The pharmacokinetics of cell-penetrating peptides

Conjugation of Therapeutic PSD-95 Inhibitors to the Cell-Penetrating Peptide Tat Affects Blood-Brain Barrier Adherence, Uptake, and Permeation

Novel stroke therapies are needed. Inhibition of the interaction between the postsynaptic density-95 (PSD-95)/disc large/ZO-1 (PDZ) domains of PSD-95 and the N-methyl-D-aspartate (NMDA) receptor has been suggested as a strategy for relieving neuronal damage. The peptides NR2B9c and N-dimer have been designed to hinder this interaction; they are conjugated to the cell-penetrating peptide Tat to facilitate blood–brain barrier (BBB) permeation and neuronal uptake. Tat-N-dimer exhibits 1000-fold better target affinity than Tat-NR2B9c, but the same magnitude of improvement is not observed in terms of therapeutic effect. Differences in BBB permeation by Tat-NR2B9c and Tat-N-dimer may explain this difference, but studies providing a direct comparison of Tat-NR2B9c and Tat-N-dimer are lacking. The aim of the present study was therefore to compare the BBB uptake and permeation of Tat-NR2B9c and Tat-N-dimer. The peptides were conjugated to the fluorophore TAMRA and their chemical stability assessed. Endothelial membrane association and cell uptake, and transendothelial permeation were estimated using co-cultures of primary bovine brain capillary endothelial cells and rat astrocytes. In vivo BBB permeation was demonstrated in mice using two-photon microscopy imaging. Tissue distribution was evaluated in mice demonstrating brain accumulation of TAMRA-Tat (0.4% ID/g), TAMRA-Tat-NR2B9c (0.3% ID/g), and TAMRA-Tat-N-dimer (0.25% ID/g). In conclusion, we demonstrate that attachment of NR2B9c or N-dimer to Tat affects both the chemical stability and the ability of the resulting construct to interact with and permeate the BBB.

A peptide for transcellular cargo delivery: Structure-function relationship and mechanism of action

The rate of transport of small molecule drugs across biological barriers, such as the blood-brain barrier, is often a limiting factor in achieving a therapeutic dose. One proposed strategy to enhance delivery across endothelial or epithelial monolayers is conjugation to cell-penetrating peptides (CPPs); however, very little is known about the design of CPPs for efficient transcellular transport. Here, we report on transcellular transport of a CPP, designated the CL peptide, that increases the delivery of small-molecule cargoes across model epithelium approximately 10-fold. The CL peptide contains a helix-like motif and a polyarginine tail. We investigated the effect of cargo, helix-like motif sequence, polyarginine tail length, and peptide stereochemistry on cargo delivery. We showed that there is an optimal helix-like motif sequence (RLLRLLR) and polyarginine tail length (R₇) for cargo delivery. Furthermore, we demonstrated that the peptide-cargo conjugate is cleaved by cells in the epithelium at the site of a two-amino acid linker. The cleavage releases the cargo with the N-terminal linker amino acid from the peptide prior to transport out of the epithelium. These studies provide new insight into the sequence requirements for developing novel CPPs for transcellular delivery of cargo.

Tissue distribution of intravenously administrated poly-arginine peptide R18D in healthy male Sprague–Dawley rats

Aim: R18D is a poly-arginine peptide that has demonstrated neuroprotection in preclinical models of excitotoxicity, stroke, hypoxic-ischemic encephalopathy and traumatic brain injury. Here, we examined the peptide’s uptake in serum. Materials & methods: Healthy, male Sprague–Dawley rats were intravenously administered either 1000 nmol/kg R18D (D-enantiomer of R18) or approximately 2.5 nmol/kg (36 ± 9 MBq) [18F]R18D, for serum and organ tissue uptake, respectively. Serum samples underwent mass spectrometric analysis to detect unbound R18D peptide. Animals administered [18F]R18D were subjected to positron emission tomography imaging. Results & conclusion: Free R18D was detected at 5 min post-infusion in serum samples. [18F]R18D was rapidly distributed to the kidney (6–7%ID/g), and a small fraction localized to the brain (0.115–0.123%ID/g) over a 60-min acquisition period.

