Structural characteristics influencing the carrier function of synthetic branched polypeptides based on poly[Lys-(DL-Ala)3)]backbone

Synthesis and Characterization of p-Borono-Phenylalanine-Branched Polypeptide-Monoclonal Antibody Ternary Systems for Potential Use in Boron Neutron Capture Therapy (BNCT)

The application of the 10B ( n,α) 7Li capture reaction to cancer radiotherapy (Boron Neutron Capture Therapy) was studied to avoid the inherent disadvantages of conventional radiation therapy. p-Borono-phenylalanine (Bph) was used as the 10B source and mAb produced against HCMB melanoma cells was applied as targeting device. Since extensive direct boronation of mAb led diminished recognition of antigens, an intermediate carrier was used. Nontoxic, biocompatible, biodegradable and weakly immunogenic branched polypeptides with a polylysine backbone was used to carry a high number of 10B. Protected 10B-Bph was coupled by four different methods to polycationic branched polypeptides. The coupling efficiency varied according to the experimental conditions, with a maximum of 90%. The chiroptical properties of the conjugates indicated an ordered conformation which increased with the number of coupled Bph. The whole body survival (WBS) and tissue distribution profile of mAb (8/6 IgG2a) were markedly altered after conjugation with Bph-branched polypeptide. Decreased WBS and intermediate-carrier-dependent accumulation in the spleen, liver and kidney was observed 24 h after iv. administration. After joining only a few chains of the highly loaded Bph-AK conjugate to mAb, the binding activity of the mAb in the ternary system was preserved compared to control.

Synthesis and spectroscopic properties of 4-ethoxymethylene-2-(1)-naphthyl-5(4H)-oxazolone-labeled fluorescent peptides

Strategies for the preparation of new fluorescent oligopeptide conjugates labeled with 4-ethoxymethylene-2-[1]-naphthyl-5(4H)-oxazolone (naOx-OEt) at the N-terminal on solid support or in solution have been devised. These procedures are simple and easy to carry out by reacting naOx-OEt or N(alpha)-naOx-amino acid with side chain protected peptide chains attached to resins. The integrity of the N-alkyl bond was maintained even after the trifluoracetic acid or HF based cleavages procedures. Our data show that the naOx fluorophore is compatible with both Fmoc/tBu and Boc/Bzl methods and also suggest that naOx-amino acid could be utilized as building blocks for solid phase peptide synthesis. Comparative analysis of fluorescence properties of naOx-conjugates indicated that the spectral properties of the fluorophore do not change after incorporating into peptides. The compact size, the definite chemical reaction for its introduction in combination with the appropriate spectral features (e.g., intense emission, pH independent fluorescent characteristics, and beneficial photobleaching dose constant and rates) and with chemical and spectral stability, naOx-based labeling could be attractive for novel cellular fluorescent techniques (e.g., in laser scanning confocal FRET) to study peptide-protein and protein-protein interactions even in biological matrices.

Amino-acid conjugates of the hapten 2-phenyl-4-ethoxymethylene-5(4H)-oxazolone. Synthesis and confirmation of structure

2-Phenyl-4-ethoxymethylene-5(4H)-oxazolone (PhOx = CHOEt) was reacted with methylamine, and 2-phenyloxazole-4-carboxylic acid was coupled with methylamine. The spectroscopic properties of the two products were compared in order to confirm that aminolysis of PhOx = CHOEt occurs by displacement of the ethoxy group to give 2-phenyl-4-(substituted-methylene)-5(4H)-oxazolones and not by attack at the oxazolone-carbonyl followed by rearrangement to give 2-phenyloxazole-4-carboxamides. Ten crystalline conjugates were prepared and characterized by reacting PhOx = CHOEt with an excess of unprotected di- and trifunctional amino acid anions followed by purification by washing them with hydrochloric acid.

The influence of branched polypeptide carriers on the immunogenicity of predicted epitopes of HSV-1 glycoprotein D

To investigate the role of synthetic polypeptide carriers in inducing an epitope-specific immune response relevant for vaccine design, peptides comprising two distinct regions of herpes simplex virus type I glycoprotein D (1-23 and 273-284) have been conjugated to the branched polypeptides with polylysine backbone, poly[L-Lys-(DL-Alam)] (AK), or poly[L-Lys-(Leui-DL-Alam)] (LAK) and to keyhole limpet haemocyanin (KLH). The magnitude, fine specificity and isotype distribution of the conjugate-, peptide-and carrier-specific antibody responses were characterized in immunized BALB/c and CBA mice. Conjugates containing the polypeptide carrier AK were the most effective in inducing HSV gD-peptide-specific antibody responses while KLH peptide conjugates resulted in conjugate-specific antibody responses without measurable peptide specificity. The efficacy of AK-peptide conjugates was verified by the dominant appearance of peptide-specific antibodies belonging to functionally efficient IgG isotopes, accompanied by low levels of carrier specific antibody responses. Preimmunization of BALB/or CBA mice with AK conjugates comprising the 1-23 or 276-284 HSV peptides resulted in prolonged survival of animals infected with a lethal dose of infectious HSV-1. The potency of these conjugates in eliciting a protective immune response shows a close correlation with the relative levels of conjugate-induced virus-specific antibodies and the neutralizing activity of sera as measured in preimmunized survivors.

