Extraction and assay of daunorubicin and its metabolites from neoplastic tissue

Analysis and pharmacokinetics of N-l-leucyldoxorubucin and metabolites in tissues of tumor-bearing BALB/c mice

Leucyldoxorubicin (Leu-Dox) was developed as a prodrug of doxorubicin (Dox) with the aim of lowering the cardiotoxicity and improving the therapeutic index produced by Dox. To support the preclinical findings on its antitumor activity and cardiotoxicity, concentrations of Leu-Dox and its metabolites were determined in plasma, heart, and tumor after the administration of Leu-Dox to tumor-bearing mice. A liquid-liquid extraction procedure employing a chloroform/2-propanol/dimethylsulfoxide (DMSO) mixture was developed. By means of high-performance liquid chromatography (HPLC) with fluorescence detection, Leu-Dox and six of its metabolites could be assayed in the tissues with high sensitivity. Detection limits ranged from 0.01 nmol/g tissue for the aglycons to 0.06 nmol/g for Dox. Recoveries were in the range of 82%-110%, and calibration curves were linear over the concentration range tested (0.1-10 nmol/g tissue, r > or = 0.998). Concentration versus time curves were constructed for plasma, heart, and tumor over the first 72 h, and areas under the curves (AUCs) for the first 48 h were determined by the trapezoidal rule. Dox was rapidly formed from Leu-Dox, reaching peak levels in plasma within 5 min and in tissues within 1 h after i.v. administration of Leu-Dox (12 mg/kg). The elimination of Leu-Dox was also fast as illustrated by final half-lives of 1.1, 0.8, and 0.9 h in the plasma, heart, and tumor, respectively. For Dox, the final half-lives were 16.7 h in plasma, 15.3 h in heart tissues, and 27.4 h in tumor tissues. AUC values determined for Leu-Dox and Dox were 221 and 51 nmol ml-1 min, 443 and 4,262 nmol g-1 min, and 153 and 1,466 nmol g-1 min in the plasma, heart, and tumor, respectively. Comparison of these values with those obtained after an equimolar dose of Dox indicated 26%, 30%, and 16% of Leu-Dox appeared as Dox in the plasma, heart, and tumor, respectively. Thus, not only is the plasma compartment not representative for calculations of the conversion of Leu-Dox into Dox in tissue, but differences in its appearance also exist between the tissue compartments. The AUC values found for Dox in the heart may explain the reduced cardiotoxicity elicited by Leu-Dox as compared with Dox; however, the values obtained for Dox in the insensitive murine colon tumor cannot explain the enhanced antitumor activity exerted by Leu-Dox in the sensitive human tumor xenografts in nude mice.

Simple and sensitive quantification of anthracyclines in mouse atrial tissue using high-performance liquid chromatography and fluorescence detection

Anthracyclines are very effective against soft tissue sarcomas, with cardiotoxicity being an important side effect after repeated administration. To estimate the relative cardiotoxicity of various anthracyclines and their metabolites, we developed an isolated mouse left atrium model. To relate an effect of doxorubicin, 4'-epidoxorubicin and their four main metabolites (doxorubicinol, epidoxorubicinol and the aglycons 7-deoxydoxorubicinon and 7-deoxydoxorubicinolon) to concentrations in the tissue instead of the incubation bath, a method of quantifying the anthracyclines in small tissue samples was developed. Atria were homogenized by sonication followed by extraction of the anthracyclines with methanol. The extract was directly analyzed by high-performance liquid chromatography with fluorescence detection. Recoveries for the six compounds tested ranged from 67.5% for 4'-epidoxorubicin to 100.6% for 7-deoxydoxorubinol aglycon with coefficients of variation of 2-3% at two spiked concentrations (0.1 and 1 nmol/mg of tissue). The calibration plots were linear (r2 greater than 0.996) over the concentration range tested (0.05-1 nmol/mg wet weight). The limits of detection (4-10 pmol/mg of tissue) were low enough to allow the determination of the anthracyclines at all relevant tissue concentrations.

Pharmacokinetics of daunorubicin and daunorubicinol in plasma, P388 and B16 tumours. Comparison with in vitro cytotoxicity data

The comparison of pharmacokinetics of DNR in mouse plasma, in the DNR naturally resistant B16 melanoma and in the DNR naturally sensitive P388 leukemia showed that there is no direct correlation between total concentrations of this drug in tumours and the sensitivity resistance of these tissues. A finding which demonstrates the inadequacy of distribution models to select new potential anticancer drugs. Cytotoxicity of DNR and its metabolites to B16 melanoma and P388 leukemia cell lines were determined in vitro. Calculated inhibitory concentrations 50 (IC50) were compared to maximal concentrations determined by pharmacokinetic studies. In all cases in vitro IC50 were lower than Cmax values. Moreover, resistant cells in vivo were found to be sensitive to DNR and metabolites when they are propagated in vitro. Tissue concentrations, as well as in vitro data, were fitted to appropriate models by an original program (FADHA) which uses the simplex method to minimize a non-linear cost function. Best fit models were chosen by statistical criteria.

Sensitive method for the determination of daunorubicin and all its known metabolites in plasma and heart by high-performance liquid chromatography with fluorescence detection

The cytostatic agent daunorubicin is effective against leukaemia. An important side-effect is cardiomyopathy, common to all anthracyclines. Since anthracycline metabolites are thought to contribute to the observed cardiotoxicity, a method for the quantitative determination of all metabolites in plasma as well as in tissues is needed as a basis for the further investigation of the correlation between toxicity and the amount of each metabolite formed. Using Sep-Pak C18 cartridges we were able to extract daunorubicin and its five metabolites, including the aglycones, with recoveries in the range 50-90%. Depending on the chemical properties of each metabolite, fluorescence detection following high-performance liquid chromatographic separation permitted detection limits as low as 0.2-0.9 nM in plasma and 0.8-3.10(-11) mol/g in tissue, at a signal-to-noise ratio of 2, which compare favourably with literature data. The method showed linearity in the ranges 1-250 nM in plasma and 0.04-4.0 nmol/g in tissue (r greater than or equal to 0.998). The accuracy determined at 10 and 100 nM for plasma and at 0.1 and 1.0 nmol/g for tissue, was in the range 86-103 and 85-110% for plasma and tissue, respectively. The within-day and between-day repeatability values were acceptable (between 2 and 12%). Because of large inter-compound differences, separate calibration curves were used for each anthracycline. Application of the assay to the analysis of plasma and tissue samples of mice after intravenous injection of daunorubicin proved successful.

New method for the determination of doxorubicin, 4'-epidoxorubicin and all known metabolites in cardiac tissue

4'-Epidoxorubicin, doxorubicin (internal standard) and eight metabolites were extracted from heart tissue homogenate by a mixture of tetrahydrofuran-water (1:2, v/v) and purified by C18 Sep-Pak cartridges. The buffer used to prepare the homogenate contained glucaric acid-1,4-lactone and glucose, to prevent decomposition of the 4'-epidoxorubicin glucuronides. Anthracyclines were separated by high-performance liquid chromatography within 14 min and detected by fluorescence. Recoveries ranged from 49 to 75%. The detection limits of the individual anthracyclines ranged from 0.5.10(-11) to 2.5.10(-11) mol/g wet weight. The peak-height ratios of the fluorescence intensities of the anthracyclines versus doxorubicin were linear from 2.5.10(-11) to 250.10(-11) mol/g wet weight. Within- and between-day precisions of the assay varied between the anthracyclines and were in the ranges 3-12% (n = 6) and 2-11% (n = 6), respectively.