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At least 19 recordsLinked to original sources
PubMed1984

Pharmacokinetic prodrug modeling: in vitro and in vivo kinetics and mechanisms of ancitabine bioconversion to cytarabine.

Conversion rates of the prodrug ancitabine to the antileukemic cytarabine have been measured in vivo (rabbits) and in vitro (in the presence of rabbit blood and human red blood cells, blood, and plasma) using HPLC analyses for the prodrug, drug, and its inactive metabolite, 1-beta-D-arabinosyluracil. These observed pH-dependent in vitro rate constants were consistent with those for chemical hydrolysis determined from controls using Tris buffers. Hydrolysis of ancitabine to cytarabine is chemically, not enzymatically, mediated. The blood concentration-time course for administered compound was described by a two-compartment open model following a rapid intravenous injection of prodrug, drug, or metabolite in each of three rabbits. The in vivo conversion rate constant (kc) following a rapid intravenous prodrug injection was estimated by simultaneous nonlinear regression of ancitabine and cytarabine blood concentration-time courses using equations for two-compartment prodrug and drug with all possible models describing potential conversion sites. The best fit was obtained for the case allowing simultaneous conversion of the prodrug in both central and peripheral compartments to the drug in the central compartment with a common value for kc. The resulting kc value (0.09 h-1, three rabbits) is similar to that for chemical hydrolysis (0.07 h-1) at 38.8 degrees C. Reasons why this agreement is regarded as fortuitous are discussed.

Ancitabine↗
PubMed1984

Aqueous conversion kinetics and mechanisms of ancitabine, a prodrug of the antileukemic agent cytarabine.

The kinetics of conversion of the prodrug ancitabine to the anticancer drug cytarabine have been studied in aqueous solutions in the pH range of 1.5-10.7, temperature range of 19.5-80.0 degrees C, ionic strength range of 10(-4) to 1.5, and in the presence of several general-base catalysts. Under all conditions ancitabine was quantitatively converted to cytarabine. The pH-rate profiles were linear with slope = 1 in alkaline pH, becoming pH independent in the region of maximum stability at pH less than or equal to 4, where buffer catalysis was found to be insignificant and kobs approximately equal to (1.12 X 10(11) h-1)-exp [-10121 deg/T]. At 30 degrees C, pH less than or equal to 4, it is calculated that an aqueous ancitabine solution will maintain 90% of its initial concentration for 12 d. A novel method for measuring general-base catalysis in competition with predominating specific-base catalysis and in the presence of secondary salt effects at constant ionic strength was developed. Three mechanisms of hydrolytic prodrug conversion are proposed: nucleophilic hydroxide addition, general base-assisted nucleophilic water attack, and spontaneous water attack.

Ancitabine↗
PubMed1990

Antiviral effect of antileukemic drugs N4-behenoyl-1-beta-D-arabinofuranosylcytosine (BH-AC) and 2,2'-anhydro-1-beta-D-arabinofuranosylcytosine (cyclo-C) against human cytomegalovirus.

The antiviral activities of antileukemic drugs 1-beta-D-arabinofuranosylcytosine (Cytarabine; Ara-C), 2,2'-anhydro-1-beta-D-arabinofuranosylcytosine (Ancitabine; Cyclo-C), and N4-behenoyl-1-beta-D-arabinofuranosylcytosine (Enocitabine; BH-AC) were evaluated in vitro against human cytomegalovirus (HCMV) in comparison with those of five other antiviral drugs. Both Ara-C and Cyclo-C showed the strongest inhibitory effect to HCMV. BH-AC inhibited the replication of HCMV and depicted almost as the same dose-response curve as Ganciclovir (DHPG). In the presence of Ara-C, Cyclo-C, or BH-AC, triphosphate forms of the nucleoside analogs were detected in the HCMV-infected cells, and synthesis of HCMV DNA was strongly suppressed. Thus, Ara-C, Cyclo-C, and BH-AC were not only antileukemic, but also antiviral in vitro. However, Ara-C and Cyclo-C may not be suitable as anti-HCMV agents, because they are cytotoxic or excreted rapidly in the urine in vivo [Van Voris, 1984; Hirayama et al., 1974]. Because of lower toxicity and longer retention in vivo, BH-AC may be expected as an anti-HCMV agent in patients with leukemia, in addition to serving as an antileukemic drug.

Ancitabine↗
PubMed2002

Clinical pharmacokinetics of cytarabine formulations.

