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

Liposomal irinotecan (HR070803) in combination with 5-fluorouracil and leucovorin in patients with advanced solid tumors: a phase 1b dose-escalation and expansion study

This phase 1b study aimed to evaluate the dose-limiting toxicity (DLT), maximum tolerated dose (MTD), pharmacokinetics, and preliminary efficacy of HR070803, a novel nanoliposomal formulation of irinotecan, in combination with 5-fluorouracil and leucovorin in patients with pretreated advanced solid tumors. This study consisted of dose-escalation and expansion stages. Dose escalation was performed with a traditional 3 + 3 design; patients received intravenous infusion of HR070803 from 60 to 80 mg/m2, followed by leucovorin (200 mg/m2) and 5-fluorouracil (2000 mg/m2) every 2 weeks. In the expansion stage, patients received treatments at selected tolerable dose. Fifteen patients received treatments at 60 mg/m2 (n = 12) and 80 mg/m2 (n = 3). DLTs occurred in 2 patients at 80 mg/m2 (grade 2 neutropenia that resulted in a dose delay of ≥ 7 days, n = 1; grade 3 febrile neutropenia, n = 1). The MTD was determined to be 60 mg/m2. The most frequent HR070803related adverse events included anorexia, leukopenia, neutropenia, nausea, fatigue, and diarrhea. SN-38, the active metabolite of irinotecan, exhibited lower maximum plasma concentrations and a prolonged terminal half-life when irinotecan was administered via nanoliposome compared to conventional injection. Overall, 4 patients achieved a partial response (confirmed, n = 2), and 9 had stable disease. The MTD of HR070803 was 60 mg/m2 when infused with 5-fluorouracil and leucovorin. Nanoliposomal encapsulation modified the pharmacokinetics of irinotecan and SN-38. HR070803 with 5-fluorouracil and leucovorin demonstrated a manageable safety profile and promising antitumor efficacy in advanced solid tumors. TRIAL REGISTRATION: Clinicaltrials.gov, NCT05086848. Retrospectively registered on Oct. 12, 2021.

Irinotecan dosing and pharmacogenomics: a comprehensive exploration based on UGT1A1 variants and emerging insights

Irinotecan is a critical anticancer drug used to treat metastatic colorectal cancer and advanced pancreatic ductal adenocarcinoma by obstructing topoisomerase 1; however, it can cause minor-to-severe and life-threatening adverse effects. UDP glucuronosyltransferase family 1 member A1 (UGT1A1) polymorphisms increase the risk of irinotecan-induced neutropenia and diarrhea. Hence, screening for UGT1A1 polymorphisms before irinotecan-based chemotherapy is recommended to minimize toxicity, whereas liposomes offer the potential to deliver irinotecan with fewer side effects in patients with pancreatic ductal adenocarcinoma. This review presents a comprehensive overview of the effects of genotype-guided dosing of irinotecan on UGT1A1*28 and UGT1A1*6 variants, incorporating pharmacogenomic research, optimal regimens for metastatic colorectal and pancreatic cancer treatment using irinotecan, guidelines for toxicity reduction, and an evaluation of the cost-effectiveness of UGT1A1 genotype testing.

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.

Physicochemical stability of irinotecan injection concentrate and diluted infusion solutions in PVC bags

Purpose. To determine the physicochemical stability of irinotecan injection concentrate and irinotecan infusion solutions after dilution in two commonly used infusion fluids (0.9% sodium chloride, 5% dextrose) in PVC bags, stored under refrigeration (2-8°C) or at room temperature either light protected or exposed to light.

Methods. Stability of irinotecan injection concentrate was determined in the original amber glass vials. Diluted irinotecan infusion solutions were aseptically prepared by further dilution of irinotecan stock solution with either 0.9% sodium chloride or 5% dextrose in PVC bags, in amounts yielding irinotecan concentrations of 0.4, 1.0, or 2.8 mg/ml. Test solutions were stored under refrigeration (2-8°C) or at room temperature either light protected or exposed to light (mixed daylight and normal laboratory fluorescent light) in parallel. Irinotecan concentrations were determined periodically throughout a 4-week storage period via a stability-indicating HPLC assay with ultraviolet detection. In addition, measurements of pH values were performed regularly and test solutions were visually examined for colour change and precipitation.

