Effects of bevacizumab on plasma concentration of irinotecan and its metabolites in advanced colorectal cancer patients receiving FOLFIRI with bevacizumab as second-line chemotherapy

Purpose

Bevacizumab (BV) prolongs the survival of colorectal cancer patients when combined with irinotecan (CPT-11)-based regimens. In the AVF2107g study, the area under the curve (AUC) ratio for bolus CPT-11/5-fluorouracil (5-FU)/leucovorin (LV) (IFL) with the BV arm to bolus IFL with placebo indicated that SN-38 concentrations may have been increased in subjects receiving BV. However, the mechanism underlying such increase remains unclear, and the difference might be caused by an imbalance between the two arms and a possible inter-subject variability of CPT-11 metabolism. Within-subject comparisons were used to evaluate the effect of BV on advanced colorectal cancer patients when administered with the FOLFIRI regimen as second-line chemotherapy.

Methods

Ten advanced colorectal cancer patients received the FOLFIRI regimen every 2 weeks. At cycle 1, BV was administered following FOLFIRI administration to allow baseline pharmacokinetic (PK) analysis of CPT-11 and its metabolites. From cycle 2, BV was administered just before FOLFIRI administration. Plasma samples were collected under the same condition (at cycle 3).

Results

There were no significant differences in the C _max and AUC_0-∞ of CPT-11, SN-38, and SN-38G between cycle 1 (without BV) and cycle 3 (with BV). PK parameters of CPT-11, SN-38, and SN-38G were not significantly affected by BV. There were no significant differences in the changes in the AUC ratio of CPT-11 to SN-38 between cycles 1 and 3, as well as in the ratio of SN-38 to SN-38G.

Conclusion

BV does not affect the plasma concentration of CPT-11 and its metabolites on FOLFIRI regimen.     

A pilot study on the safety of combining chrysin, a non-absorbable inducer of UGT1A1, and irinotecan (CPT-11) to treat metastatic colorectal cancer

Purpose: Recently, it was shown that chrysin causes upregulation of UGT1A1 in Caco-2 intestinal cells. Therefore, we proposed that oral chrysin may reduce irinotecan (CPT-11) induced diarrhoea by shifting the SN-38G/SN-38 equilibrium towards the inactive SN-38G in the gastrointestinal mucosa. The purpose of this study was to examine the safety of combining single agent CPT-11 with chrysin. Patients and methods: Twenty patients with previously treated advanced colorectal cancer were administered chrysin twice daily for 1 week preceding and succeeding treatment with single agent CPT-11 (350 mg/m² over 90 min every 3 weeks). Loperamide usage and bowel frequency/consistency were recorded by patients into a study diary and blood samples were collected for CPT-11 pharmacokinetic analysis. Results: There were no observable toxicities that could be attributed to chrysin use. The grades and frequency of delayed diarrhoea were mild, with only 10% of patients experiencing grade 3 toxicity. Loperamide usage was also modest with a median of 1–5 tablets per cycle (range: 0–22). Pharmacokinetic results revealed a mass ratio of plasma SN-38G/SN-38, which was very similar to historical controls (7.15±5.67, n=18). Conclusions: These findings, combined with the observation of clinical activity and grade 3/4 neutropenia in 25% of patients, suggest that combining chrysin with CPT-11 may be a safe and potentially useful means of preventing diarrhoea, although this needs to be further investigated in the setting of a randomised trial.     

Inhibition of intestinal microflora β-glucuronidase modifies the distribution of the active metabolite of the antitumor agent, irinotecan hydrochloride (CPT-11) in rats

Purpose: SN-38, a metabolite of irinotecan hydrochloride (CPT-11), is considered to play a key role in the development of diarrhea as well as in the antitumor activity of CPT-11. We have previously found that the inhibition of β-glucuronidase, which hydrolyzes detoxified SN-38 (SN-38 glucuronide) to reform SN-38, in the lumen by eliminating the intestinal microflora with antibiotics, markedly ameliorates the intestinal toxicity of CPT-11 in rats. In this study we compared the disposition of CPT-11 and its metabolites in rats treated with and without antibiotics. Methods: Rats were given drinking water containing 1 mg/ml penicillin and 2 mg/ml streptomycin from 5 days before the administration of CPT-11 (60 mg/kg i.v.) and throughout the experiment. CPT-11, SN-38 glucuronide and SN-38 concentrations in the blood, intestinal tissues and intestinal luminal contents were determined by HPLC. Results: Antibiotics had little or no effect on the pharmacokinetics of CPT-11, SN-38 glucuronide or SN-38 in the blood, or in the tissues or contents of the small intestine, which has less β-glucuronidase activity in its luminal contents. In contrast, antibiotics markedly reduced the AUC_1–24 h of SN-38 (by about 85%) in the large intestine tissue without changing that of CPT-11, and this was accompanied by a complete inhibition of the deconjugation of SN-38 glucuronide in the luminal contents. Conclusions: These results suggest that SN-38, which results from the hydrolysis of SN-38 glucuronide by β-glucuronidase in the intestinal microflora, contributes considerably to the distribution of SN-38 in the large intestine tissue, and that inhibition of the β-glucuronidase activity by antibiotics results in decreased accumulation of SN-38 in the large intestine. Received: 8 August 1997 / Accepted: 16 January 1998     

