Severe CPT-11 toxicity in patients with Gilbert's syndrome: two case reports

Drug-induced acute cholestatic liver damage in a patient with mutation of UGT1A1

BACKGROUND

A 54-year-old woman presented with a 3-week history of fatigue and with jaundice that began 2 days before admission. She had been undergoing treatment with flavoxate for urinary incontinence (for 2 months before admission) and with tibolone for climacteric syndrome (for 6 months before admission). Laboratory tests revealed elevated concentrations of aminotransferases, bilirubin, gamma-glutamyltransferase and alkaline phosphatase. Liver biopsy revealed histological evidence of subacute, drug-induced liver damage.

INVESTIGATIONS

Physical examination, liver function tests, serology tests, autoantibody tests, genetic analysis of the TATA box of the UGT1A1 gene, ultrasonography and CT scan; MRI cholangiography; liver biopsy.

DIAGNOSIS

Drug-related hepatitis in a patient with Gilbert's syndrome.

MANAGEMENT

Flavoxate and tibolone were discontinued. Liver function test results improved progressively and normalized after almost 2 months.

Reversible grade 4 hyperbilirubinemia in a patient with UGT1A1 7/7 genotype treated with irinotecan and cetuximab

Irinotecan-induced gastrointestinal toxicities are common and typically present in the form of diarrhea or nausea and vomiting. However, severe hyperbilirubinemia (grade 3/4) has not been previously reported in association with this chemotherapeutic agent. We report a case of prolonged grade 4 hyperbilirubinemia after a single dose of irinotecan at 125 mg/m(2). This severe toxicity was attributed to a UGT1A1 7/7 genotype and resolved to grade 2 after 8 weeks of supportive care. This case outlines the possibility of severe hepatic toxicity with moderate doses of irinotecan in patients with a UGT1A1 7/7 genotype. Despite the severity and prolonged duration of the associated irinotecan-induced hepatic toxicity, the management of similar cases should focus on intensive supportive measures because the toxicity is likely to resolve eventually.

Systemic anticancer therapy in gynecological cancer patients with renal dysfunction

Chronic kidney disease is a common occurrence in patients with gynecological cancer. Systemic anticancer treatment in such patients is a challenge for clinicians because of altered drug pharmacokinetics. For those drugs that are excreted mainly by the kidneys, decreased renal function may lead to increased systemic exposure and increased toxicity. Dose adjustment based on pharmacokinetic changes is required in this situation to avoid life-threatening toxicity. In this review, we summarize the nephrotoxicity and pharmacokinetic data of agents commonly used in systemic anticancer treatment of gynecological cancers and dose adjustment guidelines in the presence of impaired renal function. We review 17 medications that need dose adjustment (cisplatin, carboplatin, doxorubicin, epirubicin, cyclophosphamide, ifosfamide, topotecan, irinotecan, etoposide, capecitabine, bleomycin, methotrexate, actinomycin D, granulocyte-macrophage colony-stimulating factor, metoclopramide, cimetidine, and diphenhydramine) as well as 27 drugs that do not (paclitaxel, docetaxel, pegylated liposomal doxorubicin, gemcitabine, oxaliplatin, fluorouracil, vincristine, letrozole, anastrozole, tamoxifen, leuprorelin, megestrol, gefitinib, erlotinib, trastuzumab, leucovorin, granulocyte colony-stimulating factor, erythropoietin, ondansetron, granisetron, palonosetron, tropisetron, dolasetron, aprepitant, dexamethasone, lorazepam, and diazepam). We also review the formulae commonly used to estimate creatinine clearance, including Cockcroft-Gault, Chatelut, Jelliffe, Wright, and the Modification of Diet in Renal Disease study formulae.

[Irinotecan and liver dysfunctions]

During last years, irinotecan has become registered as a major cytotoxic drug in several tumor types. Since the metabolism of this drug is predominantly made in the liver, administration to patients with liver dysfunctions remains a major problem. Hyperbilirubinemia has been shown to require dose reduction. In addition, gene polymorphism of UGT1A1 was shown to be associated with a higher risk of toxicity. However, studies are still required to optimise the use of irinotecan in patients with liver dysfunctions.

Validation of Rapid Polymerase Chain Reaction-based Detection of All Length Polymorphisms in the UGT 1A1 Gene Promoter

UDP glucuronosyltransferase (UGT) 1A1 gene promoter polymorphism can affect the expression level of the UGT 1A1 enzyme. The polymorphism consists of an insertion of a TA nucleotide sequence into a (TA)6TAA sequence in the gene promoter resulting in (TA)7TAA (UGT1A1*28). This results in a reduced UGT 1A1 expression with 70% less glucuronidation capacity for bilirubin and other UGT1A1 substrates. Other polymorphisms include (TA)8TAA (UGT1A1*37) and (TA)5TAA (UGT1A1*36). The longer the TA repeats the lower the enzyme expression level. The anticancer agent irinotecan is metabolized to the active SN-38, which is further glucuronidated and detoxified by UGT 1A1. Decreased glucuronidation leads to SN-38 accumulation with severe neutropenia and diarrhea. We have developed a rapid polymerase chain reaction (PCR)-based detection of all length polymorphisms in the UGT 1A1 gene promoter. It uses PCR and DNA fragment analysis using an ABI Genetic Analyzer. Thirty-two blood samples were analyzed for UGT 1A1 promoter polymorphism. We found 2 (TA)(5)TAA/(TA)(5)TAA, 4 (TA)(5)TAA/(TA)(6)TAA, 2 (TA)(5)TAA/(TA)(7)TAA, 9 (TA)(6)TAA/(TA)(6)TAA, 11 (TA)(6)TAA/(TA)(7)TAA, 2 (TA)(7)TAA/(TA)(7)TAA, and 2 (TA)(7)TAA/(TA)(8)TAA in our sample group. To confirm the results, 6 samples with different repeats were also analyzed by DNA sequencing method. This is a rapid and reliable method for analysis of the promoter length polymorphisms of UGT 1A1 gene.

Pharmacogenetics of irinotecan: clinical perspectives on the utility of genotyping

Depending upon the UDP glucuronosyltransferase 1A1 (UGT1A1) genotype, patients are more or less susceptible to the risk of severe toxicity of irinotecan. As the US FDA-approved label of irinotecan (CPT-11, Camptosar®) has been recently revised to include UGT1A1 genotype among potential risk factors for toxicity, it is expected that UGT1A1 genotyping will be increasingly used in patients undergoing irinotecan treatment. At present, the label states that *28/*28 (7/7) genotype patients are at higher risk of neutropenia and should be treated at a lower dose of irinotecan. Although effective alternative drugs (i.e., oxaliplatin) exist for metastatic colorectal cancer (the main indication of irinotecan), recent studies have confirmed that irinotecan has an important place in the management of this disease. We feel that now is the time for addressing questions around the UGT1A1*28 testing that many oncologists might have had but remained unanswered. For example, does the test have adequate sensitivity/specificity? Can the test results be effectively utilized to guide therapy of metastatic colorectal cancer patients? Is it possible that the *1/*1 (6/6) patients are underdosed? How can the genetic prediction of irinotecan toxicity be improved? Is the UGT1A1*28 test fully predictive of the UGT1A1 deficiency in patients who are not of Caucasian origin? Clinicians and investigators interested in a discussion of each of these points could find this article a useful source.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

