Ivo Janků

Studies on 6-azauridine and 6-azacytidine—I.: Toxicity studies of 6-azauridine and 6-azacytidine in mice

Abstract The acute toxicity of 6-azauridine and 6-azacytidine after intraperitoneal injection in mice is very low. After repeated daily administration, however, the following toxic manifestations developed: leukopenia, hemorrhagic diarrhea, and finally death of the experimental animals. Mortality was related to size of daily dose, as well as to the duration of drug administration, and a linear relationship was found between the logarithm of the daily dose and the logarithm of the corresponding mean lethal time ( LT 50). Morphological findings revealed marked changes in the structure of the spleen and the lymph nodes. At a very low level of dosage (50 mg/kg daily) irritation of lymphopoiesis was seen in both organs, whereas after higher doses progressive depressions of lymphopoiesis, together with a proliferation of reticulum cells, were found. This proliferation often was accompanied by the occurrence of nuclear anomalies in the proliferated reticulum cells. Marked proliferation of the endothelial lining of blood capillaries also was observed in the lymph nodes. The cells and tissues of the small intestine, as well as of the kidney and liver; were affected only with increased dosage of both compounds; under these circumstances, necrobiotic changes of the intestinal epithelium and fatty degeneration in the liver, as well as in the cortical tubuli of the kidney, were observed.

Dose-dependent disposition kinetics and tissue accumulation of boron after intravenous injections of sodium mercaptoundecahydrododecaborate in rabbits

SummaryKinetics of boron disposition after single intravenous injections of two different doses (25 and 50 mg/kg) of mercaptoundecahydrododecaborate sodium (Na2B12H11SH; BSH) was studied in rabbits. Residual boron concentrations in various organs and tissues (heart, lungs, liver, spleen, kidney, adrenals, and brain) were also determined after seven daily injections of the same doses of BSH. Boron blood and tissue concentrations were measured by atomic emission spectrometry. In the majority of animals, the decline of boron blood concentrations after a single intravenous injection of either dose was biphasic, being consistent with a two-compartment model of boron disposition in the body. Although mean boron blood concentrations were roughly proportional to the BSH dose delivered, the mean total body clearance of boron from the body was 3 times lower (6.5±1.9 ml min−1 kg−1) after a dose of 50 mg/kg than after the injection of 25 mg/kg (22.4±7.9 ml min−1 kg−1), the difference between the means being statistically significant (P<0.05). Moreover, the mean terminal half-life of boron in blood was prolonged after the injection of 50 mg/kg (14.5±5.5 h) as compared with that found after the 25-mg/kg dose (3.5±0.9 h). On the other hand, the different BSH doses did not result in marked differences in the mean values obtained for the volume parameters—the volume of the central compartment (1.3±0.4 vs 1.3±0.5 l kg−1) and the volume of distribution at steady state (4.7±1.3 vs 6.0±4.0 l kg−1)—both of which were high, indicating extensive binding of the compound not only in the blood but also in tissues. Residual concentrations of boron found after seven daily injections of both doses of BSH were highest in the kidneys, the difference in the mean values being relatively small (33.6±6.1 vs 39.0±10.7 μg/g tissue). In the majority of other organs (heart, lung, liver, spleen, brain, adrenals), the residual concentrations after a dose of 50 mg/kg were disproportionately higher than those measured after the injection of 25 mg/kg, and the mean values corresponded to the reduced total body clearance rather than to the increased BSH dose. The saturability of BSH binding to blood and tissue proteins is suggested as a possible explanation for the dose dependency of the total clearance of boron from the body and the accumulation of BSH in organs and tissues.

Structure-intestinal transport and structure-metabolism correlations of some potential cancerostatic pyrimidine nucleosides in isolated rat jejunum

SummaryBoth transport and biotransformation processes for a series of pyrimidine nucleobases, ribonucleosides, 2′-deoxyribonucleosides, and acetyl and 5′-substituted derivatives of the cancerostatic agent araC were studied in the isolated everted rat jejunum with a continuous perfusion technique. Metabolic alterations during penetration were assessed by HPLC. 5′-Halogeno and 5′-deoxy derivatives of cytosine nucleosides exhibited higher transport rates and higher stability towards the deamination reaction than did unsubstituted derivatives. Octanol-buffer partition coefficients were estimated for the study compounds, and fragmental constants for the sugar moieties of nucleosides were assessed. With the present study compounds there was no correlation between lipophilicity and transport rate, as previously reported, but there was a correlation between lipophilicity and metabolic alteration of araC derivatives (r=0.99, n=5).

