A pharmacokinetic and pharmacodynamic analysis of CPT-11 and its active metabolite SN-38

UGT1A1 Testing in Breast Cancer: should it become routine practice in patients treated with antibody-drug conjugates?

The use of genetic testing to personalize therapeutic strategies in cancer is rapidly evolving and thus changing the landscape of treatment of oncologic patients. The UGT1A1 gene is an important component for the metabolism and glucoronidation of certain drugs, including irinotecan and sacituzumab govitecan (SG); therefore, various UGT1A1 polymorphisms leading to decreased function of the UGT1A1 enzyme may lead to increased risk of treatment-related side effects. Testing for UGT1A1 polymorphism is not routinely adopted in clinical practice; that is due to the lack of concise studies and recommendations concerning the clinical relevance of this test and its impact on the quality of life of cancer patients. The knowledge regarding UGT1A1 polymorphism and its clinical relevance will be reviewed in this article, as well as the published literature on the association between UGT1A1 polymorphism and the toxicity risk of irinotecan as well as sacituzumab govitecan. The current recommendations and guidelines on UGT1A1 testing will be discussed in detail in the hopes of providing guidance to oncologists in their clinical practice.

All You Need to Know About UGT1A1 Genetic Testing for Patients Treated With Irinotecan: A Practitioner-Friendly Guide

Irinotecan is an anticancer agent widely used for the treatment of solid tumors, including colorectal and pancreatic cancers. Severe neutropenia and diarrhea are common dose-limiting toxicities of irinotecan-based therapy, and UGT1A1 polymorphisms are one of the major risk factors of these toxicities. In 2005, the US Food and Drug Administration revised the drug label to indicate that patients with UGT1A1*28 homozygous genotype should receive a decreased dose of irinotecan. However, UGT1A1*28 testing is not routinely used in the clinic, and specific reasons include lack of access to concise information on this wide issue as well as mixed recommendations by regulatory and professional entities. To assist oncologists in assessing whether and when to use UGT1A1 genetic testing in patients receiving irinotecan-based therapies, this article provided (1) essential knowledge of UGT1A1 polymorphisms; (2) an update on the impact of UGT1A1 polymorphisms on efficacy and toxicity of contemporary irinotecan-based regimens; (3) dosing adjustments based upon the UGT1A1 genotypes, and (4) recommendations from currently available guidelines from the US and international scientific consortia and major oncology societies.

Optimal Sampling Strategies for Irinotecan (CPT-11) and its Active Metabolite (SN-38) in Cancer Patients

Irinotecan (CPT-11) is an anticancer agent widely used in the treatment of a variety of adult solid tumors. The objective of this study was to develop an optimal sampling strategy model that accurately estimates pharmacokinetic parameters of CPT-11 and its active metabolite, SN-38. This study included 221 patients with advanced solid tumors or lymphoma receiving CPT-11 single or combination therapy with 5-fluorouracil (5-FU)/leucovorin (LV) (FOLFIRI) plus bevacizumab from 4 separate clinical trials. Population pharmacokinetic analysis of CPT-11 and SN-38 was performed by non-linear mixed effects modeling. The optimal sampling strategy model was developed using D-optimality with expected distribution approach. The pharmacokinetic profiles of CPT-11 and SN-38 were best described by a 3- and 2-compartment model, respectively, with first-order elimination. Body surface area and co-administration with 5-FU/LV plus bevacizumab were significant covariates (p < 0.01) for volumes of the central compartment of CPT-11 and SN-38, and clearance of CPT-11. Pre-treatment total bilirubin and co-administration with 5-FU/LV and bevacizumab were significant covariates (p < 0.01) for clearance of SN-38. Accurate and precise predictive performance (r² > 0.99, -2 < bias (%ME) < 0, precision (% RMSE) < 12) of both CPT-11 and SN-38 was achieved using: (i) 6 fixed sampling times collected at 1.5, 3.5, 4, 5.75, 22, 23.5 hours post-infusion; or (ii) 1 fixed time and 2 sampling windows collected at 1.5, [3-5.75], [22-23.5] hours post-infusion. The present study demonstrates that an optimal sampling design with three blood samples achieves accurate and precise pharmacokinetic parameter estimates for both CPT-11 and SN-38.

Shengjiang Xiexin Decoction Alters Pharmacokinetics of Irinotecan by Regulating Metabolic Enzymes and Transporters: A Multi-Target Therapy for Alleviating the Gastrointestinal Toxicity

Shengjiang Xiexin decoction (SXD), a classic traditional Chinese medical formula chronicled in Shang Han Lun, is used in modern clinical practice to decrease gastrointestinal toxicity induced by the chemotherapeutic drug irinotecan (CPT-11). In this study, the effect of SXD on the pharmacokinetics of CPT-11 and its active metabolites (SN-38 and SN-38G), and the underlying mechanisms were further examined. An ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated for the simultaneous quantification of CPT-11, SN-38, and SN-38G in the plasma, bile, liver, intestine, and intestinal contents of control and SXD-pre-treated rats after intravenous administration of CPT-11. SXD pretreatment increased the area under the curve (AUC) and the initial plasma concentration (C₀) of CPT-11 but decreased the plasma clearance (CL). The AUC and the maximum plasma concentration (C_max) of SN-38 decreased, whereas the C_max of SN-38G increased. Compared with that of the control group, the biliary excretion of CPT-11, SN-38, and SN-38G was inhibited. The CPT-11, SN-38, and SN-38G concentrations in the liver, intestine, and intestinal contents were different between the two groups. Furthermore, the hepatic expression of multidrug resistance-associated protein-2 (Mrp-2), P-glycoprotein (P-gp), and carboxylesterase 2 (CES2) was significantly down-regulated by SXD, while the hepatic and jejunal uridine diphosphate (UDP)-glucuronosyltransferase 1A1 (UGT1A1) expression was elevated. The hydrolysis of CPT-11 to SN-38 by CES and the glucuronidation of SN-38 to SN-38G by UGT were affected by liver and jejunum S9 fractions from rats pre-treated with SXD. Therefore, this study demonstrated for the first time that SXD could alter the pharmacokinetics of CPT-11 and its metabolites to alleviate CPT-11-induced diarrhea. And the underlying mechanism of drug interaction between CPT-11 and SXD involves decreasing hepatic Mrp-2 and P-gp expression and altering the activities of CES and UGT.