A phase I and pharmacokinetic study of silybin-phytosome in prostate cancer patients

Silibinin is a polyphenolic flavonoid isolated from milk thistle with anti-neoplastic activity in several in vitro and in vivo models of cancer, including prostate cancer. Silybin-phytosome is a commercially available formulation containing silibinin. This trial was designed to assess the toxicity of high-dose silybin-phytosome and recommend a phase II dose. Silybin-phytosome was administered orally to prostate cancer patients, giving 2.5-20 g daily, in three divided doses. Each course was 4 weeks in duration. Thirteen patients received a total of 91 courses of silybin-phytosome. Baseline patient characteristics included: median age of 70 years, median baseline prostate specific antigen (PSA) of 4.3 ng/ml, and a median ECOG performance status of 0. The most prominent adverse event was hyperbilirubinemia, with grade 1-2 bilirubin elevations in 9 of the 13 patients. The only grade 3 toxicity observed was elevation of alanine aminotransferase (ALT) in one patient; no grade 4 toxicity was noted. No objective PSA responses were observed. We conclude that 13 g of oral silybin-phytosome daily, in 3 divided doses, appears to be well tolerated in patients with advanced prostate cancer and is the recommended phase II dose. Asymptomatic liver toxicity is the most commonly seen adverse event.

Intra-ethnic differences in genetic variants of the UGT-glucuronosyltransferase 1A1 gene in Chinese populations

Variants within the human UGT1A1 gene are associated with irinotecan induced severely adverse reactions and hyperbilirubinemia. Intra-ethnic differences in the genetic variation and haplotypes of UGT1A1 gene have been analyzed in the present study. Relationship between the concentrations of total serum bilirubin (T-bil) and haplotype structure of UGT1A1 in healthy people were also evaluated. We genotyped five functional polymorphisms including -3279T>G and -3156G>A in the enhancer region, (TA)6>7 in the TATA box, and 211G>A (G71R), 686C>A (P229Q) in the exon1 region of UGT1A1 in three groups of healthy Chinese ethnic populations, consisting of 264 subjects of She origin, 539 of Han origin and 273 of Dong origin. The distribution of -3279T>G, (TA)6>7, 211G>A of UGT1A1 differed greatly as between the three ethnic groups. All of six haplotypes differed considerably between at least two of the three groups, which highlighted the need to analyze clinically irinotecan toxicity relevant SNPs and haplotypes in a variety of different racial groups within the Chinese population. Total bilirubin concentration in homozygous carriers of the -3279G and (TA)7 allele were significantly higher than those in heterozygous carriers or homozygous carriers of wild-type alleles. Carriers of the variant haplotypes (-3279G; -3156A; (TA)7; 211G; 686C) had higher serum T-Bil concentrations compared with the other groups. Our results indicate that heterogeneity among different ethnic populations is possibly the result of microevolution and is relevant to studies into the effect of tailored drug treatment.

Identification of human UDP-glucuronosyltransferase isoform(s) responsible for the C-glucuronidation of phenylbutazone

Glucuronidation is a major metabolic pathway in the biotransformation of many xenobiotics and endogeneous compounds. There have been many studies on the formation of O-, N- or S-glucuronides and identification of the UDP-glucuronosyltransferase (UGT) isoforms responsible for the formation of these glucuronides. However, there is no information available on which UGT isoform(s) catalyzes C-glucuronidation. In the present study, 16 human UGTs (UGTs 1A1, 1A3, 1A4, 1A5, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28) were cloned and expressed in baculovirus-infected insect cells and investigated to determine their C-glucuronidating activity toward phenylbutazone (PB). Among the UGT isoforms investigated, only UGT1A9 catalyzed PB C-glucuronidation. Human liver and kidney microsomes, which are well known to express UGT1A9, had C-glucuronidating activity toward PB. However, the jejunum, which did not express UGT1A9, had no C-glucuronidating activity. These results demonstrate for the first time that PB C-glucuronidation is catalyzed by only UGT1A9.

Phase 1 and pharmacokinetic study of intravenous irinotecan in refractory solid tumor patients with hepatic dysfunction

PURPOSE

To determine the recommended starting doses and pharmacokinetics of irinotecan in cancer patients with impaired liver function treated on a weekly schedule.

EXPERIMENTAL DESIGN

Patients with solid tumors who had impaired liver function were enrolled into four groups based on baseline serum total bilirubin and aspartate aminotransferase (AST)/alanine aminotransferase (ALT): Group 1 (n = 19): total bilirubin 1.5 to 3.0 x institutional upper limit of normal (IULN) and ALT/AST <or=5.0 x IULN; Group 2 (n = 7): total bilirubin 3.1 to 5.0 x IULN and ALT/AST <or=5.0 x IULN; Group 3 (n = 6): total bilirubin <or=1.5 x IULN and ALT/AST 5.1 to 20.0 x IULN; Group 4 (n = 10): total bilirubin 1.5 to 3.0 x IULN and ALT/AST 5.1 to 20.0 x IULN. Irinotecan was given as a 90-minute i.v. infusion weekly for the first 4 weeks in each 6-week cycle at starting doses which escalated from 40 to as much as 75 mg/m(2). After the first treatment, doses were adjusted based on individual patient toxicities. Starting doses for patients with hepatic dysfunction were derived from the maximum tolerated doses noted in the four hepatic dysfunction groups.

RESULTS

Forty-two patients were treated. Among the most frequent adverse events were neutropenia (41%, grades 3/4), diarrhea (15%, grades 3/4), nausea (10%, grade 3), and vomiting (5%, grades 3/4). Two patients died from drug-induced neutropenic sepsis. Two patients had objective tumor responses (complete response, liver metastases from unknown primary; partial response, colon cancer). Hepatic dysfunction reduced irinotecan clearance while increasing relative exposure to the active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38). SN-38 exposures in patients receiving doses of 40 to 75 mg/m(2) were comparable to exposures in patients with normal liver function treated with a starting dose of 125 mg/m(2).

CONCLUSIONS

Irinotecan starting doses that seem to be safe for hepatically impaired patients treated with the weekly schedule are 60, 50, 60, and 40 mg/m(2) for groups 1 to 4, respectively. At these starting doses, exposure to SN-38 and the adverse event profile are similar to that observed in patients with normal liver function and antitumor activity can be observed.

TPMT, UGT1A1 and DPYD: genotyping to ensure safer cancer therapy?

