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Biomedical subjects

Y Tachibana

Publications and source records attributed to Y Tachibana.

At least 37 records · Page 2Linked to original sources
PubMed2000

Alteration of product specificity of cyclodextrin glucanotransferase from Thermococcus sp. B1001 by site-directed mutagenesis.

Cyclodextrin glucanotransferase (CGTase) from the hyperthermophilic archaeon Thermococcus sp. B1001 catalyzed the production predominantly of alpha-cyclodextrin (CD) from starch (Tachibana, Y. et al., Appl. Environ. Microbiol., 65, 1991-1997, 1999). The CGTase gene (cgtA) from this strain was cloned and sequenced. It was composed of 2217 nucleotides, and encoded a protein (739 amino acids) with a molecular mass of 83,240 Da. Recombinant CgtA expressed in Escherichia coli also catalyzed the production predominantly of alpha-CD from starch, as did native CgtA from strain B1001. Based on a substrate binding model of Bacillus circulans no. 8 CGTase, Tyr100, Trp191 and Tyr267 were specified to locate the spiral amylose and to minimize the size of the CD by saccharide aromatics interaction. In order to determine the critical residue for catalyzing production predominantly of alpha-CD, site-directed mutations were introduced in CgtA (Y100W, Tyr100-->Trp; W191Y, Trp191-->Tyr; W191F, Trp191-->Phe; Y267W, Tyr267-->Trp; Y267F, Tyr267-->Phe). Analysis of the reaction products by HPLC revealed that the mutant enzyme Y267W produced more beta- and gamma-CD than the wild-type enzyme. However, the other mutants still produced high levels of alpha-CD, suggesting that Tyr267 plays a critical role in alpha-CD production catalyzed by B1001 CGTase.

Journal Article↗
PubMed2000

Acceptor specificity of 4-alpha-glucanotransferase from Pyrococcus kodakaraensis KOD1, and synthesis of cycloamylose.

4-Alpha-glucanotransferase from a hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1 showed a broad acceptor specificity to various saccharides in an intermolecular transglycosylation reaction. In particular, the enzyme produced large amounts of transfer products of various acceptors such as D-glucose, methyl-alpha-D-glucoside, phenyl-alpha-D-glucoside, and D-xylose. It is suggested that the requirement for an effective acceptor in the intermolecular transglycosylation reaction catalyzed by this enzyme is the pyranose structure with the same configurations of the free C2-, C3-, and C4-hydroxyl groups as d-glucopyranose, like cyclomaltodextrin glucanotransferase (CGTase). However, the enzyme showed some acceptor specificities unlike those of CGTase. Analysis of the action of 4-alpha-glucanotransferase indicated that the enzyme catalyzes an intramolecular trans-glycosylation (cyclization) reaction of amylose to produce cyclic alpha-1,4-glucan (cycloamylose). The yield of cycloamylose reached 67%, and the degree of polymerization was found to range from 16 to above 55.

Journal Article↗
PubMed2000

Antitumor agents. 203. Carbazole alkaloid murrayaquinone A and related synthetic carbazolequinones as cytotoxic agents.

Murrayaquinone A (1) and murrayafoline A (3), isolated from the root bark of Murraya euchrestifolia, were identified as cytotoxic compounds. Murrayaquinone A (1) demonstrated significant cytotoxicity against SK-MEL-5 and Colo-205 cells, with ED(50) values of 2.58 and 3.85 microg/mL, respectively. In contrast, murrayafoline A (3) exhibited marginal or weak cytotoxicity against SK-MEL-5, Colo-205, HCT-8, KB, and A-549 tumor cell lines, with ED(50) values ranging from 5.31 to 7.52 microg/mL. In total, 20 carbazole alkaloids (1-20), isolated previously by Furukawa et al. from various plant sources were also evaluated for their cytotoxic profiles in the NCI's human disease-oriented, 60-cell line, in vitro antitumor screening protocol. Compounds 3 and 15 showed potent cell-line selective cytotoxicity against MOLT-4 cells, with log GI(50) values of -8.60 and -8.49 M, respectively, while 12 demonstrated better selectivity against the colon cancer subpanel. Moreover, synthetic 2-methyl- or 3-methyl-carbazolequinone derivatives with various substituents in the A-ring were evaluated against KB, SK-MEL-5, Colo-205, and HCT-8 tumor cells. 6-Methoxy- (21), 6-methyl- (22), and 6-chloro- (24) 3-methyl-carbazolequinones demonstrated significant cytotoxicity against SK-MEL-5 cells, with ED(50) values of 0.55, 0.66, and 0.83 microg/mL, respectively. Compounds 21 and 22 were also significantly cytotoxic toward KB cells, with ED(50) values of 0.76 and 0.92 microg/mL, respectively, and 21 displayed a similar level of toxicity against Colo-205 cells (ED(50) 0.87 microg/mL).

