Preparative purification of polyethylene glycol derivatives with polystyrene-divinylbenzene beads as chromatographic packing

A clear and powerful chromatographic approach to purify polyethylene glycol derivatives at a preparative scale was reported, which was based on the polystyrene-divinylbenzene beads with ethanol/water as eluants. The validity of this method was verified with the reaction mixture of mPEG-Glu and mPEG propionaldehyde diethylacetal (ALD-PEG) as the model. The target products were one-step achieved with the purity of >99% on the polymer resins column at gram scale. The method developed was free from such disadvantages as utility of toxic solvent and narrow application scope, which was combined with conventional approaches. The method developed provided an appealing and attractive alternative methods for purification of PEG derivatives at a preparative scale.     

Simple and sensitive bacterial quantification by a flow-based kinetic exclusion fluorescence immunoassay

A flow-based immunoassay system utilizing secondary-antibody coated microbeads and Cy5-secondary antibody for signal production was successfully developed to quantitate target bacteria with a kinetic exclusion assay (KinExA 3000 Instrument). It directly measured the concentration of unliganded antibody separated from the equilibrated mixture of antibody and bacteria through a 0.2 microm polyethersulfone membrane, enabling it to quantify the concentration of bacteria. The novel method demonstrated the qualities of rapidness, sensitivity, high accuracy and reproducibility, and ease to perform. Detection of Pseudomonas aeruginosa and Staphylococcus aureus was accomplished with low detection limits of 4.10 x 10(6) and 5.20 x l0(4)cells/mL, respectively, with an assay time of less than 15 min. The working ranges for quantification were 4.10 x l0(6) to 1.64 x l0(10)cells/mL for P. aeruginosa, and 5.20 x l0(4) to 1.04 x l0(9)cells/mL for S. aureus. It yielded an assay with at least 10-fold greater sensitivity than ELISA and could correctly assess the concentration of predominant bacterium spiked in the mixture of P. aeruginosa and S. aureus. With this reliable platform, the average amount of antibody bound by one cell in the maximum capability could be further provided: (1.6-2.5) x l0(5) antibodies for one P. aeruginosa cell and (2.2-2.7) x l0(8) antibodies for one S. aureus cell. The KinExA system is flexible to determine different kinds of bacteria conveniently by using anti-mouse IgG as the same immobilizing agent. However, a higher specificity of the antibodies to the target bacteria will be required for the use of this system with higher detection sensitivity.     

Evaluation of two- and three-dimensional streptavidin binding platforms for surface plasmon resonance spectroscopy studies of DNA hybridization and protein-DNA binding

Surface plasmon resonance (SPR) spectroscopy has been used to study DNA assembly, DNA hybridization, and protein-DNA interactions on two streptavidin (SA) sensor chips. On one chip, SA molecules are immobilized on a biotin-exposed surface, forming an ordered two-dimensional (2D) SA monolayer. The other chip, BIAcore's SA chip, contains SA molecules immobilized within a three-dimensional (3D) carboxylated dextran matrix. Compared to the 2D chip, the 3D SA matrix allows for a slower immobilization rate of biotinylated DNA due to diffusion limitation in the dextran matrix, but with twice the amount of the immobilized DNA due to the greater number of reactive sites, which in turn enables a higher sensitivity for DNA hybridization detection. Interestingly, having a greater DNA probe dispersion in the 3D matrix does not induce a higher DNA hybridization efficiency. In a study of protein binding to immobilized DNA (estrogen receptor to estrogen response elements), aiming at assessing the DNA sequence dependent protein binding behavior, the 2D and 3D chips produce different binding characteristics. On the 2D chip, the protein binding exhibits a better selectivity to the specific sequences, regardless of binding stringency (e.g. salt concentration), whereas on the 3D chip, the liquid handling system needs to be optimized in order to minimize transport limitations and to detect small affinity differences. Through this study we demonstrate that the physicochemical structure of SPR chips affects the apparent binding behaviors of biomolecules. When interpreting SPR binding curves and selecting a sensor chip, these effects should be taken into account.     

Inhibition of human and rat 11beta-hydroxysteroid dehydrogenase type 1 by 18beta-glycyrrhetinic acid derivatives

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) plays an important role in regulating the cortisol availability to bind to corticosteroid receptors within specific tissue. Recent advances in understanding the molecular mechanisms of metabolic syndrome indicate that elevation of cortisol levels within specific tissues through the action of 11β-HSD1 could contribute to the pathogenesis of this disease. Therefore, selective inhibitors of 11β-HSD1 have been investigated as potential treatments for metabolic diseases, such as diabetes mellitus type 2 or obesity. Here we report the discovery and synthesis of some 18β-glycyrrhetinic acid (18β-GA) derivatives (2–5) and their inhibitory activities against rat hepatic11β-HSD1 and rat renal 11β-HSD2. Once the selectivity over the rat type 2 enzyme was established, these compounds’ ability to inhibit human 11β-HSD1 was also evaluated using both radioimmunoassay (RIA) and homogeneous time resolved fluorescence (HTRF) methods. The 11-modified 18β-GA derivatives 2 and 3 with apparent selectivity for rat 11β-HSD1 showed a high percentage inhibition for human microsomal 11β-HSD1 at 10 μM and exhibited IC₅₀ values of 400 and 1100 nM, respectively. The side chain modified 18β-GA derivatives 4 and 5, although showing selectivity for rat 11β-HSD1 inhibited human microsomal 11β-HSD1 with IC₅₀ values in the low micromolar range.     

