The disposition and metabolism of 2',3'-dideoxycytidine, an in vitro inhibitor of human T-lymphotrophic virus type III infectivity, in mice and monkeys

The pharmacokinetics and metabolism of the anti-human T-lymphotrophic virus type III/lymphadenopathy-associated virus agent 2',3-dideoxycytidine have been examined in BDF1 mice and rhesus monkeys, with ancillary enzyme studies carried out on tissue derived from both the latter species and also from human subjects. For the pharmacokinetic studies, 2',3-dideoxycytidine and its catabolic product 2',3-dideoxyuridine have been separated and measured in plasma, urine, and cerebrospinal fluid by a reverse HPLC method. For metabolic studies, tritium-labeled drug (labeled in the 5- and 6-positions of the pyrimidine ring) has been employed, utilizing an ion exchange HPLC analytical method suitable for the separation of the parent nucleoside from its mono-, di-, and triphosphates in cell extracts and in tissue homogenates. The drug is rapidly cleared from plasma in a biphasic manner (terminal t 1/2 in BDF1 mice and rhesus monkeys of 67 min and 109 min, respectively) following an iv bolus dose of 325 mg/m2. This two-compartment open model is predictive of plasma concentrations during long term ip infusions in mice. Dideoxycytidine is predominantly excreted in the urine as unchanged parent compound, although a minor urinary metabolite (2,3-dideoxyuridine) is detected in the monkey but not in the mouse. Oral absorption of 2',3'-dideoxycytidine is rapid, with plasma levels approaching those seen after iv administration within 45 min in the mouse. Entry to the central nervous system is also rapid, but the cerebrospinal fluid to plasma AUC ratio after iv administration is only 0.026-0.040 in rhesus monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)

Furanose-pyranose isomerization of reduced pyrimidine and cyclic urea ribosides

Tetrahydrouridine (THU, 2) and other fully reduced cyclic urea ribofuranosyl nucleosides undergo a rapid, acid-catalyzed isomerization to their more stable ribopyranosyl form. This isomerization is characterized by a change in spectral properties and by a greater than 10-fold decrease in potency for those nucleosides that act as potent inhibitors of cytidine deaminase in their ribofuranose form. 1-(beta-D-Ribopyranosyl)hexahydropyrimidin-2-one (7) was synthesized and used in conjunction with its furanose isomer 6 as a model compound for more extensive 1H and 13C NMR, mass spectral, and kinetic studies of this isomerization. The 0.4 delta upfield shift and 4-Hz increase in the J1',2' coupling constant for the pyranose anomeric proton in the 1H NMR spectrum is indicative of a pyranose beta-CI conformation in which the aglycon and C-2' and C-4' hydroxyls are equatorial. The mass spectra of trimethylsilylated pyranose nucleosides also show a characteristic large shift in the m/z 204-217 abundance and the appearance of two new rearrangement ions at M-133 and M-206. For furanose 6 the rate of isomerization is pH and temperature dependent with pyranose 7 predominating by a factor of 6-9 equilibrium. At pH 1 and 37 degrees C, furanose 6 has an initial half-life of less than 12 min. Accordingly, this isomerization may explain the observed lack of enhanced ara-C levels in studies evaluating the oral administration of an ara-C and THU combination to species with an acidic stomach content.

Spiromustine analogues. Relationships between structure, plasma stability, and antitumor activity

Spiromustine is a hydantoin-containing nitrogen mustard currently in Phase I clinical trial. Since the in vitro plasma half-life of this compound (6.4 min, 37 degrees C, pH 7.4) appeared to be influenced by the hydantoin ring, analogues containing 2-5 methylene spacer groups between this ring and the nitrogen mustard moiety were prepared and evaluated for hydrolytic stability and antitumor activity. Stability correlated with structure and pKa values. The proximity of the hydantoin ring to the mustard function was a stabilizing factor. Activity against murine P-388 leukemia was demonstrated and a gradual decrease in this activity was observed as the hydrolytic instability increased. A relationship between analogue structure and a mass spectral rearrangement ion was identified.