Cytarabine (cytosine arabinoside, Ara-C) is an effective chemotherapeutic agent for the treatment of acute myelogenous leukaemia and lymphocytic leukaemias. As cytarabine is an S-phase-specific drug, prolonged exposure of cells to cytotoxic concentrations is critical to achieve maximum cytotoxic activity. However, the activity of cytarabine is decreased by its rapid deamination to the biologically inactive metabolite uracil arabinoside. This rapid deamination is the reason for the ongoing search for effective formulations and derivatives of cytarabine that cannot be deaminated and exhibit better pharmacokinetic parameters. Protection of cytarabine from fast degradation and elimination has been investigated by encapsulating the drug into pharmaceutically acceptable carriers. Cytarabine derivatives have shown promise in vitro and in animal models. For example, ancitabine (cyclocytidine), enocitabine and cytarabine ocfosfate have been used clinically in Japan. Cytarabine encapsulated into multivesicular liposomes has been approved in several countries for the intrathecal treatment of lymphomatous meningitis. Although many compounds have been investigated, few cytarabine derivatives are currently available for clinical use. Further research is needed to improve the efficacy of cytarabine against haematological and solid tumours.

Animals↗
PubMed1987

[Cytarabine].

Cytarabine (ara-C) is the first line agent with its excellent activity for acute myelogenous leukemia. Combination therapy of MFC (mitomycin C, 5-FU, ara-C) has been used for GI tract cancer with a synergistic effect on L-1210 mouse leukemia. In the results of research on the administration, a high dose ara-C is an effective agent in the refractory cases to the standard dose ara-C and the combination with daunorubicin is applied to a remission consolidation therapy. A small dose ara-C is used against an atypical leukemia with its mechanism of induction of differenciation. On the other hand, in the development of its derivertive compounds ancitabine or enocitabine (BH-AC) were induced to a treatment of acute myelogenous leukemia. Especially BH-AC is the first choice agent for acute myelogenous leukemia combined with other agents.

Animals↗
PubMed1997

Antioxidant activity of rat parotid saliva.

BACKGROUND: The healing-promotion property of saliva has been observed in the past, but its underlying mechanism has never been elucidated. We hypothesized a mechanism based on salivary proteins binding to redox active metal ions, rendering them nonactive in their capacity for free radical production. METHODS: Examination of this mechanism was conducted by comparing the redox activity of protein-rich saliva with protein-poor saliva. We also examined the redox activity mediated by these 2 kinds of saliva following the in vitro addition of iron, copper, and manganese. Saliva samples were analyzed for their redox activity by measuring the ascorbate-driven and saliva (diluted 1:2)-mediated conversion of salicylate to its 2,3- and 2.5-dihydroxybenzoates and catechol metabolites. RESULTS: The concentrations of salicylate metabolites formed by protein-rich saliva were significantly lower by 45% (P < .05), 66% (P < .01), and 54% (P < .05), respectively, when compared with those formed by protein-poor saliva. The capacity of saliva in suppressing redox activity was found to be inversely related to the concentrations of iron and copper added (but not manganese), but correlated well with the protein content. When the highest concentrations of iron (15 mumol/L) and copper (10 mumol/L) were added to protein-rich saliva, the concentrations of salicylate metabolites produced were only 0.3% to 1% of those of non-saliva-containing controls (P < .01). However, when these concentrations of iron and copper were added to protein-poor saliva, significantly higher values of redox activity were detected, and the concentrations of the salicylate derivatives produced were 2.1% to 8.1% of those of non-saliva-containing controls (P < .01). In contrast, when the lowest concentrations of iron (2 mumol/L) and copper (0.1 mumol/L) were added, 2.8 to 4 times lower concentrations of salicylate derivatives were produced (P < .01). CONCLUSION: These results substantiate our hypothesis that saliva has a profound capacity for reducing redox activity rendered by transition metal ions, correlating well with its protein content.

Ancitabine↗
PubMed1996

Exocytosis from rat submandibular granular tubules during cyclocytidine stimulation shows unusual features, including changes in the granule membrane.

