Pharmacogenetics of irinotecan: clinical perspectives on the utility of genotyping

Rapid detection of the irinotecan-related UGT1A1 & 5-fluorouracil related DPYD polymorphism by asymmetric polymerase chain reaction melting curve analysis

BACKGROUND

Determination of DPYD and UGT1A1 polymorphisms prior to 5-fluorouracil and irinotecan therapy is crucial for avoiding severe adverse drug effects. Hence, there is a pressing need for accurate and reliable genotyping methods for the most common DPYD and UGT1A1 polymorphisms. In this study, we introduce a novel polymerase chain reaction (PCR) melting curve analysis method for discriminating DPYD c.1236G > A, c.1679 T > G, c.2846A > T, IVS14 + 1G > A and UGT1A1*1, *28, *6 (G71R) genotypes.

METHODS

Following protocol optimization, this technique was employed to genotype 28 patients, recruited between March 2023 and October 2023, at the First Affiliated Hospital of Xiamen University. These patients included 20 with UGT1A1 *1/*1, 8 with UGT1A1 *1/*28, 4 with UGT1A1 *28/*28, 22 with UGT1A1*6 G/G, 6 with UGT1A1*6 G/A, 4 with UGT1A1*6 A/A, 27 with DPYD(c.1236) G/G, 3 with DPYD(c.1236) G/A, 2 with DPYD(c.1236) A/A, 27 with DPYD(c.1679) T/T, 2 with DPYD(c.1679) T/G, 3 with DPYD(c.1679) G/G, 28 with DPYD(c.2846A/T) A/A, 2 with DPYD(c.2846A/T) A/T, 2 with DPYD(c.2846A/T) T/T, 28 with DPYD(c.IVS14 + 1) G/G, 2 with DPYD(c.IVS14 + 1) G/G, and 2 with DPYD(c.IVS14 + 1) G/G, as well as 3 plasmid standards. Method accuracy was assessed by comparing results with those from Sanger sequencing or Multiplex quantitative PCR(qPCR). Intra- and inter-run precision of melting temperatures (Tms) were calculated to evaluate reliability, and sensitivity was assessed through limit of detection examination.

RESULTS

The new method accurately identified all genotypes and exhibited higher accuracy than Multiplex qPCR. Intra- and inter-run coefficients of variation for Tms were both ≤1.97 %, with standard deviations ≤0.95 °C. The limit of detection was 0.09 ng/μL of input genomic DNA.

CONCLUSION

Our developed PCR melting curve analysis offers accurate, reliable, rapid, simple, and cost-effective detection of DPYD and UGT1A1 polymorphisms. Its application can be easily extended to clinical laboratories equipped with a fluorescent PCR platform.

Quantitative analysis of the UDP-glucuronosyltransferase transcriptome in human tissues

UDP-glucuronosyltransferases (UGTs) are phase II drug metabolizing enzymes that play important roles in the detoxification of endogenous and exogenous substrates. The 22 human UGTs belong to four families (UGT1, UGT2, UGT3, and UGT8) and differ in their expression, substrate specificity, UDP-sugar preference, and physiological functions. Differential expression/activity of the UGTs contributes to interperson variability in drug responses and toxicity, hormone homeostasis, and disease/cancer risks. However, in normal tissues, the tissue-specific expression profiles and transcriptional regulation of the UGTs are still not fully understood. In this study, we comprehensively analyzed the transcriptome of 22 UGTs in 54 human tissues/regions using RNAseq data from GTEx. We then validated the findings in the liver and small intestine samples using real-time PCR. Our results showed large interindividual variability across tissues in the expression of each UGT and the overall composition of UGT pools, consisting of different UGTs and their splice isoforms. Our results also revealed coexpression of the UGTs, Cytochrome P450s, and many transcription factors in the liver, suggesting potential coregulation or functional coordination. Our results provide the groundwork for future studies to detail further the regulation of the expression and activity of the UGTs.

Predictive Value of ABCC2 and UGT1A1 Polymorphisms on Irinotecan-Related Toxicities in Patients with Cancer

Background: There is extensive interindividual variability in response and tolerance to anticancer drugs. This heterogeneity provides a major limitation to the "rational" use of cytotoxic drugs, and it becomes a major problem in oncology giving a narrow therapeutic window with a vital risk. Among these anticancer drugs, irinotecan can cause dose-limiting toxicities, commonly diarrhea and neutropenia. Interaction among pathways of activation/inactivation (UGT1A1) and hepatobiliary transport of irinotecan and its metabolites could, in part, explain its interindividual variability. The objective of this study was to perform an exploratory analysis to evaluate the correlation between the genetic polymorphisms of UGT1A1 and ABCC2 with the different toxicities associated with irinotecan treatment. Materials and Methods: Seventy-five patients with solid cancers were included, all were administered an irinotecan-based regimen in both Mission Bay Medical Center; and Zuckerberg San Francisco General Hospital from May 2016 to December 2016. The patients' genotyping was performed for both the UGT1A1*28 polymorphism, and the ABCC2 - 1549G>A, and ABCC2 - 1249G>A single nucleotide polymorphism. Comparisons among qualitative data were assessed using the χ²-test, and Fisher's exact test in the case of small group sizes. Results: Diarrhea was observed in 40 patients (53.3%), among them only 9 patients had high grades diarrhea (grades III and IV). Grades III/IV of nausea were more frequently associated with the ABCC2-1549 AA genotype (83.3% p = 0.004) in patients with colorectal cancer. In pancreatic cancer, a significant absence of diarrhea grades III-IV was noted in patients with the ABCC2 1249 GG genotype compared to the other ABCC2 1249 genotypes.