Results. Irinotecan injection concentrate and infusion solutions are shown to be physicochemically stable (at a level of >90% irinotecan) for 4 weeks when stored under refrigeration or light protected at room temperature, independent of the vehicle (0.9% sodium chloride, 5% dextrose) or the concentration (0.4, 1.0, or 2.8 mg/ml). Irinotecan infusion solutions exposed to daylight exhibited concentration-dependent instability, solutions were stable for only 7 to 14 days.

Conclusions. Irinotecan injection concentrate and diluted infusion solutions are shown to have adequate physicochemical stability for convenient pharmacy-based centralized preparation.

Simple liquid chromatography method for the quantification of irinotecan and SN38 in sheep plasma: application to in vivo pharmacokinetics after pulmonary artery chemoembolization using drug eluting beads

A rapid and simple liquid chromatography-fluorescence detection (LC-FD) method was developed and validated for the simultaneous quantification of irinotecan (CPT11) and SN38 in sheep plasma. Camptothecin (CPT) was used as the internal standard. A single step protein precipitation with acetonitrile was used for sample preparation. The separation was achieved using a 5 microm C18 column (250 mm x 4.5 mm, 5 microm) with a mobile phase composed of 36 mM sodium dihydrogen phosphate dehydrate and 4 mM sodium 1 heptane sulfonate-acetonitrile (72:28), the pH of the mobile phase was adjusted to 3. The flow rate was 1.45 mL/min and the fluorescence detection was operated at 355/515 nm (excitation/emission wavelengths). The run time was 13 min. The method was validated with respect to selectivity, extraction recovery, linearity, intra- and inter-day precision and accuracy, limit of quantification and stability. The method has a limit of quantification of 5 ng/mL for both CPT11 and SN38. The assay was linear over concentrations ranging from 5 to 5000 ng/mL and to 240 ng/mL for CPT11 and SN38, respectively. This method was used successfully to perform plasma pharmacokinetic studies of CPT11 after pulmonary artery embolization (PACE) in a sheep model. It was also validated for CPT11 and SN38 analysis in sheep lymph and human plasma.

Stability of irinotecan-loaded drug eluting beads (DC BeadTM) used for transarterial chemoembolization

Purpose. The aim of this study was to determine the loading efficiency, physicochemical stability, and release of irinotecan-loaded DC BeadsTM (bead size 100—300 μm, 300—500 μm) before and after mixing with nonionic contrast medium (Accupaque® 300, Imeron® 300, Ultravist ® 300) during a prolonged period of time (28 days) when stored at room temperature or refrigerated.

Methods. DC Beads TM were loaded with 50 mg irinotecan (Campto®) per milliliter beads in a 2 h loading period. Drug loading efficiency and stability were determined by measuring the irinotecan concentration in the excess solution. A free-flowing in vitro elution method for a period of 2 h and phosphate buffered solution (PBS, pH 7.2) as elution medium were used to analyze the integrity of the irinotecan-loaded. Stability of irinotecan-loaded beads after mixing with an equal volume of three different nonionic contrast agents was determined by measuring irinotecan concentrations in the excess solutions. Vials with loaded beads were stored protected from light at room temperature. Mixtures with contrast media were stored protected from light under refrigeration (2—8°C). Samples were taken periodically over a 4 week period (day 0, 1, 3, 7 and 28). A reversed phase HPLC assay with ultraviolet detection was utilized to analyze the concentration and purity of irinotecan.

Results. The loading procedure of DC BeadsTM with irinotecan drug solution resulted in a loading percentage of 96% (bead size 100—300 μm) independent of the storage time. No differences in loading levels and no irinotecan degradation products were observed over the period of 28 days, while the test vials were stored light protected at room temperature. Integrity of loaded irinotecan was also given over that same period of time according to the purity and concentration of irinotecan measured after intentional elution with PBS. Mixing of irinotecan-loaded beads (bead size 100—300 μm, 300—500 μm) with nonionic contrast media decreased the irinotecan loading efficiency by ∼5—10% during a maximum period of 24 h. However, no further elution or degradation was observed during a 4-week period when stored protected from light under refrigeration.