Cationic Arginine-Rich Peptides (CARPs): A Novel Class of Neuroprotective Agents With a Multimodal Mechanism of Action

There are virtually no clinically available neuroprotective drugs for the treatment of acute and chronic neurological disorders, hence there is an urgent need for the development of new neuroprotective molecules. Cationic arginine-rich peptides (CARPs) are an expanding and relatively novel class of compounds, which possess intrinsic neuroprotective properties. Intriguingly, CARPs possess a combination of biological properties unprecedented for a neuroprotective agent including the ability to traverse cell membranes and enter the CNS, antagonize calcium influx, target mitochondria, stabilize proteins, inhibit proteolytic enzymes, induce pro-survival signaling, scavenge toxic molecules, and reduce oxidative stress as well as, having a range of anti-inflammatory, analgesic, anti-microbial, and anti-cancer actions. CARPs have also been used as carrier molecules for the delivery of other putative neuroprotective agents across the blood-brain barrier and blood-spinal cord barrier. However, there is increasing evidence that the neuroprotective efficacy of many, if not all these other agents delivered using a cationic arginine-rich cell-penetrating peptide (CCPPs) carrier (e.g., TAT) may actually be mediated largely by the properties of the carrier molecule, with overall efficacy further enhanced according to the amino acid composition of the cargo peptide, in particular its arginine content. Therefore, in reviewing the neuroprotective mechanisms of action of CARPs we also consider studies using CCPPs fused to a putative neuroprotective peptide. We review the history of CARPs in neuroprotection and discuss in detail the intrinsic biological properties that may contribute to their cytoprotective effects and their usefulness as a broad-acting class of neuroprotective drugs.

Drug Delivery Strategies to Overcome the Blood-Brain Barrier (BBB)

The brain capillary endothelium serves both as an exchange site for gases and solutes between blood and brain and as a protective fence against neurotoxic compounds from the blood. While this "blood-brain barrier" (BBB) function protects the fragile environment in the brain, it also poses a tremendous challenge for the delivery of drug compounds to the brain parenchyma. Paracellular brain uptake of drug compounds is limited by the physical tightness of the endothelium, which is tightly sealed with junction complexes. Transcellular uptake of lipophilic drug compounds is limited by the activity of active efflux pumps in the luminal membrane. As a result, the majority of registered CNS drug compounds are small lipophilic compounds which are not efflux transporter substrates. Small molecule CNS drug development therefore focuses on identifying compounds with CNS target affinity and modifies these in order to optimize lipophilicity and decrease efflux pump interactions. Since efflux pump activity is limiting drug uptake, it has been investigated whether coadministration of drug compounds with efflux pump inhibitors could increase drug uptake. While the concept works to some extent, a lot of challenges have been encountered in terms of obtaining efficient inhibition while avoiding adverse effects.Some CNS drug compounds enter the brain via nutrient transport proteins, an example is the levodopa, a prodrug of Dopamine, which crosses the BBB via the large neutral amino acid transporter LAT1. While carrier-mediated transport of drug compounds may seem attractive, the development of drugs targeting transporters is very challenging, since the compounds should have a good fit to the binding site, while still maintaining their CNS target affinity.Receptor-mediated transport of drug compounds, especially biotherapeutics, conjugated to a receptor-binding ligand has shown some promise, although the amounts transported are rather low. This also holds true for drug-conjugation to cell-penetrating peptides. Due to the low uptake of biotherapeutics, barrier-breaching approaches such as mannitol injections and focused ultrasound have been employed with some success to patient groups with no other treatment options.

Nucleophosmin Phosphorylation as a Diagnostic and Therapeutic Target for Ischemic AKI