The Food and Drug Administration (FDA) has approved label changes for two anticancer drugs, 6-mercaptopurine (6-MP) and irinotecan, to include pharmacogenetic testing as a potential means to reduce the rate of severe toxic events. Comprehensive evaluation of the clinical benefit and cost effectiveness of screening strategies with these tests has not been completed. However, the FDA decided that evidence indicates sufficient benefit to warrant informing prescribers, pharmacists and patients of the availability of pharmacogenetic tests and their possible role in the selection and dosing of these anticancer agents. Reviewing the gene-drug-phenotype relationships of 6-MP, irinotecan and 5-fluorouracil reveals properties of these relationships that lead to a clinically useful pharmacogenetic test. Research in the near future should clarify the role of pharmacogenetic testing in reducing the risk of severe toxicity and determine how these same tests might identify a subset of patients who should safely receive higher doses of treatment to derive the same benefit as the rest of the patient population.

The cancer and leukemia group B pharmacology and experimental therapeutics committee: a historical perspective

The Chemotherapy Committee of Cancer and Leukemia Group B (CALGB) was established in the mid-1970s to assemble a group of experts in cancer chemotherapy and pharmacology who could advise the CALGB disease committees about the optimal use of drugs in the fight against cancer and to provide quality assurance for the chemotherapy section of CALGB protocols. Chaired initially by Edward Henderson and then David Van Echo, the committee was also the repository of studies in diseases for which CALGB did not have a formal committee, such as testis cancer and sarcoma. In 1990, following the appointment of Richard Schilsky as Chair, the name of the committee was changed to the Pharmacology and Experimental Therapeutics (PET) Committee to reflect a more specific focus and scientific agenda (i.e., studies of chemotherapy pharmacology and development of new agents). Three PET Committee reference pharmacology laboratories (led by Merrill Egorin, Tony Miller, and Mark Ratain) were established to measure drug concentrations in biological fluids and to perform pharmacokinetic analyses. In addition, the PET Committee embarked on a number of multi-institution phase I studies. These phase I studies included studies of special populations, including the first prospective study of an anticancer agent (paclitaxel) in patients with hepatic dysfunction. In addition, the Committee studied a number of phase I combinations destined for phase II evaluation in disease-specific committees. Following Dr. Schilsky's election as CALGB Group Chair in 1994, Mark Ratain took over as Chair of the PET Committee and continued to emphasize population pharmacology as the primary theme of the Committee's research agenda. In addition, the PET Committee began to develop novel clinical trial designs, including the first completed randomized discontinuation trial of an antineoplastic agent. Most recently, the PET Committee has launched an ambitious research program in pharmacogenetics, facilitated in large part through the recruitment of Howard McLeod as Vice Chair. This area of research is a collaborative effort with the NIH Pharmacogenetics Research Network and has the potential to definitively address the hypothesis that germ line polymorphisms are a significant determinant of the toxicity and efficacy of anticancer therapy. It is anticipated that the results of the current studies will contribute significantly to the goal of individualizing cancer treatment.

The role of pharmacogenetics in cancer therapeutics

The variability in treatment responses and narrow therapeutic index of anticancer drugs are some of the key challenges oncologists face. The knowledge of pharmacogenetics can potentially aid in the discovery, development and ultimately individualization of anticancer drugs. The identification of genetic variations that predict for drug response is the first step towards the translation of pharmacogenetics into clinical practice. This review provides an update on the results of studies assessing the effects of germline polymorphisms and somatic mutations on therapeutic outcomes and highlights the potential applications and future challenges in pharmacogenetic research pertaining to cancer therapeutics.

Pharmacogenetics of irinotecan: a promoter polymorphism of UGT1A1 gene and severe adverse reactions to irinotecan

This review focuses on a pharmacogenetic association between genetic polymorphism of UGT1A1 gene and severe adverse reactions to irinotecan. Although many studies used pharmacokinetic parameters as surrogate measures for predicting clinical outcomes of irinotecan chemotherapy, they have not produced consistent evidence. On the other hand, genotyping results of UGT1A1 gene appear to predict severe adverse reactions more straightforward than the pharmacokinetic parameters or the phenotypes of the enzymatic activity. A case-control study of Japanese cancer patients revealed that those with the variant UGT1A1 alleles were at significantly higher risk of severe adverse reactions to irinotecan, suggesting that the genotyping strategy would be clinically useful. Nevertheless, clinical importance of the pharmacogenetic testing should differ for different patient groups and for different clinical situations. We need to keep this issue in mind in applying the pharmacogenetic evidence in clinical practice.

Role of cysteine residues in the function of human UDP glucuronosyltransferase isoform 1A1 (UGT1A1)

Bilirubin glucuronidation, catalysed by UGT1A1 [UGT (UDP glucuronosyltransferase) isoform 1A1, EC 2.4.1.17], is critical for biliary elimination of bilirubin. UGT1A1 deficiency causes CN-1 (Crigler-Najjar syndrome type 1), which is characterized by potentially lethal unconjugated hyperbilirubinaemia. Nucleotide sequence analysis of UGT1A1 in two CN-1 patients revealed that patient A was homozygous for a nt 530 G-->A (where nt 530 G-->A means guanine to adenine transition at nucleotide 530) mutation, predicting a C177Y substitution, and patient B had a nt 466 T-->C mutation on one allele and a nt 1070 A-->G mutation on the other, predicting a C156R and a Q357R substitution respectively. All 11 cysteine residues of mature human UGT1A1 are highly conserved in other human UGT isoforms and in rat, mouse and Rhesus monkey UGT1A1, suggesting their functional importance. Expression of mutagenized UGT1A1 plasmids showed that substitution of any of the seven cysteine residues located within the endoplasmic reticulum cisternae (including those mutated in patients A and B) abolished UGT1A1 activity or markedly increased its apparent K(m) for bilirubin. Substitution of the three cysteine residues within the C-terminal cytosolic tail had minimal effect on basal UGT1A1 activity, but prevented UGT1A1 activation by UDP-GlcNAc. N-Ethylmaleimide did not inhibit UGT1A1 activity in native microsomes, but prevented UGT1A1 activation by UDP-GlcNAc and inhibited the activity in digitonin-permeabilized microsomes. Dithiothreitol did not affect UGT1A1 activity in human liver microsomes. Together, the results suggested that free thiol groups, but not disulphide bonding, of seven cysteine residues within the intracisternal region of human UGT1A1 are important for its catalytic activity, while cysteine residues in the cytosolic domain may be involved in its physiological activation by UDP-GlcNAc.

