Cell penetrating peptides: overview and applications to the delivery of oligonucleotides

Phosphorodiamidate Morpholino Oligomers-Loaded Nanobubbles for Ultrasound-Mediated Delivery to the Myocardium in Muscular Dystrophy

Microbubbles (MBs) and nanobubbles (NBs) can oscillate and collapse in response to ultrasound exposure, resulting in contrast and delivery effects. Therefore, the retention of the entrapped gas is an important condition in bubble formulations, especially for MBs and NBs with lipid shells, and the stability of the lipid membrane is considered to be affected. We previously developed NBs, which are polyethylene glycol-modified liposomes entrapping an ultrasound contrast gas that can serve as nucleic acid carriers and ultrasound contrast agents. In particular, NBs containing cationic lipids were useful as systemic delivery tools that can load genes and nucleic acids on their surfaces. However, the gas retention of NBs containing cationic lipids were low, leaving room for improvement as ultrasound contrast agents. In this study, we attempted to prepare NBs containing anionic lipids to improve their stability in vivo, and found that they lasted longer in contrast time than previous NBs. In order to utilize anionic NBs, we evaluated their usefulness as systemic delivery tools for cationic-peptide-conjugated phosphorodiamidate morpholino oligomers (PMO). PMO has attracted attention as a therapeutic agent for Duchenne muscular dystrophy (DMD); however, its charge neutrality makes its delivery into muscle fibers challenging, especially more difficult to apply PMO to myocardial damage. We examined the systemic delivery of PMO to the heart using a combination of anionic NBs and ultrasound. Furthermore, we evaluated the usability of octaarginine (R8), a cationic cell-penetrating peptide (CPP), in loading PMO onto the surface of NBs and verified the potential of PMO-loaded NBs as a therapy for cardiac dysfunction in muscular dystrophy.

Disrupting stroke-induced GAT-1-syntaxin1A interaction promotes functional recovery after stroke

Although stroke is a frequent cause of permanent disability, our ability to promote stroke recovery is limited. Here, we design a small-molecule stroke recovery promoting agent that works by dissociating γ-aminobutyric acid (GABA) transporter 1 (GAT-1) from syntaxin1A (Synt1A), a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein. Stroke induces an increase in GAT-1-Synt1A interaction in the subacute phase, a critical period for functional recovery. Uncoupling GAT-1-Synt1A reverses stroke-induced GAT-1 dysfunction and cortical excitability decline and enhances synaptic GABAergic inhibition and consequently cortical oscillations and network plasticity by facilitating the assembly of the SNARE complex at the synapse. Based on the molecular mechanism of GAT-1 binding to Synt1A, we design GAT-1-Synt1A blockers. Among them, ZLQ-3 exhibits the greatest potency. Intranasal use of ZLQ-3-1, a glycosylation product of ZLQ-3, substantially lessens impairments of sensorimotor and cognitive functions in rodent models. This compound, or its analogs, may serve as a promoting agent for stroke recovery.

Synthesis of Self Permeable Antisense PMO Using C5-Guanidino-Functionalized Pyrimidines at the 5'-End Enables Sox2 Downregulation in Triple Negative Breast Cancer Cells

Delivery of macromolecular drugs inside cells has been a huge challenge in the field of oligonucleotide therapeutics for the past few decades. Earliest natural inspirations included the arginine rich stretch of cell permeable HIV-TAT peptide, which led to the design of several molecular transporters with varying numbers of rigid or flexible guanidinium units with different tethering groups. These transporters have been shown to efficiently deliver phosphorodiamidate morpholino oligonucleotides, which have a neutral backbone and cannot form lipoplexes. In this report, PMO based delivery agents having 3 or 4 guanidinium groups at the C5 position of the nucleobases of cytosine and uracil have been explored, which can be assimilated within the desired stretch of the antisense oligonucleotide. Guanidinium units have been connected by varying the flexibility with either a saturated (propyl) or an unsaturated (propargyl) spacer, which showed different serum dependency along with varied cytoplasmic distribution. The effect of cholesterol conjugation in the delivery agent as well as at the 5'-end of full length PMO in cellular delivery has also been studied. Finally, the efficacy of the delivery has been studied by the PMO mediated downregulation of the stemness marker Sox2 in the triple-negative breast cancer cell line MDA-MB 231. These results have validated the use of this class of delivery agents, which permit at a stretch PMO synthesis where the modified bases can also participate in Watson-Crick-Franklin base pairing for enhanced mRNA binding and protein downregulation and could solve the delivery problem of PMO.

Enhancing drug penetration in solid tumors via nanomedicine: Evaluation models, strategies and perspectives

Effective tumor treatment depends on optimizing drug penetration and accumulation in tumor tissue while minimizing systemic toxicity. Nanomedicine has emerged as a key solution that addresses the rapid clearance of free drugs, but achieving deep drug penetration into solid tumors remains elusive. This review discusses various strategies to enhance drug penetration, including manipulation of the tumor microenvironment, exploitation of both external and internal stimuli, pioneering nanocarrier surface engineering, and development of innovative tactics for active tumor penetration. One outstanding strategy is organelle-affinitive transfer, which exploits the unique properties of specific tumor cell organelles and heralds a potentially transformative approach to active transcellular transfer for deep tumor penetration. Rigorous models are essential to evaluate the efficacy of these strategies. The patient-derived xenograft (PDX) model is gaining traction as a bridge between laboratory discovery and clinical application. However, the journey from bench to bedside for nanomedicines is fraught with challenges. Future efforts should prioritize deepening our understanding of nanoparticle-tumor interactions, re-evaluating the EPR effect, and exploring novel nanoparticle transport mechanisms.

Intranasal delivery of Borneol/R8dGR peptide modified PLGA nanoparticles co-loaded with curcumin and cisplatin alleviate hypoxia in pediatric brainstem glioma which improves the synergistic therapy

Cisplatin (cis) is a first-line chemotherapeutic used for the treatment of intractable pediatric brainstem glioma (PBSG). Its therapeutic effect in PBSG is, however, critically challenged by the hypoxic microenvironment of the tumor and the presence of the blood brain barrier (BBB). Herein, we report on the intranasal administration of borneol (Bo)/R8dGR peptide modified PLGA based nanoparticles (NP) co-loaded with curcumin and cisplatin (cur/cis). We observed that borneol modification improved the brain penetration of the nanoparticles by reduction of the expression of ZO-1 and occludin in nasal mucosa, while the R8dGR peptide modification allowed the targeting of the NP through the binding on integrin αvβ3 receptors which are present on PBSG cells. Following intranasal administration, BoR-cur/cis-NP attenuated hypoxia in the PBSG microenvironment and reduced angiogenesis, which prolonged survival of GL261-bearing PBSG mice. Therefore, intranasal administration of BoR-cur/cis-NP, which deeply penetrate PBSG, is an encouraging strategy to attenuate hypoxia which potentiates the efficacy of cisplatin in the treatment of PBSG.