Alpha-tocopheryl polyethylene glycol succinate-emulsified poly(lactic-co-glycolic acid) nanoparticles for reversal of multidrug resistance in vitro

Multidrug resistance (MDR) is one of the factors in the failure of anticancer chemotherapy. In order to enhance the anticancer effect of P-glycoprotein (P-gp) substrates, inhibition of the P-gp efflux pump on MDR cells is a good tactic. We designed novel multifunctional drug-loaded alpha-tocopheryl polyethylene glycol succinate (TPGS)/poly(lactic-co-glycolic acid) (PLGA) nanoparticles (TPGS/PLGA/SN-38 NPs; SN-38 is 7-ethyl-10-hydroxy-camptothecin), with TPGS-emulsified PLGA NPs as the carrier and modulator of the P-gp efflux pump and SN-38 as the model drug. TPGS/PLGA/SN-38 NPs were prepared using a modified solvent extraction/evaporation method. Physicochemical characterizations of TPGS/PLGA/SN-38 NPs were in conformity with the principle of nano-drug delivery systems (nDDSs), including a diameter of about 200 nm, excellent spherical particles with a smooth surface, narrow size distribution, appropriate surface charge, and successful drug-loading into the NPs. The cytotoxicity of TPGS/PLGA/SN-38 NPs to MDR cells was increased by 3.56 times compared with that of free SN-38. Based on an intracellular accumulation study relative to the time-dependent uptake and efflux inhibition, we suggest novel mechanisms of MDR reversal of TPGS/PLGA NPs. Firstly, TPGS/PLGA/SN-38 NPs improved the uptake of the loaded drug by clathrin-mediated endocytosis in the form of unbroken NPs. Simultaneously, intracellular NPs escaped the recognition of P-gp by MDR cells. After SN-38 was released from TPGS/PLGA/SN-38 NPs in MDR cells, TPGS or/and PLGA may modulate the efflux microenvironment of the P-gp pump, such as mitochondria and the P-gp domain with an ATP-binding site. Finally, the controlled-release drug entered the nucleus of the MDR cell to induce cytotoxicity. The present study showed that TPGS-emulsified PLGA NPs could be functional carriers in nDDS for anticancer drugs that are also P-gp substrates. More importantly, to enhance the therapeutic effect of P-gp substrates, this work might provide a new insight into the design of pharmacologically inactive excipients that can serve as P-gp modulators instead of drugs that are P-gp inhibitors.

Pharmacokinetic and pharmacogenetic determinants of the activity and toxicity of irinotecan in metastatic colorectal cancer patients

This study aims at establishing relationships between genetic and non-genetic factors of variation of the pharmacokinetics of irinotecan and its metabolites; and also at establishing relationships between the pharmacokinetic or metabolic parameters and the efficacy and toxicity of irinotecan. We included 49 patients treated for metastatic colorectal cancer with a combination of 5-fluorouracil and irinotecan; a polymorphism in the UGT1A1 gene (TA repeat in the TATA box) and one in the CES2 gene promoter (830C>G) were studied as potential markers for SN-38 glucuronidation and irinotecan activation, respectively; and the potential activity of CYP3A4 was estimated from cortisol biotransformation into 6β-hydroxycortisol. No pharmacokinetic parameter was directly predictive of clinical outcome or toxicity. The AUCs of three important metabolites of irinotecan, SN-38, SN-38 glucuronide and APC, were tentatively correlated with patients' pretreatment biological parameters related to drug metabolism (plasma creatinine, bilirubin and liver enzymes, and blood leukocytes). SN-38 AUC was significantly correlated with blood leukocytes number and SN-38G AUC was significantly correlated with plasma creatinine, whereas APC AUC was significantly correlated with plasma liver enzymes. The relative extent of irinotecan activation was inversely correlated with SN-38 glucuronidation. The TATA box polymorphism of UGT1A1 was significantly associated with plasma bilirubin levels and behaved as a significant predictor for neutropoenia. The level of cortisol 6β-hydroxylation predicted for the occurrence of diarrhoea. All these observations may improve the routine use of irinotecan in colorectal cancer patients. UGT1A1 genotyping plus cortisol 6β-hydroxylation determination could help to determine the optimal dose of irinotecan.

[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.