The role of Gilbert's syndrome and frequent NAT2 slow acetylation polymorphisms in the pharmacokinetics of retigabine

Retigabine (RGB) is an investigational antiepileptic drug, which undergoes extensive UGT1A1, 1A9 and 1A4-mediated N-glucuronidation and N-acetylation. The mono-acetylated metabolite of RGB has some pharmacological activity and is denoted AWD21-360. We investigated whether the pharmacokinetics (PK) of RGB and AWD21-360 are altered in subjects with Gilbert's syndrome (GS) and/or with frequent N-acetyltransferase 2 (NAT2) slow acetylator (SA) polymorphisms. Based on consistent genotyping and phenotyping screening results, 37 Caucasian subjects (21-46 years; 31 men, six women) were assigned to one of the following groups: (1) absence of GS (non-GS)/rapid acetylator (RA) (N=11); (2) GS/RA (N=8); (3) non-GS/SA (N=11); (4) GS/SA (N=7). Subjects received single and multiple (b.i.d.) 200-mg oral RGB doses over 5 days. Blood samples were collected up to 60 h after dosing for plasma PK of RGB and AWD21-360. Group comparisons were performed by ANOVA. Single-dose PK of RGB and AWD21-360 and multiple-dose PK of RGB did not differ significantly between groups. After multiple dose treatment, RA subjects showed a significantly higher total exposure to AWD21-360 of about 32% (95% CI 101.9-172.5) relative to SA subjects (P=0.0362). The UGT1A1 metabolic capacity (i.e. presence or absence of GS), however, did not significantly affect the overall exposure to AWD21-360. The results indicate that the PK of RGB is unaltered in individuals with GS, in subjects with NAT2 SA status, and in carriers of both variants, whereas the total exposure to AWD21-360 is significantly related to the RA or SA status of subjects. Results further suggest that metabolic switching to the mono-acetylated metabolite AWD21-360 may partially compensate for the impaired glucuronidation capacity in GS subjects. RGB treatment showed no significant differences in tolerability and safety between groups.

Clinical pharmacogenetics of irinotecan (CPT-11)

Irinotecan (CPT-11) is now widely used, especially for colorectal and lung cancers, whereas the drug causes severe adverse drug reactions (ADR), such as leukopenia/neutropenia or diarrhea. Irinotecan undergoes drug metabolism to form an active SN-38, which is further converted to its beta-glucuronide by UDP-glucuronosyltransferase (UGT) 1A1. A variant in the promoter of UGT1A1 gene, UGT1A1*28 allele, has been extensively studied, and pharmacogenetic relationships between the variant and ADR to irinotecan have been reported. A case-control study of Japanese cancer patients demonstrated that the patients having UGT1A1*28 were at significantly increased risk of severe ADR to irinotecan. To date, genetic variations of the UGT1A1 gene is the most important hereditary factor to predict severe ADR to irinotecan. The UGT1A1*28 is the only one variant that has multiple lines of clinical evidence in multiple races, whereas genetic variations of other UGT isoforms, drug-metabolizing enzymes and drug transporters need more confirmations of its clinical significance in multiple patient groups. At present, irinotecan chemotherapy based on a patient's UGT1A1 genetic status is scientifically reasonable.

Genetic determinants of cancer drug efficacy and toxicity: practical considerations and perspectives

Drug-metabolizing enzymes are responsible for the activation or detoxification of cytotoxic drugs. Allelic variants are present with a variable frequency in different populations around the world and have an important role in the therapeutic index of such drugs. It is known that polymorphisms in thiopurine methyltransferase and dihydropyrimidine dehydrogenase have been associated with altered drug metabolism and increased risk of severe toxicity from 6-mercaptopurine and 5-fluorouracil, respectively. Additionally, a variant number of dinucleotide-repeat sequences in the promotor for uridine 5'-diphosphate glucuronosyltransferase 1A1 influences the glucuronidation of SN-38, the active metabolite of irinotecan, which is associated with severe toxicity, including diarrhea and neutropenia. In the same way, polymorphisms in thymidylate synthase have been associated with pyrimidine-associated toxicity and also with response to chemotherapy. The examples shown in this review demonstrate the usefulness of pre-screening patients for well-characterized polymorphism to identify the best-tolerated and most-effective treatment.

Modulation of UDP-glucuronosyltransferase 1A1 in primary human hepatocytes by prototypical inducers

The primary objective of this study was to evaluate the modulation of UGT1A1 expression in human hepatocytes using prototypical CYP450 inducers. A bank of 16 human livers was utilized to obtain an estimate of the range of UGT1A1 protein expression and catalytic activity. Concentration-dependent changes in UGT1A1 response were evaluated in hepatocyte cultures after treatment with 3-methylchloranthrene, beta-napthoflavone, rifampicin, or phenobarbital. Pharmacodynamic analyses of UGT1A1 expression were conducted and compared to those of CYP450 after treatment with inducers in 2-3 different hepatocyte preparations. Additionally, expression of UGT1A1 mRNA and protein was evaluated in human hepatocytes treated with 14 different compounds known to activate differentially the human pregnane-X-receptor or constitutive androstane receptor. Pharmacodynamic modeling revealed EC50 values statistically significant between UGT1A1 and CYP2B6 after treatment with PB, but not statistically distinguishable between UGT1A1 and CYP's 1A2 or 3A4 after treatment with 3-methylchloranthrene or rifampicin, respectively. UGT1A1 was most responsive to the pregnane-X-receptor-agonists rifampicin, ritonavir, and clotrimazole at the mRNA level and, to a lesser extent, the constitutive androstane receptor-activators, phenobarbital and phenytoin. Pharmacodynamic analyses support a mechanism of coordinate regulation between UGT1A1 and a number of CYP450 enzymes by multiple nuclear receptors.

5-Fluorouracil/irinotecan induced lethal toxicity as a result of a combined pharmacogenetic syndrome: report of a case

Combination cancer chemotherapy induced toxicity can be associated with combined pharmacogenetic syndromes. Dihydropyrimidine dehydrogenase (DPD) is the principal enzyme involved in the catabolic detoxification of 5-fluorouracil (5FU). A heterozygous G > A transition at the 5' splicing donor consensus sequence in intron 14 leading to exon 14 skipping (IVS14+1 G > A, DPYD*2A) with partial loss of enzyme activity may be partly responsible for 5FU induced toxicity, whereas irinotecan associated toxicity may in part be explained by an aberrant UGT1A1 promoter (TA)(n) genotype underlying Gilbert's syndrome with reduced liver glucuronidation activity. This report describes a 44 year old white woman who suffered from severe gastrointestinal and haematological toxicity while undergoing 5FU(24h)/folinic acid/irinotecan treatment for adenocarcinoma of the sigmoid colon. Despite appropriate supportive treatment, her condition rapidly deteriorated and led to death. Molecular analysis revealed a hitherto undescribed combined pharmacogenetic syndrome, consisting of heterozygosity for the DPD IVS14+1 G > A mutation and UGT1A1 (TA)(6/7) heterozygosity, which probably contributed to the fatal outcome in this patient.

Chemotherapy of metastatic colorectal cancer

Over the past decade, metastatic colorectal cancer has evolved from a relatively resistant disease to one that is sensitive to a variety of chemotherapeutic drugs and combinations of drugs. During the same period, the median survival of patients with metastatic colorectal cancer increased from approximately 14 months to almost 20 months. First-line chemotherapy prolongs survival and delays the appearance of symptoms and should be considered in patients who are still asymptomatic. Patients with metastatic colorectal cancer and adequate performance status should be treated with a combination of fluorouracil (5-FU) and either oxaliplatin or irinotecan. Bevacizumab, the monoclonal antibody against the vascular endothelial growth factor, has been shown to prolong survival with acceptable toxicity and may be added when available. When the disease recurs, second-line chemotherapy may also prolong survival in appropriately selected patients. Typically, treatment includes 5-FU and one of the drugs not used in the first-line therapy (oxaliplatin or irinotecan). Several oral prodrugs of 5-FU are currently available. Capecitabine, approved in the United States, may be safely substituted for 5-FU in the majority of settings and combinations. Cetuximab is a monoclonal antibody against the epidermal growth factor receptor and is approved both as a single agent and in combination with irinotecan for patients with recurrent disease. This treatment may represent a second-line or third-line option in selected patients. Treatment of patients with isolated liver metastases may also include surgical or other ablative procedures. In carefully selected patients, these modalities add to the efficacy of chemotherapy and may be used with potentially curative intent. However, for the vast majority of patients with metastatic colorectal cancer treatment is palliative.

