Comparative pharmacokinetics and metabolism of doxorubicin and 4-demethoxy-4'-O-methyldoxorubicin in tumor-bearing mice

Effects induced by a 50 Hz electromagnetic field and doxorubicin on Walker-256 carcinosarcoma growth and hepatic redox state in rats

We compare the effects of an extremely low-frequency electromagnetic field (EMF) with the chemotherapeutic agent doxorubicin (DOX) on tumor growth and the hepatic redox state in Walker-256 carcinosarcoma-bearing rats. Animals were divided into five groups with one control (no tumor) and four tumor-bearing groups: no treatment, DOX, DOX combined with EMF and EMF. While DOX and DOX + EMF provided greater inhibition of tumor growth, treatment with EMF alone resulted in some level of antitumor effect (p < .05). Superoxide dismutase, catalase activity and glutathione content were significantly decreased in the liver of tumor-bearing animals as compared with the control group (p < .05). The decreases in antioxidant defenses accompanied histological findings of suspected liver damage. However, hepatic levels of thiobarbituric acid reactive substances, an indicator of lipid peroxidation, were three times lower in EMF and DOX + EMF groups than in no treatment and DOX (p < .05). EMF and DOX + EMF showed significantly lower activity of serum ALT than DOX alone (p < .05). These results indicate that EMF treatment can inhibit tumor growth, causing less pronounced oxidative stress damage to the liver. Therefore, EMF can be used as a therapeutic strategy to influence the hepatic redox state and combat cancer with reduced side-effects.

A Multiscale Physiologically-Based Pharmacokinetic Model for Doxorubicin to Explore its Mechanisms of Cytotoxicity and Cardiotoxicity in Human Physiological Contexts

PURPOSE

The mechanisms underlying doxorubicin cytotoxicity and cardiotoxicity were broadly explored but remain incompletely understood. A multiscale physiologically-based pharmacokinetic (PBPK) model was developed to assess doxorubicin dispositions at levels of system, tissue interstitial, cell, and cellular organelles. This model was adopted to explore the mechanisms-of-action/toxicity of doxorubicin in humans.

METHODS

The PBPK model was developed by analyzing data from mice and the model was verified by scaling up to predict doxorubicin multiscale dispositions in rats and humans. The multiscale dispositions of doxorubicin in human heart and tumors were explicitly simulated to elucidate the potential mechanisms of its cytotoxicity and cardiotoxicity.

RESULTS

The developed PBPK model was able to adequately describe doxorubicin dispositions in mice, rats and humans. In humans, prolonged infusion, a dosing regimen with less cardiotoxicity, was predicted with substantially reduced free doxorubicin concentrations at human heart interstitium, which were lower than the concentrations associated with oxidative stress. However, prolonged infusion did not reduce doxorubicin-DNA adduct at tumor nucleus, consistent with clinical observations that prolonged infusion did not compromise anti-tumor effect, indicating that one primary anti-tumor mechanism was DNA torsion.

CONCLUSIONS

A multiscale PBPK model for doxorubicin was developed and further applied to explore its cytotoxic and cardiotoxic mechanisms.

Quantitation of cell-associated doxorubicin by high-performance liquid chromatography after enzymatic desequestration

A method for measuring cellular concentrations of the anthracycline doxorubicin was developed. The assay involves cell lysis and protein degradation by detergent and proteinase K treatment followed by DNA hydrolysis using DNase I. Prior to high-performance liquid chromatography, samples are deproteinized by the addition of ZnSO4 and methanol. The assay is linear with respect to both the cellular drug content and the number of cells assayed over the ranges tested, and drug recovery is close to 100%. The method has a limit of detection of 50 fmol injected doxorubicin. Within run and between-day coefficients of variation have consistently been found to be in the 5% and 10% range, respectively, in different cell lines exposed to doxorubicin in vitro. The method has been evaluated in analyses of doxorubicin levels in mononuclear blood cells of patients. The assay offers several advantages over commonly used organic extraction techniques and may improve cellular drug monitoring during anthracycline therapy in patients.

Isolated single-lung perfusion with doxorubicin is pharmacokinetically superior to intravenous injection

To investigate new modalities in the treatment of pulmonary metastases we developed a model of isolated single-lung perfusion in the rat. In this study we compare the pharmacokinetics of isolated lung perfusion and intravenous doxorubicin. In the first experiment, designed to evaluate lung tissue levels of doxorubicin, 35 rats were randomized into seven groups (n = 5). The first five groups underwent isolated lung perfusion with 72.1 +/- 6.9, 118.4 +/- 12.1, 255.2 +/- 12.8, 384.1 +/- 46.2, and 457.6 +/- 32.5 micrograms/mL of doxorubicin, respectively, for 10 minutes. Groups 6 and 7 received 5 mg/kg and 7 mg/kg of intravenous doxorubicin, respectively. A second study was designed to measure heart tissue level of doxorubicin in 3 groups of 5 rats each. Two groups received 5 or 7 mg/kg of intravenous doxorubicin and a third group underwent isolated lung perfusion with 255.2 +/- 12.8 micrograms/mL of doxorubicin for 10 minutes. A third study, designed to evaluate toxicity in vivo, had a similar design, and the animals were followed up for 21 days after treatment. Lung doxorubicin concentration after isolated lung perfusion was significantly higher than after intravenous doxorubicin (p < 0.01). Tissue doxorubicin concentration was 25 and 20 times higher after isolated lung perfusion with 255.2 +/- 12.8 micrograms/mL than after 5 or 7 mg/kg of intravenous doxorubicin, respectively. Heart concentration of doxorubicin was significantly lower after isolated lung perfusion with 255.2 +/- 12.8 micrograms/mL of doxorubicin as compared with 5 or 7 mg/kg of intravenous doxorubicin (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Streptomycetes producing daunomycin and related compounds: do we know enough about them after 25 years?