Carrier design: conformational studies of amino acid (X) and oligopeptide (X-DL-Alam) substituted poly (L-lysine)

The present study was undertaken to examine the influence of the reversal of the side-chain sequential order on the conformation of branched polypeptides. At the same time, the influence of the optically active amino acid joined directly to the poly (L-Lys) backbone and the DL-Ala oligomer grafted as chain-terminating fragment were separately analyzed. Therefore two sets of polypeptides were synthesized corresponding to the general formula poly[Lys-(Xi)] (XK) and poly[Lys-(DL-Alam-Xi)] (AXK) when X = Ala, D-Ala, Leu, D-Leu, Phe, D-Phe, Ile, Pro, Glu, D-Glu, or His. For coupling amino acid X to polylysine, three types of active ester methods were compared: the use of pentafluorophenyl or pentachlorophenyl ester, and the effect of the addition of an equimolar amount of 1-hydroxy-benzotriazole. After cleavage of protecting groups, AXK polypeptides were synthesized by grafting short oligo(DL-Ala) chains to XK by using N-carboxy-DL-Ala anhydride. The CD measurements performed in water solutions of various pH values and ionic strengths were used for classification of the polypeptide conformations as either ordered (helical) or unordered. Different from what was observed with the unsubstituted poly (L-Lys), poly[Lys-(Xi)] type polypeptides can adopt ordered structure even under nearly physiological conditions (pH 7.3, 0.2M NaCl). These data suggest that the introduction of amino acid residue with either (ar) alkyl side chain (Ala, Leu, Phe) or negatively charged side chain (Glu) promotes markedly the formation of ordered structure. Comparison of chiroptical properties of poly[Lys-(DL-Alam-Xi)] and of poly[Lys-(Xi)] reveals that side-chain interactions play an important role in the stabilization of ordered solution conformation of AXK type branched polypeptides. The results give rather conclusive evidence that not only hydrophobic interactions, but also ionic attraction, can be involved in the formation and stabilization of helical conformation of branched polypeptides.

Synthetic peptides in the search for T- and B-cell epitopes

In this article, Eva Rajnavölgyi describes two aspects of the rigorous application of organic chemistry to the task of synthesizing peptides that induce immune responses. First, the development of viral peptides that activate T and B cells without the need for carrier molecules and secondly, the production of a new generation of immunologically inert carrier molecules.

Monoclonal antibody binding to peptide epitopes conjugated to synthetic branched chain polypeptide carriers

The peptide C A P D T R P A P G has been linked covalently to defined branched polypeptides with a polylysine backbone and side chains of DL-alanine or D-leucine-DL-alanine oligopeptides. The peptide was coupled via its N terminal cysteine to the side chains of the macromolecular carrier to ensure uniform orientation. The compounds were subjected to compositional analyses to characterise the degrees of substitution and secondary structural studies were performed using circular dichroism spectroscopy. The peptide selected for investigation contains the immunodominant sequence P D T R P A P which is expressed in the protein core of epithelial mucins. It is to this region that many anti-mucin monoclonal antibodies bind (Burchell et al., 1989; Price et al., 1990a,b). With these characterised constructs, it has been possible to evaluate the influence of secondary structure upon the binding of monoclonal antibodies which recognise short linear sequences in the synthetic antigenic peptide. The findings are relevant to the design and construction of synthetic immunogens and vaccines as well as to the production of synthetic analogues of clinically relevant antigens (in this case, epithelial mucins associated with breast and ovarian carcinomas).

Recent advances in solid-phase peptide synthesis and preparation of antibodies to synthetic peptides

Peptides prepared by the solid-phase peptide synthesis (SPPS) approach are used increasingly in biological research, for instance to elicit anti-peptide antibodies that will recognize the intact, cognate protein. Recent advances in SPPS are reviewed, including the use of new coupling reagents, new methods for evaluating peptide purity and new techniques of automated and multiple peptide synthesis. Methods for enhancing peptide immunogenicity are discussed such as the use of adjuvants and liposomes, and of synthetic branched polypeptides as carriers.