Recent advances in lipid nanovesicles for targeted treatment of spinal cord injury

The effective regeneration and functional restoration of damaged spinal cord tissue have been a long-standing concern in regenerative medicine. Treatment of spinal cord injury (SCI) is challenging due to the obstruction of the blood-spinal cord barrier (BSCB), the lack of targeting of drugs, and the complex pathophysiology of injury sites. Lipid nanovesicles, including cell-derived nanovesicles and synthetic lipid nanovesicles, are highly biocompatible and can penetrate BSCB, and are therefore effective delivery systems for targeted treatment of SCI. We summarize the progress of lipid nanovesicles for the targeted treatment of SCI, discuss their advantages and challenges, and provide a perspective on the application of lipid nanovesicles for SCI treatment. Although most of the lipid nanovesicle-based therapy of SCI is still in preclinical studies, this low immunogenicity, low toxicity, and highly engineerable nanovesicles will hold great promise for future spinal cord injury treatments.

Transnasal-brain delivery of nanomedicines for neurodegenerative diseases

Neurodegenerative diseases (NDs) have become a serious global health problem as the population ages. Traditionally, treatment strategies for NDs have included oral and intravenous administration; however, the blood–brain barrier (BBB) can prevent drugs from reaching the brain, rendering the treatment incomplete and the effect unsatisfactory. Additionally, the prolonged or excessive use of drugs that can cross the BBB can damage liver and kidney function. Recent studies have shown that nose-to-brain drug delivery can noninvasively bypass the BBB, allowing drugs to enter the brain through the olfactory or trigeminal nerve pathways; additionally, nanoparticle carriers can enhance drug delivery. This review introduces drug carrier nanoparticles for nose-to-brain delivery systems, compares the advantages and disadvantages of different nanoparticles, and discusses the factors influencing nose-to-brain nanomedicine delivery and enhancement strategies. We also summarize nose-to-brain delivery and nanomedicines for treating NDs, the current challenges of this approach, and the future promise of nanomedicine-based ND treatment.

A Fluorophore-Labeled Lysine Dendrimer with an Oxo-Anion-Binding Motif for Tracking Gene Transfection

A transfection vector based on a peptide dendrimer (1) has been developed and its abilities for DNA binding and transport have been investigated. By attaching a fluorophore to the vector system (1*), several steps in the transfection process could be monitored directly. As DLS and AFM studies showed, the labeled vector 1* condensed DNA into tightly packed aggregates able to enter eukaryotic cells. Co-localization experiments revealed that the ligand/plasmid complex is taken up by the endosomal pathway followed by an endosomal escape or lysosomal degradation. Afterwards, the plasmid DNA seems to enter the nucleus due to a breakdown of the nuclear envelope during mitosis, as only cells that have recently undergone mitosis showed H2B-GFP expression.

Pharmacokinetics, biodistribution and toxicology of novel cell-penetrating peptides

Cell-penetrating peptides (CPPs) have been used in basic and preclinical research in the past 30 years to facilitate drug delivery into target cells. However, translation toward the clinic has not been successful so far. Here, we studied the pharmacokinetic (PK) and biodistribution profiles of Shuttle cell-penetrating peptides (S-CPP) in rodents, combined or not with an immunoglobulin G (IgG) cargo. We compared two enantiomers of S-CPP that contain both a protein transduction domain and an endosomal escape domain, with previously shown capacity for cytoplasmic delivery. The plasma concentration versus time curve of both radiolabelled S-CPPs required a two-compartment PK analytical model, which showed a fast distribution phase (t1/2α ranging from 1.25 to 3 min) followed by a slower elimination phase (t1/2β ranging from 5 to 15 h) after intravenous injection. Cargo IgG combined to S-CPPs displayed longer elimination half-life, of up to 25 h. The fast decrease in plasma concentration of S-CPPs was associated with an accumulation in target organs assessed at 1 and 5 h post-injection, particularly in the liver. In addition, in situ cerebral perfusion (ISCP) of L-S-CPP yielded a brain uptake coefficient of 7.2 ± 1.1 µl g-1 s-1, consistent with penetration across the blood-brain barrier (BBB), without damaging its integrity in vivo. No sign of peripheral toxicity was detected either by examining hematologic and biochemical blood parameters, or by measuring cytokine levels in plasma. In conclusion, S-CPPs are promising non-toxic transport vectors for improved tissue distribution of drug cargos in vivo.

Transportan 10 Induces Perturbation and Pores Formation in Giant Plasma Membrane Vesicles Derived from Cancer Liver Cells

Continuous progress has been made in the development of new molecules for therapeutic purposes. This is driven by the need to address several challenges such as molecular instability and biocompatibility, difficulties in crossing the plasma membrane, and the development of host resistance. In this context, cell-penetrating peptides (CPPs) constitute a promising tool for the development of new therapies due to their intrinsic ability to deliver therapeutic molecules to cells and tissues. These short peptides have gained increasing attention for applications in drug delivery as well as for their antimicrobial and anticancer activity but the general rules regulating the events involved in cellular uptake and in the following processes are still unclear. Here, we use fluorescence microscopy methods to analyze the interactions between the multifunctional peptide Transportan 10 (TP10) and the giant plasma membrane vesicles (GPMVs) derived from cancer cells. This aims to highlight the molecular mechanisms underlying functional interactions which bring its translocation across the membrane or cytotoxic mechanisms leading to membrane collapse and disruption. The Fluorescence Lifetime Imaging Microscopy (FLIM) method coupled with the phasor approach analysis proved to be the winning choice for following highly dynamic spatially heterogeneous events in real-time and highlighting aspects of such complex phenomena. Thanks to the presented approach, we were able to identify and monitor TP10 translocation into the lumen, internalization, and membrane-induced modifications depending on the peptide concentration regime.

