Determination of the lactone and lactone plus carboxylate forms of 9-aminocamptothecin in human plasma by sensitive high-performance liquid chromatography with fluorescence detection

Quantitative determination of DRF-1042 in human plasma by HPLC: validation and application in clinical pharmacokinetics

A simple and sensitive high-performance liquid chromatography (HPLC) method has been developed and validated for the determination of DRF-1042, a novel orally active camptothecin (CPT) analog, in human plasma. The sample preparation was a simple deproteinization with acidified methanol yielding almost 100% recovery of DRF-1042. An isocratic reverse-phase HPLC separation was developed on a Supelcosil-LC318 column (250 x 4.6 mm, 5 microm) with mobile phase consisting of 1% v/v triethylamine acetate, pH 5.5 and acetonitrile (80:20, v/v) at a fl ow rate of 1.0 mL/min. The eluate was monitored with a fluorescence detector set at excitation and emission wavelengths of 370 and 430 nm, respectively. The standard curves were linear (r(2) > 0.999) in the concentration ranges 5.0-2004 ng/mL. The lower limit of quantification (LLQ) of the assay was 5 ng/mL. The mean measured quality control (QC) concentrations (range 5 ng/mL to 40 microg/mL) deviated from the nominal concentrations in the range of -10.5-0.08 and -14.5-7.97%, inter- and intra-day, respectively. The inter- and intra-day precisions in the measurement of QC samples at four tested concentrations, were in the range 0.64-5.89% relative standard deviation (RSD) and 0.33-14.7% RSD, respectively. The method was found to be suitable for measurement of plasma concentrations above the calibration curve after serial dilutions. Stability of DRF-1042 was confirmed in a battery of studies, viz., on bench-top, in the auto-sampler, in the stock solutions, after four quick freeze-thaw cycles, up to one month at -20 degree C in human plasma and up to 2 months in the ex vivo samples. The method is simple, sensitive and reliable and has been successfully implemented to investigate the clinical pharmacokinetics of DRF-1042 in cancer patients in a phase I clinical trial.

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.

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.

Antitumor drugs possessing topoisomerase I inhibition: applicable separation methods

Separation methods for antitumor drugs capable of topoisomerase I inhibition were reviewed in this study. Camptothecin (CPT) its related analogues seemed to be promising anticancer drugs that exhibit topoisomerase I inhibition. This group of compounds contain a closed alpha-hydroxy-delta-lactone ring (lactone form) that can undergo reversible hydrolysis to form the open-ring form (carboxylate form). In vitro pharmacological study showed that the antitumor activity of the lactone form was higher than that of the carboxylate form. Thus a quantitative method to separate these two forms is important to evaluate the pharmacokinetics and pharmacodynamics of these compounds. Nevertheless, current separation methods are complicated by the pH-dependent instability of the lactone moiety. High-performance liquid chromatography (HPLC) coupled with fluorometric detection has been widely used for the quantitation of the drug as the intact lactone form or as the total lactone carboxylate forms in biological matrices. In this report we reviewed current applicable chromatographic techniques for further bioanalytical studies of CPT derivatives including sample preparations, HPLC columns, mobile phases and additives.

Quantitation of camptothecin and related compounds

Camptothecin and congeners represent a clinically very useful class of anticancer agents. Proper identification and quantitation of the original compounds and their metabolites in biological fluids is fundamental to assess drug metabolism and distribution in animals and in man. In this paper we will review the recent literature available on the methods used for separation and quantitative determination of the camptothecin family of drugs. Complications arise from the fact that they are chemically labile, and the pharmacologically active lactone structure can undergo ring opening at physiological conditions. In addition, a number of metabolic changes usually occur, producing a variety of active or inactive metabolites. Hence, the conditions of extraction, pre-treatment and quantitative analysis are to be carefully calibrated in order to provide meaningful results.

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.