Incidence and non-genetic risk factors of irinotecan-induced severe neutropenia in Chinese adult inpatients

To analyze the incidence and nongenetic risk factors of irinotecan-induced severe neutropenia in the hospital, and provide additional reference and help for clinical treatment. A retrospective analysis of patients who received irinotecan based chemotherapy from May 2014 to May 2019 in Renmin Hospital of Wuhan University was conducted. Univariate analysis and binary logistic regression analysis with the forward stepwise method were used to assess the risk factors associated with severe neutropenia induced by irinotecan. Of the 1312 patients treated with irinotecan-based regmines, only 612 patients met the inclusion criteria, and 32 patients developed irinotecan-induced severe neutropenia. In the univariate analysis, variables associated with severe neutropenia were tumor type, tumor stage, and therapeutic regimen. In the multivariate analysis, irinotecan plus lobaplatin, lung cancer or ovarian cancer, tumor stage T2, T3, and T4, were identified as risk factors that contributed independently to irinotecan-induced severe neutropenia (P < .05), respectively. The results showed that the incidence of irinotecan-induced severe neutropenia was 5.23% in the hospital. The risk factors included tumor type (lung cancer or ovarian cancer), tumor stage (T2, T3, and T4) and therapeutic regimen (irinotecan plus lobaplatin). Therefore, for patients with these risk factors, it might be advisable to actively consider optimum management to reduce the occurrence of irinotecan-induced severe neutropenia.

Development of an LC-MS/MS Method for Measurement of Irinotecan and Its Major Metabolites in Plasma: Technical Considerations

OBJECTIVE

Irinotecan (CPT-11) is an important drug used in the treatment of several solid tumor types. To minimize its toxicity, therapeutic drug monitoring of CPT-11 and its major metabolites (SN-38, SN-38-glucuronide [SN-38G], and APC) has been proposed. We aimed to develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of CPT-11 and its major metabolites in plasma.

METHODS

Specimen preparation consisted of protein precipitation, evaporation, and reconstitution. Analyses were performed on a C18 column using reverse-phase gradient elution. Electrospray ionization and multiple reaction monitoring in positive mode were used for MS. The following heavy isotope-labeled internal standards were used: CPT-11 D10, SN-38 D3, SN-38G D3, and APC D3.

RESULTS

We found that CPT-11, SN-38G, and APC eluted at ~4.6 to 4.7 minutes, and SN-38 eluted at ~5.1 to 5.2 minutes. A second peak for SN-38 was detected at ~4.6 to 4.7 minutes. Given that the structure of SN-38 is found in CPT-11, SN-38G, and APC, and in the CPT-11 D10 used here, in-source fragmentation was the likely cause. In addition, we found that a low-level SN-38 impurity was present in CPT-11 D10 and to a lesser extent in SN-38 D3.

CONCLUSION

When developing methods for CPT-11 and its metabolites, it is important to consider the effects of in-source fragmentation and the choice of internal standards.

Inhibition of human UDP-glucuronosyltransferase enzyme by belinostat: Implications for drug-drug interactions

Belinostat is a pan-histone deacetylase (HDAC) inhibitor which recently approved for the treatment of relapsed/refractory Peripheral T-cell lymphomas (PTCL). To assess drug-drug interactions (DDIs) potential of belinostat via inhibition of UDP-glucuronosyltransferases (UGTs), the effects of belinostat on UGTs activities were investigated using the non-selective probe substrate 4-methylumbelliferone (4-MU) and trifluoperazine (TFP) by UPLC-MS/MS. Belinostat exhibited a wide range of inhibition against UGTs activities, particularly a potent non-competitive inhibition against UGT1A3, and weak inhibition against UGT1A1, 1A7, 1A8, 2B4 and 2B7. Further, in vitro-in vivo extrapolation (IVIVE) approaches were used to predict the risk of DDI arising from inhibition of UGTs. Our data indicate that the intravenous infusion of belinostat at clinical available dose can contribute a significant increase to the AUC of co-administrated drugs primarily cleared by UGT1A3 or UGT1A1, which will result in potential DDIs. In contrast, oral administrated belinostat is unlikely to cause significant DDIs through inhibition of glucuronidation.

Group-based pharmacogenetic prediction: is it feasible and do current NHS England ethnic classifications provide appropriate data?

Inter-individual variation of drug metabolising enzymes (DMEs) leads to variable efficacy of many drugs and even adverse drug responses. Consequently, it would be desirable to test variants of many DMEs before drug treatment. Inter-ethnic differences in frequency mean that the choice of SNPs to test may vary across population groups. Here we examine the utility of testing representative groups as a way of assessing what variants might be tested. We show that publicly available population information is potentially useful for determining loci for pre-treatment genetic testing, and for determining the most prevalent risk haplotypes in defined groups. However, we also show that the NHS England classifications have limitations for grouping for these purposes, in particular for people of African descent. We conclude: (1) genotyping of hospital patients and people from the hospital catchment area confers no advantage over using samples from appropriate existing ethnic group collections or publicly available data, (2) given the current NHS England Black African grouping, a decision as to whether to test, would have to apply to all patients of recent Black African ancestry to cover reported risk alleles and (3) the current scarcity of available genome and drug effect data from Africans is a problem for both testing and treatment decisions.

RS7435335 located in the UGT2B7 gene may be a possible genetic marker for the clinical response and prognosis of breast cancer patients receiving neoadjuvant chemotherapy

OBJECTIVE

To evaluate the predictive efficacy and prognostic value of rs7435335 located in the UGT2B7 gene as a genetic marker in breast cancer patients receiving neoadjuvant chemotherapy (NAC).

METHODS

A total of 190 patients with breast cancer treated with NAC were enrolled to detect the rs7435335 SNP by sequenom. Miller-Payne grades were used to evaluate the treatment efficacy. The association between rs7435335 and chemotherapy efficacy and prognosis was analyzed.

