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X Yan

Publications and source records attributed to X Yan.

At least 145 records · Page 8Linked to original sources
PubMed1996

Small molecule interactions with protein-tyrosine phosphatase PTP1B and their use in inhibitor design.

We have previously shown that a small peptide bearing the hydrolytically stable phosphotyrosyl (pTyr) mimetic, (difluorophosphonomethyl) phenylalanine (F2Pmp), is an extremely potent inhibitor of PTP1B, with an IC50 value of 100 nM [Burke, T. R., Kole, H. K., & Roller, P. P. (1994) Biochem. Biophys. Res. Commun. 204, 129-134]. We further demonstrated that removal of the peptide portion and incorporation of the difluorophosphonomethyl moiety onto a naphthalene ring system, but not a phenyl ring system, resulted in good inhibitory potency [Kole, H. K., Smyth, M. S., Russ, P. L., & Burke, T. R., Jr. (1995) Biochem, J. 311, 1025-1031]. In order to understand the structural basis for this inhibition, and to aid in the design of further analogs, we solved the X-ray structure of [1, 1-difluoro-1-(2-naphthalenyl)-methyl]phosphonic acid (6) complexed within the catalytic site of PTP1B, solved to 2.3 A resolution. In addition to showing the manner in which the phosphonate group is held within the catalytic site, the X-ray structure also revealed extensive hydrophobic interactions with the naphthalene ring system, beyond that possible with an analog bearing a single phenyl ring. It is further evident that, of the two fluorine atoms, the pro-R alpha-fluorine interacts with the enzyme to a significantly greater degree than the pro-S alpha-fluorine, forming a hydrogen bond to Phe 182. On the basis of a computer-assisted molecular modeling analysis, it was determined that addition of a hydroxyl to the naphthyl 4-position, giving [1, 1-difluoro-1-[2-(4-hydroxynaphthalenyl)] methyl]phosphonic acid (8), could potentially replace a water molecule situated in the PTP1B-6 complex, thereby allowing new hydrogen-bonding interactions with Lys 120 and Tyr 46. Compound 8 was therefore prepared and found to exhibit a doubling of affinity (Ki = 94 microM) relative to parent unsubstituted 6 (Ki = 179 microM), supporting, in principle, the development of high-affinity ligands based on molecular modeling analysis of the enzyme-bound parent.

Binding Sites↗
PubMed1996

Characterization of an Ig VH idiotope that results in specific homophilic binding and increased avidity for antigen.

mAb against GD3 ganglioside demonstrate homophilic binding in which soluble anti-GD3 mAb bind, through the GD3 binding site, to a VH idiotope (designated IdHOM) on solid phase anti-GD3 mAb. In this way, homophilic binding provides a mechanism for amplifying the binding of mAb to cell surface GD3. We show that serine 52a, within CDR2, is required for IdHOM expression, homophilic binding, and high avidity binding to cell surface GD3. Computer modeling based on the crystal structure of anti-GD3 mAb R24 showed serine 52a situated at the mouth of the GD3 binding pocket, but not directly involved with GD3 binding. Substitutions at position 52a predicted to maintain the GD3 binding pocket (e.g., threonine) resulted in the loss of IdHOM expression and homophilic binding and markedly decreased binding to cell surface GD3, but maintained low avidity GD3 binding as measured by ELISA. All other substitutions at position 52a were predicted to significantly distort the GD3 binding pocket and resulted in the loss of both homophilic binding and any detectable avidity for GD3. We have structurally defined IdHOM and conclude that this idiotope is not required for the GD3 binding pocket, but that the idiotope is necessary for homophilic binding, which is required for high avidity binding to cell surface GD3. We speculate that selection of certain VH genes may result in the expression of idiotopes that allow homophilic binding, and this may represent a general mechanism for increasing the avidity of Abs against T cell-independent Ags.

Amino Acid Sequence↗
PubMed1996

Discovery of novel, non-peptide HIV-1 protease inhibitors by pharmacophore searching.

