An overview of the recent progress in irinotecan pharmacogenetics

Synthesis and biological evaluation of novel SN38-glucose conjugate for colorectal cancer treatment

7-Ethyl-10-hydroxycamptothecin (SN38), the bioactive metabolite of irinotecan (CPT-11), has been shown to be 100-1000 times more effective than CPT-11. However, the poor water solubility and bioavailability of SN38 constrained its clinical application. In this study, we synthesized a novel SN38-glucose conjugate (FSY04) to address this issue. Our in vitro studies indicated that FSY04 had a potent inhibitory ability against colorectal cancer (CRC) cell lines of SW-480 and HCT-116 compared to the inhibitory capacity of CPT-11. Interestingly, FSY04 possessed lower cytotoxicity against normal cell lines of LO2 and 293T in contrast with CPT-11. Moreover, FSY04 is more active than CPT-11 in inducing apoptosis, inhibiting migration, and invasion. In vivo experiments suggested that half of the equivalent of FSY04 inhibited the growth of SW480 in the xenograft tumor model better than one equivalent of CPT-11. Our data demonstrated FSY04 to be a promising agent in CRC therapy.

Liposomal irinotecan (Onivyde): Exemplifying the benefits of nanotherapeutic drugs

Irinotecan is a topoisomerase inhibitor, widely used in treatment of malignancies including pancreatic ductal adenocarcinoma (PDAC) as part of the FOLFIRINOX regimen prescribed as a first-line treatment in several countries. However, irinotecan has not been successfully introduced as a second-line treatment for pancreatic cancer and few randomized clinical studies have evaluated its added value. Efficacy of liposomal irinotecan (nal-IRI) combined with 5-fluorouracil and leucovorin (5-FU/LV) was reported in the phase III NAPOLI-1 trial in metastatic PDAC following failure of gemcitabine-based therapy. Several features of nal-IRI pharmacokinetics (PK) could result in better outcomes versus nonliposomal irinotecan. Irinotecan is a prodrug that is converted to active SN-38 by carboxylesterase enzymes and inactivated by cytochrome P450 3A4/3A5. SN-38 is inactivated by UGT1A1 enzymes. Individual variations in their expression and activity could influence enhanced localized irinotecan activity and toxicity. Liposomal irinotecan exploits the enhanced permeability and retention effect in cancer, accumulating in tumor tissues. Liposomal irinotecan also has a longer half-life and higher area under the concentration-time curve (0-∞) than nonliposomal irinotecan, as the liposomal formulation protects cargo from premature metabolism in the plasma. This results in irinotecan activation in tumor tissue, leading to enhanced cytotoxicity. Importantly, despite the longer exposure, overall toxicity for nal-IRI is no worse than nonliposomal irinotecan. Liposomal irinotecan exemplifies how liposomal encapsulation of a chemotherapeutic agent can alter its PK properties, improving clinical outcomes for patients. Liposomal irinotecan is currently under investigation in other malignancies including biliary tract cancer (amongst other gastrointestinal cancers), brain tumors, and small-cell lung cancer.

Drug-Drug Interactions and Disease Status Are Associated with Irinotecan-induced Hepatotoxicity: A Cross-Sectional Study in Shanghai

