Novel liposaccharide conjugates for drug and peptide delivery

Synthesis, characterization and in vitro evaluation of amphiphilic ion pairs of erythromycin and kanamycin antibiotics with liposaccharides

The hydrophilic ion paring strategy (HIP) is a method explored to improve the cell/tissue uptake of poorly adsorbed drugs and to optimize their physico-chemical characteristics. In this context, we here describe the synthesis of some ion pairs of two model cationic antibiotics, erythromycin (ERY) and kanamycin A (KAN), with liposaccharides having different levels of lipophilicity and charge. The formation of drug-liposaccharide complexes was confirmed by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) analysis. The effect of the amphiphilic liposaccharide moieties on the antimicrobial activity of ERY and KAN was assessed by measuring the minimal inhibitory concentration (MIC) of the compounds against a panel of bacterial strains that were susceptible or resistant to the parent antibiotics. The ion pairing did not depress the in vitro antibiotic activity, although no lowering of MIC values was registered. The experimental findings would motivate the future investigation of this ion pairing strategy in drug design, for instance allowing improvement of the encapsulation efficiency of hydrophilic antibiotics in lipid-based nanocarriers, or changing their in vivo biodistribution and pharmacokinetic profile.

Design, synthesis and characterisation of mannosylated ovalbumin lipid core peptide self-adjuvanting vaccine delivery system

Peptide-based vaccine delivery can be hampered by rapid peptidase activity and poor inherent immunogenicity. The self-adjuvanting lipid core peptide system (LCP) has been shown to confer improved stability and immunogenicity on peptide epitopes of group A Streptococcus, Chlamydia, hookworm, and malaria pathogens. However, various diseases, including cancer, still require targeted delivery of their vaccine candidates. For this reason, we have selected two model peptides (ovalbumin CD4(+) and/or CD8(+) T cell epitopes), and incorporated two or four copies of either epitope into our LCP vaccine. Optimised glycosylation of ovalbumin peptides yielded 46 % when microwave-assisted double coupling with 2 eq of carbohydrate derivative, activated by N,N-diisopropylethylamine and (O-benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, was performed. All ovalbumin peptides were successfully synthesised and purified in 11-55 % yields by Fmoc- or Boc-chemistry using solid-phase peptide synthesis. The mannosylated ovalbumin peptides were nontoxic to human erythrocytes in haemolytic assay (<2 % haemolysis) and showed increased (up to 20-fold) stability in plasma.

Design, synthesis and biological evaluation of novel lipoamino acid-based glycolipids for oral drug delivery

A series of lipoamino acid-based glycolipids were synthesised. Suitably derivatised lipoamino acid derivatives were prepared and conjugated to monosaccharides (including glycosyl azides, isothiocyanates, thiols and sulphones) to yield novel O-, N-, S- and C-linked glycolipids in good yields. Their potential to improve the oral absorption of piperacillin is reported.

Caco-2 cell permeability and stability of two d-glucopyranuronamide conjugates of thyrotropin-releasing hormone

Caco-2 cell permeability and stability assays were used as an in vitro model to study the intestinal epithelial transport and stability of two analogues of thyrotropin-releasing hormone (TRH; Pyr-His-Pro-NH2). Peptide 1 (Pyr-His-Pro-D-glucopyranuronamide) was more permeable across the Caco-2 cell monolayer compared with the permeability of the parent TRH peptide (Papp=5.10+/-1.89x10(-6) cm/s c.f. Papp=0.147+/-0.0474x10(-6) cm/s respectively). The permeability of peptide 1 was improved threefold by attaching a 2-aminooctanoic acid moiety to the N-terminus to form peptide 2 (2-aminooctanoic acid-Gln-His-Pro-D-glucopyranuronamide) (Papp=16.3+/-2.47x10(-6) cm/s). The half-life for both peptide 1 and peptide 2 was approximately 20 min in a homogenate of Caco-2 cells compared with the half-life of TRH which is approximately 3 min. It was concluded that the permeability of peptides 1 and 2 was enhanced because of their increased stability, while the higher permeability of peptide 2 compared with peptide 1 may be attributed to its increased lipophilicity which results in enhanced passive diffusion.

Lipidation and glycosylation of a T cell antigen receptor (TCR) transmembrane hydrophobic peptide dramatically enhances in vitro and in vivo function

A T cell antigen receptor (TCR) transmembrane sequence derived peptide (CP) has been shown to inhibit T cell activation both in vitro and in vivo at the membrane level of the receptor signal transduction. To examine the effect of sugar or lipid conjugations on CP function, we linked CP to 1-aminoglucosesuccinate (GS), N-myristate (MYR), mono-di-tripalmitate (LP1, LP2, or LP3), and a lipoamino acid (LA) and examined the effects of these compounds on T cell activation in vitro and by using a rat model of adjuvant-induced arthritis, in vivo. In vitro, antigen presentation results demonstrated that lipid conjugation enhanced CP's ability to lower IL-2 production from 56.99%+/-15.69 S.D. observed with CP, to 12.08%+/-3.34 S.D. observed with LA. The sugar conjugate GS resulted in only a mild loss of in vitro activity compared to CP (82.95%+/-14.96 S.D.). In vivo, lipid conjugation retarded the progression of adjuvant-induced arthritis by approximately 50%, whereas the sugar conjugated CP, GS, almost completely inhibited the progression of arthritis. This study demonstrates that hydrophobic peptide activity is markedly enhanced in vitro and in vivo by conjugation to lipids or sugars. This may have practical applications in drug delivery and bioavailability of hydrophobic peptides.

