Modular Design of Poly(norbornenes) for Organelle-Specific Imaging in Tumor Cells

Through modular ROMP (ring-opening metathesis polymerization) directly from monomeric norbornenes of bioactive peptides, rhodamine B chromophore, and PEG solubilizer, we designed and synthesized a series of water-soluble poly(norbornenes) with organelle-specific imaging capability in tumor cells. For the selection of FxrFxK, TAT, and SV40 peptide sequences, these fluorescence probes exhibited different targeting specificity toward mitochondria, lysosome, and nucleolus, respectively, based on the same poly(norbornene) backbonds. More importantly, the ROMP strategy enables selective combination from various monomers and allows programmable biofunctionalization via peptide sequence permutations, which would greatly extend the biomedical applications such as imaging, diagnosis, and therapy for these synthetic polymers.

Optical and electron microscopy study of laser-based intracellular molecule delivery using peptide-conjugated photodispersible gold nanoparticle agglomerates

Background

Cell-penetrating peptides (CPPs) can act as carriers for therapeutic molecules such as drugs and genetic constructs for medical applications. The triggered release of the molecule into the cytoplasm can be crucial to its effective delivery. Hence, we implemented and characterized laser interaction with defined gold nanoparticle agglomerates conjugated to CPPs which enables efficient endosomal rupture and intracellular release of molecules transported.

Results

Gold nanoparticles generated by pulsed laser ablation in liquid were conjugated with CPPs forming agglomerates and the intracellular release of molecules was triggered via pulsed laser irradiation (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda$$\end{document}λ = 532 nm, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau _{pulse}$$\end{document}τpulse = 1 ns). The CPPs enhance the uptake of the agglomerates along with the cargo which can be co-incubated with the agglomerates. The interaction of incident laser light with gold nanoparticle agglomerates leads to heat deposition and field enhancement in the vicinity of the particles. This highly precise effect deagglomerates the nanoparticles and disrupts the enclosing endosomal membrane. Transmission electron microscopy images confirmed this rupture for radiant exposures of 25 mJ/cm\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{2}$$\end{document}2 and above. Successful intracellular release was shown using the fluorescent dye calcein. For a radiant exposure of 35 mJ/cm\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{2}$$\end{document}2 we found calcein delivery in 81 % of the treated cells while maintaining a high percentage of cell viability. Furthermore, cell proliferation and metabolic activity were not reduced 72 h after the treatment.

Conclusion

CPPs trigger the uptake of the gold nanoparticle agglomerates via endocytosis and co-resident molecules in the endosomes are released by applying laser irradiation, preventing their intraendosomal degradation. Due to the highly localized effect, the cell membrane integrity is not affected. Therefore, this technique can be an efficient tool for spatially and temporally confined intracellular release. The utilization of specifically designed photodispersible gold nanoparticle agglomerates (65 nm) can open novel avenues in imaging and molecule delivery. Due to the induced deagglomeration the primary, small particles (~5 nm) are more likely to be removed from the body.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-015-0155-8) contains supplementary material, which is available to authorized users.

Synthesis and mode of action of oligomeric sesquiterpene lactones

In this highlight we describe two case studies from our laboratory, involving the biomimetic syntheses and the biological mechanism elucidation of the bioactive oligomeric sesquiterpenoids, (+)-ainsliadimer A (4) and (−)-ainsliatrimer A (5).

Guanidiniocarbonyl pyrrole (GCP) conjugated PAMAM-G2, a highly efficient vector for gene delivery: the importance of DNA condensation

A novel hybrid compound1efficiently shuttles genetic material into HeLa cells at concentrations as low as 0.6 μM, whereas the parent compound PAMAM-G2 is ineffective even at 200 μM.

Cell-Penetrating Peptides as Carriers for Oral Delivery of Biopharmaceuticals

Oral delivery of biopharmaceuticals, for example peptides and proteins, constitutes a great challenge in drug delivery due to their low chemical stability and poor permeation across the intestinal mucosa, to a large extent limiting the mode of administration to injections, which is not favouring patient compliance. Nevertheless, cell-penetrating peptides (CPPs) have shown promising potential as carriers to overcome the epithelium, and this minireview highlights recent knowledge gained within the field of CPP-mediated transepithelial delivery of therapeutic peptides and proteins from the intestine. Two approaches may be pursued: co-administration of the carrier and therapeutic peptide in the form of complexes obtained by simple bulk mixing, or administration of covalent conjugates demanding more advanced production methodologies. These formulation approaches have their pros and cons, and which is to be preferred depends on the physicochemical properties of both the specific CPP and the specific cargo. In addition to the physical epithelial barrier, a metabolic barrier must be overcome in order to obtain CPP-mediated delivery of a cargo drug from the intestine, and a number of strategies have been employed to delay enzymatic degradation of the CPP. The mechanisms by which CPPs translocate across membranes are not fully understood, but possibly involve endocytosis as well as direct translocation, and the CPP-mediated transepithelial delivery of cargo drugs thus likely involves similar mechanisms for the initial membrane interaction and translocation. However, the mechanisms responsible for transcytosis of the cargo drug, if taken up by an endocytic mechanism, or direct translocation across the epithelium are so far not known.

