Clinical pharmacokinetics of irinotecan and its metabolites: a population analysis.

PURPOSE: To build population pharmacokinetic (PK) models for irinotecan (CPT-11) and its currently identified metabolites. PATIENTS AND METHODS: Seventy cancer patients (24 women and 46 men) received 90-minute intravenous infusions of CPT-11 in the dose range of 175 to 300 mg/m(2). The PK models were developed to describe plasma concentration profiles of the lactone and carboxylate forms of CPT-11 and 7-ethyl-10-hydroxycamptothecin (SN-38) and the total forms of SN-38 glucuronide (SN-38G), 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC), and 7-ethyl-10-[4-amino-1-piperidino]-carbonyloxycamptothecin (NPC) by using NONMEM. RESULTS: The interconversion between the lactone and carboxylate forms of CPT-11 was relatively rapid, with an equilibration half-life of 14 minutes in the central compartment and hydrolysis occurring at a rate five times faster than lactonization. The same interconversion also occurred in peripheral compartments. CPT-11 lactone had extensive tissue distribution (steady-state volume of distribution [Vss], 445 L) compared with the carboxylate form (Vss, 78 L, excluding peripherally formed CPT-11 carboxylate). Clearance (CL) was higher for the lactone form (74.3 L/h) compared with the carboxylate form (12.3 L/h). During metabolite data modeling, goodness of fit indicated a preference of SN-38 and NPC to be formed out of the lactone form of CPT-11, whereas APC could be modeled best by presuming formation from CPT-11 carboxylate. The interconversion between SN-38 lactone and carboxylate was slower than that of CPT-11, with the lactone form dominating at equilibrium. The CLs for SN-38 lactone and carboxylate were similar, but the lactone form had more extensive tissue distribution. CONCLUSION: Plasma data of CPT-11 and metabolites could be adequately described by this compartmental model, which may be useful in predicting the time courses, including interindividual variability, of all characterized substances after intravenous administrations of CPT-11.     

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.     

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 or 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.     

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.     

Adenoviral vector-mediated expression of a gene encoding secreted, EpCAM-targeted carboxylesterase-2 sensitises colon cancer spheroids to CPT-11

CPT-11 (irinotecan or 7-ethyl-10[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin) is an anticancer agent in use for the treatment of colon cancer. In order to be fully active, CPT-11 needs to be converted into SN-38 (7-ethyl-10-hydroxycamptothecin) by the enzyme carboxylesterase (CE). In humans, only a minority of CPT-11 is converted to SN-38. To increase the antitumour effect of CPT-11 by gene-directed enzyme prodrug therapy, we constructed a replication-deficient adenoviral vector Ad.C28-sCE2 containing a fusion gene encoding a secreted form of human liver CE2 targeted to the surface antigen epithelial cell adhesion molecule (EpCAM) that is highly expressed on most colon carcinoma cells. By targeting CE2 to EpCAM, the enzyme should accumulate specifically in tumours and leakage into the circulation should be minimised. Ad.C28-sCE2-transduced colon carcinoma cells expressed and secreted active CE that bound specifically to EpCAM-expressing cells. In sections of three-dimensional colon carcinoma spheroids transduced with Ad.C28-sCE2, it was shown that C28-sCE2 was capable of binding untransduced cells. Most importantly, treatment of these spheroids with nontoxic concentrations of CPT-11 resulted in growth inhibition comparable to treatment with SN-38. Therefore, Ad.C28-sCE2 holds promise in gene therapy approaches for the treatment of colon carcinoma.     

Nonlinear pharmacokinetics of CPT-11 in rats

The pharmacokinetics of a new water-soluble derivative of camptothecin. 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11), and its major metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), was investigated after i.v. administration of 1 to 40 mg/kg of CPT-11 to rats. The plasma concentration of CPT-11 decreased biexponentially. The area under the concentration-time curve increased nonlinearly as the dose increased. SN-38 was found in the plasma, bile, urine, and feces. The SN-38 level was maintained at 0.06 to 0.08 micrograms/ml for 0.5 to 5.5 h depending on the dose, followed by exponential decay. Thirty-three to 58% of the CPT-11 was excreted without metabolism into the bile and urine for 24 h. SN-38 was mainly excreted into the bile. Analysis of the clearance has shown nonlinear pharmacokinetics which was due to metabolic processes such as the conversion of CPT-11 to SN-38.     