Complexation Preferences of Dynamic Constitutional Frameworks as Adaptive Gene Vectors

The growing applications of therapeutic nucleic acids requires the concomitant development of vectors that are optimized to complex one type of nucleic acid, forming nanoparticles suitable for further trafficking and delivery. While fine-tuning a vector by molecular engineering to obtain a particular nanoscale organization at the nanoparticle level can be a challenging endeavor, we turned the situation around and instead screened the complexation preferences of dynamic constitutional frameworks toward different types of DNAs. Dynamic constitutional frameworks (DCF) are recently-identified vectors by our group that can be prepared in a versatile manner through dynamic covalent chemistry. Herein, we designed and synthesized 40 new DCFs that vary in hydrophilic/hydrophobic balance, number of cationic headgroups. The results of DNA complexation obtained through gel electrophoresis and fluorescent displacement assays reveal binding preferences of different DCFs toward different DNAs. The formation of compact spherical architectures with an optimal diameter of 100-200 nm suggests that condensation into nanoparticles is more effective for longer PEG chains and PEI groups that induce a better binding performance in the presence of DNA targets.

Use of Glycine to Augment Exon Skipping and Cell Therapies for Duchenne Muscular Dystrophy

Antisense oligonucleotide (AO)-based exon-skipping and cell therapies are the main therapeutic approaches for Duchenne muscular dystrophy (DMD). Insufficient systemic delivery leading to low therapeutic efficacy limits the former; low transplantation efficiency hampers the latter. Here we describe how glycine can address these issues by augmenting satellite proliferation and muscle regeneration, resulting in enhanced AO uptake in regenerating myofibers and cell transplantation efficiency in dystrophic mice. The dual functionality of glycine demonstrated in AO-based exon-skipping and cell therapies presents a simple and efficient method to augment AO potency and cell transplantation efficacy in DMD and other muscle diseases.

Therapeutic nanotechnologies for Alzheimer's disease: a critical analysis of recent trends and findings

Alzheimer's Disease (AD) is an irreversible neurodegenerative disease for which no disease modifying therapies are presently available. Besides the identification of pathological targets, AD presents numerous clinical and pharmacological challenges such as efficient active delivery to the central nervous system, cell targeting, and long-term dosing. Nanoparticles have been explored to overcome some of these challenges as drug delivery vehicles or drugs themselves. However, early promises have failed to materialize as no nanotechnology-based product has been able to reach the market and very few have moved past preclinical stages. In this review, we perform a critical analysis of the past decade's research on nanomedicine-based therapies for AD at the preclinical and clinical stages. The main obstacles to nanotechnology products and the most promising approaches were also identified, including renewed promise with gene editing, gene modulation, and vaccines.

Exogenous loading of extracellular vesicles, virus-like particles, and lentiviral vectors with supercharged proteins

Cell membrane-based biovesicles (BVs) are important candidate drug delivery vehicles and comprise extracellular vesicles, virus-like particles, and lentiviral vectors. Here, we introduce a non-enzymatic assembly of purified BVs, supercharged proteins, and plasmid DNA called pDNA-scBVs. This multicomponent vehicle results from the interaction of negative sugar moieties on BVs and supercharged proteins that contain positively charged amino acids on their surface to enhance their affinity for pDNA. pDNA-scBVs were demonstrated to mediate floxed reporter activation in culture by delivering a Cre transgene. We introduced pDNA-scBVs containing both a CRE-encoding plasmid and a BV-packaged floxed reporter into the brains of Ai9 mice. Successful delivery of both payloads by pDNA-scBVs was confirmed with reporter signal in the striatal brain region. Overall, we developed a more efficient method to load isolated BVs with cargo that functionally modified recipient cells. Augmenting the natural properties of BVs opens avenues for adoptive extracellular interventions using therapeutic loaded cargo.

Development of Therapeutic RNA Manipulation for Muscular Dystrophy

Approval of therapeutic RNA molecules, including RNA vaccines, has paved the way for next-generation treatment strategies for various diseases. Oligonucleotide-based therapeutics hold particular promise for treating incurable muscular dystrophies, including Duchenne muscular dystrophy (DMD). DMD is a severe monogenic disease triggered by deletions, duplications, or point mutations in the DMD gene, which encodes a membrane-linked cytoskeletal protein to protect muscle fibers from contraction-induced injury. Patients with DMD inevitably succumb to muscle degeneration and atrophy early in life, leading to premature death from cardiac and respiratory failure. Thus far, the disease has thwarted all curative strategies. Transcriptomic manipulation, employing exon skipping using antisense oligonucleotides (ASO), has made significant progress in the search for DMD therapeutics. Several exon-skipping drugs employing RNA manipulation technology have been approved by regulatory agencies and have shown promise in clinical trials. This review summarizes recent scientific and clinical progress of ASO and other novel RNA manipulations, including RNA-based editing using MS2 coat protein-conjugated adenosine deaminase acting on the RNA (MCP-ADAR) system illustrating the efficacy and limitations of therapies to restore dystrophin. Perhaps lessons from this review will encourage the application of RNA-editing therapy to other neuromuscular disorders.

Nose-to-brain drug delivery for the treatment of Alzheimer's Disease: Current advancements and challenges

INTRODUCTION

The irreversible destruction of neurons, progressive loss of memory and cognitive behavior, high cost of therapy, and impact on society desire a better, effective, and affordable treatment of AD. The nose-to-brain drug delivery approach holds a great potential to access the brain without any hindrance of BBB and result in higher bioavailability thus better therapeutic efficacy of anti-AD drugs.

AREAS COVERED

The present review article highlighted the current facts and worldwide statistics of AD and its detailed etiology. Followed by barriers to brain delivery, nose-to-brain delivery, their limitations, and amalgamation with various novel carrier systems. We have emphasized recent advancements in nose-to-brain delivery using mucoadhesive, stimuli-responsive carriers, polymeric nanoparticles, lipid nanoparticles, protein/peptide delivery for treatment of AD.

EXPERT OPINION

The available therapies are symptomatic, mitigate the symptoms of AD at the initial stages. In this lieu, nose-to-brain delivery has the ability to overcome these limitations and increase drug bioavailability in the brain. Various novel strategies including stimuli-responsive systems, nanoparticles, etc. enhance the nasal drug permeation, protects the drug, and enhance its therapeutic potency. Although, successful preclinical data does not assure the clinical success of the therapy and hence exhaustive clinical investigations are needed to make the therapy available for patients.