Phase II study of capecitabine and cisplatin in previously untreated advanced biliary tract cancer

Purpose One of the significant dose-limiting toxicities of irinotecan hydrochloride (CPT-11) is severe diarrhea due to impairment of the intestinal membrane induced by the excreted CPT-11 and its metabolites. AST-120 (Kremezin) is a prominent oral adsorbent that consists of porous spherical carbonic particles. To evaluate whether Kremezin can prevent the diarrhea induced by CPT-11, we investigated the adsorption characteristics of CPT-11 and its metabolites onto Kremezin in vitro and in vivo. Methods For in vitro studies, Kremezin was added to each solution containing one of the camptothecin drugs (CPT-11, SN-38, and SN-38-glucuronide), and adsorption activities were determined under various conditions. For in vivo studies, CPT-11 was consecutively administered, and the occurrence of diarrhea was compared between Kremezin-treated and non-treated rats. Results Kremezin drastically adsorbed the camptothecin drugs in vitro, and the adsorption percentages of the camptothecin drugs for 60 min were more than 85%. In addition, the frequency of diarrhea in Kremezin-treated rats decreased by approximately half of that in the non-treated rats. Conclusion Kremezin showed potent adsorption capacities for the camptothecin drugs and mitigated the symptoms of diarrhea in rats. These results suggest that Kremezin is useful to prevent the diarrhea in clinical CPT-11 chemotherapy.     

Phase I dose-finding and pharmacokinetic trial of irinotecan (CPT-11) administered every two weeks

Objectives:This trial was performed to determine themaximum tolerated dose (MTD), dose-limiting toxicity (DLT), andpharmacokinetic profile of irinotecan (CPT-11) when administered on aonce-every-2-week schedule. Patients and methods:CPT-11was administered to successive cohorts of patients at progressivelyincreasing starting doses ranging from 125 to 350 mg/m². TheMTD and DLTs were determined both for CPT-11 alone and for CPT-11followed by filgrastim (G-CSF). Plasma samples were obtained during thefirst 24 hours after initial dosing to determine the totalconcentrations (lactone + carboxylate forms) of CPT-11; of theactive metabolite SN-38; and of SN-38 glucuronide (SN-38G). Results:Neutropenic fever was the DLT for CPT-11 atthe 300 mg/m² dose level. When G-CSF was added, doseescalation beyond 350 mg/m² could not be achieved due tograde 2–3 toxicities that prevented on-time retreatment withCPT-11. Severe, late diarrhea was uncommon on this schedule. Peak plasmaconcentrations of SN-38 and SN-38G were approximately 2.5% and4.2% of the corresponding peak plasma concentration for CPT-11,respectively. The harmonic mean terminal half-lives for CPT-11, SN-38,and SN-38G were 7.1 hours, 13.4 hours, and 12.7 hours, respectively. Nopredictive correlation was observed between CPT-11 or SN-38 peakconcentration or AUC and first-cycle diarrhea, neutropenia, nausea, orvomiting. Across the range of doses studied, mean CPT-11 clearance was14.0 ± 4.0 l/h/m² and volume of distribution was 146± 45.9 l/m². Conclusions:Whenadministered every two weeks, the recommended phase II starting dose ofCPT-11 is 250 mg/m² when given alone and 300 mg/m²when supported by G-CSF. This every-two-week regimen offers a tolerableand active alternative to weekly or every-three-week single-agent CPT-11therapy.     