A Pharmacokinetic and Pharmacodynamic Analysis of CPT-11 and Its Active Metabolite SN-38

In the present study, an attempt was made to determine the precise pharmacokinetics of 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) and its active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38). The relationship between pharmacokinetic parameters and pharmacodynamic effects was also investigated to elucidate the cause of interpatient variation in side effects. Thirty-six patients entered the study. CPT-11, 100 mg/m², was administered by IV infusion over 90 min weekly for four consecutive weeks. The major dose-limiting toxicities were leukopenia and diarrhea. There was a positive correlation between the area under the concentration-time curve (AUC) of CPT-11 and percent decrease of WBC ( r =0.559). On the other hand, episodes of diarrhea had a better correlation with the AUC of SN-38 ( r =0.606) than that of CPT-11 ( r =0.408). Multivariate analysis revealed that the AUC of SN-38, AUC of CPT-11 and indocyanine green retention test were significant variables for the incidence of diarrhea and that both performance status and AUC of CPT-11 were significant variables for percent decrease of WBC. The large interpatient variability of the degree of leukopenia and diarrhea is due to a great plasma pharmacokinetic variation in CPT-11 or SN-38. The AUCs of CPT-11 and SN-38 obtained from the first administration of CPT-11 correlate with toxicities, but it is impossible to predict severe side effects before the administration of CPT-11 at the present time.     

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:
AUC_CPT-11=3.7891★C2.5+14.0479*C13.5+1.5463
AUC_SN-38=0.5319★C2.5+19.1468*C13.5+72.7349
where C2.5 and C13.5 are the plasma concentration of CPT-11 (μg/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.     

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     

Metabolism and pharmacokinetics of the camptothecin analogue CPT-11 in the mouse

A new water-soluble derivative of camptothecin, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11), did not exhibit potent antitumor activity in vitro against experimental tumor cells. The 50% effective doses of CPT-11 against KB and L1210 cells were 1100 and 5500 ng/ml, respectively. These values were markedly higher than those of camptothecin (CPT, 0.98 and 3.7 ng/ml) or 7-ethyl-10-hydroxycamptothecin (SN-38, 0.37 and 3.6 ng/ml). CPT-11 was found to be converted into SN-38 in mouse serum. In vitro incubation of CPT-11 in mouse serum or tissue homogenate enhanced the growth-inhibitory activity much more than that expected from the concentration of CPT-11. This enhancement of the activity coincided with that expected from the SN-38 concentration in incubated serum or homogenate, though the contribution of CPT-11 could not be refuted. SN-38 is considered to play a major role in the antitumor activity when CPT-11 is incubated in serum or homogenate. The plasma CPT-11 concentration decreased biexponentially after i.v. administration of CPT-11 into mice with a biological half-life of 0.8 to 1.1 h. The area under the plasma CPT-11 concentration-time curve showed dose dependency. The SN-38 concentration decreased for the first 30 min after administration and was then maintained for a few hours at about 0.1 microgram/ml after i.v. administration of 20 and 40 mg/kg of CPT-11 followed by the log-linear terminal phase with a half-life of about 2 h which was independent of the dose. It is suggested that the maintenance of plasma SN-38 concentration might be necessary for it to exhibit antitumor activity in vivo.     

Drug-administration sequence does not change pharmacodynamics and kinetics of irinotecan and cisplatin.

