Relationship between the pharmacokinetics of irinotecan and diarrhea during combination chemotherapy with cisplatin

Individualization of Irinotecan Treatment: A Review of Pharmacokinetics, Pharmacodynamics, and Pharmacogenetics

Since its clinical introduction in 1998, the topoisomerase I inhibitor irinotecan has been widely used in the treatment of solid tumors, including colorectal, pancreatic, and lung cancer. Irinotecan therapy is characterized by several dose-limiting toxicities and large interindividual pharmacokinetic variability. Irinotecan has a highly complex metabolism, including hydrolyzation by carboxylesterases to its active metabolite SN-38, which is 100- to 1000-fold more active compared with irinotecan itself. Several phase I and II enzymes, including cytochrome P450 (CYP) 3A4 and uridine diphosphate glucuronosyltransferase (UGT) 1A, are involved in the formation of inactive metabolites, making its metabolism prone to environmental and genetic influences. Genetic variants in the DNA of these enzymes and transporters could predict a part of the drug-related toxicity and efficacy of treatment, which has been shown in retrospective and prospective trials and meta-analyses. Patient characteristics, lifestyle and comedication also influence irinotecan pharmacokinetics. Other factors, including dietary restriction, are currently being studied. Meanwhile, a more tailored approach to prevent excessive toxicity and optimize efficacy is warranted. This review provides an updated overview on today’s literature on irinotecan pharmacokinetics, pharmacodynamics, and pharmacogenetics.

Pharmacokinetics and safety of DTS-108, a human oligopeptide bound to SN-38 with an esterase-sensitive cross-linker in patients with advanced malignancies: a Phase I study

Background

DTS-108 is a hydrosoluble prodrug, where the SN-38 moiety is covalently linked to a 20-amino acid vector peptide by a specific esterase-sensitive cross-linker, releasing 7-ethyl-10-hydroxycampthotecin (SN-38) by esterase bond cleavage.

Methods

The pharmacokinetics of DTS-108, adverse events graded according to NCI-CTCv3.1, dose-limiting toxicities at cycle 1, the maximum tolerated dose (MTD), and the recommended Phase II dose (RP2D) of intravenous DTS-108 (1–2 hours) every 2 weeks were evaluated in a first-in-human Phase I study in patients with advanced/metastatic carcinomas, according to an accelerated dose escalation design. SN-38 and SN-38 glucuronide (SN-38G) levels were evaluated with fluorescence high-performance liquid chromatography (HPLC) test, then liquid chromatography–tandem mass spectrometry (LC/MS/MS) methods.

Results

Forty-two patients received DTS-108 across 14 dosing cohorts (range 3–416 mg/m²). At 416 mg/m², three out of six patients had grade 4 neutropenia thereby defining the MTD and the RP2D at 313 mg/m². Fluorescence HPLC was inaccurate to quantify DTS-108 and its metabolites (SN-38 and SN-38G). New processes and analytical LC/MS/MS methods for testing SN-38 were implemented. At a dose of 313 mg/m², mean DTS-108, SN-38, and SN-38G area under the plasma concentration–time curve to infinity (coefficients of variation %) were 439,293 (24%), 1,992 (34%), and 4,538 (46%) h·ng/mL. Stable disease (according to Response Evaluation Criteria in Solid Tumors) was observed in nine patients.

Conclusion

Assessing SN-38 concentration using fluorescence HPLC is questionable since this method failed to monitor dose escalation of DTS-108, a new topoisomerase I inhibitor, due to ex vivo degradation. LC/MS/MS methods were consistent in evaluating SN-38 exposures allowing drug monitoring. The maximum tolerated dose of DTS-108 was 416 mg/m². The RP2D for intravenous DTS-108 was 313 mg/m² every 2 weeks in patients with advanced/metastatic solid tumors.

Clinical observations on associations between the UGT1A1 genotype and severe toxicity of irinotecan

BACKGROUND

Severe toxicity is commonly observed in cancer patients receiving irinotecan (CPT-11). UDP glucuronosyltransferase1A1 (UGT1A1) catalyzes the glucuronidation of the active metabolite SN-38 but the relationship between UGT1A1 and severe toxicity remains unclear. Our study aimed to assess this point to guide clinical use of CPT-11.

