Biomedical subjects

D S Zaharko

Publications and source records attributed to D S Zaharko.

At least 19 recordsLinked to original sources

PubMed1993

Chloroquinoxaline sulfonamide: a sulfanilamide antitumor agent entering clinical trials.

Chloroquinoxaline sulfonamide (CQS) has been developed to the clinical trial stage based on its activity in the Human Tumor Colony Forming Assay (HTCFA). In the HTCFA, CQS demonstrated inhibition of colony formation against breast, lung, melanoma and ovarian carcinomas. The mechanism of action of CQS is unknown. It does not appear to inhibit folate metabolism as does the structurally similar sulfaquinoxaline. Preclinical toxicology studies in dogs and rats have shown that CQS is toxic to lymphoid organs, bone marrow, gastrointestinal tract, pancreas, CNS, adrenal glands and testes. Toxicity was generally reversible with the exception of testicular atrophy in dogs and rats which occurred late and was not reversible within the study time frame. The pharmacokinetic data indicate that CQS binds to serum proteins in a dose and species specific manner. Terminal half-lives appear to vary between species from 60 hours in mice, 15 hours in rats, and 45-132 hours in dogs. Preliminary data indicate a longer terminal half-life in humans. Two phase I trials are ongoing using a 60 min infusion schedule once every 28 days. The starting dose for each trial was 18 mg/m2.

Animals↗

PubMed1991

Cyclopentenyl cytosine: interspecies predictions based on rodent plasma and urine kinetics.

A hybrid compartmental-physiological model for cyclopentenyl cytosine (CPE-C) is designed on the basis of early limited rodent pharmacokinetic data. Application of model independent pharmacokinetics and biochemical knowledge was first used to conceptualize such a model. The approach was to scale the physiological parameters of the model (compartmental clearances) and keep constant the anatomic parameters of the model (compartment volumes). Scaling of physiological mechanisms was based on body weight/surface area ratios. Using these principles, simulations with the model can reasonably anticipate the in vivo behavior of (CPE-C) in several species (mouse, rat, dog). The model is useful in understanding species differences in pharmacokinetic behavior of CPE-C.

Animals↗

PubMed1989

Could interspecies differences in the protein binding of flavone acetic acid contribute to the failure to predict lack of efficacy in patients?

We investigated the differences in plasma protein binding of flavone acetic acid (FAA) in mice and men in an attempt to explain the inter-species differences in response. In vitro data indicate both qualitative and quantitative differences in FAA protein binding: approximately 80% is bound in humans, with two different types of binding site identified; in mice, 70% is bound and only one binding site could be described. Protein binding is dose-dependent in both species. Plasma samples from 20 patients receiving FAA showed that most achieved levels that would be active in mice. We conclude that these differences in protein binding are insufficient to explain totally the observed differences in response.

Animals↗

PubMed1988

Augmentation of natural killer activity, induction of IFN and development tumor immunity during the successful treatment of established murine renal cancer using flavone acetic acid and IL-2.

The investigational drug flavone acetic acid (FAA) has been previously shown to systemically augment NK activity in vivo in normal mice within 24 h of i.p. or i.v. administration. The current study investigates the ability of FAA, and/or rIL-2, to augment NK activity and antitumor responses in mice bearing murine renal cancer (Renca). The results demonstrate that FAA potently augments NK activity in the blood, spleen, and liver of Renca-bearing mice and that the administration of rIL-2 in addition to FAA results in a further augmentation of NK activity over that observed with FAA alone. Renca-bearing mice treated with FAA (200 to 250 mg/kg) plus rIL-2 exhibited a significantly increased incidence of long term survivors (59%) over that observed following treatment with FAA (0%) or rIL-2 (5%) alone. Therapeutic synergy between FAA and rIL-2 was observed against primary tumors, minimal residual disease, and experimental-induced pulmonary metastases. Mice cured of Renca by FAA plus rIL-2 treatment were largely resistant to rechallenge with Renca suggesting a role for T lymphocytes. The augmentation of NK activity and the therapeutic effects of FAA coincided with the rapid induction of high titers of serum IFN of the alpha/beta type within 4 h of FAA administration. Subsequent studies demonstrated that the contribution of FAA could be partially replaced by the administration of several doses of human rIFN-alpha A/D Bg1 before the initiation of rIL-2 administration. The observed synergistic antitumor effects of FAA plus rIL-2 coincided with the augmentation of NK activity, induction of IFN-alpha/beta, and induction of long lasting tumor immunity. Overall, these results suggest that this approach may obviate the need for adoptive immunotherapy in association with rIL-2 administration for at least some tumor types.