Rapid Endolysosomal Escape and Controlled Intracellular Trafficking of Cell Surface Mimetic Quantum-Dots-Anchored Peptides and Glycopeptides

A novel strategy for the development of a high performance nanoparticules platform was established by means of cell surface mimetic quantum-dots (QDs)-anchored peptides/glycopeptides, which was developed as a model system for nanoparticle-based drug delivery (NDD) vehicles with defined functions helping the specific intracellular trafficking after initial endocytosis. In this paper, we proposed a standardized protocol for the preparation of multifunctional QDs that allows for efficient cellular uptake and rapid escaping from the endolysosomal system and subsequent cytoplasmic molecular delivery to the target cellular compartment. Chemoselective ligation of the ketone-functionalized hexahistidine derivative facilitated both efficient endocytic entry and rapid endolysosomal escape of the aminooxy/phosphorylcholine self-assembled monolayer-coated QDs (AO/PCSAM-QDs) to the cytosol in various cell lines such as human normal and cancer cells, while modifications of these QDs with cell-penetrating arginine-rich peptides showed poor cellular uptake and induced self-aggregation of AO/PCSAM-QDs. Combined use of hexahistidylated AO/PCSAM-QDs with serglycine-like glycopeptides, namely synthetic proteoglycan initiators (PGIs), elicited the entry and controlled intracellular trafficking, Golgi localization, and also excretion of these nanoparticles, which suggested that the present approach would provide an ideal platform for the design of high performance NDD systems.

Second Generation TQ-Ligation for Cell Organelle Imaging

Bioorthogonal ligations play a crucial role in labeling diverse types of biomolecules in living systems. Herein, we describe a novel class of ortho-quinolinone quinone methide (oQQM) precursors that show a faster kinetic rate in the "click cycloaddition" with thio-vinyl ether (TV) than the first generation TQ-ligation in both chemical and biological settings. We further demonstrate that the second generation TQ-ligation is also orthogonal to the widely used strain-promoted azide-alkyne cycloaddition (SPAAC) both in vitro and in vivo, revealing that these two types of bioorthogonal ligations could be used as an ideal reaction pair for the simultaneous tracking of multiple elements within a single system. Remarkably, the second generation TQ-ligation and SPAAC are effective for selective and simultaneous imaging of two different cell organelles in live cells.

Enhanced oral bioavailability of insulin using PLGA nanoparticles co-modified with cell-penetrating peptides and Engrailed secretion peptide (Sec)

Biodegradable polymer nanoparticle drug carriers are an attractive strategy for oral delivery of peptide and protein drugs. However, their ability to cross the intestinal epithelium membrane is largely limited. Therefore, in the present study, cell-penetrating peptides (R8, Tat, penetratin) and a secretion peptide (Sec) with N-terminal stearylation were introduced to modify nanoparticles (NPs) on the surface to improve oral bioavailability of peptide and protein drugs. In vitro studies conducted in Caco-2 cells showed the value of the apparent permeability coefficient (Papp) of the nanoparticles co-modified with Sec and penetratin (Sec-Pen-NPs) was about two-times greater than that of the nanoparticles modified with only penetratin (Pen-NPs), while the increase of transcellular transport of nanoparticles modified together with Sec and R8 (Sec-R8-NPs), or Sec and Tat (Sec-Tat-NPs), was not significant compared with nanoparticles modified with only R8 (R8-NPs) or Tat (Tat-NPs). Using insulin as the model drug, in vivo studies performed on rats indicated that compared to Pen-NPs, the relative bioavailability of insulin for Sec-Pen-NPs was 1.71-times increased after ileal segments administration, and stronger hypoglycemic effects was also observed. Therefore, the nanoparticles co-modified with penetratin and Sec could act as attractive carriers for oral delivery of insulin.

