A synthetic sialic acid analog that is resistant to the receptor-destroying enzyme can be used by influenza C virus as a receptor determinant for infection of cells

A synthetic sialic acid analog, N-acetyl-9-acetamido-9-deoxy-neuraminic acid, can be used by influenza C virus as a receptor determinant for attachment to cells. In contrast to the natural determinant, N-acetyl-9-O-acetylneuraminic acid, the synthetic sialic acid is resistant to the action of the receptor-destroying acetylesterase of this virus. The sialic acid analog was enzymatically transferred to the surface of Madin-Darby canine kidney cells that are resistant to infection because of a lack of receptors. Influenza C virus was able to infect the modified cells through requiring a 10-fold larger amount of the sialic acid analogue on the cell surface compared to the natural receptor determinant. The quantitative difference is accounted for mainly by a less efficient binding of influenza C virus to the analog. Thus, in our system, inactivation of the receptor by the viral esterase is not required for the initiation of an influenza C virus infection.

The effects of cytosine arabinoside on RNA-primed DNA synthesis by DNA polymerase alpha-primase

Oligonucleotides containing a specific initiation site for polymerase alpha-primase (pol alpha-primase) were used to measure the effects of cytosine arabinoside triphosphate and cytosine arabinoside monophosphate (araCMP) in DNA on RNA-primed DNA synthesis. Primase inserts araCMP at the 3' terminus of a full-length RNA primer with a 400-fold preference over CMP. The araCMP is elongated efficiently by pol alpha in the primase-coupled reaction. Extension from RNA 3'-araCMP is 50-fold less efficient than from CMP, and extension from DNA 3'-araCMP is 1600-fold less efficient than from dCMP. Using araCMP-containing templates, primer synthesis is reduced 2-3-fold, and RNA-primed DNA synthesis is reduced 2-8-fold. The efficiency of polymerization past a template araCMP by pol alpha is reduced 180-fold during insertion of dGMP opposite araCMP and 35-fold during extension from the araCMP:dGMP 3' terminus. These results show that the pol alpha-primase efficiently incorporates araCMP as the border nucleotide between RNA and DNA and suggest that the inhibitory effects of araC most likely result from slowed elongation of pol alpha and less so from inhibition of primer synthesis by primase.

Nature of the early folding intermediate of ribonuclease A

A previous study of the folding pathway of the major unfolded species of ribonuclease A by pulsed hydrogen exchange [Udgaonkar, J. B., & Baldwin, R. L. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 8197-8201] showed that there is a major early folding intermediate (Il) that resembles a molten globule species in having stable secondary structure while lacking buried tyrosine side chains. Earlier work showed that there is also a late native-like folding intermediate (IN) that can bind the specific inhibitor 2'CMP and that has buried tyrosine side chains. Results are reported here indicating that Il has a well-developed tertiary structure even though its tyrosine side chains are not buried. First, optical stopped-flow experiments suggest that Il binds 2'CMP. Second, the protection against hydrogen exchange is similar in Il and IN for almost all protected amide protons studied. Third, analysis of the mechanism of hydrogen exchange in Il confirms the large protection factors reported earlier for probes in the beta-sheet of ribonuclease A and indicates that the beta-sheet is formed in Il. Other experiments are also reported that test the interpretation of pulsed hydrogen exchange studies of the folding pathway of ribonuclease A.

5-Fluoro-2'-deoxycytidine 5'-monophosphate is a mechanism-based inhibitor of thymidylate synthase

Thymidylate synthase (TS) is inhibited by 5-fluoro-2'-deoxycytidine 5'-monophosphate (FdCMP). From initial velocity measurements, the apparent Ki for the binary FdCMP-enzyme complex was about 20 microM. In the presence of 5,10-methylene-5,6,7,8-tetrahydrofolate (CH2H4folate), FdCMP causes a time-dependent inactivation of the enzyme and formation of a TS-FdCMP-CH2H4 folate complex. The ternary complex contains one mol of inhibitor per monomer of enzyme, and can be readily isolated on nitrocellulose filters. Dissociation of the ternary complex is quite slow (t1/2 approximately 16 h), and yields unchanged FdCMP. As with the corresponding complex formed with 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP), the TS-FdCMP-CH2H4 folate complex shows a differential absorbance maximum at 326 nm, and is stable to SDS-PAGE. Taken together, these results indicated that FdCMP is a slow, tight binding inhibitor of TS and has a mechanism of inhibition similar to that of FdUMP.