Sequential secretory changes in granular tubule cells caused by the secretagogue cyclocytidine (75 mg/kg i.p.) were studied at the ultrastructural level, in perfusion (n = 5 animals) and immersion (n = 8 animals) fixed rat submandibular glands, using the periodic acid-thiocarbohydrazide-silver proteinate technique (PA-TCH-SP). The onset of secretion varied from 45 to 75 minutes after administering the cyclocytidine. During the initial stages of overt secretion, structural changes occurred irregularly in a progressive fashion with: (1) an increase in granule membrane staining with PA-TCH-SP and a parallel alignment of the secretory granules with the adjacent apical plasma membrane, which developed a honeycomb-like appearance; (2) docking of these secretory granules to the apical plasma membrane; (3) early secretion of some secretory granules in a semiclassical exocytotic fashion (but this was rarely witnessed). During stages (1) and (2), the cytochemical characteristics of the membrane of the secretory granules, as well as of the plasma membrane, suggest a priming process is occurring. After these initial preparatory phases, further structural changes occurred in the granule membranes with a gradually progressive formation of microvesicles and granule fusions; secretion continued in an explosive manner with proteinaceous material being transferred to lumina in at least three different ways: (1) by typical exocytosis (but it was infrequent); (2) from granules fused intracellularly into aggregates (compound exocytosis); and (3) some apocrine-type of secretion through bleb formation. The formation of these intracellular aggregations was associated with the microvesicles in the granule membranes and some aggregates became very large. Secretion of their contents into lumina occurred through elongated membrane channels. The material secreted included microvesicular forms that had become interiorised in the granular aggregates, and any cytoplasm that may also have been entrapped.

Ancitabine↗
PubMed1981

Treatment of acute nonlymphocytic leukemia in adults: response to 2,2-anhydro-1-B-D-arabinofuranosyl-5-fluorocytosine and thioguanine on the L-12 protocol.

Fifty-one adult patients with acute nonlymphocytic leukemia (excluding acute promyelocytic leukemia) were treated on the L-12 protocol. The L-12 differed from the preceding L-6 in that 2,2-anhydro-1-B-D-arabinofuranosyl-5-fluorocytosine (AAFC), replaced arabinosylcytosine (ara-C) together with 6-thioguanine (TG) for remission induction. Achievement of remission was followed by an extended 14-week multi-drug consolidation program. With this more intense regimen, an overall complete remission rate of 49% and a median remission duration of 23.7 months were achieved; these results were not significantly better than the 57% complete remission rate and 8.6 months median remission duration obtained with the L-6 regimen. Four year disease-free survival was 22% on the L-12 compared with 16% on the L-6 protocol. No relationship between prognosis and FAB classification was found on either the L-6 or the L-12 protocol.

Adolescent↗
PubMed1989

Diaziquone and 2,2'-anhydro-arabinosyl-5-fluorocytosine for the treatment of children with relapsed or refractory acute nonlymphoblastic leukemia.

The authors treated 30 patients ages 1 to 19 with relapsed or refractory acute non-lymphoblastic leukemia (ANLL) with the combination of diaziquone (AZQ) and 2,2'-anhydro-arabinosyl-5-fluorocytosine (AAFC) intravenously in two dose schedules. The first 12 patients were treated with 19 courses of AZQ 30 mg/m2 X 3 days and AAFC 600 mg/m2/dose every 12 hours X 10 doses. An additional patient was treated with three courses at 80% of the above doses. Hepatic toxicity was National Cancer Institute Grade III in eight of 22 and Grade IV in one of 22 courses. Infectious complications were severe in all patients, including responders. One patient achieved a complete remission and one a partial remission; the latter died with marrow aplasia after a second course. Altogether three patients developed profound aplasia and died before marrow recovery. The authors treated a second group of 17 patients with AZQ 22.5 mg/m2/day X 3 days and AAFC 450 mg/m2/dose every 12 hours X 10 doses. Three patients achieved a complete remission and one patient a partial remission for 3, 4, 9, and 9 months, respectively. The remainder had progressive disease or no response. All patients developed profound myelosuppression but no toxic deaths occurred. Hepatic toxicity was reduced. Therapy induced cytoreduction of bone marrow was determined by flow cytometry in ten patients; none of these patients responded during the interval studied. Although AZQ and AAFC are active in childhood ANLL with acceptable toxicity, the combination does not appear more active than AZQ used alone. Future studies should define the role of AZQ in combination with other agents.

Adolescent↗
PubMed1991

Successful reinduction therapy with amsacrine and cyclocytidine in acute nonlymphoblastic leukemia in children. A report from the Childrens Cancer Study Group.

Amsacrine (AMSA) and cyclocytidine were studied as retrieval therapy in 122 pediatric patients with acute nonlymphoblastic leukemia (ANLL). Patients either failed to achieve sustained initial remissions or were in relapse. Induction therapy consisted of intravenous (IV) AMSA (75 mg/m2) from days 1 to 5 and subcutaneous cyclocytidine (600 mg/m2) from days 1 to 7. Maintenance therapy consisted of IV etoposide (VP-16) (100 mg/m2) for 5 days and IV AMSA (100 mg/m2) on day 1. Of 122 patients, 109 were evaluable. There were 13 early deaths. Ninety-six patients received adequate therapy defined as completion of two courses of therapy. Of these 96 patients, 52 achieved complete remission. Fifteen of 33 patients who failed initial induction achieved complete remission. Eighteen of 39 patients who were resistant to anthracyclines had complete responses. There was no direct evidence of AMSA-induced cardiotoxicity. Remission duration was 28 days to 3 or more years (median, 98 days). AMSA and cyclocytidine were effective retrieval therapy for patients who were in relapse or unresponsive to frontline therapy. Duration of remission was short (median, 98 days).