Conclusions. Irinotecan-loaded DC BeadsTM are shown to have adequate physicochemical stability over a period of at least 28 days when stored light protected at room temperature. Due to concerns of microbiological overgrowth refrigeration should always be considered. The preparation of admixtures of irinotecan-loaded beads with contrast medium in centralized cytotoxic preparation units is not recommended, because of rapid elution of 5—10% of irinotecan from the loaded beads. Furthermore, physicians see no advantages of admixtures due to the wide variation of mixing ratios of drug-loaded beads with contrast medium. In addition varying volumes of 0.9% sodium chloride solution are to be admixed during the chemoembolization procedure

Novel SN-38-incorporating polymeric micelles, NK012, eradicate vascular endothelial growth factor-secreting bulky tumors

7-Ethyl-10-hydroxy-camptothecin (SN-38), a biological active metabolite of irinotecan hydrochloride (CPT-11), has potent antitumor activity but has not been used clinically because it is a water-insoluble drug. For delivery by i.v. injection, we have successfully developed NK012, a SN-38-releasing nanodevice. The purpose of this study is to investigate the pharmacologic character of NK012 as an anticancer agent, especially in a vascular endothelial growth factor (VEGF)-secreting tumor model. The particle size of NK012 was approximately 20 nm with a narrow size distribution. NK012 exhibited a much higher cytotoxic effect against lung and colon cancer cell lines as compared with CPT-11. NK012 showed significantly potent antitumor activity against a human colorectal cancer HT-29 xenograft as compared with CPT-11. Enhanced and prolonged distribution of free SN-38 in the tumor was observed after the injection of NK012. NK012 also had significant antitumor activity against bulky SBC-3/Neo (1,533.1 +/- 1,204.7 mm(3)) and SBC-3/VEGF tumors (1,620.7 +/- 834.0 mm(3)) compared with CPT-11. Furthermore, NK012 eradicated bulky SBC-3/VEGF tumors in all mice but did not eradicate SBC-3/Neo tumors. In the drug distribution analysis, an increased accumulation of SN-38 in SBC-3/VEGF tumors was observed as compared with that in SBC-3/Neo tumors. NK012 markedly enhanced the antitumor activity of SN-38, especially in highly VEGF-secreting tumors, and could be a promising SN-38-based formulation.

Phase II study of protracted irinotecan infusion and a low-dose cisplatin for metastatic gastric cancer

AIM: To test protracted irinotecan infusion plus a low-dose cisplatin in this Phase II trial to decrease its toxicity.

METHODS: The eligibility criteria were: (1) histologically proven measurable gastric cancer; (2) performance status of 0 or 1; (3) no prior chemotherapy or completion of prior therapy at least 4 wk before enrollment; (4) adequate function of major organs; (5) no other active malignancy; and (6) written informed consent. The regimen consisted of irinotecan (60 mg/m²) on d 1 and 15 by 24-h infusion and cisplatin (10 mg/m²) on d 1, 2, 3, 15, 16, and 17. Treatment was repeated every 4 wk.

RESULTS: Thirty-one patients were registered between April 2000 and January 2001. The response rate for all 31 patients, 20 patients without prior chemotherapy, and 11 patients with prior chemotherapy was 52% (16/31), 60% (12/20), and 36% (4/11), respectively. The median survival time was 378 d. The median number of courses given to all patients was 2. Grade 4 neutropenia occurred in 11 (35%) patients, while grade 3 to 4 diarrhea or nausea occurred in 1 (3%) and 3 (10%) patients, respectively. Fatigue was minimal as grade 1 fatigue was found only in 3 (10%) patients. Other adverse events were mild and no treatment-related deaths occurred.

CONCLUSION: This regimen showed a high level of activity and acceptable toxicity in patients with metastatic gastric cancer.