Fifteen novel non-peptide HIV-1 protease inhibitors were identified by flexible 3D database pharmacophore searching of the NCI DIS 3D database. The pharmacophore query used in the search was derived directly from the X-ray determined structures of protease/inhibitor complexes. These 15 inhibitors, belonging to nine different chemical classes, are promising leads for further development. The two best inhibitors found, NSC 32180, a "dimer" of 4-hydroxycoumarin, and NSC 117027, a "tetramer" of 2-hydroxy quinone, had ID50 values of 0.32 and 0.75 microM for HIV-1 protease inhibition, respectively, and two other inhibitors had ID50 values close to 1 microM. Among the potent inhibitors, NSC 158393 not only demonstrated activity against HIV-1 protease (ID50 1.7 microM) but also exhibited promising antiviral activity in HIV-1-infected CEM-SS cells (EC50 = 11.5 microM). Validation of the pharmacophore used in the search was accomplished by conformational analysis. The binding modes of the most potent inhibitor found in our studies, NSC 32180, were predicted employing docking and molecular dynamics techniques.

Amino Acid Sequence↗
PubMed1996

4'-O-[2-(2-fluoromalonyl)]-L-tyrosine: a phosphotyrosyl mimic for the preparation of signal transduction inhibitory peptides.

Development of phosphotyrosyl (pTyr) mimetics which are stable to protein-tyrosine phosphatases (PTPs), yet can retain biological potency when incorporated into peptides, is an active area of drug development. Since a majority of pTyr mimetics derive their "phosphofunctionality" from phosphorus-containing moieties, such as phosphonates, evolution of new inhibitors and modes of prodrug derivatization have been restricted to chemistries appropriate for phosphorus-containing moieties. A new, nonphosphorus-containing pTyr mimetic has recently been reported, L-O-(2-malonyl)tyrosine (OMT,5), which can be incorporated into peptides that exhibit good PTP and Src homology 2 (SH2) domain inhibitory potency. For phosphonate-based pTyr mimetics such as phosphonomethyl phenylalanine (Pmp,2) introduction of fluorines alpha to the phosphorus has provided higher affinity pTyr mimetics. This strategy has now been applied to OMT, and herein is reported 4'-O-[2-(2-fluoromalonyl)]-L-tyrosine (FOMT,6) a new fluorine-containing nonphosphorus pTyr mimetic. Incorporation of FOMT into appropriate peptides results in good inhibition of both PTP and SH2 domains. In an assay measuring the inhibition of PTP 1B-mediated dephosphorylation of phosphorylated insulin receptor, the peptide Ac-D-A-D-E-X-L-amide exhibited a 10-fold enhancement in inhibitory potency for X = FOMT (19) (IC(50) = 10 microM) relative to the unfluorinated peptide, X = OMT (18) (IC(50) = 10 microM. Molecular modeling indicated that this increased affinity may be attributable to new hydrogen-bonding interactions between the fluorine and the enzyme catalytic site, and not due to lowering of pKa values. In a competition binding assay using the p85 PI 3-kinase C-terminal SH2 domain GST fusion construct, the inhibitory peptide, Ac-D-X-V-P-M-L-amide, showed no enhancement of inhibitory potency for X = FOMT (22) (IC(50) = 18 microM) relative to the unfluorinated peptide, X = OMT (21) (IC(50) = 14 microM). The use of FOMT would therefore appear to have particular potential for the development of PTP inhibitors.

Amino Acid Sequence↗
PubMed1996

Precision targeting of protein kinases. An affinity label that inactivates the cGMP- but not the cAMP-dependent protein kinase.

Although the cAMP-dependent (PKA) and cGMP-dependent protein kinases (PKG) usually participate in unrelated biological processes, their enzymological properties are decidedly similar. Based upon the multitude of comparative studies conducted to date, it appears that these two enzymes exhibit very similar peptide substrate specificities. Furthermore, most inhibitors that have been reported for PKG serve in a nearly equal capacity for PKA. Consequently, the task of distinguishing between these enzymes, especially under in vivo conditions, has proved to be daunting. However, we have recently found that PKA will only phosphorylate non-amino acid residues whose alpha-configuration corresponds to that found in L-amino acids, whereas PKG will catalyze the phosphorylation of residues corresponding to both L- and D-amino acids (Wood, J., Mendelow, M., Yan, X., Corbin, J.D., Francis, S.H., and Lawrence, D.S. (1996) J. Biol. Chem. 271, 174-179). Based on these results, we have designed a potent affinity label for PKG (KI = 21.1 +/- 4.7 microM), that has no measurable activity toward PKA. This represents the first example of an peptide-based inactivator that fully distinguishes between these two closely related enzymes. These results suggest that a similar strategy may provide highly specific inactivators for other protein kinases as well.