Adolescent↗
PubMed1977

Mathematical model for cyclocytidine pharmacokinetics.

The pharmacokinetics of the drug cyclocytidine in humans were modeled by using a physiological and anatomical approach. Each pertinent tissue is represented by a single compartment, and these compartments are linked together by the circulatory system. Each compartment is then represented by an ordinary differential equation that represents the rate of change in drug concentration as function of convecting transport, metabolism, and urinary clearance. The models for cyclocytidine and cytarabine are linked together by a hydrolysis term in each equation set. The resulting equation sets are then solved numerically to predict the concentration of both drug species in situ. The models use physiological blood flows, tissue volumes, and clearance parameters. The results of the model show that cyclocytidine can act as a reservoir for cytarabine in vivo over the time studied. This effect is confined to relatively long times and relatively low plasma concentrations.

Ancitabine↗
PubMed1982

Drug stability in liposomal suspensions: hydrolysis of indomethacin, cyclocytidine, and p-nitrophenyl acetate.

First-order rate constants (kL) for hydrolysis of p-nitrophenyl acetate, cationic cyclocytidine, and anionic indomethacin in the presence of buffered liposomal suspensions of positive, negative, and neutral charge were compared to those determined in the corresponding buffers (kB) using the ratio, Rk = kL/kB. Association between the reactants and the liposomes was evaluated by comparing assays for concentration in the filtrates (CF) with the total concentration in the liposomal suspension (CT) using RC = CF/CT. Liposomes did not influence cyclocytidine hydrolysis rates and no association was observed (Rk congruent to RC congruent to 1). In contrast, indomethacin showed approximately 80% reduction in hydrolysis rate and approximately 80% liposome association value (Rk congruent to 0.2 congruent to RC). In neutral and negatively charged liposomal suspensions, p-nitrophenyl acetate displayed approximately 30% decrease in kB (Rk congruent to 0.7) together with approximately 90% liposomal association (RC congruent to 0.1). However, hydrolysis was greatly accelerated in positively charged liposomal suspensions. Loss was described by a biexponential equation where alpha is the fast and beta is the slow pre-exponential coefficient and alpha/beta/kB = 39:6:1. The observed relationships between hydrolysis rates and reactant-liposome associations are reconciled in terms of the hydrophilicity of the reactants and the potential influence of the liposomes on the expected transition states for the hydrolysis reactions.

Ancitabine↗
PubMed1976

A new hamster fibrosarcoma model for in vitro/in vivo evaluation of cancer chemotherapeutic agents.

A hamster fetal cell clone has been developed for in vitro chemotherapeutic studies as well as in an in vivo fibrosarcoma model system. Highly reproducible quantitative in vitro chemotherapeutic data can be obtained with this cell line within 5 days, and as few as 10(2) cells produce rapidly growing fibrosarcomas when injected subcutaneously into adult hamsters. We found using these cells in vitro that 1-beta-D-arabinofuranosylcytosine (ara-C) can antagonize the effect of 5-azacytidine (aza-C) if given simultaneously or if aza-C treatment is preceded by a 2-hr exposure to ara-c. Using the same cell line as in vivo model for chemotherapy it was also shown that ara-C and cyclocytidine significantly inhibited tumor growth. This hamster cell line may be quite useful as an in vitro/in vivo model system for the study of cancer chemotherapeutic agents.

Ancitabine↗
PubMed1984

Evaluation of cyclocytidine in reinduction and maintenance therapy of children with acute nonlymphocytic leukemia previously treated with cytosine arabinoside: a report from Children's Cancer Study Group.