Cellular uptake of 2-aminopyridine-modified peptide nucleic acids conjugated with cell-penetrating peptides

Cell-penetrating peptides (CPPs) have been extensively used to deliver peptide nucleic acid (PNA) in cells. We have previously found that replacement of cytosine in triplex-forming PNAs with 2-aminopyridine (M) not only enhanced RNA binding, but also improved cellular uptake of PNAs. In this study, we used confocal fluorescence microscopy to evaluate the ability of CPPs to further improve cellular uptake of M-modified PNAs. We found that PNAs conjugated with Tat and octa-arginine peptides were effectively taken up in MCF7 cells when supplied in cell media at 1 μM. Remarkably, M-modified PNA without any CPP conjugation also showed strong uptake when the concentration was increased to 5 μM. Majority of PNA conjugates remained localized in distinct cytoplasmic vesicles, as judged by dot-like fluorescence patterns. However, M-modified PNAs conjugated with Tat, octa-arginine, and even a simple tri-lysine peptide also showed dispersed fluorescence in cytoplasm and were taken up in nuclei where they localized in larger vesicles, most likely nucleoli. Endosomolytic peptides or chemicals (chloroquine and CaCl₂ ) did not release the conjugates from cytosolic vesicles, which suggested that the PNAs were not entrapped in endosomes. We hypothesize that M-modified PNAs escape endosomes and accumulate in cellular compartments rich in RNA, such as nucleoli, stress granules, and P-bodies.

Chemistry of Peptide-Oligonucleotide Conjugates: A Review

Peptide-oligonucleotide conjugates (POCs) represent one of the increasingly successful albeit costly approaches to increasing the cellular uptake, tissue delivery, bioavailability, and, thus, overall efficiency of therapeutic nucleic acids, such as, antisense oligonucleotides and small interfering RNAs. This review puts the subject of chemical synthesis of POCs into the wider context of therapeutic oligonucleotides and the problem of nucleic acid drug delivery, cell-penetrating peptide structural types, the mechanisms of their intracellular transport, and the ways of application, which include the formation of non-covalent complexes with oligonucleotides (peptide additives) or covalent conjugation. The main strategies for the synthesis of POCs are viewed in detail, which are conceptually divided into (a) the stepwise solid-phase synthesis approach and (b) post-synthetic conjugation either in solution or on the solid phase, especially by means of various click chemistries. The relative advantages and disadvantages of both strategies are discussed and compared.

Internal Oligoguanidinium Transporter: Mercury-Free Scalable Synthesis, Improvement of Cellular Localization, Endosomal Escape, Mitochondrial Localization, and Conjugation with Antisense Morpholino for NANOG Inhibition to Induce Chemosensitization of Taxol in MCF-7 Cells

A nontoxic delivery vehicle is essential for the therapeutic applications of antisense phosphorodiamidate morpholino oligonucleotides (PMOs). Though guanidinium-rich or arginine-rich cellular transporter conjugated Vivo-PMO or PPMO has been developed for in vivo application, however, either their toxicity or stability has become an issue. Previously, we reported nonpeptidic internal guanidinium transporter (IGT) mediated delivery of PMO for gene silencing and got encouraging results. In this paper, we report the synthesis of IGT using a Hg-free method for scale up and N-terminal modification of IGT with a suitable hydrophobic or lipophilic group to improve the cell permeability, endosomal escape, and mitochondrial localization and to reduce toxicity in the MTT assay. For the delivery of PMO, IGT-PMO conjugate was synthesized to target NANOG in cells, a transcription factor required for cancer stem cell proliferation and embryonic development and is involved in many cancers. Our data shows IGT-PMO-facilitated NANOG inhibition, and thereby the prevention of EpCAM-N-Cadherin-Vimentin axis mediated epithelial to mesenchymal transition (EMT) in MCF-7 cells. Moreover, unlike taxol, NANOG inhibition influences the expression of stemness factor c-Myc, Hh-Gli signaling proteins, other cancer related factors, and their respective phenotypes in cancer cells. To the best of our knowledge, this is the first report to illustrate that the IGT-PMO-mediated NANOG inhibition increases the therapeutic potential of taxol and induces G0-G1 arrest in cancer cells to prevent cancer progression. However, it warrants further investigation in other cancer cells and preclinical platforms.

Non-cationic Material Design for Nucleic Acid Delivery

Nucleic acid delivery provides effective options to control intracellular gene expression and protein production. Efficient delivery of nucleic acid typically requires delivery vehicles to facilitate the entry of nucleic acid into cells. Among non-viral delivery vehicles, cationic materials are favored because of their high loading capacity of nucleic acids and prominent cellular uptake efficiency through electrostatic interaction. However, cationic moieties at high dosage tend to induce severe cytotoxicity due to the interference on cell membrane integrity. In contrast, non-cationic materials present alternative delivery approaches with less safety concerns than cationic materials. In this Progress Report, principles of non-cationic material design for nucleic acid delivery are discussed. Examples of such non-cationic platforms are highlighted, including complexation or conjugation with nucleic acids and self-assembled nucleic acid structures.

Cell-Penetrating Peptides Enhance the Activity of Human Fibroblast Growth Factor 2 by Prolonging the Retention Time: A New Vision for Drug-Delivery Systems

Cell-penetrating peptides (CPPs) are defined by their ability to deliver cargo into cells and have been studied and developed as a promising drug-delivery system (DDS). However, the issue of whether the CPPs that have already entered the cells can be re-released or reused has not been studied. The purpose of this research was to construct CPP-conjugated human fibroblast growth factor 2 (hFGF2) and investigate whether they can be re-released from the cell membrane for reuse. This study combined hFGF2 with Tat or Ara27, a newly developed CPP derived from the zinc knuckle (CCHC-type) family protein of Arabidopsis. Human dermal fibroblast (HDF) was treated with Tat-conjugated hFGF2 (tFGF2) and Ara27-conjugated hFGF2 (NR-FGF2) for both long and short durations, and the effects on cell growth were compared. Furthermore, tFGF2 and NR-FGF2 re-released from the cells were quantified and the effects were evaluated by culturing HDF in a conditioned medium. Interestingly, the proliferation of HDF increased only when NR-FGF2 was treated for 1 h in endocytosis-independent manner. After 1 h, NR-FGF2 was significantly re-released, reaching a maximum concentration at 5 h. Furthermore, increased proliferation of HDF cultured in the conditioned medium containing re-released NR-FGF2 was discovered. While previous studies have focused on the delivery of cargo and its associated applications, this study has revealed that combinations of superior CPPs and therapeutics can be expected to prolong both the retention time and the cell-penetrating capacity, even in the presence of external factors. Therefore, CPPs can be applied in the context of topical drugs and cosmetics as a new DDS approach.