Chimeric enzymes. Structure-function analysis of segments of sn-1,2-diacylglycerol choline- and ethanolaminephosphotransferases

The Saccharomyces cerevisiae CPT1 and EPT1 genes represent structural genes that encode distinct choline- and choline/ethanolaminephosphotransferases, respectively. To explore the function of linear segments of these enzymes, a series of 14 EPT1-CPT1 chimeric gene constructs and the parental wild-type genes were expressed in a cpt1 ept1 double null mutant background completely devoid of phosphoamino alcohol transferase activity. Eleven of the chimeric genes expressed functional enzymes. The CDP-amino alcohol and sn-1,2-diacylglycerol (DAG) substrate specificities and essential phospholipid cofactor requirements of the parental and chimeric enzymes were investigated using a mixed micellar assay system. Chimeric enzymes exhibited a pattern of CDP-amino alcohol affinities that defined a structural domain sufficient to confer CDP-amino alcohol specificity. When wild-type enzymes were investigated using a chemically defined series of DAGs, each possessed a distinct characteristic pattern of utilization. Chimeric enzymes exhibited DAG acyl chain specificity profiles that either conformed to parental wild-type patterns or represented novel substrate specificities. Correlation of these outcomes with their underlying structural modifications permitted the assignment of an internal, linear region of 218 amino acids sufficient to confer DAG acyl chain specificity; this region contained three predicted transmembrane segments. Neither wild-type enzyme showed significant acyl chain selectivity with respect to phospholipid activation when a homologous series of chemically defined phosphatidylcholines were employed, suggesting that enzyme recognition of the fatty acyl moieties of the DAG substrate and phospholipid activator is fundamentally different. Analysis of chimeric enzymes dependence on phospholipid activators suggested the involvement of discontinuous protein segments participating in the interaction with phospholipid cofactors.

Nucleotide Regulation of a calcium-activated cation channel in the rat insulinoma cell line, CRI-G1

The nucleotide regulation of a calcium-activated nonselective cation (Ca-NS+) channel has been investigated in the rat insulinoma cell line CRI-G1. The activity of the channel is reduced by both AMP and ADP (1-100 microM) in a concentration-dependent manner, with AMP being more potent than ADP. At lower concentrations (0.1-5 microM), both ADP and AMP activate the channel in some patches. Examination of the nucleotide specificity of channel inhibition indicates a high selectivity for AMP over the other nucleotides tested with a rank order of potency of AMP > UMP > CMP > or = GMP. Cyclic nucleotides also modulate channel activity in a complex, concentration-dependent way. Cyclic AMP exhibits a dual effect, predominantly increasing channel activity at low concentrations (0.1-10 microM) and reducing it at higher concentrations (100 microM and 1 mM). Specificity studies indicate that the cyclic nucleotide site mediating inhibition of channel activity exhibits a strong preference for cyclic AMP over cyclic GMP, with cyclic UMP being almost equipotent with cyclic AMP. Cyclic IMP and cyclic CMP are not active at this site. The cyclic nucleotide site mediating activation of the channel shows much less nucleotide specificity than the inhibitory site, with cyclic AMP, cyclic GMP and cyclic IMP being almost equally active.

Decoupling of melting domains in immobilized ribonuclease A

Ribonuclease A has been immobilized on silica beads through glutaraldeyde-mediated chemical coupling in order to improve the stability of the protein against thermal denaturation. The thermodynamic and binding properties of the immobilized enzyme have been studied and compared with those of the free enzyme. The parameters describing the binding of the inhibitor 3'-CMP (Ka and delta H) as monitored by spectrophotometry and calorimetry were not significantly affected after immobilization. Conversely both the stability and unfolding mechanism drastically changed. Thermodynamic analysis of the DSC data suggests that uncoupling of protein domains has occurred as a consequence of the immobilization. The two state approximation of the protein unfolding process is not longer valid for the immobilized RNase. Protein stability strongly depends on the hydrophobicity properties of the support surface as well as on the presence of the inhibitor and pH. For example, after immobilization on a highly hydrophobic surface, the enzyme is partially in the unfolded state. The binding of a ligand is able to reorganize the protein structure into a native-like conformation. The refolding rates are different for the two protein domains and vary as a function of pH and presence of the inhibitor 3'-CMP.

