Molecular umbrella conjugate for the ocular delivery of siRNA.

The synthesis, computer modeling, and biological activity of an octawalled molecular umbrella short interfacing RNA (siRNA) conjugate is described. This molecular umbrella-siRNA conjugate exhibited mRNA knockdown activity in vitro in the absence of a transfection reagent. Evaluation of this molecular umbrella conjugate in vivo, using the rat eye via intravitreal injection, resulted in sequence specific mRNA knockdown in the retina with no obvious signs of toxicity, as judged by ophthalmic examination.

ß-Turn sequences promote stability of peptide substrates for kinases within the cytosolic environment.

A strategy was developed to extend the lifetime of an peptide-based substrate for Abl kinase in the cytosolic environment. Small ß-turn structures were added to the peptide's N-terminus to block entry into peptidase catalytic sites. The influence of the size of the ß-turn and two covalent cross-linking strategies on the rate of hydrolysis was assessed. The most peptidase-resistant substrate was degraded at a rate of 0.6 pmol mg(-1) s(-1) and possessed a half-life of 20.3 ± 1.7 min in a Baf/BCR-ABL cytosolic lysate, representing 16- and 40-fold improvements, respectively, over that of a control peptide lacking the ß-turn structure. Furthermore, the kcat/KM value of this peptide was 432 µM(-1) min(-1), a 1.25× increase over the unmodified control, verifying that the added ß-turn did not hinder the substrate properties of the peptide. This improved peptide was microinjected into single Baf/BCR-ABL cells and substrate phosphorylation measured. Zero to forty percent of the peptide was phosphorylated in the single cells. In contrast, when the control peptide without a ß-turn was loaded into cells, the peptide was too rapidly degraded to detect phosphorylation. This work demonstrates that small ß-turn structures can render peptides more resistant to hydrolysis while retaining substrate efficacy and shows that these stabilized peptides have the potential to be of high utility in single-cell enzyme assays.

Stimulated release of cholesterol from liposomal membranes by a PEGylated phospholipid.

PEGylated phospholipids are commonly used to increase the blood-circulation time of liposomes by providing a steric barrier around them. This paper documents a fundamentally new property of these lipids-an ability to stimulate the release of cholesterol from phospholipid membranes. Evidence for such stimulation has been obtained by measuring the transport of dehydroergosterol (DHE), a fluorescent simulant of cholesterol, from donor liposomes made from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000 (DSPE-PEG(2000)), and DHE to acceptor liposomes made from POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), and cholesterol. The potential of PEGylated lipids to serve as novel cholesterol-lowering agents is briefly discussed.

A molecular umbrella approach to the intracellular delivery of small interfering RNA.

A series of diwalled and tetrawalled molecular umbrellas have been synthesized using cholic acid, spermidine, and lysine as starting materials. Coupling of these molecular umbrellas to an octaarginine peptide afforded agents that were capable of promoting the transport of small interfering RNA to HeLa cells, as judged by the knockdown of enhanced green fluorescent protein expression. The efficiency of this knockdown was found to increase with an increasing number of facially amphiphilic walls present, and also when a cleavable disulfide linker was replaced with a noncleavable, maleimido moiety; i.e., a group that is not susceptible to thiolate-disulfide interchange. The knockdown efficiency that was observed for one tetrawalled molecular umbrella-octaargine conjugate was comparable to that observed with a commercially available transfection agent, Lipofectamine 2000, but the conjugate showed less cytotoxicity.

Design of a beta-hairpin peptide-intercalator conjugate for simultaneous recognition of single stranded and double stranded regions of RNA.

Designing receptors that bind RNA is a challenging endeavor because of the unique and sometimes complex structure of RNA. However these structural features provide regions for ligands to bind using different types of interactions. To increase specificity and binding affinity to RNA, divalent systems have been designed which incorporate more than one binding motif into one molecule. Using this approach, we have designed a two part heteroconjugate, WKWK-Int, which contains a beta-hairpin peptide covalently linked to an RNA intercalator. This heteroconjugate was designed to bind duplex RNA through intercalation and simultaneously interact with a single stranded bulge region using the side chains of the beta-hairpin peptide. We have used fluorescence anisotropy experiments to show that the heteroconjugate has an increased binding affinity over either one of the individual ligands. Additionally, RNase footprinting experiments show that the structure of the peptide is necessary for the protection of one particular base in the RNA bulge region. When tested against other RNA molecules containing a stem-bulge structure, the designed heteroconjugate was found to be specific for this RNA sequence. This work provides evidence that the covalent linkage of two weak RNA ligands can greatly increase the binding affinity and also provide specificity to the binding event.

The structure of well-folded beta-hairpin peptides promotes resistance to peptidase degradation.

To investigate the effect of peptide secondary structure on proteolytic resistance, we have synthesized a series of peptides based on a well-folded beta-hairpin, WKWK. Mutations were made within the peptide which either decreased or increased the propensity to form beta-hairpin structures and one scrambled sequence was used as an unstructured control. The peptides were incubated with three different enzymes, alpha-chymotrypsin, trypsin, and pronase E, which represented both specific and non-specific proteases. The reactions were quenched at varying time points and analyzed with RP-HPLC to determine the rate of degradation for each of the peptides. We found that an increase in structure correlates well with an increase in resistance to degradation. We have shown that having both strong side chain interactions and a rigid D-Pro-Gly beta-turn resulted in the most proteolytic resistant peptides. The results from this study suggest that beta-hairpin structure is a viable way to provide added protease resistance to a peptide.