Bepridil in combination with anthracyclines to reverse anthracycline resistance in cancer patients.

The use of calcium antagonists as multidrug resistance reversing agents is limited by acute cardiac toxicity which, for verapamil, becomes prohibitive when concentrations in plasma approach those required in vitro for its action. A new calcium antagonist, bepridil, is as active as verapamil in reversing drug resistance in vitro. In addition, bepridil has some more favourable pharmacological properties compared with verapamil and other calcium antagonists. 14 patients with progressive advanced cancer, resistant to doxorubicin or epirubicin, were treated with the same anthracycline in combination with bepridil. Bepridil was administered in a continuous 36 h infusion at 22 mg/kg/36 h, with a dose scheme which should result in a steady state plasma concentration of approximately 5 mumol/l, able to reverse anthracycline resistance in vitro. Pharmacokinetic studies demonstrated a median bepridil plasma concentration of 5.3 mumol/l (range 2.6-19.3 mumol/l), at the time of administration of the anthracycline. No acute cardiac toxicity was observed and apparently bepiridil did not induce an increase or change in anthracycline toxicity. However, 2 patients developed overt chronic heart failure after treatment discontinuation, which caused 1 patient's death, and a significant reduction in left ventricular ejection fraction was seen in 4 patients. This chronic cardiac toxicity could be related to the total anthracycline dose received. 5 patients attained short lasting minor responses, 3 had stable disease and 6 progressed. Immunohistochemical studies in 7 tumours failed to reveal P-glycoprotein expression. Further trials with escalating doses of bepridil in combination with multiple drug resistance related anticancer agents are warranted.

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.

Comparative metabolism and pharmacokinetics of doxorubicin and 4'-epidoxorubicin in plasma, heart and tumor of tumor-bearing mice.

Epidoxorubicin, a stereoisomer of doxorubicin, shows comparable antitumor activity but diminished cardiotoxicity compared with the latter. To find a pharmacokinetic basis for the observed difference in cardiotoxicity between the drugs, concentrations of doxorubicin, epidoxorubicin and all known metabolites were measured in the plasma, heart and tumor tissue of BALB/c mice bearing colon-26 tumors. Both drugs were injected at the same dose (10 mg/kg) as an i.v. bolus. Plasma, heart and tumor samples were obtained from two mice sacrificed at regular intervals over 48 h. Plasma and tissue extracts were analyzed by HPLC with fluorescence detection. The parent compounds and the two 7d-aglycones were present in all three compartments, whereas doxorubicinol (Aol) and epidoxorubicinol (Eol) could only be detected in the plasma and heart. Half-lives and AUCs of doxorubicin and its metabolites were higher than the corresponding values for epidoxorubicin and its metabolites in all three compartments.

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.

Improved method for the determination of 4'-epidoxorubicin and seven metabolites in plasma by high-performance liquid chromatography.

4'-Epidoxorubicin, its seven metabolites and doxorubicin, as internal standard, were efficiently extracted from plasma using C18 Sep-Pak cartridges. The recoveries ranged from 58% for doxorubicin aglycone up to 98% for 4'-epidoxorubicin glucuronide. The anthracyclines were separated by reversed-phase high-performance liquid chromatography within 9 min and analysed by fluorescence. The assay was sensitive to 3 X 10(-10) M for the glucuronides up to 12 X 10(-10) M for 7-deoxydoxorubicin aglycone. The peak-height ratio of the fluorescence intensities of the anthracyclines versus doxorubicin showed a linear correlation with the concentration from the detection limit up to 2.5 X 10(-7) M (correlation coefficient r2 greater than 0.99). Within-day and between-day precision of the assay were in the ranges 2-14% (n = 6) and 2-11% (n = 6), respectively.

Metabolism of epidoxorubicin in animals: absence of glucuronidation.

Metabolism of epidoxorubicin was studied in plasma of seven different animal species at 2 h after administration of 4 mg/kg. None of the animals showed significant glucuronidation of epidoxorubicin, although small amounts of the glucuronides could be detected in the rabbit. However, large differences in formation of epidoxorubicinol and 7-deoxy (7d) doxorubicinol aglycone were observed between the species. These phenomena may be relevant for interspecies differences with regard to anthracycline-induced histomorphological changes in for example, heart tissues and cardiotoxicity in relation to formation of 7d aglycones.