Pharmacogenetic testing: proofs of principle and pharmacoeconomic implications

Several proofs of principle have established that pharmacogenetic testing for mutations altering expression and functions of genes associated with drug disposition and response can decrease the "trial-and-error" dosing and reduce the risk of adverse drug reactions. These proofs of principle include thiopurine methyltransferase and thiopurine therapy, dihydropyrimidine dehydrogenase/thymidylate synthase and 5-fluorouracil therapy, folate enzyme MTHFR and methotrexate therapy, UGT1A1 and irinotecan therapy and CYP450 2C9 and S-warfarin therapy. These evidences advocate for the prospective identification of mutations associated with drug response, serious adverse reactions and treatment failure. More recent evidence with the HLA basis of hypersensitivity to the retroviral agent abacavir demonstrates the potential of pharmacogenetic testing and its pharmacoeconomic implications. With the convergence of rising drug costs and evidence supporting the clinical benefits of pharmacogenetic testing, it will be important to demonstrate the improved net health outcomes attributed to the additional costs for this testing.

New approaches to prevent intestinal toxicity of irinotecan-based regimens

BACKGROUND

Irinotecan is a selective inhibitor of topoisomerase I, an enzyme part of the replication and transcription system of DNA. Irinotecan is employed, with different modalities, in the treatment of metastatic colorectal cancer, and recently it has been officially approved in association with fluorouracil (FU) and leucovorin (LV) as a first-line option in metastatic colorectal cancer.

RESULTS

One of the problems linked to the administration of this drug is the high intestinal toxicity, which constitutes its dose limiting toxicity (DLT). In routine practice, loperamide is employed as symptomatic drug for the treatment of CPT-11-induced diarrhoea, but is not completely adequate to control the problem. The role of the intestinal bacterial microflora in the pathogenesis of CPT-11-induced intestinal toxicity has been recently discovered. The active metabolite of CPT-11, SN38, is generated from CPT-11 by sieric carboxylesterase, and subsequently conjugated to SN38-G by hepatic UDP-glucuronyltransferase. SN38-G is the inactive metabolite of CPT-11 and is excreted into the small intestine, from which it is eliminated in the faeces. Some studies have shown the ability of intestinal bacterial beta-glucoronidases to transform SN38-G into SN38, causing direct damage to the intestinal mucosa. Thus, alternative strategies such as intestinal alkalinization and anti-cyclooxygenase 2 (COX-2) therapy have been explored.

CONCLUSIONS

In this review, we will illustrate the mechanisms which cause the CPT-11-induced diarrhoea and the potential measures available to prevent it.

UGT1A1 gene variations and irinotecan treatment in patients with metastatic colorectal cancer

SN-38 is the active metabolite of irinotecan and it is metabolised through conjugation by uridine diphosphate glucuronosyl transferase (UGT1A1). The major toxicity of irinotecan therapy is diarrhoea, which has been related to the enzymatic activity of UGT1A1. We examined the influence of the UGT1A1 gene promoter polymorphism in the toxicity profile, in the response rate and in the overall survival (OS) in 95 patients with metastatic colorectal cancer treated with an irinotecan-containing chemotherapy. Genotypes were determined by analysing the sequence of TATA box of UGT1A1 of genomic DNA from the patients. Clinical parameters and genotypes were compared by univariate and multivariate statistical methods. The more frequent adverse effects were asthenia (34 patients), diarrhoea (29 patients) and neutropenia (20 patients). Severe diarrhoea was observed in 7/10 homozygous (70%) and 15/45 heterozygous (33%) in comparison to 7/40 (17%) wild-type patients (P=0.005). These results maintained the statistical significance in logistic regression analysis (P=0.01) after adjustment for other clinical relevant variables. The presence of severe haematological toxicity increased from wild-type patients to UGT1A1(*)28 homozygotes, but without achieving statistical significance. No relationship was found between the UGT1A1(*)28 genotypes and infection, nausea or mucositis. In univariate studies, patients with the UGT1A1(*)28 polymorphism showed a trend to a poorer OS (P=0.09). In the multivariate analysis, the genotype was not related to clinical response or to OS. The role of the UGT1A1 genotype as a predictor of toxicity in cancer patients receiving irinotecan demands the performance of a randomized trial to ascertain whether genotype-adjusted dosages of the drug can help to establish safe and effective doses not only for patients with the UGT1A1(*)28 homozygous genotype but also for those with the most common UGT1A1 6/6 or 6/7 genotype.

Relevance of different UGT1A1 polymorphisms in irinotecan-induced toxicity: a molecular and clinical study of 75 patients

PURPOSE

We wanted to assess polymorphisms in the uridine diphosphoglucuronosyl transferase 1A1 (UGT 1A1) gene: the TATA box polymorphism and UGT 1A1 G71R and Y486D mutations in the coding sequence, the main mutations characterizing Gilbert's syndrome, as predictors of severe toxic event occurrence after irinotecan (CPT-11) administration. Therefore, we set up a rapid, sensitive, and reliable technique in routine practice to detect before CPT-11 treatment, the at-risk patients.

EXPERIMENTAL DESIGN

Seventy-five patients with advanced colorectal cancer and treated with CPT-11 and 5-fluorouracil, entered the study. We used the Pyrosequencing technology a real-time sequencing method, to detect the UGT 1A1 TATA box polymorphisms and mutations in the coding regions. Patients were also assessed for both biochemical and clinical evaluation and tolerance to treatment.

RESULTS

No G71R and Y486D mutations were found in our population. Frequencies for UGT 1A1 TATA box polymorphisms were 41, 47, and 9% for wild-type 6/6, heterozygous 6/7, and Gilbert's syndrome 7/7, respectively. Tolerance to treatment decreased with increased number of TA repeat with 71% of the patients in 7/7 group who experienced grade 3/4 toxicity.

CONCLUSIONS

The method we set up is suitable for the detection of UGT 1A1 polymorphism in routine practice before irinotecan treatment. It could help to detect the patients homozygous or heterozygous for Gilbert's syndrome, at-risk of CPT 11-induced toxicity, and thus could help to individualize the dose to optimize efficacy and limit toxicity.

