Biodegradable dendrimers for drug delivery

Dendrimers, as a type of artificial polymers with unique structural features, have been extensively explored for their applications in biomedical fields, especially in drug delivery. However, one important concern about the most commonly used dendrimers exists - the nondegradability, which may cause side effects induced by the accumulation of synthetic polymers in cells or tissues. Therefore, biodegradable dendrimers incorporating biodegradability with merits of dendrimers such as well-defined architectures, copious internal cavities and surface functionalities, are much more promising for developing novel nontoxic drug carriers. Herein, we review the recent advances in design and synthesis of biodegradable dendrimers, as well as their applications in fabricating drug delivery systems, with the aim to provide researchers in the related fields a good understanding of biodegradable dendrimers for drug delivery.

Cationic liposome-nucleic acid complexes for gene delivery and silencing: pathways and mechanisms for plasmid DNA and siRNA

Motivated by the promises of gene therapy, there is great interest in developing non-viral lipid-based vectors for therapeutic applications due to their low immunogenicity, low toxicity, ease of production, and the potential of transferring large pieces of DNA into cells. In fact, cationic liposome (CL) based vectors are among the prevalent synthetic carriers of nucleic acids (NAs) currently used in gene therapy clinical trials worldwide. These vectors are studied both for gene delivery with CL-DNA complexes and gene silencing with CL-siRNA (short interfering RNA) complexes. However, their transfection efficiencies and silencing efficiencies remain low compared to those of engineered viral vectors. This reflects the currently poor understanding of transfection-related mechanisms at the molecular and self-assembled levels, including a lack of knowledge about interactions between membranes and double stranded NAs and between CL-NA complexes and cellular components. In this review we describe our recent efforts to improve the mechanistic understanding of transfection by CL-NA complexes, which will help to design optimal lipid-based carriers of DNA and siRNA for therapeutic gene delivery and gene silencing.

Hyaluronan-based Glycoclusters as Probes for Chemical Glycobiology

A strategy is described for the synthesis of β-(1,3)-GlcA-GlcNAc dimeric and tetrameric glycoclusters through the conjugation of disaccharide groups onto a diaminodiamide aromatic scaffold by reductive amination.

Dendritic Cationic Lipids with Highly Charged Headgroups for Efficient Gene Delivery

Gene therapy is expected to lead to powerful new approaches for curing many diseases, a potential that is currently explored in worldwide clinical trials. Nonviral DNA delivery systems are desirable to overcome the inherent problems of viral vectors, but their current efficiency requires improvement and the understanding of their mechanism of action is incomplete. We have synthesized new multivalent cationic lipids with highly charged dendritic headgroups to probe the structure-transfection efficiency relationships of cationic liposome (CL)-DNA complexes, a prevalent nonviral vector. The lipid headgroups are constructed from ornithine cores and ornithine or carboxyspermine endgroups. The dendritic lipids were prepared on a gram scale, using a synthetic scheme that permits facile variation of the lipid building blocks headgroup, spacer, and hydrophobic moiety. They carry four to sixteen positive charges in their headgroups. Complexes of DNA with mixtures of the dendritic lipids and neutral 1,2-dioleoyl-sn-glycero phosphatidylcholine (DOPC) exhibit novel structures at high contents of the highly charged lipids, while the well-known lamellar phase is formed at high contents of DOPC. DNA complexes of the new dendritic lipids efficiently transfect mammalian cells in culture without cytotoxicity and, in contrast to lamellar complexes, maintain high transfection efficiency over a broad range of composition.