In this study, 11 patients with solid tumors were randomized to receive irinotecan (CPT-11; 200 mg/m2) as a 90-min i.v. infusion, immediately followed by cisplatin (CDDP; 80 mg/m2) as a 3-h i.v. infusion in the first course and the reversed sequence in the second course or vice versa. No significant differences in any toxicity were observed between the treatment schedules (decrease in absolute neutrophil count, 74.7 +/- 18.3 versus 80.3 +/- 18.0%; P = 0.41). CPT-11 lactone clearance was similar to single agent data and not significantly different between study courses (60.4 +/- 17.1 versus 65.5 +/- 16.3 liter/h/m2; P = 0.66). The kinetic profiles of the major CPT-11 metabolites SN-38, SN-38 glucuronide, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidinolcarbonyloxycamptothecine (APC), and 7-ethyl-10-[4-N-(1-piperidino)-1-amino]carbonyloxycamptothecine (NPC) were also sequence independent (P > or = 0.20). In addition, CPT-11 had no influence on the clearance of nonprotein-bound CDDP (40.8 +/- 16.7 versus 50.3 +/- 18.6 liter/h/m2; P = 0.08) and the platinum DNA-adduct formation in peripheral leukocytes in either sequence (1.94 +/- 2.20 versus 2.42 +/- 1.62 pg Pt/microg DNA; P = 0.41). These data indicate that the toxicity of the combination CPT-11 and CDDP is schedule independent and that there is no mutual pharmacokinetic interaction.     

Usefulness of one-point plasma SN-38G/SN-38 concentration ratios as a substitute for UGT1A1 genetic information after irinotecan administration

Background

It was recently reported that genetic polymorphisms of UDP glucuronyltransferase-1 polypeptide A1 (UGT1A1), a glucuronidation enzyme, were associated with irinotecan (CPT-11) metabolism. The active metabolite of CPT-11, 7-ethyl-10-hydroxycamptothecin (SN-38) was glucuronidated (SN-38G) by UGT1A1. Genetic polymorphisms of UGT1A1 were associated with potentially serious adverse events, including neutropenia. Several studies have suggested that the dose of CPT-11 should be decreased in patients homozygous for UGT1A1*6 or UGT1A1*28, or double heterozygotes (*6/*28). However, the reference dose for patients with these genetic polymorphisms is unclear.

Methods

We investigated the relationship between the SN-38G/SN-38 concentration ratio and the dose of CPT-11 in 70 patients with colorectal cancer who received FOLFIRI-based regimens, by measuring the plasma concentrations of CPT-11, SN-38, and SN-38G.

Results

The SN-38G/SN-38 concentration ratio was lower in patients who were homozygous for UGT1A1*6, heterozygous for UGT1A1*6 or UGT1A1*28, or were double heterozygotes compared with patients with wild-type genes. The relative decreases in the SN-38G/SN-38 concentration ratio in patients homozygous for UGT1A1*6 and in double heterozygotes were greater than in patients heterozygous for UGT1A1*6 or UGT1A1*28. Interestingly, decreases in the SN-38G/SN-38 concentration ratio were associated with decreases in the neutrophil count and the final infusion dose of CPT-11.

Conclusion

Our results suggest that the SN-38G/SN-38 concentration ratio is an important factor for guiding dose adjustments, even in patients with wild-type genes. Therefore, the SN-38G/SN-38 concentration ratio, as an index of the patient’s metabolic capacity, is useful for assessing dose adjustments of CPT-11.     

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.     

Intracellular roles of SN-38, a metabolite of the camptothecin derivative CPT-11, in the antitumor effect of CPT-11.