Encapsulation of lipopeptides within liposomes: Effect of number of lipid chains, chain length and method of liposome preparation

The purpose of this study was to systematically investigate the effect of lipid chain length and number of lipid chains present on lipopeptides on their ability to be incorporated within liposomes. The peptide KAVYNFATM was synthesized and conjugated to lipoamino acids having acyl chain lengths of C8, C12 and C16. The C12 construct was also prepared in the monomeric, dimeric and trimeric form. Liposomes were prepared by two techniques: hydration of dried lipid films (Bangham method) and hydration of freeze-dried monophase systems. Encapsulation of lipopeptide within liposomes prepared by hydration of dried lipid films was incomplete in all cases ranging from an entrapment efficiency of 70% for monomeric lipoamino acids at a 5% (w/w) loading to less than 20% for di- and trimeric forms at loadings of 20% (w/w). The incomplete entrapment of lipopeptides within liposomes appeared to be a result of the different solubilities of the lipopeptide and the phospholipids in the solvent used for the preparation of the lipid film. In contrast, encapsulation of lipopeptide within liposomes prepared by hydration of freeze-dried monophase systems was high, even up to a loading of 20% (w/w) and was much less affected by the acyl chain length and number than when liposomes were prepared by hydration of dried lipid films. Freeze drying of monophase systems is better at maintaining a molecular dispersion of the lipopeptide within the solid phospholipid matrix compared to preparation of lipid film by evaporation, particularly if the solubility of the lipopeptide in solvents is markedly different from that of the polar lipids used for liposome preparation. Consequently, upon hydration, the lipopeptide is more efficiently intercalated within the phospholipid bilayers.

Design, Synthesis, and Evaluation of a Liposaccharide Drug Delivery Agent: Application to the Gastrointestinal Absorption of Gentamicin

The design, synthesis, and evaluation of a liposaccharide (11) for use as an agent to enhance the gastrointestinal absorption of charged, hydrophilic drugs with poor membrane permeability is reported. 11 was designed to possess both surfactant and ion-pairing properties and was conveniently synthesized from d-glucuronic acid (2) and N-Boc-lipoamino acid (5) precursors in eight steps in good yield. Isothermal titration microcalorimetry was used to determine the critical micelle concentration of 11 (in PBS) to be 2.09 +/- 0.01 mM with an enthalpy of demicellization of 4.91 +/- 0.11 kJ/mol. The ability of 11 to enhance the gastrointestinal absorption of the aminoglycoside antibiotic gentamicin (1), a hydrophilic polycation with negligible oral bioavailability, was assessed in vivo using rats. Rats dosed orally with a mixture of 11 (100 mg/kg) and 1 (60 mg/kg) had a statistically significant (P < or = 0.034) increase in Cmax, AUC120, and percent absolute bioavailability (F) compared to control 1 (60 mg/kg) alone. The highest bioavailability (F = 9.1 +/- 2.0%) was achieved by dosing with the mixture 11 (100 mg/kg) and 1 (15 mg/kg). This represents a 6-fold increase in bioavailability compared to the control (F = 1.4 +/- 0.3%). These results suggest that the molar ratio of 1:11 may be critical in optimizing the delivery system, a finding ascribed in part to the ion-pairing properties of 11. The effect of 11 on the gastrointestinal mucosa was assessed using light microscopy to examine tissue samples from rats used in the pharmacokinetic study. No morphological changes were found in either the esophagi or duodena of the rats examined. One rat dosed with 11 (100 mg/kg) and 1 (60 mg/kg) exhibited slight gastric erosion, which could be attributed to 11.

Synthesis of C-terminal glycopeptides from resin-bound glycosyl azides via a modified Staudinger reaction

The solid-phase synthesis of glycopeptides containing the sugar at the C-terminus is reported. The method is demonstrated on a model, the endogenous antinociceptive peptide Leu-enkephalin. 2,3,4-Tri-O-acetyl-1-azido-1-deoxy-beta-D-glucopyranuronic acid was synthesized and immobilized onto a variety of derivatized resins. Conjugation of the first amino acid was accomplished by reaction of the resin-bound glycosyl azide with an activated amino acid, in one step, via a modified Staudinger reaction. Standard solid-phase peptide synthesis then resulted in the desired amide-linked glycopeptide. Reaction conditions and reagents for the glycosylation were varied to optimize the yield and purity of the product. The optimum conditions were found to be the use of a 4-fold molar excess of activated amino acid and 3-fold excess of tri-n-butylphosphine in tetrahydrofuran. This methodology is generally applicable to most peptide sequences and is compatible with both Boc- and Fmoc- synthetic strategies on a variety of resins.