MATERIALS AND METHODS

89 cancer patients with advanced disease received CPT-11-based chemotherapy for at least two cycles. Toxicity, including GI and hematologic toxicity was recorded in detail and UGT1A1 variants were genotyped. Regression analysis was used to analyse relationships between these variables and tumor response.

RESULTS

The prevalence of grade III-IV diarrhea was 10.1%, this being more common in patients with the TA 6/7 genotype (5 of 22 patients, 22.7%) (p<0.05). The prevalence of grade III-IV neutropenia was 13.4%and also highest in patients with the TA 6/7 genotype (4 of 22 patients; 18.2%) but without significance (p>0.05). The retreatment total bilirubin levels were significantly higher in TA6/7 patients (mean, 12.75μmol/L) with compared to TA6/6 (mean, 9.92 μmol/L) with p<0.05.

CONCLUSIONS

Our study support the conclusion that patients with a UGT1A1*28 allele (s) will suffer an increased risk of severe irinotecan-induced diarrhea, whether with mid-or low-dosage. However, the UGT1A1*28 allele (s) did not increase severe neutropenia. Higher serum total bilirubin is an indication that patients UGT1A1 genotype is not wild-type, with significance for clinic usage of CPT-11.

Effect of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) micelles on pharmacokinetics and intestinal toxicity of irinotecan hydrochloride: potential involvement of breast cancer resistance protein (ABCG2)

Objectives

Intestinal toxicity and low levels of systemic drug exposure are among the major problems associated with tumour therapy. We have developed poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (PEO-PPO-PEO) micelles loaded with irinotecan hydrochloride (CPT-11) hoping to decrease CPT-11-induced intestinal toxicity while increasing its systemic exposure. In addition, we have investigated the potential involvement of breast cancer resistance protein (BCRP) in biliary excretion, pharmacokinetics, and intestinal toxicity of CPT-11.

Methods

PEO-PPO-PEO micelles were prepared using PEO20-PPO70-PEO20 and lecithin. The effect of PEO-PPO-PEO micelles on BCRP-mediated cellular accumulation and transport efflux of CPT-11 was evaluated in MDCKII/BCRP cells. The biliary excretion, intestinal damage, and pharmacokinetic study of CPT-11-loaded PEO-PPO-PEO micelles were investigated in rats.

Key findings

The obtained micelles could effectively inhibit BCRP-mediated CPT-11 efflux in MDCKII/BCRP cells, and significantly decrease the drug biliary excretion in rats. Moreover, intestinal toxicity, assessed by microscopic examination of pathological damage, was ameliorated in rats injected with PEO-PPO-PEO micelles compared with rats injected with CPT-11 alone. Treatment with PEO-PPO-PEO micelles resulted in prolonged circulation time in blood and increased bioavailability of CPT-11 and SN-38 (7-ethyl-10-hydroxycamptothecin).

Conclusions

PEO-PPO-PEO micelles were identified as promising carriers able to reduce intestinal toxicity and increase antitumour therapeutic effect of CPT-11. The study indicated a potential involvement of BCRP in CPT-11 pharmacokinetics and CPT-11-induced intestinal toxicity.

Life-threatening toxicities in a patient with UGT1A1*6/*28 and SLCO1B1*15/*15 genotypes after irinotecan-based chemotherapy

INTRODUCTION

To explore severe toxicities induced by irinotecan-based chemotherapy and UGT1A1*6/*28 and SLCO1B1*15/*15 genotypes.

CASE REPORT

A 66-year-old Japanese male diagnosed with left pharyngeal carcinoma (T2N2bM0, stage IVA) was treated with irinotecan (70 mg/m(2)) on days 1, 8 and 15 in combination with docetaxel (60 mg/m(2)) on day 1 of a 28-day cycle. After the first cycle, he suffered marked toxicities, including grade 4 diarrhea and febrile grade 4 neutropenia. Plasma concentrations of irinotecan, SN-38 and SN-38G were measured, and extensive accumulation of SN-38 was observed. Genotyping of UGT1A1 and OATP1B1 proteins showed UGT1A1*6/*28 and SLCO1B1*15/*15, respectively, which are known to lead to extremely low glucuronidation and transport activities of substrate drugs.