Nose-to-brain delivery of enveloped RNA - cell permeating peptide nanocomplexes for the treatment of neurodegenerative diseases

Direct nose-to-brain (N-to-B) delivery enables the rapid transport of drugs to the brain, while minimizing systemic exposure. The objective of this work was to engineer a nanocarrier intended to enhance N-to-B delivery of RNA and to explore its potential utility for the treatment of neurological disorders. Our approach involved the formation of electrostatically driven nanocomplexes between a hydrophobic derivative of octaarginine (r8), chemically conjugated with lauric acid (C12), and the RNA of interest. Subsequently, these cationic nanocomplexes were enveloped (enveloped nanocomplexes, ENCPs) with different protective polymers, i.e. polyethyleneglycol - polyglutamic acid (PEG-PGA) or hyaluronic acid (HA), intended to enhance their stability and mucodiffusion across the olfactory nasal mucosa. These rationally designed ENCPs were produced in bulk format and also using a microfluidics-based technique. This technique enabled the production of a scalable nanoformulation, exhibiting; (i) a unimodal size distribution with a tunable mean size, (ii) the capacity to highly associate (100%) and protect RNA from degradation, (iii) the ability to preserve its physicochemical properties in biorelevant media and prevent the premature RNA release. Moreover, in vitro cell culture studies showed the capacity of ENCPs to interact and be efficiently taken-up by CHO cells. Finally, in vivo experiments in a mouse model of Alzheimer's disease provided evidence of a statistically significant increase of a potentially therapeutic miRNA mimic in the hippocampus area and its further effect on two mRNA targets, following its intranasal administration. Overall, these findings stress the value of the rational design of nanocarriers towards overcoming the biological barriers associated to N-to-B RNA delivery and reveal their potential value as therapeutic strategies in Alzheimer's disease.

Peptide-conjugate antisense based splice-correction for Duchenne muscular dystrophy and other neuromuscular diseases

Duchenne muscular dystrophy (DMD) is an X-linked disorder characterized by progressive muscle degeneration, caused by the absence of dystrophin. Exon skipping by antisense oligonucleotides (ASOs) has recently gained recognition as therapeutic approach in DMD. Conjugation of a peptide to the phosphorodiamidate morpholino backbone (PMO) of ASOs generated the peptide-conjugated PMOs (PPMOs) that exhibit a dramatically improved pharmacokinetic profile. When tested in animal models, PPMOs demonstrate effective exon skipping in target muscles and prolonged duration of dystrophin restoration after a treatment regime. Herein we summarize the main pathophysiological features of DMD and the emergence of PPMOs as promising exon skipping agents aiming to rescue defective gene expression in DMD and other neuromuscular diseases. The listed PPMO laboratory findings correspond to latest trends in the field and highlight the obstacles that must be overcome prior to translating the animal-based research into clinical trials tailored to the needs of patients suffering from neuromuscular diseases.

Aptamer-peptide conjugates as a new strategy to modulate human α-thrombin binding affinity

Aptamers are single-stranded RNA or DNA molecules that specifically recognize their targets and have proven valuable for functionalizing sensitive biosensors. α-thrombin is a trypsin-like serine proteinase which plays a crucial role in haemostasis and thrombosis. An abnormal activity or overexpression of this protein is associated with a variety of diseases. A great deal of attention was devoted to the construction of high-throughput biosensors for accurately detect thrombin for the early diagnosis and treatment of related diseases. Herein, we propose a new approach to modulate the interaction between α-thrombin and the aptamer TBA₁₅. To this end, TBA₁₅ was chemically conjugated to two peptide sequences (TBA-G₃FIE-Ac and TBA-G₃EIF-Ac) corresponding to a short fragment of the acidic region of the human factor V, which is known to interact directly with exosite I. Surface Plasmon Resonance (SPR) results showed enhanced analytical performances of thrombin with TBA-G₃EIF-Ac than with TBA wild-type, reaching a limit of detection as low as 44.9 pM. Electrophoresis mobility shift assay (EMSA) corroborated the SPR results. Molecular dynamics (MD) simulations support experimental evidences and provided further insight into thrombin/TBA-peptide interaction. Our findings demonstrate that the combination of TBA₁₅ with key interacting peptides offers good opportunities to produce sensitive devices for thrombin detection and potential candidates to block thrombin activity.

Diverse Properties of Guanidiniocarbonyl Pyrrole-Based Molecules: Artificial Analogues of Arginine

The guanidinium moiety, which is present in active sites of many enzymes, plays an important role in the binding of anionic substrates. In addition, it was also found to be an excellent binding motif for supramolecular chemistry. Inspired by Nature, scientists have developed artificial receptors containing guanidinium scaffolds that bind to a variety of oxoanions through hydrogen bonding and charge pairing interactions. However, the majority of binding studies is restricted to organic solvents. Polyguanidinium based molecules can form efficient complexes in aqueous solvents due to strong electrostatic interactions. However, they only have moderate association constants, which are significantly decreased in the presence of competing anions and salts. Hence, to improve the binding affinity of the guanidinium moiety, our group developed the cationic guanidiniocarbonyl pyrrole (GCP) moiety. This rigid planar analogue binds efficiently to oxoanions, like carboxylates even in aqueous solvents. The lower p K_a value (7-8) of GCP compared to guanidinium derivatives (p K_a 13) favors the formation of strong, hydrogen bonded ion pairs. In addition, carboxylate binding is further enhanced by additional amide hydrogen bond donors located at the five position of the pyrrole core. Moreover, the design has allowed for introducing secondary interactions between receptor side chains and guest molecules, which allows for optimizing binding specificity and selectivity. The spectroscopic data confirmed stabilization of guanidiniocarbonyl pyrrole/oxoanion complexes through a combination of ion pairing and multiple hydrogen bonding interactions. The key role of the ionic interaction in a polar solvent, is demonstrated by a zwitterion derivative of the guanidiniocarbonyl pyrrole, which self-assembles in both dimethyl sulfoxide and pure water with association constants of K > 10¹⁰ M^-1 and K = 170 M^-1, respectively. In this Account, we discuss strategies for making GCP functionalized compounds, in order to boost their ability to bind oxoanions. Then we explore how these building blocks have been incorporated into different synthetic molecules and peptide sequences, highlighting examples that demonstrated the versatility of this binding scaffold. For instance, the high oxoanion binding property of GCP-based compounds was exploited to generate a detectable signal for sensing applications, thus improving selectivity and sensitivity in aqueous solution. Moreover, peptides and molecules containing GCP have shown excellent gene transfections properties. Furthermore, the self-assembly and zwitterionic behavior of zwitterionic GCP analogues was used to develop variety of supramolecular architectures such as stable supramolecular β-helix structure, linear supramolecular oligomers, one-dimensional rods or two-dimension sheets, fibers, vesicles, soft nanospheres, as well as stimuli responsive supramolecular gels.

