Disposition of tricyclic nucleoside-5'-monophosphate in blood and plasma of patients during phase I and II clinical trials.

Tricyclic nucleoside-5'-monophosphate (TCN-P) and its dephosphorylated metabolite tricyclic nucleoside (TCN) have been measured in the blood and plasma of patients receiving TCN-P by rapid iv infusion in a phase I trial at daily doses of 24-55 mg/m2 for 5 days and in patients receiving TCN-P in a phase II trial at a single dose of 250 mg/m2. TCN-P was rapidly accumulated by rbcs and had an initial half-life in blood of 6.1 hours and a terminal half-life of 89.2 hours. Total-body blood clearance of TCN-P was 2.6 ml/minute/m2. The concentration of TCN-P in blood was not related to the dose of TCN-P and did not increase over 5 days' administration in the phase I patients. Plasma contained little detectable TCN-P even 5 minutes after administration. Plasma contained low concentrations of TCN, up to 0.4 microgram/ml, which were maintained over several days. TCN did not accumulate in the plasma with repeated administration of TCN-P in the phase I patients. No other metabolites of TCN-P, apart from TCN, were detected in blood or plasma. No relationship was detected between pharmacokinetics and toxic response of TCN-P in the phase II patients.

Effects of advanced leukemia on hepatic drug-metabolizing activity in the mouse.

Mice that had received 10(6) P388 leukemia cells IV 8 days previously exhibited a decrease in the components of the hepatic microsomal mixed function oxidase, with a 58% decrease in cytochrome P-450, and up to a 60% decrease in hepatic microsomal metabolism of biphenyl. Liver weight was increased by 49% due to infiltration of the liver with leukemic cells. Changes in liver drug-metabolizing activity and liver weight were not seen 6 days after administration of P388 leukemia. There was a small increase in serum liver enzyme but no increase in total serum bilirubin in tumor-bearing mice. In vivo total-body plasma clearance of cyclophosphamide, a drug metabolized by hepatic cytochrome P-450, was decreased to 53 ml/min/kg in mice that had received P388 cells 8 days earlier, as against 97.2 ml/min/kg in control mice. Cytochrome P-450-independent metabolism of [14C]5-fluorouracil, measured by means of [14C]CO2 in the breath over 3 h, was decreased to 21% of the dose administered by 8 days after tumor cell administration, compared with 31% of the dose in control mice. P388 leukemia cells growing in the ascitic form in the intraperitoneal cavity of mice did not release an inhibitor of 5-fluorouracil metabolism into the ascitic fluid. Total-body plasma clearance of indocyanine green was decreased to 11 ml/min/kg by 8 days after P388 cell administration, compared with 36 ml/min/kg in control mice. The decrease in indocyanine green clearance might reflect a decrease in hepatic blood flow in the tumor-bearing mice. A possible explanation for the decrease in hepatic drug metabolism caused by P388 leukemia is that the hepatocytes are deprived of oxygen and nutrients by the tumor in the liver, coupled with or caused by a physical obstruction of hepatic blood flow.

Metabolism and disposition of 3-amino-1,5-dihydro-5-methyl-1-beta-D-ribofuranosyl-1,4,5,6, 8-pentaazaacenaphthylene in the rat.

Tricyclic nucleoside (TCN, NSC 154020) is a 7-deazapurine nucleoside possessing antitumor activity towards certain tumor cell lines in vitro. In vivo, TCN is readily interconvertible with its 5'-monophosphate ester. The present study demonstrates that TCN is metabolized by rat liver microsomes to a ring-opened bicyclic metabolite with loss of cytotoxicity toward Chinese hamster ovary cells in culture. Metabolism is mediated by hydrogen peroxide generated by the rat liver microsomes but is not dependent on cytochrome P-450. Isolated hepatocytes prepared from rat do not form detectable amounts of the ring-opened bicyclic metabolite. Unchanged TCN and the ring-opened bicyclic metabolite are excreted in the bile of rats with a cannulated bile duct, comprising 42 and 12% of an i.v. dose of TCN in 8 hr, respectively. The ring-opened bicyclic metabolite is not formed by red blood cells in vitro and could not be detected in blood in vivo. The fact that the ring-opened bicyclic metabolite appears in bile suggests that liver cells not present or not active in isolated hepatocyte preparations might produce the metabolite. Alternatively, the metabolite might be formed directly from TCN in bile, perhaps by hydrogen peroxide excreted into bile. In vivo, 56% of radiolabel was found in the upper and lower gastrointestinal tract and the feces 24 hr after an i.p. or i.v. dose of 100 mg of [5-methyl-14C]TCN/sq m. Urinary excretion of radiolabel was 21% of the dose of [14C]TCN in 24 hr. Biliary excretion of radiolabel was 65% of the dose of [14C]TCN in 8 hr. The fraction of radioactivity undergoing enterohepatic cycling with reabsorption from the gastrointestinal tract after excretion in bile is 84%.