Background Ischemic AKI lacks a urinary marker for early diagnosis and an effective therapy. Differential nucleophosmin (NPM) phosphorylation is a potential early marker of ischemic renal cell injury and a therapeutic target.Methods Differential NPM phosphorylation was assessed by mass spectrometry in NPM harvested from murine and human primary renal epithelial cells, fresh kidney tissue, and urine before and after ischemic injury. The biologic behavior and toxicity of NPM was assessed using phospho-NPM mutant proteins that either mimic stress-induced or normal NPM phosphorylation. Peptides designed to interfere with NPM function were used to explore NPM as a therapeutic target.Results Within hours of stress, virtually identical phosphorylation changes were detected at distinct serine/threonine sites in NPM harvested from primary renal cells, tissue, and urine. A phosphomimic NPM protein that replicated phosphorylation under stress localized to the cytosol, formed monomers that interacted with Bax, a cell death protein, coaccumulated with Bax in isolated mitochondria, and significantly increased cell death after stress; wild-type NPM or a phosphomimic NPM with a normal phosphorylation configuration did not. Three renal targeted peptides designed to interfere with NPM at distinct functional sites significantly protected against cell death, and a single dose of one peptide administered several hours after ischemia that would be lethal in untreated mice significantly reduced AKI severity and improved survival.Conclusions These findings establish phosphorylated NPM as a potential early marker of ischemic AKI that links early diagnosis with effective therapeutic interventions.

Cell penetrating peptides: the potent multi-cargo intracellular carriers

Introduction: Cell penetrating peptides (CPPs) known as protein translocation domains (PTD), membrane translocating sequences (MTS), or Trojan peptides (TP) are able to cross biological membranes without clear toxicity using different mechanisms, and facilitate the intracellular delivery of a variety of bioactive cargos. CPPs could overcome some limitations of drug delivery and combat resistant strains against a broad range of diseases. Despite delivery of different therapeutic molecules by CPPs, they lack cell specificity and have a short duration of action. These limitations led to design of combined cargo delivery systems and subsequently improvement of their clinical applications. Areas covered: This review covers all our studies and other researchers in different aspects of CPPs such as classification, uptake mechanisms, and biomedical applications. Expert opinion: Due to low cytotoxicity of CPPs as compared to other carriers and final degradation to amino acids, they are suitable for preclinical and clinical studies. Generally, the efficiency of CPPs was suitable to penetrate the cell membrane and deliver different cargos to specific intracellular sites. However, no CPP-based therapeutic approach has approved by FDA, yet; because there are some disadvantages for CPPs including short half-life in blood, and nonspecific CPP-mediated delivery to normal tissue. Thus, some methods were used to develop the functions of CPPs in vitro and in vivo including the augmentation of cell specificity by activatable CPPs, specific transport into cell organelles by insertion of corresponding localization sequences, incorporation of CPPs into multifunctional dendrimeric or liposomal nanocarriers to improve selectivity and efficiency especially in tumor cells.

Chemical biology tools for probing transcytosis at the blood-brain barrier

A BBB vehicle library is validated, establishing a SAR for uptake. Merging AMT/RMT motifs chemoselectively increased permeability.

Absorptive- and receptor-mediated transcytosis (AMT/RMT) are widely studied strategies to deliver therapeutics across the blood–brain barrier (BBB). However, an improved understanding of the mechanism surrounding trafficking is required that could promote delivery. Accordingly, we designed a flexible platform that merged AMT and RMT motifs on a single scaffold to probe various parameters (ligand, affinity, valency, position) in a screening campaign. During this process we adapted an in vitro BBB model to reliably rank transcytosis of the vehicle library. Our results demonstrate heightened uptake and trafficking for the shuttles, with a structure–activity relationship for transcytosis emerging. Notably, due to their small size, the majority of shuttles demonstrated increased permeation compared to transferrin, with the highest performing shuttle affording a 4.9-fold increase. Consequently, we have identified novel peptide conjugates that have the capacity to act as promising brain shuttles.

Quantitation of Super Basic Peptides in Biological Matrices by a Generic Perfluoropentanoic Acid-Based Liquid Chromatography-Mass Spectrometry Method

