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R E Parks

Publications and source records attributed to R E Parks.

At least 37 records · Page 2Linked to original sources
PubMed1986

Changes in nucleoside transport of HL-60 human promyelocytic cells during N,N-dimethylformamide induced differentiation.

The rate of nucleoside transport decreased profoundly in human promyelocytic leukemia HL-60 cells after myeloid differentiation was induced by 5-6 days of exposure to 0.8% N,N-dimethylformamide (DMF). The facilitated diffusion of 100 microM radiolabeled adenosine and 2'-deoxyadenosine, measured by rapid transport assays, decreased 10- to 20-fold. The transport of 2 microM coformycin or 2'-deoxycoformycin, which is mediated by the same mechanism and was monitored by the adenosine deaminase titration assay, decreased 29-fold. The reduction in nucleoside transport capacity after DMF treatment was confirmed by a 19-fold decrease in the number of specific binding sites per cell (from 24-30 X 10(4) to 1.2-1.7 X 10(4)) for [3H]-6-p-nitrobenzylthioinosine, a nucleoside transport inhibitor. The binding affinity of 6-p-nitrobenzylthioinosine was not altered significantly and nucleoside transport remained sensitive to the transport inhibitors, 6-p-nitrobenzylthioinosine, dipyridamole, and dilazep after DMF-induced maturation. Time-dependence studies showed that the rate of 100 microM deoxyadenosine transport was unchanged for the first 24 h of exposure to DMF but fell to about 36% of control rates at 24-26 h and then gradually decreased further to about 4-5% of control rates after 5-6 days. In contrast, transport rates of the purine bases were reduced only 2- to 3-fold in HL-60 cells after 5 days of DMF treatment. The rates of adenosine and deoxyadenosine transport were unchanged or reduced by no more than 2-fold after 5-6 days of exposure to 0.8% DMF in the following human tumor cell lines that are not inducible with DMF: ARH-77 (multiple myeloma), KG-1 (acute myelogenous), and K-562 (chronic myelogenous). Thus, changes in nucleoside transport may serve as an early, membrane-associated marker of differentiation of the HL-60 cell line.

Adenosine↗
PubMed1986

Mechanism of activation of triciribine phosphate (TCN-P) as a prodrug form of TCN.

The tricyclic nucleotide triciribine phosphate (TCN-P) was synthesized as a water-soluble derivative of the tricyclic nucleoside TCN (L. B. Townsend et al, INSERM 81:37, 1978). Growth of L1210 cells in vitro was inhibited equally by TCN and TCN-P. A requirement for adenosine kinase activity for activation of both TCN and TCN-P was established by the observation that growth inhibition by either compound was decreased 200-fold by the adenosine kinase inhibitor 5-iodotubercidin and greater than 5000-fold in L1210/T, an adenosine kinase-deficient subline. The TCN/TCN-P resistance of L1210/T cells was correlated with lack of formation of intracellular TCN-P from either TCN or TCN-P. Thus, it appeared that TCN-P was hydrolyzed to TCN and then rephosphorylated intracellularly. Both the horse serum-containing culture medium and the intact cells possessed nucleotide phosphatase activity, which may contribute to the hydrolysis of TCN-P to TCN in the L1210 cell cultures. The requirement for hydrolysis of TCN-P to TCN for formation of intracellular TCN-P from exogenous TCN-P was also shown directly by the observation that human erythrocytes, which lack ectophosphatases, readily formed intracellular TCN-P from TCN but not from TCN-P when incubated in buffer.

Acenaphthenes↗
PubMed1985

Role of adenosine uptake and metabolism by blood cells in the antiplatelet actions of dipyridamole, dilazep and nitrobenzylthioinosine.