Salivary drug monitoring of irinotecan and its active metabolite in cancer patients

 To assess the clinical usefulness of salivary monitoring of irinotecan (CPT-11) and its active metabolite (SN-38), we examined the clinical pharmacological profile of both drugs in 9 patients with thoracic malignancies who received 60 mg/m² CPT-11 (21 courses). Plasma and unstimulated whole saliva were collected over a 24-h period, and concentrations of CPT-11 and SN-38 were measured by high-performance liquid chromatography. Both CPT-11 and SN-38 were detectable in saliva, and the concentration-time curves in plasma and saliva showed a very similar pattern. A good correlation was observed between the saliva concentration (C_s) and the plasma concentration (C_p) for both CPT-11 and SN-38 (r=0.732, P<0.0001 and r = 0.611, P<0.0001, respectively). The area under the concentration-time curve calculated for saliva (AUC_s) correlated with that generated for plasma (AUC_p) for both CPT-11 and SN-38 (r = 0.531, P = 0.012 and r = 0.611, P = 0.0025, respectively). These results suggest that it may be feasible to use saliva instead of plasma for pharmacokinetics/pharmacodynamics studies of CPT-11. Received: 13 July 1996 / Accepted: 15 December 1996     

Antitumour activity of NK012, SN-38-incorporating polymeric micelles,in hypovascular orthotopic pancreatic tumour

Human pancreatic cancer is refractory to chemotherapy partly because of blockage to penetration of anticancer agents. This issue must be taken into account particularly for the drug delivery system (DDS). The aim of the present study is to investigate how NK012 (SN-38-incorporating polymeric micelles) categorised as DDS exerts its antitumour effect in an orthotopic pancreatic tumour model compared with gemcitabine and irinotecan hydrochloride (CPT-11), a low-molecular-weight prodrug of a 7-ethyl-10-hydroxy-camptothecin (SN-38).The maximum tolerated doses (MTDs) of NK012 (30 mg/kg/d), CPT-11 (66.7 mg/kg/d) and gemcitabine (16.5 mg/kg/d) were administered to mice bearing human pancreatic cancer cell (SUIT-2) xenografts implanted orthotopically. Antitumour effects of these compounds were evaluated. Drug distribution within the tumour was examined by fluorescence microscopy and high performance liquid chromatography (HPLC).NK012 exerted potent antitumour effects compared with CPT-11 and gemcitabine. A high concentration of NK012 and SN-38 released from NK012 had been observed until 192 h. On the other hand, SN-38 converted from CPT-11 was detected only 1 h postinjection. Fluorescence from NK012 was detected up to 48 h, whereas that from CPT-11 almost disappeared by 24 h postinjection.NK012 appeared to exert potent antitumour activity against intractable stroma-rich orthotopic pancreatic tumour xenografts due to its sufficient accumulation followed by the effective sustained release of SN-38 from NK012.     

Pharmacokinetics of CPT-11 in rhesus monkeys

Purpose: To examine the pharmacokinetic relationships between humans and monkeys, we studied the disposition of 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) and its active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), in rhesus monkeys. Methods: CPT-11 was administered to a total of six monkeys at doses of 3, 7, 15 and 25 mg/kg by intravenous infusion for 10 min and plasma concentrations and pharmacokinetic parameters of CPT-11 determined. Results: Maximum plasma concentrations at 25 mg/kg reached around 10 000 ng/ml, and dropped to 500 ng/ml in 8 h. Plasma concentrations of SN-38 remained between 2 and 10 ng/ml. Mean values of systemic clearance, mean residence time and distribution volume at steady state, the major pharmacokinetic parameters for CPT-11, were 13.3 (ml/min per kg), 192 (min) and 2553 (ml/kg), respectively. The initial plasma concentration ratio of lactone to total CPT-11, 76%, declined to about 20% within 75 min, and the final ratio was about 40% at 8 h; the initial ratio of SN-38 was 72%, dropped to 34% within 70 min and finally recovered to 55% at 8 h. Conclusion: Comparison with human data revealed that systemic clearances of CPT-11 and the maximum AUC of SN-38 were not as different between humans and monkeys as between humans and mice, but the metabolic conversion of CPT-11 into SN-38 in monkeys was significantly lower than in humans. Received: 19 December 1996 / Accepted: 9 May 1997     

Relationship between the Pharmacokinetics of Irinotecan and Diarrhea during Combination Chemotherapy with Cisplatin