Adenosine Triphosphate↗
PubMed1996

Precision substrate targeting of protein kinases. The cGMP- and cAMP-dependent protein kinases.

The cAMP-dependent (PKA) and cGMP-dependent protein kinases (PKG) share a strong primary sequence homology within their respective active site regions. Not surprisingly, these enzymes also exhibit overlapping substrate specificities, a feature that often interferes with efforts to elucidate their distinct biological roles. In this report, we demonstrate that PKA and PKG exhibit dramatically different behavior with respect to the phosphorylation of alpha-substituted alcohols. Although PKA will phosphorylate only residues that contain an alpha-center configuration analogous to that found in L-serine, PKG utilizes residues that correspond to both L- and D-serine as substrates. The PKG/PKA selectivity of these substrates is the highest ever reported.

Amino Acid Sequence↗
PubMed1996

Pharmacokinetic, angiographic, and histologic comparison of catheter-directed chemoembolization versus systemic chemotherapy in a canine model.

Chemotherapy with selective intraarterial embolization may promote sustained contact of the drug with the tumor and thus could be more effective in the treatment. In this phenomenon, pharmacokinetics of a drug such as mitomycin C (MMC) play a significant role in guiding the therapy. Therefore, we have compared the pharmacokinetics of MMC and assessed angiographic, morphologic, and histologic changes in the kidney following intravenous MMC versus renal artery infusion with and without embolization with embolic agents, Rhizoma Bletillae (RB) and Gelfoam (GF). Dogs randomly divided into four groups underwent selective infusion protocols. Blood samples from renal and common iliac veins were analyzed for MMC levels. Angiography and pathology were performed at 4 days. Intravenous MMC (IV-MMC) caused significantly lower renal vein MMC levels than intraarterial MMC (IA-MMC) and GF + MMC. RB + MMC produced the lowest MMC levels in both veins (p < 0.05). Common iliac MMC levels were not significantly different after IV-MMC, IA-MMC, or GF + MMC. Angiographic and histologic studies showed extensive bleeding, necrosis, and vasculitis with thrombosis of the target kidneys after RB + MMC, GF + MMC, or IA-MMC, but not IV-MMC. Selective Rhizoma Bletillae chemoembolization can decrease systemic levels of MMC. Gelfoam does not provide sustained local release of MMC or decrease systemic levels of MMC compared with intravenous infusion. Selective renal MMC infusion without an effective embolic agent does not reduce systemic levels compared with intravenous delivery.

Adjuvants, Pharmaceutic↗
PubMed1996

[Expression of placental alkaline phosphatase in esophageal cancer cell line Eca109].

The expression and property of alkaline phosphatase (ALP) in Eca109 cells, a cell line derived from human esophageal carcinoma were studied with specific inhibition assay and poly-acrylamide gel electrophoresis. The results showed that ALP of Eca109 cells was heat stable and was strongly inhibited by L-phenyalanine, but slightly inhibited by urea. Prednisolone could cause dramatic increase in activity of ALP, but no change in ALP isozyme spectrum and concomitant increase in lactic dehydrogenase activity were found after prednisolone treatment. The results suggested that placental alkaline phosphatase as an oncofetal gene product could be expressed ectopically by Eca109 cells and prednisolone could specifically induce increase in its activity.

Alkaline Phosphatase↗
PubMed1996

[A new zoonosis--investigation of Gardnerella vaginalis disease of fox. V. Studies serotype of Gardnerella vaginalis in fox].