Adenosine (Ado, 10 microM) did not inhibit ADP-induced human platelet aggregation in whole blood. However, if the blood was preincubated with dipyridamole (10 microM), a potent inhibitor of the erythrocytic nucleoside transport system (NTS), Ado acted as a strong inhibitor of platelet aggregation. Similarly, Ado inhibited platelet aggregation in whole blood in the presence of other potent NTS inhibitors, dilazep (1 microM) and p-nitrobenzylthioinosine (NBMPR, 1 microM). RA 233 (10 microM), an analog of dipyridamole which is a potent inhibitor of platelet cAMP phosphodiesterase (PDE), did not evoke the Ado effect in whole blood. However, in platelet-rich plasma (PRP), RA 233 potentiated strongly Ado-mediated inhibition, whereas dipyridamole, dilazep and NBMPR were without activity. 5'-Methylthioadenosine (MTA), an Ado receptor antagonist, reversed the inhibition produced by a nucleoside transport system inhibitor plus Ado in whole blood. Dipyridamole (10 microM), dilazep (1 microM) or NBMPR (1 microM) blocked [14C]Ado (10 microM) uptake by blood cells in whole blood, whereas RA 233 (10 microM) was not effective. The combination of 2'-deoxycoformycin (dCF, 5 microM), a tight-binding inhibitor of adenosine deaminase (ADA), plus 5-iodotubercidin (ITu, 10 microM), a potent inhibitor of adenosine kinase (Ado kinase), gave comparable Ado-mediated inhibition of platelet aggregation in whole blood as was obtained when the blood was pretreated with dilazep. These studies suggest that the in vivo antiplatelet actions of drugs such as dipyridamole and dilazep result from their abilities to block erythrocytic Ado uptake and subsequent metabolism, thus elevating the extracellular steady-state concentration of the physiologically occurring, antiplatelet agent, Ado.

Adenosine↗
PubMed1985

Differential incorporation of 2'-deoxyadenosine into human peripheral lymphocytes.

Human peripheral lymphocytes incubated with 2'-deoxycoformycin and 2'-deoxyadenosine (dAdo) reached a plateau in dATP accumulation after 4 hr that lasted for up to 24 hr. Total dATP accumulation did not exceed 15% of the control ATP concentration in the lymphocytes. In contrast, the human CCRF-CEM T lymphoblastic cell line and human erythrocytes showed a nearly linear pattern of dATP formation throughout the incubation period. By 6 hr the dATP concentration in the CCRF-CEM cells exceeded the control ATP concentration. A comparison of dATP accumulation in purified peripheral T and B lymphocytes indicated differences between these cells that favor greater dATP formation in the B lymphocytes. Incorporation studies with several adenosine analogs demonstrated that arabinosyladenine, 2-F-arabinosyladenine, tubercidin, formycin A, and 9-(2'-deoxy-2'-fluoro-beta-D-ribofuranosyl)adenine form corresponding amounts of analog triphosphate in the T and B cell-enriched lymphocytes. 9-(2'-Deoxy-2'-fluoro-beta-D-arabinofuranosyl)adenine (2'-F-araA) was the only compound to show an incorporation pattern similar to that observed with dAdo by forming analog triphosphate only in the B cell-enriched lymphocyte population. Nucleoside kinase measurements showed no significant differences in dAdo, adenosine, or 2'-deoxycytidine kinase activities between the T and B lymphocytes. The inability of the T cells to incorporate dAdo or the analog 2'-F-araA into their nucleotide pools may indicate the existence of a highly specific catabolic enzyme(s).

Adenosine Deaminase↗
PubMed1985

Nucleotidase activities of human peripheral lymphocytes.