CONCLUSION

The severe toxicities in this patient are attributable to the extensive accumulation of SN-38, which may result from a synergistic or additive effect of low metabolic (UGT1A1*6/*28) and transport (SLCO1B1*15/*15) capabilities.

Effects of breast cancer resistance protein inhibitors and pharmaceutical excipients on decreasing gastrointestinal toxicity of camptothecin analogs

AIM

To investigate the effect of breast cancer resistance protein (BCRP) inhibitors and pharmaceutical excipients on reducing the biliary excretion of camptothecins (CPT), ameliorating delayed-type diarrhea and intestinal mucosa damage induced by CPT.

METHODS

The cumulative biliary excretion of irinotecan (CPT-11) and hydroxycamptothecin (HCPT) with or without BCRP inhibitors and excipients was investigated in rats. The gastrointestinal toxicity, assessed as the diarrheal score, body weight change and microscopic pathological damage was also determined in rats.

RESULTS

Breast cancer resistance protein (BCRP) exhibited important effects on the biliary excretion of CPT. Coadministration of BCRP inhibitors such as GF120918 and cyclosporin A reduced the biliary excretion of CPT-11 and HCPT. Pharmaceutical excipients such as Pluronic F68 and PEG 2000 stearate also showed inhibitory effects on BCRP and similarly reduced CPT biliary excretion. The observed gastrointestinal toxicity was ameliorated by coadministration of BCRP inhibitors and excipients compared with injection of CPT-11 and HCPT alone.

CONCLUSION

The use of excipients as inhibitors of BCRP is safe and relatively non-toxic, and may lead to important pharmacotherapeutic benefits by decreasing the gastrointestinal toxicity of CPT.

[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.

Phase I and pharmacologic study of irinotecan and amrubicin in advanced non-small cell lung cancer

PURPOSE

We conducted a Phase I trial of irinotecan (CPT-11), a topoisomerase I inhibitor, combined with amrubicin, a topoisomerase II inhibitor. The aim was to determine the maximum tolerated dose (MTD) of amrubicin combined with a fixed dose of CPT-11 as well as the dose-limiting toxicities (DLT) of this combination in patients with advanced non-small cell lung cancer.

PATIENTS AND METHODS

Eleven patients with stage IIIB or IV disease were treated at 3-week intervals with amrubicin (5-min intravenous injection on days 1-3) plus 60 mg/m2 of CPT-11 (90-min intravenous infusion on days 1 and 8). The starting dose of amrubicin was 25 mg/m2, and it was escalated in 5 mg/m2 increments until the maximum tolerated dose was reached.

RESULTS

The 30 mg/m2 of amrubicin dose was one dose level above the MTD, since three of the five patients experienced DLT during the first cycle of treatment at this dose level. Diarrhea and leukopenia were the DLT, while thrombocytopenia was only a moderate problem. Amrubicin did not affect the pharmacokinetics of CPT-11, SN-38 or SN-38 glucuronide. Except for one patient, the biliary index on day-1 correlated well with the percentage decrease of neutrophils in a sigmoid Emax model. There were five partial responses among 11 patients for an overall response rate of 45%.

CONCLUSION

The combination of amrubicin and CPT-11 seems to be active against non-small cell lung cancer with acceptable toxicity. The recommended dose for Phase II studies is 60 mg/m2 of CPT-11 (days 1 and 8) and 25 mg/m2 of amrubicin (days 1-3) administered every 21 days.

A phase II trial of weekly fractionated irinotecan and cisplatin for advanced gastric cancer

PURPOSE

This study was to evaluate the activity and the safety of a combination chemotherapy regimen of weekly fractionated irinotecan and cisplatin in advanced gastric cancer patients.

METHODS

Patients with advanced gastric adenocarcinoma with either chemotherapy-naive or only one prior chemotherapy regimen received irinotecan 50 mg/m2 followed by cisplatin 30 mg/m2. Both drugs were administered weekly for 3 consecutive weeks, followed by 1-week rest. Treatment was repeated until disease progression occurred. Response evaluation was performed according to the RECIST criteria.