On-bead synthesis and binding assay of chemoselectively template-assembled multivalent neoglycopeptides

The investigation of recognition events between carbohydrates and proteins, especially the control of how spatial factors and binding avidity are correlated in, remains a great interest for glycomics. Therefore, the development of efficient methods for the rapid evaluation of new ligands such as multivalent glycoconjugates is essential for diverse diagnostic or therapeutic applications. In this paper we describe the synthesis of chemoselectively-assembled multivalent neoglycopeptides and the subsequent recognition assay on a solid support. Aminooxylated carbohydrates (betaLac-ONH(2) 4, alphaGalNAc-ONH(2) 9 and alphaMan-ONH(2) 13) have been prepared as carbohydrate-based recognition elements and assembled as clusters onto a cyclopeptidic scaffold by an oxime-based strategy in solid phase. Further binding tests between lectins and beads of resin derivatized with neoglycopeptides displaying clustered lactoses, N-acetylgalactoses and mannoses (18-20) have shown specific recognition and enhanced affinity through multivalent interactions, suggesting that the local density of carbohydrate-based ligands at the bead surface is crucial to improve the interaction of proteins of weak binding affinity. This solid phase strategy involving both molecular assembly and biological screening provides a rapid and efficient tool for various applications in glycomics.

A flexible method for preparation of peptide homo- and heterodimers functionalized with affinity probes, chelating ligands, and latent conjugating groups

Dimerization of peptides can provide high binding entities to serve as targeted diagnostics or therapeutics. We developed methods for the preparation of homo- and heterodimer peptides bearing functional molecules (affinity probes, chelating ligands, or latent conjugating moieties). Monomer peptides, optionally bearing spacer groups, are tethered using a bifunctional linker, (di-succinimidyl glutarate, DSG) to provide the dimers. Protected or unprotected peptides can be employed for dimer assembly. Multiple lysine N(epsilon)-amino groups are controlled using the (4,4-dimethyl-2,6-dioxocyclohex-1-ylidene)-3-methylbutyl (ivDde) protecting group. Functional molecules are optionally incorporated into the component peptides or into the assembled dimer. The methods are efficient and scaleable.

Synthesis of multitopic neoglycopeptides displaying recognition and detection motifs

We describe herein the synthesis of cyclic decapeptide template displaying clustered carbohydrate recognition motifs and detection agent on spatially separated domains. Such multitopic labeled neoglycopeptides represent attractive tools for binding assays with carbohydrate binding proteins in glycomic research.

Peptide dendrimers

Dendrimers are branched structures and represent a fast growing field covering many areas of chemistry. Various types of dendrimers differing in composition and structure are mentioned, together with their practical use spanning from catalysis, transport vehicles to synthetic vaccines. The main stress is given to peptide dendrimers, namely, multiple antigenic peptides (MAPs). Their synthesis, physicochemical properties, biological activities, etc. have been described with many examples. MAPs can be used as diagnostics, mimetics, for complexation of different cations, as vaccines against parasites, bacteria, viruses, etc.

Sequential oligopeptide carriers, SOCn, as scaffolds for the reconstitution of antigenic proteins: applications in solid phase immunoassays

A new class of helicoid type sequential oligopeptide carriers (SOC), for anchoring antigenic epitopes, has been modeled from the repetitive Lys-Aib-Gly (SOC(n)-I) and Aib-Lys-Aib-Gly (SOC(n)-II) units aiming to the development of scaffolds with predetermined 3D structures. Conformational analysis showed that the SOC(n) carriers adopt 3(10)-helical structures, while the SOC(n)-conjugates retain their original active conformations and they interact neither to the carriers nor to each other. It is concluded that the helicoid structure of SOC(n) helps the reconstitution and/or mimicking of the native forms of the epitopes so that potent antigens are generated for developing specific, sensitive and reproducible immunoassays.

Facile preparation of DNA-tagged carbohydrates

We report here that unprotected carbohydrates (maltose, lactose, cellobiose, and maltoheptaose) can be attached to the aminoalkylated oligonucleotides under mild reductive-amination conditions (aqueous borate buffer, pH 8.0, NaBH(3)CN, 60 degrees C) without notable side reactions. Quadruplex-forming G-rich oligonucleotide, 5'-aminoalkyl d(TGGGGT), is glycosylated with maltoheptaose to afford a novel DNA-assisted tetrasaccharide cluster motif.