Peptides represent a promising modality for the design of novel therapeutics that can potentially modulate traditionally non-druggable targets. Cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs) are two large families that are being explored extensively as drug delivery vehicles, imaging reagents, or therapeutic treatments for various diseases. Many CPPs and AMPs are cationic among which a significant portion is extremely basic and hydrophilic (e.g., nona-arginine). Despite their attractive therapeutic potential, it remains challenging to directly analyze and quantify these super cationic peptides from biological matrices due to their poor chromatographic behavior and MS response. Herein, we describe a generic method that combines solid phase extraction and LC-MS/MS for analysis of these peptides. As demonstrated, using a dozen strongly basic peptides, low μM concentration of perfluoropentanoic acid (PFPeA) in the mobile phase enabled excellent compound chromatographic retention, thus avoiding co-elution with solvent front ion suppressants. PFPeA also had a charge reduction effect that allowed the selection of parent/ion fragment pairs in the higher m/z region to further reduce potential low molecular weight interferences. When the method was coupled to the optimized sample extraction process, we routinely achieved low digit ng/ml sensitivity for peptides in plasma/tissue. The method allowed an efficient evaluation of plasma stability of CPPs/AMPs without fluorescence derivatization or other tagging methods. Importantly, using the widely studied HIV-TAT CPP as an example, the method enabled us to directly assess its pharmacokinetics and tissue distribution in preclinical animal models.

Zerumbone Induces Apoptosis in Breast Cancer Cells by Targeting αvβ3 Integrin upon Co-Administration with TP5-iRGD Peptide

Cell-penetrating peptides (CPPs) are highly promising tools to deliver therapeutic molecules into tumours. αVβ3 integrins are cell-matrix adhesion receptors, and are considered as an attractive target for anticancer therapies owing to their roles in the process of metastasis and angiogenesis. Therefore, this study aims to assess the effect of co-administration of zerumbone (ZER) and ZERencapsulated in hydroxypropyl-β-cyclodextrin with TP5-iRGD peptide towards cell cytotoxicity, apoptosis induction, and proliferation of normal and cancerous breast cells utilizing in vitro assays, as well as to study the molecular docking of ZER in complex with TP5-iRGD peptide. Cell viability assay findings indicated that ZER and ZERencapsulated in hydroxypropyl-β-cyclodextrin (ZER-HPβCD) inhibited the growth of estrogen receptor positivebreast cancer cells (ER⁺ MCF-7) at 72 h treatment with an inhibitory concentration (IC)₅₀ of 7.51 ± 0.2 and 5.08 ± 0.2 µg/mL, respectively, and inhibited the growth of triple negative breast cancer cells (MDA-MB-231) with an IC₅₀ of 14.96 ± 1.52 µg/mL and 12.18 ± 0.7 µg/mL, respectively. On the other hand, TP5-iRGD peptide showed no significant cytotoxicity on both cancer and normal cells. Interestingly, co-administration of TP5-iRGD peptide in MCF-7 cells reduced the IC₅₀ of ZER from 7.51 ± 0.2 µg/mL to 3.13 ± 0.7 µg/mL and reduced the IC₅₀ of ZER-HPβCD from 5.08 ± 0.2 µg/mL to 0.49 ± 0.004 µg/mL, indicating that the co-administration enhances the potency and increases the efficacy of ZER and ZER-HPβCD compounds. Acridine orange (AO)/propidium iodide (PI) staining under fluorescence microscopy showed evidence of early apoptosis after 72 h from the co-administration of ZER or ZER-HPβCD with TP5-iRGD peptide in MCF-7 breast cancer cells. The findings of the computational modelling experiment provide novel insights into the ZER interaction with integrin αvβ3 in the presence of TP5-iRGD, and this could explain why ZER has better antitumor activities when co-administered with TP5-iRGD peptide.

Dystrophin R16/17 protein therapy restores sarcolemmal nNOS in trans and improves muscle perfusion and function

Background

Delocalization of neuronal nitric oxide synthase (nNOS) from the sarcolemma leads to functional muscle ischemia. This contributes to the pathogenesis in cachexia, aging and muscular dystrophy. Mutations in the gene encoding dystrophin result in Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). In many BMD patients and DMD patients that have been converted to BMD by gene therapy, sarcolemmal nNOS is missing due to the lack of dystrophin nNOS-binding domain.

Methods

Dystrophin spectrin-like repeats 16 and 17 (R16/17) is the sarcolemmal nNOS localization domain. Here we explored whether R16/17 protein therapy can restore nNOS to the sarcolemma and prevent functional ischemia in transgenic mice which expressed an R16/17-deleted human micro-dystrophin gene in the dystrophic muscle. The palmitoylated R16/17.GFP fusion protein was conjugated to various cell-penetrating peptides and produced in the baculovirus-insect cell system. The best fusion protein was delivered to the transgenic mice and functional muscle ischemia was quantified.