Alkaloids↗
PubMed2000

Anti-HIV agents 45(1) and antitumor agents 205.(2) two new sesquiterpenes, leitneridanins A and B, and the cytotoxic and anti-HIV principles from Leitneria floridana.

Two new sesquiterpenes, leitneridanin A (1) and leitneridanin B (2), and seven known compounds, lirioresinol B, (-)-pinoresinal, (+)-lariciresinol, quassimarin (3), simalikalactone D (4), 1-methoxycanthinone (5), and 5-methoxycanthinone (6), were isolated from Leitneria floridana. Their structures were identified on the basis of spectral data. In vitro biological evaluation showed that 5 is a potent anti-HIV agent (EC(50) 0.26 g/mL; TI >39) and that 3-6 suppressed the growth of a panel of human tumor cell lines (KB, A-549, HCT-8, CAKI-1, MCF-7, and SK-MEL-2). Compounds 3 and 4 were significantly active, with ED(50) values in the range of 0.26-0.012 g/mL.

Anti-HIV Agents↗
PubMed2000

Crystal structure of the low-temperature phase of beta Cu1.75Se analysed by electron diffraction

The beta phase of Cu1.75Se has an anti-fluorite structure, where one in eight tetrahedral copper sites are vacant. Powder X-ray diffraction measurements on Cu1.75Se showed that the beta phase transformed to a two-phase mixture of (alpha + beta) at approximately 250 K, and then the beta phase changed to a new phase at approximately 180 K. Powder X-ray and electron diffraction measurements revealed that the low-temperature phase of the beta phase has a superstructure of (2alpha(fcc) x 2alpha(fcc) x 2alpha(fcc)) type, where alpha(fcc) is the lattice parameter of the original beta phase. The superstructure was interpreted to originate from the ordering copper vacancies. The new phase was referred to as the beta' phase.

Journal Article↗
PubMed2000

Characterization of human lung cancer cells resistant to 4'-O-demethyl-4beta-(2"-nitro-4"-fluoroanilino)-4-desoxypodophyllotoxin , a unique compound in the epipodophyllotoxin antitumor class.

A new semi-synthetic podophyllotoxin derivative, 4'-O-demethyl-4beta-2"-nitro-4"-fluoroanilino)-4-desoxypo dophyllotoxin (compound 1), an analog of GL-331 (compound 2), is a potent and broad-spectrum inhibitor of cultured human cancer and drug-resistant cell growth. In general, 4'-demethylepipodophyllotoxin analogs, including 2, exert anti-tumor activity by targeting the nuclear enzyme DNA topoisomerase II, but 1 is not an enzyme inhibitor. Unlike the cytotoxic activity of compound 2, cell killing by 1 is dose-limiting and a significant fraction of cells (30-40%) survive treatment. As an approach to investigate mechanism of action, 1-resistant A549 (human lung cancer) sub-lines were selected and characterized. Results of the work show that 1-resistant cells: (i) are moderately cross-resistant (2- to 3-fold) to various cytotoxic drugs via a P-glycoprotein-independent mechanism, (ii) have an altered growth habit, (iii) are deficient in normal attachment on plastic and collagen substrata, and (iv) have an altered plasma membrane protein composition including several proteins in the 140->200 kDa molecular mass range and a doublet of phosphoserine-containing proteins of about 135 kDa. Since 1 treatment of cells affects neither cellular attachment or membrane-protein phosphorylation, the changes observed in 1-resistant cells are interpreted as a survival response to drug action.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Antitumor agents. 196. Substituted 2-thienyl-1,8-naphthyridin-4-ones: their synthesis, cytotoxicity, and inhibition of tubulin polymerization.

