Pharmacokinetic behaviour of phenylglyoxal bis(guanylhydrazone) (PGBG) after intravenous administration in rabbits.

Phenylglyoxal bis(guanylhydrazone) (PGBG) is a synthesized analogue of methylglyoxal bis(guanylhydrazone) (MGBG), which has demonstrated anti-parasitic activity in rabbits. The pharmacokinetic behaviour of PGBG after intravenous administration (10 mg/kg bodyweight) was studied in five rabbits. Plasma concentrations of PGBG were measured by high-performance liquid chromatography. Plasma PGBG concentrations decreased rapidly and were not detectable beyond 90 min after treatment. The mean [+/- standard deviation (SD)] volume of distribution at steady state (Vdss) was 2.19 +/- 0.47 l/kg and the mean plasma clearance value (Cl) was 29.99 +/- 3.98 ml/min kg. This drug is rapidly eliminated from the body in rabbits, having a short elimination half-life (0.93 h) and mean residence time (1.21 h).

Pharmacokinetic profile of Mitoguazone (MGBG) in patients with AIDS related non-Hodgkin's lymphoma.

Mitoguazone is a unique chemotherapeutic agent whose activity is believed to result primarily from the competitive inhibition of S-adenosyl-methionine decarboxylase leading to a disruption in polyamine biosynthesis. Initial clinical trials demonstrated that the dose-limiting toxicities (mucositis and myelosuppression) of Mitoguazone were both dose and schedule dependent. Early pharmacokinetic studies of Mitoguazone in man revealed a prolonged half-life. Concurrent with a recent Phase II trial of Mitoguazone in patients with AIDS related non-Hodgkin's lymphoma, the single dose pharmacokinetics of Mitoguazone were characterized. Twelve patients received 600 mg/m2 of intravenous Mitoguazone over 30 minutes on an intermittent every 2 week schedule. Blood, urine, cerebrospinal fluid (CSF), pleural fluid and tissue samples were collected and analyzed by HPLC. Mitoguazone was cleared from the plasma triexponentially with a harmonic mean terminal half-life of 175 hours and a mean residence time of 192 hours. Peak plasma levels occurred immediately post-infusion, ranged from 6.47 to 42.8 micrograms/ml, and remained (for an extended period) well above the reported concentration for inhibition of polyamine biosynthesis. Plasma clearance averaged 4.73 l/hr/m2 with a relatively large apparent volume of distribution at steady-state of 1012 l/m2 indicating tissue sequestration. Renal excretion of unchanged Mitoguazone accounted for an average of 15.8% of the dose within 48 to 72 hours post-administration. Detectable levels of drug were present in random voided samples eight days post-dose. Mitoguazone levels in CSF ranged from 22 to 186 ng/ml post-dose with CSF/plasma ratios ranging from 0.6% to 7%. The pleural fluid/plasma ratio was approximately 1. Tissue levels of Mitoguazone were highest in the liver followed by lymph node, spleen and the brain.

Influence of melanoma B16 on the pharmacokinetics of mitoguazone in mice.

In this study, the influence of different stages and transplantation routes of the experimentally widely used solid tumor melanoma B16 on the pharmacokinetics of the antineoplastic agent mitoguazone was investigated in B6D2F1 mice. It could be shown that changes of the pharmacokinetic parameters as well as the distribution pattern of this drug were clearly influenced and dependent on the tumor stage but not by the tumor inoculation route. Advanced melanoma (d16) led to a sharp decrease in the terminal elimination half-life as well as to decreased spleen levels and increased initial liver concentrations of the drug. With respect to the results obtained in leukemia P388-bearing mice it can be concluded that the tumor stage as well as the tumor model are to be considered as important factors in which way and to which extent a tumor may alter the pharmacokinetics of antineoplastic agents.

Influence of leukemia P388 on the pharmacokinetics of mitoguazone in B6D2F1 mice.