Involvement of UDP-glucuronosyltransferase activity in irinotecan-induced delayed-onset diarrhea in rats

We assessed the involvement of UDP-glucuronosyltransferase (UGT) activity in episodes of irinotecan hydrochloride (CPT-11)-induced delayed-onset diarrhea using a mutant rat strain with an inherited deficiency of UGT1A (Gunn rats). Gunn rats exhibited severe diarrhea after the intravenous administration of CPT-11 at a dose of 20 mg/kg, whereas Wistar rats did not. In the epithelium of the small intestine and cecum in Gunn rats, the shortening of villi, degeneration of crypts, and destruction of the nucleus were observed. The AUC, MRT, and t (1/2) of CPT-11, and the AUC of 7-ethyl-10-hydroxycamptothecin (SN-38) in plasma were, respectively, 1.6-fold, 1.5-fold, 1.7-fold, and 6.5-fold higher, and the cumulative biliary excretion rate of SN-38 was 2.3-fold higher, in Gunn rats than Wistar rats. SN-38 glucuronide excreted via bile in Wistar rats was not de-conjugated in the small intestinal lumen. The SN-38 AUC values in small intestinal tissues were also 5.0 to 5.8-fold higher in Gunn rats than Wistar rats. In conclusion, Gunn rats developed severe delayed-onset diarrhea after i.v. administration of CPT-11 at a much lower dose. Severe intestinal impairments would be induced in Gunn rats through exposure to SN-38 at high levels for a long period mainly via the intestinal lumen and partially via the bloodstream. These results clarified that the deficiency of UGT activity contributed greatly to the induction of the CPT-11-induced delayed-onset diarrhea and epithelial impairment in the intestine. In the clinic, great care is needed when using chemotherapy with CPT-11 in patients with poor UGT activity.

The role of chrysin and the ah receptor in induction of the human UGT1A1 gene in vitro and in transgenic UGT1 mice

The flavonoid chrysin is an important dietary substance and induces UGT1A1 protein expression in cell culture. As a representative of the class of dietary flavonoids, clinical investigations have been considered as a means of inducing hepatic UGT1A1 expression. We demonstrate the necessity of a xenobiotic response element (XRE) in support of chrysin induction of UGT1A1 in the human hepatoma cell line HepG2. Receptor binding assays confirm that chrysin is a ligand for the Ah receptor by competition with [3H]2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, key differences in Ah receptor recognition and activation of UGT1A1 by chrysin exist when compared with classical mechanisms of UGT1A1 induction by TCDD. Ah receptor degradation, an indicator of Ah receptor activation, does not occur after chrysin treatment, and chrysin cannot transactivate the Ah receptor in a TCDD-dependent fashion. Knock-down of the Ah receptor by siRNA indicates that chrysin uses the Ah receptor in conjunction with other factors through MAP kinase signaling pathways to maximally induce UGT1A1. Most importantly, oral treatment of chrysin to transgenic mice that express the human UGT1 locus is unable to induce UGT1A1 expression in either the small intestine or liver.

CONCLUSION

Although the implications for chrysin as an atypical agonist of the Ah receptor are intriguing at the molecular level, the relevance of chrysin-induced transcription for the purpose of clinical therapies or to regulate phase 2-dependent glucuronidation is questionable given the lack of in vivo regulation of human UGT1A1 by chrysin in a transgenic animal model.

Role of pharmacogenetics in irinotecan therapy

In the treatment of advanced colorectal cancer, irinotecan has become one of the most important drugs, despite its sometimes unpredictable adverse effects. To understand why some patients experience severe adverse effects (diarrhea and neutropenia), while others do not, the metabolic pathways of this drug have to be unraveled in detail. Individual variation in expression of several phase I and phase II metabolizing enzymes and ABC-transporters involved in irinotecan metabolism and excretion, at least partly explains the observed pharmacokinetic interpatient variability. Although the difference in expression-level of these proteins to a certain amount is explained by physiologic and environmental factors, the presence of specific genetic determinants also does influence their expression and function. In this review, the role of genetic polymorphisms in the main enzyme-systems (carboxylesterase, cytochrome P450 3A, and uridine diphosphate-glucuronosyltransferase) and ABC-transporters (ABCB1, ABCC2, and ABCG2) involved in irinotecan metabolism, are discussed. Since at this moment the field of pharmacogenetics and pharmacogenomics is rapidly expanding and simultaneously more rapid and cost-effective screening methods are emerging, a wealth of future data is expected to enrich our knowledge of the genetic basis of irinotecan metabolism. Eventually, this may help to truly individualize the dosing of this (and other) anti-cancer agent(s), using a personal genetic profile of the most relevant enzymes for every patient.

Pharmacokinetics and pharmacodynamics of irinotecan and its metabolites from plasma and saliva data in patients with metastatic digestive cancer receiving Folfiri regimen

PURPOSE

Irinotecan is extensively metabolized into at least four compounds and previous pharmacokinetic-pharmacodynamic studies have given varying results. We hypothesized that saliva, a noninvasive, safe and painless biological sampling process, could be a good predictor of the behavior of irinotecan and its metabolites.

METHODS

Thirty-five patients with metastatic digestive cancer were treated with a Folfiri regimen every 2 weeks. The irinotecan-administered dose was 180 mg/m(2); 17 patients participated in a dose-escalating study. Irinotecan and its metabolites (SN-38, SN-38G, APC, NPC) were quantified in plasma and saliva by high-performance liquid chromatography with fluorescence detection.

RESULTS

The mean irinotecan systemic clearance and steady-state volume of distribution values were 14.3 l/h/m(2) and 211 l/m(2), respectively. The intrapatient variability (22-28%) was far lower than the interindividual variability (33-88%). Age and weight were the two physiological parameters that influenced drug disposition. For irinotecan, SN-38, APC and NPC, similar pharmacokinetic profiles were observed from plasma and saliva data. The saliva/plasma AUC ratios averaged 1 for irinotecan, 0.3 for SN-38, 0.17 for APC and 0.27 for NPC. Neutropenia, diarrhea and nausea were the main toxicities encountered. From both plasma and saliva data, the percentage decrease in neutrophil count appeared to be related to irinotecan and SN-38 AUCs.

CONCLUSIONS

All these findings provide a rationale for an individual adaptation of irinotecan dosing. In case of difficult venous access, the titration of irinotecan and of its active metabolite SN-38 in saliva may prove relevant.