Two phase I trials of irinotecan (CPT-11) in combination with cisplatin were conducted. In both cases, the dose-limiting toxicities were leukopenia and/or diarrhea. During these trials the pharmacokinetics of CPT-11 and its active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), were investigated to evaluate the relationship between pharmacokinetic parameters and diarrhea, since this is an unpredictable and severe toxicity of combination chemotherapy using CPT-11 and cisplatin. Twenty-three previously untreated patients with advanced lung cancer were evaluated in the pharmacokinetic study. Ten patients received CPT-11 at 80 or 90 mg/m² plus cisplatin at 60 mg/m². The other 13 patients received CPT-11 at 80 or 90 mg/m² plus cisplatin at 80 mg/m² with the granulocyte colony-stimulating factor support (2 μg/kg × 16 days). CPT-11 was given as a 90-min intravenous infusion on days 1, 8, and 15. Cisplatin was given on day 1. The pharmacokinetics of CPT-11 and SN-38 were analyzed on day 8 during the first course of treatment. The maximum tolerated dose of CPT-11 was 90 mg/m² in both phase I trials. The severity of diarrhea was best correlated with the peak plasma concentration of SN-38 among the pharmacokinetic parameters tested. In addition, patients with a plasma SN-38 level > 12.4 ng/ml at 1.75 h after the start of CPT-11 infusion had a higher incidence of Eastern Cooperative Oncology Group grade 3–4 diarrhea than those with a lower SN-38 level ( P =0.0003). Stepwise logistic regression analysis identified the SN-38 concentration as a significant contributor to the development of diarrhea ( P =0.0021). We conclude that there is a clear relationship between the SN-38 concentration and diarrhea during chemotherapy with CPT-11 plus cisplatin.     

Modified irinotecan hydrochloride (CPT-11) administration schedule improves induction of delayed-onset diarrhea in rats

Purpose: Clinically, diarrhea is the major dose-limiting toxicity of irinotecan hydrochloride (CPT-11). Using a rat model, we attempted to decrease the incidence of delayed-onset diarrhea by modifying the administration schedule of CPT-11, and studied the pharmacokinetics in this model in relation to the incidence of diarrhea. Methods: CPT-11 (total dose, 240 mg/kg) was administered intravenously (i.v.) to rats according to various schedules, and the incidence of delayed-onset diarrhea was monitored. Results: Administration of CPT-11 at a dose of 60 mg/kg once daily for four consecutive days induced severe diarrhea, while at 30 mg/kg twice daily at an interval of 9 h (daily dose 60 mg/kg) for four consecutive days alleviated the diarrheal symptoms, and at 30 or 40 mg/kg once daily for eight or six consecutive days, respectively, diarrhea was hardly induced. With the first schedule, mucosal impairment of the cecal epithelium was observed, including wall thickening, edema, decrease in crypt number and size, and formation of pseudomembrane-like substance, whereas these changes were less severe with the second schedule and were hardly observed with the other two schedules. The areas under the plasma and cecal tissue concentration-time curves (AUC_pla and AUC_cec), the maximum plasma concentrations (C_max) and the biliary excretions of CPT-11 and its metabolites, 7-ethyl-10-hydroxycamptothecin (SN-38) and SN-38 glucuronide (SN-38G) in rats depended on the daily dose of CPT-11. Exceptionally, CPT-11 C_max was significantly lower and SN-38 AUC_cec was larger in the animals treated at 30 mg/kg twice daily than in those treated at 60 mg/kg once daily. Conclusion: These results suggested that the duration of exposure to both CPT-11 and SN-38 of the intestinal epithelium and CPT-11 plasma C_max are closely related to the incidence and severity of CPT-11-induced delayed-onset diarrhea in rats. Received: 16 June 1999 / Accepted: 26 April 2000     

Down-regulation of lipids transporter ABCA1 increases the cytotoxicity of Nitidine

Purpose

This study examined the pharmacokinetics of irinotecan (CPT-11), active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), SN-38 glucuronide (SN-38G) amrubicin (AMR), and active metabolite amrubicinol (AMR-OH) after intravenous administration of this combination therapy in rats.

Methods

Male Sprague-Dawley rats were treated with 10 mg/kg CPT-11 with 10 mg/kg AMR. AMR, AMR-OH, CPT-11, SN-38 and SN-38G were measured in plasma, bile, and tissues using high-performance liquid chromatography.

Results

Co-administration of CPT-11 resulted in a significant decrease in plasma concentrations and area under the curves (AUC) of AMR-OH compared with treatment with AMR alone. On the other hand, co-administration of AMR resulted in a slight increase in the initial plasma concentration of SN-38; however, there were no differences in AUC values in CPT-11 and SN-38. The cumulative biliary excretion curves of AMR, CPT-11, and their active metabolites were not changed. CPT-11 inhibited the conversion of AMR to AMR-OH in rat cytosolic fractions.