Phase I and pharmacokinetic study of Bay 38-3441, a camptothecin glycoconjugate, administered as a 30-minute infusion daily for five days every 3 weeks in patients with advanced solid malignancies

Bay 38-3441 is a camptothecin glycoconjugate which stabilizes the active lactone form of camptothecin and allows selective uptake into tumor cells. We conducted a phase I study of Bay 38-3441 administered as a 30-minute infusion daily for five consecutive days every 21 days. Thirty-one patients were enrolled at 8 dose levels. Most common nonhematologic side effects were diarrhea (29%), vomiting (19%), nausea (19%), lethargy (13%), and abdominal pain (10%). The main hematologic toxicity was prolonged neutropenia. Nine patients had a best response of stable disease with a median duration of 2.7 months (range: 2.3-20.6 months). The study was closed without reaching the maximum tolerated dose (MTD) due to excessive toxicity in a companion trial resulting in termination of development of this agent. Bay 38-3441 was well tolerated in this study with granulocytopenia as the main hematologic toxicity. This study showed that glycoconjugation is a feasible delivery technique for camptothecin.

Differential rates of glucuronidation for 7-ethyl-10-hydroxy-camptothecin (SN-38) lactone and carboxylate in human and rat microsomes and recombinant UDP-glucuronosyltransferase isoforms

7-ethyl-10-hydroxy-camptothecin (SN-38), the active metabolite of the anti-cancer agent irinotecan, contains a lactone ring that equilibrates with a carboxylate form. Since SN-38 lactone is the active and toxic form, it is prudent to examine whether the more soluble carboxylate is a surrogate for SN-38 lactone conjugation. Therefore, relative rates of glucuronidation and isoform specificity of SN-38 lactone and carboxylate were characterized. The stability of SN-38 lactone and carboxylate in incubation mixtures of microsomes and UDP-glucuronosyltransferase (UGT) isoforms was used to determine optimal incubation times. Microsomal incubations were conducted using rat and human intestinal and hepatic microsomes and human and rat recombinant UGT1A isoforms. Where estimates of lactone and carboxylate glucuronidation rates could not be established due to short incubation times and detection limits, kinetic modeling was used to recover these rate constants. The stability experiments revealed that the lactone was stabilized by rat microsomes, however, the opposite was observed in human microsomes and recombinant isoforms. For all tissues and most UGT isoforms examined, the lactone consistently had catalytic rates up to 6-fold greater than the carboxylate. The rank order of glucuronidation for both SN-38 lactone and carboxylate was 1A7 > 1A1 > 1A9 > 1A8 and 1A7 > 1A8 > 1A1 for human and rat isoforms, respectively. This study provides further support that SN-38 lactone and carboxylate may be considered pharmacokinetically distinct agents. The in vivo impact of this conjugation difference is unknown, since variations in protein binding and transport proteins may affect intracellular concentrations of the lactone or carboxylate.

Simple non-ion-paired high-performance liquid chromatographic method for simultaneous quantitation of carboxylate and lactone forms of 14 new camptothecin derivatives

SN-38 (7-ethyl-10-hydroxycamptothecin) is an active metabolite derived from the semi-synthetic compound camptothecin (CPT) named Irinotecan (CPT-11). The antitumor activity of SN-38 is 1000-fold more potent than the parent CPT-11. Fourteen new derivatives of camptothecin have recently been developed by Yakult Honsha (Tokyo, Japan). Here we describe a simple and cost-effective high-performance liquid chromatography (HPLC) method without an ion-pairing agent, which allows the simultaneous determination of both lactone and carboxylate forms of SN-38 and other camptothecin derivatives. A weak linear relationship between the HPLC retention factors (ln k') and the cellular concentrations of these compounds was observed. These results suggest that low-polarity compounds easily accumulate in cancer cells and may circumvent drug resistance. The HPLC analysis herein described is expected to greatly assist in derivative synthesis and chemical modification of camptothecin-based antitumor drugs.