Adjuvants, Immunologic↗

PubMed1987

Flavone acetic acid (LM 975, NSC 347512). A novel antitumor agent.

Flavone acetic acid (FAA) is a synthetic flavonoid compound which has recently begun clinical trials as an antitumor agent based on its striking activity in solid tumor model systems. The pharmacologic behavior of FAA in animals appears to be predictive of both its cytotoxic efficacy and its toxicity to normal tissues (principally the central nervous system and gastrointestinal tract). The design and conduct of phase I studies in man are based upon these principles, with the goal of maximizing their safety and efficacy.

Animals↗

PubMed1986

Differences in DNA damage produced by incorporation of 5-aza-2'-deoxycytidine or 5,6-dihydro-5-azacytidine into DNA of mammalian cells.

The effects of 5-aza-2'-deoxycytidine (aza-dCyd) and 5,6-dihydro-5-azacytidine (H2-aza-Cyd) on the integrity of DNA from several mammalian cell lines were compared using the alkaline elution technique. While both compounds have been shown to inhibit DNA methylation, a direct comparison of their effects on DNA structure has not previously been reported. Exposure of L1210 cells to H2-aza-Cyd (1-100 micrograms/ml) and simultaneous labeling with [14C]thymidine for 24 h resulted in the production of single-strand breaks in DNA, which were significantly repaired when cells were incubated in drug-free medium for an additional 24 h. This differed from our previous findings for aza-dCyd, confirmed here in parallel experiments, which showed that this compound produces alkali-labile lesions that persist for 48 h. The DNA effects of both drugs were significantly reduced when cells were prelabeled with [14C]thymidine, indicating that production of DNA lesions requires incorporation of the anomalous base. Studies utilizing pulse-labeled DNA indicated that aza-dCyd has little effect on the rate of DNA elongation, whereas H2-aza-Cyd produced a complete inhibition for at least 6 h after drug removal. The contrasting pattern of DNA damage induced by these compounds in L1210 was also observed in two human lymphoblastoid cells lines, one of which was derived from a patient with xeroderma pigmentosum. We had previously concluded that alkali-labile sites in DNA from aza-dCyd-treated cells probably arise due to the chemical instability of aza-dCyd. In contrast, incorporated H2-aza-Cyd is chemically stable. The single-strand breaks produced in H2-aza-Cyd treated cells were not of the alkali-labile type, and may represent an accumulation of DNA replication fragments and/or intermediates in an excision repair process. Thus, the DNA lesions produced by the two drugs have markedly different characteristics, and H2-aza-Cyd should not be considered to be merely a stable pharmacological congener of aza-dCyd.

Animals↗

PubMed1986

Potential roles for preclinical pharmacology in phase I clinical trials.

Concepts elucidated from preclinical pharmacology studies have made a substantial impact on the clinical use of anticancer drugs. However, the majority of animal pharmacology results have not been available until after drugs have entered clinical trials. Since clinical pharmacokinetic measurements are already part of many phase I trials, human data could be directly compared with mouse data if mouse pharmacology studies were completed before clinical trials were initiated. Once the starting dose in a phase I clinical trial has been evaluated, subsequent doses are escalated until the maximum tolerated dose is reached. The rate of escalation is empirically defined by a modified Fibonacci series. This universal escalation scheme is applied to all drugs, with no modifications based upon pharmacology or other factors. If the starting dose is far removed from the maximum tolerated dose, a large number of dose escalations are required. Consequently, most patients receive subtherapeutic doses, and the amount of resources allocated to each drug increases. We are exploring potential strategies for controlling the rate of dose escalation based upon pharmacokinetic determinations in mouse and man. Retrospective analyses indicate that 20%-50% savings in the total number of dose escalations are possible.

Aminoacridines↗

PubMed1986

Therapeutic and pharmacokinetic relationships of flavone acetic acid: an agent with activity against solid tumors.