RESULTS

Forty-seven patients (13 chemo-naive, 34 prior chemotherapy) were enrolled. Of 46 evaluable patients, overall response rate was 25.5% (95% CI, 12.9-39.3%) and disease control rate was 63.8% (95% CI, 50.9-79.5%) by intent-to-treat analysis. The time to progression and overall survival duration were 21 and 44 weeks, respectively. One-year survival rate was 41.6%. The most frequent grade 4 toxicity was neutropenia, which was the major cause of treatment delay. Non-hematological toxicities of grade 3-4 were rare with occurrence rate of 14.9% for anorexia and emesis.

CONCLUSIONS

Fractionated irinotecan combined with cisplatin with 3-week-on and 1-week-off schedule produced favorable clinical results for advanced gastric cancer. Because of the feasible efficacy and low non-hematologic toxicity, this treatment could be a promising salvage regimen in patients who have failed to taxanes.

Toxicity of the topoisomerase I inhibitors

The topoisomerase I inhibitors represent a class of antineoplastic agents with a wide spectrum of activity against malignancies. Currently available topo-isomerase I inhibitors are derivatives of the parent compound, camptothecin. Irinotecan is most active against gastrointestinal (GI) tumours, and has predominantly GI and haematological toxicities. Significant pharmacokinetic variability occurs in patients with hepatic dysfunction, particularly those with glucuronidation pathway deficiencies. The toxicity of topotecan is principally haematological with little extramedullary toxicity. Topotecan is well-tolerated in patients with significant hepatic dysfunction; however, patients with even mild renal insufficiency require significant dose reductions. This article discusses the toxicities of these drugs in detail, including the need for dose adjustments in selected patient populations.

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.

Reduced gastrointestinal toxicity following inhibition of the biliary excretion of irinotecan and its metabolites by probenecid in rats

PURPOSE

To ameliorate the late-onset of severe gastrointestinal toxicity provoked by irinotecan (CPT-11), which may be related to the biliary excretion of CPT-11 and/or its metabolites.

METHODS

Effects of probenecid, an inhibitor of MRP2/ABCC2, on the biliary excretion and mucosal intestinal tissue concentration of CPT-11 and its metabolites were examined in rats. CPT-11-induced late-onset gastrointestinal toxicity was also evaluated.

RESULTS

Coadministration of probenecid reduced the biliary excretion of CPT-11, an active metabolite (SN-38) and its glucuronide by half with a concomitant increase in their plasma concentration. When the dose of CPT-11, in the presence of probenecid, was set at half that in its absence, the plasma SN-38 concentration was maintained at the same level as the control, whereas the mucosal intestinal tissue concentration of SN-38 was reduced. Under this condition, CPT-11-induced watery diarrhea, changes in intestinal marker enzymes and body weight reduction were much less in the probenecid-treated group, although the degree of bone marrow suppression was almost the same as that in the control.

CONCLUSIONS

Coadministration of probenecid with a reduced dose of CPT-11 potently reduces both SN-38 exposure and CPT-11-induced late-onset toxicity in gastrointestinal tissues, possibly by inhibiting the biliary excretion of CPT-11 and/or its metabolites.

Common human UGT1A polymorphisms and the altered metabolism of irinotecan active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38)

