Pharmacogenetics of irinotecan metabolism and transport: An update

Tumori Journal, 2018

Colorectal cancer, one of the most frequent types of cancer worldwide, has a high mortality rate. Irinotecan (CPT-11) has been approved for the treatment of advanced or metastatic disease either as a single agent or, more commonly, as part of combined chemotherapeutic regimens. Treatment with irinotecan is often accompanied by severe toxicity (e.g. neutropenia and diarrhea) that can result in treatment interruption or cessation, thus jeopardizing the patient's prognosis and quality of life. Irinotecan is bioactivated into its metabolite SN-38, which is subsequently detoxified by uridine diphosphate-glucuronosyl transferases (mainly UGT1A1). Further, ABC transporters (i.e. ABCB1, ABCC1-ABCC6, and ABCG2) are responsible for drug efflux into bile and urine whereas OATP transporters (SLCO1B1) enable its influx from blood into hepatocytes. Genetic polymorphisms in these enzymes/pumps may result in increased systemic SN-38 level, directly correlating with toxicity. Contemporary research is focused on the clinical implementation of genetic screenings for validated gene variations prior to treatment onset, allowing tailored individual doses or treatment regimens.

Clinical Cancer Research, 2010

JNCI Journal of the National Cancer Institute, 2004

Background: Irinotecan is a topoisomerase I inhibitor that has been approved for use as a first-and second-line treatment for colorectal cancer. The response to irinotecan is variable, possibly because of interindividual variation in the expression of the enzymes that metabolize irinotecan, including cytochrome P450 3A4 (CYP3A4) and uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). We prospectively explored the relationships between CYP3A phenotype, as assessed by erythromycin metabolism and midazolam clearance, and the metabolism of irinotecan and its active metabolite SN-38. Methods: Of the 30 white cancer patients, 27 received at least two treatments with irinotecan administered as one 90-minute infusion (dose, 600 mg) with 3 weeks between treatments, and three received only one treatment. Before the first and second treatments, patients underwent an erythromycin breath test and a midazolam clearance test as phenotyping probes for CYP3A4. Erythromycin metabolism was assessed as the area under the curve for the flux of radioactivity in exhaled CO 2 within 40 minutes after administration of [N-methyl-14 C]erythromycin. Midazolam and irinotecan were measured by high-performance liquid chromatography. Genomic DNA was isolated from blood and screened for genetic variants in CYP3A4 and UGT1A1. All statistical tests were two-sided. Results: CYP3A4 activity varied sevenfold (range ‫؍‬ 0.223%-1.53% of dose) among patients, whereas midazolam clearance varied fourfold (range ‫؍‬ 262-1012 mL/min), although intraindividual variation was small. Erythromycin metabolism was not statistically significantly associated with irinotecan clearance (P ‫؍‬ .090), whereas midazolam clearance was highly correlated with irinotecan clearance (r ‫؍‬ .745, P<.001). In addition, the presence of a UGT1A1 variant with a (TA) 7 repeat in the promoter (UGT1A1*28) was associated with increased exposure to SN-38 (435 ng · h/mL, 95% confidence interval [CI] ‫؍‬ 339 to 531 ng · h/mL in patients who are homozygous for wild-type UGT1A1; 631 ng · h/mL, 95% CI ‫؍‬ 499 to 762 ng · h/mL in heterozygous patients; and 1343 ng · h/mL, 95% CI ‫؍‬ 0 to 4181 ng · h/mL in patients who are homozygous for UGT1A1*28) (P ‫؍‬ .006). Conclusion: CYP3A4 phenotype, as assessed by midazolam clearance, is statistically significantly associated with irinotecan pharmacokinetics. Evaluation of midazolam clearance combined with UGT1A1*28 genotyping may assist with optimization of irinotecan chemotherapy. [J Natl Cancer Inst 2004;96:1585-92]