Human Multidrug Resistance Associated Protein 4 Confers Resistance to Camptothecins

PURPOSE

The multidrug resistance associated protein (MRP) 4 is a member of the adenosine triphosphate (ATP)-binding cassette transporter family. Camptothecins (CPTs) have shown substantial anticancer activity against a broad spectrum of tumors by inhibiting DNA topoisomerase I, but tumor resistance is one of the major reasons for therapeutic failure. P-glycoprotein, breast cancer resistance protein, MRP1, and MRP2 have been implicated in resistance to various CPTs including CPT-11 (irinotecan), SN-38 (the active metabolite of CPT-11), and topotecan. In this study, we explored the resistance profiles and intracellular accumulation of a panel of CPTs including CPT, CPT-11, SN-38, rubitecan, and 10-hydroxy-CPT (10-OH-CPT) in HepG2 cells with stably overexpressed human MRP4. Other anticancer agents such as paclitaxel, cyclophosphamide, and carboplatin were also included.

METHODS

HepG2 cells were transfected with an empty vehicle plasmid (V/HepG2) or human MRP4 (MRP4/HepG2). The resistance profiles of test drugs in exponentially growing V/HepG2 and MRP4/HepG2 cells were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) assay with 4 or 48 h exposure time of the test drug in the absence or presence of various MRP4 inhibitors. The accumulation of CPT-11, SN-38, and paclitaxel by V/HepG2 and MRP4/HepG2 cells was determined by validated high-performance liquid chromatography methods.

RESULTS

Based on the resistance folds from the MTT assay with 48 h exposure time of the test drug, MRP4 conferred resistance to CPTs tested in the order 10-OH-CPT (14.21) > SN-38 carboxylate (9.70) > rubitecan (9.06) > SN-38 lactone (8.91) > CPT lactone (7.33) > CPT-11 lactone (5.64) > CPT carboxylate (4.30) > CPT-11 carboxylate (2.68). Overall, overexpression of MRP4 increased the IC50 values 1.78- to 14.21-fold for various CPTs in lactone or carboxylate form. The resistance of MRP4 to various CPTs tested was significantly reversed in the presence of dl-buthionine-(S,R)-sulfoximine (BSO, a gamma-glutamylcysteine synthetase inhibitor), MK571, celecoxib, or diclofenac (all MRP4 inhibitors). In addition, the accumulation of CPT-11 and SN-38 over 120 min in MRP4/HepG2 cells was significantly reduced compared to V/HepG2 cells, whereas the addition of celecoxib, MK571, or BSO significantly increased their accumulation in MRP4/HepG2 cells. There was no significant difference in the intracellular accumulation of paclitaxel in V/HepG2 and MRP4/HepG2 cells, indicating that P-glycoprotein was not involved in the observed resistance to CPTs in this study. MRP4 also conferred resistance to cyclophosphamide and this was partially reversed by BSO. However, MRP4 did not increase resistance to paclitaxel, carboplatin, etoposide (VP-16), 5-fluorouracil, and cyclosporine.

CONCLUSIONS

Human MRP4 rendered significant resistance to cyclophosphamide, CPT, CPT-11, SN-38, rubitecan, and 10-OH-CPT. CPT-11 and SN-38 are substrates for MRP4. Further studies are needed to explore the role of MRP4 in resistance, toxicity, and pharmacokinetics of CPTs and cyclophosphamide.

In vitro conversion of irinotecan to SN-38 in human plasma

Irinotecan is an active cytotoxic agent for various cancers, and is converted to SN-38, its most active metabolite, by carboxylesterase converting enzyme (CCE) in vivo. Although the primary metabolic site is in the liver, ex vivo studies have proven that irinotecan is also converted to SN-38 in intestines, plasma and tumor tissues. The present study attempted to elucidate the in vitro conversion efficiency in human plasma, and to examine possible inter-individual variability and its clinical significance. Plasma samples were taken from 57 patients with lung cancer, 3 patients with benign pulmonary diseases and 9 healthy volunteers. After addition of 157 mM irinotecan to plasma, time courses of SN-38 concentration, measured by high-performance liquid chromatography (HPLC), were investigated. All subjects showed linear increase in SN-38 concentration during the first 60-min period, followed by a plateau. Mean and standard deviation of the conversion rate in the first 60 min were 515.9 +/- 50.1 pmol/ml/h (n = 69), with a coefficient of variation of 0.097. Although most of the subjects showed comparable conversion rates, 3 subjects had significantly higher conversion rates. In conclusion, the results of this study suggest that the enzyme activity of CCE in human plasma may show inter-individual variability.

Pharmacology of cytotoxic agents: a helpful tool for building dose adjustment guidelines in the elderly

Aging is associated with multidimensional changes, including alterations in physiological functions, co-morbidities and poly-medications. These changes may lead to modifications in the absorption, distribution, metabolism and excretion of drugs. The lack of a scientific basis for optimal drug dosing in the elderly is a major problem. The development and validation of guidelines are therefore essential to improve treatment administration and monitoring in elderly patients. Even though it has been widely demonstrated that standard therapies used in adults may be of great benefit in the elderly, there may be a higher incidence of toxicity. This could be avoided by using dosage individualization based on a sound knowledge of the physiological factors implicated in the pharmacokinetic (PK) characteristics of the drugs administered and in their observed pharmacodynamic (PD) effects in each patient. The so-called "population modeling" approach renders such studies feasible by allowing the analysis of PK-PD relationships from sparse observational data.