Targeting the HIV RNA genome: high-hanging fruit only needs a longer ladder

Small molecules targeting the enzymes responsible for human immunodeficiency virus (HIV) maturation, DNA synthesis and its subsequent chromosomal integration as ribonucleotide-free double-stranded DNA remain the mainstay of combination antiretroviral therapy. For infected individuals harboring drug-susceptible virus, this approach has afforded complete or near-complete viral suppression. However, in the absence of a curative strategy, the predictable emergence of drug-resistant variants requires continued development of improved antiviral strategies, inherent to which is the necessity of identifying novel targets. Regulatory elements that mediate transcription, translation, nucleocytoplasmic transport, dimerization, packaging and reverse transcription of the (+) strand RNA genome should now be considered viable targets for small molecule, peptide- and oligonucleotide-based therapeutics. Where target specificity and cellular penetration and toxicity have been the primary obstacle to successful “macromolecule therapeutics”, this chapter summarizes (a) novel approaches targeting RNA motifs whose three-dimensional structure is critical for biological function and consequently may be less prone to resistance-conferring mutations and (b) improved methods for delivery.

Mitophagy induced by nanoparticle-peptide conjugates enabling an alternative intracellular trafficking route

The intracellular behaviors of nanoparticles are fundamentally important for the evaluation of their biosafety and the designs of nano carrier-assisted drug delivery with high therapeutic efficacy. It is still in a great need to discover how functionalized nanoparticles are transported inside the cells, for instance, in a complicated fashion of translocation between different types of cell organelles. Here we report a new understanding of the interactions between nanoparticles and cells by the development of polyoxometalates nanoparticle-peptide conjugates and investigation of their intracellular trafficking behaviors. The as-prepared nanoparticles are featured with a unique combination of fluorescence and high contrast for synchrotron X-ray-based imaging. Functional surface modification with peptides facilitates effective delivery of the nanoparticles onto the target organelle (mitochondria) and subsequent intracellular trafficking in a dynamic mode. Interestingly, our experimental results have revealed that autophagy of mitochondria (mitophagy) can be induced by NP-peptide as a cellular response for recycling the damaged organelles, through molecular mediation associated with the change of mitochondrial membrane potential. The biological effects induced by NP-peptide reciprocally affect the distribution patterns and fates of nanoparticles in the cell metabolism by providing an alternative route of intracellular trafficking. The new understanding of the mutual activities between nanoparticles and cells will enrich our approaches in the development of nanobiotechnology and nano-medicine for disease treatments.

Compact, Programmable, and Stable Biofunctionalized Upconversion Nanoparticles Prepared through Peptide-Mediated Phase Transfer for High-Sensitive Protease Sensing and in Vivo Apoptosis Imaging

Protease represents an important class of biomarkers for disease diagnostics and drug screening. Conventional fluorescence-based probes for in vivo protease imaging suffer from short excitation wavelengths and poor photostability. Upconversion nanoparticles (UCNPs) hold great promise for biosensing and bioimaging because of their deep-tissue excitability, robust photostability, and minimal imaging background. However, producing highly stable and compact biofunctionalized UCNP probes with optimal bioresponsivity for in vivo imaging of protease activities still remains challenging and has not been previously demonstrated. Herein, we report facile preparation of highly compact and stable biofunctionalized UCNPs through peptide-mediated phase transfer for high-sensitive detection of protease in vitro and in vivo. We demonstrate that the polyhistidine-containing chimeric peptides could displace oleic acid molecules capped on UCNPs synthesized in organic solvents and, thereby, directly transfer UCNPs from the chloroform phase to the water phase. The resulting UCNPs possess high stability, programmable surface properties, and a compact coating layer with minimized thickness for efficient luminescence resonance energy transfer (LRET). On the basis of this strategy, we prepared LRET-based UCNP probes with optimal bioresponsivity for in vitro high-sensitive detection of trypsin and in vivo imaging of apoptosis for chemotherapy efficacy evaluation. The reported strategy could be extended to construct a variety of peptide-functionalized UCNPs for various biomedical applications.

Enzyme-Activatable Cell-Penetrating Peptides through a Minimal Side Chain Modification

Activatable cell-penetrating peptides are of great interest in drug delivery because of their enhanced selectivity which can be controlled by the external stimuli that trigger their activation. The use of a specific enzymatic reaction to trigger uptake of an inert peptide offers a relevant targeting strategy because the activation process takes place in a short time and only in areas where the specific cell surface enzyme is present. To this aim, the lysine side chain of Tat peptides was modified with an enzyme-cleavable domain of minimal size. This yielded blocked Tat-peptides which were inactive but that could be activated by coincubation with the selected enzymes.