RESULTS

Altogether, 42 cases (22.1%) achieved pathologic complete response (pCR). The results of the univariate analysis showed that rs7435335 had no statistically significant difference with pCR and Miller-Payne grades (P > 0.05). When grouping was done in accordance with the ER status, the pCR and Miller-Payne grades significantly associated with rs7435335 ( P < 0.05) only in the ER-negative group. Multivariate logistic regression analysis suggested that rs7435335 in the ER-negative group was an independent predictor of pCR ( P < 0.05). Survival analysis showed that the disease-free survival (DFS) time in patients with GA genotype was longer than that of GG genotype, and rs7435335 predicted the DFS in the ER-negative group.

CONCLUSION

The UGT2B7 rs7435335 is associated with the NAC efficacy and prognosis. Patients with GA genotype have better efficacy and prognosis. Rs7435335 was found to be a possible gene marker for pCR and prognosis in ER-negative patients who received NAC.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

An internally and externally validated nomogram for predicting the risk of irinotecan-induced severe neutropenia in advanced colorectal cancer patients

Background:

In Asians, the risk of irinotecan-induced severe toxicities is related in part to UGT1A1*6 (UGT, UDP glucuronosyltransferase) and UGT1A1*28, variant alleles that reduce the elimination of SN-38, the active metabolite of irinotecan. We prospectively studied the relation between the UGT1A1 genotype and the safety of irinotecan-based regimens in Japanese patients with advanced colorectal cancer, and then constructed a nomogram for predicting the risk of severe neutropenia in the first treatment cycle.

Methods:

Safety data were obtained from 1312 patients monitored during the first 3 cycles of irinotecan-based regimen in a prospective observational study. In development of the nomogram, multivariable logistic regression analysis was used to test the associations of candidate factors to severe neutropenia in the first cycle. The final nomogram based on the results of multivariable analysis was constructed and validated internally using a bootstrapping technique and externally in an independent data set (n=350).

Results:

The UGT1A1 genotype was confirmed to be associated with increased risks of irinotecan-induced grade 3 or 4 neutropenia and diarrhoea. The final nomogram included type of regimen, administered dose of irinotecan, gender, age, UGT1A1 genotype, Eastern Cooperative Oncology Group performance status, pre-treatment absolute neutrophil count, and total bilirubin level. The model was validated both internally (bootstrap-adjusted concordance index, 0.69) and externally (concordance index, 0.70).

Conclusions:

Our nomogram can be used before treatment to accurately predict the probability of irinotecan-induced severe neutropenia in the first cycle of therapy. Additional studies should evaluate the effect of nomogram-guided dosing on efficacy in patients receiving irinotecan.

Clinical validity of new genetic biomarkers of irinotecan neutropenia: an independent replication study

The overall goal of this study was to provide evidence for the clinical validity of nine genetic variants in five genes previously associated with irinotecan neutropenia and pharmacokinetics. Variants associated with absolute neutrophil count (ANC) nadir and/or irinotecan pharmacokinetics in a discovery cohort of cancer patients were genotyped in an independent replication cohort of 108 cancer patients. Patients received single-agent irinotecan every 3 weeks. For ANC nadir, we replicated UGT1A1*28, UGT1A1*93 and SLCO1B1*1b in univariate analyses. For irinotecan area under the concentration-time curve (AUC0-24), we replicated ABCC2 -24C>T; however, ABCC2 -24C>T only predicted a small fraction of the variance. For SN-38 AUC0-24 and the glucuronidation ratio, we replicated UGT1A1*28 and UGT1A1*93. In addition to UGT1A1*28, this study independently validated UGT1A1*93 and SLCO1B1*1b as new predictors of irinotecan neutropenia. Further demonstration of their clinical utility will optimize irinotecan therapy in cancer patients.

Personalization of the immunosuppressive treatment in renal transplant recipients: the great challenge in "omics" medicine

Renal transplantation represents the most favorable treatment for patients with advanced renal failure and it is followed, in most cases, by a significant enhancement in patients’ quality of life. Significant improvements in one-year renal allograft and patients’ survival rates have been achieved over the last 10 years primarily as a result of newer immunosuppressive regimens. Despite these notable achievements in the short-term outcome, long-term graft function and survival rates remain less than optimal. Death with a functioning graft and chronic allograft dysfunction result in an annual rate of 3%–5%. In this context, drug toxicity and long-term chronic adverse effects of immunosuppressive medications have a pivotal role. Unfortunately, at the moment, except for the evaluation of trough drug levels, no clinically useful tools are available to correctly manage immunosuppressive therapy. The proper use of these drugs could potentiate therapeutic effects minimizing adverse drug reactions. For this purpose, in the future, “omics” techniques could represent powerful tools that may be employed in clinical practice to routinely aid the personalization of drug treatment according to each patient’s genetic makeup. However, it is unquestionable that additional studies and technological advances are needed to standardize and simplify these methodologies.

Effect of UGT1A1, UGT1A3, DIO1 and DIO2 polymorphisms on L-thyroxine doses required for TSH suppression in patients with differentiated thyroid cancer

AIM

To evaluate the impact of genetic polymorphisms in uridine 5'-glucuronosylytansferases UGT1A1 and UGT1A3 and iodothyronine-deiodinases types 1 and 2 on levothyroxine (T4 ; 3,5,3',5'-triiodo-L-thyronine) dose requirement for suppression of thyrotropin (TSH) secretion in patients with differentiated thyroid cancer (DTC).

METHODS

Patients (n = 268) submitted to total thyroidectomy and ablation by (131) I, under T4 therapy for at least 6 months were recruited in three public institutions in Brazil. Multivariate regression modelling was applied to assess the association of T4 dosing with polymorphisms in UGT1A1 (rs8175347), UGT1A3 (rs3806596 and rs1983023), DIO1 (rs11206244 and rs2235544) and DIO2 (rs225014 and rs12885300), demographic and clinical variables.

RESULTS

A regression model including UGT1A haplotypes, age, gender, body weight and serum TSH concentration accounted for 39% of the inter-individual variation in the T4 dosage. The association of T4 dose with UGT1A haplotype is attributed to reduced UGT1A1 expression and T4 glucuronidation in liver of carriers of low expression UGT1A1 rs8175347 alleles. The DIO1 and DIO2 genotypes had no influence of T4 dosage.