Conclusions

CPT-11 did not affect the pharmacokinetic of AMR but decreased the plasma concentration of AMR-OH and might affect the formation of AMR-OH from AMR in hepatocytes.     

Modulation of glucuronidation of SN-38, the active metabolite of irinotecan, by valproic acid and phenobarbital

 Purpose: Irinotecan (CPT-11) is hydrolyzed to its active metabolite SN-38 which is subsequently conjugated by uridine diphosphate glucuronosyl transferase (UDP-GT) to the glucuronide (SN-38G). Both preclinical and clinical data indicate that conjugation is a primary clearance mechanism for SN-38 with the plasma glucuronide levels being substantially higher than those of SN-38. This investigation was designed to determine the possibility of modulation of glucuronidation of SN-38 and its effect on the disposition of the parent drug and metabolites. Methods: Female Wistar rats were pretreated with 200 mg/kg valproic acid (VPA), an inhibitor of glucuronidation, 5 min prior to the administration of 20 mg/kg irinotecan. The control rats were given 20 mg/kg irinotecan only. To study the effect of inducers of UDP-GT activity, rats were pre- treated with phenobarbital (PB) before irinotecan administration. Results: Pretreatment with VPA caused a 99% inhibition in the formation of SN-38G leading to a 270% increase in the area under plasma concentration-time curve (AUC) of SN-38 compared with the control rats. The irinotecan estimations were unchanged in the two groups. PB pretreatment caused a 1.7-fold increase in the AUC of SN-38G and a concomitant 31% and 59% reduction in the AUCs of SN-38 and irinotecan, respectively. Conclusions: The most plausible explanation for the alterations in SN-38G disposition is inhibition of SN-38 conjugation by VPA and induction of the conjugation by PB. Received: 5 February 1996 / Accepted: 30 July 1996     

Phase 1 trial of irinotecan (CPT-11) in patients with recurrent malignant glioma: a North American Brain Tumor Consortium study

This study was conducted to determine the maximum tolerated dose and dose-limiting toxicity of irinotecan (CPT-11) administered every 3 weeks to adults with progressive malignant glioma who were treated with enzyme inducing antiepileptic drug (EIAED) therapy, and to compare the pharmacokinetics with those in patients not on EIAED therapy treated at the recommended phase 2 dose for other cancers. The CPT-11 dose was 350 mg/m(2) i.v. every 3 weeks and remained fixed in patients not on EIAED therapy, but the dose was escalated by 50-mg/m(2) increments in patients on EIAED therapy. CPT-11 and its metabolites SN-38, SN-38 glucuronide (SN-38G), and APC (7-ethyl-10[4-N-(5 aminopentanoic acid)-1-piperidine]-carbonyloxycamptothecin) were characterized in both groups. Patients on EIAEDs received 350 to 800 mg/m(2) of CPT-11. Dose-limiting toxicity was due to grade 3 diarrhea despite maximal doses of loperamide. The systemic levels of CPT-11, APC, SN-38G, and SN-38 were all lower in the EIAED group. There was a moderate-to-fair relationship between CPT-11 dose and the area under the curve (AUC) for CPT-11 and APC over the 2, but no relationship dosage range of 350 to 800 mg/m between CPT-11 dose and the AUC for SN-38 or SN-38G. At the 750-mg/m(2) dose, the AUC for CPT-11 (21.6 microg x h/ml) matched the AUC (21.6 microg x h/ml) in the non-EIAED group treated with 350 mg/m(2) of CPT-11. We conclude that the recommended phase 2 dose of CPT-11 for patients on EIAEDs is 750 mg/m(2) when given every 3 weeks. A phase 2 study of patients with recurrent malignant glioma is ongoing to assess the efficacy of CPT-11 when the dose is stratified according to the use of EIAEDs.     

