MD Simulation of AEDG Peptide Complexes with New K2R Dendrimer and Dendrigraft

Biocompatible peptide dendrimers and dendrigrafts have useful properties for application in biomedicine. In previous papers the computational approach for study lysine dendrimers and dendrigrafts as well as their complexes with various medical peptides was used. In this paper the comparison of complex formation between molecules of therapeutic AEDG tetrapeptide and novel K2R peptide dendrimer or DG2 dendrigraft of near the same size and charge was fulfilled. The systems consisting of 16 therapeutic AEDG tetrapeptide molecules and one dendrimer or one dendrigraft were studied by molecular dynamics simulation. Full atomic models of these molecules in water with explicit counterions were used for this goal. First of all, the process of complex formation was studied. It was obtained that peptide molecules were attracted by both branched molecules and were quickly adsorbed by them. Times of complexes formation as well as size, anisotropy and structure of each complex were calculated. It was demonstrated that both K2R dendrimer and DG2 dendrigraft are effective for complexation of these peptide molecules but new dendrimer complex is more stable than dendrigraft complex because it has almost twice more hydrogen bonds with peptide molecules and 33% more ion pairs with their charged groups.

Size and Structure of Empty and Filled Nanocontainer Based on Peptide Dendrimer with Histidine Spacers at Different pH

Novel peptide dendrimer with Lys-2His repeating units was recently synthesized, studied by NMR (Molecules, 2019, 24, 2481) and tested as a nanocontainer for siRNA delivery (Int. J. Mol. Sci., 2020, 21, 3138). Histidine amino acid residues were inserted in the spacers of this dendrimer. Increase of their charge with a pH decrease turns a surface-charged dendrimer into a volume-charged one and should change all properties. In this paper, the molecular dynamics simulation method was applied to compare the properties of the dendrimer in water with explicit counterions at two different pHs (at normal pH with neutral histidines and at low pH with fully protonated histidines) in a wide interval of temperatures. We obtained that the dendrimer at low pH has essentially larger size and size fluctuations. The electrostatic properties of the dendrimers are different but they are in good agreement with the theoretical soft sphere model and practically do not depend on temperature. We have shown that the effect of pairing of side imidazole groups is much stronger in the dendrimer with neutral histidines than in the dendrimer with protonated histidines. We also demonstrated that the capacity of a nanocontainer based on this dendrimer with protonated histidines is significantly larger than that of a nanocontainer with neutral histidines.

Dendrimeric HIV-peptide delivery nanosystem affects lipid membranes structure

The aim of this study was to evaluate the nature and mechanisms of interaction between HIV peptide/dendrimer complexes (dendriplex) and artificial lipid membranes, such as large unilayered vesicles (LUV) and lipid monolayers in the air–water interface. Dendriplexes were combined as one of three HIV-derived peptides (Gp160, P24 and Nef) and one of two cationic phosphorus dendrimers (CPD-G3 and CPD-G4). LUVs were formed of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) or of a mixture of DMPC and dipalmitoyl-phosphatidylglycerol (DPPG). Interactions between dendriplexes and vesicles were characterized by dynamic light scattering (DLS), fluorescence anisotropy, differential scanning calorimetry (DSC) and Langmuir–Blodgett methods. The morphology of formed systems was examined by transmission electron microscopy (TEM). The results suggest that dendriplexes interact with both hydrophobic and hydrophilic regions of lipid bilayers. The interactions between dendriplexes and negatively charged lipids (DMPC–DPPG) were stronger than those between dendriplexes and liposomes composed of zwitterionic lipids (DMPC). The former were primarily of electrostatic nature due to the positive charge of dendriplexes and the negative charge of the membrane, whereas the latter can be attributed to disturbances in the hydrophobic domain of the membrane. Obtained results provide new information about mechanisms of interaction between lipid membranes and nanocomplexes formed with HIV-derived peptides and phosphorus dendrimers. These data could be important for the choosing the appropriate antigen delivery vehicle in the new vaccines against HIV infection.

A Self-Assembling Amphiphilic Peptide Dendrimer-Based Drug Delivery System for Cancer Therapy

Despite being a mainstay of clinical cancer treatment, chemotherapy is limited by its severe side effects and inherent or acquired drug resistance. Nanotechnology-based drug-delivery systems are widely expected to bring new hope for cancer therapy. These systems exploit the ability of nanomaterials to accumulate and deliver anticancer drugs at the tumor site via the enhanced permeability and retention effect. Here, we established a novel drug-delivery nanosystem based on amphiphilic peptide dendrimers (AmPDs) composed of a hydrophobic alkyl chain and a hydrophilic polylysine dendron with different generations (AmPD KK2 and AmPD KK2K4). These AmPDs assembled into nanoassemblies for efficient encapsulation of the anti-cancer drug doxorubicin (DOX). The AmPDs/DOX nanoformulations improved the intracellular uptake and accumulation of DOX in drug-resistant breast cancer cells and increased permeation in 3D multicellular tumor spheroids in comparison with free DOX. Thus, they exerted effective anticancer activity while circumventing drug resistance in 2D and 3D breast cancer models. Interestingly, AmPD KK2 bearing a smaller peptide dendron encapsulated DOX to form more stable nanoparticles than AmPD KK2K4 bearing a larger peptide dendron, resulting in better cellular uptake, penetration, and anti-proliferative activity. This may be because AmPD KK2 maintains a better balance between hydrophobicity and hydrophilicity to achieve optimal self-assembly, thereby facilitating more stable drug encapsulation and efficient drug release. Together, our study provides a promising perspective on the design of the safe and efficient cancer drug-delivery nanosystems based on the self-assembling amphiphilic peptide dendrimer.

A Study with Peptide Dendrimers Reveals an Extreme pH Dependence of Antibiotic Activity Above pH 7.4

The presence of ionizable groups in antimicrobial peptides (AMPs) often induces a pH-dependent activity. Herein we report that removing eight low p<i>K</i>_a amino termini in antimicrobial peptide dendrimer (AMPD) <b>G3KL</b> provides dendrimer <b>XC1</b> with a broader pH-activity range. Furthermore, raising the pH to 8.0 reveals strong activities against <i>Klebsiella pneumoniae</i> and methicillin resistant <i>Staphylococcus aureus</i> (MRSA) against which these AMPDs are inactive at pH 7.4. We observe a similar effect with polymyxin B on MRSA. Binding experiments with a fluorescent AMPD and the effect of high salt concentration suggest that the activity increase reflects stronger electrostatic binding to the bacteria at high pH. pH-profiling of other polycationic antimicrobials (polymers, peptidomimetics, foldamers, dendrimers) might similarly enhance their activity range, with possible use for topical treatments.