Soluble adamantyl glycosphingolipid analogs as probes of glycosphingolipid function

Despite the extensive structural characterization of glycosphingolipids (GSLs), their functions in cell physiology and pathobiology remain elusive. This is largely owing to the fact that they are difficult to handle, being insoluble in aqueous media, and that no one gene alone determines their synthesis. The heterogeneity of the lipid moiety provides a further confounding factor. GSLs are central components within lipid rafts, which are major foci for transmembrane signaling and interactions between eukaryotic cells and microbial pathogens. GSL receptor function often requires the lipid moiety, and lipid-free sugar analogs are ineffective inhibitors. In order to overcome some of these problems, we have synthesized adamantyl GSL analogs which, in part, mimic GSL membrane receptor function in solution. These compounds are made by replacing the endogenous fatty acid with an adamantan frame. This rigid hydrophobic structure surprisingly increases the water solubility of the conjugate and retains receptor function. These GSL mimics provide probes to study GSL receptor function within cells. They compete with native GSLs for ligand binding and are taken up by cells to potentially alter GSL-mediated interaction. We are focused on two derivatives, adamantyl globotriaosyl ceramide and adamantyl sulfogalactosyl ceramide, and have used these analogs to probe GSL function in microbial pathology and hsp70 function. This chapter describes the syntheses and uses of these mimics.

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.

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.

Overexpression of vimentin: role in the invasive phenotype in an androgen-independent model of prostate cancer

The androgen-sensitive LNCaP prostate cancer cell line is less invasive than hormone-insensitive lines. CL1, an aggressive, hormone-insensitive LNCaP subline derived by continuous passaging in hormone-depleted medium, was compared with the parental cell line by cDNA microarray analysis. The gene coding for the intermediate filament protein vimentin was found to be highly up-regulated in the CL1 subline. This difference was confirmed by Northern and Western blots and visualized by immunofluorescence microscopy. To assess the contribution of vimentin to the invasive phenotype, LNCaP cells were stably transfected to overexpress vimentin, and the CL1 cells were transfected with vimentin antisense construct. The invasiveness of the transfected cells was tested using an in vitro invasion assay. We were able to demonstrate that decreasing vimentin expression in the constitutively vimentin-expressing CL1 cells led to a significant decrease in their invasiveness but that forcing expression of vimentin in the LNCaP cells did not augment their invasiveness. These findings imply that vimentin expression contributes to the invasive phenotype but cannot confer it alone.