Construction of antibody-like nanoparticles for selective protein sequestration in living cells

We demonstrate the successful construction of fluorescently labeled magnetic antibody-like nanoparticles (ANPs) via a facile one-step surface-initiated in situ molecular imprinting approach over silica coated magnetite (Fe3O4@SiO2) core-shell nanocomposites. The as-prepared ANPs had a highly compact structure with an overall size of 83 ± 5 nm in diameter and showed excellent aqueous dispersion stability. With the predetermined high specificity to the target protein and high biocompatibility, the ANPs enabled rapid, efficient, selective and optically trackable sequestration of target proteins within living cells. This work represents the first example of fully artificially engineered multifunctional ANPs for the intracellular protein-sequestration without disruption of the cells. The established approach may be further extended to generate ANPs for various proteins of interest and provide useful tools for related biological research and biomedical applications.

Protamine-oligonucleotide-nanoparticles: Recent advances in drug delivery and drug targeting

Application of oligonucleotides as active compounds has become a crucial field of pharmaceutical research in recent years. In order to improve inadequate transfection rate and to avoid rapid enzymatic degradation of antisense oligonucleotides (AS-ODNs) a novel nanoparticulate delivery system was reported by our group at the beginning of 2000. AS-ODNs are condensed by the polycationic peptide protamine into solid particles in the size range of 100-200nm. Nanoparticle formation is driven by a self-assembling process based on electrostatic interactions between the oppositely charged biomolecules. This new delivery system was named "proticles" and showed very efficient protection against enzymatic digestion, high transfection rates and significant antisense effects in vitro. Throughout broader research, this promising approach was enlarged, and AS-ODNs were replaced by siRNA or CpG-oligonucleotides to address the aspect of immune-modulation and vaccination. More recent studies on proticles verified upscaling of the self-assembling process as well as the potential of proticle formulations for active drug targeting, like tumor- or atherosclerotic plaque targeting. Thereby also the application for diagnostic purposes was emphasized. This review will focus on the characterization of the nucleoprotein protamine as well as on the variety of possible nucleotides/peptides which were already assembled into the proticle matrix. Furthermore it will provide an insight into the broad area of application where proticles can present a valuable tool for successful oligonucleotide delivery.

Surface modification and local orientations of surface molecules in nanotherapeutics

Nanotechnology has emerged as a powerful tool for various therapeutic applications, solving many difficulties in both diagnosis and treatment. However, many obstacles in complex biological systems have impeded the successful application of therapeutic nanoparticles, and fine-tuning nanoparticle properties have become extremely important in developing highly effective nanomedicines. To this end, particles have been engineered in various ways, with a special emphasis on surface modifications. The nanoparticle surface contacts the biological environment, and is a crucial determinant of the response. Thus, surface coating, surface charge, conjugated molecules, shape, and topography have enormous impacts on the total behavior of nanoparticles, including their biodistribution, stability, target localization, cellular interaction, uptake, drug release, and toxicity. Hence, engineering of the particle surface would provide wider dimensions of control for the specific and precise functions in the development of smart nanomedicines. Moreover, local orientation of nanoparticles in vivo and orientations of surface molecules are critical for their efficacy. Herein, we analyze surface functionalities, focusing on their mechanisms and respective advantages, and summarize results of surface engineering and renovating applications of nanoparticles.

Oligonucleotide delivery with cell surface binding and cell penetrating Peptide amphiphile nanospheres

A drug delivery system designed specifically for oligonucleotide therapeutics can ameliorate the problems associated with the in vivo delivery of these molecules. The internalization of free oligonucleotides is challenging, and cytotoxicity is the main obstacle for current transfection vehicles. To develop nontoxic delivery vehicles for efficient transfection of oligonucleotides, we designed a self-assembling peptide amphiphile (PA) nanosphere delivery system decorated with cell penetrating peptides (CPPs) containing multiple arginine residues (R4 and R8), and a cell surface binding peptide (KRSR), and report the efficiency of this system in delivering G-3129, a Bcl-2 antisense oligonucleotide (AON). PA/AON (peptide amphiphile/antisense oligonucleotide) complexes were characterized with regards to their size and secondary structure, and their cellular internalization efficiencies were evaluated. The effect of the number of arginine residues on the cellular internalization was investigated by both flow cytometry and confocal imaging, and the results revealed that uptake efficiency improved as the number of arginines in the sequence increased. The combined effect of cell penetration and surface binding property on the cellular internalization and its uptake mechanism was also evaluated by mixing R8-PA and KRSR-PA. R8 and R8/KRSR decorated PAs were found to drastically increase the internalization of AONs compared to nonbioactive PA control. Overall, the KRSR-decorated self-assembled PA nanospheres were demonstrated to be noncytotoxic delivery vectors with high transfection rates and may serve as a promising delivery system for AONs.