Flavone acetic acid is a novel structure which exhibits an interesting spectrum of antitumor activity in preclinical studies. It has little antitumor activity in the leukemias and pronounced antitumor activity in solid tumors. Preclinical therapeutic, toxicologic, and pharmacokinetic studies are summarized and considered together to introduce the concept of a therapeutic window of effective plasma concentrations and effective exposure times in attempts to maximize therapeutic effects and minimize toxic effects. Plasma concentrations, predicted to fall from 600 to 100 micrograms/ml over 10 hours resulting from 267 mg/kg ip bolus injections in mice are curative to sc implanted colon 38. Doses of 356 mg/kg and higher cause acute lethality in many mice. Iv doses cause acute lethality in mice more frequently than ip doses, which suggests a peak toxic effect. However, iv infusions in mice, which also can be curative to colon 38, can also result in a lethal effect, although more delayed, even though the predicted plasma concentrations are much below the peak plasma concentrations that appear to be necessary for acute lethality. Plasma concentrations, 100 to 600 micrograms/ml predicted to result from single doses that are therapeutic and not acutely lethal in mice, if maintained by infusion in dogs for 28 hours or longer result in delayed lethality. We conclude that relatively high plasma concentrations (greater than 100 micrograms/ml) are needed for therapeutic activity with this antitumor agent and that lethality can result from two distinctly different causes. An acute lethality can result from an excessively high peak plasma concentration (greater than 600 micrograms/ml). A delayed lethality can result from a too-long exposure (greater than 24 hrs) at therapeutically effective plasma concentrations (100-600 micrograms/ml). We also note that unexpected kinetic differences exist among the mouse, dog, and man. Whereas usually with antitumor agents plasma clearances are proportional to body surface area, and hence faster in small species, quite the opposite is true with flavone acetic acid. Mice exhibit a slower plasma clearance relative to dogs and man.

Animals↗

PubMed1985

Arabinosyl-5-azacytosine: plasma kinetics and therapeutic response (L1210) in vitro and in vivo in mice.

Arabinosyl-5-azacytosine (Ara-AC) was studied in vitro and in vivo in kinetic and therapeutic experiments. This compound is degraded fairly rapidly in mouse plasma in vitro at 37 degrees C (t 1/2 = 130 min) and even more rapidly in vivo (terminal t 1/2 = 76 mins, with a three phase plasma clearance curve, single dose iv 200 mg/kg). In vitro clonogenic assays with L1210 exposed to Ara-AC indicated that cytotoxic concentrations of 1 to 10 micrograms/ml were optimal at exposure times of 72 hours or longer (3 to 4 logs of L1210 cell kill). Extrapolating this information to in vivo infusion therapeutic studies in mice illustrated that optimal therapy (estimated 8 logs of L1210 cell kill) was also achieved at plasma concentrations of between 1 to 10 micrograms/ml for 72 hours of infusion. Infusions of 96 hours resulted in some lethal toxicity and 144 hour infusions were 100% lethal.

Animals↗

PubMed1985

Plasma kinetics and effects of 5,6-dihydro-5-azacytidine in mice and L1210 tumor.

The plasma kinetics of 5,6-dihydro-5-azacytidine (DHAC) was determined in mice using an HPLC method following an intravenous dose of 2000 mg/kg (LD10). Pharmacokinetic parameters calculated from these single dose data were sufficient to predict steady state plasma concentrations produced by s.c. infusion of DHAC. Lethal toxicity (LD66) occurred at an infusion rate of 37 mg/kg/h (111mg/m2/h), corresponding to a plasma steady-state DHAC concentration 38 +/- 14 micrograms/ml when the infusion time was 96 h; no lethality occurred at infusion times of 72 h or less. In vitro clonogenic assays and in vivo therapeutic experiments with L1210 tumor indicated that increasing the exposure time at concentrations near 25 micrograms/ml from 24 to 72 h increased the cell kill only slightly. The maximum log cell kill of L1210 estimated from either in vitro or in vivo data was 1.5 logs.

Animals↗

PubMed1985

Comparison of the in vitro cytotoxicity (L1210) of 5-aza-2'-deoxycytidine with its therapeutic and toxic effects in mice.

The in vitro and in vivo cytotoxic effects of 5-aza-2'-deoxycytidine (DAC) on L1210 leukemia are reported and related to the pharmacokinetics of DAC in CDF mice. L1210-bearing mice (1 X 10(4) cells, i.v.) given DAC i.v. (6.5-225 mg/kg) on day 3 showed a 50-212% increase in lifespan (ILS), with an estimated 3-6 log cell kill of L1210. Optimal effects with late treatment were obtained when DAC was given either on a multiple-dose regimen (10 mg/kg i.v., q 3 hr X 4, day 3 or 5) or by a constant s.c. infusion (2.0 mg/kg/hr X 12 hr, day 3), ILS 328-414%. Following 10 or 100 mg/kg i.v., plasma DAC declined in a triexponential manner with an intermediate elimination t 1/2 of 31 min. Urinary excretion accounted for 28.5% of DAC plasma clearance. When L1210 cells were exposed to DAC in vitro (0.5-100 micrograms/ml for 24-120 hr) a maximum 3-4 log cell kill was obtained. Both in vivo and in vitro response to DAC demonstrated the importance of exposure time as a determinant of cell kill. DAC is estimated to be more cytotoxic in vivo than in vitro. The critical cytotoxic concentration of DAC appears to be between 0.5 and 1.0 microgram/ml.