The clinical development of 9-aminocamptothecin

9-Aminocamptothecin (9-AC) is a topoisomerase I-targeting agent first synthesized by Wani and Wall in 1986. Because of its potent in vitro effects and promising preclinical activity in colorectal cancer animal models, it was designated a high-priority compound for further drug development by the NCI. In 1993, 9-AC first entered clinical trials as a 72-hour intravenous (i.v.) infusion. Predictable myelosuppression was the major dose-limiting toxicity, and pharmacokinetic studies showed a relatively short plasma half-life and unstable lactone ring. Unfortunately, phase II studies using this schedule showed minimal or no activity in tumors such as colorectal and lung cancer. Modest activity was observed in ovarian cancer and in refractory lymphomas. Efforts to improve systemic drug exposure by utilizing alternative schedules of administration of 9-AC such as prolonged, continuous intravenous infusions have also been tested. However, phase II studies of 120-hour weekly infusions of 9-AC have not shown improved activity against solid tumors such as colorectal cancer. More recently, a daily times 5 days i.v. administration schedule has been tested. Currently, further development of intravenously administered 9-AC for the treatment of colorectal cancer is not promising. Thus, topotecan and irinotecan remain the only two successfully developed topoisomerase I-targeting drugs in the United States. This experience with 9-AC raises important questions regarding how to best select new topoisomerase I-targeting drugs for future clinical development.

Determination of camptothecin analogs in biological matrices by high-performance liquid chromatography

Several analogs of the topoisomerase I inhibitor camptothecin (CPT) have been introduced in clinical practice in the last decade. All CPT analogs are sensitive to a pH-dependent reversible conversion between a pharmacologically active lactone form and its inactive, lactone ring-opened, carboxylate form. The reversible conversion is also dependent on the, sometimes species-dependent, protein binding properties of the two forms, resulting in different lactone to carboxylate plasma ratios for the various analogs. Pharmacokinetic analysis of the CPT analogs is helpful in understanding the pharmacodynamic outcome of drug treatment, in clinical as well preclinical studies. Measurement of these analogs is habitually complicated by the chemical instability of the lactone moiety and necessitates a rapid centrifugation of the blood sample, preferably at the bedside of the patient, to collect the plasma supernatant. Since the lactone forms of these drugs are able to diffuse across cell membranes, including those of the red blood cells, rapid collection and processing is even necessary in the case where only the total concentrations of the CPT analogs are to be measured. Sample pretreatment procedures of the CPT analogs topotecan, irinotecan, 9-aminocamptothecin and lurtotecan are summarized and discussed in this review.

Bioanalytical method validation design for the simultaneous quantitation of analytes that may undergo interconversion during analysis

In the analysis of post-dose biological samples for quantitative determination of two analytes that can potentially undergo interconversion, it is essential to minimize the interconversion during the multiple steps of the bioanalytical method. However, even after optimizing the conditions of each step, some interconversion may be unavoidable. Even then, a method can be developed for the accurate simultaneous determination of the two analytes in post-dose biological samples if the composition, in terms of the ratio of the concentrations of the two analytes, of the calibration standards and quality control (QC) samples are selected judiciously, in relation to the composition of the unknown samples to be analyzed. As an example of such interconverting analytes, a delta-hydroxy acid compound (analyte 1) and its delta-lactone (analyte 2) were selected as model compounds that can potentially undergo interconversion. The effects of changing the relative concentrations of the two analytes in QC samples vis-à-vis the calibration standards on the performance of the method under conditions were investigated where: (a) the interconversion between the two analytes was minimized; (b) the conversion of analyte 2 to analyte 1 was enhanced; (c) the interconversion between the two analytes was enhanced. The results showed that the method performance, as measured by the accuracy and precision of the QC samples, was not acceptable when the ratio of concentration of analyte 1 to that of analyte 2 in the QC samples was different from that in the calibration standards and the conditions used facilitated the conversion of one analyte to the other. However, when the relative concentration of the two analytes in the QC samples was identical to that of the calibration standards, the method performance was acceptable under all three conditions of interconversion. This was because the same degree of interconversion took place in the QC samples and calibration standards. The purpose of QC samples in bioanalytical methods is to gauge how the method will perform for the analysis of post-dose test samples and hence, ideally, the relative concentrations of the analytes in QC samples, should be selected to mimic the anticipated concentrations in the test samples. However, the relative concentrations of the analytes in test samples may not be known a-priori, or may change from sample to sample; therefore, it is not always possible to construct QC samples that exactly mimic the relative concentrations of analytes in the test samples. Thus, in order to cover the variety of test samples, the method should include, in addition to QC samples that contain the analytes at the same relative concentration as in the calibration standards, QC samples with relative concentrations that are different from those in the calibration standards, including those that contain only analyte 1 and only analyte 2. In addition, the conditions adopted for the method should favor the minimization of the conversion of the analyte that is expected to be the major component in the post-dose test samples.