Model of chemotherapy-induced myelosuppression with parameter consistency across drugs

PURPOSE

To develop a semimechanistic pharmacokinetic-pharmacodynamic model describing chemotherapy-induced myelosuppression through drug-specific parameters and system-related parameters, which are common to all drugs.

PATIENTS AND METHODS

Patient leukocyte and neutrophil data after administration of docetaxel, paclitaxel, and etoposide were used to develop the model, which was also applied to myelosuppression data from 2'-deoxy-2'-methylidenecytidine (DMDC), irinotecan (CPT-11), and vinflunine administrations. The model consisted of a proliferating compartment that was sensitive to drugs, three transit compartments that represented maturation, and a compartment of circulating blood cells. Three system-related parameters were estimated: baseline, mean transit time, and a feedback parameter. Drug concentration-time profiles affected the proliferation of sensitive cells by either an inhibitory linear model or an inhibitory E(max) model. To evaluate the model, system-related parameters were fixed to the same values for all drugs, which were based on the results from the estimations, and only drug-specific parameters were estimated. All modeling was performed using NONMEM software.

RESULTS

For all investigated drugs, the model successfully described myelosuppression. Consecutive courses and different schedules of administration were also well characterized. Similar system-related parameter estimates were obtained for the different drugs and also for leukocytes compared with neutrophils. In addition, when system-related parameters were fixed, the model well characterized chemotherapy-induced myelosuppression for the different drugs.

CONCLUSION

This model predicted myelosuppression after administration of one of several different chemotherapeutic drugs. In addition, with fixed system-related parameters to proposed values, and only drug-related parameters estimated, myelosuppression can be predicted. We propose that this model can be a useful tool in the development of anticancer drugs and therapies.

Factors affecting the pharmacokinetics of CPT-11: the body mass index, age and sex are independent predictors of pharmacokinetic parameters of CPT-11

This study was conducted to describe the relationship between pharmacokinetics of CPT-11 and its active metabolite SN-38, and clinical values with special emphasis on the influence of relative weight referring to the appropriateness of a conventional dose adjustment method by body surface area (BSA). Thirty-six patients received 100 mg/m2 of CPT-11 intravenously over 90 min. Body Mass Index (BMI) was used as a measure of relative weight which is calculated from the equation: BMI=weight(kg)/[height(m)]2. The area under the concentration-time curve (AUC) of CPT-11 was significantly correlated with sex, age, poorer creatinine clearance and indocyanine green retention test (ICG). The peak plasma concentration (Cmax) of CPT-11 was significantly correlated with sex a larger BMI, BSA and age. The AUC of SN-38 was significantly correlated with ICG. The volume of distribution at steady state of CPT-11 inversely correlated with BMI. Multiple regression analysis revealed that the best fitting model with significant independent predictors for AUC of CPT-11 included age and sex (F=6.93, R2=0.29). That of Cmax of CPT-11 included sex and BMI (F=8.96, R2=0.35). The only independent predictor of AUC of SN-38 was ICG (F=7.75, R2=0.19). These results indicated that several factors affect pharmacological behaviors of CPT-11 even in patients with normal organ functions. The dose modification method based solely on BSA is not sufficient to reduce interpatient variability of cancer chemotherapy. The influence of relative weight, sex and age on pharmacokinetics/pharmacodynamics should be taken into consideration in every pharmacological approach to establish the ideal dose modification method.

Risk factors determining chemotherapeutic toxicity in patients with advanced colorectal cancer

Antitumour therapy in advanced colorectal cancer has limited efficacy. For decades, fluorouracil has been the main anticancer drug for the treatment of colorectal cancer. Recently, however, new agents have been introduced: raltitrexed, irinotecan and oxaliplatin. Currently, the dosage for an individual patient is calculated from the estimated body surface area of the patient. Toxicity, however, frequently necessitates decreasing the dosage, extending the dose interval or even discontinuing treatment. Risk factors with predictive value for toxicity have been identified in several studies. These risk factors are often determined by the pharmacokinetic and pharmacodynamic properties of the drug. In this review, the risk factors for toxicity of the cytotoxic agents used in the treatment of advanced colorectal cancer are considered. For fluorouracil, age, gender, performance status, genetic polymorphism of dihydropyridine dehydrogenase, drug administration schedule, circadian rhythm of plasma concentrations, history of previous chemotherapy-related diarrhoea, xerostomia, low neutrophil levels, and drug-drug interactions have been identified as affecting chemotherapeutic toxicity. For raltitrexed, gender and renal and hepatic impairment, and for oxaliplatin, renal impairment and circadian rhythm of plasma concentrations, respectively, can be considered as risk factors for toxicity. In addition, age, performance status, bilirubinaemia, genetic polymorphism of uridine 5'-diphosphate-glucuronyltransferase-1A1 and drug administration schedule have been shown to be related to irinotecan toxicity. The available literature suggests that dose adjustment based on these risk factors can be used to individualise the dose in order to decrease toxicity and to improve the therapeutic index. This also applies to therapeutic drug monitoring, which has been shown to be effective controlling the toxicity of fluorouracil in some studies. Future research is warranted to assess the potential advantage of dose individualisation of chemotherapy founded on risk factors, over direct dose calculation from the estimated body surface area, with regard to toxicity, therapeutic index, and quality of life, in patients with advanced colorectal cancer.