Combined topoisomerase I inhibition for the treatment of metastatic colon cancer

The objective of this study was to define the maximally tolerated dose (MTD) and response rate of a combination of two topoisomerase I inhibitors, topotecan and irinotecan, in patients with metastatic colon cancer. Eleven patients, the majority with previously progressive disease on 5-fluorouracil-based regimens, were enrolled onto a phase I/II dose escalation trial utilizing continuous infusion topotecan for 2 weeks and weekly irinotecan x 3 with cycles repeated every 28 days. Dosages of topotecan utilized included 0.2 and 0.25mg/m2/day. Irinotecan was administered at a dose of 62 mg/m2 by i.v. bolus. Patients were followed for toxicity and response. The MTD of the combination of agents was found to be 0.25mg/m2/day for topotecan and 62 mg/m2 for irinotecan. The most common serious toxicities were diarrhea and nausea/vomiting. Only one patient experienced grade III neutropenia. There were no complete or partial responses. However, four patients had prolonged disease stabilization (SD) of up to 324 days and this group remained on protocol therapy for an average of 227 days (p=0.0005 versus patients not achieving SD). We concluded that the MTD for this combination of topoisomerase I inhibitors, given on this particular schedule, has been defined. This combination cannot be recommended as a first- or second-line therapy for patients with metastatic colon cancer based on the responses observed. However, approximately one-third of patients achieved prolonged disease stabilization. Topotecan with irinotecan may be useful as a palliative regimen for a subgroup of colon cancer patients.

Relationship of baseline serum bilirubin to efficacy and toxicity of single-agent irinotecan in patients with metastatic colorectal cancer

PURPOSE

To examine the predictive value of baseline serum bilirubin measurement for chemotherapy-related toxicity or efficacy among patients receiving irinotecan for metastatic colorectal cancer.

METHODS

We performed a secondary analysis of a cohort of 287 patients treated in a multicenter, phase III study with single-agent irinotecan administered either weekly or once every 3 weeks. Patients were grouped into three categories of baseline bilirubin measurements (0 to 0.4, 0.5 to 0.9, and 1.0 to 1.5 mg/dL). We performed analyses of overall survival, time to progression, and treatment-related toxicity based on bilirubin category, as well as using bilirubin as a continuous variable.

RESULTS

With a median follow-up of 15.8 months, baseline serum bilirubin was not predictive of 1-year survival (42.4%, bilirubin 0 to 0.4; 42.3%, bilirubin 0.5 to 0.9; 48.1%, bilirubin 1.0 to 1.5 mg/dL), median overall survival (10.1, 9.7, and 15.6 months, respectively; P =.5), or median time to progression (2.8, 3.0, and 4.1 months, respectively; P =.5). Patients with elevated bilirubin had a significantly greater risk grade 3 to 4 neutropenia; however, this was limited to patients treated on a weekly schedule (P trend =.03) and not once every 3 weeks (P trend =.8). Other toxicities were not significantly different by initial bilirubin measurement.

CONCLUSION

Although modest elevations of bilirubin (1.0 to 1.5 mg/dL) are associated with increased grade 3 to 4 neutropenia in patients treated with weekly irinotecan, baseline serum bilirubin does not reliably predict overall irinotecan-related toxicity or efficacy. Additional methods, including potential application of pharmacogenetic information, are needed to optimize irinotecan dosing and tailor therapy to individual patients.

A phase I and pharmacokinetic study of irinotecan in patients with hepatic or renal dysfunction or with prior pelvic radiation: CALGB 9863

BACKGROUND

To ascertain if hepatic or renal dysfunction or prior pelvic radiation (XRT) leads to increased toxicity at a given dose of irinotecan and to characterize the pharmacokinetics of irinotecan and its major metabolites in patients with hepatic or renal dysfunction.

PATIENTS AND METHODS

Adults with tumors appropriate for irinotecan therapy and who had abnormal liver or renal function tests or had prior radiation to the pelvis were eligible. Patients were assigned to one of four treatment cohorts: I, aspartate aminotransferase (AST) > or = 3x upper limit of normal and direct bilirubin <1.0 mg/dl; II, direct bilirubin 1.0-7.0 mg/dl; III, creatinine 1.6-5.0 mg/dl with normal liver function; IV, prior pelvic XRT with normal liver and renal function. Starting with reduced doses of either 145 or 225 mg/m(2), irinotecan was administered every 3 weeks to at least three patients within each cohort. Irinotecan and its metabolites in the blood were measured in all patients.

RESULTS

Thirty-five patients were evaluable for toxicity. No dose-limiting toxicity was seen in cohort I, although only three patients were treated and at a dose of 225 mg/m(2). Patients with elevations of direct bilirubin had dose-limiting toxicities, even though the starting dose was 145 mg/m(2). These same patients appeared to have comparable exposure to the active metabolite SN-38 as normal patients treated with full-dose irinotecan. Patients with elevations of creatinine or with prior pelvic radiotherapy did not appear to have increased risk of toxicity at the doses explored in this study.

CONCLUSIONS

Patients with elevated bilirubin treated with irinotecan have an increased risk of toxicity and a dose reduction is recommended. Patients with elevated AST, creatinine or prior pelvic radiation do not appear to have increased sensitivity to irinotecan, but the data are not adequate to support a specific dosing recommendation.

Pharmacogenomics of human UDP-glucuronosyltransferase enzymes

UDP-glucuronosyltransferase (UGT) enzymes comprise a superfamily of key proteins that catalyze the glucuronidation reaction on a wide range of structurally diverse endogenous and exogenous chemicals. Glucuronidation is one of the major phase II drug-metabolizing reactions that contributes to drug biotransformation. This biochemical process is also involved in the protection against environmental toxicants, carcinogens, dietary toxins and participates in the homeostasis of numerous endogenous molecules, including bilirubin, steroid hormones and biliary acids. Over the years, significant progress was made in the field of glucuronidation, especially with regard to the identification of human UGTs, study of their tissue distribution and substrate specificities. More recently, the degree of allelic diversity has also been revealed for several human UGT genes. Some polymorphic UGTs have demonstrated a significant pharmacological impact in addition to being relevant to drug-induced adverse reactions and cancer susceptibility. This review focuses on human UGTs, the description of the nature of polymorphic variations and their functional impact. The pharmacogenomic implication of polymorphic UGTs is presented, more specifically the role of UGT polymorphisms in modifying cancer risk and their impact on individual risk to drug-induced toxicities.

Cancer pharmacogenetics

The large number of active combination chemotherapy regimens for most cancers has led to the need for better information to guide the 'standard' treatment for each patient. In an attempt to individualise therapy, pharmacogenetics and pharmacogenomics (a polygenic approach to pharmacogenetic studies) encompass the search for answers to the hereditary basis for interindividual differences in drug response. This review will focus on the results of studies assessing the effects of polymorphisms in drug-metabolising enzymes and drug targets on the toxicity and response to commonly used chemotherapy drugs. In addition, the need for polygenic pharmacogenomic strategies to identify patients at risk for adverse drug reactions will be highlighted.