High-performance liquid chromatographic analysis of the anticancer drug irinotecan (CPT-11) and its active metabolite SN-38 in human plasma

A rapid, sensitive, and specific high-performance liquid chromatography (HPLC) method for the simultaneous determination of irinotecan (CPT-11) and its active metabolite SN-38 in human plasma is described. The analytes are quantified as the totals of their carboxylate and lactone form. The sample pretreatment consisted of a simple protein precipitation with acetonitrile-methanol (1:1, v/v), after which CPT-11 and SN-38 were quantitatively converted to their carboxylate form by adding 0.01 mol/L sodium tetraborate (pH, 9). Chromatography was carried out on a Zorbax SB-C18 column with fluorescence detection. The method has been validated, and stability tests under various clinically relevant conditions have been performed. The lower limit of quantification (LLOQ) was 5.0 ng/mL for CPT-11 and 0.5 ng/mL for SN-38. Standard concentration ranges were linear between 5 and 1,500 ng/mL for CPT-11 and between 0.5 and 100 ng/mL for SN-38. This assay is simple, rapid, and very useful for therapeutic monitoring of CPT-11 and SN-38.

Determination of 9-nitrocamptothecin and its metabolite 9-aminocamptothecin in human plasma using high-performance liquid chromatography with ultraviolet and fluorescence detection

A high-performance liquid chromatography assay is described for the determination of the investigational anti-cancer drug 9-nitrocamptothecin (9-NC) and its metabolite 9-aminocamptothecin (9-AC) as the total of their lactone and carboxylate forms. The sample pre-treatment consisted of a deproteinisation step and a quantitative acid-catalyzed conversion of all 9-NC and 9-AC into their lactone forms and a subsequent solid-phase extraction. Redissolved extracts were analyzed on a Prodigy analytical column, using a mixture of methanol-phosphate buffer (pH 2.5). Detection was concomitantly performed with UV for 9-NC and fluorimetrically for 9-AC. The lower limit of quantifications were 10 ng/ml and 2.5 ng/ml for the determination of 9-NC and 9-AC, respectively, using 500 microl of plasma. The presented method was successfully applied to a clinical pharmacokinetic study.

Irinotecan pharmacokinetics-pharmacodynamics: the clinical relevance of prolonged exposure to SN-38

We have shown previously that the terminal disposition half-life of SN-38, the active metabolite of irinotecan, is much longer than earlier thought. Currently, it is not known whether this prolonged exposure has any relevance toward SN-38-induced toxicity. Here, we found that SN-38 concentrations present in human plasma for up to 3 weeks after a single irinotecan infusion induce significant cytotoxicity in vitro. Using pharmacokinetic data from 26 patients, with sampling up to 500 h, relationships were evaluated between systemic exposure (AUC) to SN-38 and the per cent decrease in absolute neutrophil count (ANC) at nadir, or by taking the entire time course of ANC into account (AOC). The time course of SN-38 concentrations (AUC(500 h)) was significantly related to this AOC (P<0.001). Based on these findings, a new limited-sampling model was developed for SN-38 AUC(500 h) using only two timed samples: AUC(500 h)=(6.588 x C(2.5 h))+(146.4 x C(49.5 h))+15.53, where C(2.5 h) and C(49.5 h) are plasma concentrations at 2.5 and 49.5 h after start of infusion, respectively. The use of this limited-sampling model may open up historic databases to retrospectively obtain information about SN-38-induced toxicity in patients treated with irinotecan.

Impact of body-size measures on irinotecan clearance: alternative dosing recommendations

PURPOSE

To evaluate relationships between various body-size measures and irinotecan (CPT-11) clearance and metabolism in cancer patients, and to provide future dosing recommendations for this agent.

PATIENTS AND METHODS

Pharmacokinetic data were obtained from 82 adult patients (50 men, 32 women; median age, 54 years) receiving CPT-11 as a 90-minute intravenous infusion (dose range, 175 to 350 mg/m(2)). In each patient, plasma samples were collected at timed intervals in the first administration of a 3-week schedule, and CPT-11 and its metabolite, SN-38, were measured by a liquid chromatographic assay.

RESULTS

The mean (+/- SD) CPT-11 clearance was 33.6 +/- 10.8 L/h, with an interindividual variability (IIV) of 32.1%. When clearance was adjusted for body-surface area (BSA), the IIV was similar (34.0%). In addition, in a multiple linear regression analysis, none of the studied measures (BSA, lean body mass, [adjusted] ideal body weight, and body mass index) was a significant covariate (P >.13; r(2) <.014) in our population. Similarly, BSA did not significantly contribute to variability in the relative extent of conversion to SN-38 (P =.26).