Kinetics of transport and metabolism of 1-β-d-arabinofuranosylcytosine and structural analogs by everted perfused rat jejunum

Few reports have dealt with the kinetics and metabolism of AraC and analogs by rat intestine. Using everted rat jejunum with continuous perfusion, it was possible to demonstrate that AraC and Cyd cross the intestinal barrier(s) by a carrier mediated process which was saturable and exhibited fairly good fitting of the flux rate by Michaelis-Menten equation. The transport rate of different analogs was not consistent with the pH-partition theory of membrane transport of drugs being rather dependent on the chemical structure of the nucleoside. A free amino group of cytosine increased the rate of transport within the present series of AraC analogs. There was a detectable deaminase as well as esterase activity towards AraC and its analogs in rat jejunum.

The effect of structural modifications of 5-fluorouracil derivatives on their transport and biodegradation by isolated rat jejunum

SummaryThe continuous-perfusion technique was used in an isolated segment of everted rat jejunum to study transport and biotransformation processes in a series of cancerostatic derivatives of 5-fluorouracil. Metabolic alterations during penetration of the intestinal wall were assessed by high-performance liquid chromatography (HPLC). Octanol-buffer partition coefficients were measured, and the lipophilicity of the study compounds and fragmental constants for their sugar moieties were assessed. In the present series of 5-fluorouracil derivatives, there was no correlation between lipophilicity and metabolic cleavage to 5-fluorouracil, but a correlation was found between lipophilicity and the transport rate. Remarkable stability of the nucleoside bond and high biotransport were observed with 5′-chloro-5-fluorouridine, suggesting a different mode of activation for this derivative.

Changes in electroretinogram and serum potassium during l-DOPA treatment in parkinsonism

SummaryThe relationship of l-DOPA plasma level, parameters of ERG and severity of extrapyramidal symptoms after a single dose of l-DOPA was investigated in 11 patients suffering from parkinsonism of idiopathic or arteriosclerotic origin.After a drug-free night, each patient received his/her usual morning dose of l-DOPA. In the subsequent 3 h, the ERG recordings, blood levels and clinical ratings of extrapyramidal symptoms significantly dropped after a delay of 60 min in relation to the occurrence of the peak plasma l-DOPA level.The initial “b” wave amplitudes as well as initial serum potassium values were abnormally high. There was a statistically significant correlation between the decrease of “b” wave amplitude (Δ“b”) and the potassium “normalization index” (i.e. the ratio between the observed decrease of serum potassium and the pretreatment difference from the middle normal potassium value).A definite interpretation of the data cannot be provided until more knowledge about the origin of “b” wave of ERG is available. It can be concluded tentatively that dopaminergic processes influence electrophysiological reactivity of the retina.

Studies on 6-azauridine and 6-azacytidine—IV.: Correlations between metabolism and central nervous effects of 6-azacytidine

Abstract Effects of 6-azacytidine on exploratory activity were studied in mice and rats. After 200 to 800 mg of 6-azacytidine per kilogram were injected intraperitoneally, the exploratory activity of rats remained practically unaffected, whereas in mice this activity was depressed in a manner proportional to dosage. The lethal effects of nicotine also were antagonized in the mouse when higher doses of the compound (2.5 to 5.0 g/kg) were administered intraperitoneally. Neither changes in behavior nor antagonism to nicotine were observed in the same species after the injection of 6-azacytidine into the cerebral ventricles. In the cat, however, 50 to 100 mg of 6-azacytidine per kilogram, administered into the lateral cerebral ventricles, after a period of latency, produced ataxia and finally loss of postural reflexes. The possible role of deamination of 6-azacytidine, with the formation of 6-azauridine, in the production of the central effects of 6-azacytidine in different animal species is discussed.

Calculation of kinetic constants for an open two-compartmental model from drug excretion data.

Abstract Under the assumption that the body exhibits properties of an open two-compartmental system the rate constants governing drug distribution and elimination may be estimated after a rapid intravenous injection of the drug from the decline of the drug excretion rates by means of simple formulas. Analogue computer simulation of the kinetic behaviour of the open two-compartmental system with the use of the estimated rate constants showed a reasonable fit to drug excretion found in the experiment.