CONCLUSION

UGT1A haplotypes associate with T4 dosage in DTC patients, but the effect accounts for only 2% of the total variability and recommendation of pre-emptive UGT1A genotyping is not warranted.

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.

Digging up the human genome: current progress in deciphering adverse drug reactions

Adverse drug reactions (ADRs) are a major clinical problem. In addition to their clinical impact on human health, there is an enormous cost associated with ADRs in health care and pharmaceutical industry. Increasing studies revealed that genetic variants can determine the susceptibility of individuals to ADRs. The development of modern genomic technologies has led to a tremendous advancement of improving the drug safety and efficacy and minimizing the ADRs. This review will discuss the pharmacogenomic techniques used to unveil the determinants of ADRs and summarize the current progresses concerning the identification of biomarkers for ADRs, with a focus on genetic variants for genes encoding drug-metabolizing enzymes, drug-transporter proteins, and human leukocyte antigen (HLA). The knowledge gained from these cutting-edge findings will form the basis for better prediction and management for ADRs, ultimately making the medicine personalized.

Genotype and phenotype concordance for pharmacogenetic tests through proficiency survey testing

CONTEXT

Pharmacogenetic testing is becoming increasingly important for drugs such as irinotecan, warfarin, clopidogrel, codeine, and the tricyclic antidepressant drugs. Laboratories certified to perform pharmacogenetic testing must demonstrate successful performance on proficiency testing surveys.

OBJECTIVES

To examine the performance of laboratories subscribing to pharmacogenetic proficiency testing surveys for genes that encode CYP2C9, VKORC1, UGT1A1, CYP2C19, and CYP2D6.

DATA SOURCES

College of American Pathologists Pharmacogenetic Proficiency Survey (PGX), 2007-2011.

CONCLUSIONS

For all 5 genes challenged, there was good performance among participating laboratories for reporting wild types (95.4%-99.1% correct). For CYP2C9, VKORC1, and UGT1A1, there was no statistical difference in the percentage correctly detected for variant alleles compared to wild type. For CYP2C19, participating laboratories were greater than 90% successful in detecting variant genotypes of *1/*2, *1/*8, and *2/*3. However, several laboratories failed to detect *2/*2, *2/*4 and *1/*17 variant genotypes. For CYP2D6, laboratories were successful in detecting the most important variant genotypes (*1/*4, *1/*2, *4/*10, *10/*10, *2/*4, *2/*10) but not some of the less frequently encountered variant genotypes (*1/*10, *2/*3, *1/*35, *4/*5, and *1/*1XN). The interpretation of phenotypes by participating laboratories was largely consistent with the genotypes reported, with errors in genotyping leading to errors in phenotype assignment. Improvements in genotyping accuracy are needed for some pharmacogenetics laboratories with reference to CYP2C19 and CYP2D6.

Pharmacogenomics: historical perspective and current status

Pharmacogenomics and its predecessor pharmacogenetics study the contribution of genetic factors to the interindividual variability in drug efficacy and safety. One of the major goals of pharmacogenomics is to tailor drugs to individuals based on their genetic makeup and molecular profile. From early findings in the 1950s uncovering inherited deficiencies in drug metabolism that explained drug-related adverse events, to nowadays genome-wide approaches assessing genetic variation in multiple genes, pharmacogenomics has come a long way. The evolution of pharmacogenomics has paralleled the evolution of genotyping technologies, the completion of the human genome sequencing and the HapMap project. Despite these advances, the implementation of pharmacogenomics in clinical practice has yet been limited. Here we present an overview of the history and current applications of pharmacogenomics in patient selection, dosing, and drug development with illustrative examples of these categories. Some of the challenges in the field and future perspectives are also presented.

Pharmacogenomics of chemotherapeutic susceptibility and toxicity

The goal of personalized medicine is to tailor a patient's treatment strategy on the basis of his or her unique genetic make-up. The field of oncology is beginning to incorporate many of the strategies of personalized medicine, especially within the realm of pharmacogenomics, which is the study of how inter-individual genetic variation determines drug response or toxicity. A main objective of pharmacogenomics is to facilitate physician decision-making regarding optimal drug selection, dose and treatment duration on a patient-by-patient basis. Recent advances in genome-wide genotyping and sequencing technologies have supported the discoveries of a number of pharmacogenetic markers that predict response to chemotherapy. However, effectively implementing these pharmacogenetic markers in the clinic remains a major challenge. This review focuses on the contribution of germline genetic variation to chemotherapeutic toxicity and response, and discusses the utility of genome-wide association studies and use of lymphoblastoid cell lines (LCLs) in pharmacogenomic studies. Furthermore, we highlight several recent examples of genetic variants associated with chemotherapeutic toxicity or response in both patient cohorts and LCLs, and discuss the challenges and future directions of pharmacogenomic discovery for cancer treatment.

Can knowledge of germline markers of toxicity optimize dosing and efficacy of cancer therapy?

The systemic treatment of cancer with traditional cytotoxic chemotherapeutic agents and more targeted agents is often complicated by the onset of adverse drug reactions. Pharmacogenetic prediction of adverse drug reactions might have consequences for dosing and efficacy. This review discusses relevant examples where the germline variant-toxicity relationship has been validated as an initial step in developing clinically useful pharmacogenetic markers and provides examples where germline variants have influenced dosing strategies and/or survival or other outcomes of efficacy. This review will also provide insight into the reasons why more pharmacogenetic markers have not been routinely integrated into clinical practice.