It is known that 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11), a semisynthesized derivative of camptothecin (CPT), has a potent antitumor activity in vivo, but 7-ethyl-10-hydroxycamptothecin (SN-38), a metabolite of CPT-11, shows much stronger cytotoxicity in vitro than CPT-11. In this study, we demonstrated that the relaxation of SV40 DNA plasmids by type I DNA topoisomerase prepared from P388 murine leukemia cells was inhibited by 50% by SN-38 at approximately 1 microM, although CPT-11 at 1 mM slightly inhibited the relaxation. SN-38 and CPT showed strong, time-dependent inhibitory activity against DNA synthesis of P388 cells. However, CPT-11 weakly inhibited DNA synthesis independently of time with coincident inhibition of the total thymidine uptake by the cells. By alkaline and neutral elution assays, it was demonstrated that SN-38 caused much more frequent DNA single-strand breaks in P388 cells than did CPT-11. The same content of SN-38 and a similar frequency of single-strand breaks were detected in the cells treated with SN-38 at 0.1 microM or with CPT-11 at 100 microM. Therefore, single-strand breaks by CPT-11 seem to be due to SN-38 produced from CPT-11 in cells. These results indicate that CPT-11 itself possesses a marginal antiproliferative effect but that SN-38 plays an essential role in the mechanism of action of CPT-11.     

Alleviation of side effects induced by irinotecan hydrochloride (CPT-11) in rats by intravenous infusion

Purpose Irinotecan hydrochloride (CPT-11) is a potent topoisomerase I inhibitor and is established and used widely as an antitumor agent. However, it sometimes causes severe side effects such as myelosuppression and diarrhea. These dose-limiting toxicities prevent the adoption of CPT-11 in aggressive chemotherapy. Thus we sought to determine in a rat model whether extending the period of infusion of CPT-11 would ameliorate the adverse reactions.Methods CPT-11 was administered intravenously (i.v.) to rats at a dose of 60 mg/kg per day for four consecutive days as a bolus injection or as 3-, 8- or 24-h infusions, and then blood cell counts and the incidence of acute and delayed-onset diarrhea were monitored.Results Serious acute and delayed-onset diarrhea and marked decreases in the number of neutrophils and lymphocytes were observed in the bolus injection group. These symptoms were alleviated in the infusion groups with the degree of alleviation dependent on infusion time. In the bolus injection group, mucosal impairment of the cecal epithelium including wall thickening, edema, a decrease in the number and size of crypts, and the formation of a pseudomembrane-like substance was observed, whereas these changes were less severe in the infusion groups. Areas under the plasma concentration-time curves (AUC_pla) of CPT-11 and its metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), differed little among the bolus injection group, and the 3-h and 8-h infusion groups. However, the AUC_pla values of CPT-11 and SN-38 were significantly decreased and increased, respectively, in the 24-h infusion group. The maximum plasma concentrations (C_max) of CPT-11 decreased with increasing infusion time, but those of SN-38 did not.Conclusions It was confirmed that the side effects of CPT-11 were alleviated by extending the infusion time. The pharmacokinetic parameters suggested that the C_max of CPT-11 is closely related to the incidence and severity of adverse reactions such as myelosuppression and acute and delayed-onset diarrhea.Abbreviations AUC_cec Area under the cecal tissue concentration-time curve - AUC_mar Area under the bone marrow tissue concentration-time curve - AUC_pla Area under the plasma concentration-time curve - C_max Maximum concentration - CL_tot Total clearance - CPT Camptothecin - CPT-11 Irinotecan hydrochloride [7-ethyl-10-(4-(piperidino)-1-piperidino)carbonyloxycamptothecin] - G-CSF Granulocyte colony-stimulating factor - HPLC High-performance liquid chromatography - i.v. Intravenous(ly) - MRT Mean residence time - SN-38 7-Ethyl-10-hydroxycamptothecin - SN-38G SN-38 glucuronide - T_1/2 Half-life - UGT UDP-glucuronosyltransferase     

Determinants of CPT-11 and SN-38 activities in human lung cancer cells.