The aim of the present study was to investigate the influence of different stages of leukemia P388 on the pharmacokinetics of the antineoplastic agent mitoguazone in mice. It could be shown that, independent of the tumor stage investigated, the total clearance of mitoguazone is slightly reduced reflecting a moderate increase of AUC in the serum of leukemia-bearing animals. Furthermore, in an advanced tumor stage the drug levels in kidneys, liver, spleen and serum were found to be elevated to some extent in comparison to tumor-free controls in contrast to an earlier stage of leukemia. In conclusion, the tumor stage has to be considered as an important factor to which extent a neoplasia may alter the pharmacokinetics of drugs used for anticancer chemotherapy.

Ambazone as a membrane active antitumor drug.

Ambazone (1,4-benzoquinone guanylhydrazone thiosemicarbazone) was found to be active against various transplantable tumors in mice as well as rats. When administered orally for 4-9 days, the effective therapeutic dose ranged between 60 and 125 mg/kg. The antineoplastic effect of ambazone appeared to be mediated, at least in part, by the immune system. In order to characterize the drug, biophysical and biophysicochemical studies were carried out using thin-layer chromatography, absorption spectroscopy and polarographic measurements. The distribution of ambazone in an n-octanol/water system indicated low hydrophobicity, thereby excluding the possibility of a preferential contribution from hydrophobic forces to the mode of action of ambazone. Ambazone undergoes three protonation reactions with pK values at 10.69 (equilibrium between the negatively charged and neutral forms), 7.39 (equilibrium between the neutral and singly positively charged form) and 6.22 (equilibrium between the singly and doubly positively charge form). Interaction of the drug with model membrane system was monitored by spectrophotometric and fluorescence measurements. Using the fluorescence label 1-anilino-8-naphthalenesulfonic acid (ANS) as a probe pointed to the interaction of ambazone with the inner area of the phospholipid bilayer matrix of liposomes as being nonspecific. Ambazone induces an overall increase in the cellular cAMP content of leukemia cells and macrophages. So far, membrane interaction has provided a molecular basis for both immunological and antineoplastic activities of the drug. By performing DNA melting experiments, it was shown that neutral or singly positively charged ambazone species stabilize the secondary structure of DNA, while the doubly positively charged form binds more strongly and destabilizes the DNA. After oral administration to rats and mice, ambazone was found to be incompletely absorbed from the gastrointestinal tract, to an extent of about 35-50%. Absorbed ambazone binds only weakly to plasma proteins, whereas its binding to red blood cells is relatively strong. The mutagenic potential of ambazone shown in bacterial systems and human lymphocytes corresponds to its relatively weak interaction with DNA. The toxic action of ambazone on the intestine is believed to be due to inhibition by the drug of bacterial DNA, RNA and protein syntheses. It is assumed that the reported affinity of ambazone for different cellular targets, i.e., membranes, nucleic acids and proteins, contributes to the overall antibacterial effect. The weak antiviral activity of ambazone in the Sendai virus/chicken embryo fibroblast system is probably the result of the interaction with Sendai virus NH glycoprotein.

Influence of age on antileukemic action, subacute toxicity and tissue distribution of ambazone in B6D2F1 mice.

The influence of age of experimental animals on the antileukemic activity, toxicity and distribution of ambazone, a new potential antineoplastic agent, was studied in 2- and 12-month-old B6D2F1 mice. The predominant effect observed was a significant reduction of the antileukemic action of this compound in old-aged mice. Together with a slight increase in several toxicity parameters this caused a marked reduction of the therapeutic index in 12-month-old mice compared to younger individuals. Furthermore, a general tendency to increased ambazone levels in liver, kidneys and thymus of old-aged mice was observed. Our data therefore provide further evidence that age has to be taken into consideration as one factor that may account for the variety of drug response frequently observed during clinical therapy with anticancer agents.

[Kinetics of the transformation of dihydroambazone into ambazone]. / Kinetik der Umwandlung von Dihydroambazon in Ambazon.

The oxidation of dihydroambazone (1) by oxygen is dependent on the pH-values of the solutions used. This transformation can be inhibited and excluded, respectively, by ascorbic acid using defined concentrations. The oxidation product ambazone (2) was determined spectroscopically at different pH-values. The rate of transformation in serum depends on the temperature and can also be inhibited with ascorbic acid.

Properties and physiological function of the polyamine transport system.

