The pharmacokinetics of topotecan and its carboxylate form following separate intravenous administration to the dog

Pharmacokinetic modeling of the blood-stable camptothecin analog AR-67 in two different formulations

AR-67 is a lipophilic camptothecin analog currently under clinical investigation using a Cremophor EL based formulation. However, as potential toxicity limitations exist in the clinical use of Cremophor, an alternative cyclodextrin (SBE-β-CD) based formulation has been proposed. Pharmacokinetic (PK) studies were conducted in mice and the SBE-β-CD based formulation was compared with the Cremophor EL formulation. PK studies were conducted following intravenous or oral administration of AR-67 in either Cremophor or SBE-β-CD formulation in mice. Noncompartmental analysis was used to determine the plasma and tissue drug distribution. A non-linear mixed effects (population) PK model was developed to fit both the oral and intravenous data and to estimate key PK parameters. The effect of formulation was explored as a covariate in the PK model. AR-67 in the SBE-β-CD formulation had similar plasma PK and biodistribution to that in the Cremophor EL formulation. The proposed two-compartment model described the plasma PK of AR-67 in both formulations adequately. AR-67 in the SBE-β-CD formulation exhibited dose linearity following both oral and intravenous administration. Our studies indicate that SBE-β-CD is a viable alternative to Cremophor EL as a pharmaceutical excipient for formulating AR-67.

Oral topotecan: Bioavailability, pharmacokinetics and impact of ABCG2 genotyping in Chinese patients with advanced cancers

Oral topotecan (Hycamtin(®)) has been recently approved for the treatment of relapsed small cell lung cancer (SCLC) in 2007, however, the bioavailability and pharmacokinetic data of topotecan for Chinese patients is still limited. Xinze(®) is a new and the only capsule formulation of topotecan used in China that is similar to Hycamtin(®). The current study aimed to investigate the absolute bioavailability and pharmacokinetics of Xinze(®) in Chinese patients with advanced cancers. On day 1, an IV dose of 1.5 mg/m(2)/d as a 30 min continuous infusion was administered. Patients took the oral topotecan at one of two dose levels: 1.5 mg/m(2)/d (six patients) or 1.9 mg/m(2)/d (seven patients) on day 2. Plasma pharmacokinetics of total topotecan and topotecan in the lactone form were performed on both days using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Single-nucleotide polymorphisms (SNPs) identified in exon 5 (421C>A) and in exon 2 (34G>A) in ATP-binding cassette sub-family G member 2 (ABCG2) were analyzed by direct sequencing. Safety assessments were performed throughout the study. The maximum plasma concentration (Cmax) reached at 1-2 h and the elimination half-life time (T1/2) was approximately 4.2 h after oral administration. The absolute bioavailability of total topotecan in the 1.5 mg/m(2)/d and 1.9 mg/m(2)/d groups averaged 41.23 ± 11.8% and 36.00 ± 14.8%, respectively. The patients with heterozygous SNPs had essentially the same bioavailability and pharmacokinetics. The bioavailability of topotecan after oral administration illustrates good systemic exposure at dosages of 1.5 mg/m(2)/d and 1.9 mg/m(2)/d over a five-day schedule in Chinese patients. On a dose-normalized basis, the values of Cmax and AUC0-t for total topotecan in Chinese patients were higher than in Caucasians following oral and intravenous administration, while the T1/2 was consistent.

Development and validation of a liquid chromatography-tandem mass spectrometry method for topotecan determination in beagle dog plasma and its application in a bioequivalence study

Topotecan (TPT) is an important anti-cancer drug that inhibits topoisomerase I. A sensitive and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method that potentially determines TPT in beagle dog plasma is needed for a bioequivalence study of TPT formulations. We developed and validated LC-MS/MS to evaluate TPT in beagle dog plasma in terms of specificity, linearity, precision, accuracy, stability, extraction recovery and matrix effect. Plasma samples were treated with an Ostro(TM) sorbent plate (a robust and effective tool) to eliminate phospholipids and proteins before analysis. TPT and camptothecin (internal standard) were separated on an Acquity UPLC BEH C18 column (1.7 µm, 2.1 × 50 mm) with 0.1% formic acid and methanol as the mobile phase at a flow rate of 0.25 mL/min. TPT was analyzed using positive ion electrospray ionization in multiple-reaction monitoring mode. The obtained lower limit of quantitation was 1 ng/mL (signal-to-noise ratio > 10). The standard calibration curve for TPT was linear (correlation coefficient > 0.99) at the concentration range of 1-400 ng/mL. The intra-day and inter-day precision, accuracy, stability, extraction recovery and matrix effect of TPT were within the acceptable limits. The validated method was successfully applied in a bioequivalence study of TPT in healthy beagle dogs.