Irinotecan-induced hepatotoxicity can cause severe clinical complications in patients; however, the underlying mechanism and factors affecting hepatotoxicity have rarely been investigated. In this cross-sectional study, we screened all clinical, demographic, medication and genetic variables among 126 patients receiving irinotecan and explored potential associations with the incidence and time to onset of irinotecan-induced hepatotoxicity. Approximately 38.9% of the patients suffered from hepatotoxicity after irinotecan administration. The presence of cardiovascular diseases (CVDs) increases the incidence of hepatotoxicity approximately 2.9-fold and doubles the hazard of time to hepatotoxicity. Patients with liver metastasis had a more than 4-fold higher risk of hepatotoxicity and a 3.5-fold increased hazard of time to hepatotoxicity compared to those without liver metastasis. Patients who took CYP3A inducers had a 4.4-fold increased incidence of hepatotoxicity, and furthermore, concomitant use of platinum-based antineoplastics revealed 4.2 times the hazard of time to hepatotoxicity compared to those receiving antimetabolites. The cumulative dose of irinotecan (5-9 cycles) increased hepatotoxicity by 8.5 times. However, the genotypes and phenotypes of UGT1A1*28/*6 failed to be predictive factors of hepatotoxicity. The findings of this study suggest that irinotecan-induced hepatotoxicity is not directly associated with genetic variables but is mostly related to concomitant use of CYP3A inducers and platinum, as well as the presence of liver metastasis and CVD. Thus, close monitoring of liver function is recommended, especially in patients with liver impairment or using CYP3A inducers and platinum antineoplastic drugs, which may be the best way to prevent hepatotoxicity. This article is protected by copyright. All rights reserved.

GSH-responsive SN38 dimer-loaded shape-transformable nanoparticles with iRGD for enhancing chemo-photodynamic therapy

Accurate tumor targeting, deep penetration and superb retention are still the main pursuit of developing excellent nanomedicine. To achieve these requirements, a stepwise stimuli-responsive strategy was developed through co-administration tumor penetration peptide iRGD with shape-transformable and GSH-responsive SN38-dimer (d-SN38)-loaded nanoparticles (d-SN38@NPs/iRGD). Upon intravenous injection, d-SN38@NPs with high drug loading efficiency (33.92 ± 1.33%) could effectively accumulate and penetrate into the deep region of tumor sites with the assistance of iRGD. The gathered nanoparticles simultaneously transformed into nanofibers upon 650 nm laser irradiation at tumor sites so as to promote their retention in the tumor and burst release of reactive oxygen species for photodynamic therapy. The loaded d-SN38 with disulfide bond responded to the high level of GSH in tumor cytoplasm, which consequently resulted in SN38 release and excellent chemo-photodynamic effect on tumor. In vitro, co-administering iRGD with d-SN38@NPs+laser showed higher cellular uptake, apoptosis ratio and multicellular spheroid penetration. In vivo, d-SN38@NPs/iRGD+laser displayed advanced penetration and accumulation in tumor, leading to 60.89% of tumor suppression in 4T1 tumor-bearing mouse model with a favorable toxicity profile. Our new strategy combining iRGD with structural transformable nanoparticles greatly improves tumor targeting, penetrating and retention, and empowers anticancer efficacy.

Host genetic profiling to increase drug safety in colorectal cancer from discovery to implementation

Adverse events affect the pharmacological treatment of approximately 90% of colorectal cancer (CRC) patients at any stage of the disease. Chemotherapy including fluoropyrimidines, irinotecan, and oxaliplatin is the cornerstone of the pharmacological treatment of CRC. The introduction of novel targeted agents, as anti-EGFR (i.e. cetuximab, panitumumab) and antiangiogenic (i.e. bevacizumab, ziv-aflibercept, regorafenib, and ramucirumab) molecules, into the oncologist's toolbox has led to significant improvements in the life expectancy of advanced CRC patients, but with a substantial increase in toxicity burden. In this respect, pharmacogenomics has largely been applied to the personalization of CRC chemotherapy, focusing mainly on the study of inhered polymorphisms in genes encoding phase I and II enzymes, ATP-binding cassette (ABC)/solute carrier (SLC) membrane transporters, proteins involved in DNA repair, folate pathway and immune response. These research efforts have led to the identification of some validated genetic markers of chemotherapy toxicity, for fluoropyrimidines and irinotecan. No validated genetic determinants of oxaliplatin-specific toxicity, as peripheral neuropathy, has thus far been established. The contribution of host genetic markers in predicting the toxicity associated with novel targeted agents' administration is still controversial due to the heterogeneity of published data. Pharmacogenomics guidelines have been published by some international scientific consortia such as the Clinical Pharmacogenomics Implementation Consortium (CPIC) and the Dutch Pharmacogenetics Working Group (DPWG) strongly suggesting a pre-treatment dose adjustment of irinotecan based on UGT1A1*28 genotype and of fluoropyrimidines based on some DPYD genetic variants, to increase treatment safety. However, these recommendations are still poorly applied at the patient's bedside. Several ongoing projects in the U.S. and Europe are currently evaluating how pharmacogenomics can be implemented successfully in daily clinical practice. The majority of drug-related adverse events are still unexplained, and a great deal of ongoing research is aimed at improving knowledge of the role of pharmacogenomics in increasing treatment safety. In this review, the issue of pre-treatment identification of CRC patients at risk of toxicity via the analysis of patients' genetic profiles is addressed. Available pharmacogenomics guidelines with ongoing efforts to implement them in clinical practice and new exploratory markers for clinical validation are described.

