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Vincent Poon

Publications and source records attributed to Vincent Poon.

8 recordsLinked to original sources
PubMed2006

Polyvalent inhibitors of anthrax toxin that target host receptors.

Resistance of pathogens to antimicrobial therapeutics has become a widespread problem. Resistance can emerge naturally, but it can also be engineered intentionally, which is an important consideration in designing therapeutics for bioterrorism agents. Blocking host receptors used by pathogens represents a powerful strategy to overcome this problem, because extensive alterations to the pathogen may be required to enable it to switch to a new receptor that can still support pathogenesis. Here, we demonstrate a facile method for producing potent receptor-directed antitoxins. We used phage display to identify a peptide that binds both anthrax-toxin receptors and attached this peptide to a synthetic scaffold. Polyvalency increased the potency of these peptides by >50,000-fold in vitro and enabled the neutralization of anthrax toxin in vivo. This work demonstrates a receptor-directed anthrax-toxin inhibitor and represents a promising strategy to combat a variety of viral and bacterial diseases.

Acetylation↗
PubMed2006

Statistical pattern matching facilitates the design of polyvalent inhibitors of anthrax and cholera toxins.

Numerous biological processes involve the recognition of a specific pattern of binding sites on a target protein or surface. Although ligands displayed by disordered scaffolds form stochastic rather than specific patterns, theoretical models predict that recognition will occur between patterns that are characterized by similar or "matched" statistics. Endowing synthetic biomimetic structures with statistical pattern matching capabilities may improve the specificity of sensors and resolution of separation processes. We demonstrate that statistical pattern matching enhances the potency of polyvalent therapeutics. We functionalized liposomes with an inhibitory peptide at different densities and observed a transition in potency at an interpeptide separation that matches the distance between ligand-binding sites on the heptameric component of anthrax toxin. Pattern-matched polyvalent liposomes inhibited anthrax toxin in vitro at concentrations four orders of magnitude lower than the corresponding monovalent peptide, and neutralized this toxin in vivo. Statistical pattern matching also enhanced the potency of polyvalent inhibitors of cholera toxin. This facile strategy should be broadly applicable to the detection and neutralization of toxins and pathogens.

Animals↗
PubMed2006

Synthesis of polyvalent inhibitors of controlled molecular weight: structure-activity relationship for inhibitors of anthrax toxin.

We describe a novel method to synthesize activated polymers of controlled molecular weight and apply this method to investigate the relationship between the structure and activity of polyvalent inhibitors of anthrax toxin. In particular, we observe an initial sharp increase in potency with increasing ligand density, followed by a plateau where potency is independent of ligand density. Our simple strategy for designing polyvalent inhibitors of controlled molecular weight and ligand density will be broadly applicable for designing inhibitors for a variety of pathogens and toxins, and for elucidating structure-activity relationships in these systems. Our results also demonstrate a role for kinetics in influencing inhibitory potency in polyvalent systems. Finally, our work presents a synthetic route to polyvalent inhibitors that are more structurally defined and effective in vivo. This control over inhibitor composition will be generally useful for the optimization of inhibitor potency and pharmacokinetics, and for the eventual application of these molecules in vivo.

Animals↗
PubMed2005

Insulin regulates the membrane arrival, fusion, and C-terminal unmasking of glucose transporter-4 via distinct phosphoinositides.

Insulin increases glucose uptake into muscle via glucose transporter-4 (GLUT4) translocation to the cell membrane, but the regulated events in GLUT4 traffic are unknown. Here we focus on the role of class IA phosphatidylinositol (PI) 3-kinase and specific phosphoinositides in the steps of GLUT4 arrival and fusion with the membrane, using L6 muscle cells expressing GLUT4myc. To this end, we detected the availability of the myc epitope at the cell surface or intravesicular spaces and of the cytosol-facing C-terminal epitope, in cells and membrane lawns derived from them. We observed the following: (a) Wortmannin and LY294002 at concentrations that inhibit class IA PI 3-kinase reduced but did not abate the C terminus gain, yet the myc epitope was unavailable for detection unless lawns or cells were permeabilized, suggesting the presence of GLUT4myc in docked, unfused vesicles. Accordingly, GLUT4myc-containing vesicles were detected by immunoelectron microscopy of membranes from cells pretreated with wortmannin and insulin, but not insulin or wortmannin alone. (b) Insulin caused greater immunological availability of the C terminus than myc epitopes, suggesting that C terminus unmasking had occurred. Delivering phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P(3)) to intact cells significantly increased lawn-associated myc signal without C terminus gain. Conversely, phosphatidylinositol 3-phosphate (PI3P) increased the detection of C terminus epitope without any myc gain. We propose that insulin regulates GLUT4 membrane arrival, fusion, and C terminus unmasking, through distinct phosphoinositides. PI(3,4,5)P(3) causes arrival and fusion without unmasking, whereas PI3P causes arrival and unmasking without fusion.

Androstadienes↗
PubMed2003

Pastoral counseling among Chinese churches: a Canadian study.

This article reports the results of a survey of Canadian Chinese pastors (N 20) regarding their experiences and attitudes related to pastoral counseling. It identifies common concerns encountered during pastoral counseling, as well as key areas of church concerns. Results of the survey indicate that pastoral counseling may be more important than is currently recognized by Chinese pastors, particularly in key areas of marriage, family life, and general relationship issues. The authors discuss possible implications of the survey relative to training and equipping Chinese pastors to engage more in pastoral counseling as an integral part of their parish ministry.

Adult↗
PubMedDate not supplied

Synthesis of potent inhibitors of anthrax toxin based on poly-L-glutamic acid.

We report the synthesis of biodegradable polyvalent inhibitors of anthrax toxin based on poly-L-glutamic acid (PLGA). These biocompatible polyvalent inhibitors are at least 4 orders of magnitude more potent than the corresponding monovalent peptides in vitro and are comparable in potency to polyacrylamide-based inhibitors of anthrax toxin assembly. We have elucidated the influence of peptide density on inhibitory potency and demonstrated that these inhibitory potencies are limited by kinetics, with even higher activities seen when the inhibitors are preincubated with the heptameric receptor-binding subunit of anthrax toxin prior to exposure to cells. These polyvalent inhibitors are also effective at neutralizing anthrax toxin in vivo and represent attractive leads for designing biocompatible anthrax therapeutics.

Absorbable Implants↗
PubMedDate not supplied

Functional characterization of peptide-based anthrax toxin inhibitors.

We have identified an optimized peptide inhibitor that can be used to develop potent anthrax toxin therapeutics. Anthrax toxin, an essential virulence factor of Bacillus anthracis, elicits many of the symptoms associated with the disease, and is responsible for death. The toxin is composed of a cell-binding component, protective antigen, and two enzymatic components, edema factor and lethal factor. The three proteins are secreted individually by the bacterium and then assemble into functional complexes on the surface of mammalian cells. These complexes are endocytosed, and the enzymatic components are translocated into the cytosol, where they exert their activities. We screened a phage display library for peptides that can bind the heptameric cell-binding subunit of anthrax toxin, and identified a novel peptide that can block toxin assembly. We made a series of mutant peptides and attached these peptides to polymer backbones to assess their inhibitory activities in vitro. This series of truncated peptide mutants was used to identify a minimal peptide sequence, TYWWLD, that can be used to develop potent polyvalent inhibitors of anthrax toxin.

Amino Acid Sequence↗