Several B lymphoblastic cell lines are known to be relatively resistant to the combination of 2'-deoxyadenosine with an adenosine deaminase inhibitor. These cell lines are believed to have a greater capacity to dephosphorylate 2'-deoxyadenosine nucleotides, thus preventing excessive accumulation of potentially toxic metabolites. In this study, the 2'-deoxynucleoside 5'-monophosphate dephosphorylating activities of human peripheral lymphocytes were examined. Peripheral lymphocytes have at least three nucleotide 5'-monophosphate nucleotidases distinguished by different pH optimums, substrate preference, Mg2+ requirement, inhibitors, and molecular weights. Two of the enzymes appeared to be cytosolic, only one of which had significant substrate activity with dAMP. This enzyme had an acidic pH optimum (5.0), no Mg2+ requirement, was inhibited by tartrate, and demonstrated broad substrate specificity. The other cytosolic nucleotidase required Mg2+, had a pH optimum of 5.5 to 6.0, was activated by 2'-deoxyinosine, and demonstrated a substrate preference for 3'- and 5'-monophosphate 2'-deoxynucleosides of hypoxanthine, guanine, uracil, and thymine. The third enzyme, ecto 5'-nucleotidase, is associated with the cell membrane. Although the ecto 5'-nucleotidase activity was higher in the B lymphocytes, the cytosolic nucleotidases were similar in activity in the T and B lymphocytes.

B-Lymphocytes↗
PubMed1985

5'-Deoxy-5'-methylthioadenosine phosphorylase--III. Role of the enzyme in the metabolism and action of 5'-halogenated adenosine analogs.

5'-Deoxy-5'-halogenated adenosines are alternative substrates for 5'-deoxy-5'-methylthioadenosine phosphorylase (MTAPase), an enzyme responsible for the metabolism of 5'-deoxy-5'-methylthioadenosine (MTA), a by-product of polyamine biosynthesis. The relative reactivity of these nucleosides with MTAPase from HL-60 human promyelocytic leukemia cells is MTA greater than 5'-deoxy-5'-fluoroadenosine (5'-FlAdo) greater than 5'-chloro-5'-deoxyadenosine (5'-ClAdo) greter than 5'-bromo-5'-deoxyadenosine (5'-BrAdo) greater than 5'-deoxy-5'-iodoadenosine (5'-IAdo). In MTAPase-containing cells, the adenine released from the 5'-halogenated adenosine was incorporated into adenine nucleotide pools; cleavage by (MTAPase appeared to be the rate-limiting step in this process. 5'-BrAdo and 5'-IAdo were growth inhibitors (EC50 values less than 10 microM) of MTAPase-containing cell lines (HL-60 human promyelocytic leukemia and the L5178Y murine lymphoblastic leukemia) but were much less active (EC50 values greater than 65 microM) against MTAPase-deficient cell lines (the CCRF-CEM human T cell leukemia and the L1210 murine leukemia). The full cytotoxicity of these compounds, therefore, appeared to be related to their phosphorolysis by MTAPase. Indirect evidence suggests that 5-halogenated ribose-1-phosphate derivatives of 5'-BrAdo or 5'-IAdo produced by the MTAPase reaction were the active metabolites of these 5'-halogenated adenosines.

Adenine Nucleotides↗
PubMed1985

Nonenzymatic glycosylation of erythrocytic proteins in normal and diabetic subjects. Enzymes of nucleoside and nucleotide metabolism.

A modification of the technique of Glyco-Gel affinity column chromatography has been employed to separate glycosylated proteins from nonglycosylated proteins of hemolysates. When glycosylation in hemolysates of 11 type I diabetic subjects was compared with that from 7 normal subjects, significant increases were found in glycosylation of hemoglobin (Hb) (12.1 +/- 6.0% versus 4.7 +/- 0.5%) and purine nucleoside phosphorylase (PNP) (5.3 +/- 3.0% versus 2.1 +/- 0.5%). However, no differences were found for nucleoside diphosphokinase (NDPK) (1.5 +/- 1.1% versus 1.0 +/- 0.4%) and adenylate kinase (AMPK) (0.5 +/- 0.4% versus 0.7 +/- 0.2%). Linear relationships were seen between glycosylated Hb and glycosylated PNP (r = 0.97) or glycosylated NDPK (r = 0.81). On incubation of hemolysates from normal individuals with high glucose (1500 mg/dl or 83 mM) and NaCNBH3 (20 mM), linear increases in the degrees of glycosylation were seen with time. After 18 h, the percentages of glycosylation of Hb, PNP, NDPK, and AMPK were increased from normal values to 31, 24, 11, and 3, respectively. When partially purified human erythrocytic PNP was incubated with various monosaccharides (20 mM) in the presence of NaCNBH3 for 6 h, glycosylation increases of 2-5-fold were seen in the order ribose greater than mannose greater than galactose greater than glucose.