Current Medicinal Chemistry

Irinotecan, a camptothecin analogue, is a prodrug which requires bioactivation to form the active metabolite SN-38. SN-38 acts as a DNA topoisomerase I poison. Irinotecan has been widely used in the treatment of metastatic colorectal cancer, small cell lung cancer and several other solid tumors. However, large inter-patient variability in irinotecan and SN-38 disposition, as well as severe but unpredictable diarrhea limits the clinical potential of irinotecan. Intense clinical pharmacology studies have been conducted to elucidate its complicated metabolic pathways and to provide scientific rationale in defining strategies to optimize drug therapy. Irinotecan is subjected to be shunted between CYP3A4 mediated oxidative metabolism to form two inactive metabolites APC or NPC and tissue carboxylesterase mediated hydrolysis to form SN-38 which is eventually detoxified via glucuronidation by UGT1A1 to form SN-38G. The pharmacology of this compound is further complicated by the existence of genetic inter-individual differences in activation and deactivation enzymes of irinotecan (e.g., CYP3A4, CYP3A5, UGT1A1) and sharing competitive elimination pathways with many concomitant medications, such as anticonvulsants, St. John ’ s Wort, and ketoconazole. Efflux of the parent compound and metabolites out of cells by several drug transporters (e.g., Pgp, BCRP, MRP1, MRP2) also occurs. This review highlights the latest findings in drug activation, transport mechanisms, glucuronidation, and CYP3A-mediated drug-drug interactions of irinotecan in order to unlock some of its complicated pharmacology and to provide ideas for relevant future studies into optimization of this promising agent.

Clinical Cancer Research, 2008

Irinotecan is an important drug for the treatment of solid tumors. Although genes involved in irinotecan pharmacokinetics have been shown to influence toxicity, there are no data on pharmacodynamic genes. CDC45L, NFKB1, PARP1,TDP1, and XRCC1 have been shown to influence the cytotoxic action of camptothecins, including irinotecan. Polymorphisms in the drug target of camptothecins, topoisomerase I (TOP1), and downstream effectors may influence patient outcomes to irinotecan therapy. We undertook a retrospective candidate gene haplotype association study to investigate this hypothesis. Experimental Design: Haplotype compositions of six candidate genes were constructed in European (n = 93), East Asian (n = 94), and West African (n = 95) populations. Haplotypetagging single nucleotide polymorphisms (htSNP) were selected based on genealogic relationships between haplotypes. DNA samples from 107 European, advanced colorectal cancer patients treated with irinotecan-based regimens were genotyped for htSNPs as well as three coding region SNPs. Associations between genetic variants and toxicity (grade 3/4 diarrhea and neutropenia) or efficacy (objective response) were assessed. Results: TOP1 and TDP1 htSNPs were related to grade 3/4 neutropenia (P = 0.04) and response (P = 0.04), respectively. Patients homozygous for an XRCC1 haplotype (GGCC-G) were more likely to show an objective response to therapy than other patients (83% versus 30%; P = 0.02). This effect was also seen in a multivariate analysis (odds ratio, 11.9; P = 0.04). No genetic variants were associated with diarrhea. Conclusions: This is the first comprehensive pharmacogenetic investigation of irinotecan pharmacodynamic factors, and our findings suggest that genetic variation in the pharmacodynamic genes may influence the efficacy of irinotecan-containing therapies in advanced colorectal cancer patients.

Clinical cancer research : an official journal of the American Association for Cancer Research, 2001

CPT-11 belongs to the class of topoisomerase I inhibitors, and it acts as a prodrug of SN-38, which is approximately 100-1000-fold more cytotoxic than the parent drug. CPT-11 has shown a broad spectrum of antitumor activity in preclinical models as well as clinically, with responses observed in various disease types including colorectal, lung, cervical, and ovarian cancer. The pharmacokinetics and metabolism of CPT-11 are extremely complex and have been the subject of intensive investigation in recent years. Both CPT-11 and SN-38 are known in an active lactone form and an inactive carboxylate form, between which an equilibrium exists that depends on the pH and the presence of binding proteins. CPT-11 is subject to extensive metabolic conversion by various enzyme systems, including esterases to form SN-38, UGT1A1 mediating glucuronidation of SN-38, as well as CYP3A4, which forms several pharmacologically inactive oxidation products. Elimination routes of CPT-11 also depend on the pre...