7-Ethyl-10-hydroxycamptothecin (SN-38) is the pharmacologically active metabolite of irinotecan, in addition to being responsible for severe toxicity. Glucuronidation is the main metabolic pathway of SN-38 and has been shown to protect against irinotecan-induced gastrointestinal toxicity. The purpose of this study was to determine whether common polymorphic UDP-glucuronosyltransferase (UGT) affects SN-38 glucuronidation. First, kinetic characterization of SN-38-glucuronide (SN-38-G) formation was assessed for all known human UGT1A and UGT2B overexpressed in human embryonic kidney 293 cells. To assess the relative activity of UGT isoenzymes for SN-38, rates of formation of SN-38-G were monitored by liquid chromatography/mass spectrometry analysis and normalized by level of UGT cellular expression. Determination of intrinsic clearances predicts that hepatic UGT1A1 and UGT1A9 and the extrahepatic UGT1A7 are major components in SN-38-G formation, whereas a minor role is suggested for UGT1A6, UGT1A8, and UGT1A10. In support of the involvement of UGT1A9, a strong coefficient of correlation was observed in the glucuronidation of SN-38 and a substrate, mainly glucuronidate, by UGT1A9 (flavopiridol) by human liver microsomes (coefficient of correlation, 0.905; p = 0.002). In vitro functional experiments revealed a negative impact of the UGT1A1 allelic variants. Residual activities of 49, 7, 8, and 11% were observed for UGT1A1*6 (G(71)R), UGT1A1*27 (P(229)Q), UGT1A1*35 (L(233)R), and UGT1A1*7 (Y(486)D), respectively. Common variants of UGT1A7, UGT1A7*3 (N(129)K;R(131)K;W(208)R), and UGT1A7*4 (W(208)R), displayed residual activities of 41 and 28% compared with the UGT1A7*1 allele. Taken together, these data provide the evidence that molecular determinants of irinotecan response may include the UGT1A polymorphisms studied herein and common genetic variants of the hepatic UGT1A9 isoenzyme yet to be described.

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.

Direct translation of a protracted irinotecan schedule from a xenograft model to a phase I trial in children

PURPOSE

In a preclinical model of neuroblastoma, administration of irinotecan daily 5 days per week for 2 consecutive weeks ([qd x 5] x 2) resulted in greater antitumor activity than did a single 5-day course with the same total dose. We evaluated this protracted schedule in children.

PATIENTS AND METHODS

Twenty-three children with refractory solid tumors were enrolled onto a phase I study. Cohorts received irinotecan by 1-hour intravenous infusion at 20, 24, or 29 mg/m(2) (qd x 5) x 2 every 21 days.

RESULTS

The 23 children (median age, 14.1 years; median prior regimens, two) received 84 courses. Predominant diagnoses were neuroblastoma (n = 5), osteosarcoma (n = 5), and rhabdomyosarcoma (n = 4). The dose-limiting toxicity was grade 3/4 diarrhea and/or abdominal cramps in six of 12 patients treated at 24 mg/m(2), despite aggressive use of loperamide. The maximum-tolerated dose (MTD) on this schedule was 20 mg/m(2)/d. Five patients had partial responses and 16 had disease stabilization. On day 1, the median systemic exposure to SN-38 (the active metabolite of irinotecan) at the MTD was 106 ng-h/mL (range, 41 to 421 ng-h/mL).

CONCLUSION

This protracted schedule is well tolerated in children. The absence of significant myelosuppression and encouraging clinical responses suggest compellingly that irinotecan be further evaluated in children using the (qd x 5) x 2 schedule, beginning at a dose of 20 mg/m(2). These results imply that data obtained from xenograft models can be effectively integrated into the design of clinical trials.

In vitro sensitivity of fresh ovarian carcinoma specimens to CPT-11 (irinotecan)

OBJECTIVE

Irinotecan (CPT-11) is a DNA topoisomerase I inhibitor which has shown activity in vitro against several cancer cell lines and some promising clinical responses in phase I and II trials in various solid tumors. The cytotoxicity of CPT-11 on human ovarian epithelial malignancies was tested in vitro utilizing the ATP chemosensitivity assay. Flow cytometry was also performed on the fresh carcinoma specimens.

METHODS

Fresh tumor samples were obtained at laparotomy from 20 patients with primary adenocarcinoma of the ovary and 1 patient with heavily pretreated recurrent ovarian carcinoma. Tumors were plated in an in vitro system and treated with varying doses of both CPT-11 and its active metabolite SN-38 (7-ethyl-10-hydroxycamptothecin), in addition to a panel of standard chemotherapeutic agents used in treating ovarian cancer. On the sixth day after incubation, ATP levels in remaining cells were measured using a luminometer as an indication of the amount of cell kill compared to untreated controls.