Adenylate Kinase↗
PubMed1984

Transport of deoxycoformycin in human erythrocytes. Measurement by adenosine deaminase titration and radioisotope assays.

The assay of residual adenosine deaminase (ADA) activity was used as a sensitive measure of the transport of deoxycoformycin (dCF) into human erythrocytes. Contrary to prior reports from this laboratory, the inactivation of intraerythrocytic ADA by dCF was linear rather than log-linear, with time. Linear inactivation rates were also seen when erythrocytes were preloaded with a 5-fold excess of calf intestinal ADA. The uptake of tritium-labeled dCF molecules and the rate of inactivation of ADA molecules showed an approximate 1:1 stoichiometry. The nucleoside transport inhibitors, 6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine (NBMPR) and dipyridamole, and the permeant, uridine, inhibited dCF transport with Ki values of 35 nM, 45 nM, and 340 microM respectively. The affinity of dCF for the nucleoside transporter was low with a Ki of approximately 10 mM for the inhibition of adenosine influx.

Adenosine Deaminase Inhibitors↗
PubMed1984

Characterization of a defect in the pathway for converting 5'-deoxy-5'-methylthioadenosine to methionine in a subline of a cultured heterogeneous human colon carcinoma.

5'-Deoxy-5'-methylthioadenosine (methylthioadenosine) is cleaved to adenine and 5-methylthioribose-1-phosphate (methylthioribose-1-P). Methylthioribose-1-P is converted to 2-keto-4-methylthiobutyrate ( ketomethylthiobutyrate ) which is transaminated to methionine. We report that one subline of a heterogeneous human colon carcinoma, DLD-1 Clone D, only forms methylthioribose-1-P from methylthioadenosine or 5'-deoxy-5'-methylthioinosine (methylthioinosine), a deaminated derivative of methylthioadenosine, whereas Clone A converts methylthioadenosine and methylthioinosine to methionine, as shown by growth studies in culture of Clone A and Clone D cells and radioactive studies utilizing [methyl-14C]methylthioadenosine or [methyl-14C]methylthioinosine in the presence of extracts of these cells lines. To characterize this defect, we utilized three protein fractions isolated from rat liver which together convert methylthioribose-1-P to ketomethylthiobutyrate . Addition of only Fraction A to Clone D sonicates restores its ability to convert methylthioadenosine to methionine. This fraction is responsible for converting methylthioribose-1-P to 5- methylthioribulose -1-phosphate; radioactive studies confirm this observation. Thus, Clone D is deficient in an enzyme contained in Fraction A; this represents a qualitative biochemical difference between the two clones derived from a single human tumor.

Adenosine↗
PubMed1984

Synthesis and biological evaluation of 6-amino-1H-pyrrolo[3,2-c]pyridin-4(5H)-one (3,7-dideazaguanine).

The synthesis of 6-amino-1H-pyrrolo[3,2-c]pyridin-4(5H)-one (3,7-dideazaguanine, 2) has been accomplished from 3-(ethoxycarbonyl)pyrrole-2-acetonitrile. In contrast to 3-deazaguanine, compound 2 did not show any antitumor, antiviral, or antibacterial properties. Furthermore, it was not a substrate for hypoxanthine-guanine phosphoribosyltransferase or purine nucleoside phosphorylase.

Animals↗
PubMed1983

Forskolin: a potential antimetastatic agent.