Percutaneous transperitoneal approach to a pelvic kidney for endourological removal of staghorn calculus

Percutaneous access to a pelvic kidney was obtained by retrograde nephrostomy in combination with continuous observation and displacement of bowel loops via a laparoscope. A staghorn calculus was removed by ultrasonic lithotripsy and mechanical extraction, and the patient was discharged from the hospital 5 days later.

A phase I and pharmacokinetic study of dihydro-5-azacytidine (NSC 264880)

5,6-Dihydro-5-azacytidine (DHAC; NSC 264880) is an analogue of 5-azacytidine that does not possess the hydrolytically unstable 5,6-imino bond of the parent compound. Thus, unlike 5-azacytidine, DHAC is stable in aqueous solution and may be administered by prolonged i.v. infusion, potentially avoiding acute toxicities associated with bolus administration of 5-azacytidine. In this study, patients with advanced cancer were treated with DHAC administered as a 24-h constant i.v. infusion every 28 days. Treatment began at a dose of 1 g/sq m and was escalated to the maximum-tolerated dose of 7 g/sq m, where the limiting toxicity was pleuritic chest pain. Other toxicities included nausea and vomiting, which were not limiting. There was no evidence for myelosuppression, nephrotoxicity, or hepatotoxicity. DHAC was measured in plasma, urine, and ascites by a sensitive and specific reverse-phase high-performance liquid chromatography assay capable of detecting 50 ng of drug per ml. Steady-state plasma levels were achieved with 8 h and ranged from 10.0 to 20.5 micrograms of DHAC per ml at the maximum-tolerated dose. Total-body clearance of 311 +/- 76 ml/min/sq m and postinfusion half-lives between 1 and 2 h were observed. Between 8 and 20% of the administered dose was excreted unchanged in urine. While ascites DHAC levels in a patient with ovarian cancer were comparable to plasma levels, postinfusion elimination was slower from this compartment than from plasma. No correlation was observed between DHAC plasma levels and duration or intensity of dose-limiting pleuritic chest pain. One patient with progressive Hodgkin's lymphoma demonstrated stabilization of disease for seven treatment cycles, and two patients with aggressive lymphoma demonstrated dramatic, although transient, disease responses. A dose of 7 g/sq m is recommended for Phase II trials of DHAC using this schedule.

Distribution, elimination, metabolism and bioavailability of hexamethylenebisacetamide in rats

Hexamethylenebisacetamide (HMBA), an in vitro differentiating agent, was studied for its pharmacodynamic actions in animals. Plasma stability, organ distribution, excretion, oral bioavailability, and estimates of pharmacokinetic parameters and acute lethality were determined in rats. The single dose intraperitoneal LD50 was greater than 3000 mg/kg in both mice and rats. The drug was stable in plasma from several different species during an 8 h in vitro incubation at 37 degrees C. Following a single intravenous (iv) bolus injection (1000 mg/kg) to rats, HMBA was removed from the plasma with a half time of 2.2 +/- 0.5 h, and 65 +/- 8% of the dose was excreted unchanged in the urine during the first 24 h after dosing. During an 8 h iv infusion, plasma concentrations of 4 mM were easily maintained with no apparent adverse effects. Drug was uniformly distributed, with highest concentrations found in thymus, kidney, liver, and lymph node throughout the first 24 h after a single iv bolus dose. In vivo metabolism was very small, and the presence of apparent metabolites was undetectable until 48 h after iv administration. Oral bioavailability was good (32%), with peak plasma concentrations of 2 mM achieved one hour after oral administration. After oral dosing urinary excretion and plasma decay were comparable to similar data obtained after iv dosing.

Evidence for the presence of DNase-actin complex in L1210 leukemia cells

L1210 leukemia cell cytosol was analysed for the presence of DNase I activity. No free activity was determined in crude cytosol. DNase I enzyme was found to occur in a latent form bound to cytoplasmic actin. DNase-actin complex was partially isolated by Sephadex filtration and DNase I-like activity was demonstrated after SDS gel electrophoresis of the complex and enzyme renaturation. The results were compared with those for synthetic complex of pancreatic bovine DNase I and chicken muscle actin.