Cancer Chemotherapy and Pharmacology, 2010

Purpose Effects of genetic polymorphisms/variations of ABCB1, ABCC2, ABCG2 and SLCO1B1 in addition to ''UGT1A1*28 or *6'' on irinotecan pharmacokinetics/ pharmacodynamics in Japanese cancer patients were investigated. Methods Associations between transporter haplotypes/

Cancer Chemotherapy and Pharmacology, 1995

Two patients were treated with CPT-11 for colorectal cancer and had a percutaneous biliary catheter for extrahepatic biliarj obstruction. The first patient was treated with CPT-11 according to the 100-mg/m 2 weekly therapeutic schedule, and the second patient was treated every 3 weeks, with a dose of 350 mg/m 2 being given at the first course, after which it was decreased to 300 mg/m 2 for the following courses. In plasma, the active identified metabolite of CPT-11, SN-38, occurred mainly in the form of a glucuronide conjugate. CPT-11 was mainly excreted in bile and urine as CPT-11. The cumulative biliary and urinary excretion of CPT-11 and its metabolites (SN-38 and SN-38 glucuronide conjugate) over a period of up to 48 h ranged from 25% (100 mg/m 2 weekly) to 50% (300 mg/m 2 every 3 weeks). This means that CPT-11 can be excreted under other, not yet identified metabolite forms.

Journal of Vascular and Interventional Radiology, 2018

Differences in drug metabolism associated with UGT1A1 polymorphism could result in individualized local response to hepatic chemoembolization with irinotecan-eluting beads (DEBIRI) or predictable toxicities. Five patients with inoperable hepatic metastases from colorectal or anal malignancies treated with DEBIRI were assessed for UGT1A1 mutations, No difference in AUC for SN38 in normal liver and tumor tissue samples was noted with variant (VAR) or wild-type (WT) UBT1A1 (p = 0.16 and p = 0.05 respectively). Plasma SN-38 AUC was significantly lower in WT compared to VAR patients (p<0.000l). UGT1A1 genotype may not be predictive of hematological toxicity following DEBIRI.

Cancer research, 2000

Irinotecan unexpectedly causes severe toxicity of leukopenia or diarrhea. Irinotecan is metabolized to form active SN-38, which is further conjugated and detoxified by UDP-glucuronosyltransferase (UGT) 1A1 enzyme. Genetic polymorphisms of the UGT1A1 would affect an interindividual variation of the toxicity by irinotecan via the alternation of bioavailability of SN-38. In this case-control study, retrospective review of clinical records and determination of UGT1A1 polymorphisms were performed to investigate whether a patient with the variant UGT1A1 genotypes would be at higher risk for severe toxicity by irinotecan. All patients previously received irinotecan against cancer in university hospitals, cancer centers, or large urban hospitals in Japan. We identified 26 patients who experienced severe toxicity and 92 patients who did not. The relationship was studied between the multiple variant genotypes (UGT1A1*28 in the promoter and UGT1A1*6, UGT1A1*27, UGT1A1*29, and UGT1A1*7 in the coding region) and the severe toxicity of grade 4 leukopenia (<0.9 ؋ 10 9 /liter) and/or grade 3 (watery for 5 days or more) or grade 4 (hemorrhagic or dehydration) diarrhea. Of the 26 patients with the severe toxicity, the genotypes of UGT1A1*28 were homozygous in 4 (15%) and heterozygous in 8 (31%), whereas 3 (3%) homozygous and 10 (11%) heterozygous were found among the 92 patients without the severe toxicity. Multivariate analysis suggested that the genotype either heterozygous or homozygous for UGT1A1*28 would be a significant risk factor for severe toxicity by irinotecan (P < 0.001; odds ratio, 7.23; 95% confidence interval, 2.52-22.3). All 3 patients heterozygous for UGT1A1*27 encountered severe toxicity. No statistical association of UGT1A1*6 with the occurrence of severe toxicity was observed. None had UGT1A1*29 or UGT1A1*7. We suggest that determination of the UGT1A1 genotypes might be clinically useful for predicting severe toxicity by irinotecan in cancer patients. This research warrants a prospective trial to corroborate the usefulness of gene diagnosis of UGT1A1 polymorphisms prior to irinotecan chemotherapy.