Polyamine transport was examined in Chinese hamster ovary (CHO) cells because of the unique potential these cells hold for utilizing genetic approaches to study the mechanisms of polyamine transport, its regulation, and its function. Parental (control) CHO cells were shown to contain a polyamine transport system with characteristics consistent with polyamine-uptake properties described in other cell types. Polyamines appear to cross the plasma membrane via an energy-requiring transport system specific for putrescine, spermidine, spermine, and their analogues. A mutant line, CHOMG, selected for resistance to the toxicity of methylglyoxal bis(guanylhydrazone), was shown to lack a functional polyamine transport system. CHOMG cells provided the negative controls necessary to examine the role of polyamine transport in maintenance of intracellular polyamine levels and in the regulation of the polyamine metabolic enzymes. It was found that the repression of ornithine decarboxylase activity by polyamines and the induction of spermidine/spermine-N1 acetyltransferase by polyamine analogues including bis(ethyl)spermine derivatives required the presence of a functional polyamine transport system. The CHO-CHOMG model was also shown to provide a means for establishing the importance of the polyamine transport system in the toxicity of polyamine analogues. The inability of alpha-difluoromethylornithine-treated CHOMG cells to utilize extracellular polyamines to replenish depleted intracellular polyamine levels suggested a means by which polyamine transport-positive cells may be identified. Such a selection procedure will permit the use of CHOMG cells in the isolation of genes encoding proteins involved in polyamine transport.

[Mitoguazone (methylglyoxal bis(guanylhydrazone))--its status and prospects]. / Mitoguazon (Methylglyoxal-bis-guanylhydrazon)--Stand und Perspektiven.

Because of its severe side effects, initial clinical trials of the antineoplastic compound mitoguazone (Methyl-GAG, M-G) were ceased in the middle of 1960s. One decade later pharmacokinetically guided dose schedules as well as new experimental data on the antiproliferative mechanism of action stimulated new clinical studies. First results indicated that M-G had single-agent activity against various tumors such as acute leukemia and malignant lymphoma connected with acceptable tolerance. M-G seems to be effective especially in combination with other antineoplastic drugs. Its final evaluation may be reserved to further randomized trials. Recently, the psoriasis vulgaris is expected to be an additional field of the application of M-G. In this minireview data on synthesis, preclinical pharmacology, pharmacokinetics, biochemical effects and toxicology of M-G are given. Furthermore, clinical findings on M-G concerning its pharmacokinetic behaviour, antitumor and antipsoriatic activities are described.

Alterations in bone marrow and blood mononuclear cell polyamine and methylglyoxal bis(guanylhydrazone) levels: phase I evaluation of alpha-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) treatment of human hematological malignancies.

Nine patients with hematological malignancies were treated with difluoromethylornithine and methylglyoxal bis(guanylhydrazone). The number of circulating blast cells decreased in all of the patients treated with DFMO and MGBG for longer than 1 wk. Morphological evidence of myeloid maturation was evident in four patients with leukemia and the circulating M Protein decreased in one patient with multiple myeloma. The polyamine content of the mononuclear cells in both the peripheral blood and bone marrow was transiently increased after the initial MGBG dose. During administration of DFMO decreases were achieved in the peripheral blood mononuclear cell putrescine levels in 7 patients, spermidine levels in 5 patients, and spermine levels in 4 patients. Alterations in bone marrow mononuclear cell polyamine levels were similar to those which occurred in the peripheral cells. An average of 9 days of DFMO treatment was required to lower mononuclear cell polyamine levels. Three of the 4 evaluable patients receiving multiple MGBG doses had an increased mononuclear cell content of MGBG after DFMO pretreatment. Enhancement of cellular MGBG levels was not directly correlated to the degree of cellular polyamine depletion.

Enhanced uptake of spermidine and methylglyoxal-bis(guanylhydrazone) by rat liver mitochondria following outer membrane lysis.

