Reversed-phase high-performance liquid chromatography method for the simultaneous quantitation of the lactone and carboxylate forms of the novel natural product anticancer agent 10-hydroxycamptothecin in biological fluids and tissues

Camptothecins are indole alkaloids isolated from a Chinese tree, Camptotheca acuminata, and have a wide spectrum of anticancer activity in vitro and in vivo. A novel camptothecin congener 10-hydroxycamptothecin (HCPT) has been shown to be more active and less toxic than camptothecin, and the lactone HCPT is believed to be responsible for its anticancer activity. In the present study, a reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection was developed and validated for the simulataneous analysis of HCPT for lactone form (I) and carboxylate form (II) in plasma, urine and feces and tissues. Biological samples were prepared by a liquid-liquid extraction method using ice-cold methanol-acetonitrile (1:1, v/v). This method was shown to be reproducible and reliable, with intra- and inter-day variations being less than 7%, and accuracy being 94.3%–102.7%. The limits of determination were 2 ng/ml, 2 ng/ml, 2 ng/g, and 10 ng/ml for HCPT forms I and II in rat plasma, urine, feces, and tissues, respectively. The assay was liner over the range 2–2000 ng/ml (r=0.999, P<0.001) with recoveries of greater than 90% for plasma and urine and approximately 70–80% for feces and tissues homogenates through the extraction procedure. This analytic procedure has been successfully applied to a pharmacokinetic study of HCPT in experimental animals and should be useful in the future human studies.     

Liquid chromatographic quantitation of the lactone and the total of lactone and carboxylate forms of 9-nitrocamptothecin in human plasma

Simple and sensitive high-performance liquid chromatography (HPLC) assays were developed and validated for the quantitation of the investigational anticancer drug 9-nitrocamptothecin (9-NC) as the lactone form and as the total of the lactone(I) and carboxylate(II) forms in human plasma. For the assay of lactone form (9NC-lac), the analytical method involved a protein precipitation step with adding a mixture of cold acetonitril-chloroform (5:1 (v/v), -20 degrees C) to plasma sample that stabilized the pH-dependent conversion of I to II. After evaporation under gentle stream of nitrogen gas (40 degrees C) the dry extract was dissolved in mobile phase (pH 5.5). For determination of the total of the lactone and carboxylate forms of the drug (9NC-tot), plasma samples were deproteinated with cold acetonitril (-20 degrees C) acidified with perchloric acid (5%), which resulted in the conversion of the carboxylate into the lactone form. After centrifugation the upper solvent was evaporated (nitrogen, 40 degrees C) and the dry extract was dissolved in mobile phase (pH 3.5). All separations were performed on a RP-C(8) column, using a mixture of acetonitril-water as eluent (pH 3.5 for total form and pH 5.5 for lactone form) and UV detection. The presented assay was linear over a concentration range of 25-1500 ng/ml with lower limit of quantitation of 25 ng/ml for both 9NC-tot and 9NC-lac. Within-run and between-run precision was always less than 7.5% in the concentration range of interest. The reported assay method showed good characteristics of linearity, sensitivity, selectivity and precision allowing applying in pharmacokinetic studies.     

Sensitive high-performance liquid chromatographic method for the determination of the lactone form and the lactone plus hydroxy-acid forms of the new camptothecin derivative DX-8951 in human plasma using fluorescence detection

A sensitive quantitation of the lactone form and the lactone plus hydroxy-acid forms of DX-8951, a camptothecin derivative, in human plasma has been investigated by high-performance liquid chromatography (HPLC). This assay method consisted of two analytical procedures. In Procedure I, the lactone form was collected by the stepwise separation on a C₁₈ cartridge. In Procedure II, the lactone plus hydroxy-acid forms were collected using another batch of the plasma sample by co-elution of the two forms from a C₁₈ cartridge with acidic solution. The hydroxy-acid form of DX-8951 was quantitated from the difference of the lactone plus hydroxy-acid forms and the lactone form. Thereafter, these pre-treated samples were assayed by HPLC under the same HPLC conditions with a spectrofluorometer and a reverse-phase ODS column. The mobile phase was acetonitrile/0.05 M potassium dihydrogen phosphate (pH 3) (18:82, v/v) at a flow-rate of 1.0 ml/min. For the assay of the lactone form and the lactone plus hydroxy-acid forms of DX-8951 in plasma, analytical method were validated over the range 0.2–50 ng/ml.     