145 strains Gardnerella vaginalis isolated in foxes were isolated from 13 main farms raising foxes in six provinces (regions), China, after antigenicity and immunogenicity of the strains were measured, 1-3 appropriate strains were selected from each farm raising foxes for serotype studies. Cross agglutinin absorption test confirmed that selected 26 strains Gardnerella vaginalis were divided into three serotypes and then the representing strains were used to produce typing serum. Among remaining 119 strain, 108 strains were typable with the typing sera, and 11 strains can't be set. Among three serotypes, serotype I made up 79.1% of the strains. It was shown that serotype I was the principal serotype of Gardnerella vaginalis of fox in China. The test also confirmed that 5 strains of Gardnerella vaginalis isolated from racoon dog, 4 strain Gardnerella vaginalis from mink and 2 strains Gardnerella vaginalis from canine also belonged to serotype I. Supersonic antigben was produced with three serotypes, representative strains. By agar immuno-diffusion test, it confirmed that the antigens of three serotypes formed a obvious blending precipitating line with the homologous or heterologous serotype antiserum. It indicated common antigen existed among all serotypes. The agar immuno-diffusion test results revealed that the precipitating line of the homologous serotype completely blended. It is our opinion that the method of serotyping is reliable.

Animals↗
PubMed1996

[Clinical study on effect of xinjikang capsule in reversing left ventricular hypertrophy].

The study was conducted on the patients suffering from left ventricular hypertrophy (LVH). Ninety four cases of LVH were randomly divided into treated group (74 cases) and control group (20 cases) treated with Xinjikang capsule (XJK) and Metoprolo respectively. The results showed that XJK has remarkable reverse effects on LVH (P < 0.01). The control group although showed some effect of improvement, in comparison with pretreatmental measurement the difference was insignificanty (P > 0.05). While in comparing the two groups, the difference of effect was very significant (P < 0.01). XJK could also alleviate and eliminate to the cause of LVH, such as improving heart function and microcirculation, decreasing blood viscosity, apolipoprotein, myocardial oxygen consumption, increasing superoxide dismutase. All these parameters measured after XJK treatment were significantly different from that before treatment. The difference of them between XJK treated group and control group was also significant (P < 0.01 or P < 0.05). It suggested XJK capsule has reversing effect on LVH.

Animals↗
PubMed1995

L-O-(2-malonyl)tyrosine: a new phosphotyrosyl mimetic for the preparation of Src homology 2 domain inhibitory peptides.

Inhibition of Src homology 2 (SH2) domain-binding interactions affords one potential means of modulating protein-tyrosine kinase-dependent signaling. Small phosphotyrosyl (pTyr)-containing peptides are able to bind to SH2 domains and compete with larger pTyr peptides or native pTyr-containing protein ligands. Such pTyr-containing peptides are limited in their utility as SH2 domain inhibitors in vivo due to their hydrolytic lability to protein-tyrosine phosphatases (PTPs) and the poor cellular penetration of the ionized phosphate moiety. An important aspect of SH2 domain inhibitor design is the creation of pTyr mimetics which are stable to PTPs and have reasonable bioavailability. To date, most PTP-resistant pTyr mimetics which bind to SH2 domains are phosphonates such as (phosphonomethyl)phenylalanine (Pmp, 2), [(monofluorophosphono)methyl]phenylalanine (FPmp, 3) or [(difluorophosphono)methyl]-phenylalanine (F2Pmp, 4). Herein we report the incorporation of a new non-phosphorus-containing pTyr mimetic, L-O-(2-malonyl)tyrosine (L-OMT, 5), into SH2 domain inhibitory peptides using the protected analogue L-N alpha-Fmoc-O'-(O",O"-di-tert-butyl-2-malonyl)tyrosine (6) and solid-phase peptide synthesis techniques. Five OMT-containing peptides were prepared against the following SH2 domains: the PI-3 kinase C-terminal p85 SH2 domain (Ac-D-(L-OMT)-V-P-M-L-amide, 10, IC50 = 14.2 microM), the Src SH2 domain (Ac-Q-(L-OMT)-E-E-I-P-amide, 11, IC50 = 25 microM, and Ac-Q-(L-OMT)-(L-OMT)-E-I-P-amide, 14, IC50 = 23 microM), the Grb2 SH2 domain (Ac-N-(L-OMT)-V-N-I-E-amide, 12, IC50 = 120 microM), and the N-terminal SH-PTP2 SH2 domain (Ac-L-N-(L-OMT)-I-D-L-D-L-V-amide, 13, IC50 = 22.0 microM). These results show that peptides 10, 11, 13, and 14 have reasonable affinity for their respective SH2 domains, with the IC50 value for the SH-PTP2 SH2 domain-directed peptide 13 being equivalent to that previously observed for the corresponding F2Pmp-containing peptide. OMT may afford a new structural starting point for the development of novel and useful SH2 domain inhibitors.