Carbon tetrachloride-induced increase in the antitumor activity of cyclophosphamide in mice: a pharmacokinetic study.

Carbon tetrachloride is an hepatotoxin that depresses hepatic microsomal cytochrome P-450 and other enzyme activities. Cyclophosphamide is an anticancer drug that is activated by hepatic microsomal cytochrome P-450, while the products of cyclophosphamide metabolism by cytochrome P-450 can be metabolized by other hepatic enzymes. Carbon tetrachloride pretreatment has been found to increase the in vivo antitumor activity of cyclophosphamide against murine leukemia P-388. Carbon tetrachloride did not, however, affect the direct cytotoxicity of cyclophosphamide or 4-hydroxycyclophosphamide to cells in culture. Pharmacokinetic studies in mice revealed a delayed plasma disappearance of cyclophosphamide after carbon-tetrachloride pretreatment with an apparent initial half-time of 20.4 min compared to 9.0 min in non carbon-tetrachloride-pretreated mice. Plasma levels of total alkylating activity and plasma 4-hydroxycyclophosphamide increased more slowly and reached a lower peak, but were maintained for a longer time period in mice pretreated with carbon-tetrachloride than in untreated mice. The half-life for plasma elimination of 4-hydroxycyclophosphamide in untreated mice was 12 min and in carbon-tetrachloride-pretreated mice 27 min. There was, however, no difference in the area under the curve for either plasma total alkylating activity or plasma 4-hydroxycyclophosphamide between the two groups. It is suggested that prolonged exposure of tumor cells to 4-hydroxycyclophosphamide might be responsible for the increased antitumor activity of cyclophosphamide following carbon-tetrachloride pretreatment.

High-performance liquid chromatographic assay of the antineoplastic agent tricyclic nucleoside 5'-phosphate and its disposition in rabbit.

Anion-exchange and reversed-phase high-performance liquid chromatographic procedures are described for the assay of the antineoplastic agent tricyclic nucleoside 5'-phosphate (TCNP) and its metabolite tricyclic nucleoside (TCN) in biological fluids. Disposition of TCNP has been studied in rabbit. TCNP is eliminated from blood and plasma with a biologic half-life of about 7.5 h. Apparent volume of distribution is 43.2 l/m2 and total body plasma TCNP clearance is 67.8 ml/min/m2. TCNP is hydrolyzed by plasma and probably other tissues to TCN which is present in blood and plasma at about one-tenth the concentration of TCNP. There is no accumulation of TCNP or TCN in blood or plasma over 2 days of administration. In 24 h 2.4% of a dose of TCNP is excreted in bile of a rabbit with a cannulated bile duct as unchanged TCNP and 30.7% as TCN. TCN is excreted in bile at an initial concentration half the maximum solubility of TCN in rabbit bile. Excretion of TCNP and TCN over 24 h in the urine of a rabbit with a cannulated bile duct is 1.5% and 5.2% of the dose, respectively.

Effect of cyclophosphamide pretreatment on the short-term disposition and biliary excretion of adriamycin metabolites in rat.

The effect of pretreatment with cyclophosphamide 180 mg/kg upon the short-term disposition of adriamycin in anesthetized rat 4 days later was studied. There was a significant decrease in plasma adriamycin clearance, from 125 to 48 ml/min/kg, and a significant decrease in the apparent volume of the peripheral compartment of adriamycin distribution, from 51.7 to 25.6 l/kg, in cyclophosphamide-pretreated as against control rats. Biliary excretion of adriamycin over 2.5 h was increased significantly by 114% in cyclophosphamide-pretreated rats and there was a small but nonsignificant increase in biliary adriamycinol excretion and a decrease in excretion of adriamycin aglycones. Cyclophosphamide pretreatment was associated with an 83% increase in bile flow. Cyclophosphamide pretreatment had no significant effect upon the utilization of adriamycin or upon the formation of adriamycin metabolites by rat isolated hepatocytes. The results suggest that NADPH-cytochrome P-450 reductase, which is decreased 40% by cyclophosphamide pretreatment, is not rate-limiting in elimination of adriamycin. Biliary excretion of adriamycin is increased when plasma adriamycin clearance is decreased, suggesting that cyclophosphamide pretreatment affects a pathway besides biliary excretion that is responsible for the short-term removal of adriamycin from plasma.