Cytotoxic peptide conjugates of dinuclear arene ruthenium trithiolato complexes

Novel dinuclear arene ruthenium trithiolato complexes containing a water-soluble peptide moiety in one of the three thiolato bridges were designed and evaluated against A2780 human ovarian cancer cells and against their cisplatin-resistant mutant A2780cisR.

A versatile pH-responsive platform for intracellular protein delivery using calcium phosphate nanoparticles

A highly biocompatible nanoplatform for the intracellular delivery of different proteins, exhibiting pH-responsive release and efficient endosomal escape.

Poly-α,β-aspartyl-Arg-Gly-Asp-Phe: a novel polymeric nanomedicine

High anti-thrombotic efficacy, action target and nano-structure of a novel nanomedicine were described.

Targeting mitochondria with small molecules: the preparation of MitoB and MitoP as exomarkers of mitochondrial hydrogen peroxide

Small molecules can be physicochemically targeted to mitochondria using the lipophilic alkyltriphenylphosphonium (TPP) group. Once in the mitochondria the TPP-conjugate can detect or influence processes within the mitochondrial matrix directly. Alternatively, the conjugate can behave as a prodrug, which is activated by release from the TPP group either using an internal or external instruction. Small molecules can be designed that can be used in any cell line, tissue or whole organism, allow temporal control, and be applied in a reversible dose-dependent fashion. An example is the detection and quantification of hydrogen peroxide in mitochondria of whole living organisms by MitoB. Hydrogen peroxide produced within the mitochondrial matrix is involved in signalling and implicated in the oxidative damage associated with aging and a wide range of age-associated conditions including cardiovascular disease, neurodegeneration, and cancer. MitoB accumulates in mitochondria and is converted into the exomarker, MitoP, by hydrogen peroxide in the mitochondrial matrix. The hydrogen peroxide concentration is determined from the ratio of MitoP to MitoB after a period of incubation, and this ratio is determined by mass spectrometry using d15-MitoP and d15-MitoB as standard. Here we describe the synthesis of MitoB and MitoP and the deuterated standards necessary for this method of quantification.

Delivery of SiC-based nanoparticles into live cells driven by cell-penetrating peptides SAP and SAP-E

Cell-penetrating peptides enhance nanoparticle delivery into cells most efficiently if surface and peptide functional groups “match” to form non-covalent conjugates.

Phosphorescent proteins for bio-imaging and site selective bio-conjugation of peptides and proteins with luminescent cyclometalated iridium(III) complexes

A new bio-conjugation reaction for site selective modification of proteins and peptides with phosphorescent iridium(III) complexes has been developed; the Ir(III)-modified proteins and peptides display long emission lifetimes and large Stoke shifts that can be used for bio-imaging studies.

Peptide-coated liposomal fasudil enhances site specific vasodilation in pulmonary arterial hypertension

This study sought to develop a liposomal delivery system of fasudil—an investigational drug for the treatment of pulmonary arterial hypertension (PAH)—that will preferentially accumulate in the PAH lungs. Liposomal fasudil was prepared by film-hydration method, and the drug was encapsulated by active loading. The liposome surface was coated with a targeting moiety, CARSKNKDC, a cyclic peptide; the liposomes were characterized for size, polydispersity index, zeta potential, and storage and nebulization stability. The in vitro drug release profiles and uptake by TGF-β activated pulmonary arterial smooth muscle cells (PASMC) and alveolar macrophages were evaluated. The pharmacokinetics were monitored in male Sprague–Dawley rats, and the pulmonary hemodynamics were studied in acute and chronic PAH rats. The size, polydispersity index (PDI), and zeta potential of the liposomes were 206–216 nm, 0.058–0.084, and −20–42.7 mV, respectively. The formulations showed minimal changes in structural integrity when nebulized with a commercial microsprayer. The optimized formulation was stable for >4 weeks when stored at 4 °C. Fasudil was released in a continuous fashion over 120 h with a cumulative release of 76%. Peptide-linked liposomes were taken up at a higher degree by TGF-β activated PASMCs; but alveolar macrophages could not engulf peptide-coated liposomes. The formulations did not injure the lungs; the half-life of liposomal fasudil was 34-fold higher than that of plain fasudil after intravenous administration. Peptide-linked liposomal fasudil, as opposed to plain liposomes, reduced the mean pulmonary arterial pressure by 35–40%, without influencing the mean systemic arterial pressure. This study establishes that CAR-conjugated inhalable liposomal fasudil offers favorable pharmacokinetics and produces pulmonary vasculature specific dilatation.