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

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

Pharmacogenomic information in the Warning section of drug labels: A comparison between labels in the United States and those in five other countries/regions

WHAT IS KNOWN AND OBJECTIVE

Clinically validated pharmacogenomic information useful for patient selection and/or dose adjustment is included in drug labels. However, the label information may differ among countries. This commentary summarizes the pharmacogenomic information on drug labels in different countries.

COMMENT

We selected six drugs, namely, clopidogrel, atomoxetine, irinotecan, mercaptopurine, abacavir and carbamazepine and compared the pharmacogenomic information in the "Warning" section of these drug labels in the United States and 5 other countries/regions.

WHAT IS NEW AND CONCLUSION

The pharmacogenomic information in drug labels is not well harmonized across countries/regions, possibly due to differences in population characteristics such as relevant allele frequencies, variable genetic test availability and differences in insurance coverage. Further and periodical investigations of this issue would be useful.

Effect of UGT, SLCO, ABCB and ABCC polymorphisms on irinotecan toxicity

BACKGROUND AND OBJECTIVES

Evaluate the relationship between the presence of polymorphisms in genes involved in the pharmacodynamics of irinotecan (UGT1A, SLCO1B1, ABCB1 and ABCC2) and the safety of irinotecan in the treatment of metastatic colorectal cancer (mCRC).

PATIENTS AND METHODS

Prospective observational, single-centre study of 30 months duration, which included patients diagnosed with mCRC treated with FOLFIRI was carried out. Toxicity was evaluated in each treatment cycle according to the Common Terminology Criteria for Adverse Events (CTCAE) v.4.0 NCI. Genomic DNA was obtained with a peripheral blood sample from an extraction method based on alkaline lysis. Genetic characterisation was performed using the LigthCycler®480 platform and allele-specific HybProbe® fluorescent probes. Analysed polymorphisms were: UGT1A1*28, UGT1A1*60, UGT1A7*1,*2,*3,*4, UGT1A7*12, UGT1A9*22, SLCO1B1 (rs11045879), ABCC2 (rs717620) and ABCB1 (rs1045642).

RESULTS

Thirty-four patients were included (73.5% were male, mean age 59.9 years [27-81]) in the study. Polymorphisms rs8175347, rs17868323, rs3832043, rs11692021 and rs7577677 were associated with a higher incidence of adverse effects. Furthermore, it was observed that those patients with wild-type in UGT family genes analysed have lower rates of toxicity associated with irinotecan treatment than those with certain mutated allele (P=.010).

CONCLUSIONS

These results suggest that the presence of certain polymorphisms in the UGT1A family of genes is related to the development of toxicity during treatment with irinotecan.