The reduction of uridine 5'-diphosphate and uridine 5'-triphosphate in some transplantable rat hepatomas

The reduction of uridine 5'-diphosphate (UDP) and uridine 5'-triphosphate (UTP) has been studied in normal adult rat liver, the Dunning hepatoma, and Morris 5123D and 7793 hepatomas. A new paper chromatographic method that separates and quantitates all the major products of the reduction and hydrolysis or other reactions of the substrate has been devised. All of the above tissues were able to reduce UDP and UTP at relatively slow rates ranging from 0.25 nmole of deoxycompound formed (deoxyuridine 5'-triphosphate) per mg protein per hr for liver to 3.5 nmoles deoxyuridine 5'-triphosphate for the Morris 7793 hepatoma when UTP was the substrate. In general, UTP was a better substrate than UDP. The method may also be used to measure cytidine 5'-diphosphate (CDP) reduction, and under the same conditions, the reduction of CDP proceeded at about 6 times the rate of UTP reduction in the Dunning hepatoma. Like CDP reduction, the reduction of UTP was strongly modulated by ATP. Reduction of UTP was insignificant with no ATP or 1.5 micronmoles ATP added to the reaction mixture and was maximal with 0.25 micronmole. The reduction of UTP was inhibited by deoxyuridine 5'-monophosphate, deoxythymidine 5'-triphosphate, deoxycytidine 5'-triphosphate, and deoxyribose 1'-phosphate. The effects of deoxyadenosine 5'-triphosphate varied, depending on its concentration in the reaction medium and whether UDP or UTP was a substrate. However, hydroxyurea did not inhibit reduction of UDP or UTP at concentrations that strongly inhibited CPD reduction. All of the tissues were able to hydrolyze [alpha-32P]deoxyuridine 5'-triphosphate readily to the diphosphate and monophosphate. It is suggested that the enzyme that reduces UTP or UDP may be different in these tissues from the enzyme that reduces CDP.

Factors affecting deoxycytidylate deaminase activity in some transplantable rat hepatomas

Dunning hepatoma has a low activity of deoxycytidylate deaminase, comparable to that of normal adult rat liver. This activity seems inconsistent with the rapid proliferation rate of the tumor. Factors which might affect the activity of deoxycytidylate deaminase in the Dunning hepatoma have been examined in it and compared to the Novikoff hepatoma which has high activity of this enzyme. The low activity in Dunning hepatoma does not appear to be the result of any inhibition or, possibly, proteolytic enzyme as judged by mixing experiments, nor does it appear to be due to in vivo differences in nucleotide concentrations especially deoxycytidine 5'-monophosphate, deoxycytidine 5'-triphosphate, or deoxyguanosine 5'-monophosphate which might either help stabilize the enzyme, allosterically increase its activity, or inhibit it. The Dunning hepatoma does not convert cytosine deoxyriboside to uridine deoxyriboside at a significant rate, and the formation of uridine deoxyriboside from deoxyuridine monophosphate is 1% or less during a 30-min incubation of high-speed supernatant fraction from the tumor in either the presence or absence of fluoride. It is concluded that the Dunning hepatoma probably has intrinsically low deoxycytidylate deaminase activity.

Thymidylate synthetase activity in the Novikoff hepatoma

The mechanism by which injected methotrexate increases thymidylate synthetase activity in the Novikoff hepatoma has been studied. Folic acid injection causes a similar increase in enzyme activity in hepatoma after 16 hr but the action of folic acid and methotrexate is not additive. The increase in activity of thymidine 5'-phosphate synthetase in the hepatoma caused by methotrexate is not affected by actinomycin D, but is inhibited 50% by puromycin and 100% by cycloheximide. High-speed supernatent fraction prepared from hepatoma of animals treated with methotrexate has, initially, one-half the specific thymidine 5'-phosphate synthetase activity of untreated controls. Upon addition of increasing amounts of tetrahydrofolate, the specific enzyme activity in the supernatant fraction from the methotrexate-treated animals rises to double that of the controls. Puromycin added to homogenates of Novikoff hepatoma consistently increases enzyme activity by approximately 20%. One hypothesis consistent with these results and results reported by others is presented.