Folding pathway of guanidine-denatured disulfide-intact wild-type and mutant bovine pancreatic ribonuclease A

The refolding kinetics of guanidine-denatured disulfide-intact bovine pancreatic ribonuclease A (RNase A) and its proline-42-to-alanine mutant (Pro42Ala) have been studied by monitoring tyrosine burial and 2'-cytidine monophosphate (2'CMP) inhibitor binding. The folding rate for wild-type RNase A is faster in the presence of the inhibitor 2'CMP than in its absence, indicating that the transition-state structure in the rate-determining step is stabilized by 2'CMP. The folding rate monitored by 2'CMP binding to the major slow-folding species of Pro42Ala RNase A is faster than the folding rate monitored by tyrosine burial; however, the folding rate monitored by inhibitor binding to the minor slow-folding species is decreased significantly over the folding rate monitored by tyrosine burial, indicating that the major and minor slow-folding species of Pro42Ala fold to the native state with different transition-state conformations in the rate-determining step.

Clinical pharmacology of 1-beta-D-arabinofuranosylcytosine-5'-stearylphosphate, an orally administered long-acting derivative of low-dose 1-beta-D-arabinofuranosylcytosine

1-beta-D-Arabinofuranosylcytosine-5'-stearylphosphate (cytarabine ocfosfate, stearyl-ara-CMP) is a newly synthesized 5'-alkylphosphate derivative of 1-beta-D-arabinofuranosylcytosine (ara-C), which is lipophilic, resistant to inactivation by deamination, and orally active. Pharmacology of this drug was studied in patients with hematological malignancies. The concentrations of stearyl-ara-CMP, ara-C (its active metabolite), and 1-beta-D-arabinofuranosyluracil (ara-U, its inactive metabolite) were determined by radioimmunoassay. When six patients received a single p.o. dose of the drug (500 mg/m2), stearyl-ara-CMP, ara-C, and ara-U could be detected in the plasma for at least 72 h afterwards. The plasma disappearance curve of stearyl-ara-CMP corresponded to a one-compartment open model with first-order absorption kinetics. The peak plasma level (Cmax) was 322 +/- 218 nM, and the predicted time to reach Cmax (Tmax) was 6.5 +/- 4.5 h, while the elimination half-life (t1/2) was very long (32.0 +/- 8.4 h). The plasma ara-C level increased slowly to a Cmax of 26.3 +/- 12.7 nM (Tmax, 13.3 +/- 4.7 h) after stearyl-ara-CMP administration. This level was quite low compared with that achieved by low-dose s.c. ara-C therapy, but ara-C persisted longer in the plasma in the former case, and the area under the curve was similar for both regimens. For ara-U, the Cmax, Tmax, and t1/2 were 483 +/- 315 nM, 23.6 +/- 4.0 h, and 19.6 +/- 5.3 h, respectively. No stearyl-ara-CMP was detected in the urine, and only 8.0% of the administered dose was excreted as ara-C and ara-U within 72 h. The stearyl-ara-CMP concentration in the cerebrospinal fluid was below the limit of detection in three patients without meningeal involvement at 6 h. During clinical use of stearyl-ara-CMP, macrocytic anemia was observed, and some patients also developed megaloblastic change of their erythroblasts, suggesting a mild and persistent cytostatic effect. In conclusion, p.o. therapy with stearyl-ara-CMP achieved prolonged maintenance of the plasma drug level. Thus, the drug released a very low dose of ara-C over a long period in plasma and tissues and had a prolonged mild antineoplastic effect in patients with hematological malignancies.