Simple and rapid determination of irinotecan and its metabolite SN-38 in plasma by high-performance liquid-chromatography: application to clinical pharmacokinetic studies

Irinotecan (CPT-11) is an anticancer agent widely employed in the treatment of colorectal carcinoma. A simple, rapid and sensitive high-performance liquid chromatographic method for the simultaneous determination of CPT-11 and its metabolite SN-38 in plasma, and their preliminary clinical pharmacokinetics are described. Both deproteinisation of plasma specimens (100 microl) and addition of the internal standard, camptothecin (CPT), are achieved by incorporating to samples 100 microl of a solution of CPT (1 microg/ml) in acetonitrile-1 mM orthophosphoric acid (90:10); 200 microl of this acidified acetonitrile solution, drug-free, is also added to accomplish complete deproteinisation: this procedure reduces sample preparation time to a minimum. After deproteinisation, samples are treated with potassium dihydrogenphosphate (0.1 M) and injected into a Nucleosil C18 (5 microm, 250 x 4.0 mm) column. Mobile phase consists of potassium dihydrogenphosphate (0.1 M)-acetonitrile (67:33), at a flow-rate of 1 ml/min. CPT-11, SN-38 and CPT are detected by fluorescence with excitation wavelength set at 228 nm and emission wavelengths of CPT-11, SN-38 and CPT fixed, respectively, at 450, 543 and 433 nm. The limits of quantitation for CPT-11 and SN-38 are 1.0 and 0.5 ng/ml, respectively. This method shows good precision: the within day relative standard deviation (RSD) for CPT-11 (1-10000 ng/ml) is 5.17% (range 2.15-8.27%) and for SN-38 (0.5-400 ng/ml) is 4.33% (1.32-7.78%); the between-day RSDs for CPT-11 and SN-38, in the previously described ranges, are 6.82% (5.03-10.8%) and 4.94% (2.09-9.30%), respectively. Using this assay, plasma pharmacokinetics of CPT-11, SN-38 and its glucuronidated form, SN-38G, have been determined in one patient receiving 200 mg/m2 of CPT-11 as a 90 min intravenous infusion. The peak plasma concentration of CPT-11 at the end of the infusion is 3800 ng/ml. Plasma decay is biphasic with a terminal half-life of 11.6 h. The volume of distribution at steady state (Vss) is 203 l/m2, and the total body clearance (Cl) is 14.8 l/h x m2. The maximum concentrations of SN-38 and SN-38G reach 28.9 and 151 ng/ml, respectively.

Phase I and pharmacologic study of irinotecan administered as a 96-hour infusion weekly to adult cancer patients

PURPOSE

We conducted a phase I and pharmacologic study of a weekly 96-hour infusion of irinotecan to determine the maximum-tolerated dose, define the toxicity profile, and characterize the clinical pharmacology of irinotecan and its metabolites.

PATIENTS AND METHODS

In 26 adult patients with solid tumors, the duration and dose rate of infusion were escalated in new patients until toxicity was observed.

RESULTS

In 11 patients who were treated with irinotecan at 12.5 mg/m(2)/d for 4 days weekly for 2 of 3 weeks, dose-limiting grade 3 diarrhea occurred in three patients and grade 3 thrombocytopenia occurred in two patients. The recommended phase II dose is 10 mg/m(2)/d for 4 days given weekly for 2 of 3 weeks. At this dose, the steady-state plasma concentration (Css) of total SN-38 (the active metabolite of irinotecan) was 6.42 +/- 1.10 nmol/L, and the Css of total irinotecan was 28.60 +/- 17.78 nmol/L. No patient experienced grade 3 or 4 neutropenia during any cycle. All other toxicities were mild to moderate. The systemic exposure to SN-38 relative to irinotecan was greater than anticipated, with a molar ratio of the area under the concentration curve (AUC) of SN-38 to irinotecan of 0.24 +/- 0.08. One objective response lasting 12 months in duration was observed in a patient with metastatic colon cancer.

CONCLUSION

The recommended phase II dose of irinotecan of 10 mg/m(2)/d for 4 days weekly for 2 of 3 weeks was extremely well tolerated. Further efficacy testing of this pharmacologic strategy of administering intermittent low doses of irinotecan is warranted.

Clinical applications of the camptothecins

The camptothecin topoisomerase I-targeting agents are new class of antitumor drugs with demonstrated clinical activity in human malignancies, such as colorectal cancer and ovarian cancer. Currently, irinotecan and topotecan are the most widely used camptothecin analogs in clinical use and clinical trials are ongoing to better characterize their spectra of clinical activity, to determine their optimal schedules of administration and to define their use in combination with other chemotherapeutic agents. Newer camptothecin analogs in clinical development, such as 9-aminocamptothecin, 9-nitrocamptothecin, GI147211 and DX-8951f, are also being studied to determine if they have improved toxicity and efficacy profiles compared with existing analogs. Other potential clinical applications include the use of camptothecin derivatives as radiation sensitizers or as antiviral agents. The successful development of the camptothecins as antitumor agents highlights the importance of topoisomerase I as a target for cancer chemotherapy.

Clinical pharmacology of camptothecins

Camptothecins (CPTs) are a unique class of chemotherapeutic agent which inhibit DNA synthesis by inhibiting topoisomerase I activity. Structure-activity studies on the original CPT alkaloid led to the development of the new analogues irinotecan (CPT-11), topotecan, and 9-aminocamptothecin, which have improved water solubility and lower toxicity. CPT analogues exhibit interesting pharmacokinetic/pharmacodynamic and metabolic properties that are of major research and clinical interest. This review describes the clinical pharmacology of these 3 CPT analogues. Specific areas such as absorption after extravascular administration, pharmacokinetic/pharmacodynamic variability, metabolism, and administration in special populations are discussed.