The growing need of highly potent anticancer agents has stimulated the investigation of streptomycetes producing daunomycin-type anthracyclines. This review compares the features of production strains and their mutants and emphasizes the necessity of application of biochemical and biophysical analytical methods for better understanding these microorganisms and, above all, their further improving and practical usage.

Diversity of effects of two antitumor anthracycline analogs on the pathway of activation of PKC in intact human platelets

Two antitumor antibiotics doxorubicin and daunorubicin were tested for their ability to influence the activation of protein kinase C in human platelets. Daunorubicin was found to inhibit the phosphorylation of the 40 K PKC substrate induced by thrombin and 12-O-tetradecanoyl-phorbol-13-acetate as well as the phosphorylation of the 20 K protein induced by thrombin. The serotonin release associated to these phosphorylative events was also inhibited by daunorubicin. In contrast the effects of doxorubicin, though inhibitory on the release reaction, were always stimulatory of the phosphorylations. Doxorubicin alone was able to induce the phosphorylation of both 40 K and 20 K phosphoproteins in a concentration-dependent manner. Whereas the stimulation by doxorubicin was not influenced by pretreatment with dibutyryl-cyclic-AMP which inhibits the effects of thrombin, this effect was inhibited by daunorubicin, neomycin and stimulated by the diacylglycerol-kinase inhibitor R 59 022. It is proposed that doxorubicin activates the protein kinase C by causing the breakdown of phosphoinositides.

Doxorubicin cellular pharmacokinetics and DNA breakage in a multi-drug resistant B16 melanoma cell line

Mechanisms of anthracycline resistance have been investigated in a B16 murine melanoma cell subline selected by continuous in vitro exposure to increasing concentrations of doxorubicin (DX). Altered drug pharmacokinetics were observed in resistant B16 cells as compared to the sensitive counterpart. In fact, cellular DX uptake - as determined by a fluorescence method - was lower in resistant than in sensitive cells. Furthermore, drug efflux rate was shown to be higher in resistant than in sensitive cells; treatment of cells with the metabolic inhibitor sodium azide decreased drug efflux rate in resistant but not in sensitive cells, suggesting the presence of an energy-dependent drug extrusion mechanism in the resistant B16 cells. However, since drug-induced cell killing did not correlate with cellular DX contents in sensitive and resistant cells, drug resistance of B16 subline could not be completely explained by the observed differences in drug pharmacokinetics. Since drug-induced DNA breaks have been related to drug cytotoxicity, DNA cleavage was also measured by alkaline elution methods. The number of DNA breaks produced by DX was decreased in resistant cells as compared to sensitive cells at the same cellular drug accumulation. The results are consistent with the view that anthracycline resistance may be multifactorial and probably arises following multiple biochemical changes.

High-performance liquid chromatographic bioanalysis of anthracycline cytostatic drugs

In the past decade high-performance liquid chromatography (HPLC) has developed into the most powerful tool available for the analysis of anthracycline antitumour drugs in all kinds of biological matrices. The results of drug level monitoring studies have contributed significantly to a better understanding of the pharmacokinetics and metabolic disposition of these drugs. Some aspects of anthracycline HPLC analysis in plasma samples are discussed, including the chromatographic separation and detection, sampling procedures, storage of plasma samples and sample pre-treatment.

In vivo characterization of a doxorubicin resistant B16 melanoma cell line

A doxorubicin-resistant line of B16 melanoma (B16VDXR) was obtained in vitro by continuous exposure to increasing concentrations of doxorubicin of an in vitro line (B16V) derived from the in vivo transplanted B16 melanoma. When injected s.c. into mice, B16VDXR exhibited histological features, metastatic behaviour, doubling time and tumourigenic potential similar to those of the parental B16V line. Tumours obtained by implantation of B16VDXR, however, had longer latency and permitted a longer survival time than B16V and had, as in vitro, a higher DNA content. After i.v. inoculation, B16VDXR cells had lower lung colonizing capability compared to B16V. B16V and B16VDXR had significantly lower metastatic potential compared to the B16 melanoma from which they derived. Doxorubicin treatment significantly delayed the growth of B16 and B16V transplanted s.c. and increased the life span of animals bearing B16V. B16VDXR was resistant to doxorubicin treatment when the in vitro resistance index was greater than 100. While the doxorubicin-resistance phenotype was stable in vitro for 50 passages, in vivo the resistance phenotype was lost in 5 passages and tumours grown from s.c. inocula of mixtures of similar percentages of sensitive and resistant cells behaved as sensitive tumours. Cis-diamminedichloroplatinum (II), although marginally active in animals bearing B16V, was highly effective in B16VDXR bearing animals, suggesting a collateral cis-diamminedichloroplatinum (II) sensitivity of the B16VDXR line. After a single i.v. administration, doxorubicin reached initially, in the B16VDXR line, levels similar to those found in the B16 and B16V lines, but its release was faster from the resistant line in comparison with the sensitive ones. Doxorubicin-resistance was not overcome by more frequent treatments with doxorubicin. This doxorubicin-resistant tumour line obtained in vitro and used as a first in vivo transplant, may be a suitable metastaizing model for in vivo study of the mechanisms of resistance and of collateral sensitivity and for screening new drugs.