As part of our continuing search for potential anticancer drug candidates in the 2-aryl-1,8-naphthyridin-4-one series, we have synthesized a series of substituted 2-thienyl-1, 8-naphthyridin-4-ones. Most compounds showed significant cytotoxic effects (log GI(50) < -4.0; log molar drug concentration required to cause 50% growth inhibition) against a variety of human tumor cell lines in the National Cancer Institute's in vitro screen, including cells derived from solid tumors such as non-small-cell lung, colon, central nervous system, melanoma, ovarian, prostate, and breast cancers. The most active compounds (31-33,40) demonstrated strong cytotoxic effects with ED(50) values in the micromolar or submicromolar range in most of the tumor cell lines. The most cytotoxic compounds inhibited tubulin polymerization at concentrations substoichiometric to the tubulin concentration. The most potent inhibitors of polymerization (40,42,43) had effects comparable to those of the potent antimitotic natural products podophyllotoxin and combretastatin A-4 and to that of NSC 664171, a particularly potent, structurally related analogue. Only compound 40 was a potent inhibitor of the binding of radiolabeled colchicine to tubulin, and it was both the most cytotoxic agent and the most effective inhibitor of polymerization among the newly synthesized compounds.

Antineoplastic Agents↗
PubMed1999

Antitumor agents. 194. Synthesis and biological evaluations of 4-beta-mono-, -di-, and -trisubstituted aniline-4'-O-demethyl-podophyllotoxin and related compounds with improved pharmacological profiles.

As a continuation of our structure-activity relationship studies, several new 4-beta-substituted 4'-O-demethyl-4-desoxypodophyllotoxins bearing mono-, di-, or trisubstituted anilines have been synthesized and evaluated as inhibitors of DNA topoisomerase II and tumor cell growth in tissue culture. Selected compounds were further evaluated as cytotoxic agents using a clonogenic survival assay. The target compounds include 4'-O-demethyl-4beta-[(4' '-(benzimidazol-2' '-yl)anilino]-4-desoxypodophyllotoxin (21), 4'-O-demethyl-4beta-(-)-(4' '-camphanamido-anilino)-4-desoxypodophyllotoxin (25), 4-beta-disubstituted-anilino-4'-demethyl-4-desoxypodophyllotoxins (18-20, 26), 4-alpha-disubstituted-anilino-4'-demethyl-4-desoxypodophyllotoxin (27), 4-beta-trisubstituted-anilino-4'-demethyl-desoxypodophyllotoxin (22, 23), and 4'-O-demethyl-4beta-[4' '-(benzimidazol-2' '-yl)amino]-4-desoxypodophyllotoxin (24). Among the target series, 19, 21, and 24 displayed significant growth inhibitory action against a panel of tumor cell lines including human epidermoid carcinoma of the nasopharynx (KB) and its etoposide-resistant (KB7B) and vincristine-resistant (vin20c KB) subclones, lung carcinoma (A549), human ileocecal carcinoma (HCT-8), human kidney carcinoma (CAKI-1), breast adenocarcinoma (MCF-7), and human malignant melanoma (SK-MEL-2) cells. Compounds 19, 21, 24, and 25 were "cleavable-complex"-forming DNA topoisomerase II inhibitors with either improved or similar activity compared with the prototype drug etoposide (VP-16). Compound 21 was the most active analogue, being 10-fold more potent than etoposide in both cell killing and topoisomerase II inhibition in vitro assays. Using mouse models of antitumor activity, 21 was effective against (P388/0) leukemia but not against the growth of a (MCF7) mammary tumor.

Animals↗
PubMed1999

Cerebellar hypoperfusion and developmental dysphasia in a male.

A male with developmental dysphasia is documented with fine motor dysfunction whose improvement in expressive language was associated with increased cerebellar perfusion, as detected by serial N-isopropyl-p-[iodine-123] iodoamphetamine single photon emission computed tomography (SPECT). His expressive language has been improving since 6 years, 8 months of age, and his verbal intelligence quotient improved from less than 45 at 5 years of age to 80 at 8 years of age. Compared with the SPECT findings at 4 years of age, the ratio of the average pixel values of the cerebellum to the frontal cortices increased at 9 years of age (from 0.81 to 1.03-1.09 in the hemisphere and from 0.66 to 0.98 in the vermis). However, he was not able to understand stories presented orally even at 9 years, 4 months of age. These results suggest that developmental dysphasia, which mostly involves expressive impairment, in this patient could have been the result of delayed maturation of cerebellar function, mainly that of the vermis.

Brain↗
PubMed1999

Purification and characterization of an extremely thermostable cyclomaltodextrin glucanotransferase from a newly isolated hyperthermophilic archaeon, a Thermococcus sp.