A study of children in relapse with acute nonlymphocytic leukemia (ANLL) previously maintained in remission with combination chemotherapy including cytosine arabinoside (Ara-C) was undertaken by Children's Cancer Study Group (CCSG) to assess the efficacy of cyclocytidine (Cyclo-C), a depot Ara-C, compared to parenteral Ara-C given every 12 hr. The reinduction protocol consisted of daunomycin combined with either Ara-C (Regimen 1) or Cyclo-C (Regimen 2). One-hundred thirty eligible patients were entered on the randomized study. Hematologic toxicity was significant in both regimens and resulted in four drug-related deaths. Cardiac toxicity was observed in five patients, manifested only by abnormal echocardiogram or electrocardiogram patterns in three and congestive heart failure in two patients. Seventy-seven of 112 evaluable patients achieved M-1 or M-2A marrow remissions (69%): 46 of 60 on Regimen 1 (75%), 30 of 52 on Regimen 2 (60%). The remission rate between the two regimens was not significantly different. There was no significant difference in the duration of remission comparing maintenance cyclophosphamide combined with Ara-C or with Cyclo-C. Addition of VP-16 and CCNU to the maintenance therapy did not prolong the duration of remission. This study indicates that patients with childhood ANLL previously treated with Ara-C and daunomycin can obtain a successful second remission. A single daily subcutaneous dose of Cyclo-C was found to be as efficacious as Ara-C given intravenously every 12 hr. The single dose schedule provides a convenient way to treat patients with relapsed ANLL in the outpatient setting.

Adolescent↗
PubMed1993

Ultrastructural changes in salivary glands after different adrenergic and cholinergic stimulations. A long-term morphological study in the rat.

We have compared four different sialogogues and their degranulating effect on serous and mucous cells, and their long-term effects. From this and earlier experiments, even within the groups of alpha- and beta-adrenergic agents used, the effects varied on the serous and mucous cells. Previous studies have shown that cyclocytidine effectively degranulates serous cells without signs of cellular damage, while carbachol predominantly affects mucous acinar cells but gives early rise to permanent gland damage. Noradrenaline affects both serous and mucous cells, predominantly affecting serous cells with initial mitochondrial damage. Clonidine partially depletes both serous and mucous cells of their granules, producing permanent cellular damage. One month after a single injection of cyclocytidine the early findings described had disappeared. Carbachol showed permanent damage to salivary gland parenchyma, and both noradrenaline and clonidine demonstrated a long-term effect on acinar mucinous cells.

Ancitabine↗
PubMed1985

Survival of L1210 leukemia cells and normal hematopoietic stem cells following in vivo administration of cyclocytidine.

The survival of L1210 cells following increasing doses of cyclocytidine (cyclo-C) was determined by spleen colony assay. For single dose, cyclo-C was effective reaching a fractional survival of less than 10(-3) at 10 mg/mouse. This is significantly more effective than a similar dose of arabinosyl cytosine (ara-C) given by rapid infusion. The time-survival curve demonstrated extended cytotoxicity following a single 10 mg/mouse dose of cyclo-C as expected for a long-acting agent. When a 24-hour infusion was examined, however, ara-C was more effective than cyclo-C by a factor of about 10. The clinical implication of this is discussed.

Ancitabine↗
PubMed1978

Stimulation of secretion of epidermal growth factor and amylase of cyclocytidine.

Radioimmunoassays and immunocytochemical techniques were used to assess the effect of cyclocytidine, an antitumor agent, on the level and localization of Epidermal Growth Factor (EGF) in the submandibular gland of the male mouse. A single intraperitoneal injection of 150 mg/kg of cyclocytidine caused, within 6 h, a degranulation of the granular convoluted tubules (GCT) cells and reduced the concentration of immunoreactive EGF in gland extracts by more than 90%. This effect was largely abolished by the administration of dibenzyline but not by propranolol, indicating that the secretory effect of the drug on the GCT cells is mediated by alpha-adrenergic receptors. By immunocytochemical staining revealed the same trends in changes in EGF concentration as the radioimmunoassays. However, even at the peak of the cyclocytidine effect there were cells which retained their secretory granules and apparently their EGF complement. In addition, there was a lobular variation in the secretory response. Cyclocytidine caused a transiet increase in the blood level of EGF. Furthermore, it stimulated amylase secretion from the gland, which also involved alpha-adrenergic receptors. Cyclocytidine will be useful in future analyses of the release of various biologically active substances from the GCT cells of the mouse submandibular gland.

Adrenergic alpha-Antagonists↗
PubMed1979

Physiologically based pharmacokinetic models for anticancer drugs.

The rationale and history of the development of physiologically based pharmacokinetic models are briefly reviewed in this paper. The methods of model construction and the previous application of this type of model to anticancer drugs are discussed. Future research should be focused on the following areas: (1) interspecies scaling, (2) the effects of disease states on the pharmacokinetics of anticancer drugs, and (3) the applications of pharmocokinetics to the studies of growth behavior of cancer cells. The ultimate goal will be to utilize this basic information to design an optimal dosage regimen and treatment schedule for the safe and effective cancer chemotherapy of each individual patient.

Ancitabine↗