Forskolin, a diterpene from the roots of an Indian plant, Coleus forskohlii, is a potent platelet aggregation inhibitor and has been examined for its effects on (a) tumor-induced human platelet aggregation and (b) pulmonary tumor colonization in mice. These studies employed a subline of B16 murine melanoma, B16-F10 (highly metastatic to lungs). Forskolin (2 microM) strongly inhibits the melanoma cell-induced human platelet aggregation. A single dose of forskolin (82 micrograms/mouse) administered intraperitoneally 30 or 60 min prior to tail vein injection of cultured B16-F10 cells (2 or 3 X 10(5) cells/mouse) reduced tumor colonization in the lungs by more than 70%. Similar results were obtained in three separate experiments. These findings raise the possibility that forskolin could prove of value in the clinic for the prevention of cancer metastasis.

Animals↗
PubMed1983

5'-deoxy-5'-methylthioadenosine phosphorylase--II. Role of the enzyme in the metabolism and antineoplastic action of adenine-substituted analogs of 5'-deoxy-5'-methylthioadenosine.

The biological activities of several previously synthesized [J. A. Montgomery et al., J. med. Chem. 17, 1197 (1974)] adenine-substituted analogs of 5'-deoxy-5'-methylthio- or 5'-deoxy-5'-ethyl-thioadenosine, including the 2-fluoroadenine, 2-chloroadenine, 2,6-diaminopurine, 8-azaadenine, and 4-aminopyrazolo [3,4-d]pyrimidine-containing derivatives, have been reexamined. It is demonstrated that many of these analogs are cleaved to their respective free base analogs by 5'-deoxy-5'-methyl-thioadenosine phosphorylase (MTAPase), an enzyme associated with polyamine biosynthesis, and that this reaction is necessary for the cytotoxic action of these MTA analogs to be fully expressed. Evidence to support this includes: (1) the growth of two MTAPase-containing human colon carcinoma cell lines (the HCT-15 and DLD-1 lines) was inhibited by these analogs, whereas an MTAPase-deficient cell line, the CCRF-CEM human T-cell leukemia, was relatively insensitive to their cytotoxic action; (2) extracts of the MTAPase-containing colon carcinoma cell lines were able to cleave these analogs to their respective free base analogs; in contrast, extracts of MTAPase-deficient CCRF-CEM cells were unable to cleave these analogs; (3) intact colon carcinoma cells converted these MTA analogs to their corresponding 5'-phosphorylated analog nucleotides, whereas CCRF-CEM cells did not, at least to detectable levels; and (4) the MTA analog, 5'-deoxy-5'-ethylthio-4-aminopyrazolo [3,4-d]pyrimidine ribonucleoside, which is not a substrate of MTAPase, did not form analog nucleotides and was essentially noncytotoxic to all cell lines tested, whereas the corresponding adenine analog, 4-aminopyrazolo [3,4-d]pyrimidine, readily formed analog nucleotides and was highly cytotoxic to all the lines. It is postulated that the corresponding adenine analog 5'-phosphorylated nucleotides are the primary active metabolites of these MTA analogs, having been formed by the cleavage of these nucleosides to free adenine analogs by MTAPase, followed by the conversion of these base analogs to analog nucleotides by adenine phosphoribosyltransferase and the enzymes of adenine nucleotide phosphorylation. This pathway represents a novel drug-activation system for the synthesis of analog nucleotides and has the potential to be exploited chemotherapeutically.

Adenosine↗
PubMed1983

Residual myelographic contrast material seen on the chest radiograph.

Oily contrast material remaining after myelography may escape through the lumbar needle track and enter the dependent thoracic extradural spaces as droplets and collections in the intercostal spaces. Until these intercostal collections are absorbed, which takes place slowly over a period of one or more years, they can produce densities on the chest radiograph. The authors report 26 such cases representing three different patterns of distribution.

Absorption↗
PubMed1983

Conversion of 5'-deoxy-5'-methylthioadenosine and 5'-deoxy-5'-methylthioinosine to methionine in cultured human leukemic cells.