Phase I and pharmacokinetic study of irinotecan (CPT-11) administered daily for three consecutive days every three weeks in patients with advanced solid tumors

BACKGROUND: We conducted a phase I and pharmacokinetic study to determinethe maximum tolerable dose (MTD), toxicities, pharmacokineticprofile, and antitumor activity of Irinotecan (CPT-11) in patientswith refractory solid malignancies. PATIENTS AND METHODS: Forty-six patients were entered in this phase I study. CPT-11was administered intravenously over 30 minutes for 3 consecutivedays every 3 weeks. Dose levels ranged from 33 mg/m²/day to115 mg/m²/day on days 1 through 3. The pharmacokinetics of totalCPT-11 and its active metabolite SN-38 were assayed by HPLC. RESULTS: The combination of leukopenia and diarrhea was dose-limitingtoxicity at 115 mg/m²/day dose level, since 50% of the patients(5/10) experienced either grade 3–4 leukopenia, or diarrhea,or both. Leukopenia appeared to be a cumulative toxicity, witha global increase in its incidence and severity upon repeatedadministration of CPT-11. Other toxicities included nausea,vomiting, fatigue and alopecia. CPT-11 and active metaboliteSN-38 inetics were determined in 21 patients (29 courses). BothCPT-11 and SN-38 pharmacokinetics presented a high interpatientvariability. CPT-11 mean maximum plasma concentrations reached2034 ng/ml at the MTD (115 mg/m²). The terminal-phase half-lifewas 8.3 h and the mean residence time 10.2 h. The mean volumeof distribution at steady state was 141 l/m²/h. CPT-11 reboundconcentrations were observed in many courses at about 0.5 to1 hour following the end of the i.v. infusion, which is suggestiveof enterohepatic recycling. Total body clearance did not varywith increased dosage (mean=14.3 l/h/m²), indicating linearpharmacokinetics within the dose range administered in thistrial. The total area under the plasma concentration versustime curve (AUC) increased proportionally to the CPT-11 dose.Mean metabolite SN-38 peak levels reached 41 ng/ml at the MTD.A significant correlation was observed between CPT-11 area underthe curve (AUC) and its corresponding metabolite SN-38 AUC (r=0.52,p < 0.05). S-38 rebound concentrations were observed in manycourses at about 0.5 to 1 hour following the end of the i.v.infusion, which is suggestive of enterohepatic recycling. Mean24-h urinary excretion of CPT-11 accounted for 10% of the administereddose by the third day, whereas SN-38 urinary excretion accountedfor 0.18% of the CPT-11 dose. In this phase I trial, the hemato-logicaltoxicity correlated with neither CPT-11 nor SN-38 AUC. Diarrheagrade correlated significantly with CPT-11 AUC. Two partial(breast adenocarcinoma and carcinoma of unknown primary) and2 minor (hepatocarcinoma and pancreatic adenocarcinoma) responseswere observed. CONCLUSION: The MTD for CPT-11 administered in a 3 consecutive-days-every-3weeks schedule in this patient population is 115 mg/m²/day.The recommended dose for phase II studies is 100 mg/m²/day. CPT-11, camptothecin analogue, topoisomerase I inhibitor, phase I, pharmacokinetics     

Disposition of irinotecan and SN-38 following oral and intravenous irinotecan dosing in mice

The present study was conducted to quantitate the disposition of irinotecan lactone and its active metabolite SN-38 lactone in mice following oral and intravenous administration, and to evaluate the systemic exposure of irinotecan lactone and SN-38 lactone associated with antitumor doses of irinotecan lactone in mice bearing human tumor xenografts. Nontumor-bearing mice were given a single oral or intravenous irinotecan dose (5, 10, 40, or 75 mg/kg), and serial plasma samples were subsequently obtained. Irinotecan and SN-38 lactone plasma concentrations were measured using an isocratic HPLC assay with fluorescence detection. The disposition of intravenous irinotecan lactone was modeled using a two-compartment pharmacokinetic model, and the disposition of oral irinotecan and SN-38 lactone was modeled with noncompartmental methods. Irinotecan lactone showed biphasic plasma disposition following intravenous dosing with a terminal half-life ranging between 1.1 to 3 h. Irinotecan lactone disposition was linear at lower doses (5 and 10 mg/kg), but at 40 mg/kg irinotecan lactone clearance decreased and a nonlinear increase in irinotecan lactone AUC was observed. The steady-state volume of distribution ranged from 19.1 to 48.1 l/m². After oral dosing, peak irinotecan and SN-38 lactone concentrations occurred within 1 h, and the irinotecan lactone bioavailability was 0.12 at 10 mg/kg and 0.21 at 40 mg/kg. The percent unbound SN-38 lactone in murine plasma at 1000 ng/ml was 3.4 ± 0.67%, whereas at 100 ng/ml the percent unbound was 1.18 ± 0.14%. Irinotecan and SN-38 lactone AUCs in micebearing human neuroblastoma xenografts were greater than in nontumor-bearing animals. Systemic exposure to unbound SN-38 lactone in nontumor-bearing animals after a single oral irinotecan dose of 40, 10, and 5 mg/kg was 28.3, 8.6, and 2.9 ng h/ml, respectively. Data from the present study provide important information for the design of phase I studies of oral irinotecan. Received: 30 August 1996 / Accepted: 27 November 1996     