Using companion and coupled diagnostics within strategy to personalize targeted medicines

Regulatory authorities expect the pharmaceutical and biotechnology industries to accelerate their development of companion diagnostics and companion therapeutics towards the goal of personalized medicine, and expect health services to fund, prescribers to adopt and patients to accept these new therapeutic technologies. Expected benefits from more systematic development of combination products (companion diagnostic and its companion therapeutic) are expected to include safer and improved clinical and cost-effective use of medicines, more efficient patient selection for clinical trials, more cost-effective treatment pathways for health services, and a more profitable approach for drug developers. This review discusses challenges to timely development of companion diagnostics and provides case studies of single and multiple protein and genetic biomarkers of clinical response and risk of adverse drug effects.

Blood-direct InvaderPlus® as a new method for genetic testing

Aim: This study compared the efficiency of Blood-direct InvaderPlus® with existing methods for detecting genetic polymorphisms by using clinical samples, and to determine whether this new method can be used for future clinical studies. Materials & methods: We developed a new method, called Blood-direct InvaderPlus, for detecting genetic polymorphisms. Whole-blood samples were subjected to genetic analysis with the new method and also the conventional method. Results: The results obtained with the new method were consistent with those of direct sequencing. Blood-direct InvaderPlus was able to detect gene polymorphisms of UGT1A1*6, *27, *28, *60, VKORC1 -1639G>A, VKORC1 1173T>C and CYP2C9 *2 and *3 much faster than the conventional methods. Conclusion: Blood-direct InvaderPlus allowed accurate, simple and rapid detection of genetic polymorphisms.

Functional characterization of ABCC2 promoter polymorphisms and allele-specific expression

Multidrug resistance protein 2 (MRP2, ABCC2) is an efflux membrane transporter highly expressed in liver, kidney and intestine with important physiological and pharmacological roles. The goal of this study was to investigate the functional significance of promoter region polymorphisms in ABCC2 and potential allele specific expression. Twelve polymorphisms in the 1.6 kb region upstream of the translation start site were identified by resequencing 247 DNA samples from ethnically diverse individuals. Luciferase reporter gene assays showed that ABCC2 -24C>T both alone and as part of a common haplotype (-24C>T/-1019A>G/-1549G>A) increased promoter function 35% compared to the reference sequence (P < 0.0001). No other common variants or haplotypes affected ABCC2 promoter activity. Allele specific expression was also investigated as a mechanism to explain reported associations of the synonymous ABCC2 3972C>T variant with pharmacokinetic phenotypes. In Caucasian liver samples (n=41) heterozygous for the 3972C>T polymorphism, the 3972C allele was preferentially transcribed relative to the 3972T allele (P < 0.0001). This allelic imbalance was particularly apparent in samples with haplotypes containing two or three promoter/UTR variants (-1549G>A, -1019A>G and -24C>T). The observed allelic imbalance was not associated with hepatic or renal ABCC2 mRNA expression. Additional mechanisms will need to be explored to account for the interindividual variation in ABCC2 expression and MRP2 function.

Using germline genomics to individualize pediatric cancer treatments

The amazing successes in cure rates for children with cancer over the last century have come in large part from identifying clinical, genetic, and molecular variables associated with response to therapy in large cooperative clinical trials and stratifying therapies according to the predicted risk of relapse. There is an expanding interest in identifying germline genomic variants, as opposed to genetic variants within the tumor, that are associated with susceptibility to toxicity and for risk of relapse. This review highlights the most important germline pharmacogenetic and pharmacogenomic studies in pediatric oncology. Incorporating germline genomics into risk-adapted therapies will likely lead to safer and more effective treatments for children with cancer.

Genetic variations and haplotype diversity of the UGT1 gene cluster in the Chinese population

Vertebrates require tremendous molecular diversity to defend against numerous small hydrophobic chemicals. UDP-glucuronosyltransferases (UGTs) are a large family of detoxification enzymes that glucuronidate xenobiotics and endobiotics, facilitating their excretion from the body. The UGT1 gene cluster contains a tandem array of variable first exons, each preceded by a specific promoter, and a common set of downstream constant exons, similar to the genomic organization of the protocadherin (Pcdh), immunoglobulin, and T-cell receptor gene clusters. To assist pharmacogenomics studies in Chinese, we sequenced nine first exons, promoter and intronic regions, and five common exons of the UGT1 gene cluster in a population sample of 253 unrelated Chinese individuals. We identified 101 polymorphisms and found 15 novel SNPs. We then computed allele frequencies for each polymorphism and reconstructed their linkage disequilibrium (LD) map. The UGT1 cluster can be divided into five linkage blocks: Block 9 (UGT1A9), Block 9/7/6 (UGT1A9, UGT1A7, and UGT1A6), Block 5 (UGT1A5), Block 4/3 (UGT1A4 and UGT1A3), and Block 3′ UTR. Furthermore, we inferred haplotypes and selected their tagSNPs. Finally, comparing our data with those of three other populations of the HapMap project revealed ethnic specificity of the UGT1 genetic diversity in Chinese. These findings have important implications for future molecular genetic studies of the UGT1 gene cluster as well as for personalized medical therapies in Chinese.

Pharmacogenomics in early-phase oncology clinical trials: is there a sweet spot in phase II?

Many clinical trials of oncology drugs now include at least a consideration of pharmacogenomics, the study of germline or acquired genetic factors governing a drug's response and toxicity. Besides the potential benefit to patients from the consideration of personalized pharmacogenomic information when making treatment decisions, the incentive is clear for oncology drug developers to incorporate pharmacogenomic factors in the drug development process, because pharmacogenomic biomarkers may allow predictive characterization of subpopulations within a disease that may particularly respond or may allow preidentification of patients at highest risk for adverse events. There is, however, a lack of agreement in actual practice about at what point in the oncology clinical drug development process pharmacogenomic studies should be incorporated. In this article, we examine the recent growth of pharmacogenomics in oncology clinical trials, especially in early-phase studies, and examine several critical questions facing the incorporation of pharmacogenomics in early oncologic drug development. We show that phase II clinical trials, in particular, have a favorable track record for showing positive pharmacogenomic signals, worthy of additional follow-up and validation, and that the phase II setting holds significant promise for potentially accelerating and informing future phase III trials. We conclude that phase II trials offer an ideal "sweet spot" for routine incorporation of pharmacogenomic questions in oncology drug development.