Animals↗

PubMed1985

Immunological concepts and the combination of cyclophosphamide with 5-aza-2'-deoxycytidine on L1210 in vivo.

Experiments were designed to demonstrate the synergism of low dose cyclophosphamide (CY), (15 mg/kg or 45 mg/M2) in combination with 5-aza-2'deoxycytidine (DAC). This dose of CY increased the cytotoxic response to DAC on L1210 tumor in mice by an additional 4 logs of L1210 cell kill or an approximate doubling of the response to DAC alone. These data support the hypothesis that CY at this low dose selectively inhibits suppressor t-cells which normally function to prevent the full cytotoxic potential of DAC from being realized.

Animals↗

PubMed1985

DNA alkali-labile sites induced by incorporation of 5-aza-2'-deoxycytidine into DNA of mouse leukemia L1210 cells.

The effects of 5-aza-2'-deoxycytidine on DNA in mouse L1210 leukemia cells were investigated using the alkaline elution technique. By comparing the DNA elution rate at pH 12.1 and 12.6, it was found that the drug produced DNA alkali-labile lesions. Alkali-labile sites were present only in DNA strands that were synthesized in the presence of the drug. They persisted for at least 48 h after drug treatment, and only after 72 h did the number of alkali-labile sites decline, thus suggesting a slow repair process. The production of alkali-labile sites was found to be concentration dependent and observable at concentrations which were effective in inhibiting the clonogenic viability of L1210 cells and which are attainable in vivo. 5-Aza-2'-deoxycytidine did not cause other DNA lesions such as DNA double-strand breaks or DNA-protein cross-links. Two hypotheses were considered to explain the origin of alkali-labile lesions in DNA that has incorporated 5-aza-2'-deoxycytidine: (a) the production of apyrimidinic sites by a glycosylase that recognizes and removes aza-cytosine from DNA and (b) the alkali-catalyzed decomposition of azacytosine residues to ring-opened products which could lead to alkali-induced DNA strand scission through a beta-elimination mechanism. The second hypothesis was considered to be the more probable and suggests that the alkali lability may be a means by which one could determine the extent of substitution and precise location of azacytosine residues or their ring-opened products in DNA.

Alkalies↗

PubMed1985

Experimental chemotherapy (L1210) with 5-aza-2'-deoxycytidine in combination with pyran copolymer (MVE-4), an immune adjuvant.

The life-span of CDF1 (BALB/c X DBA/2)F1 mice that received intraperitoneal implants with 10(5) L1210 tumor cells was prolonged to 23 days (compared to 8 days in L1210 tumor-implanted, untreated mice) when 5-aza-2'-deoxycytidine (DAC) was given to the mice after the tumor cells were allowed to metastasize (3 days after implant); DAC, however, resulted in no cures (survival beyond 48 days). When the pyran copolymer MVE-4, an immune adjuvant, was given the day after DAC, 25% of the mice treated were cured and the life-span of dying mice was increased by 7 days. When MVE-4 was repeated weekly for 4 weeks, 79% of treated mice were cured. Cured mice were able to resist a subsequent challenge of approximately 2 logs of L1210 cells. This combination of DAC plus MVE-4 was more effective than DAC alone only if the tumor cells and MVE-4 were given intraperitoneally. When this combination was repeated weekly, it became lethally toxic after 3 weeks, but only to L1210-tumor-bearing mice and not to normal mice. When DAC alone was given 2 days before tumor implant, it induced an apparent immune effect so that mice could resist a subsequent challenge of approximately 1.5-2 logs of L1210 cells. Support for part of the antitumor action of DAC exerted through the immune system was given by data that show that later treatment with noncurative doses of DAC is superior to early treatment in mice with large L1210 tumor burdens.

Adjuvants, Immunologic↗

PubMed1984

Observations on the effects of cyclophosphamide, phosphoramide mustard and some activated oxazaphosphorines on murine L1210 leukemia.