A risk-benefit assessment of irinotecan in solid tumours

Irinotecan is a water-soluble camptothecin analogue. Its cytotoxicity effects are exerted through interaction with the topoisomerase I-DNA complex, eventually leading to cell death. In preclinical studies, irinotecan has demonstrated a broad spectrum of activity in vitro and in vivo, and synergistic effects have been observed when it is administered in combination with other antineoplastic agents. Phase I studies of irinotecan conducted in Europe, Japan and the US have provided useful information on optimal dosage and scheduling, as well as thorough evaluation of the toxicity profile of the drug. Phase II and III trials utilising either irinotecan alone or in innovative combinations with other drugs are currently in progress. Available data indicate that irinotecan alone or in combination with other cytotoxic agents has therapeutic potential in several types of malignancy, including colorectal, lung, ovarian, cervical and gastric cancers and non-Hodgkin's lymphoma. It is the first drug since fluorouracil to possess consistent antitumour activity against metastatic colorectal cancer. The principal toxicities associated with irinotecan are diarrhoea and leucopenia. Effective strategies have been developed to circumvent both the early- and delayed-onset diarrhoea induced by irinotecan, thus allowing safer delivery of this promising agent in the clinical setting.

Oral versus intraperitoneal administration of irinotecan in the treatment of human neuroblastoma in nude mice

The present study evaluated the plasma pharmacokinetics of irinotecan (CPT-11) and its effects against a human neuroblastoma in xenograft, given by different administration routes. One-third of the LD50 was administered either intraperitoneally (59 mg/kg mouse weight (MW)) or orally (404 mg/kg MW) to nude mice. The plasma levels of CPT-11 and its active metabolite SN-38 decreased rapidly when CPT-11 was administered intraperitoneally, but remained relatively high for 4-8 h after oral administration. Then, a human neuroblastoma xenograft was inoculated in another set of 21 nude mice. When the estimated tumor weight reached 150-200 mg, CPT-11 was administered in the total LD50 either intraperitoneally or orally in three doses at 4-day intervals (q4d x3) to the mice in each experimental group. Oral administration was found to be superior to intraperitoneal injection in terms of tumor inhibition and to be an effective route for CPT-11 administration in the treatment of human neuroblastoma in nude mice.

New chemotherapeutic agents for the treatment of non-small cell lung cancer: the Japanese experience

Non-small cell lung cancer (NSCLC) is refractory to systemic chemotherapy, compared with small cell lung cancer. Until recently, only five drugs--cisplatin, vindesine, mitomycin, ifosfamide, and vinblastine--could produce overall response rates of 15% against NSCLC. However, recent efforts have contributed to the development of new drugs with activity against NSCLC, including irinotecan hydrochloride (CPT-11), paclitaxel, docetaxel, vinorelbine, and gemcitabine. Combination chemotherapy against NSCLC using these agents has demonstrated high response rates. In Japan, various combination chemotherapy and combined-modality regimens employing CPT-11 have been evaluated for their efficacy. Randomized controlled trials to establish new state-of-the-art treatments for NSCLC are ongoing.

Clinical pharmacokinetics of irinotecan

This article reviews the clinical pharmacokinetics of a water-soluble analogue of camptothecin, irinotecan [CPT-11 or 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxy-camptoth eci n]. Irinotecan, and its more potent metabolite SN-38 (7- ethyl-10-hydroxy-camptothecin), interfere with mammalian DNA topoisomerase I and cancer cell death appears to result from DNA strand breaks caused by the formation of cleavable complexes. The main clinical adverse effects of irinotecan therapy are neutropenia and diarrhoea. Irinotecan has shown activity in leukaemia, lymphoma and the following cancer sites: colorectum, lung, ovary, cervix, pancreas, stomach and breast. Following the intravenous administration of irinotecan at 100 to 350 mg/m2, mean maximum irinotecan plasma concentrations are within the 1 to 10 mg/L range. Plasma concentrations can be described using a 2- or 3-compartment model with a mean terminal half-life ranging from 5 to 27 hours. The volume of distribution at steady-state (Vss) ranges from 136 to 255 L/m2, and the total body clearance is 8 to 21 L/h/m2. Irinotecan is 65% bound to plasma proteins. The areas under the plasma concentration-time curve (AUC) of both irinotecan and SN-38 increase proportionally to the administered dose, although interpatient variability is important. SN-38 levels achieved in humans are about 100-fold lower than corresponding irinotecan concentrations, but these concentrations are potentially important as SN-38 is 100- to 1000-fold more cytotoxic than the parent compound. SN-38 is 95% bound to plasma proteins. Maximum concentrations of SN-38 are reached about 1 hour after the beginning of a short intravenous infusion. SN-38 plasma decay follows closely that of the parent compound with an apparent terminal half-life ranging from 6 to 30 hours. In human plasma at equilibrium, the irinotecan lactone form accounts for 25 to 30% of the total and SN-38 lactone for 50 to 64%. Irinotecan is extensively metabolised in the liver. The bipiperidinocarbonylxy group of irinotecan is first removed by hydrolysis to yield the corresponding carboxylic acid and SN-38 by carboxyesterase. SN-38 can be converted into SN-38 glucuronide by hepatic UDP-glucuronyltransferase. Another recently identified metabolite is 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxy-camptothecin (APC). This metabolite is a weak inhibitor of KB cell growth and a poor inducer of topoisomerase I DNA-cleavable complexes (100-fold less potent than SN-38). Numerous other unidentified metabolites have been detected in bile and urine. The mean 24-hour irinotecan urinary excretion represents 17 to 25% of the administered dose. Recovery of SN-38 and its glucuronide in urine is low and represents 1 to 3% of the irinotecan dose. Cumulative biliary excretion is 25% for irinotecan, 2% for SN-38 glucuronide and about 1% for SN-38. The pharmacokinetics of irinotecan and SN-38 are not influenced by prior exposure to the parent drug. The AUC of irinotecan and SN-38 correlate significantly with leuco-neutropenia and sometimes with the intensity of diarrhoea. Certain hepatic function parameters have been correlated negatively with irinotecan total body clearance. It was noted that most tumour responses were observed at the highest doses administered in phase I trials, which indicates a dose-response relationship with this drug. In the future, these pharmacokinetic-pharmacodynamic relationships will undoubtedly prove useful in minimising the toxicity and maximise the likelihood of tumour response in patients.