Inhibition of CMP-N-acetylneuraminic acid:lactosylceramide sialyltransferase by nucleotides, nucleotide sugars and nucleotide dialdehydes

The effects of nucleotides, nucleotide sugars and nucleotide dialdehydes on the activity and kinetics of cytidine 5'-monophospho-N-acetylneuraminic acid:lactosylceramide (alpha 2-->3) sialyltransferase (SAT-1) in microsomes derived from embryonic chick brain were investigated. Although under physiological conditions this enzyme utilizes a CMP-sugar as substrate, it was found that UDP-dialdehyde was an effective inhibitor of SAT-1 activity. CMP-dialdehyde was only slightly more efficient at inhibiting SAT-1 activity. Similar findings were found for the inhibitory effects of UDP versus CMP. In addition, two UDP-sugars (UDP-Gal and UDP-GalNAc) were also slightly inhibitory. Kinetic analyses demonstrate that both UDP- and CMP-dialdehydes are competitive inhibitors of SAT-1 activity. The data suggests that the substrate specificity of microsomal SAT-1 resides more in the sugar moiety, rather than in the nucleotide portion of the substrate.

Inhibition of CMP-sialic acid transport in human liver and colorectal cancer cell lines by a sialic acid nucleoside conjugate (KI-8110)

The sialic acid nucleoside conjugate KI-8110 has been shown to inhibit the formation of hepatic metastases from human colorectal cancer cell lines in a nude mouse intrasplenic injection model. The compound does not inhibit sialyltransferases from either human colorectal tumor cells or human liver. Transport of CMP-sialic acid into endoplasmic reticulum and Golgi vesicles is inhibited and can account for the reduction in surface sialic acid found on treated cell lines. Only a 50% inhibition of CMP-sialic acid transport could be achieved suggesting the presence of more than one transport protein with differing specificities.

Influences of postnatal age and dietary nucleotides on plasma fatty acids in the weanling rat

Dietary nucleotides seem to play a number of physiologic roles during early life. They are improved in the maintenance of the immune system, intestinal maturation, and lipid metabolism. Nucleotides affect the conversion of essential fatty acids into their long-chain polyunsaturated (PUFA) derivatives in both preterm and at-term newborn infants. This work examines the effect of postnatal age and dietary nucleotides on the fatty acid composition of total plasma lipids and lipid fractions in the rat. Weanling rats (21 days old) were divided into three groups. The first group was killed, and the other two groups were fed a standard semipurified diet, and the same diet supplemented with 250 mg each of CMP, UMP, AMP, GMP, and IMP per 100 g of diet for 4 weeks. Advancing postnatal age led to an increase of total plasma fatty acids, especially saturated, and PUFA of the n-6 series, whereas PUFA of the n-3 series decreased. The fatty acid profile of plasma phospholipids (PL) exhibited minor changes, although there was a tendency to show lower levels of saturates and PUFA of the n-3 series and increased levels of PUFA of the n-6 series. Cholesteryl esters showed a response similar to that of PL, although the increase in arachidonic acid (20:4n-6) was significant. For triglycerides, linoleic acid (18:2n-6) and monounsaturates increased their levels, whereas saturates decreased. Dietary nucleotides mediated a significant increase in total plasma fatty acids, namely monounsaturated fatty acids and PUFA of both n-6 and n-3 series as compared with the control group. The relative fatty acid composition of PL and cholesteryl esters was mostly unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Concerted CMP-dependent [3H]inositol labeling of phosphoinositides and agonist activation of phospholipase C in rat brain cortical membranes

