The effect of the structure of branched polypeptide carrier on intracellular delivery of daunomycin

Polypeptide-Based Systems: From Synthesis to Application in Drug Delivery

Synthetic polypeptides are biocompatible and biodegradable macromolecules whose composition and architecture can vary over a wide range. Their unique ability to form secondary structures, as well as different pathways of modification and biofunctionalization due to the diversity of amino acids, provide variation in the physicochemical and biological properties of polypeptide-containing materials. In this review article, we summarize the advances in the synthesis of polypeptides and their copolymers and the application of these systems for drug delivery in the form of (nano)particles or hydrogels. The issues, such as the diversity of polypeptide-containing (nano)particle types, the methods for their preparation and drug loading, as well as the influence of physicochemical characteristics on stability, degradability, cellular uptake, cytotoxicity, hemolysis, and immunogenicity of polypeptide-containing nanoparticles and their drug formulations, are comprehensively discussed. Finally, recent advances in the development of certain drug nanoformulations for peptides, proteins, gene delivery, cancer therapy, and antimicrobial and anti-inflammatory systems are summarized.

Cellular Uptake Mechanism of Cationic Branched Polypeptides with Poly[l-Lys] Backbone

Cationic macromolecular carriers can be effective carriers for small molecular compounds, drugs, epitopes, or nucleic acids. Polylysine-based polymeric branched polypeptides have been systematically studied on the level of cells and organisms as well. In the present study, we report our findings on the cellular uptake characteristics of nine structurally related polylysine-based polypeptides with cationic side chains composed of (i) single amino acid (poly[Lys(X_i)], X_iK) or (ii) oligo[dl-alanine] (poly[Lys(dl-Ala_m)], AK) or (iii) oligo[dl-alanine] with an additional amino acid (X) at the terminal position (poly[Lys(X_i-dl-Ala_m)] (XAK)) or (iv) at the position next to the polylysine backbone (poly[Lys(dl-Ala_m-X_i)] (AXK)). In vitro cytotoxicity and cellular uptake were characterized on HT-29 human colon carcinoma and HepG2 human hepatocarcinoma cell lines. Data indicate that the polycationic polypeptides studied are essentially nontoxic in the concentration range studied, and their uptake is very much dependent on the side chain structure (length, identity of amino acid X, and distance between the terminal positive charges) and also on the cell lines. Our findings in uptake inhibition studies suggest that predominantly macropinocytosis and caveole/lipid raft mediated endocytosis are involved. The efficacy of their internalization is markedly influenced by the hydrophobicity and charge properties of the amino acid X. Interestingly, the uptake properties of the these polypeptides show certain similarities to the entry pathways of several cell penetrating peptides.

Smart branched polymer drug conjugates as nano-sized drug delivery systems

Branched polymers own special properties derived from their intrinsic characteristics. These properties make them ideal candidates to be used as carriers for an improved generation of polymer-drug conjugates.

Development of an oxime bond containing daunorubicin-gonadotropin-releasing hormone-III conjugate as a potential anticancer drug

Here, we report on the synthesis and biological properties of a conjugate in which daunorubicin (Dau) as chemotherapeutic agent was attached through an oxime bond to gonadotropin-releasing hormone-III (GnRH-III) as targeting moiety. In vitro toxicity and the cytostatic effect of the conjugate on MCF-7 human breast and C26 murine colon cancer cell lines were determined, and the results were compared with those obtained for the free daunorubicin, as well as with the doxorubicin containing derivative. In vivo antitumor effect of daunorubicin-GnRH-III was studied on Balb/c female mice transplanted with C26 tumor. Our data indicate that the daunorubicin-GnRH-III conjugate had a lower toxic effect than the free daunorubicin and it was essentially nontoxic up to 15 mg (Dau content)/kg body weight. The treatment of the C26 tumor bearing mice with the conjugate led to tumor growth inhibition and longer survival time in comparison with the controls and with the administration of the free drug. When mice were treated twice with the conjugate (on days 4 and 7 after tumor transplantation), 46% tumor growth inhibition was obtained. In this case, the increase of the median survival time was 38% compared to the controls.

In vitro cytotoxicity, chemotactic effect, and cellular uptake of branched polypeptides with poly[L-lys] backbone by J774 murine macrophage cell line

Branched polypeptides with polylysine backbone are promising candidates for selective delivery of drugs, epitopes. or reporter molecules. We reported earlier that polylysine-based polypeptides with polyanionic character were internalized by murine bone marrow derived macrophages via class A scavenger receptor. In the present studies, our investigations were extended to seven polypeptides with different amino acid composition and charge properties. We report on our findings on the concentration-dependent influence of these compounds on survival and chemotaxis of the murine macrophage-like cell line J774 and internalization properties of the polypeptides by J774 cells. Our observations indicate that the polypeptides regardless of their charge properties were essentially nontoxic and did not alter significantly the chemotaxis of J774 cells; therefore, the polypeptides suit the requirements for nontoxic and "neutral" carrier molecules. We also demonstrated that the polypeptides were internalized efficiently by J774 cells, depending on their chemical structure and charge properties. Using the scavenger receptor-ligand fucoidan as inhibitor, we established that the scavenger receptor played a role-in accordance with findings on murine bone marrow derived macrophages in the internalization only of the polyanionic polypeptides.

Evaluation of conformation and association behavior of multivalent alanine-rich polypeptides

PURPOSE

Helical alanine-rich polypeptides with functional groups displayed along the backbone can display desired molecules such as saccharides or therapeutic molecules at a prescribed spacing. Because these polypeptides have promise for application as biomaterials, the conformation and association of these molecules have been investigated under biologically relevant conditions.

METHODS

Three polypeptide sequences, 17-H-3, 17-H-6, and 35-H-6, have been produced through recombinant techniques. Circular dichroic (CD) spectroscopy was used to monitor the secondary structure of the polypeptides in PBS (phosphate buffered saline, pH 7.4). The aggregation behavior in PBS was monitored via analytical ultracentrifugation and non-denaturing polyacrylamide gel electrophoresis.

RESULTS

The three polypeptides adopt a highly helical structure at low and ambient temperatures, and when heated, undergo a helix-to-coil transition, typical of other alanine-rich peptide sequences. The melting temperatures and van't Hoff enthalpies, extracted from the CD data, suggest similar stability of the sequences. Although alanine-rich sequences can be prone to aggregation, there is no indication of aggregation for the three polypeptides at a range of concentrations relevant for possible biological applications.

CONCLUSIONS

The helical polypeptides are monomeric under biologically relevant conditions enabling application of these polypeptides as useful scaffolds for ligand or drug display.