RESULTS

Twelve of the 21 tumors were evaluable for a response to CPT-11. Of the 12 tumors tested, 7 were found to have median effect doses of CPT-11 significantly under the clinically achievable peak plasma concentration (range 1.00 x 10(-4) to 44.67 microM) and 11 of the 12 tumors showed sensitivity to the active metabolite SN38 with median effect doses ranging from 2.00 x 10(-4) to 0.147 microM. Some of these tumors showed resistance to the standard agents, such as platinum, based on our assay. The heavily pretreated recurrent tumor tested was very sensitive to both CPT-11 and SN38 by our assay. The results of flow cytometry showed that the tumors were composed of heterogeneous populations of cells with mean S phase fractions varying from 7.0 to 17.3%. The only tumor not sensitive to SN38 showed the highest mean S phase activity of 17.3%.

CONCLUSIONS

Overall, these results suggest that CPT-11 deserves further investigation as a clinically useful chemotherapeutic agent for ovarian cancer.

Irinotecan: a new antineoplastic agent for the management of colorectal cancer

OBJECTIVE

To review the pharmacologic, pharmacokinetic, therapeutic, and safety aspects of irinotecan, a new antineoplastic agent, and to assess its role in the treatment of colorectal and lung cancer.

DATA SOURCES

English-language articles from the MEDLINE database, January 1990-March 1998; Pharmacia & Upjohn Company; published articles and meeting abstracts.

STUDY SELECTION

Studies in humans with cancer, clinical case reports, and open clinical studies were reviewed. Efficacy studies were limited to trials with at least 20 evaluable patients.

DATA EXTRACTION

Relevant data were extracted from published reports and abstracts.

DATA SYNTHESIS

Irinotecan is an effective agent for the treatment of advanced colorectal cancer. It demonstrates significant activity as a first-line agent and in patients with disease that is refractory to fluorouracil-containing regimens. Activity against lung cancer has also been demonstrated. Limited data indicate activity against cancers of the ovary, cervix, stomach, and in non-Hodgkin's lymphomas. Major toxicity consists of myelosuppression and diarrhea.

CONCLUSIONS

Irinotecan is a useful addition to the antineoplastic drug family and offers significant efficacy for treatment of patients with fluorouracil-refractory colorectal cancer.

A phase I clinical and pharmacologic study of a carboplatin and irinotecan regimen combined with recombinant human granulocyte-colony stimulating factor in the treatment of patients with advanced nonsmall cell lung carcinoma

BACKGROUND

This Phase I study was designed to determine the toxicity and efficacy of a carboplatin and irinotecan (CPT-11) regimen with recombinant human granulocyte colony-stimulating factor (rhG-CSF) support for patients with advanced nonsmall cell lung carcinoma.

METHODS

Treatment consisted of carboplatin administered intravenously (i.v.) on Day 1 plus CPT-11 i.v. on Days 1, 8, and 15. The carboplatin dose was calculated using Calvert's formula, where the target area under the plasma concentration versus the time curve (AUC) was 5 or 6 mg x min/mL. rhG-CSF (2 microg/kg) was administered daily, except on Days 1, 8, and 15, until the leukocyte count exceeded 20,000/mm3 (10,000/mm3 after Day 16). Cycles were repeated every 4 weeks. Groups entered the trial at escalating CPT-11 and carboplatin dose levels of 60 mg/m2 and 5 mg x min/mL, 70/5 and 60/6.

RESULTS

Twenty-one patients were enrolled in this study, of whom 20 were assessable for toxicity and therapeutic efficacy. Two of 6 patients experienced Grade 4 diarrhea at the 70/5 dose level, suggesting that this was the maximum tolerated dose (MTD). However, the 60/6 dose level was included because toxicities were very mild at the 60/5 dose level. At the 60/6 dose level, 1 of 6 patients experienced severe, life-threatening toxicity. Therefore, subsequent dose escalation was stopped and the study terminated. There were 7 responses (35%) among the 20 patients. At the 60/6 dose level (n=5), the observed carboplatin AUC after aiming for a target AUC of 6 was 5.9+/-0.9 mg x min/mL, as expected, although the AUCs of both CPT-11 and its active metabolite, SN-38, were lower than expected.

CONCLUSIONS

The recommended doses for Phase II studies are 60 mg/m2 of CPT-11 and a target AUC of 5 mg x min/mL for carboplatin, plus rhG-CSF. The combination of AUC-based carboplatin and CPT-11 with rhG-CSF support appears to be an active regimen in the treatment of patients with NSCLC.

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.

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.