Irinotecan (CPT-11) is a semisynthetic camptothecin derivative with a broad spectrum of anti-tumour activity. Carboxylesterase (CE) catalyses the conversion of CPT-11 to SN-38 (7-ethyl-10-hydroxycamptothecin), the active form of CPT-11. The antiproliferative effects of CPT-11 and SN-38, CE-activity and topoisomerase I protein expression were investigated in five human small-cell lung cancer (SCLC) cell lines and four human non-small-cell lung cancer (NSCLC) cell lines. Antiproliferative activity, expressed as IC50 values, was determined using the MTT assay. CPT-11 was significantly more active in SCLC than in NSCLC cell lines (P = 0.0036), whereas no significant difference between histological types was observed with SN-38. A significant correlation (r2 = 0.52, P = 0.028) was observed between CE activity and chemosensitivity to CPT-11 but not to SN-38, and significantly higher CE activity was observed in SCLC compared with NSCLC cell lines (P = 0.025). Western blotting experiments showed topoisomerase I protein expressions within a factor of 2, and a granular nuclear staining was detectable in all cell lines by immunocytochemistry of cytospins. No correlation was observed between protein expression and sensitivity to CPT-11 or SN-38. Cellular and medium concentrations of CPT-11 and SN-38 were measured by high-performance liquid chromatography (HPLC) in one SCLC cell line with high CE activity and high sensitivity to CPT-11, and one NSCLC cell line with low sensitivity to CPT-11 and CE activity. Intracellular concentrations of CPT-11 and SN-38 were higher in the SCLC cell line, and this was associated with an increase in cellular uptake of CPT-11 compared with the medium, and an increased intracellular formation of SN-38. In conclusion, CE activity appears to be associated with higher sensitivity to CPT-11 in human lung cancer cell lines and may partly explain the difference in the in vitro sensitivity to CPT-11 between SCLC and NSCLC cells. The assessment of CE activity in clinical material of lung cancer patients undergoing treatment with CPT-11 may be warranted. However, other mechanisms may influence sensitivity to CPT-11, possibly including drug transport.     

Relationship between Development of Diarrhea and the Concentration of SN-38, an Active Metabolite of CPT-11, in the Intestine and the Blood Plasma of Athymic Mice Following Intraperitoneal Administration of CPT-11

Severe diarrhea occurred during daily intraperitoneal administration of 7-ethyl-10-[4-(l-piperidino)-l-piperidino]carbonyloxycamptothecin (CPT-11) at a dose of 50 mg/kg in athymic mouse. Serial determination of CPT-11 and 7-ethyl-10-hydroxycamptothecin (SN-38), with the use of an on-line solid extraction HPLC system, demonstrated that much higher levels of the compounds are retained in the intestine and the blood plasma after five consecutive daily injections than after a single injection. Histologic examination of the gastrointestinal tract showed hemorrhagic colitis on day 7 and later after five consecutive daily injections of CPT-11. The direct cause of diarrhea associated with CPT-11 administration is considered to be enterocolitis caused by high levels of SN-38 and/or CPT-11 retained for a long period in the intestine.     

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.     

Identification and kinetics of a β-glucuronide metabolite of SN-38 in human plasma after administration of the camptothecin derivative irinotecan

Irinotecan (7-ethyl-10-{4-[1-piperidino]-1-piperidino}carbonyloxycamptothecin), also known as CPT-11, is a promising semi-synthetic derivative of camptothecin with significant activity against a range of tumour types. The pharmacokinetic behaviour of its principal and presumedly active metabolite, SN-38 (7-ethyl-10-hydroxycamptothecin), displays wide inter-patient variation. During the high-performance liquid chromatographic (HPLC) analysis of plasma samples collected from a patient given CPT-11, we observed several unidentified peaks that were not present in pre-infusion samples. In this paper we describe the manner in which one of these was determined to be a -glucuronide of SN-38. The total plasma concentrations of this metabolite were quantified following digestion with -glucoronidase and were found to be greater than those of SN-38 in the patient studied. The elimination phases of the plasma concentration profile of SN-38 and its glucoronide were parallel, suggesting that the transformation of SN-38 to the glucuronide is the rate-limiting step in the elimination of SN-38 and could play a key role in its pharmacokinetics.This work was presented in part at the 8th NCI-EORTC Symposium on New Drugs in Cancer Therapy, Amsterdam, 15–18 March 1994. L. P. Rivory is the recipient of an NHMRC/INSERM Exchange Fellowship