Genetic variation of human UDP-glucuronosyltransferase: implications in disease and drug glucuronidation

The uridine diphosphate (UDP)-glucuronosyltransferases (UGTs) are key enzymes in human detoxication of xeno- and endobiotics. Potentially toxic endogenous compounds such as bilirubin, or exogenous compounds such as drugs, pesticides, and carcinogens, are generally transformed into water-soluble glucuronides for excretion in bile and urine. The UGTs are encoded by a multigene family in humans. A relatively small number of human enzymes catalyze the glucuronidation of thousands of compounds. Genetic variations and single nucleotide polymorphisms (SNPs) within the UGT genes are remarkably common, and lead to genetic polymorphisms. The multiplicity of transferases, some exhibiting overlapping substrate specificity, may provide functional compensation for genetic deficit in some cases. Genetic variation may cause different phenotypes by affecting expression levels or activities of individual UGTs. This inter-individual variation in UGTs has resulted in functional deficit affecting endogenous metabolism and leading to jaundice and other diseases. Disruption of the normal metabolic physiology, by the reduction of bile acid excretion or steroid glucuronidation, may lead to cholestasis and organ dysfunction. Deficient glucuronidation of drugs and xenobiotics have an important pharmacological impact, which may lead to drug-induced adverse reactions, and even cancer. Additional novel polymorphisms in this gene family are yet to be revealed and studied, but will have a profound effect on the development of new drugs and therapies.

The camptothecins

Supported by detailed understanding of their mechanism of action, and facilitated by chemical manipulations that have amplified their solubility, the camptothecins have advanced to the forefront of several areas of therapeutic and developmental chemotherapy. Additive and synergistic laboratory interactions with other cytotoxic drugs have been exploited to allow development of camptothecin-based multidrug regimens, which are showing important activity in several malignancies. Topotecan and irinotecan are already in widespread use in clinical practice, and newer agents with promising preclinical activity are in various stages of clinical assessment. As knowledge of molecular and biochemical mechanisms of action and resistance continues to expand, newer and better camptothecin-based strategies for treatment of malignant disease are likely to evolve.

Pharmacogenetics in cancer treatment

Interindividual variability in the efficacy and toxicity of drug therapy is associated with polymorphisms in genes encoding drug-metabolizing enzymes, transporters, or drug targets. Pharmacogenetics aims to identify individuals predisposed to high risk of toxicity from conventional doses of cancer chemotherapeutic agents. We review the role of genetic polymorphisms in UGT1A1 and TPMT, as well as mutations in DPD, in influencing drug disposition and toxicity. Recent studies show that pharmacogenetic determinants may also influence treatment outcomes. We discuss the clinical significance of polymorphisms in TS, MTHFR, and FCGR3A, as well as the polymorphic DNA repair genes XPD and XRCC1, in influencing response to chemotherapy and survival outcomes. Finally, the potential implications of transporter pharmacogenetics in influencing drug bioavailability are addressed.

Irinotecan: mechanisms of tumor resistance and novel strategies for modulating its activity

Camptothecins are broad-spectrum anticancer drugs that specifically target DNA topoisomerase I (Topo I). The formation of a cleavable drug-Topo I-DNA complex results in lethal double-strand DNA breakage and cell death. However, de novo or acquired clinical resistance to camptothecins is common. Studies of the camptothecin analog irinotecan suggest the following general mechanisms of resistance: (i) variable levels of the enzymes involved in the conversion of irinotecan; (ii) reduced cellular accumulation from active drug efflux; (iii) reduced levels of Topo I expression; (iv) alterations in the structure of Topo I from different mutations; (v) alterations in the cellular response to camptothecin-Topo I-DNA complex formation, which involves proteasome degradation of Topo I and/or enhanced DNA repair; and (vi) activation of the transcription factor nuclear factor kappa B by DNA damage and subsequent suppression of apoptosis. Multiple approaches using pharmacological and biological modulation to circumvent the above mechanisms of resistance have been incorporated into ongoing clinical trials and are expected to enhance the antitumor activity of irinotecan and reduce its systemic toxicity.

Dosage adjustment and pharmacokinetic profile of irinotecan in cancer patients with hepatic dysfunction

PURPOSE

To determine the recommended dose (RD) and the pharmacokinetic profile of irinotecan and its metabolites in cancer patients with hyperbilirubinemia.

PATIENTS AND METHODS

Patients were assigned to four treatment groups according to their baseline total bilirubin level. Patients in group I (bilirubin within normal range) and group II (bilirubin 1.0 to 1.5 times upper limit of normal [ULN]) received a dose of 350 mg/m(2) every 3 weeks. Patients in groups III (bilirubin 1.51 to 3.0 times ULN) and IV (bilirubin > 3.1 times ULN) received starting doses of 175 and 100 mg/m(2), respectively. RDs were defined according to the dose-limiting toxicity (DLT) experienced at cycle 1.

RESULTS

Thirty-three patients including 21 gastrointestinal cancers were included. Grade 4 febrile neutropenia and diarrhea were common DLTs in patients with hyperbilirubinemia. At a dose of irinotecan 350 mg/m(2), DLTs were observed in two of seven and one of five patients in groups I and II, respectively. In group III, escalated doses of irinotecan 175, 200, and 240 mg/m(2) were associated with DLTs in one of seven, one of five, and three of six patients, respectively. No DLT was observed in group IV. High bilirubin and alkaline phosphatase levels were associated with an exponential decrease in the clearance of irinotecan. Pharmacokinetic analysis showed that the relative increase in exposure was likely caused by reduced biliary excretion.

CONCLUSION

We showed that baseline total bilirubin level could be used to determine the appropriate dose of irinotecan in cancer patients with hepatic dysfunction. Doses of 350 mg/m(2) and 200 mg/m(2) were considered RDs in patients with bilirubin values <or= 1.5 times ULN and 1.51 to 3.0 times ULN, respectively.

UGT1A1*28 polymorphism as a determinant of irinotecan disposition and toxicity

The metabolism of irinotecan (CPT-11) involves sequential activation to SN-38 and detoxification to the pharmacologically inactive SN-38 glucuronide (SN-38G). We have previously demonstrated the role of UGT1A1 enzyme in the glucuronidation of SN-38 and a significant correlation between in vitro glucuronidation of SN-38 and UGT1A1 gene promoter polymorphism. This polymorphism (UGT1A1*28) is characterized by the presence of an additional TA repeat in the TATA sequence of the UGT1A1 promoter, ((TA)7TAA, instead of (TA)6TAA). Here we report the results from a prospective clinical pharmacogenetic study to determine the significance of UGT1A1*28 polymorphism on irinotecan disposition and toxicity in patients with cancer. Twenty patients with solid tumors were treated with a 90 min i.v. infusion of irinotecan (300 mg m(-2)) once every 3 weeks. The frequency of UGT1A1 genotypes was as follows: 6/6--45%, 6/7--35% and 7/7--20%, with allele frequencies of 0.375 and 0.625 for (TA)7TAA and (TA)6TAA, respectively. Patients with the (TA)7TAA polymorphism had significantly lower SN-38 glucuronidation rates than those with the normal allele (6/6>6/7>7/7, P = 0.001). More severe grades of diarrhea and neutropenia were observed only in patients heterozygous (grade 4 diarrhea, n = 1) or homozygous (grade 3 diarrhea/grade 4 neutropenia, n = 1 and grade 3 neutropenia, n = 1) for the (TA)7TAA sequence. The results suggest that screening for UGT1A1*28 polymorphism may identify patients with lower SN-38 glucuronidation rates and greater susceptibility to irinotecan induced gastrointestinal and bone marrow toxicity.

