Interfacial interactions between poly[L-lysine]-based branched polypeptides and phospholipid model membranes

Transcytosis of Nanomedicine for Tumor Penetration

The diffusion of nanomedicines used to treat tumors is severely hindered by the microenvironment, which is a challenge that has emerged as a bottleneck for the effective outcome of nanotherapies. Classical strategies for enhancing tumor penetration rely on passive movement in the extracellular matrix (ECM). Here, we demonstrate that nanomedicine also penetrates tumor lesions via an active trans-cell transportation process. This process was discovered by directly observing the movement of nanoparticles between cells, evaluating the intracellular trafficking pathway of nanoparticles via Rab protein labeling, comparing endocytosis-exocytosis between nanoparticles administered with inhibitors, and correlating the transcytosis process with the micro-CT distribution of nanomedicines. We also demonstrated that enhanced tumor penetration promotes the therapeutic efficacy of a photodynamic therapeutic nanomedicine. Our research thus suggests that transcytosis could be an important positive factor for designing cancer nanomedicines.

Counting charges on membrane-bound peptides

Quantifying the number of charges on peptides bound to interfaces requires reliable estimates of (i) surface coverage and (ii) surface charge, both of which are notoriously difficult parameters to obtain, especially at solid/water interfaces. Here, we report the thermodynamics and electrostatics governing the interactions of l-lysine and l-arginine octamers (Lys₈ and Arg₈) with supported lipid bilayers prepared.

Quantifying the number of charges on peptides bound to interfaces requires reliable estimates of (i) surface coverage and (ii) surface charge, both of which are notoriously difficult parameters to obtain, especially at solid/water interfaces. Here, we report the thermodynamics and electrostatics governing the interactions of l-lysine and l-arginine octamers (Lys₈ and Arg₈) with supported lipid bilayers prepared from a 9 : 1 mixture of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (sodium salt) (DMPG) from second harmonic generation (SHG) spectroscopy, quartz crystal microbalance with dissipation monitoring (QCM-D) and nanoplasmonic sensing (NPS) mass measurements, and atomistic simulations. The combined SHG/QCM-D/NPS approach provides interfacial charge density estimates from mean field theory for the attached peptides that are smaller by a factor of approximately two (0.12 ± 0.03 C m^–2 for Lys₈ and 0.10 ± 0.02 C m^–2 for Arg₈) relative to poly-l-lysine and poly-l-arginine. These results, along with atomistic simulations, indicate that the surface charge density of the supported lipid bilayer is neutralized by the attached cationic peptides. Moreover, the number of charges associated with each attached peptide is commensurate with those found in solution; that is, Lys₈ and Arg₈ are fully ionized when attached to the bilayer. Computer simulations indicate Lys₈ is more likely than Arg₈ to “stand-up” on the surface, interacting with lipid headgroups through one or two sidechains while Arg₈ is more likely to assume a “buried” conformation, interacting with the bilayer through up to six sidechains. Analysis of electrostatic potential and charge distribution from atomistic simulations suggests that the Gouy–Chapman model, which is widely used for mapping surface potential to surface charge, is semi-quantitatively valid; despite considerable orientational preference of interfacial water, the apparent dielectric constant for the interfacial solvent is about 30, due to the thermal fluctuation of the lipid–water interface.

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.

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.

Quantification of the force of nanoparticle-cell membrane interactions and its influence on intracellular trafficking of nanoparticles

Understanding the interaction of nanoparticles (NPs) with the cell membrane and their trafficking through cells is imperative to fully explore the use of NPs for efficient intracellular delivery of therapeutics. Here, we report a novel method of measuring the force of NP-cell membrane interactions using atomic force microscopy (AFM). Poly(D,L-lactide-co-glycolide) (PLGA) NPs functionalized with poly-L-lysine were used as a model system to demonstrate that this force determines the adhesive interaction of NPs with the cell membrane and in turn the extent of cellular uptake of NPs, and hence that of the encapsulated therapeutic. Cellular uptake of NPs was monitored using AFM imaging and the dynamics of their intracellular distribution was quantified using confocal microscopy. Results demonstrated that the functionalized NPs have a five-fold greater force of adhesion with the cell membrane and the time-lapse AFM images show their rapid internalization than unmodified NPs. The intracellular trafficking study showed that the functionalized NPs escape more rapidly and efficiently from late endosomes than unmodified NPs and result in 10-fold higher intracellular delivery of the encapsulated model protein. The findings described herein enhance our basic understanding of the NP-cell membrane interaction on the basis of physical phenomena that could have wider applications in developing efficient nanocarrier systems for intracellular delivery of therapeutics.