Use of Glucose-Fructose to Enhance the Exon Skipping Efficacy

Exon-skipping antisense oligonucleotides (AOs) are promising treatments for muscle-related genetic ailments including Duchenne muscular dystrophy (DMD), but clinical translation is unfortunately hampered by insufficient systemic delivery. Here we describe that how one can employ a glucose-fructose injection mixture to improve muscle uptake and functional outcomes of DMD AOs in energy-deficient peripheral muscles of mdx mice. The potentiating effect of glucose-fructose on AOs in energy-deficient muscles offers a simple and economical method for enhancing AO potency, reducing screening costs for researchers and accelerating the translation of nucleic acid-based therapeutics in DMD and other muscular dystrophies.

The Assembly of Fluorescently Labeled Peptide-Oligonucleotide Conjugates via Orthogonal Ligation Strategies

Efficient intracellular delivery is critical to the successful application of synthetic antisense oligonucleotides (ASOs) to modulate gene expression. The conjugation of cell-penetrating peptides (CPPs) to ASOs has been shown to significantly improve their intracellular delivery. It is important, however, that formation of the covalent linkage between the peptide and oligonucleotide is efficient and orthogonal, to ensure high yields and a homogeneous product. Described herein are efficient and facile methodologies for the conjugation of peptides to ASOs, and their subsequent labeling with various moieties such as fluorescent dyes for intracellular tracking studies.

Potential of Lipid Nanoparticles (SLNs and NLCs) in Enhancing Oral Bioavailability of Drugs with Poor Intestinal Permeability

Lipid-based drug delivery systems has become a popular choice for oral delivery of lipophilic drugs with dissolution rate limited oral absorption. Lipids are known to enhance oral bioavailability of poorly water-soluble drugs in multiple ways like facilitating dissolution as micellar solution, enhancing the lymphatic uptake and acting as inhibitors of efflux transporters. Lipid nanoparticles are matrix type lipid-based carrier systems which can effectively encapsulate both lipophilic and hydrophilic drugs. Lipid nanoparticles namely solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) are versatile drug delivery system and can be used for multiple routes of delivery like parenteral, topical, ocular, transdermal, and oral. Lipid nanoparticles are particularly attractive vehicles for peroral delivery of drugs with oral bioavailability problems as they are composed of lipid excipients which are cheap, easily available, and non-toxic; manufacturing technique is simple and readily scalable for large-scale production; the formulations provide controlled release of active components and have no stability issue. A large number of drugs have been incorporated into lipid nanoparticles with the objective of overcoming their poor oral bioavailability. This review tries to assess the potential of lipid nanoparticles for enhancing the oral bioavailability of drugs with permeability limited oral absorption such as drugs belonging to class IV of Biopharmaceutic Classification System (BCS) and protein and peptide drugs and also discusses the mechanism behind the bioavailability enhancement and safety issues related to such delivery systems.

Potential of Peptide Nucleic Acids in Future Therapeutic Applications

Peptide nucleic acids (PNA) are synthetic analog of DNA with a repeating N-(2-aminoethyl)-glycine peptide backbone connected to purine and pyrimidine nucleobases via a linker. Considering the unique properties of PNA, including resistance to enzymatic digestion, higher biostability combined with great hybridization affinity toward DNA and RNA, it has attracted great attention toward PNA- based technology as a promising approach for gene alteration. However, an important challenge in utilizing PNA is poor intracellular uptake. Therefore, some strategies have been developed to enhance the delivery of PNA in order to reach cognate site. Although PNAs primarily demonstrated to act as an antisense and antigene agents for inhibition of transcription and translation of target genes, more therapeutic applications such as splicing modulation and gene editing are also used to produce specific genome modifications. Hence, several approaches based on PNAs technology have been designed for these purposes. This review briefly presents the properties and characteristics of PNA as well as different gene modulation mechanisms. Thereafter, current status of successful therapeutic applications of PNA as gene therapeutic intervention in different research areas with special interest in medical application in particular, anti-cancer therapy are discussed. Then it focuses on possible use of PNA as anti-mir agent and PNA-based strategies against clinically important bacteria.

Recent preclinical and clinical advances in oligonucleotide conjugates

INTRODUCTION

Oligonucleotide therapeutics have the potential to change the way disease is treated due to their ability to modulate gene expression of any therapeutic target in a highly specific and potent manner. Unfortunately, this drug class is plagued with inherently poor pharmacological characteristics, which need to be overcome. The development of a chemical modification library for oligonucleotides has addressed many of the initial challenges, but delivery of these payloads across plasma membranes remains difficult. The latest technological advances in oligonucleotide therapeutics utilizes direct conjugation to targeting ligands, which has improved bioavailability and target tissue exposure many-fold. The success of this approach has resulted in numerous clinical programs over the past 5 years.

AREAS COVERED

We review the literature on oligonucleotide conjugate strategies which have proven effective preclinically and clinically. We summarize the chemical modifications which allow parenteral administration as well as evaluate the efficacy of a multitude of conjugate approaches including lipids, peptides, carbohydrates, and antibodies.

EXPERT OPINION

The success of future conjugate strategies will likely rely on the effective combination of characteristics from earlier technologies. High-affinity ligand-receptor interactions can be critical to achieving meaningful accumulation in target tissues, but pharmacokinetic modulators which increase the circulating half-life may also be necessary. Synthesis of these approaches has the potential to bring the next breakthrough in oligonucleotide therapeutics.