CONCLUSION

BSA is not a predictor of CPT-11 clearance or SN-38 pharmacokinetics and does not contribute to reducing kinetic variability. These findings provide a rationale for the conduct of a comparative phase III study between BSA-based dosing and flat or fixed dosing of CPT-11.

Separation methods for camptothecin and related compounds

This paper reviews working procedures for the analytical determination of camptothecin and analogues. We give an overview of aspects such as the chemistry, structure-activity relationships, stability and mechanism of action of these antitumor compounds. The main body of the review describes separation techniques. Sample treatment and factors influencing high-performance liquid chromatography development are delineated. Published high-performance liquid chromatographic methods are summarized to demonstrate the variability and versatility of separation techniques and a critical evaluation of separation efficiency, detection sensitivity and specificity of these methods is reported.

Analytical approaches for traditional chinese medicines exhibiting antineoplastic activity

Traditional Chinese medicines have attracted great interest in recent researchers as alternative antineoplastic therapies. This review focuses on analytical approaches to various aspects of the antineoplastic ingredients of traditional Chinese medicines. Emphasis will be put on the processes of biological sample extraction, separation, clean-up steps and the detection. The problems of the extraction solvent selection and different types of column chromatography are also discussed. The instruments considered are gas chromatography, capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) connected with various detectors (ultraviolet, fluorescence, electrochemistry, mass, etc.). In addition, determinations of antineoplastic herbal ingredients, including camptothecin, taxol (paclitaxel), vinblastine. vincristine, podophyllotoxin, colchicine, and their related compounds, such as irinotecan, SN-38, topotecan, 9-aminocamptothecin, docetaxel (taxotere) and etoposide, are briefly summarized. These drugs are structurally based on the herbal ingredients, and some of them are in trials for clinical use. Evaluation of potential antineoplastic herbal ingredients, such as harringtonine, berberine, emodin, genistein, berbamine, daphnoretin, and irisquinone, are currently investigated in laboratories. Other folk medicines are excluded from this paper because their antineoplastic ingredients are unknown.

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

OBJECTIVES

This trial was performed to determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), and pharmacokinetic profile of irinotecan (CPT-11) when administered on a once-every-2-week schedule.

PATIENTS AND METHODS

CPT-11 was administered to successive cohorts of patients at progressively increasing starting doses ranging from 125 to 350 mg/m2. The MTD and DLTs were determined both for CPT-11 alone and for CPT-11 followed by filgrastim (G-CSF). Plasma samples were obtained during the first 24 hours after initial dosing to determine the total concentrations (lactone + carboxylate forms) of CPT-11; of the active metabolite SN-38; and of SN-38 glucuronide (SN-38G).

RESULTS

Neutropenic fever was the DLT for CPT-11 at the 300 mg/m2 dose level. When G-CSF was added, dose escalation beyond 350 mg/m2 could not be achieved due to grade 2-3 toxicities that prevented on-time retreatment with CPT-11. Severe, late diarrhea was uncommon on this schedule. Peak plasma concentrations of SN-38 and SN-38G were approximately 2.5% and 4.2% of the corresponding peak plasma concentration for CPT-II, 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. No predictive correlation was observed between CPT-11 or SN-38 peak concentration or AUC and first-cycle diarrhea, neutropenia, nausea, or vomiting. Across the range of doses studied, mean CPT-11 clearance was 14.0 +/- 4.0 l/h/m2 and volume of distribution was 146 +/- 45.9 l/m2.

CONCLUSIONS

When administered every two weeks, the recommended phase II starting dose of CPT-11 is 250 mg/m2 when given alone and 300 mg/m2 when supported by G-CSF. This every-two-week regimen offers a tolerable and active alternative to weekly or every-three-week single-agent CPT-11 therapy.