Dual 7-ethyl-10-hydroxycamptothecin conjugated phospholipid prodrug assembled liposomes with in vitro anticancer effects

7-Ethyl-10-hydroxycamptothecin (SN38), as a highly active topoisomerase I inhibitor, is 200-2000-fold more cytotoxic than irinotecan (CPT-11) commercially available as Camptosar®. However, poor solubility and low stability extensively restricted its clinical utility. In this report, dual SN38 phospholipid conjugate (Di-SN38-PC) prodrug based liposomes were developed in order to compact these drawbacks. Di-SN38-PC prodrug was first synthesized by inhomogeneous conjugation of two SN38-20-O-succinic acid molecules with L-α-glycerophosphorylcholine (GPC). The assembly of the prodrug was carried out without any excipient by using thin film method. Dynamic light scattering (DLS), transmission electron microscope (TEM) and cryogenic transmission electron microscopy (cyro-TEM) characterization indicated that Di-SN38-PC can form spherical liposomes with narrow particle size (<200nm) and negatively charged surface (-21.6±3.5mV). The loading efficiency of SN38 is 65.2 wt.% after a simple calculation. In vitro release test was further performed in detail. The results demonstrated that Di-SN38-PC liposomes were stable in neutral environment but degraded in a weakly acidic condition thereby released parent drug SN38 effectively. Cellular uptake studies reflected that the liposomes could be internalized into cells more significantly than SN38. In vitro antitumor activities were finally evaluated by MTT assay, colony formation assay, flow cytometry, RT-PCR analysis and Western Blot. The results showed that Di-SN38-PC liposomes had a comparable cytotoxicity with SN38 against MCF-7 and HBL-100, and a selective promotion of apoptosis of tumor cells. Furthermore, a pharmacokinetics test showed that Di-SN38-PC liposomes had a longer circulating time in blood compared with the parent drug. All the results indicate that Di-SN38-PC liposomes are an effective delivery system of SN38.

Virtual Clinical Studies to Examine the Probability Distribution of the AUC at Target Tissues Using Physiologically-Based Pharmacokinetic Modeling: Application to Analyses of the Effect of Genetic Polymorphism of Enzymes and Transporters on Irinotecan Induced Side Effects

Purpose

To establish a physiologically-based pharmacokinetic (PBPK) model for analyzing the factors associated with side effects of irinotecan by using a computer-based virtual clinical study (VCS) because many controversial associations between various genetic polymorphisms and side effects of irinotecan have been reported.

Methods

To optimize biochemical parameters of irinotecan and its metabolites in the PBPK modeling, a Cluster Newton method was introduced. In the VCS, virtual patients were generated considering the inter-individual variability and genetic polymorphisms of enzymes and transporters.

Results

Approximately 30 sets of parameters of the PBPK model gave good reproduction of the pharmacokinetics of irinotecan and its metabolites. Of these, 19 sets gave relatively good description of the effect of UGT1A1 *28 and SLCO1B1 c.521T>C polymorphism on the SN-38 plasma concentration, neutropenia, and diarrhea observed in clinical studies reported mainly by Teft et al. (Br J Cancer. 112(5):857-65, 20). VCS also indicated that the frequency of significant association of biliary index with diarrhea was higher than that of UGT1A1 *28 polymorphism.

Conclusion

The VCS confirmed the importance of genetic polymorphisms of UGT1A1 *28 and SLCO1B1 c.521T>C in the irinotecan induced side effects. The VCS also indicated that biliary index is a better biomarker of diarrhea than UGT1A1 *28 polymorphism.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-017-2153-z) contains supplementary material, which is available to authorized users.