Construction and Evaluation of the Tumor-Targeting, Cell-Penetrating Multifunctional Molecular Probe iCREKA

A novel tumor stroma targeting and membrane-penetrating cyclic peptide, named iCREKA, was designed and labeled by fluorescein isothiocyanate (FITC) and positron emitter ¹⁸F to build the tumor-targeting tracers. The FITC-iCREKA was proved to have significantly higher cellular uptake in the glioma U87 cells in the presence of activated MMP-2 than that in absence of activated MMP-2 by cells fluorescence test in vitro. The tumor tissue fluorescence microscope imaging demonstrated that FITC-iCREKA accumulated in the walls of the blood vessels and the surrounding stroma in the glioma tumor at 1 h after intravenous injection. While at 3 h after injection, FITC-iCREKA was found to be uptaken in the tumor cells. However, the control FITC-CREKA can only be found in the tumor stroma, not in the tumor cells, no matter at 1 h or 3 h after injection. The whole-animal fluorescence imaging showed that the glioma tumor could be visualized clearly with high fluorescence signal. The microPET/CT imaging further demonstrated that 18F-iCREKA could target U87MG tumor in vivo from 30 min to 2 h after injection. The present study indicated the iCREKA had the capacity of tumor stroma targeting and the membrane-penetrating. It was potential to be developed as the fluorescent and PET tracers for tumor imaging.

Synthesis, Characterization, and Function of an RNA-Based Transfection Reagent

A synthetic 8-mer, amphipathic, trans-acting poly-2'-O-methyluridylic thiophosphate triester RNA element (2'-OMeUtaPS) can be prepared using solid-phase synthesis protocols. 2'-OMeUtaPS efficiently mediates the delivery of uncharged polyA-tailed phosphorodiamidate morpholino (PMO) sequences in HeLa pLuc 705 cells, as evidenced by flow cytometry measurements. In this cell line, 2'-OMeUtaPS-mediated transfection of an antisense polyA-tailed PMO sequence induces alternative splicing of an aberrant luciferase pre-mRNA splice site, leading to restoration of functional luciferase, as quantitatively measured using a typical luciferase assay. 2'-OMeUtaPS is also potent at delivering an uncharged antisense polyA-tailed PMO sequence in muscle cells of the mdx mouse model of muscular dystrophy; targeting the polyA-tailed PMO sequence against a splice site of the pre-mRNA encoding mutated dystrophin triggers an alternate splicing event that results in excision of the mutated exon (exon 23) from the pre-mRNA and production of functional dystrophin, as demonstrated by agarose gel electrophoresis. © 2018 by John Wiley & Sons, Inc.

Assessing histidine tags for recruiting deoxyribozymes to catalyze peptide and protein modification reactions

We evaluate the ability of hexahistidine (His6) tags on peptide and protein substrates to recruit deoxyribozymes for modifying those substrates. For two different deoxyribozymes, one that creates tyrosine-RNA nucleopeptides and another that phosphorylates tyrosine side chains, we find substantial improvements in yield, kobs, and Km for peptide substrates due to recruiting by His6/Cu(2+). However, the recruiting benefits of the histidine tag are not observed for larger protein substrates, likely because the tested deoxyribozymes either cannot access the target peptide segments or cannot function when these segments are presented in a structured protein context.

LLO-mediated Cell Resealing System for Analyzing Intracellular Activity of Membrane-impermeable Biopharmaceuticals of Mid-sized Molecular Weight

Cell-based assays have become increasingly important in the preclinical studies for biopharmaceutical products such as specialty peptides, which are of interest owing to their high substrate specificity. However, many of the latter are membrane impermeable and must be physically introduced into cells to evaluate their intracellular activities. We previously developed a "cell-resealing technique" that exploited the temperature-dependent pore-forming activity of the streptococcal toxin, streptolysin O (SLO), that enabled us to introduce various molecules into cells for evaluation of their intracellular activities. In this study, we report a new cell resealing method, the listeriolysin O (LLO)-mediated resealing method, to deliver mid-sized, membrane-impermeable biopharmaceuticals into cells. We found that LLO-type resealing required no exogenous cytosol to repair the injured cell membrane and allowed the specific entry of mid-sized molecules into cells. We use this method to introduce either a membrane-impermeable, small compound (8-OH-cAMP) or specialty peptide (Akt-in), and demonstrated PKA activation or Akt inhibition, respectively. Collectively, the LLO-type resealing method is a user-friendly and reproducible intracellular delivery system for mid-sized membrane-impermeable molecules into cells and for evaluating their intracellular activities.

Synthesis, Characterization, and Evaluation of Triptolide Cell-Penetrating Peptide Derivative for Transdermal Delivery of Triptolide

Triptolide (TP) has been used as one of the most common systemic treatments for various diseases since the 1960s. However, TP displays diverse side effects on various organs, which limits its clinical application. To overcome this issue, numerous C-14-hydroxyl group derivatives of TP have been synthesized. In this research, the C-14-hydroxyl group of TP is modified by a cell-penetrating peptide polyarginine (R₇). The derivative TP-disulfide-CR₇ (TP-S-S-CR₇) containing a disulfide linkage between TP and R₇ possesses less toxicity at various concentrations on the immortal human keratinocyte (HaCaT) cell line by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay compared with free TP. Treating HaCaT cells with TP (100 nM) could increase intracellular ROS (reactive oxygen species) and decrease the activity of SOD (superoxide dismutase). Meanwhile, treating HaCaT cells with equimolar concentration of TP-S-S-CR₇ did not cause both of the above TP-induced alterations. In addition, TP-S-S-CR₇ did not show significant dermal toxicity on guinea pigs and could efficiently overcome the barrier of corneum and then reach epidermis and dermis within 2 h of transdermal administration. In addition, there was a relatively lower concentration of TP in blood indicating less toxicity on organs. Such results suggest that topical therapy using polyarginine is possible by the transdermal delivery of TP.

pH-Dependent Membrane Interactions of the Histidine-Rich Cell-Penetrating Peptide LAH4-L1

The histidine-rich designer peptide LAH4-L1 exhibits antimicrobial and potent cell-penetrating activities for a wide variety of cargo including nucleic acids, polypeptides, adeno-associated viruses, and nanodots. The non-covalent complexes formed between the peptide and cargo enter the cell via an endosomal pathway where the pH changes from neutral to acidic. Here, we investigated the membrane interactions of the peptide with phospholipid bilayers and its membrane topology using static solid-state NMR spectroscopy. Oriented ¹⁵N solid-state NMR indicates that in membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) 3:1 mol/mole and at neutral pH, the peptide adopts transmembrane topologies. Furthermore, ³¹P and ²H solid-state NMR spectra show that liquid crystalline 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and POPC/POPS 3:1 liposomes retain a bilayer macroscopic phase even at the highest peptide concentrations investigated, with an oblate orientational distribution of the phospholipids at a peptide/lipid ratio of 1:5. At pH 5, as it occurs in the endosome, the alignment of LAH4-L1 at a peptide/lipid ratio of 1:25 is predominantly parallel to POPC/POPS 3:1 bilayers (prolate deformation) when at the same time it induces a considerable decrease of the deuterium order parameter of POPC/²H₃₁-POPS 3:1. In addition, when studied in mechanically supported lipid membranes, a pronounced disordering of the phospholipid alignment is observed. In the presence of even higher peptide concentrations, lipid spectra are observed that suggest the formation of magnetically oriented or isotropic bicelles. This membrane-disruptive effect is enhanced for gel phase DMPC membranes. By protonation of the four histidines in acidic environments, the overall charge and hydrophobic moment of LAH4-L1 considerably change, and much of the peptide is released from the cargo. Thus, the amphipathic peptide sequences become available to disrupt the endosomal membrane and to assure highly efficient release from this organelle.