Cancer biomarkers

Biomarkers have many potential applications in oncology, including risk assessment, screening, differential diagnosis, determination of prognosis, prediction of response to treatment, and monitoring of progression of disease. Because of the critical role that biomarkers play at all stages of disease, it is important that they undergo rigorous evaluation, including analytical validation, clinical validation, and assessment of clinical utility, prior to incorporation into routine clinical care. In this review we address key steps in the development of biomarkers, including ways to avoid introducing bias and guidelines to follow when reporting results of biomarker studies.

Germline pharmacogenomics in oncology: decoding the patient for targeting therapy

Pharmacogenomics is the study of genetic factors determining drug response or toxicity. The use of pharmacogenomics is especially desirable in oncology because the therapeutic index of oncology drugs is often narrow, the need for favorable drug response is often acute, and the consequences of drug toxicity can be life-threatening. In this review, we examine the state of pharmacogenomics in oncology, focusing only on germline pharmacogenomic variants. We consider several critical points when assessing the quality of pharmacogenomic findings and their relevance to clinical use, and discuss potential confounding factors limiting interpretation and implementation. Several of the most extensively studied drug-gene pairs (irinotecan and UGT1A1; tamoxifen and CYP2D6; 5-fluorouracil and DPYD) are inspected in depth as illustrations of both the state of advancement-and the current limitations of-present knowledge. We argue that there will likely soon be a critical mass of important germline pharmacogenomic biomarkers in oncology which deserve clinical implementation to provide optimal, personalized oncologic care. We conclude with a vision of how routine clinical testing of such germline markers could one day change the paradigm for cancer care.

Molecular predictors of response to chemotherapy in colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of cancer mortality worldwide. In the last decade, median overall survival has increased significantly with the introduction of new cytotoxics and biologic therapies. Notably, the definition of molecular markers predicting benefit with epidermal growth factor receptor (EGFR)-targeted agents has led to important advances in the personalized treatment of CRC. Data derived from multiple phase III trials have indicated that KRAS mutations can be considered a highly specific negative biomarker of response to anti-EGFR monoclonal antibodies. The predictive value of additional mutations and deregulations of the signaling pathways downstream of the EGFR such as BRAF, NRAS, PIK3CA, or PTEN is under intensive investigation. In addition, status of microsatellite instability and molecular markers related to the metabolism of chemotherapy agents has shown promising ability to select patients with higher chances of response to cytotoxic agents. Although attempts to identify predictive factors for efficacy to antiangiogenic therapies have been disappointing, further research on this field will maximize their therapeutic index. Determination of molecular predictive factors before selection of chemotherapy is rapidly approaching us to the paradigm of individualized treatment of CRC.

Impact of UGT2B7 His268Tyr polymorphism on the outcome of adjuvant epirubicin treatment in breast cancer

INTRODUCTION

Epirubicin is a common adjuvant treatment for breast cancer. It is mainly eliminated after glucuronidation through uridine diphosphate-glucuronosyltransferase 2B7 (UGT2B7). The present study aimed to describe the impact of the UGT2B7(His268Tyr) polymorphism on invasive disease-free survival in breast cancer patients after epirubicin treatment.

METHODS

This is a pharmacogenetic study based on samples collected from 745 breast cancer patients of the Austrian Tumor of breast tissue: Incidence, Genetics, and Environmental Risk factors (TIGER) cohort who did not present metastases at baseline. This cohort included 205 women with epirubicin-based combination chemotherapy, 113 patients having received chemotherapy without epirubicin and 427 patients having received no chemotherapy at all. Of the epirubicin-treated subgroup, 120 were subsequently treated with tamoxifen. For all women UGT2B7(His268Tyr) was genotyped. Invasive disease-free survival was assessed using Kaplan-Meier and Cox's proportional hazard regression analysis.

RESULTS

Among the 205 epirubicin-treated patients, carriers of two UGT2B7(268Tyr) alleles had a mean invasive disease-free survival of 8.6 (95% confidence interval (CI) 7.9 to 9.3) years as compared to 7.5 (95% CI 6.9 to 8.0) years in carriers of at least one UGT2B7(268His) allele (adjusted hazard ratio (HR) = 2.64 (95% CI 1.22 to 5.71); P = 0.014). In addition, the impact of the UGT2B7(His268Tyr) polymorphism became even more pronounced in patients subsequently treated with tamoxifen (adjusted HR = 5.22 (95% CI 1.67 to 26.04); P = 0.015) whereas no such difference in invasive disease-free survival was observed in patients not receiving epirubicin.

CONCLUSIONS

Breast cancer patients carrying the UGT2B7(268Tyr/Tyr) genotype may benefit most from adjuvant epirubicin-based chemotherapy. These results warrant confirmation in further studies.

Development of molecular biomarkers in individualized treatment of colorectal cancer

Colorectal cancer is a leading cause of cancer mortality despite recent expansion of treatment options in metastatic colorectal cancer (mCRC). Our knowledge about key signaling pathways in colorectal tumors has contributed to the identification of specific molecular markers of response to targeted agents. In this review we discuss well-established and potential predictive biomarkers of benefit with epidermal growth factor receptor (EGFR) inhibitors. Data derived from multiple phase III trials have indicated that KRAS mutations can be considered a highly specific negative biomarker of response to anti-EGFR monoclonal antibodies. Other molecular aberrations in pathways downstream of EGFR such as BRAF, NRAS, and PIK3CA mutations, and PTEN loss are also reviewed. Moreover biomarkers of efficacy to classic chemotherapeutic agents as well as recent advances regarding high-throughput technologies and circulating tumor cells are also considered. Personalized cancer medicine in the mCRC scenario seems to be near reality, but validation of many biomarkers in prospective clinical trials is urgently warranted.