Liquid chromatography determination of 10-hydroxycamptothecin in human serum by a column-switching system containing a pre-column with restricted access media and its application to a clinical pharmacokinetic study

A simple, rapid, sensitive column-switching HPLC method is described for the analysis of the 10-hydroxycamptothecin (HCPT) in human serum. A pre-column containing restricted access media (RAM) is used for the sample clean-up and trace enrichment and is combined with a C18 column for the final separation. The analytical time is 8 min. The HCPT is monitored with fluorescence detector, excitation and emission wavelengths being 385 and 539 nm, respectively. There is a linear response range of 1-1000 ng/ml with correlation coefficient of 0.998 while the limit of quantification is 0.1 ng/ml. The intra-day and inter-day variations are less than 5%. This analytic procedure has been applied to a pharmacokinetic study of HCPT in clinical patients and the pharmacokinetic parameters of one-compartment model are calculated.     

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 α-hydroxy-δ-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.     

Simultaneous determination of the lactone and carboxylate forms of irinotecan (CPT-11) and its active metabolite SN-38 by high-performance liquid chromatography: application to plasma pharmacokinetic studies in the rat

Irinotecan (CPT-11) and its main metabolite SN-38 are potent anticancer derivatives of camptothecin (CPT), with active lactone and inactive carboxylate forms coexisting. A simple and sensitive HPLC method using the ion-pairing reagent tetrabutylammonium hydrogen sulfate (TBAHS) was developed to simultaneously determine all four analytes in rat plasma samples. Camptothecin (CPT) was used as internal standard. The mobile phase was 0.1M potassium dihydrogen phosphate containing 0.01 M TBAHS (pH 6.4)-acetonitrile (75:25, v/v). Separation of the compounds was carried out on a Hypersil C18 column, monitored at 540 nm (excitation wavelength at 380 nm). All four compounds gave linear response as a function of concentration over 0.01-10 microM. The limit of quantitation in rat plasma was 0.01, 0.008, 0.005 and 0.005 microM for CPT-11 lactone, CPT-11 carboxylate, SN-38 lactone and SN-38 carboxylate, respectively. The method was successfully used in the study on the effect of coadministered thalidomide on the plasma pharmacokinetics of CPT-11 and SN-38 in rats. Coadministered thalidomide (100mg/kg body weight by intraperitoneal injection) significantly increased the AUC(0-10h) values of CPT-11 lactone and CPT-11 carboxylate by 32.6% and 30.3 %, respectively, (P < 0.01), but decreased the values by 19.2% and 32.4% for SN-38 lactone and carboxylate, respectively, (P < 0.05). Accordingly, the value of total body clearance (CL) of CPT-11 lactone was significantly lower in combination group compared to the control (1.329 versus 1.837 L/h/kg, P = 0.0002). Plasma t(1/2beta) values for SN-38 lactone and carboxylate were significantly (P < 0.01) smaller in rats with coadministered thalidomide, as compared to rats receiving CPT-11 alone. Further studies are needed to explore the underlying mechanisms for the observed kinetic interaction between CPT-11 and thalidomide.     

Simple and sensitive high performance liquid chromatographic method for the simultaneous quantitation of the lactone and carboxylate forms of topotecan in human plasma

A selective and highly sensitive isocratic high performance liquid chromatographic (HPLC) method is described for simultaneous determination of lactone and carboxylate species of topotecan, in plasma. The method utilizes a protein precipitation step with cold methanol (-20 degrees C) for sample preparation followed by separation on a Novapack C(18) column using ammonium acetate buffer, acetonitrile and triethylamine (84:16:1.5, v/v) containing tetrabutyl ammonium hydrogen sulfate (TBAHS) (2 mM) with a pH of 5 as the mobile phase. The eluted peaks were detected by a fluorescence detector was set at an excitation wavelength of 380 nm and an emission wavelength of 527 nm. The method was validated in the range of lactone and carboxylate forms of topotecan concentrations from 0.05 to 75 ng/ml. Intra- and inter-day precision expressed by the relative standard deviation was less than 8.50% and inaccuracy did not exceed 10% for lactone and carboxylate forms of topotecan. The limit of quantitation was 0.05 ng/ml using 0.50 ml plasma. Stability studies in plasma and plasma extract indicated that topotecan is stable for at least 2 weeks at -70 degrees C.     