Topotecan preceded by oxaliplatin using a 3 week schedule: a phase I study in advanced cancer patients

Combinations of topoisomerase I (topo I) poisons and platinum derivatives have synergistic antitumoral effects. However, their clinical development is limited by supra-additive haematological toxicity. The aim of this study was to determine whether sustained doses of topotecan and oxaliplatin could be achieved using a synergistic sequence. 34 advanced cancer patients and 186 cycles were evaluable for toxicity over five dosing levels. Oxaliplatin at 85-110 mg/m(2) was given on day 1, followed by topotecan 0.5-1.25 mg/m(2)/day x 5 from day 1 to 5, every 3 weeks. Plasma pharmacokinetics (PK) of total and ultrafiltrable platinum, total and lactone forms of topotecan were determined in the first cycle. The dose-limiting toxicity (DT) was identified as grade 4 thrombocytopenia. The occurrence of grade 4 thrombocytopenia did not correlate with topotecan PK, but it did with the patient's characteristics. Severe thrombocytopenia was seen in 1/8 of patients without clinical or biological evidence of malnutrition, with a creatinine clearance higher than 1 ml/s, and no more than two previous chemotherapy regimens, while it was seen in 8/10 patients with one of these characteristics (P<0.004). In conclusion, the recommended doses of oxaliplatin 110 mg/m(2) and topotecan 1 mg/m(2)/day, every 3 weeks can be administered to patients with a favourable general status and pretreatment characteristics and a phase II study is worthwhile in ovarian cancer patients.

The impact of pharmacogenomics on gastrointestinal cancer therapy

Recently, we have seen major advances in the chemotherapy of gastrointestinal tumors, in particular colorectal cancer, leading to a substantial increase in overall survival of the patients. However, clinical efficacy and also toxicity of a given chemotherapy are still largely unpredictable for the individual patient. Amongst other variables, genetic polymorphisms determine the interindividual heterogeneity in both toxicity and therapeutic efficacy. In this review we present current evidence on host genetic polymorphisms that affect the toxicity or efficacy of three drugs commonly used for the treatment of gastrointestinal malignancies, 5-fluorouracil, irinotecan and oxaliplatin.

The development of camptothecin analogs in childhood cancers

Camptothecin analogs, agents that target the intranuclear enzyme topoisomerase I, represent a promising new class of anticancer drugs for the treatment of childhood cancer. In preclinical studies, camptothecins, such as topotecan and irinotecan, are highly active against a variety of pediatric malignancies including neuroblastomas, rhabdomyosarcomas, gliomas, and medulloblastomas. In this paper, we review the status of completed and ongoing clinical trials and pharmacokinetic studies of camptothecin analogs in children. These and future planned studies of this novel class of cytotoxic agents are critical to defining the ultimate role of topoisomerase I poisons in the treatment of childhood cancer.

Randomized multicenter phase II study comparing a combination of fluorouracil and folinic acid and alternating irinotecan and oxaliplatin with oxaliplatin and irinotecan in fluorouracil-pretreated metastatic colorectal cancer patients

PURPOSE

To assess antitumor activity and safety of two regimens in advanced colorectal cancer (CRC) patients with proven fluorouracil (5-FU) resistance in a randomized phase II study: 5-FU/folinic acid (FA) combined with alternating irinotecan (also called CPT-11) and oxaliplatin (FC/FO tritherapy), and an oxaliplatin/irinotecan (OC) combination.

PATIENTS AND METHODS

Sixty-two patients were treated: arm FC/FO (32 patients) received, every 4 weeks, FA 200 mg/m(2) followed by a 400-mg/m(2) 5-FU bolus injection, then a 600-mg/m(2) continuous infusion of 5-FU on days 1 and 2 every 2 weeks administered alternately with irinotecan (180 mg/m(2) on day 1) and oxaliplatin (85 mg/m(2) on day 15). Arm OC (30 patients) received oxaliplatin 85 mg/m(2) and irinotecan 200 mg/m(2) every 3 weeks.

RESULTS

In an intent-to-treat analysis, two partial responses lasting 10.7 and 16 months were observed with the tritherapy regimen, and seven (median duration, 11 months; range, 10.6 to 11.4 months) were observed with the bitherapy regimen. Median progression-free and overall survival times were 8.2 and 9.8 months, respectively, in the FC/FO arm and 8.5 and 12.3 months, respectively, in the OC arm. Main grade 3/4 toxicities were, respectively, neutropenia, 53% and 47%; febrile neutropenia, 13% and 3%; diarrhea, 19% and 10%; vomiting, 6% and 13%; and neurosensory toxicity, 3% and 3%. No treatment-related deaths occurred.

CONCLUSION

The every-3-weeks OC combination is safe and active in advanced 5-FU-resistant CRC patients. The lower activity data seen with the tritherapy regimen may be related to the lower dose intensities of irinotecan and oxaliplatin in this schedule.

Polymorphisms of metabolizing enzymes and transporter proteins involved in the clearance of anticancer agents

BACKGROUND

The efficacies and toxicities of anticancer agents vary greatly among patients. This is attributable to the activities of drug-metabolizing enzymes and membrane transporters, primarily determined by polymorphisms of the functions of genes encoding these proteins.

DESIGN

We reviewed the available literature on drug-metabolizing enzymes and membrane transporters, especially their physiological functions, genetic and functional polymorphisms, and involvement in metabolism, pharmacokinetics and toxicity of anticancer agents.

RESULTS

Nine enzymes metabolizing anticancer agents have been shown to have genetic polymorphisms: dihydropyrimidine dehydrogenase, cytochrome P450, NAD(P)H:quinone oxidoreductase 1, N-acetyltransferase 2, thiopurine methyltransferase, glutathione S-transferase, and uridine diphosphate glucuronosyltransferase. Decreased activities of these proteins can cause not only inherited metabolic disorders, but also extraordinarily severe toxicity in cancer patients given chemothearpy. Transporter proteins mediate cellular uptake and secretion of organic anions and cations. These proteins have recently been shown to play critical roles in the clearance of anticancer agents, although relations between patients' genetics backgrounds and the clinical significance of drug actions are poorly understood.

CONCLUSIONS

Further studies should be focused on dosing and selection of anticancer agents, based on the type and extent of metabolic variation among individuals, in order to avoid adverse reactions and therapeutic failure.

Pharmacogenetics and cancer therapy

Pharmacogenetics is the study of how genetic variations affect drug response. These variations can affect a patient's response to cancer drugs, for which there is usually a fine line between a dosage that has a therapeutic effect and one that produces toxicity. Gaining better insight into the genetic elements of both the patient and the tumour that affect drug efficacy will eventually allow for individualized dosage determination and fewer adverse effects.