Pharmacokinetics of procainamide in rats with extrahepatic biliary obstruction.

The pharmacokinetics of the widely used antiarrhythmic agent, procainamide, was studied in rats with extrahepatic biliary obstruction produced by ligation of the common bile duct. Various biological fluids, including plasma, saliva, and urine, were analyzed for procainamide and/or its major metabolite, N-acetylprocainamide. Ligation of the common bile duct immediately prior to intravenous administration of 50 mg/kg procainamide did not alter plasma, saliva, or urine concentrations of procainamide, indicating that biliary excretion was of minor importance in the elimination of procainamide. However, bile duct ligation allowed to persist for 4 days significantly elevated plasma, saliva, and urine levels of procainamide. While the increase in urinary procainamide paralleled the increase observed in plasma, salivary concentrations did not. Bile duct ligation did not appear to impair nonmicrosomal acetylation of procainamide, although a significantly greater amount of unchanged drug was found in the urine after 24 hr. Pharmacokinetic analysis via the two-compartment open model showed that bile duct ligation caused a decrease in overall clearance from approximately 61.94 to 28.71 ml/kg/min. This reduction probably resulted from the decreased microsomal metabolism of procainamide. The significant reduction in the apparent volume of distribution from 3.76 to 2.72 liter/kg could be the result of reduced binding sites. There was also a significant increase in the elimination half-life of procainamide from 47.39 to 78.64 min in bile duct ligated rats.

Excretion of procainamide into bile and saliva in rats with chronic renal failure.

The excretion of the widely used antiarrhythmic agent procainamide into the bile and saliva of rats with chronic renal failure (CRF) induced by a two stage-total nephrectomy was studied. Chronic renal failure significantly elevates plasma, salivary, and biliary procainamide levels compared to normal and sham operated rats at all time periods studied. However, while the increase in salivary excretion parallels that of plasma, biliary excretion does not. Results indicate that there is probably saturation of an active transport mechanism for procainamide into bile and that bile cannot compensate for increased drug levels which accumulate during CRF. Salivary excretion, though increased during CRF, also cannot compensate for elevated procainamide levels. Moreover, CRF does not appear to impair non-microsomal acetylation of procainamide, the major biotransformation reaction in the metabolism of this drug.

Investigation of digoxin, quinidine, and disopyramide interactions in rats utilizing parotid saliva, blood, and other tissues.

Blood, parotid saliva, heart, liver, and kidney concentrations of digoxin and quinidine were determined in rats chronically treated with digoxin and in nontreated (control) rats after the administration of quinidine (20 mg/kg ip) and disopyramide (10 mg/kg ip). The results indicated that digoxin concentrations increased significantly and proportionally in parotid saliva and plasma after quinidine, but did not increase after disopyramide. With the exception of the liver, which showed an increase in digoxin concentrations, tissue concentrations of digoxin did not differ from control animals. In rats pretreated chronically with digoxin, quinidine concentrations in plasma, parotid saliva, or heart tissue did not differ significantly from control animals, but were significantly lower than controls in liver and kidney tissues. The results presented here lend additional support to the hypothesis that the increase in digoxin plasma concentration following quinidine administration is primarily due to interference with renal excretion and displacement of digoxin by quinidine binding sites. Furthermore, its was demonstrated that disopyramide has little or no effect on plasma digoxin levels in rats.

Quantitation and comparison of phenobarbital levels in the plasma, saliva, and cerebrospinal fluid of the rat, and the demonstration of an alteration of drug passage by ethanol.

In this study, the ability and extent of three biological fluids--plasma, saliva, and cerebrospinal fluid--to compartmentalize intravenously administered phenobarbital was examined and correlated. The three fluid compartments show markedly different levels of phenobarbital, though this probably does not reflect qualitative differences in the barriers that separate them, but rather in the nature of the compartments themselves. In addition to the quantitation and correlation of drug levels in the various compartments, intravenous administration of 400 mg/kg ethanol following the intravenous administration of 20 mg/kg phenobarbital was shown to alter the passage of phenobarbital into the different fluid compartments, causing a significant increase in the phenobarbital level of cerebrospinal fluid as compared to controls receiving no ethanol. Though the effect seen in the cerebrospinal fluid is significant, while the effect in saliva is not (though the trend was present), it is felt that the action of ethanol to alter drug passage is a non-specific effect on the vasculature. This finding of altered drug passage may help explain the observed synergistic interaction of ethanol and various sedative drugs.