Anti-microRNA targeting using peptide-based nanocomplexes to inhibit differentiation of human pancreatic stellate cells

Aim: To develop novel peptide-based nanocomplexes (NCs) for delivery of anti-miRNA oligonucleotides to human-derived pancreatic stellate cells (hPSCs), precursors of cancer-associated fibroblasts. Materials & methods: NCs of anti-miRNA oligonucleotides and cell-penetrating peptides (different variants) were formed and characterized. The effects of anti-miR-199a delivery on hPSC differentiation and 3D heterospheroid formation were investigated. Results: Dimeric cell-penetrating peptide based NCs (NC-2) showed 130-fold higher uptake by hPSCs compared with monomer-based NCs (NC-1) and tenfold higher uptake compared with general fibroblasts and different pancreatic tumor cells. Interestingly, delivery of anti-miR-199a inhibited hPSC differentiation into cancer-associated fibroblasts and inhibited the size of 3D heterospheroids comprised of hPSCs and tumor cells. Conclusion: Our NCs present a highly efficient anti-miRNA delivery system to hPSCs to inhibit their protumorigenic activity.

Evaluation of Amphiphilic Peptide Modified Antisense Morpholino Oligonucleotides In Vitro and in Dystrophic mdx Mice

A series of amphiphilic peptides modified PMO (Pt-PMO) were prepared, and their antisense effect and toxicity were evaluated both in vitro and in mdx mice. The results showed that the exon-skipping performance of Pt-PMO are relative to the structure of the conjugated peptide: the Pt3/Pt4 composed of six/seven arginines and one myristoylation modified PMO showed more efficacy and with less toxicity as compared to others, confirming that appropriate hydrophilic-lipophilic balance (HLB) and cationic sequence numbers play a crucial role in improving cell uptake and corresponding exon-skipping efficiency. This was observed particularly in enhanced delivery efficiency of PMO comparable to B-PMO in vitro, while 6-fold improved exon-skipping was achieved against naked PMO in vivo. The multi-PMO modified Pt8-PMO also showed improved exon-skipping both in vitro and in vivo, though there is lower efficiency in systemic delivery as compared to Pt4-PMO. These data suggest that with optimization of peptide in component, charge density has clear potential for exploration towards achieving higher efficiency of antisense oligonucleotide systemic delivery, and thus is more applicable for clinical application.

Nose-to-brain delivery of BACE1 siRNA loaded in solid lipid nanoparticles for Alzheimer's therapy

We designed a delivery system to obtain an efficient and optimal nose-to-brain transport of BACE1 siRNA, potentially useful in the treatment of Alzheimer's disease. We selected a cell-penetrating peptide, the short peptide derived from rabies virus glycoprotein known as RVG-9R, to increase the transcellular pathway in neuronal cells. The optimal molar ratio between RVG-9R and BACE1 siRNA was elucidated. The complex between the two was then encapsulated. We propose chitosan-coated and uncoated solid lipid nanoparticles (SLNs) as a nasal delivery system capable of exploiting both olfactory and trigeminal nerve pathways. The coating process had an effect on the zeta potential, obtaining positively-charged nanoparticles, and on siRNA protection. The positive charge of the coating formulation ensured mucoadhesiveness to the particles and also prolonged residence time in the nasal cavity. We studied the cellular transport of siRNA released from the SLNs using Caco-2 as a model of epithelial-like phenotypes. We found that siRNA permeates the monolayer to a greater extent when released from any of the studied formulations than from bare siRNA, and primarily from chitosan-coated SLNs.

Histidine-rich designer peptides of the LAH4 family promote cell delivery of a multitude of cargo

The histidine-rich designer peptides of the LAH4 family exhibit potent antimicrobial, transfection, transduction and cell-penetrating properties. They form non-covalent complexes with their cargo, which often carry a negative overall charge at pH 7.4 and include a large range of molecules and structures such as oligonucleotides, including siRNA and DNA, peptides, proteins, nanodots and adeno-associated viruses. These complexes are thought to enter the cells through an endosomal pathway where the acidification of the organelle is essential for efficient endosomal escape. Biophysical measurements indicate that, upon acidification, almost half the peptides are released from DNA cargo, leading to the suggestion of a self-promoted uptake mechanism where the liberated peptides lyse the endosomal membranes. LAH4 derivatives also help in cellular transduction using lentiviruses. Here, we compare the DNA transfection activities of LAH4 derivatives, which vary in overall charge and/or the composition in the hydrophobic core region. In addition, LAH4 is shown to mediate the transport of functional β-galactosidase, a large tetrameric protein of about 0.5 MDa, into the cell interior. Interestingly, the LAH1 peptide efficiently imports this protein, while it is inefficient during DNA transfection assays. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Cell-Penetrating Peptide Spirolactam Derivative as a Reversible Fluorescent pH Probe for Live Cell Imaging

A colorless and nonfluorescent spirolactam derivative, RhB-R₁₂K, was synthesized by amide condensation between the carboxyl group of rhodamine B (RhB) and the amino group of cell-penetrating peptide (CPP). The fluorescence intensity of RhB-R₁₂K sharply increased as the pH value decreased from 8.0 to 4.9, demonstrating sensitive and reversible response to intracellular pH distribution. This CPP probe was completely water soluble, had low cytotoxicity, was membrane permeable, and was suitable for pH measurement in various organelles by choosing organelle-specific CPP sequences. Interestingly, CPPs acted not only as carriers but also as indispensable parts of fluorophores here. The presence of active groups on the peptides potentially allows for modification with additional dyes to construct multifunctional and ratiometric probes for cell imaging.