AtNHX8, a member of the monovalent cation: proton antiporter-1 family in Arabidopsis thaliana, encodes a putative Li/H antiporter

The Arabidopsis monovalent cation:proton antiporter-1 (CPA1) family includes eight members, AtNHX1-8. AtNHX1 and AtNHX7/SOS1 have been well characterized as tonoplast and plasma membrane Na+/H+ antiporters, respectively. The proteins AtNHX2-6 have been phylogenetically linked to AtNHX1, while AtNHX8 appears to be related to AtNHX7/SOS1. Here we report functional characterization of AtNHX8. AtNHX8 T-DNA insertion mutants are hypersensitive to lithium ions (Li+) relative to wild-type plants, but not to the other metal ions such as sodium (Na+), potassium (K+) and caesium (Cs+). AtNHX8 overexpression in a triple-deletion yeast mutant AXT3 that exhibits defective Na+/Li+ transport specifically suppresses sensitivity to Li+, but does not affect Na+ sensitivity. Likewise, AtNHX8 overexpression complemented sensitivity to Li+, but not Na+, in sos1-1 mutant seedlings, and increased Li+ tolerance of both the sos1-1 mutant and wild-type seedlings. Results of Li+ and K+ measurement of loss-of-function and gain-of-function mutants indicate that AtNHX8 may be responsible for Li+ extrusion, and may be able to maintain K+ acquisition and intracellular ion homeostasis. Subcellular localization of the AtNHX8-enhanced green fluorescent protein (EGFP) fusion protein suggested that AtNHX8 protein is targeted to the plasma membrane. Taken together, our findings suggest that AtNHX8 encodes a putative plasma membrane Li+/H+ antiporter that functions in Li detoxification and ion homeostasis in Arabidopsis.     

Phosphatidylinositol 4,5-bisphosphate is important for stomatal opening

Previously, we demonstrated that a protein that binds phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] inhibits both light-induced stomatal opening and ABA-induced stomatal closing. The latter effect is due to a reduction in free PtdIns(4,5)P(2), decreasing production of inositol 1,4,5-trisphosphate and phosphatidic acid by phospholipases C and D. However, it is less clear how PtdIns(4,5)P(2) modulates stomatal opening. We found that in response to white light irradiation, the PtdIns(4,5)P(2)-binding domain GFP:PLCdelta1PH translocated from the cytosol into the plasma membrane. This suggests that the level of PtdIns(4,5)P(2) increases at the plasma membrane upon illumination. Exogenously administered PtdIns(4,5)P(2) substituted for light stimuli, inducing stomatal opening and swelling of guard cell protoplasts. To identify PtdIns(4,5)P(2) targets we performed patch-clamp experiments, and found that anion channel activity was inhibited by PtdIns(4,5)P(2). Genetic analyses using an Arabidopsis PIP5K4 mutant further supported the role of PtdIns(4,5)P(2) in stomatal opening. The reduced stomatal opening movements exhibited by a mutant of Arabidopsis PIP5K4 (At3g56960) was countered by exogenous application of PtdIns(4,5)P(2). The phenotype of reduced stomatal opening in the pip5k4 mutant was recovered in lines complemented with the full-length PIP5K4. Together, these data suggest that PIP5K4 produces PtdIns(4,5)P(2) in irradiated guard cells, inhibiting anion channels to allow full stomatal opening.     

Spermatinamine, the first natural product inhibitor of isoprenylcysteine carboxyl methyltransferase, a new cancer target

Isoprenylcysteine methyltransferase (Icmt) catalyzes the carboxyl methylation of oncogenic proteins in the final step of a series of post-translational modifications. The inhibition of Icmt provides an attractive and novel anticancer target. A natural product high-throughput screening campaign was conducted to discover inhibitors of Icmt. The Australian marine sponge, Pseudoceratina sp., yielded spermatinamine, a novel alkaloid with a bromotyrosyl-spermine-bromotyrosyl sequence, as the bioactive constituent. Its structure was determined by 1D and 2D NMR spectroscopy. Spermatinamine is the first natural product inhibitor of Icmt.     

Synthesis and biological evaluation of cinnamyl compounds as potent antitumor agents

A series of cinnamyl compounds related to 2'-hydroxycinnamaldehyde were synthesized and their antitumor effects against human cancer cells evaluated. Hydroxylamine derivative 6 inhibited the growth of human cancer cells and human colon tumor xenograft in nude mice. Its antitumor effects belong to the induction of apoptosis and arresting cell cycle at G(2)/M phase, which is confirmed by detection of apoptosis markers and cell cycle analysis.     

The discovery of highly selective erbB2 (Her2) inhibitors for the treatment of cancer

The synthesis and biological evaluation of potent and selective inhibitors of the erbB2 kinase is presented. Based on the 4-anilinoquinazoline chemotype, the syntheses of several new series of erbB2 inhibitors are described with quinazoline and pyrido[4,3-d]pyrimidine cores. The vast majority of these compounds are found to be >100x selective over the closely related EGFR kinase. Two lead compounds are further shown to have low clearance and moderate bioavailability in rat.