5'-Deoxy-5'-methylthioadenosine and 5'-deoxy-5'-methylthioinosine, which are metabolized to the methionine precursor, 5-methylthioribose-1-phosphate, by 5'-deoxy-5'-methylthioadenosine phosphorylase and purine nucleoside phosphorylase, respectively, can serve as sources of methionine for cultured HL-60 promyelocytic leukemia cells. CCRF-CEM T-cell leukemia cells, which lack 5'-deoxy-5'-methylthioadenosine phosphorylase, convert 5'-deoxy-5'-methylthioinosine (but not 5'-deoxy-5'-methylthioadenosine) to methionine; this conversion is blocked by purine nucleoside phosphorylase inhibitors. Therefore, the pathway for the conversion of 5-methylthioribose-1-phosphate to methionine is present in both human leukemic lines.

Adenosine↗
PubMed1983

Biochemical pharmacology and toxicology of formycin alone and in combination with 2'-deoxycoformycin (pentostatin).

The toxicology and pharmacology of formycin both as a single agent and combined with the adenosine deaminase inhibitor 2'-deoxycoformycin (dCF) were examined in outbred Swiss mice heterozygous for the nude gene (nu/+). The LD10 for formycin alone given on a daily x 5 schedule was 21 mg/kg. When the animals were pretreated with 1 mg/kg of dCF 1 hour prior to each dose of formycin, toxicity was approximately doubled, ie, LD10 was reduced to 10 mg/kg. Death was associated with hepatic toxicity in both treatment regimens; suppression of leukocyte counts was mild except at doses greater than the LD10. Formycin nucleotides were detected by high-performance liquid chromatography in the livers of mice treated with formycin either alone or combined with dCF. When isolated rat hepatocytes were incubated for 2 hours with either formycin or dCF plus formycin, analog nucleotides accumulated in the cells. Cellular ATP decreased to below the limits of detection, whereas a large peak corresponding to formycin-5'-triphosphate was present. This replacement of cellular ATP by formycin-5'-triphosphate may help explain the hepatic toxicity observed.

Adenosine Deaminase Inhibitors↗
PubMed1982

Effects of the chiral isomers of erythro- and threo-9-(2-hydroxy-3-nonyl)adenine on purine metabolism in sarcoma 180 cells.

The effects of the chiral isomers of erythro- and threo-9-(2-hydroxy-3-nonyl)adenines (EHNA and THNA) on purine metabolism in Sarcoma 180 cells have been determined. At concentrations of 10-80 microM [10- to 1000-fold greater than their Ki values with adenosine deaminase (ADA)], all isomers inhibited purine salvage and biosynthesis de novo. Although (+)-EHNA, the most potent ADA inhibitor, exerted the greatest effects, there was no direct correlation between the potency of ADA inhibition and the secondary effects on purine metabolism, e.g. (+)-EHNA is about 2-fold more inhibitory than (-)-EHNA in blocking purine base incorporation but about 250-fold more potent as an inhibitor of ADA (Ki of (+)-EHNA = 2 nM; Ki of (-)-EHNA = 500 nM [Bessodes et al., Biochem. Pharmac. 31, 879 (1982)]). All the isomers inhibited the incorporation of radiolabeled purine bases (adenine, guanine and hypoxanthine) and nucleosides (guanosine and inosine) into acid-soluble nucleotides and of glycine into 5'-phosphoribosyl-formylglycineamide. Unlike the results of Henderson et al. [Biochem. Pharmac. 26, 1967 (1977)] with Ehrlich ascites cells, the incorporation of adenosine into nucleotides was only slightly inhibited in Sarcoma 180 cells. (+)-EHNA did not inhibit the activities of 5-phosphoribosyl-1-pyrophosphate (PRPP) synthetase, purine phosphoribosyltransferases or nucleotide kinases in cell extracts. Accumulation of PRPP was inhibited only under conditions that fostered rapid synthesis.

Adenine↗