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Biomedical subjects

K Cheng

Publications and source records attributed to K Cheng.

At least 55 records · Page 3Linked to original sources
PubMed1999

Identification and initial structure-activity relationships of a novel non-peptide quinolone GnRH receptor antagonist.

Screening of the Merck sample collection for non-peptide compounds with binding affinity for the rat GnRH receptor led to the identification of the substituted quinolone (1) as a lead compound in the search for a non-peptide GnRH receptor antagonist. Substantial improvements in potency (approximately 300 fold) were achieved by addition of an alkyl amine at the 4-position, a 3,5-dimethylphenyl group at the 3-position and 6-nitro-7-chloro-substitution of the 1 H-quinolone core.

Animals↗
PubMed1999

Investigation of the 4-O-alkylamine substituent of non-peptide quinolone GnRH receptor antagonists.

Synthesis and in vitro activity of the enantiomers of quinolone GnRH antagonist (+/-)-1 are reported. Chiral amino alcohols were prepared from the appropriate cyclic D- or L-amino acids by the Amdt-Eistert homologation followed by reduction of the resulting esters. Incorporation of these pharmacophores was achieved via a novel Mitsunobu alkylation of 4-hydroxyquinolones. The key amine pharmacophore for binding to the rat GnRH receptor was most active in the S-configuration. Ring size was not important for potency with 4, 5, 6, and 7-membered ring amines exhibiting similar potency.

Animals↗
PubMed1999

Synthesis and biological activities of spiroheterocyclic growth hormone secretagogues.

The synthesis and biological activities of a series of spiroheterocyclic growth hormone secretagogues are reported. Modification of the spiroindane part-structure of the prototypal secretagogue L-162,752 revealed that the spiroindane could be replaced with spirobenzodihydrothiophen derivatives to enhance not only in vitro potency but also oral activity. In this study non-aromatic D-2-amino-4-cyclohexylbutanoic analogs (8a-8d) were also identified to be active secretagogues.

Animals↗
PubMed1999

Bcl-xL blocks activation of related adhesion focal tyrosine kinase/proline-rich tyrosine kinase 2 and stress-activated protein kinase/c-Jun N-terminal protein kinase in the cellular response to methylmethane sulfonate.

The stress-activated protein kinase/c-Jun N-terminal protein kinase (JNK) is induced in response to ionizing radiation and other DNA-damaging agents. Recent studies indicate that activation of JNK is necessary for induction of apoptosis in response to diverse agents. Here we demonstrate that methylmethane sulfonate (MMS)-induced activation of JNK is inhibited by overexpression of the anti-apoptotic protein Bcl-xL, but not by caspase inhibitors CrmA and p35. By contrast, UV-induced JNK activity is insensitive to Bcl-xL. The results demonstrate that treatment with MMS is associated with an increase in tyrosine phosphorylation of related adhesion focal tyrosine kinase (RAFTK)/proline-rich tyrosine kinase 2 (PYK2), an upstream effector of JNK and that this phosphorylation is inhibited by overexpression of Bcl-xL. Furthermore, overexpression of a dominant-negative mutant of RAFTK (RAFTK K-M) inhibits MMS-induced JNK activation. The results indicate that inhibition of RAFTK phosphorylation by MMS in Bcl-xL cells is attributed to an increase in tyrosine phosphatase activity in these cells. Hence, treatment of Bcl-xL cells with sodium vanadate, a tyrosine phosphatase inhibitor, restores MMS-induced activation of RAFTK and JNK. These findings indicate that RAFTK-dependent induction of JNK in response to MMS is sensitive to Bcl-xL, but not to CrmA and p35, by a mechanism that inhibits tyrosine phosphorylation and thereby activation of RAFTK. Taken together, these findings support a novel role for Bcl-xL that is independent of the caspase cascade.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1999

Potent, orally bioavailable somatostatin agonists: good absorption achieved by urea backbone cyclization.

Backbone cyclization of urea-based somatostatin agonists resulted in novel, orally bioavailable agonists. Binding assays confirmed that the resulting conformationally constrained cyclic ureas retained the potency of their acyclic counterparts. SAR studies subsequently led to highly potent analogs, selective for receptor subtype 2, and having good oral bioavailability.

Administration, Oral↗
PubMed1999

The voltammetric behavior of bone marrow of leukaemia and its clinical application.