The extremely thermophilic anaerobic archaeon strain B1001 was isolated from a hot-spring environment in Japan. The cells were irregular cocci, 0.5 to 1.0 micrometers in diameter. The new isolate grew at temperatures between 60 and 95 degrees C (optimum, 85 degrees C), from pH 5.0 to 9.0 (optimum, pH 7.0), and from 1.0 to 6.0% NaCl (optimum, 2.0%). The G+C content of the genomic DNA was 43.0 mol%. The 16S rRNA gene sequencing of strain B1001 indicated that it belongs to the genus Thermococcus. During growth on starch, the strain produced a thermostable cyclomaltodextrin glucanotransferase (CGTase). The enzyme was purified 1,750-fold, and the molecular mass was determined to be 83 kDa by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Incubation at 120 degrees C with SDS and 2-mercaptoethanol was required for complete unfolding. The optimum temperatures for starch-degrading activity and cyclodextrin synthesis activity were 110 and 90 to 100 degrees C, respectively. The optimum pH for enzyme activity was pH 5.0 to 5.5. At pH 5.0, the half-life of the enzyme was 40 min at 110 degrees C. The enzyme formed mainly alpha-cyclodextrin with small amounts of beta- and gamma-cyclodextrins from starch. This is the first report on the presence of the extremely thermostable CGTase from hyperthermophilic archaea.

Amino Acid Sequence↗
PubMed1999

A comparative study of Embelia schiperi and Embelia keniensis on blood glucose and triglycerides in normal and epinephrine-induced hyperglycemic mice.

Intraperitoneal administration of the methanol extract of Embelia schiperi (ES) to normal mice caused a significant decrease in blood glucose (p < 0.01) and a significant increase in triglycerides 4 hours after administration at 100 mg/kg (p < 0.01). The toluene fraction of Embelia keniensis methanol extract (TS) showed hypoglycemic and lipid lowering activity 7 hours after intraperitoneal administration at 100 mg/kg. In addition, TS (100 mg/kg) administration significantly decreased blood glucose in epinephrine-induced hyperglycemic mice (p < 0.01). Moreover, ES tended to increase while TS tended to decrease the blood triglycerides in epinephrine-induced hyperglycemic mice. On the other hand, no changes in blood cholesterol were observed after the administration of ES or TS in normal and epinephrine-induced hyperglycemic mice. We found that two species from Embelia, ES and TS, have different activities on blood glucose and triglycerides in normal and epinephrine-induced hyperglycemic mice.

Animals↗
PubMed1999

Biological activity profiles of 1alpha,25-dihydroxyvitamin D2, D3, D4, D7, and 24-epi-1alpha,25-dihydroxyvitamin D2.

We have synthesized several 1alpha,25-dihydroxyvitamin D [1alpha,25(OH)2D] derivatives and evaluated their biological activity in terms of their binding affinity for the vitamin D receptor (VDR) and vitamin D-binding protein (DBP), antiproliferative or differentiation-inducing effects on human promyelocytic leukemic HL-60 cells, and transcriptional activity on a rat 25-hydroxyvitamin D3-24-hydroxylase gene promoter, including two vitamin D-responsive elements (VDREs), and human osteocalcin gene promoter, including a VDRE in transfected human osteosarcoma MG-63 cells. Furthermore, human VDR- or retinoic acid X receptor alpha (RXR alpha)-mediated luciferase activities of the derivatives were also measured by a one-hybrid system in human epitheloid carcinoma, cervix HeLa cells and African green monkey kidney CV-1 cells. Binding affinity for VDR, bone-resorbing activity, antiproliferative and cell-differentiating effects, transactivation potencies on target genes and VDR- or RXR alpha-mediated gene regulations of 1alpha,25(OH)2D2 and 1alpha,25(OH)2D4 were almost comparable to the effects of 1alpha,25(OH)2D3 while 24-epi-1alpha,25(OH)2D2 and 1alpha,25(OH)2D7 were much less active than 1alpha,25(OH)2D3 in these respects. This is the first report concerning biological assessment of 1alpha,25(OH)2D2, 1alpha,25(OH)2D3, 1alpha,25(OH)2D4, 24-epi-1alpha,25(OH)2D2 and 1alpha,25(OH)2D7 at the molecular level, especially with regards to the structural differences at the 24R- or 24S-methyl group and a double bond between carbons 22 and 23 in the side chain of 1alpha,25(OH)2D derivatives.