Isolated rat liver mitochondria rapidly bound the 14C-labeled organic cations spermidine, a physiologically important polyamine, and methylglyoxal-bis(guanylhydrazone) (MGBG), an anticancer drug. This rapid, Mg2+-sensitive, respiration-independent binding is assumed to involve adsorption to anionic surface groups. A slower progressive uptake of the organic cations exhibited respiration dependence, indicating that it involves transport across the inner mitochondrial membrane into the matrix compartment. Addition of digitonin, to lyse the outer mitochondrial membrane, caused an increase in the mitochondrial content of the organic cations and enhanced the rate of progressive, respiration-dependent cation uptake. The data are consistent with the interpretation that the outer mitochondrial membrane limits access of the organic cations, spermidine and MGBG, to the inner mitochondrial membrane. This conclusion is supported also by published data indicating that outer membrane lysis enhances inhibitory effects of the organic cations on mitochondrial respiration. The uptake of spermidine by mitochondria was inhibited by MGBG.

Pharmacokinetics of 14C-ambazone in rats.

In rats, the pharmacokinetics of 14C-ambazone after i.v. and oral administration was studied. The results demonstrate that the compound is incompletely absorbed from the gastrointestinal tract, penetrates rapidly and to a high degree into various tissues and is preferentially eliminated via the kidneys. After i.v. administration of 50 mg/kg b.m. disposition half-life in whole blood is about 6-7 h. The extent of absorption from the gastrointestinal tract is about 40%.

Polyamines increase in human peripheral blood and bone marrow mononuclear cells following administration of methylglyoxal bis(guanylhydrazone).

Eight patients who had refractory leukemia and 1 patient with refractory multiple myeloma were treated with the polyamine biosynthesis inhibitors methylgloxal bis(guanylhydrazone) (MGBG) and difluoromethylornithine (DFMO). After the first dose of MGBG there was an increase in polyamine content in the mononuclear cells of both the peripheral blood and the bone marrow despite the administration of DFMO in all patients with leukemia. Putrescine levels increased in the mononuclear cells of all patients, cellular spermidine levels increased in 4 and cellular spermine levels increased in 5 patients. The cellular polyamine levels remained elevated above the pretreatment levels for up to 1 week in some patients. Subsequent treatment with MGBG, administered after 1-2 weeks of DFMO treatment, also promoted increases in mononuclear cell polyamine concentrations. Since enhanced tumor cell uptake of MGBG after DFMO priming is hypothesized to be dependent on a decrease in cellular polyamine levels, the increase in cellular polyamines after MGBG has important implications for the scheduling of this drug combination. From these observations, withholding MGBG until DFMO treatment has produced a decrease in tumor cell polyamine concentrations would be the schedule most likely to enhance the uptake of MGBG.

Distribution of 14C-ambazone in normal and leukemia P 388-bearing mice.

There is some evidence in the literature that the pharmacokinetics of anticancer agents can be influenced by the presence of a tumor. Therefore several authors recommend pharmacokinetic studies of such drugs to be performed also in tumor-bearing animals (2, 5, 7). The aim of the present study was to evaluate the influence of different stages and routes of inoculation of leukemia P 388 in B6D2F1-hybrid mice on the tissue distribution of ambazone, a new potential antineoplastic drug. It could be emphasized that the drug levels in liver, kidneys and thymus were higher in advanced tumor-bearing than in control animals whereas in the spleen and in whole blood the opposite was true. The differences can be explained partially by changes in the erythrocyte binding of ambazone.

Effect of altered inflation on pulmonary uptake of methylglyoxal bis(guanylhydrazone).

The effects of increased pulmonary ventilation on uptake of an exogenous, nonmetabolized polyamine analog, methylglyoxal bis(guanylhydrazone) [MGBG] were investigated in rat lungs perfused in situ with buffer containing 4.5% bovine serum albumin, 5.6 mM glucose and plasma levels of amino acids. The perfusate was equilibrated and the lungs were ventilated with warmed, humidified O2/N2/CO2 (20:75:5). A 28% increase in lung inflation rapidly accelerated MGBG uptake at low (1.5 microM) but not at high (50 microM) substrate concentration, a change which appeared to reflect a decrease in the apparent Km of the uptake pathway. This effect was not associated with acute alterations in pulmonary vascular permeability or resistance, nor with instability of the preparations. Taken with observations made previously, these results suggest that deformation of the tissue by increased inflation may account for increased MGBG uptake by lungs from rats subjected to partial pneumonectomy.