Phase I and pharmacologic study of oral (PEG-1000) 9-aminocamptothecin in adult patients with solid tumors

PURPOSE

9-Amino-20(S)-camptothecin (9-AC) is a specific inhibitor of topoisomerase-I. Recently, a bioavailability of approximately 48% for the oral PEG-1000 formulation was reported. We conducted a phase I and pharmacokinetic study of the oral PEG-1000 formulation of 9-AC to define the maximum-tolerated dose, toxicity profiles, pharmacokinetic-dynamic relationships, and preliminary antitumor activity in patients with solid tumors.

PATIENTS AND METHODS

Patients were treated with oral (PEG-1000) 9-AC given once a day for 7 or 14 days at doses ranging from 0.25 to 1.1 mg/m(2)/d; cycles were repeated every 21 days. For pharmacokinetic analysis, plasma sampling was performed on days 1 and 6 or 8 of the first course using a validated high-performance liquid chromatographic assay.

RESULTS

Thirty patients were entered onto the study; three patients were not assessable for toxicity and response. Twenty-seven patients received a total of 89 courses. The dose-limiting toxicities (DLTs) were myelosuppression and diarrhea at a dose of 1.1 mg/m(2)/d for 14 days. Pharmacokinetics showed a substantial interpatient variation of the area under the plasma concentration-time curve (AUC) of 9-AC. The intrapatient variability was extremely small. A significant correlation was observed between the percentage decrease in WBC count and the AUC of 9-AC lactone (r(2) = 0.86). One partial response was noted in a patient with metastatic colorectal cancer.

CONCLUSION

DLTs in this phase I study of oral 9-AC daily for 14 days every 21 days were myelosuppression and diarrhea. The recommended dose for phase II studies is 0.84 mg/m(2)/d. In view of the substantial interpatient variability in AUC and the availability of a limited sampling model, a pharmacokinetic guided phase II study should be considered.

Simultaneous determination of the lactone and carboxylate forms of the camptothecin derivative CPT-11 and its metabolite SN-38 in plasma by high-performance liquid chromatography

CPT-11 (irinotecan) and mainly its metabolite SN-38 are potent antitumor derivatives of camptothecin. As the active lactone forms of both CPT-11 and SN-38 exist in pH-dependent equilibrium with their respective less potent open-ring hydroxy acid species, the simultaneous monitoring of both forms of both compounds is relevant. CPT-11 and SN-38 derivatives have quite different fluorescence responses. In order to avoid any compromise on the wavelength setting, we developed chromatographic conditions allowing simple automated wavelength setting changes which have been prevented using existing methods involving conventional C18 columns. This was achieved by means of a Symmetry C18 column combined to a gradient elution program using acetonitrile and 75 mM ammonium acetate plus 7.5 mM tetrabutylammonium bromide at pH 6.4. The developed conditions allowed an elution order suitable for a simple automated wavelength change in respect to reliable peak integration. CPT-11 and SN-38 derivatives were detected at lambda ex=362 nm/lambda em=425 nm and lambda ex=375 nm/lambda em =560 nm, respectively. The developed method allowed the detection of amounts less than 3 pg of each derivative injected on column. The method was successfully applied to pharmacokinetic and toxicokinetic studies in rat and dog.

Determination of irinotecan (CPT-11) and its active metabolite SN-38 in human plasma by reversed-phase high-performance liquid chromatography with fluorescence detection

Sensitive high-performance liquid chromatographic assays have been developed to determine the levels of the lactone and lactone plus carboxylate (total) forms of the antitumor agent irinotecan (CPT-11) and its active metabolite SN-38, in human plasma. The related compound camptothecin was used as the internal standard. The selective sample pretreatment for the lactone forms involved a single solvent extraction with acetonitrile-n-butyl chloride (1:4, v/v), whereas the sample clean-up for the total forms was a simple protein precipitation with aqueous perchloric acid-methanol (1:1, v/v), which results in the conversion of the carboxylate to the lactone forms. Chromatography was carried out on a Hypersil ODS column, with detection performed fluorimetrically. The methods have been validated, and stability tests under various conditions have been performed. The lower limits of quantitation are 0.5 and 2.0 ng/ml for the lactone and total forms, respectively. The assays have been used in a single pharmacokinetic experiment in a patient to investigate the applicability of the method in vivo.