the UGT1A1*6 polymorphism is a potential predictor of severe neutropenia caused by irinotecan in Japanese cancer patients.

Phase 1 study of oxaliplatin and irinotecan in pediatric patients with refractory solid tumors: a children's oncology group study

BACKGROUND

For this report, the authors estimated the maximum tolerated dose (MTD) and investigated the toxicities of oxaliplatin combined with irinotecan in children with refractory solid tumors.

METHODS

Oxaliplatin was administered on Days 1 and 8 in combination with irinotecan on Days 1 through 5 and Days 8 through 12 of a 21-day cycle. An oral cephalosporin was administered daily to ameliorate irinotecan-associated diarrhea. Pharmacokinetic studies of oxaliplatin and uridine diphosphate glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) genotyping were performed.

RESULTS

Thirteen patients were enrolled. Dose-limiting diarrhea (n = 3), serum lipase elevation (n = 3), serum amylase elevation (n = 2), colitis, abdominal pain, and headache (n = 1 each) occurred at the first dose level (oxaliplatin at a dose of 60 mg/m(2); irinotecan at a dose of 20 mg/m(2)). Only 1 of 7 patients who received reduced doses of both agents (40 mg/m(2)/dose oxaliplatin; 15 mg/m(2)/dose irinotecan) experienced a dose-limiting toxicity (DLT): diarrhea. When the oxaliplatin dose was re-escalated (60 mg/m(2)) with irinotecan at a dose of 15 mg/m(2), 2 of 3 patients had a DLT (1 episode of diarrhea, 1 episode of hypokalemia). Myelosuppression was minimal. One patient had a complete response, and another patient had stable disease for 6 cycles of therapy. The median oxaliplatin area under the concentration versus time curve (AUC(0-->infinity)) was 5.9 microg . hour/mL (range, 1.8-7.6 microg . hour/mL). The frequency of the 6/6, 6/7, and 7/7 UGT1A1 promoter genotypes was 5 of 10, 4 of 10, and 1 of 10, respectively.

CONCLUSIONS

The oxaliplatin MTD was 40 mg/m(2) per dose on Days 1 and 8 in combination with irinotecan 15 mg/m(2) per dose on Days 1-5 and Days 8-12. There was some evidence of antitumor activity; however, severe toxicity, both expected (diarrhea) and unexpected (elevation in pancreatic enzymes), was observed.

Comprehensive pharmacogenetic analysis of irinotecan neutropenia and pharmacokinetics

PURPOSE

We aim to identify genetic variation, in addition to the UGT1A1*28 polymorphism, that can explain the variability in irinotecan (CPT-11) pharmacokinetics and neutropenia in cancer patients.

PATIENTS AND METHODS

Pharmacokinetic, genetic, and clinical data were obtained from 85 advanced cancer patients treated with single-agent CPT-11 every 3 weeks at doses of 300 mg/m(2) (n = 20) and 350 mg/m(2) (n = 65). Forty-two common variants were genotyped in 12 candidate genes of the CPT-11 pathway using several methodologies. Univariate and multivariate models of absolute neutrophil count (ANC) nadir and pharmacokinetic parameters were evaluated.

RESULTS

Almost 50% of the variation in ANC nadir is explained by UGT1A1*93, ABCC1 IVS11 -48C>T, SLCO1B1*1b, ANC baseline levels, sex, and race (P < .0001). More than 40% of the variation in CPT-11 area under the curve (AUC) is explained by ABCC2 -24C>T, SLCO1B1*5, HNF1A 79A>C, age, and CPT-11 dose (P < .0001). Almost 30% of the variability in SN-38 (the active metabolite of CPT-11) AUC is explained by ABCC1 1684T>C, ABCB1 IVS9 -44A>G, and UGT1A1*93 (P = .004). Other models explained 17%, 23%, and 27% of the variation in APC (a metabolite of CPT-11), SN-38 glucuronide (SN-38G), and SN-38G/SN-38 AUCs, respectively. When tested in univariate models, pretreatment total bilirubin was able to modify the existing associations between genotypes and phenotypes.

CONCLUSION

On the basis of this exploratory analysis, common polymorphisms in genes encoding for ABC and SLC transporters may have a significant impact on the pharmacokinetics and pharmacodynamics of CPT-11. Confirmatory studies are required.