Multiple anchoring of myelopeptides on sequential oligopeptide carriers (SOC(n)): synthesis, conformation and studies in human leukemia cells

Myelopeptides, MP-6 (Val-Asp-Pro-Pro) and MP-4 (Phe-Arg-Pro-Arg-Ile-Met-Thr-Pro), induce metabolic changes in human leukemia cells, HL-60, characteristic of the differentiation process, which should be regarded as a promising therapeutic approach in cancer and related diseases. With the aim to optimize the differentiation effect of MPs, they were coupled to the Lys-N(epsilon)H(2) groups of a sequential oligopeptide carrier Ac-(Lys-Aib-Gly)(4), SOC(4), and the constructs obtained were studied. The rigid 3(10) secondary structure of the carrier is preserved even after linkage of the MPs, which also maintain their initial conformations without interacting either with each other or with the carrier, as demonstrated by (1)H nuclear magnetic resonance (NMR) spectroscopy. It is concluded that the carrier accommodates the presentation of MPs, thus improving their differentiation effect on human leukemia cells.

Photoresponsive dendritic azobenzene peptides

Two dendritic peptides containing a branched lysine core and up to eight azobenzene moieties in the periphery were synthesized on solid support employing the omega-amino acid 4-(aminomethyl)phenylazobenzoic acid. With an additional peptidic tail consisting of an oligolysine portion, water solubility was achieved for the dendrimers, which allowed for the characterization of the cis/trans photoisomerization of the dendritic azobenzene species in both organic and aqueous media. Despite the interactions between the chromophores, which occur particularly in aqueous media, at higher dilution the photoisomerization process was found to proceed to extents that should permit photomodulation of molecular recognition processes between ligands grafted to the photosensitive azobenzene units and receptor molecules.

Multipeptide-metalloporphyrin assembly on a dendrimer template and photoinduced electron transfer based on the dendrimer structure

To construct an artificial photosynthetic system, peptide dendrimers [n-(X-HLY)PAMAMs: X = R, E; Y= L, F; n=4, 8, 16, 32 and 64 segments], in which amphiphilic alpha-helix peptides (X-HLY: R-HLL, E-HLL and R-HLF) were introduced at the end groups of polyamidoamine dendrimers (PAMAMs), were designed and synthesized. The peptide dendrimers 64-(X-HLY)PAMAMs are novel synthetic biopolymers with an enormous molecular weight, about 160 kDa, and with a regulated amino acid sequence and three-dimensional conformation. The peptide dendrimers bound Fe(III)- or Zn(II)-mesoporphyrin IX per two alpha-helices; this afforded a multimetalloporphyrin assembly similar to the natural light-harvesting antennae in photosynthetic bacteria. Circular dichroism studies and peroxidase activity measurements revealed that metalloporphyrins were coordinated to the peptide dendrimers in a regulated manner and packed more densely with the growth of the dendrimer generation. Fluorescence quenching and photoreduction studies with methylviologen demonstrated that the photoinduced electron-transfer function with the peptide dendrimer-multi-Zn-MP was accomplished more effectively as the dendrimer generation increased. Thus, the three-dimensional assembly of metalloporphyrins and peptides in the dendrimer was an effective module for light-harvesting antennae in an artificial photosynthetic system.

A diepitopic sequential oligopeptide carrier (SOCn) as mimic of the sm autoantigen: synthesis, conformation and biological assays

Anti-Sm (Sm: U1-U6 RNA-protein complex) antibodies are usually considered highly specific for systemic lupus erythematosus (SLE), while anti-U1RNP (U1RNP: U1RNA-protein complex) are thought of as diagnostic criteria for the mixed connective tissue disease (MCTD). However, both antibody specificities coexist in SLE and MCTD, in varying percentages. Although the anti-Sm/anti-U1RNP immunological cross-reactivity has been initially attributed to a common motif, PPXY(Z)PP (where X, Y, Z are various amino acids), found in the Sm, U1-A and U1-C autoantigens, it appears that the conformational features of the Sm epitopes also play an important role in the immunoreactivity. The PPGMRPP and PPGIRGP main epitopes of the Sm antigen were coupled in duplicate to the tetrameric Ac-(Lys-Aib-Gly)4-OH, SOC4, carrier to form the [(PPGMRPP)2, (PPGIRGP)2]-SOC4 construct as a mimic of the native Sm. It was found that: (i) the 3(10) helical structure of SOC4 allows the epitopes to adopt an exposed orientation, similar to their free forms, that facilitates their recognition from the anti-Sm antibodies, and (ii) the U1-RNP cross-reactivity is minimized.