[3H]Inositol ([3H]Ins) labeling of phosphoinositides was studied in rat brain cortical membranes. [3H]Ins was incorporated into a common lipid pool through both CMP-dependent and independent mechanisms. These are as follows: (1) a reverse reaction catalyzed by phosphatidyl-inositol (PtdIns) synthase, and (2) the reaction performed by the PtdIns headgroup exchange enzyme, respectively. Membrane phosphoinositides prelabeled in either CMP-dependent or independent fashions were hydrolyzed by guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)- and carbachol-stimulated phospholipase C. Unlike CMP-dependent labeling, however, CMP-independent incorporation of [3H]Ins into lipids was inhibited by 1 mM (0.04%) sodium deoxycholate. Thus, when PtdIns labeling and phospholipase C stimulation were studied in a concerted fashion, [3H]Ins was incorporated into lipids primarily through the PtdIns synthase-catalyzed reaction because of the presence of deoxycholate required to observe carbachol-stimulation of phospholipase C. Little direct breakdown of [3H]PtdIns was detected because production of myo-[3H]inositol 1-monophosphate was minimal and myo-[3H]inositol 1,4-bisphosphate was the predominant product. Although PtdIns labeling and 3H-polyphosphoinositide formation were unaffected by GTP gamma S and carbachol and had no or little lag period, GTP gamma S- and carbachol-stimulated appearance of 3H-Ins phosphates exhibited an appreciable lag (10 min). Also, flux of label from [3H]Ins to 3H-Ins phosphates was restricted to a narrow range of free calcium concentrations (10-300 nM). These results show the concerted activities of PtdIns synthase, PtdIns 4-kinase, and phospholipase C, and constitute a simple assay for guanine nucleotide-dependent agonist stimulation of phospholipase C in a brain membrane system using [3H]Ins as labeled precursor.

5'-CMP stimulates phospholipase A-mediated hydrolysis of phosphatidylinositol in permeabilized pituitary GH3 cells

We showed previously that 5'-CMP activates PtdIns-Ins base exchange and reversal PtdIns synthase in permeabilized rat pituitary GH3 cells. Here we report another effect of 5'-CMP on PtdIns metabolism in these cells. In permeabilized GH3 cells prelabelled with [3H]Ins and incubated in buffer with LiCl and a free Ca2+ concentration of 0.1 microM but without added Ins, 5'-CMP stimulated formation of glycerophospho[3H]inositol (GroP[3H]Ins) after a lag period of at least 5 min. This effect was concentration-dependent; the apparent Km was 0.30 +/- 0.02 mM. CDP and CTP stimulated GroPIns formation less effectively than did 5'-CMP, but cytidine, 2'-CMP, 3'-CMP, 5'-AMP and 5'-GMP had no effect. 5'-CMP stimulated formation of lysoPtdIns also. In permeabilized GH3 cells prelabelled with [3H]arachidonic acid, 5'-CMP stimulated release of [3H]arachidonic acid without a measurable lag period. These data show that 5'-CMP stimulates a phospholipase A activity in permeabilized GH3 cells that hydrolyses PtdIns.

Phosphatidylinositol synthase and phosphatidylinositol/inositol exchange reactions in turkey erythrocyte membranes

Unlike human erythrocytes, those from avian species, such as turkeys and chicks, rapidly incorporate myo-[3H]inositol into membrane phospholipids. The mechanisms regulating [3H]Ins labelling of phosphatidylinositol have been investigated using turkey erythrocyte membranes. In the absence of added nucleotides, [3H]inositol incorporation appears to proceed via phosphatidylinositol/inositol exchange, with a Km for inositol of 0.01 mM. The reaction was dependent upon divalent cations, either Mg2+ or Mn2+, with the latter metal ion being the more effective. [3H]Inositol incorporation was accelerated by CMP, especially when the concentration of Ins was greater than the Km for the exchange reaction. CMP-dependent labelling of PtdIns had a Km for inositol of 0.3 mM and for CMP of 0.015 mM. Divalent cations were also required for this reaction: activity peaked at 0.5 mM-Mn2+ and declined at higher concentrations. At relatively high concentrations, Mg2+ was more effective than Mn2+, with peak activity being achieved above 10 mM. CMP-dependent incorporation of [3H]inositol appears to reflect an exchange reaction catalysed by PtdIns synthase. Definitive evidence for the occurrence of PtdIns synthase in turkey erythrocyte membranes was obtained by demonstrating the formation of [14C]CMP-phosphatidate from [14C]CMP. The radioactivity could be efficiently chased from [14C]CMP-phosphatidate in the presence of unlabelled inositol. The detection of PtdIns synthase activity in morphologically simple turkey erythrocytes should help to clarify the subcellular distribution of this important component of the phosphatidylinositol cycle.