Spectroscopic techniques applied to the study of laminin fragments inserted into model membranes

The influence of four laminin-derived peptides on bilayer organization is studied. Spectroscopic methods applied were based on pyrene fluorescence properties (quenching, I1/I3, and monomer/excimer equilibrium), asymmetric membrane fluorescence (NBD-PE/dithionite), and polarization fluorescence (TMA-DPH). Also, the ability of these peptides to release carboxyfluorescein entrapped in vesicles was determined. Results suggest that these peptides do not noticeably modify the packing and motion of lipids (in the gel state), but coat its surface, preventing penetration of quenchers and chemical reactants. Nevertheless, their presence promotes a soft release of entrapped CF after incubation at 37 degrees C.

Uptake of Branched Polypeptides with Poly[l-Lys] Backbone by Bone-Marrow Culture-Derived Murine Macrophages: The Role of the Class A Scavenger Receptor

Selective delivery of antiparasitic or antibacterial drugs into infected macrophages could be a promising approach for improved therapies. Methotrexate conjugate with branched chain polypeptides exhibited pronounced anti-Leishmania activity in vitro and in vivo as reported here earlier. To identify structural requirements for efficient uptake of branched polypeptides, we have studied murine bone marrow culture-derived macrophages (BMMphi) from 129/ICR mice. We report on the translocation characteristics of structurally closely related compounds labeled with 5(6)-carboxyfluorescein. We found that this process is dependent on experimental conditions (e.g. polypeptide concentration, incubation time, and temperature). Using specific inhibitors as well as macrophages from wild-type and class-A scavenger receptor knockout (SR-A -/-) mice, we demonstrated that SR-A was involved in the endocytosis of some polypeptides depending on their charge. Uptake could be blocked by unlabeled polypeptide, by SR-A inhibitors, and by specific anti-SR-A monoclonal antibody. The polyanionic polypeptide poly[Lys(Succ-Glu(1.0)-dl-Ala(3.8))] (SuccEAK) with high charge density translocated more efficiently than poly[Lys(Ac-Glu(1.0)-dl-Ala(3.8))] (AcEAK), which had a lower anionic charge density. On the basis of experimental data presented, SuccEAK can be considered as a potential candidate for the design of a macromolecular carrier for specific drug delivery of bioactive entities into macrophages via SR-A.

Interaction of poly-L-arginine with dihexadecyl phosphate/phosphatidylcholine liposomes

In the present study, mixed liposomes of dihexadecyl phosphate sodium salt:phosphatidylcholine:cholesterol at a 1:19:9.5 molar ratio were allowed to interact with poly-L-arginine at temperatures below and above the main phase transition of the liposomal membrane. The interaction led to the formation of aggregates, which gradually increased in size and eventually precipitated. It was, however, possible, during the initial stage of the experiments, when the ratio of guanidinium group relative to phosphate was smaller than ca. 40%, to determine their size and charge and observe their morphology in aqueous dispersion. Fluorescence experiments established that the liposomes are not ruptured during their interaction with poly-L-arginine. Instead, they are attached at the polypeptide chain through the guanidinium-phosphate complementary pair. Fluorescence quenching experiments indicated that the poly-L-arginine chain is accessible for interaction with iodides dissolved in the aqueous phase when the temperature of the liposomal dispersion is below the main lipid phase transition. It is, however, partitioned in the interior of the membrane at temperatures exceeding this main lipid phase transition.