Pharmacogenomics and adverse drug reactions

Adverse drug reactions (ADRs) observed during drug development have been the cause for discontinuing development of many drugs. In addition, serious but rare ADRs observed after marketing have led to withdrawal of some drugs. A priori identification of individuals at risk of developing ADRs for a given drug will help develop strategies to reduce the risk for ADRs in these patients. US FDA initiatives and efforts at reducing ADRs to make drugs safer are described, including updating of drug labels to include genomic information intended to reduce ADRs. Pharmacogenomics can also be harnessed to identify individuals at risk of developing serious ADRs and to treat these individuals with alternative therapy, thus converting ADRs that are traditionally considered unavoidable to avoidable ADRs.

Pharmacogenetic tests in cancer chemotherapy: what physicians should know for clinical application

Significant efforts to develop pharmacogenomic predictors have been made to guide more effective and safer chemotherapy. Although a considerable amount of data has been generated from numerous experimental or clinical studies, there is a large gap between pharmacogenomic knowledge and clinical application. This review will focus on eight pharmacogenetic tests including TYMS, DPYD, UGT1A1, CYP2D6, EGFR, KRAS, FCGR3A, and BRCA1/2 to predict toxicity or response to commonly used chemotherapeutic agents. We will discuss the current level of evidence, if the current pharmacogenetic tests are appropriate for clinical application, and how to integrate the pharmacogenomic information into routine clinical practice.

The future role of personalized medicine in the treatment of glioblastoma multiforme

Glioblastoma multiforme (GBM) remains one of the most malignant primary central nervous system tumors. Personalized therapeutic approaches have not become standard of care for GBM, but science is fast approaching this goal. GBM's heterogeneous genomic landscape and resistance to radiotherapy and chemotherapy make this tumor one of the most challenging to treat. Recent advances in genome-wide studies and genetic profiling show that there is unlikely to be a single genetic or cellular event that can be effectively targeted in all patients. Instead, future therapies will likely require personalization for each patient's tumor genotype or proteomic profile. Over the past year, many investigations specifically focused simultaneously on strategies to target oncogenic pathways, angiogenesis, tumor immunology, epigenomic events, glioma stem cells (GSCs), and the highly migratory glioma cell population. Combination therapy targeting multiple pathways is becoming a fast growing area of research, and many studies put special attention on small molecule inhibitors. Because GBM is a highly vascular tumor, therapy that directs monoclonal antibodies or small molecule tyrosine kinase inhibitors toward angiogenic factors is also an area of focus for the development of new therapies. Passive, active, and adoptive immunotherapies have been explored by many studies recently, and epigenetic regulation of gene expression with microRNAs is also becoming an important area of study. GSCs can be useful targets to stop tumor recurrence and proliferation, and recent research has found key molecules that regulate GBM cell migration that can be targeted by therapy. Current standard of care for GBM remains nonspecific; however, pharmacogenomic studies are underway to pave the way for patient-specific therapies that are based on the unique aberrant pathways in individual patients. In conclusion, recent studies in GBM have found many diverse molecular targets possible for therapy. The next obstacle in treating this fatal tumor is ascertaining which molecules in each patient should be targeted and how best to target them, so that we can move our current nonspecific therapies toward the realm of personalized medicine.

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.

Integrating genomic-based clinical decision support into electronic health records

There is a growing consensus that the first and most necessary step to improving the efficiency, cost–effectiveness and quality of healthcare systems can be achieved through the implementation of interoperable patient-centric electronic health record (EHR) systems across hospitals and clinics. Targeted therapeutics (including screening, prevention and disease management) through EHR-based clinical decision support delivery may drive both the acceptance and adoption of EHR systems by providing personalized information at the point-of-care. The realization of targeted therapeutics will depend on the resolution of current political, ethical, socioeconomical and technical challenges surrounding EHR implementation efforts. There is a growing need for broad-based consensus initiatives to foster an essential level of standardization for EHRs. The timeliness of these issues is underlined by the rapid emergence of private sector efforts in this potentially lucrative field, from direct-to-consumer testing to Google-, or Microsoft-owned personal health data. This review discusses the potential value for adopting healthcare technology, with a focus on personalized medicine, and highlights the challenges that remain to achieve this.

Three novel single nucleotide polymorphisms of UGT1A9 in a Thai population

The human UDP-glucuronosyltransferase, UGT1A9, catalyzes glucuronidation of various endobiotics and xenobiotics. In this study, we sequenced the promoter and exon 1 regions of the UGT1A9 gene in 93 Thai individuals and identified 7 genetic polymorphisms. The allele frequencies of all 3 novel single nucleotide polymorphisms (SNPs): 454A>G and 455A>C (N152A) and 760C>T (R254X) were 0.005. The other 4 known polymorphisms, -688A>C, -440T>C, -331C>T and -118A(T)(10)AT (UGT1A9(*)1b), were identified and found to have frequencies of 0.124, 0.978, 0.968 and 0.532, respectively.

Relations between strain and gender dependencies of irinotecan toxicity and UGT1A1, CES2 and TOP1 expressions in mice

Irinotecan hydrochloride (CPT-11) can display severe toxicities in individual cancer patients. CPT-11 is bio-activated through CES, detoxified through UGT1A1 and inhibits TOP1. CPT-11 toxicity and UGT1A1, CES2 and TOP1 mRNAs and UGT1A1 protein were determined in male and female C57BL/6, B6D2F1 and B6CBAF1, as potential models for tailoring CPT-11 delivery. CPT-11 was administered intravenously (40-90 mg/kg/day for 4 days at 7h after light onset). The relations between dose and lethal toxicity or body weight loss were steep and similar in C57BL/6 (lethality, p=0.001; weight loss, p=0.002) and B6D2F1 (p=0.01; p=0.03, respectively), but weak in B6CBAF1. Females displayed less toxicity than males (p<0.001). Mean mRNA expression of UGT1A1 was highest in B6CBAF1 (p=0.039) and in females (p<0.001). Both CES2 and TOP1 varied according to strain and gender (p<0.001). The three gene expression data explained the most severe toxicity of CPT-11 in male B6D2F1, but displayed inconsistent relations with toxicity in the other groups. Mean UGT1A1 protein expression was highest in males as compared to females, and so by approximately 8-fold in C57BL/6 as compared to B6D2F1 (p<0.0001). Genetic background and gender significantly altered the molecular prediction of irinotecan toxicity by UGT1A1, CES2 and TOP1 mRNA expressions.