Role of UDP-Glucuronosyltransferase 1A1 in the Metabolism and Pharmacokinetics of Silymarin Flavonolignans in Patients with HCV and NAFLD

Silymarin is the most commonly used herbal medicine by patients with chronic liver disease. Silymarin flavonolignans undergo rapid first-pass metabolism primarily by glucuronidation. The aims of this investigation were: (1) to determine the association of UGT1A1*28 polymorphism with the area under the plasma concentration-time curves (AUCs) for silybin A (SA) and silybin B (SB); (2) to evaluate the effect of UGT1A1*28 polymorphism on the profile of flavonolignan glucuronide conjugates found in the plasma; and (3) to investigate the role of UGT1A1 enzyme kinetics on the pharmacokinetics of SA and SB. AUCs and metabolic ratios for thirty-three patients with chronic liver disease administered oral doses of silymarin were compared between different UGT1A1*28 genotypes. The AUCs, metabolic ratios, and the profiles of major SA and SB glucuronides did not differ significantly among the three UGT1A1 genotypes. In contrast, an increase in the proportion of sulfated flavonolignan conjugates in plasma was observed in subjects with UGT1A1*28/*28 genotype compared to subjects carrying wild type alleles. Differences in SA and SB in vitro intrinsic clearance estimates for UGTIA1 correlated inversely with SA and SB exposures observed in vivo indicating a major role for UGT1A1 in silymarin metabolism. In addition, a significant difference in the metabolic ratio observed between patients with NAFLD and HCV suggests that any effect of UGT1A1 polymorphism may be obscured by a greater effect of liver disease on the pharmacokinetics of silymarin. Taken together, these results suggest the presence of the UGT1A1*28 allele does not contribute significantly to a large inter-subject variability in the pharmacokinetics of silybin A and silybin B which may obscure the ability to detect beneficial effects of silymarin in patients with liver disease.

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.

Effect of hesperidin on the pharmacokinetics of CPT-11 and its active metabolite SN-38 by regulating hepatic Mrp2 in rats

The usage of irinotecan hydrochloride (CPT-11) chemotherapy is hindered by its dose-limiting diarrhea which appears to be associated with the intestinal exposure to SN-38, the active metabolite of CPT-11. Hesperidin, a safe and natural food ingredient flavonoid, exhibits various biological properties. Accumulated evidence showed that the regulatory effect of hesperidin on the expression of Mrp2 in the liver may be one of the critical factors controlling the biliary excretion of SN-38. This study examined the effect of hesperidin on the pharmacokinetics of CPT-11 and SN-38 as well as the regulatory effect on the hepatic expression of Mrp2. Compared with the control group, the AUC_5-t was increased to 115% of CPT-11 and 122% of SN-38; the CL was decreased to 87% for CPT-11; the tissue concentration was increased in the liver, kidney and colon; and the accumulated biliary excretion was significantly decreased to 77% for CPT-11 and 76% for SN-38 in hesperidin-treated rats. Furthermore, the expression of Mrp2 in the liver was significantly decreased to 37% in the hesperidin-treated rats compared with that of the control group. These results indicate that oral administration of hesperidin significantly increased the AUC_5-t and reduced the clearance of CPT-11 and SN-38, possibly by decreasing the hepatic expression of Mrp2, and thus inhibiting the biliary excretion of CPT-11 and SN-38. The results from this present study suggest that hesperidin may reduce the exposure of CPT-11 and SN-38 in the intestine by reducing the amount of biliary excretion of CPT-11 and SN-38. Copyright © 2016 John Wiley & Sons, Ltd.

A unified analytic framework for prioritization of non-coding variants of uncertain significance in heritable breast and ovarian cancer

BACKGROUND

Sequencing of both healthy and disease singletons yields many novel and low frequency variants of uncertain significance (VUS). Complete gene and genome sequencing by next generation sequencing (NGS) significantly increases the number of VUS detected. While prior studies have emphasized protein coding variants, non-coding sequence variants have also been proven to significantly contribute to high penetrance disorders, such as hereditary breast and ovarian cancer (HBOC). We present a strategy for analyzing different functional classes of non-coding variants based on information theory (IT) and prioritizing patients with large intragenic deletions.