CPT-11 in human colon-cancer cell lines and xenografts: Characterization of cellular sensitivity determinants

CPT-11, a new semisynthetic derivative of camptothecin, is active in a number of tumor types in the clinic, including colon cancer. CPT-11 is a drug that is converted into the active metabolite SN-38 by a carboxylesterase. Experiments were performed to obtain more insight in the cellular characteristics in 5 unselected human colon-cancer cell lines that account for the differential sensitivity to CPT-11 and SN-38. In vitro, the sensitivity to CPT-11 and SN-38 was highest in LS174T and COLO 320 cells, intermediate in SW1398 cells and lowest in COLO 205 and WiDr cells. SN-38 was 130 to 570 times more active than CPT-11. CPT-11 induced complete remissions in 6 out of 12 COLO 320 tumors grown as subcutaneous xenografts, but was not effective in WiDr tumors. The cellular carboxylesterase activity did not relate to the sensitivity to CPT-11. The enzyme activity was higher in normal mouse tissues, i.e., serum and liver, than in COLO 320 or WiDr xenografts, indicating that tumor carboxylesterase is of minor importance for CPT-11 efficacy. The topoisomerase-l mRNA expression in tumor cells was not predictive of the antiproliferative effects of CPT-11 or SN-38. We observed a positive relationship between the DNA topoisomerase-1 activity and the cellular sensitivity to carboxylesterase-activated CPT-11 (r = 0.75, p < 0.1) as well as to SN-38 (r = 0.89, p < 0.05). The higher topoisomerase-1 activity in COLO 320 cells and tumors when compared with that in WiDr cells and tumors reflected the differences in sensitivity to the drug(s). In conclusion, the DNA topoisomerase-1 activity was the best determinant for CPT-11/SN-38 sensitivity in this panel of unselected human colon-cancer cell lines. Int. J. Cancer, 70:335–340, 1997. © 1997 Wiley-Liss, Inc.     

Correlative analysis of plasma SN-38 levels and DPD activity with outcomes of FOLFIRI regimen for metastatic colorectal cancer with UGT1A1 *28 and *6 wild type and its implication for individualized chemotherapy

It remains uncertain whether there is an correlation between clinical pharmacokinetic parameters and outcomes for metastatic colorectal cancer especially with UGT1A1 *28 and *6 wild type (*1/*1-*1/*1) for serious events associated with Irinotecan are largely excluded. This study retrospectively analyzed the relationship between Irinotecan metabolite levels and outcomes of UGT1A1 *1/*1-*1/*1 genotype arrangement. Blood samples (n = 244) were collected for analysis of plasma DPD activity (before first chemotherapy) and SN-38 levels (1.5 and 49 hour after CPT-11 administration). Clinical variables such as toxicity and outcomes were then assessed. Of the *1/*1 -*1/*1 genotype combination, the median progression free survival of the C_{SN-38 1.5 h} > 50.24 ng/ml subset was remarkably longer than that of the C_{SN-38 1.5 h} ≤ 50.24 ng/ml subset. However, there were no differences between the C_{SN-38 49 h} > 15.25 ng/ml subgroup and the ≤ 15.25 ng/ml group. It was lower DPD activity that responsible for the relatively higher incidence of bone marrow hypocellular, diarrhea, and oral mucositis in the C_{SN-38 1.5 h} > 50.24 ng/ml and C_{SN-38 49 h} > 15.25 ng/ml subsets. Therefore, plasma SN-38 levels is related to outcomes for UGT1A1 *1/*1-*1/*1 genotype, to improve efficacy, patients with C_{SN-38 1.5 h} lower than 50.24 ng/ml, CPT-11 dosage could be added in next chemmotherapy on SN-38 plasma level monitoring. Additionally, in patients with DPD activity below 3.18 before treatment, appropriate reduction of 5-FU dose could be considered to minimize the incidence of adverse events.     