Peptide Targeting of Fluorescein-Based Sensors to Discrete Intracellular Locales

Fluorescein-based sensors are the most widely applied class of zinc probes but display adventitious localization in live cells. We present here a peptide-based localization strategy that affords precision in targeting of fluorescein-based zinc sensors. By appending the zinc-selective, reaction-based probe Zinpyr-1 diacetate (DA-ZP1) to the N-terminus of two different targeting peptides we achieve programmable localization and avoid unwanted sequestration within acidic vesicles. Furthermore, this approach can be generalized to other fluorescein-based sensors. When appended to a mitochondrial targeting peptide, the esterase-activated profluorophore 2',7'-dichlorofluorescein diacetate can be used effectively at concentrations four-times lower than previously reported for analogous, non-acetylated derivatives. These results demonstrate on-resin or in-solution esterification of fluorescein to be an effective strategy to facilitate peptide-based targeting in live cells.

Identification of BP16 as a non-toxic cell-penetrating peptide with highly efficient drug delivery properties

Antimicrobial peptides are an interesting source of non-cytotoxic drug delivery vectors. Herein, we report on the identification of a new cell-penetrating peptide (KKLFKKILKKL-NH2, BP16) from a set of antimicrobial peptides selected from a library of cecropin-melittin hybrids (CECMEL11) previously designed to be used in plant protection. This set of peptides was screened for their cytotoxicity against breast adenocarcinoma MCF-7, pancreas adenocarcinoma CAPAN-1 and mouse embryonic fibroblast 3T3 cell lines. BP16 resulted to be non-toxic against both malignant and non-malignant cells at concentrations up to 200 μM. We demonstrated by flow cytometry and confocal microscopy that BP16 is mainly internalized in the cells through a clathrin dependent endocytosis and that it efficiently accumulates in the cell cytoplasm. We confirmed that the cell-penetrating properties of BP16 are retained after conjugating it to the breast tumor homing peptide CREKA. Furthermore, we assessed the potential of BP16 as a drug delivery vector by conjugating the anticancer drug chlorambucil to BP16 and to a CREKA-BP16 conjugate. The efficacy of the drug increased between 6 and 9 times when conjugated to BP16 and between 2 and 4.5 times when attached to the CREKA-BP16 derivative. The low toxicity and the excellent cell-penetrating properties clearly suggest that BP16 is a suitable vector for the delivery of therapeutic agents into cells.

Live-cell targeting of his-tagged proteins by multivalent N-nitrilotriacetic acid carrier complexes

Selective and fast labeling of proteins in living cells is a major challenge. Live-cell labeling techniques require high specificity, high labeling density, and cell permeability of the tagging molecule to target the protein of interest. Here we report on the site-specific, rapid, and efficient labeling of endogenous and recombinant histidine-tagged proteins in distinct subcellular compartments using cell-penetrating multivalent chelator carrier complexes. In vivo labeling was followed in real time in living cells, demonstrating a high specificity and high degree of colocalization in the crowded cellular environment.

A modular designed copolymer with anti-thrombotic activity and imaging capability

Through a modular ROMP (ring-opening metathesis polymerization) strategy, a random copolymer with anti-thrombotic activity and imaging capability has been constructed from RGD, rhodamine B and PEG modified norbornene monomers. As we expected, these tri-component polynorbornenes exhibit significant enhancement in anti-thrombotic efficacy and bioavailability in vivo.

Proline-rich antimicrobial peptides: potential therapeutics against antibiotic-resistant bacteria

The increasing resistance of pathogens to antibiotics causes a huge clinical burden that places great demands on academic researchers and the pharmaceutical industry for resolution. Antimicrobial peptides, part of native host defense, have emerged as novel potential antibiotic alternatives. Among the different classes of antimicrobial peptides, proline-rich antimicrobial peptides, predominantly sourced from insects, have been extensively investigated to study their specific modes of action. In this review, we focus on recent developments in these peptides. They show a variety of modes of actions, including mechanism shift at high concentration, non-lytic mechanisms, as well as possessing different intracellular targets and lipopolysaccharide binding activity. Furthermore, proline-rich antimicrobial peptides display the ability to not only modulate the immune system via cytokine activity or angiogenesis but also possess properties of penetrating cell membranes and crossing the blood brain barrier suggesting a role as potential novel carriers. Ongoing studies of these peptides will likely lead to the development of more potent antimicrobial peptides that may serve as important additions to the armoury of agents against bacterial infection and drug delivery.