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

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

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

PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

High-performance liquid chromatographic method for the simultaneous determination of the camptothecin derivative irinotecan hydrochloride, CPT-11, and its metabolites SN-38 and SN-38 glucuronide in rat plasma with a fully automated on-line solid-phase extraction system, PROSPEKT

We established a high-performance liquid chromatography (HPLC) method for the simultaneous determination of the camptothecin (CPT) derivative, irinotecan hydrochloride (CPT-11) and its metabolites, 7-ethyl-10-hydroxycamptothecin (SN-38) and SN-38 glucuronide (SN-38G) in rat plasma with a fully automated on-line solid-phase extraction system, PROSPEKT. Plasma samples were pretreated with 0.146 M H3PO4 to inactivate carboxylesterase and beta-glucuronidase in rat plasma, and added with the internal standard solution (0.146 M H3PO4 containing 1 microgram/ml CPT) and then analyzed. The method was validated for CPT-11 (5 to 25,000 ng/ml), SN-38 (5 to 2500 ng/ml) and SN-38G (2.5 to 500 ng/ml). This method enabled the determination of many samples within a relatively short time with easy sample preparation. It also had four advantages compared with conventional determination methods, i.e. automation of a complicated sample preparation, time-saving by the simultaneous determination of three compounds, the direct determination of SN-38G, and the small amount of plasma required for the determination.

Effective irinotecan (CPT-11)-containing liposomes: intraliposomal conversion to the active metabolite SN-38

Irinotecan hydrochloride (CPT-11) is a prodrug of SN-38, which is an active metabolite with antitumor activity and side toxicity. The activities of CPT-11 and SN-38 depend on the closed lactone ring form of SN-38. We have examined the tissue distributions of the closed and open forms of CPT-11 and SN-38 in Lewis lung carcinoma-bearing mice after the administration of liposomal CPT-11 (S-Lip) and polyethyleneglycol (PEG)-modified S-Lip (S-PEG). The plasma concentrations of closed CPT-11 and SN-38 were increased by liposomalization, and their blood circulation was prolonged by the PEG modification. The concentrations of closed CPT-11 and SN-38 in tumors were elevated by both the liposomalization and PEG modification. The closed/total ratio of SN-38 in the tumors of the S-PEG group was greater than that of the CPT-11 solution (Sol) group. Thus, SN-38 was thought to be generated in intact liposomes containing CPT-11. The bile concentration of closed SN-38, which is responsible for CPT-11-induced intestinal disorder, was decreased by liposomalization. In an in vitro experiment, the SN-38/CPT-11 ratio in the tumor cells of the S-Lip group was found to be higher than that of the Sol group, and the ratio of the closed form of SN-38 was increased by the liposomalization. Laser scanning confocal microscopy showed the generation of SN-38 in the liposomal membrane after the incubation of S-Lip with carboxylesterase. It is therefore considered that a part of CPT-11 is converted to SN-38 in the intact liposomes.

Phase I and pharmacokinetic trial of oral irinotecan administered daily for 5 days every 3 weeks in patients with solid tumors

PURPOSE

We conducted a phase I dose-escalation trial of orally administered irinotecan (CPT-11) to characterize the maximum-tolerated dose (MTD), dose-limiting toxicities (DLTs), pharmacokinetic profile, and antitumor effects in patients with refractory malignancies.

PATIENTS AND METHODS

CPT-11 solution for intravenous (IV) use was mixed with CranGrape juice (Ocean Spray, Lakeville-Middleboro, MA) and administered orally once per day for 5 days every 3 weeks to 28 patients. Starting dosages ranged from 20 to 100 mg/m2/d.

RESULTS

Grade 4 delayed diarrhea was the DLT at the 80 mg/m2/d dosage in patients younger than 65 years of age and at the 66 mg/m2/d dosage in patients 65 or older. The other most clinically significant toxicity of oral CPT-11 was neutropenia. A linear relationship was found between dose, peak plasma concentration, and area under the concentration-time curve (AUC) for both CPT-11 and SN-38 lactone, implying no saturation in the conversion of irinotecan to SN-38. The mean metabolic ratio ([AUC(SN-38 total) + AUC(SN-38G total)]/AUC(CPT-11 total)) was 0.7 to 0.8, which suggests that oral dosing results in presystemic conversion of CPT-11 to SN-38. An average of 72% of SN-38 was maintained in the lactone form during the first 24 hours after drug administration. One patient with previously treated colorectal cancer and liver metastases who received oral CPT-11 at the 80 mg/m2/d dosage achieved a confirmed partial response.