CMP activates reversal of phosphatidylinositol synthase and base exchange by distinct mechanisms in rat pituitary GH3 cells

CMP is known to activate phosphatidylinositol (PtdIns)/inositol (Ins) base exchange and has been reported to activate reversal of PtdIns synthase also. Because it is possible that PtdIns synthase acting in the reverse direction, followed by re-incorporation of ambient Ins, could be responsible for base-exchange activity, we characterized these processes in rat pituitary GH3 cells. In permeabilized GH3 cells prelabelled with [3H]Ins and incubated in buffer with LiCl but without added Ins, CMP stimulated rapid accumulation of [3H]Ins and decreases in [3H]PtdIns; the Km for CMP was 1.7 mM. CDP and CTP were less effective, whereas 2'-CMP, 3'-CMP, other nucleoside monophosphates and cytidine did not influence this process. In permeabilized cells prelabelled to isotopic equilibrium with [3H]Ins and [32P]Pi, CMP stimulated decreases in both the 32P and 3H labelling of PtdIns, but did not increase that of [32P]phosphatidic acid. These findings demonstrate that in the absence of added Ins the effect of CMP is not via activation of base exchange nor via a phospholipase D, but by reversal of PtdIns synthase. In permeabilized cells prelabelled with [3H]Ins and [32P]Pi, unlabelled Ins inhibited loss of 32P labelling of PtdIns caused by CMP while markedly stimulating loss of 3H labelling of PtdIns and release of [3H]Ins. These data demonstrate that Ins inhibits reversal of PtdIns synthase, but stimulates base exchange. We conclude that in GH3 cells reversal of PtdIns synthase and PtdIns/Ins base exchange are both stimulated by CMP, but are distinct processes.

Deoxyribonucleoside triphosphate pools and Ara-CTP levels in P388 murine leukemic cells treated with 1-B-D-arabinofuranosylcytosine-5'-stearylphosphate which is a newly synthesized derivative of 1-B-D-arabinofuranosylcytosine

1-B-D-arabinofuranosylcytosine-5'-stearylphosphate (C18PCA), which is an Ara-CMP ester and one of the most promising orally effective anti-leukemic drugs, is a newly synthesized derivative of Ara-C. The antitumor effect of C18PCA and Ara-C was investigated against the P388 ascites tumor in BDF1 mice. Treatment with C18PCA (100 mg kg-1, orally) and Ara-C (40 mg kg-1, subcutaneously) was administered on days 1, 3 and 5 after tumor inoculation. The percentage increase in lifespans of the mice treated with C18PCA or Ara-C were 84.4% and 53.9%, respectively. The determination of the plasma Ara-C concentration revealed that the plasma concentration of Ara-C was retained much longer in mice which orally received C18PCA than in those which received Ara-C. By using high-performance liquid chromatography, it was revealed that the deoxyribonucleoside triphosphate pools increased gradually but Ara-CTP concentration once increased, then decreased rapidly when Ara-C was administered subcutaneously. On the other hand, both the intracellular deoxyribonucleoside triphosphate (dNTP) pools and Ara-CTP level increased gradually after oral administration of C18PCA. We concluded that these longer-term biochemical effects, even if the plasma concentration of Ara-C and Ara-CTP level were low, might be correlated with antitumor effects of C18PCA.

Quinazoline folate analogs inhibit the catalytic activity of thymidylate synthase but allow binding of 5-fluorodeoxyuridylate

We have investigated some unusual aspects of the inhibition of mammalian thymidylate synthase (TS) by the folate antimetabolite, 10-propargyl-5,8-dideaza-folic acid (CB 3717). From our results, we conclude that binding of CB 3717 metabolites to one subunit of L1210 TS modified the conformation of the second active site of this enzyme so that it retained the ability to bind 5-fluro-2'-deoxyuridine-5'-monophosphate (FdUMP) but not its catalytic activity. Exposure of intact mouse L1210 cells to CB 3717 resulted in inactivation of cellular TS activity, yet desalted cytosol preparations from these cells retained the ability to bind FdUMP. The same effect was found with several analogs of CB 3717. Complexes of FdUMP formed in vitro with TS from cells exposed to CB 3717 were covalent and co-migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with complexes of FdUMP, folate cofactor, and TS from cells not exposed to CB 3717. In the presence of dUMP, a tightly bound complex rapidly formed between isolated pure TS and the pentaglutamate of CB 3717 but not the monoglutamate form of this compound. Binding experiments using CB 3717 pentaglutamate-inhibited TS suggested a stoichiometry of 1 mol of FdUMP bound per mol of dimeric TS.