METHODS

We captured and enriched for coding and non-coding variants in genes known to harbor mutations that increase HBOC risk. Custom oligonucleotide baits spanning the complete coding, non-coding, and intergenic regions 10 kb up- and downstream of ATM, BRCA1, BRCA2, CDH1, CHEK2, PALB2, and TP53 were synthesized for solution hybridization enrichment. Unique and divergent repetitive sequences were sequenced in 102 high-risk, anonymized patients without identified mutations in BRCA1/2. Aside from protein coding and copy number changes, IT-based sequence analysis was used to identify and prioritize pathogenic non-coding variants that occurred within sequence elements predicted to be recognized by proteins or protein complexes involved in mRNA splicing, transcription, and untranslated region (UTR) binding and structure. This approach was supplemented by in silico and laboratory analysis of UTR structure.

RESULTS

15,311 unique variants were identified, of which 245 occurred in coding regions. With the unified IT-framework, 132 variants were identified and 87 functionally significant VUS were further prioritized. An intragenic 32.1 kb interval in BRCA2 that was likely hemizygous was detected in one patient. We also identified 4 stop-gain variants and 3 reading-frame altering exonic insertions/deletions (indels).

CONCLUSIONS

We have presented a strategy for complete gene sequence analysis followed by a unified framework for interpreting non-coding variants that may affect gene expression. This approach distills large numbers of variants detected by NGS to a limited set of variants prioritized as potential deleterious changes.

Pharmacologic resistance in colorectal cancer: a review

Colorectal cancer (CRC) persists as one of the most prevalent and deadly tumor types in both men and women worldwide. This is in spite of widespread, effective measures of preventive screening, and also major advances in treatment options. Despite advances in cytotoxic and targeted therapy, resistance to chemotherapy remains one of the greatest challenges in long-term management of incurable metastatic disease and eventually contributes to death as tumors accumulate means of evading treatment. We performed a comprehensive literature search on the data available through PubMed, Medline, Scopus, and the ASCO Annual Symposium abstracts through June 2015 for the purpose of this review. We discuss the current state of knowledge of clinically relevant mechanisms of resistance to cytotoxic and targeted therapies now in use for the treatment of CRC.

OATP1B1 and tumour OATP1B3 modulate exposure, toxicity, and survival after irinotecan-based chemotherapy

Background:

Treatment of advanced and metastatic colorectal cancer with irinotecan is hampered by severe toxicities. The active metabolite of irinotecan, SN-38, is a known substrate of drug-metabolising enzymes, including UGT1A1, as well as OATP and ABC drug transporters.

Methods:

Blood samples (n=127) and tumour tissue (n=30) were obtained from advanced cancer patients treated with irinotecan-based regimens for pharmacogenetic and drug level analysis and transporter expression. Clinical variables, toxicity, and outcomes data were collected.

Results:

SLCO1B1 521C was significantly associated with increased SN-38 exposure (P<0.001), which was additive with UGT1A1*28. ABCC5 (rs562) carriers had significantly reduced SN-38 glucuronide and APC metabolite levels. Reduced risk of neutropenia and diarrhoea was associated with ABCC2–24C/T (odds ratio (OR)=0.22, 0.06–0.85) and CES1 (rs2244613; OR=0.29, 0.09–0.89), respectively. Progression-free survival (PFS) was significantly longer in SLCO1B1 388G/G patients and reduced in ABCC2–24T/T and UGT1A1*28 carriers. Notably, higher OATP1B3 tumour expression was associated with reduced PFS.

Conclusions:

Clarifying the association of host genetic variation in OATP and ABC transporters to SN-38 exposure, toxicity and PFS provides rationale for personalising irinotecan-based chemotherapy. Our findings suggest that OATP polymorphisms and expression in tumour tissue may serve as important new biomarkers.

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

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

Association analysis of UGT1A genotype and haplotype with SN-38 glucuronidation in human livers

AIM

7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan, is mainly eliminated hepatically through glucuronidation by UGT1A1 and UGT1A9 enzymes. This study comprehensively investigates the effects of UGT1A1 and UGT1A9 genetic polymorphism on SN-38 glucuronidation activity.