Cell penetrating peptides: efficient vectors for delivery of nanoparticles, nanocarriers, therapeutic and diagnostic molecules

Efficient delivery of therapeutic and diagnostic molecules to the cells and tissues is a difficult challenge. The cellular membrane is very effective in its role as a selectively permeable barrier. While it is essential for cell survival and function, also presents a major barrier for intracellular delivery of cargo such as therapeutic and diagnostic agents. In recent years, cell-penetrating peptides (CPPs), that are relatively short cationic and/or amphipathic peptides, received great attention as efficient cellular delivery vectors due to their intrinsic ability to enter cells and mediate uptake of a wide range of macromolecular cargo such as plasmid DNA (pDNA), small interfering RNA (siRNAs), drugs, and nanoparticulate pharmaceutical carriers. This review discusses the various uptake mechanisms of these peptides. Furthermore, we discuss recent advances in the use of CPP for the efficient delivery of nanoparticles, nanocarriers, DNA, siRNA, and anticancer drugs to the cells. In addition, we have been highlighting new results for improving endosomal escape of CPP-cargo molecules. Finally, pH-responsive and activable CPPs for tumor-targeting therapy have been described.

Early endosomal escape of a cyclic cell-penetrating peptide allows effective cytosolic cargo delivery

Cyclic heptapeptide cyclo(FΦRRRRQ) (cFΦR4, where Φ is l-2-naphthylalanine) was recently found to be efficiently internalized by mammalian cells. In this study, its mechanism of internalization was investigated by perturbing various endocytic events through the introduction of pharmacologic agents and genetic mutations. The results show that cFΦR4 binds directly to membrane phospholipids, is internalized into human cancer cells through endocytosis, and escapes from early endosomes into the cytoplasm. Its cargo capacity was examined with a wide variety of molecules, including small-molecule dyes, linear and cyclic peptides of various charged states, and proteins. Depending on the nature of the cargos, they may be delivered by endocyclic (insertion of cargo into the cFΦR4 ring), exocyclic (attachment of cargo to the Gln side chain), or bicyclic approaches (fusion of cFΦR4 and cyclic cargo rings). The overall delivery efficiency (i.e., delivery of cargo into the cytoplasm and nucleus) of cFΦR4 was 4-12-fold higher than those of nonaarginine, HIV Tat-derived peptide, or penetratin. The higher delivery efficiency, coupled with superior serum stability, minimal toxicity, and synthetic accessibility, renders cFΦR4 a useful transporter for intracellular cargo delivery and a suitable system for investigating the mechanism of endosomal escape.

Effect of lanthanide complex structure on cell viability and association

A systematic study of the effect of hydrophobicity and charge on the cell viability and cell association of lanthanide metal complexes is presented. The terbium luminescent probes feature a macrocyclic polyaminocarboxylate ligand (DOTA) in which the hydrophobicity of the antenna and that of the carboxyamide pendant arms are independently varied. Three sensitizing antennas were investigated in terms of their function in vitro: 2-methoxyisophthalamide (IAM(OMe)), 2-hydroxyisophthalamide (IAM), and 6-methylphenanthridine (Phen). Of these complexes, Tb-DOTA-IAM exhibited the highest quantum yield, although the higher cell viability and more facile synthesis of the structurally related Tb-DOTA-IAM(OMe) platform renders it more attractive. Further modification of this latter core structure with carboxyamide arms featuring hydrophobic benzyl, hexyl, and trifluoro groups as well as hydrophilic amino acid based moieties generated a family of complexes that exhibit high cell viability (ED50 > 300 μM) regardless of the lipophilicity or the overall complex charge. Only the hexyl-substituted complex reduced cell viability to 60% in the presence of 100 μM complex. Additionally, cellular association was investigated by ICP-MS and fluorescence microscopy. Surprisingly, the hydrophobic moieties did not increase cell association in comparison to the hydrophilic amino acid derivatives. It is thus postulated that the hydrophilic nature of the 2-methoxyisophthalamide antenna (IAM(OMe)) disfavors the cellular association of these complexes. As such, responsive luminescent probes based on this scaffold would be appropriate for the detection of extracellular species.