Metabolic activation of irinotecan during intra-arterial chemotherapy of metastatic colorectal cancer

Biotransformation of irinotecan (CPT-11) into its pharmacologic active metabolite SN-38 was investigated in patients treated for advanced colorectal cancer. A dose of 180 mg/m(2) CPT-11 was administered to 6 patients by 60 min hepatic intra-arterial infusion (HAI) via a surgically implanted Port-a-Cath? system. Blood samples were collected from 0 to 360 min after start of HAI, and CPT-11 plus metabolites were analysed by a selective reversed phase HPLC method. The objective of this study was to evaluate the extent to which SN-38 is generated after HAI of irinotecan given at a low dose of 180 mg/m(2). In a second investigation, CPT-11 was administered via conventional intravenous infusion (dose 180 mg/m(2), 60 min infusion time, 11 patients) and CPT-11 plus metabolites were quantified using identical analytical procedure. Compared to i.v. infusion, the pharmacokinetics of CPT-11 and SN-38 were altered by HAI. The mean c(max) of CPT-11 after HAI was reduced by 37%, whereas the mean c(max) of SN-38 increased by 60%. HAI resulted in a desired, increased metabolic conversion of CPT-11 into SN-38 and might improve the regional availability of the pharmacologic active metabolite SN-38 at the site of tumor. Plasma concentrations of the metabolites SN-38 glucuronide and APC remained unaffected by the route of administration.     

Activation and antitumor activity of CPT-11 in plasma esterase-deficient mice

Purpose: To examine the antitumor activity and the pharmacokinetics of CPT-11 (irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin) in a plasma esterase-deficient scid mouse model, bearing human tumor xenografts. Experimental design: Plasma carboxylesterase (CE)-deficient mice were bred with scid animals to develop a strain that would allow growth of human tumor xenografts. Following xenotransplantation, the effect of the plasma esterase on antitumor activity following CPT-11 administration was assessed. In addition, detailed pharmacokinetic studies examining plasma and biliary disposition of CPT-11 and its metabolites were performed. Results: In mice lacking plasma carboxylesterase, the mean SN-38 systemic exposures were approximately fourfold less than that observed in control animals. Consistent with the pharmacokinetic data, four to fivefold more CPT-11 was required to induce regressions in human Rh30 xenografts grown in esterase-deficient scid mice, as opposed to those grown in scid animals. Additionally, the route of elimination of CPT-11, SN-38, and SN-38 glucuronide (SN-38G) was principally in the bile. Conclusions: The pharmacokinetic profile for CPT-11 and its metabolites in the esterase-deficient mice more closely reflects that seen in humans. Hence, these mice may represent a more accurate model for antitumor studies with this drug and other agents metabolized by CEs.     

Synergistic antitumor activity of the novel SN-38-incorporating polymeric micelles, NK012, combined with 5-fluorouracil in a mouse model of colorectal cancer, as compared with that of irinotecan plus 5-fluorouracil

The authors reported in a previous study that NK012, a 7-ethyl-10-hydroxy-camptothecin (SN-38)-releasing nano-system, exhibited high antitumor activity against human colorectal cancer xenografts. This study was conducted to investigate the advantages of NK012 over irinotecan hydrochloride (CPT-11) administered in combination with 5-fluorouracil (5FU). The cytotoxic effects of NK012 or SN-38 (an active metabolite of CPT-11) administered in combination with 5FU was evaluated in vitro in the human colorectal cancer cell line HT-29 by the combination index method. The effects of the same drug combinations was also evaluated in vivo using mice bearing HT-29 and HCT-116 cells. All the drugs were administered i.v. 3 times a week; NK012 (10 mg/kg) or CPT11 (50 mg/kg) was given 24 hr before 5FU (50 mg/kg). Cell cycle analysis in the HT-29 tumors administered NK012 or CPT-11 in vivo was performed by flow cytometry. NK012 exerted more synergistic activity with 5FU compared to SN-38. The therapeutic effect of NK012/5FU was significantly superior to that of CPT-11/5FU against HT-29 tumors (p = 0.0004), whereas no significant difference in the antitumor effect against HCT-116 tumors was observed between the 2-drug combinations (p = 0.2230). Cell-cycle analysis showed that both NK012 and CPT-11 tend to cause accumulation of cells in the S phase, although this effect was more pronounced and maintained for a more prolonged period with NK012 than with CPT-11. Optimal therapeutic synergy was observed between NK012 and 5FU, therefore, this regimen is considered to hold promise of clinical benefit, especially for patients with colorectal cancer.