MATERIALS & METHODS

Genetic polymorphisms and combinational haplotypes of UGT1A1 and UGT1A9, SN-38 glucuronidation activities, and protein levels of UGT1A1 and UGT1A9 were determined using a set of over 45 Chinese livers.

RESULTS

UGT1A1 reduced function variants UGT1A1*6, *28, *60 and *1B exhibited additive effect. The number of UGT1A1 reduced function alleles was associated with decreased SN-38G formation rates and UGT1A protein levels. UGT1A9 I399C>T and UGT1A9*1b, which were highly linked, were associated with increased SN-38 glucuronidation activity and UGT1A protein levels. However, further analysis based on UGT1A9-1A1 haplotypes confirmed that their increased effect was partly due to their close linkage with UGT1A1 reduced function alleles.

CONCLUSION

UGT1A1 genetic polymorphisms have a more important function in human liver SN-38 glucuronidation activity than UGT1A9. Original submitted 7 November 2013; Revision submitted 30 January 2014.

Pharmacogenetics of ABC and SLC transporters in metastatic colorectal cancer patients receiving first-line FOLFIRI treatment

OBJECTIVE

Membrane transporters are widely recognized as important determinants of drug disposition and response, generating increasing interest on the pharmacological implications of their genetic variations. The aim of this study was to elucidate the predictive/prognostic role of ATP-binding cassette (ABC) and solute carrier (SLC) protein polymorphisms on irinotecan (FOLFIRI regimen) outcome.

PATIENTS AND METHODS

A total of 250 White metastatic colorectal cancer patients homogenously treated with a first-line FOLFIRI regimen were genotyped for a panel of variants in five transporter genes. The primary study endpoints were the response rate (partial or complete response), overall survival, and time to progression. Toxicity was considered a secondary endpoint. Irinotecan pharmacokinetic data of 71 patients were used for polymorphism functional analysis.

RESULTS

Two variants of the ABCG2 (-15622C>T, rs7699188) gene were found to be predictive (P < 0.01) of the response rate. High-order relationships of ABC/SLC markers with previously investigated genetic (UGT1A1 polymorphisms) and nongenetic (primary tumor site) factors that helped determine the response rate were highlighted. A prognostic effect of the ABCB1 rs2032582 variant on patient overall survival emerged (P = 0.0074). The ABCG2 rs7699788 variant was also seen to be associated with grade 3-4 nonhematological toxicity (P = 0.0012). The ABCG2 (-15622C>T, rs7699188) and ABCB1 (rs2032582) polymorphisms were not found to be associated with pharmacokinetic parameters.

CONCLUSION

This study showed that ABC/SLC polymorphisms have a crucial contribution toward the FOLFIRI outcome. This could represent a further step toward personalized therapy.

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.

Prodrug and nanomedicine approaches for the delivery of the camptothecin analogue SN38

SN38 (7-ethyl-10-hydroxy camptothecin) is a prominent and efficacious anticancer agent. It is poorly soluble in both water and pharmaceutically approved solvents; therefore, the direct formulation of SN38 in solution form is limited. Currently, the water soluble prodrug of SN38, irinotecan (CPT-11), is formulated as a low pH solution and is approved for chemotherapy. However, CPT-11, along with most other water-soluble prodrugs shows unpredictable inter-patient conversion to SN38 in vivo, instability in the physiological environment and variable dose-related toxicities. More recently, macromolecular prodrugs (i.e. EZN-2208, IMMU-130) and nanomedicine formulations (i.e. nanoemulsions, polymeric micelles, lipid nanocapsule/nanoparticle, and liposomes) of SN38 have been investigated for improved delivery to cancer cells and tissues. Specifically, these carriers can take advantage of the EPR effect to direct drug preferentially to tumour tissues, thereby substantially improving efficacy and minimising side effects. Furthermore, oral delivery has been shown to be possible in preclinical results using nanomedicine formulations (i.e. dendrimers, lipid nanocapsules, polymeric micelles). This review summarizes the recent advances for the delivery of SN38 with a focus on macromolecular prodrugs and nanomedicines.