Effect of CPT-11 on lipid peroxide level in mouse tissues

We examined the effects of CPT-11 on lipid peroxide level and glutathione peroxidase (GSHpx) activity as indices of the toxicity of this antitumor agent in mouse and rat tissues. After CPT-11 (100 mg/kg, i.p.) administration, the lipid peroxide level in the heart increased 1.5 fold (mice) and 1.3 fold (rats) over the control levels. GSHpx activity decreased to 64% of the control. In the lung, the lipid peroxide level and GSHpx activity increased 2.5 fold and decreased to 74% after CPT-11 administration, respectively, compared with the control values. These results suggested that CPT-11 may cause cardiotoxicity and pulmotoxicity. In rat bone marrow, the lipid peroxide level increased on the 2nd day after CPT-11 injection. We suggest that in both single and combination treatment with CPT-11, the possibility of side effects should be taken into consideration.

Clinical trials of irinotecan hydrochloride (CPT, campto injection, topotecin injection) in Japan

CPT-11 was synthesized in 1984 at the laboratory of Yakult Honsha. Phase I study of CPT-11 was begun in 1986. The appropriate doses for phase II studies were decided to be 100 mg/m2 weekly or 150 mg/m2 every 2 weeks. Phase II study was conducted and this drug was approved for NSCLC, SCLC, uterine cancer and ovarian cancer by MHW in 1994. It obtained approval for stomach cancer, colorectal cancer, breast cancer, skin cancer and non-Hodgkin's lymphoma in 1995. The combination chemotherapies including CPT-11 have been conducted by using various regimens such as CPT-11 + CDDP, CPT-11 + VP-16, CPT-11 + 5-FU and CBDCA + CPT-11. In stage IV SCLC two prospective randomized controlled trials are on going comparing CPT-11 vs. CPT-11 + CDDP vs. VDS + CDDP and CPT-11 + CDDP vs. VDS + CDDP. In advanced SCLC Japanese Clinical Oncology Group (JCOG) started a randomized controlled trial comparing CPT-11 + CDDP vs. VP-16 + CDDP. In stage III NSCLC the dose escalation studies of CPT-11 (CPT-11) in the combination with TRT are ongoing by JCOG. The problem of CPT-11 in the combination chemotherapy and combined modality is that it is quite difficult to increase the dose of CPT-11 to full dose to obtain the maximum effect.

A limited sampling model for estimating pharmacokinetics of CPT-11 and its metabolite SN-38

The objective of this study was to develop a limited sampling model (LSM) to estimate the area under the curve (AUC) of 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) and that of 7-ethyl-10-hydroxycamptothecin (SN-38) as predictive pharmacokinetic variables for leukopenia and episodes of diarrhea induced by CPT-11 administration. The model was developed with a training set consisting of pharmacokinetic studies in 36 patients who received a 90-min i.v. infusion of CPT-11 at a dose of 100 mg/m2. A multiple regression analysis of CPT-11 or SN-38 concentrations observed at each time point in the training set was used to predict the AUC of CPT-11 or SN-38. The final sampling models using only two time points were: AUCCPT-11 = 3.7891*C2.5 + 14.0479*C13.5 + 1.5463 AUCSN-38 = 0.5319*C2.5 + 19.1468*C13.5 + 72.7349 where C2.5 and C13.5 are the plasma concentration of CPT-11 (micrograms/ml) or SN-38 (ng/ml) at 2.5 and 13.5 h after the initiation of CPT-11 infusion, respectively. The models were validated prospectively on a separate test data set of 12 patients receiving the same dose of CPT-11 investigated in a previous study. Validation of the final LSM on the test data set gave values of root mean square error (RMSE) of 12.72% and 5.97% for the AUC of CPT-11 and that of SN-38, respectively. The model can be used to monitor the AUCs of both CPT-11 and SN-38 for the early prediction of toxicities and to establish a pharmacokinetically based dose modification strategy for safe administration of CPT-11.

Pharmacological correlation between total drug concentration and lactones of CPT-11 and SN-38 in patients treated with CPT-11

The pharmacokinetics of 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) and its active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), were examined to establish the pharmacokinetic variability of the active lactones of CPT-11 and SN-38 in comparison with that of the total (lactone and carboxylates) plasma CPT-11 and SN-38. Twelve patients with malignancies were entered in the study. All received 100 mg/m2 of CPT-11 by intravenous drip infusion over 90 min. Blood was sampled at 10 time points in heparin-containing syringes. Analysis by high-performance liquid chromatography showed that the ratio of CPT-11 lactone to total CPT-11 concentration was highest (66%) just after the end of infusion and gradually decreased to 30% at 24 h. Almost 70% of SN-38 lactone was detected after the end of infusion and this decreased to 50% within 24 h. The standard errors of percent lactone of CPT-11 of SN-38 to total drug concentration at each sampling point were less than 12%. The area under the concentration-time curve (AUC) of total CPT-11 and that of total SN-38 were significantly correlated with the AUCs of the lactone CPT-11 and those of lactone SN-38, respectively. We conclude that, for practical purposes, monitoring of total CPT-11 and SN-38 has essentially the same clinical significance as monitoring of lactone CPT-11 and SN-38.