Amino Acid Sequence↗
PubMed1995

Protein-tyrosine phosphatase inhibition by a peptide containing the phosphotyrosyl mimetic, L-O-malonyltyrosine.

Peptides containing phosphonate based non-hydrolyzable phosphotyrosyl (pTyr) mimetics previously have been shown to be competitive inhibitors of protein-tyrosine phosphatases (PTPs). These agents suffer from low cellular penetration which is partially attributable to ionization of the phosphonate group at physiological pH. We have developed the non-phosphorus containing pTyr mimetic, L-O-malonyltyrosine (L-OMT) and herein demonstrate using a PTP 1B enzyme assay that it is superior to phosphonomethyl phenylalanine (Pmp) as a pTyr mimetic when incorporated into the hexamer peptide Ac-D-A-D-E-X-L-amide (X = D,L-Pmp, IC50 = 200 microM; X = L-OMT, IC50 = 10 microM). Prodrug protection of L-OMT as its carboxylic acid diester could potentially increase cellular penetration, thereby making this a valuable reagent for cellular studies.

Amino Acid Sequence↗
PubMed1995

Conformationally constrained phosphotyrosyl mimetics designed as monomeric Src homology 2 domain inhibitors.

Inhibitors of specific src homology 2 (SH2) domain binding interactions could potentially afford new therapeutic approaches toward a variety of diseases, including several cancers. To date SH2 domain inhibitors have been confined to small phosphotyrosyl (pTyr)-containing peptides that appear to bind along the surface of SH2 domains with specific recognition features protruding into the protein. Among these protrusions is the pTyr residue itself, which is inserted into a well-formed binding pocket. In the present study monomeric pTyr mimetics were prepared having key aspects of their structure constrained to conformations of the bound pTyr residue observed in the previously reported X-ray structure of a pTyr-peptide bound to the Lck SH2 domain. The resulting constrained pTyr mimetics were examined for inhibitory potency in six SH2 domain constructs: Lck, Src, Grb2, and the C-terminal SH2 domains of PLC gamma (PLC gamma-C) and the p85 subunit of PI-3 kinase (p85-C), as well as the N-terminal SH2 domain of SH PTP2. Although inhibition constants were in the millimolar range, it was observed that capping pTyr as its N alpha-acetyl carboxamide [(L)-1] provided a roughly 2-3-fold increase in potency relative to free pTyr. Diastereomeric indanylglycine-based analogues (+/-)-3a,b were essentially inactive. Of note was methanobenzazocine (+/-)-2. While being racemic and a partial pTyr structure, this analogue retained full binding potency of the enantiomerically pure N alpha-acetyl pTyr amide (L)-1. Modification and elaboration of 2 could potentially result in small molecule inhibitors having greater potency.

Amino Acid Sequence↗
PubMed1995

Inhibitory effects of medroxyprogesterone acetate (MPA) and the pure antiestrogen EM-219 on estrone (E1)-stimulated growth of dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in the rat.