Animals↗
PubMed1998

Antitumor agents. 185. Synthesis and biological evaluation of tridemethylthiocolchicine analogues as novel topoisomerase II inhibitors.

Several 1,2,3-tridemethyldeacetylthiocolchicine derivatives have been synthesized and evaluated for cytotoxic activity against various human tumor cell lines and for their inhibitory effects on DNA topoisomerases in vitro. Exhaustive demethylation of thiocolchicine analogues completely changes their biological profiles. Instead of displaying antitubulin activity, most target compounds inhibited topoisomerase II activity. Only compounds with a larger side chain, such as 15a, 23a, and 24a, did not interfere with topoisomerase II enzymatic functions. The cytotoxicity of target compounds was reduced by 3 orders of magnitude compared to that of colchicine in most cell lines. The hydrophilicity of phenolic compounds might prevent drug passage through the cell plasma membrane and, thus, be responsible for the relatively weak cytotoxicity. To test this hypothesis, 27-30 were prepared from 16a by protecting all hydroxy groups with esters with an aim to facilitate drug transportation. In vitro cytotoxicity assays indicated that 27 was more potent than its parent compound in all tested tumor cell lines and showed tissue selective cytotoxicity with a significant inhibitory effect against KB cells (IC50 = 2.7 microg/mL). Therefore, we propose that 27 acts as a prodrug, liberating 16a to exert its antitopoisomerase activity and, finally, to cause cell death.

Antineoplastic Agents↗
PubMed1998

Antitumor agents. 181. Synthesis and biological evaluation of 6,7,2',3',4'-substituted-1,2,3,4-tetrahydro-2-phenyl-4-quinolones as a new class of antimitotic antitumor agents.

A novel series of 6,7,2',3',4'-substituted-1,2,3,4-tetrahydro-2-phenyl- 4-quinolones were synthesized and evaluated for interactions with tubulin and for cytotoxic activity against a panel of human tumor cell lines, including ileocecal carcinoma (HCT-8), breast cancer (MCF-7), lung carcinoma (A-549), epidermoid carcinoma of the nasopharynx (KB), renal cancer (CAKI-1), and melanoma cancer (SKMEL-2). Most compounds (18, 20, 22-27) showed potent cytotoxic and antitubulin effects. The most active compounds (23, 26, 27) demonstrated strong cytotoxic effects with ED50 values in the nanomolar or subnanomolar range in almost all tumor cell lines. Three active racemates (20, 22, 25) were separated into the enantiomers, and generally, the optically pure (-)-isomers (20a, 22a, 25a) exhibited greater biological activity than the racemates or (+)-isomers. Cytotoxicity and antitubulin activity were closely correlated, with the most active compounds (23, 26, 27) having effects comparable to those of colchicine, podophyllotoxin, and combretastatin A-4.

Antibiotics, Antineoplastic↗
PubMed1998

Antitumor agents. Part 186: Synthesis and biological evaluation of demethylcolchiceinamide analogues as cytotoxic DNA topoisomerase II inhibitors.

Demethylation of colchiceinamide (2) and its analogues (3-10) afforded a novel class of mammalian DNA topoisomerase II inhibitors (2a-10a) without displaying tubulin inhibitory activity. All target compounds inhibited the catalytic activity of topoisomerase II at drug concentrations at 100 microM. An in vitro cytotoxicity assay indicated that compounds 3a and 8a were strong and tissue-selective cytotoxic agents against the MCF-7 breast cancer cell line (IC50 = 0.36 and 0.48 microgram/mL, respectively) and the CAKI-1 renal cancer cell line (IC50 = 0.72 and 0.96 microgram/mL, respectively).

Antineoplastic Agents↗
PubMed1998

Mitochondrial encephalomyopathy (Kearns-Sayre syndrome) with complete atrioventricular block: a case report.

A pacemaker was implanted into a 17-year-old man with cardiac failure due to complete atrioventricular block complicated by mitochondrial encephalomyopathy (Kearns-Sayre syndrome). Due to the possible complication of latent myocardial dysfunction, it was decided to implant the dual chamber pacemaker (DDD) and the operation mode was set to DDD 70 ppm 1 year after implantation; this alleviated the cardiac failure. In this case, the necessity of preventive pacemaker implantation in the early stage of cardiac failure was recognized.

Adolescent↗