Synthetic multivalent ligands in the exploration of cell-surface interactions

Processes such as cell-cell recognition and the initiation of signal transduction often depend on the formation of multiple receptor-ligand complexes at the cell surface. Synthetic multivalent ligands are unique probes of these complex cell-surface-binding events. Multivalent ligands can be used as inhibitors of receptor-ligand interactions or as activators of signal transduction pathways. Emerging from these complementary applications is insight into how cells exploit multivalent interactions to bind with increased avidity and specificity and how cell-surface receptor organization influences signaling and the cellular responses that result.

Ligand-presenting assembly: a method for C- and N-terminal antigen presentation

Achiral dicarboxylic acids were coupled with 2 eq. of the free alpha-amino groups of two fully side-chain protected peptide chains while these were still attached to a synthesis resin. Cleavage from the resin with simultaneous side-chain deprotection afforded two assembled peptide chains with free C-terminals. Suitable functionalization of the achiral dicarboxylic acid alternatively permitted continued peptide synthesis in a C to N orientation leading to a final peptide assembly which, after cleavage from the resin, may have multiple N to C and C to N presentation of one or more epitopes.

The position of the LysN epsilon H2-grafted antigens along the sequential oligopeptide carrier, Ac-(Aib-Lys-Aib-Gly)n (SOCn-II), influences the antibody recognition: application to the Sm main autoimmune epitope

A sequential oligopeptide carrier of antigenic peptides is presented, incorporating two Aib residues in each repetitive moiety: Ac-(Aib-Lys-Aib-Gly)(n) (SOC(n) -II; n = 2-4). The conformational study, by (1)H-nmr, CD, and Fourier transform ir spectroscopy, indicated that the SOC(n) -II carrier displays a pronounced 3(10)-helix, compared to the Ac-(Lys-Aib-Gly)(n) (SOC(n) -I) carrier of the same approximately backbone length, previously reported. One of the dominant autoimmune epitopes of the Sm and U1RNP cellular components, the PPGMRPP sequence, was coupled to the Lys-N(epsilon)H(2) groups of the SOC(n) -II carrier and used as antigenic substrate for detecting anti-Sm/U1RNP autoantibodies in ELISA assays. Anti-Sm antibodies are highly specific for systemic lupus erythematosus, while anti-U1RNP are specific for mixed connective tissue disease. The anti-(PPGMRPP)(5)-SOC(n) -II ELISA was compared with the anti-(PPGMRPP)(n) -SOC(n) -I ELISA, provided that both antigenic substrates possess the same amount of the epitope replicates. The significance of the lysine positions along the oligopeptide backbone of the carrier for a favorable antibody recognition of the anchored antigens is also examined.

Preparation and application of O-amino-serine, Ams, a new building block in chemoselective ligation chemistry

The non-codable amino acid O-amino-serine, Ams, has been prepared in both L- and D-forms as the orthogonally protected derivative, Fmoc-Ams(Boc)-OH (1 and 2). This new amino acid derivative is useful for chemoselective ligations. Under acidic conditions and in the presence of all other common amino acid functionalities, the oxyamine function selectively forms oxime linkages with aldehydes. The Ams residue has been incorporated into both ends of the peptide sequence Asp-Leu-Trp-Gln-Lys using standard SPPS. The deprotected peptide has been used for chemical ligation to afford a peptide dimer as well as a glycopeptide. Ams racemization was found to be negligible, as monitored by HPLC separation of Ams dipeptide diastereomers.