Membrane permeation of arginine-rich cell-penetrating peptides independent of transmembrane potential as a function of lipid composition and membrane fluidity

Membrane potential drives direct translocation of cell-penetrating peptides

Cell-penetrating peptides (CPPs) are frequently employed as drug delivery agents with rapid cellular uptake, however, the uptake mechanism and the detailed translocation pathway are at present not completely understood. Both endocytosis and direct translocation through membrane pores have been observed in experiments and simulations under different conditions. Here we report the molecular dynamics simulations providing evidence for the direct translocation of CPPs across the membrane driven by the membrane electrostatic potential. The local membrane potential can be produced by the ion concentration imbalance across the membrane, which is ubiquitous in biological environments. Moreover, if positively charged CPPs are adsorbed on the membrane, this further enhances the membrane potential, opening membrane pores through which CPPs can be instantly transported in a chain-like configuration. The classical nucleation theory is applied to estimate the translocation time by calculating the changes in the free energy upon transferring CPPs across the membrane at different potentials, showing good agreement with available experimental measurements. The revealed CPP translocation mechanism can be broadly relevant for cellular processes in biology.

Coated microneedles mediated intradermal delivery of octaarginine/BRAF siRNA nanocomplexes for anti-melanoma treatment

BRAF is the most frequently mutated gene in skin melanoma. Applying BRAF siRNA (siBraf) to silencing BRAF gene is a current frontline therapy for melanoma. However, delivery of macromolecular siRNA into the tumor site and introduction of siRNA into the tumor cells remain as challenges. In this study, we for the first time developed a siBraf delivery system based on cell penetrating peptide octaarginine (R8) nanocomplexes combined with coated microneedles (MNs), i.e. R8/siBraf coated MNs, for targeted anti-melanoma treatment. The R8/siBraf nanocomplexes were optimized based on the internalization of siBraf by A375 cells. In vitro A375 cell experiments presented that R8/siBraf can enhance siBraf transfection, silence BRAF gene, and inhibit tumor cells growth, comparable to polyethylenimine (PEI)/siBraf. R8/siBraf coated MNs can effectively deliver R8/siBraf into the disease site. In vivo anti-melanoma experiments indicated that R8/siBraf coated MNs can significantly inhibit the melanoma development, induce the tumor cells apoptosis, and suppress their proliferation. The BRAF gene in tumor were also significantly silenced in vivo. SiBraf intradermal delivery via combining MNs and R8 nanocomplexes is a promising approach for skin melanoma treatment, which exploited both virtues of MNs and cell penetrating peptide to obtain the targeting inhibition efficacy on skin melanoma.

Synthetic molecular evolution of hybrid cell penetrating peptides

Peptides and analogs such as peptide nucleic acids (PNA) are promising tools and therapeutics, but the cell membrane remains a barrier to intracellular targets. Conjugation to classical cell penetrating peptides (CPPs) such as pTat_48–60 (tat) and pAntp_43–68 (penetratin) facilitates delivery; however, efficiencies are low. Lack of explicit design principles hinders rational improvement. Here, we use synthetic molecular evolution (SME) to identify gain-of-function CPPs with dramatically improved ability to deliver cargoes to cells at low concentration. A CPP library containing 8192 tat/penetratin hybrid peptides coupled to an 18-residue PNA is screened using the HeLa pTRE-LucIVS2 splice correction reporter system. The daughter CPPs identified are one to two orders of magnitude more efficient than the parent sequences at delivery of PNA, and also deliver a dye cargo and an anionic peptide cargo. The significant increase in performance following a single iteration of SME demonstrates the power of this approach to peptide sequence optimization.

Therapeutic peptide nucleic acids can be delivered into cells by conjugation to cell penetrating peptides (CPPs), but efficiency is usually low. Here the authors use synthetic molecular evolution and a luciferase-based library screen to generate new CPPs with improved efficiency and lower toxicity.

Penetration in 3D tumor spheroids and explants: Adding a further dimension to the structure-activity relationship of cell-penetrating peptides

Drug delivery into tumors and metastases is a major challenge in the eradication of cancers such as epithelial ovarian carcinoma. Cationic cell-penetrating peptides (CPPs) are a promising group of delivery vehicles to mediate cellular entry of molecules that otherwise poorly enter cells. However, little is known about their penetration behavior in tissues. Here, we investigated penetration of cationic CPPs in 3D ovarian cancer spheroids and patient-derived 3D tumor explants. Penetration kinetics and distribution after long-term incubation were imaged by confocal microscopy. In addition, spheroids and tumor explants were dissociated and cell-associated fluorescence determined by flow cytometry. CPPs with high uptake activity showed enhanced sequestration in the periphery of the spheroid, whereas less active CPPs were able to penetrate deeper into the tissue. CPPs consisting of d-amino acids were advantageous over l-amino acid CPPs as they showed less but long lasting cellular uptake activity, which benefitted penetration and retention over time. In primary tumor cultures, in contrast to nonaarginine, the amphipathic CPP penetratin was strongly sequestered by cell debris and matrix components pointing towards arginine-rich CPPs as a preferred choice. Overall, the data show that testing in 3D models leads to a different choice of the preferred peptide in comparison to a standard 2D cell culture.

Novel peptide MT23 for potent penetrating and selective targeting in mouse melanoma cancer cells

Cell-penetrating peptides (CPPs) have a great potential for intracellular delivery of cell-impermeable biological macromolecules in clinical therapy. However, their lack of cell and tissue specificity remains the primary limitation for their clinical development as drug delivery vehicles. In this study, based on phage display and an in silico approach, we found a novel CPP-MT23 with mouse melanoma cell specificity, it can only enter B16 melanoma cancer cells and without any cytotoxicity, Moreover, MT23 showed higher penetration efficiency based on fluorescence microcopy and quantitative assay, and it has capability for mediating functional Apoptin into cells in vitro or in vivo. Moreover, MT23-Apoptin can significantly inhibit tumor growth and induce the cell apoptosis in B16 tumor bearing mice. To sum up, all the results implicated that MT23 has the potential to deliver exogenous therapeutic proteins for further use and it also expected to lay the foundation for developing human melanoma cancer cell specific CPP.

Self-aggregation propensity of the Tat peptide revealed by UV-Vis, NMR and MD analyses

The self-aggregation propensity of unlabeled and TAMRA-labeled Tat₁₁ peptides has been revealed for the first time by UV-Vis, NMR and MD analyses.