The electrochemical voltammetric behavior of bone marrow of leukaemia has been investigated by a self-devised cytosensing system. The two anodic peaks of erythrocytes (red blood cells, RBC) in bone marrow of leukaemia appeared at 0.73 +/- 0.03 and 0.83 +/- 0.02V vs. SCE, respectively, on the first scan. The anodic peak of leukocytes (white blood cells, WBC) appeared at 0.32 +/- 0.03V vs. SCE. The anodic peak of RBC at 0.83V disappeared when the patients were cured. The experimental results show that the voltammetric behavior of erythrocytes is in constant contact with the initial stage of leukaemia. The cyclic voltammetric behavior of 40 cases of leukaemia including acute myeloid leukaemia (AML) and chronic myeloid leukaemia (CML) and 10 cases of healthy volunteer peripheral blood was studied. The cyclic voltammetric behavior of erythrocytes may provide a simple and specific marker for diagnosis of leukaemia.

Bone Marrow↗
PubMed1999

Studies of hydroxypropyl methylcellulose donut-shaped tablets.

Simple uncoated compressed tablets with a central hole (donut shape) or multihole tablets were prepared. Theophylline and diltiazem hydrochloride were used as model drugs to investigate in vitro drug release from donut-shaped tablets. The effects of hole size, the number of holes, drug solubility, and stirring rate on release kinetics were investigated. As for the donut-shaped tablets, the duration of zero-order drug release could be up to 80-90%. When the hole size was increased, the release rate increased, and the duration of linear drug release was longer. The durations of linear drug release of two-hole and three-hole tablets were longer than that of the single-hole tablets. As the drug solubility increased, the duration of linear drug release was shortened. However, three stirring rates (50 rpm, 100 rpm, 150 rpm) had little effect on the drug release.

Diltiazem↗
PubMed1999

[Extensive transbasal approach for removal of tumours in the nasal, sphenoid and clival regions].

OBJECTIVE: To improve operative results of removal of the tumors in midline cranial base and the reconstruction of defect at frontal base through modification of the operative approach and techniques. METHODS: Extensive transbasal approach was used in 15 patients with tumours in the nasal, sphenoid and clival regions. RESULTS: The tumor was removed in 10 patients, near totally removed in 4 and partial removed in 1. The operative results of all patients were excellent except an elderly patient with mild operative morbidity. CONCLUSIONS: The procedure we used expand the operative indications for the tumors situated at the midline cranial base and improve the operative results. The procedure has advantages such as wide operative space, reliable reconstruction of the frontal base, and no severe complications.

Adult↗
PubMed1999

[Random amplified polymorphic DNA analysis on Curcuma wenuujin and C. sichuanensis].

OBJECTIVE: To discuss the problem of classifying Curcuma for Medical purposes. METHOD: RAPD was used to detect the DNA polymorphism within and among Curcuma wenyujin, C. sichuanensis and C. aromatica. RESULT: It is hard to differentiate between C. wenyujin and C. sichuanensis from the DNA level. The relationship between C. wenyujin and C. aromatica was also analyzed. CONCLUSION: Based on the morphological and chemical data, it is suggested that these two species should be combined into one and that classification based on peduncle central or peduncle lateral may not be right. This method will help to some degree to solve the problem of certifying the medicinal plant Curcuma.

Curcuma↗
PubMed1998

Synthesis and biological activities of potent peptidomimetics selective for somatostatin receptor subtype 2.

A series of nonpeptide somatostatin agonists which bind selectively and with high affinity to somatostatin receptor subtype 2 (sst2) have been synthesized. One of these compounds, L-054,522, binds to human sst2 with an apparent dissociation constant of 0.01 nM and at least 3,000-fold selectivity when evaluated against the other somatostatin receptors. L-054,522 is a full agonist based on its inhibition of forskolin-stimulated adenylate cyclase activity in Chinese hamster ovary-K1 cells stably expressing sst2. L-054,522 has a potent inhibitory effect on growth hormone release from rat primary pituitary cells and glucagon release from isolated mouse pancreatic islets. Intravenous infusion of L-054,522 to rats at 50 microgram/kg per hr causes a rapid and sustained reduction in growth hormone to basal levels. The high potency and selectivity of L-054, 522 for sst2 will make it a useful tool to further characterize the physiological functions of this receptor subtype.

Animals↗
PubMed1998

Mutation of a Shc binding site tyrosine residue in ErbB3/HER3 blocks heregulin-dependent activation of mitogen-activated protein kinase.