The L1210 tumor system was used in vitro and in vivo in comparative studies with activated cyclophosphamide analogs, cyclophosphamide and phosphoramide mustard. All the above compounds gave substantial cell kills (5 logs) of L1210 in vivo at doses that were non-toxic, but slight differences were noted. ASTA Z 7557 had a slight advantage in cure rate over cyclophosphamide when these drugs were given i.v. or i.p. to early tumor (i.p.). However, cyclophosphamide had the advantage in cure rate when drug administration was i.v. to advanced tumor. At equimolar concentrations in vitro ASTA Z 7557 was more cytotoxic than either phosphoramide mustard or acrolein. In vivo, the activated cyclophosphamide derivatives caused some unusual toxicities at therapeutic doses that were not seen with cyclophosphamide. The toxicities manifested as spastic responses and acute deaths on rapid i.v. or i.p. injections and as chronic liver atrophies and fibrosis with i.p. treatment.

Animals↗

PubMed1984

Effects of 5-aza-2'-deoxycytidine in combination with the biochemical modulator thymidine or the immune modulator pyran copolymer on L1210 leukemia-bearing mice.

The purpose of these studies was to investigate the potential modulation by thymidine in vivo of the antitumor action of 5-aza-2'-deoxycytidine (DAC). During the course of these investigations it was observed that DAC given as a single dose to mice bearing late L1210 tumor resulted in cell kills estimated to be close to 6 logs. Because of the potentially large antigen load released by such a cell kill, the immune modulator pyran copolymer was also tested in combination with DAC. Thymidine increased the cytotoxicity of DAC but not in a selective fashion. Doses of DAC in combination with thymidine were more toxic to host mice than equivalent doses of DAC alone, but no therapeutic benefit was apparent with this combination at maximally tolerated doses. A single dose of pyran copolymer and DAC appears to result in an adjuvant action that eliminates the few remaining L1210 cells refractory to DAC chemotherapy. Doses of DAC alone that result in lengthy increases in survival times but no cures resulted in a substantial number of cures when used in combination with pyran copolymer.

Animals↗

PubMed1984

Effects of dose and duration of exposure on 5-aza-2'-deoxycytidine cytotoxicity for L1210 leukemia in vitro.

We have investigated the effects of 5-aza-2'-deoxycytidine (DAC) on the growth and clonogenic potential of L1210 leukemia in vitro. Cells were exposed to DAC (0.001-100 micrograms/ml) for periods of 1-120 hrs. Following drug removal, cell growth in suspension culture was measured for up to 7 days, and cell survival was estimated by a colony-formation assay. When cell clonogenicity was plotted against DAC concentration in log-log axis, curves for each exposure time were linear between 0.01 and 0.5 micrograms/ml of DAC, but survival leveled off to a constant percentage for drug concentrations greater than 0.5 micrograms/ml. Percent survival decreased as exposure time increased up to 24 hrs; however, increases in exposure time greater than 24 hrs did not consistently decrease survival any further. At the lower concentrations this leveling of cytotoxicity is due to the spontaneous decomposition of DAC and to the lack of cytotoxicity of the breakdown products. At the higher concentrations the cause of the leveling remains uncertain. Incubation of L1210 with DAC at concentrations greater than 0.5 micrograms/ml for greater than or equal to 24 hrs resulted in total inhibition of measurable cell growth for 72-96 hrs following drug removal. Sequential colony-formation assays at various intervals following drug removal demonstrated a time-dependent increase in cell clonogenicity at a rate approximating the growth rate of untreated L1210 cells. This suggests that despite total cytostasis of the major population of cells, a small fraction of cells is capable of dividing at a near normal rate if removed from the drug environment. Implications of these results for in vivo applications of DAC are discussed.

Animals↗

PubMed1983

Modulation of deoxycytidine metabolism in vivo with high-dose thymidine in mice.

The question of whether selective biochemical modulation of deoxycytidine (dCyd) metabolism by thymidine (dThd) could be quantitated in vivo was addressed. Plasma clearance of [5-3H]dCyd was altered significantly by prior administration (2 hr) of dThd (3,600 mg/kg). The plasma half-life (beta-phase) of [5-3H]dCyd was raised approximately fourfold by dThd. Although dThd consistently caused an increase in the [5-3H]dCyd incorporated into the DNA of the spleen, duodenum, and femur marrow, there was no clear-cut difference between normal (BALB/c X DBA/2)F1 mice and L1210 tumor-bearing (BALB/c X DBA/2)F1 mice that could be translated into a selective advantage. Analysis of tritiated nucleotides in the spleens of normal and L1210 tumor-bearing mice indicated a greater incorporation of [5-3H]dCyd into the dCyd nucleotide pools of L1210 tumor-bearing mice than of normal mice. An analysis with the use of the proportionality constant kappa representing the combined effects of transport, pool sizes, and metabolic incorporation of [5-3H]dCyd into DNA showed that kappa decreased in each organ studied after dThd administration.

Animals↗