Topotecan exposure estimation in pediatric acute myeloid leukemia supported by LC-MS-based drug monitoring and pharmacokinetic analysis

Individualization of the topotecan dosing can reduce inter-patient variability, toxicity, and at the same time increases chemotherapy efficacy. Topotecan dosing based on simultaneous drug monitoring and pharmacokinetic analysis can yield more accurate and precise estimation of the topotecan systemic exposure than that attainable with the fixed dosing approach. Therefore, a combined approach could provide a tool assisting the clinicians in individualization of the topotecan dosing. The aim of the study was to estimate the topotecan exposure in pediatric patients with acute myeloid leukemia (AML) based on the plasma concentration-time data and using the pharmacokinetic analysis. The primary goal was achieve the correct estimation of the target plasma area against the topotecan concentration-time curve (AUC) in a 5 day course of cladribine followed by monitored topotecan in pediatric patients with recurrent/refractory AML. A sensitive and selective reversed-phase liquid chromatographic-mass spectrometry (LC-MS) assay was developed to quantify total topotecan in the human plasma samples. This method, with its lower quantification limit of 1 ng/ml, was validated over a linear range of 1-150 ng/ml. Under the proposed approach, the topotecan dosing was selected so as to achieve the final AUC value of 140±20 ng/ml h. The presented analytical and pharmacokinetic data demonstrate that the proposed approach can be a practical, useful, efficient, and accurate tool for individualizing the topotecan dosing in children with AML.

Review role of topotecan in gynaecological cancers: current indications and perspectives

BACKGROUND

Ovarian cancer is the fourth cause of death from gynaecological cancer and cervical cancer is the first in women <45 years old in developing countries. The aim of this article is to review the role of topotecan (Hycamtin), a semi-synthetic alkaloid derivative of camptothecin, in ovarian and cervical cancer in monotherapy and in combination.

METHODS

This article reviews the mechanism of action, pharmacokinetics, toxicity and efficacy of topotecan. The paper also reports the principal phases II and III studies of topotecan in advanced or recurrent ovarian and cervical cancer.

RESULTS

Topotecan (Hycamtin), currently indicated for the treatment of relapsed ovarian cancer, has demonstrated activity both in platinum-sensitive and in platinum-resistant disease. The combination cisplatin-topotecan for the treatment of advanced and recurrent cervical cancer has demonstrated a clinical benefit in terms of response rate, overall survival and progression free survival. Haematological toxicity of topotecan also is easy to manage and not cumulative, especially with the weekly scheduled recently introduced in clinical practice.

CONCLUSION

Topotecan (Hycamtin) will continue to play a role in the treatment of advanced ovarian and cervical cancer, in monotherapy or in combination with other cytotoxic agents.

Preparation and characterization of camptothecin solid lipid nanoparticles

Camptothecin (CA), an antitumor drug, was incorporated into solid lipid nanoparticles (SLNs) prepared by high-pressure homogenization. A Taguchi orthogonal experimental design was used to study the influence of four different variables, with each variable having three value levels on nanoparticle size. Analysis of variance (ANOVA) has been used to evaluate the preparation of CA-SLNs and perform product optimization. The optimized CA-SLNs suspension was lyophilized using mannitol and glucose as cryoprotectants. The physicochemical characteristics of CA-SLNs were evaluated using transmission electron microscopy (TEM), electrophoresis, and differential scanning calorimetry (DSC). The release of camptothecin from CA-SLNs in various media was evaluated using a high-performance liquid chromatography (HPLC) method. The results showed that the concentration of emulsifier and the homogenization pressure had a significant influence on the particle size. The optimized CA-SLNs had an average diameter of about 200 nm, exhibited monodispersity with Dw/Dn of 1.06, and carried a negative charge. The optimal cryoprotectants consisted of 10% mannitol and 5% glucose in nanoparticle suspension. Lyophilized product was reconstituted in distilled water within 0.5 min without change of nanoparticle size. Camptothecin might exist in an amorphous state in SLNs. In vitro results showed that drug release was achieved for up to one week, and the released camptothecin quickly changed to open carboxylate form in the biological pH phosphate buffer. The results indicate that SLNs might be good potential sustained-release delivery vehicles for camptothecin or other lipophilic drugs.