The comparison of biophysical properties of DB-67 and its ester DB-67-4ABTFA determined by fluorescence spectroscopy methods

Fluorescence spectroscopy methods are applied to the study of camptothecin analogue DB-67 and its ester DB-67-4ABTFA (trifluoroacetic acid salt of 20(S)-aminobutyrate substituted DB-67). Camptothecin and many of its analogues exhibit anticancer properties. They are fluorescent compounds, so using the method of fluorescence anisotropy measurements and fluorescence spectra recording many biophysical properties can be determined including affinity to proteins and membranes. One can also observe the process of conversion of the ester into DB-67. Active lactone form of camptothecin in fluids at pH 7.4 hydrolyses and converts into inactive carboxylate. Process of camptothecin deactivation is accelerated in plasma and after about 2h the total conversion to carboxylate form occurs. It is caused by fast and irreversible binding of carboxylate form to the human serum albumin (HSA). Camptothecin carboxylate bound to HSA does not lactonise. On the other hand, camptothecin lactone binding to membranes is reversible, but as long as lactone form bound to membranes does not hydrolyse. Knowledge of binding properties to proteins and membranes permits to select among many camptothecin analogues the ones exhibiting desirable behavior in physiological conditions: high affinity of lactone form to membranes and low affinity of carboxylate form to albumin. The studied DB-67 and DB-67-4ABTFA fulfill these requirements.     

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

Two sensitive reversed-phase high-performance liquid chromatographic fluorescence methods, with simple sample handling at the site of the patient, are described for the determination of the lactone and lactone plus carboxylate forms of 9-aminocamptothecin (9AC). For 9AC lactone, the sample preparation was a liquid–liquid extraction with acetonitrile–n-butyl chloride (1:4, v/v), whereas the sample preparation for 9AC total (lactone plus carboxylate) was a simple deproteinization with 5% perchloric acid–methanol (1:1, v/v), which results in the conversion of the carboxylate into the lactone form. The lower limits of quantitation were 50 pg/ml and 100 pg/ml for 9AC lactone and 9AC total, respectively. The within-run precisions at four tested concentrations were ≤6.3% for 9AC lactone and ≤5.3% for 9AC total. The between-run precisions were ≤8.9% and ≤5.6%, respectively. The assays were developed to enable pharmacological analysis of 9AC in a bioavailability and oral phase I study in patients with solid tumors.     

Determination of plasma topotecan and its metabolite N-desmethyl topotecan as both lactone and total form by reversed-phase liquid chromatography with fluorescence detection

Topotecan (TPT) undergoes hepatic N-demethylation forming N-desmethyl topotecan (NDS). To evaluate the effect of drug-drug interactions on NDS disposition in children receiving TPT we developed and validated a sensitive and specific HPLC-fluorescence detection method for lactone and total (lactone plus carboxylate) TPT and NDS. Deproteinized plasma is vortexed, centrifuged, and the methanolic extract diluted with water for the lactone form of NDS and TPT or diluted with 1.5% phosphoric acid for NDS and TPT total. A 100 microL sample is injected onto a Varian ChromGuard RP column attached to an Agilent SB-C(18) reversed-phase analytical column held at 50 degrees C. The mobile phase (flow-rate, 0.8 mL/min) consists of methanol-aqueous buffer (27:73, v/v) (75 mM potassium phosphate and 0.2% triethylamine, pH 6.5). TPT and NDS were detected with excitation and emission wavelengths set at 376 and 530 nm, respectively. The standard curves for both forms of TPT ranged from 0.25 to 80 ng/mL, and for NDS ranged from 0.10 to 8.0 ng/mL. Within-day and between-day precision (% RSD) was 相似文献