Functional variants in ADH1B and ALDH2 coupled with alcohol and smoking synergistically enhance esophageal cancer risk

BACKGROUND & AIMS

Esophageal squamous cell carcinoma (ESCC) is prevalent among Asian populations, with marked regional variations in incidence and mortality. Patients with ESCC have a very poor prognosis, but detection of ESCC at earlier stages could improve clinical outcome. Therefore, identification of epidemiologic factors that influence the development of ESCC would facilitate prevention and/or early detection of the disease.

METHODS

We performed a 2-step genome-wide association study with subsequent replication analysis using a total of 1070 Japanese ESCC cases and 2836 controls. We also used logistic regression analysis to estimate the effect of gene-gene and gene-environmental interactions.

RESULTS

We identified the significant associations of ESCC with 4q21-23 and 12q24 regions, which include nonsynonymous single nucleotide polymorphisms (SNP) in ADH1B (rs1229984, P = 6.76 x 10(-35)) and ALDH2 (rs671, P = 3.68 x 10(-68)) that were previously shown to be associated with ESCC susceptibility. Multiple logistic regression analysis revealed SNP rs671, rs1229984, alcohol drinking, and smoking as the independent risk factors for ESCC (odds ratios of 1.66, 1.85, 1.92, and 1.79, respectively). Moreover, individuals who had both genetic and lifestyle-related risk factors had a nearly 190 times higher risk of ESCC than those who had neither of these.

CONCLUSIONS

We found 2 known functional variants involved in the metabolism of alcohol and tobacco by-products as the most significant risk factors for the development of ESCC in a Japanese population. The individuals carrying both risk genotypes have a higher baseline risk of ESCC that is substantially increased by 2 lifestyle risk factors.

UGT1A1*28 genotype predicts gastrointestinal toxicity in patients treated with intermediate-dose irinotecan

AIMS

Variants in UGT1A1 have previously been associated with toxicity from irinotecan chemotherapy. We conducted a pragmatic prospective cohort study to establish the relevance of UGT1A1 variants in the prediction of severe diarrhea and neutropenia in patients with colorectal cancer receiving irinotecan in a routine clinical setting.

MATERIALS & METHODS

Genotyping of UGT1A1*28 and c.-3156G>A was undertaken in an unselected, prospective cohort of 96 individuals treated with irinotecan at a single major UK oncology centre. Data on cytotoxic drugs received, and toxicity for all irinotecan treatment cycles were collected from case notes. Over 95% (92/96) of patients received an intermediate dose of irinotecan (180 mg/m(2), twice weekly). Irinotecan was given in combination with other cytotoxic drugs in 93/96 subjects and Grade 3 or 4 toxicity occurred in 23% of subjects.

RESULTS

No association was found between UGT1A1*28 or c.-3156G>A and neutropenia. However, individuals carrying two copies of UGT1A1*28 (p = 0.04; OR: 14; 95% CI: 1.1-185) or c.-3156G>A (p = 0.03) had a significantly increased risk of diarrhea over all cycles.

CONCLUSION

Our findings indicate that UGT1A1 genotyping is not a good predictor of hematological toxicity in patients treated with intermediate irinotecan doses. However, it may be useful in the identification of patients at risk of severe diarrhea.

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.

Predictive role of the UGT1A1, UGT1A7, and UGT1A9 genetic variants and their haplotypes on the outcome of metastatic colorectal cancer patients treated with fluorouracil, leucovorin, and irinotecan

PURPOSE

UGT1A1*28 is considered the main pharmacogenetic predictor of the toxicity outcome of irinotecan-treated patients. We evaluated the effect of other UGT1A variants and haplotypes involved in 7-ethyl-10-hydroxycamptothecin (SN-38) glucuronidation on severe toxicity and efficacy of fluorouracil, leucovorin, and irinotecan (FOLFIRI).

PATIENTS AND METHODS

In addition to UGT1A1*28, UGT1A1*60, UGT1A1*93, UGT1A7*3, and UGT1A9*22 were genotyped in 250 metastatic colorectal cancer patients, and associations with severe hematologic and nonhematologic toxicity, objective response, time to progression (TTP), and overall survival were evaluated. In a subset of 71 patients, pharmacokinetic data were also available.

RESULTS

UGT1A7*3 was the only marker of severe hematologic toxicity after the first cycle (odds ratio [OR], 3.94; 95% CI, 1.05 to 14.82; P = .04) in a multivariate analysis. It was also associated with glucuronidation ratio (SN-38G area under the curve [AUC]/SN-38 AUC) and biliary index (irinotecan AUC) x (SN-38 AUC/SN-38G AUC). Haplotype I (all the reference sequence alleles but UGT1A9*22) was a predictor of severe hematologic toxicity during the entire course of therapy (OR, 0.39; 95% CI, 0.19 to 0.82; P = .01), together with sex (OR, 2.08; 95% CI, 1.01 to 4.28; P = .05). In addition to UGT1A1*28, haplotype II (all the variant alleles but UGT1A9*22) was associated with a response rate (OR, 8.61; 95% CI, 1.75 to 42.38; P = .01). UGT1A1*28 was the only marker associated with TTP.

CONCLUSION

We propose that UGT1A variants additional to UGT1A1*28 might improve the prediction of the outcome of colorectal cancer patients treated with FOLFIRI. A UGT1A haplotype-based approach might be an efficacious strategy to achieve treatment individualization of FOLFIRI.

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.

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.