CONCLUSION

The MTD and recommended phase II dosage for oral CPT-11 is 66 mg/m2/d in patients younger than 65 years of age and 50 mg/m2/d in patients 65 or older, administered daily for 5 days every 3 weeks. The DLT of diarrhea is similar to that observed with IV administration of CPT-11. The biologic activity and favorable pharmacokinetic characteristics make oral administration of CPT-11 an attractive option for further clinical development.

Bradycardia induced by irinotecan: a case report

Irinotecan chloride (CPT-11) is a new semi-synthetic camptothecin analogue which has encouraging antitumor activity against various malignancies. The major and unique toxicity of CPT-11 is diarrhea. Cardiovascular toxicity is rare and has not been found in clinical trials performed in Japan except for a very few cases of insignificant tachycardiac arrhythmia. We report a case of a 69-year-old man with recurrent colon cancer who suffered from bradycardia induced by infusion of CPT-11. Other toxicities including hematological toxicity and diarrhea were mild. Pharmacokinetic analysis using a limited sampling model revealed that the occurrence of bradycardia did not correlate with the excess of drug exposure. Although all of the cholinergic actions reported in the literature were mild, cardiotoxicity may come to be a clinically significant problem. If the events were examined more thoroughly, the cholinergic effect may be discovered more frequently. To administer CPT-11 safely needs meticulous monitoring not only for hematological toxicity and diarrhea but also for other cholinergic actions including bradycardia.

Multiplicity of biliary excretion mechanisms for the camptothecin derivative irinotecan (CPT-11), its metabolite SN-38, and its glucuronide: role of canalicular multispecific organic anion transporter and P-glycoprotein

A frequent dose-limiting effect of irinotecan (CPT-11) is its gastrointestinal toxicity (diarrhea), which is thought to be related to biliary excretion of CPT-11 and its metabolites. Accordingly, we have investigated the mechanism of biliary excretion of these compounds. In vivo pharmacokinetic studies revealed that the biliary excretion of the four anionic forms of CPT-11 and its metabolites was reduced in Eisai hyperbilirubinemic rats, which carry a mutation of the hepatic canalicular multispecific organic anion transporter (cMOAT) gene. The protein encoded by this gene is expressed on the bile canalicular membrane and is responsible for the transport of organic anions into bile. Detailed analysis using isolated liver bile canalicular membrane vesicles to identify transport systems showed that cMOAT is responsible for biliary excretion of the low-affinity component of the carboxylate form of CPT-11 and the high-affinity component of both the lactone and carboxylate forms of SN-38 glucuronide. The carboxylate form of SN-38 is transported by cMOAT alone. Transport of the high-affinity component of CPT-11 was inhibited by verapamil and PSC-833, but their effect on the transport of its low-affinity component was minimal. In addition, ATP dependence in the uptake of CPT-11 by membrane vesicles obtained from a P-glycoprotein (P-gp)-overexpressing cell line was observed. Thus P-gp may be responsible for transport of the high-affinity component of the carboxylate form of CPT-11.

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

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

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

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

Clinical pharmacokinetics of irinotecan

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

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

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

A 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: AUCCPT-11 = 3.7891*C2.5 + 14.0479*C13.5 + 1.5463 AUCSN-38 = 0.5319*C2.5 + 19.1468*C13.5 + 72.7349 where C2.5 and C13.5 are the plasma concentration of CPT-11 (micrograms/ml) or SN-38 (ng/ml) at 2.5 and 13.5 h after the initiation of CPT-11 infusion, respectively. The models were validated prospectively on a separate test data set of 12 patients receiving the same dose of CPT-11 investigated in a previous study. Validation of the final LSM on the test data set gave values of root mean square error (RMSE) of 12.72% and 5.97% for the AUC of CPT-11 and that of SN-38, respectively. The model can be used to monitor the AUCs of both CPT-11 and SN-38 for the early prediction of toxicities and to establish a pharmacokinetically based dose modification strategy for safe administration of CPT-11.