[Antitumor activity of a novel analog of cytarabine, 4-amino-1-beta-D-arabinofuranosyl-2(1H)-pyrimidinone 5'-(sodium octadecyl phosphate) monohydrate (YNK01)]

4-Amino-1-beta-D-arabinofuranosyl-2(1H)-pyrimidinone 5'-(sodium octadecyl phosphate) monohydrate (YNK01) was an orally active depot form of 1-beta-D-arabinofuranosylcytosine (Ara-C). In the present study, antitumor activity of YNK01 was compared with it of Ara-C in vitro and in vivo. The activity of a main metabolite of YNK01, 5'-carboxypropylphosphate of Ara-C (C-C3PCA), was also studied. Growth inhibitory activity of YNK01 against various cultured tumor cells was 1/32-1/1,100 of that of Ara-C. YNK01 exhibited antitumor activity against L1210 leukemia in mice after i.v., i.p. or p.o. administration. The activity did not depend on the administration routes. Compared with Ara-C, the activity was comparable in both i.v. and i.p. administrations, but greater in p.o. administration. Oral administration of YNK01 showed similar antitumor spectrum to i.p. administration of Ara-C. Oral activity of YNK01 against L1210 leukemia did not depend on the administration schedules but depended on a total administration dose. In contrast, activity of Ara-C greatly depended on the schedules, and the frequent i.p, administration showed greatest activity. Growth inhibitory activity of C-C3PCA against cultured tumor cells was 1/2-1/7 of Ara-C. The metabolite exhibited activity against L1210 leukemia in mice after i.p. administration. These results suggest that YNK01 is a clinically useful drug with p.o. administration for cancers as well as Ara-C.

The effect of DNA replication on mutation of the Saccharomyces cerevisiae CDC8 gene

Incubation in YPD medium under permissive conditions when DNA replication is going on, strongly stimulates the induction of cdc+ colonies of UV-irradiated cells of yeast strains HB23 (cdc8-1/cdc8-3), HB26 (cdc8-3/cdc8-3) and HB7 (cdc8-1/cdc8-1). Inhibition of DNA replication by hydroxyurea, araCMP, cycloheximide or caffeine or else by incubation in phosphate buffer pH 7.0, abolishes this stimulation. Thus the replication of DNA is strongly correlated with the high induction of cdc+ colonies by UV irradiation. It is postulated that these UV-induced cdc+ colonies arise as the result infidelity in DNA replication.

Fosfadecin and fosfocytocin, new nucleotide antibiotics produced by bacteria

Two new nucleotide antibiotics, fosfadecin and fosfocytocin, have been isolated from the culture filtrates of Pseudomonas viridiflava PK-5 and Pseudomonas fluorescens PK-52, respectively. These antibiotics were purified by column chromatographies using adsorption, gel filtration and ion exchange resins. On the basis of the spectroscopic and degradation studies, the chemical structures of fosfadecin and fosfocytocin were determined. These antibiotics were either enzymatically or chemically hydrolyzed to generate fosfomycin and a new antibiotic, fosfoxacin, which are also produced in the culture filtrates. They showed antibacterial activity against Gram-positive and Gram-negative bacteria. The antibacterial activity of these nucleotide antibiotics was weaker than that of fosfomycin and fosfoxacin.

On the inhibition of deoxycytidylate hydroxymethylase by 5-fluoro-2'-deoxycytidine 5'-monophosphate

Studies were performed to determine whether 5-fluoro-2'-deoxycytidine 5'-monophosphate (FdCMP) is an inhibitor of deoxycytidylate hydroxymethylase and whether it could form an isolable covalent complex with the enzyme and the cofactor, 5,10-methyl-enetetrahydrofolate. The results showed that although FdCMP is a competitive inhibitor of dCMP hydroxymethylase, it does not cause time-dependent inhibition of the enzyme in the presence of cofactor. Further, although uv difference spectral evidence was found for FdCMP-cofactor-enzyme complex, the complex was not sufficiently stable to isolate on nitrocellulose filters. We conclude that FdCMP is not a mechanism-based inhibitor of dCMP hydroxymethylase.