Cell-penetrating peptoids: introduction of novel cationic side chains

During the last decade peptoid-based molecular transporters have been broadly applied. They are highly valued for their easy synthesis and their superior stability against enzymatic degradation. The special structure of peptoids generally allows introducing a variety of different side chains. Yet, the cationic side chains of cell-penetrating peptoids displayed solely lysine- or arginine-like structures. Thus this report is intended to extend the spectrum of cationic peptoid side chains. Herein, we present novel functional groups, like polyamines, aza-crown ethers, or triphenylphosphonium ions that are introduced into peptoids for the first time. In addition, the obtained peptoids were tested for their cell-penetrating properties.

Cell-penetrating peptides: design, synthesis, and applications

The intrinsic property of cell-penetrating peptides (CPPs) to deliver therapeutic molecules (nucleic acids, drugs, imaging agents) to cells and tissues in a nontoxic manner has indicated that they may be potential components of future drugs and disease diagnostic agents. These versatile peptides are simple to synthesize, functionalize, and characterize yet are able to deliver covalently or noncovalently conjugated bioactive cargos (from small chemical drugs to large plasmid DNA) inside cells, primarily via endocytosis, in order to obtain high levels of gene expression, gene silencing, or tumor targeting. Typically, CPPs are often passive and nonselective yet must be functionalized or chemically modified to create effective delivery vectors that succeed in targeting specific cells or tissues. Furthermore, the design of clinically effective systemic delivery systems requires the same amount of attention to detail in both design of the delivered cargo and the cell-penetrating peptide used to deliver it.

Investigation of homeodomain membrane translocation properties: insights from the structure determination of engrailed-2 homeodomain in aqueous and membrane-mimetic environments

In addition to their well-known DNA-binding properties, homeodomains have the ability to efficiently translocate across biological membranes through still poorly-characterized mechanisms. To date, most biophysical studies addressing the mechanisms of internalization have focused on small synthetic peptides rather than full-length globular homeodomains. In this work, we characterized the conformational properties of chicken Engrailed 2 homeodomain (En2HD) in aqueous solution and in membrane mimetic environments using circular dichroism, Trp fluorescence, and NMR spectroscopy. En2HD adopts a well-defined three-helical bundle fold in aqueous solution. The Trp-48 residue, which is critical for internalization, is fully buried in the hydrophobic core. Circular dichroism and fluorescence reveal that a conformational transition occurs in anionic lipid vesicles and in micelles. En2HD loses its native three-dimensional structure in micellar environments but, remarkably, near-native helical secondary structures are maintained. Long-range interactions could be detected using site-directed spin labels, indicating that the three helices do not adopt extended orientations. Noncovalent paramagnetic probes yielded information about helix positioning and unveiled the burial of critical aromatic and basic residues within the micelles. Our results suggest that electrostatic interactions with membranes may be determinant in inducing a conformational change enabling Trp-48 to insert into membranes.

Bisubstrate UDP-peptide conjugates as human O-GlcNAc transferase inhibitors

Inhibitors of OGT (O-GlcNAc transferase) are valuable tools to study the cell biology of protein O-GlcNAcylation. We report OGT bisubstrate-linked inhibitors (goblins) in which the acceptor serine in the peptide VTPVSTA is covalently linked to UDP, eliminating the GlcNAc pyranoside ring. Goblin1 co-crystallizes with OGT, revealing an ordered C₃ linker and retained substrate-binding modes, and binds the enzyme with micromolar affinity, inhibiting glycosyltransfer on to protein and peptide substrates.

Inhibitors of OGT (O-GlcNAc transferase) are valuable tools to study the cell biology of protein O-GlcNAcylation. We report OGT bisubstrate-linked inhibitors (goblins) in which the acceptor serine in the peptide VTPVSTA is covalently linked to UDP, inhibiting glycosyltransfer on to protein and peptide substrates.

Polypeptides with quaternary phosphonium side chains: synthesis, characterization, and cell-penetrating properties

Polypeptides bearing quaternary phosphonium side chains were synthesized via controlled ring-opening polymerization of chlorine-functionalized amino acid N-carboxyanhydride monomers followed by one-step nucleophilic substitution reaction with triethylphosphine. The conformation of the resulting polypeptides can be controlled by modulating the side-chain length and α-carbon stereochemistry. The phosphonium-based poly(l-glutamate) derivatives with 11 σ-bond backbone-to-charge distance adopt stable α-helical conformation against pH and ionic strength changes. These helical, quaternary phosphonium-bearing polypeptides exhibit higher cell-penetrating capability than their racemic and random-coiled analogues. They enter cells mainly via an energy-independent, nonendocytic cell membrane transduction mechanism and exhibit low cytotoxicity, substantiating their potential use as a safe and effective cell-penetrating agent.