Pharmacokinetics of Irinotecan With and Without Panitumumab Coadministration in Patients With Metastatic Colorectal Cancer

This study examined the effects of panitumumab, a human monoclonal antibody against epidermal growth factor receptor (EGFR), on irinotecan pharmacokinetics. This phase I, open-label, multicenter, single-arm study enrolled patients with metastatic colorectal cancer (mCRC) without prior exposure to an EGFR inhibitor. In cycle 1, patients received irinotecan (180 mg/m(2) intravenously [IV]) on day 1 and panitumumab (6 mg/kg IV) on Day 4. In cycle 2 (2 weeks after cycle 1 panitumumab administration) and subsequent every-2-week cycles, patients received panitumumab followed immediately by irinotecan until disease progression or intolerability. Primary and secondary endpoints included Cmax and AUC of irinotecan after irinotecan infusion in cycles 1 and 2, and adverse events, respectively. Nineteen of 27 treated patients were eligible for pharmacokinetic analysis. Pharmacokinetic profiles of irinotecan with or without panitumumab coadministration were nearly identical. The 90% confidence intervals for ratios of geometric means for irinotecan Cmax and AUC with or without panitumumab were within the 80-125% interval, indicating that panitumumab had no apparent effects on irinotecan pharmacokinetics. Adverse events were as expected for irinotecan plus panitumumab combination therapy.

Personalized medicine: is it a pharmacogenetic mirage?

The notion of personalized medicine has developed from the application of the discipline of pharmacogenetics to clinical medicine. Although the clinical relevance of genetically-determined inter-individual differences in pharmacokinetics is poorly understood, and the genotype-phenotype association data on clinical outcomes often inconsistent, officially approved drug labels frequently include pharmacogenetic information concerning the safety and/or efficacy of a number of drugs and refer to the availability of the pharmacogenetic test concerned. Regulatory authorities differ in their approach to these issues. Evidence emerging subsequently has generally revealed the pharmacogenetic information included in the label to be premature. Revised drugs labels, together with a flurry of other collateral activities, have raised public expectations of personalized medicine, promoted as 'the right drug at the right dose the first time.' These expectations place the prescribing physician in a dilemma and at risk of litigation, especially when evidence-based information on genotype-related dosing schedules is to all intent and purposes non-existent and guidelines, intended to improve the clinical utility of available pharmacogenetic information or tests, distance themselves from any responsibility. Lack of efficacy or an adverse drug reaction is frequently related to non-genetic factors. Phenoconversion, arising from drug interactions, poses another often neglected challenge to any potential success of personalized medicine by mimicking genetically-determined enzyme deficiency. A more realistic promotion of personalized medicine should acknowledge current limitations and emphasize that pharmacogenetic testing can only improve the likelihood of diminishing a specific toxic effect or increasing the likelihood of a beneficial effect and that application of pharmacogenetics to clinical medicine cannot adequately predict drug response in individual patients.

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.

Camptothecin-based regimens for treatment of ewing sarcoma: past studies and future directions

New therapies are needed to improve survival for patients with Ewing sarcoma. Over the past decade, camptothecin agents such as topotecan and irinotecan have demonstrated activity against Ewing sarcoma, especially in combination with alkylating agents. Previous studies have shown camptothecin-based combinations to be tolerable outpatient strategies that are attractive for salvage therapy. This paper highlights important issues related to drug dosing, schedule of administration, pharmacokinetics, toxicity, and activity of commonly used camptothecin-based regimens. Also discussed are strategies for incorporating these regimens into therapy for newly diagnosed patients, including several potential possibilities for combination with targeted agents.