Detection of CMP-N-acetylneuraminic acid hydroxylase activity in fractionated mouse liver

The finding that N-glycoloylneuraminic acid (Neu5Gc) in pig submandibular gland is synthesized by hydroxylation of the sugar nucleotide CMP-Neu5Ac [Shaw & Schauer (1988) Biol. Chem. Hoppe-Seyler 369, 477-486] prompted us to investigate further the biosynthesis of this sialic acid in mouse liver. Free [14C]Neu5Ac, CMP-[14C]Neu5Ac and [14C]Neu5Ac glycosidically bound by Gal alpha 2-3- and Gal alpha 2-6-GlcNAc beta 1-4 linkages to fetuin were employed as potential substrates in experiments with fractionated mouse liver homogenates. The only substrate to be hydroxylated was the CMP-Neu5Ac glycoside. The product of the reaction was identified by chemical and enzymic methods as CMP-Neu5Gc. All of the CMP-Neu5Ac hydroxylase activity was detected in the high-speed supernatant fraction. The hydroxylase required a reduced nicotinamide nucleotide [NAD(P)H] coenzyme and molecular oxygen for activity. Furthermore, the activity of this enzyme was enhanced by exogenously added Fe2+ or Fe3+ ions, all other metal salts tested having a negligible or inhibitory influence. This hydroxylase is therefore tentatively classified as a monooxygenase. The cofactor requirement and CMP-Neu5Ac substrate specificity are identical to those of the enzyme in high-speed supernatants of pig submandibular gland, suggesting that this is a common route of Neu5Gc biosynthesis. The relevance of these results to the regulation of Neu5Gc expression in sialoglycoconjugates is discussed.

Synthesis and biological properties of purine and pyrimidine 5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl analogues of AMP, GMP, IMP, and CMP

Methyl 2,3-O-isopropylidene-D-ribofuranoside (1) was converted to 1-O-acetyl-5-bromo-5-deoxy-2,3-di-O-benzoyl-D-ribofuranose (6) in five steps with good yield. The Arbuzov condensation of compound 6 with triethyl phosphite resulted in the synthesis of 1-O-acetyl-2,3-di-O-benzoyl-5-deoxy-5-(diethoxyphosphinyl)-D-ribofuranos e (7). Compound 7 was used for direct glycosylation of both purine and pyrimidine bases. The glycosylation was accomplished with the dry silylated heterocyclic base in the presence of trimethylsilyl triflate. Deblocking of the glycosylation products gave exclusively the beta anomer of the 5'-phosphonate analogues of 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]adenine (13), 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]guanosin e (16), 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]hypoxant hine (17), and 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]cytosine (15), described here for the first time. The target compounds as well as their intermediates showed no in vitro antiviral or antitumor activity, although phosphorylation of 15 and 16 to di- and triphosphate analogues was demonstrated with use of isolated cellular enzymes.

Reconstitution of Golgi vesicle CMP-sialic acid and adenosine 3'-phosphate 5'-phosphosulfate transport into proteoliposomes

We have previously shown that Golgi apparatus vesicles transport nucleotide sugars and nucleotide sulfate into their lumen. These transport activities are organelle and substrate specific and are characterized by apparent Km for nucleotide derivatives in the low micromolar range. As part of our goal of purifying and characterizing the above transport proteins, we have reconstituted a protein extract from rat liver Golgi membranes into phosphatidylcholine liposomes. The resulting proteoliposomes transport CMP-N-acetylneuraminic acid (CMP-AcNeu) and adenosine 3'-phosphate 5'-phosphosulfate with very similar affinity and inhibition characteristics as intact Golgi vesicles. Sialic acid and sodium sulfate, which are transported only very slowly into the lumen of Golgi vesicles, are transported at low rates by the reconstituted proteoliposomes. Neither rough endoplasmic reticulum-derived vesicles nor proteoliposomes made from proteins of the rough endoplasmic reticulum transport CMP-AcNeu. The above results demonstrate that this reconstituted system can be used for further purification and characterization of nucleotide sugar and nucleotide sulfate translocator proteins. This approach should also be useful to study membrane transport proteins of lysosomes and endosomes.