The ErbB2 and ErbB3 proteins together constitute a functional coreceptor for heregulin (neuregulin). Heregulin stimulates the phosphorylation of both coreceptor constituents and initiates a variety of other signaling events, which include phosphorylation of the Shc protein. The role of Shc in heregulin-stimulated signal transduction through the ErbB2.ErbB3 coreceptor was investigated here. Heregulin was found to promote ErbB3/Shc association in NIH-3T3 cells expressing endogenous ErbB2 and recombinant ErbB3. A mutant ErbB3 protein was generated in which Tyr-1325 in a consensus Shc phosphotyrosine-binding domain recognition site was mutated to Phe (ErbB3-Y/F). This mutation abolished the association of Shc with ErbB3 and blocked the activation of mitogen-activated protein kinase by heregulin. Whereas heregulin induced mitogenesis in NIH-3T3 cells transfected with wild-type ErbB3 cDNA, this mitogenic response was markedly attenuated in NIH-3T3 cells transfected with the ErbB3-Y/F cDNA. These results showed a specific interaction of Shc with the ErbB3 receptor protein and demonstrated the importance of this interaction in the activation of mitogenic responses by the ErbB2. ErbB3 heregulin coreceptor complex.

3T3 Cells↗
PubMed1998

ErbB3 (HER3) interaction with the p85 regulatory subunit of phosphoinositide 3-kinase.

ErbB3 (HER3), a unique member of the ErbB receptor family, lacks intrinsic protein tyrosine kinase activity and contains six Tyr-Xaa-Xaa-Met (YXXM) consensus binding sites for the SH2 domains of the p85 regulatory subunit of phosphoinositide 3-kinase. ErbB3 also has a proline-rich sequence that forms a consensus binding site for the SH3 domain of p85. Here we have investigated the interacting domains of ErbB3 and p85 by a unique application of the yeast two-hybrid system. A chimaeric ErbB3 molecule containing the epidermal growth factor receptor protein tyrosine kinase domain was developed so that the C-terminal domain of ErbB3 could become phosphorylated in the yeast system. We also generated several ErbB3 deletion and Tyr-->Phe site-specific mutants, and observed that a single ErbB3 YXXM motif was necessary and sufficient for the association of ErbB3 with p85. The incorporation of multiple YXXM motifs into the ErbB3 C-terminus enabled a stronger ErbB3/p85 interaction. The proline-rich region of ErbB3 was not necessary for interaction with p85. However, either deletion or mutation of the p85 SH3 domain decreased the observed ErbB3/p85 association. Additionally an ErbB3/p85 SH3 domain interaction was detected by an assay in vitro. These results were consistent with a model in which pairs of phosphorylated ErbB3 YXXM motifs co-operate in binding to the tandem SH2 domains of p85. Although a contributing role for the p85 SH3 domain was suggested, the N- and C-terminal SH2 domains seemed to be primarily responsible for the high-affinity association of p85 and ErbB3.

Chimera↗
PubMed1998

Synthesis and biological activities of phenyl piperazine-based peptidomimetic growth hormone secretagogues.

A new class of potent, orally active phenyl piperazine-based GH secretagogues have been discovered from attempts to mimic the arrangement of the phenyl substituent in the spiroindanyl piperidine and spiroindoline sulfonamide privileged structures of 4 and 1, respectively. The best of these compounds, 18 (EC50 = 2.8 nM) is nearly as potent as MK-0677 for releasing GH from rat pituitary cells.

Animals↗
PubMed1998

A potent, orally bioavailable benzazepinone growth hormone secretagogue.

The identification of L-739,943 (8b), a potent, orally bioavailable benzolactam growth hormone secretagogue, is obtained from zwitterionic L-692,429 through modification of its amino acid side chain and replacement of the acidic 2'-tetrazole with the neutral and potency enhancing 2'-(N-methylaminocarbonylamino)methyl substituent. L-739,943 is orally active for the release of growth hormone in beagle dogs at doses as low as 0.5 mg/kg. Oral bioavailability in dogs of 8b is 24% at a dose of 2 mg/kg with a mean drug Cmax of 145 +/- 46 ng/mL. L-739,943 represents a significant breakthrough in terms of both potency and oral bioavailability as compared to the prototype benzolactam L-692,429.

Administration, Oral↗
PubMed1998

Tripeptide growth hormone secretagogues.

A series of C-terminus capped dipeptides and tripeptides was synthesized as growth hormone (GH) secretagogues. Among them, tripeptide Aib-D-Trp-D-homoPhe-OEt showed low nanomolar activity in the rat pituitary assay. Thus, we have demonstrated that the GH secretagogue activity of the hexa-hepta-GH releasing peptides can be mimicked at the tripeptide level.

Amino Acid Sequence↗