Estrogens are well known to play a predominant role in promoting the growth of DMBA-induced mammary tumors in the rat. Estrone (E1), a steroid having weak estrogenic activity, is one of most important estrogens in post-menopausal women, where it is converted into the potent estrogen estradiol (E2) by 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) in many peripheral tissues, including the mammary gland. In this report, we have studied the effect of a new antiestrogen (EM-219) (N-butyl, N-methyl-11-(3', 17'beta-dihydroxy-17'alpha-ethinyl-estra-1'3'5'(10'), 14'-tetraen-7'alpha-yl) undecanamide) on E1-stimulated growth of DMBA-induced mammary tumors and compared its effect with that of medroxyprogesterone acetate (MPA) alone or in combination. After 18 days, ovariectomy (OVX) reduced total tumor area to 29.6 +/- 7.1% of the original size, while E1 (1.0 microgram, twice daily) caused a 139 +/- 21% increase in tumor size in OVX animals. MPA (1.5 mg, twice daily) partially reversed the stimulatory effect of E1 to 66.0 +/- 9.0%, while the antiestrogen EM-219 (40 micrograms, twice daily) decreased tumor size to 70.0 +/- 10%. Combination of these two compounds led to a further inhibition of tumor size to 30.7 +/- 7.4% of the value found in OVX animals treated with E1. Tumor E2 levels decreased from 1688 +/- 155 pmoles/kg tissue in OVX animals receiving E1 to 709 +/- 92, 1347 +/- 98, and 184 +/- 11 pmoles/kg tissue in MPA-, EM-219-, and MPA+EM-219-treated OVX-E1 animals, respectively. Treatment of OVX animals with E1 increased by 69% the reductive activity of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) while MPA abolished completely this effect of E1. In the oxidative direction, treatment with E1, E1 + MPA, or E1 + EM-219 had minimal or no significant effect on the activity of 17 beta-HSD (vs OVX), while the combined treatment with MPA+EM-219 induced a 2-fold increase in 17 beta-HSD activity, thus leading to an increased conversion of E2 into E1. The present data show that combination of the pure antiestrogen EM-219 with MPA exerts a greater reduction in DMBA-induced mammary tumor growth and intratumoral E2 levels stimulated by E1 than either compound used alone. This interactive effect of the antiestrogen and MPA could at least partially be related to the increased inactivation of E2 into E1.(ABSTRACT TRUNCATED AT 400 WORDS)

17-Hydroxysteroid Dehydrogenases↗
PubMed1995

Dietary protein quality alters ornithine decarboxylase activity but not vitamin B-6 nutritional status in rats.

Weanling male rats were fed diets that varied in protein quality (casein or wheat gluten) and vitamin B-6 (0.0, 0.5, 1.0 and 1.5 mg pyridoxine HCl/kg diet) to test the hypotheses that low protein quality would depress vitamin B-6 nutritional status and that activity of ornithine decarboxylase (ODC) would be a sensitive functional indicator of vitamin B-6 nutritional status. The wheat gluten diet depressed body weight gain approximately 17% at higher vitamin B-6 levels, as expected. However, vitamin B-6 nutritional status was not worse in gluten-fed compared with casein-fed groups, as evidenced by static measures (B-6 vitamer concentrations in plasma and tissues) and a functional indicator (tryptophan load test). The activity of ODC (holo- and total) in liver, kidney and small intestine did not vary significantly at the three higher levels of vitamin B-6 intake. In groups fed casein, total ODC activity in these tissues was two- to fivefold higher in rats fed diets containing 0.0 mg vitamin B-6/kg compared with higher B-6 levels, without corresponding differences in ODC mRNA abundance in liver and kidney. Concentrations of B-6 vitamers (except pyridoxal phosphate in plasma) increased linearly with dietary vitamin B-6 in plasma, liver, kidney and intestine. These data suggest that low quality protein fed as wheat gluten suppresses growth but not vitamin B-6 nutritional status, and that ODC activity is not a sensitive functional indicator of marginal vitamin B-6 status.

Animals↗
PubMed1995

[A new zoonosis--investigation of Gardnerella vaginalis disease of fox. IV. Study of dot-ELISA for the detection of serum antibody of Gardnerella vaginalis disease of fox].

192 Gardnerella vaginalis antibody positive sera from artifically infected foxes, immunized foxes and foxes that the bacterial examination were positive were analysed by the established Dot-ELISA. The results showed that 187/192 were positive, the positive rate was 97.3%. Block and cross tests showed that the method was specific. The method was 28.1 times sensitive as PAT and 5.5 times sensitive as MAT respectively. The repeatability of the test was good and the positive coincidence rate among the three techniques was 100%.

Animals↗
PubMed1995

[Amplifying Helicobacter pylori's urease gene by nested polymerase chain reaction].

By using nested polymerase chain reaction (PCR) composed of three primers that derived from Helicobacter pylori's (Hp) urease gene region, we have not only successfully amplified control Hp and 214 clinic samples but also studied deeply preparation of the sample, composition of PCR reaction liquid and circulatory mental conditions of the PCR. So this method shortens the operation time, simplifies processes and reduces costs. Compared with urease test (54%) and Warthin-Starry silver stained test (50%), ever used the positive rate of PCR is the highest (61%), so our method is more specific, sensitive, simple, rapid and accurate, and could be applied to the routine clinical detection.

Adolescent↗