Results

Among five candidate cell-penetrating peptides, the mutant HIV trans-acting activator of transcription (TAT) protein transduction domain (mTAT) was the best in transferring the R16/17.GFP protein to the muscle. Systemic delivery of the mTAT.R16/17.GFP protein to micro-dystrophin transgenic mice successfully restored sarcolemmal nNOS without inducing T cell infiltration. More importantly, R16/17 protein therapy effectively prevented treadmill challenge-induced force loss and improved muscle perfusion during contraction.

Conclusions

Our results suggest that R16/17 protein delivery is a highly promising therapy for muscle diseases involving sarcolemmal nNOS delocalizaton.

Electronic supplementary material

The online version of this article (10.1186/s10020-019-0101-6) contains supplementary material, which is available to authorized users.

Hitting Undruggable Targets: Viewing Stabilized Peptide Development through the Lens of Quantitative Systems Pharmacology

Stabilized peptide therapeutics have the potential to hit currently undruggable targets, dramatically expanding the druggable genome. However, major obstacles to their development include poor intracellular delivery, rapid degradation, low target affinity, and membrane toxicity. With the emergence of multiple stabilization techniques and screening technologies, the high efficacy of various bioactive peptides has been demonstrated in vitro, albeit with limited success in vivo. We discuss here the chemical and pharmacokinetic barriers to achieving in vivo efficacy, analyze the characteristics of FDA-approved peptide drugs, and propose a developmental tool that considers the molecular properties of stabilized peptides in a comprehensive and quantitative manner to achieve the necessary rates for in vivo delivery to the target, efficacy, and ultimately clinical translation.

The use of tail-anchored protein chimeras to enhance liposomal cargo delivery

Background

Liposomes are employed as drug delivery vehicles offering a beneficial pharmacokinetic/distribution mechanism for in vivo therapeutics. Therapeutic liposomes can be designed to target specific cell types through the display of epitope-specific targeting peptides on their surface. The majority of peptides are currently attached by chemical modification of lipid constituents. Here we investigate an alternative and novel method of decorating liposomes with targeting ligand, using remotely and spontaneously inserting chimeric tail-anchored membrane (TA) proteins to drug loaded liposomes.

Methods and results

An artificial TA protein chimera containing the transmembrane domain from the spontaneously inserting TA protein cytochrome b5 (Cytb5) provided a robust membrane tether for the incorporation of three different targeting moieties into preformed liposomes. The moieties investigated were the transactivator of transcription (TAT) peptide, the EGF-receptor binding sequence GE11 and the placental and tumour homing ligand CCGKRK. In all cases, TA protein insertion neither significantly altered the size of the liposomes nor reduced drug loading. The efficacy of this novel targeted delivery system was investigated using two human cell lines, HeLa M and BeWo. Short term incubation with one ligand-modified TA chimera, incorporating the TAT peptide, significantly enhanced liposomal delivery of the encapsulated carboxyfluorescein reporter.

Conclusion

The Cytb5 TA was successfully employed as a membrane anchor for the incorporation of the desired peptide ligands into a liposomal drug delivery system, with minimal loss of cargo during insertion. This approach therefore provides a viable alternative to chemical conjugation and its potential to accommodate a wider range of targeting ligands may provide an opportunity for enhancing drug delivery.

Disruption of the Rbm38-eIF4E Complex with a Synthetic Peptide Pep8 Increases p53 Expression

Rbm38 is a p53 target and an RNA-binding protein known to suppress p53 translation by preventing eukaryotic translation initiation factor 4E (eIF4E) from binding to p53 mRNA. In this study, we show that synthetic peptides corresponding to the binding interface between Rbm38 and eIF4E, including an 8 amino acid peptide (Pep8) derived from Rbm38, are effective in relieving Rbm38-mediated repression of p53. Molecular simulations showed that Ser-6 in Pep8 forms a hydrogen bond with Asp-202 in eIF4E. Substitution of Ser-6 with Lys, but not with Asp, enhanced the ability of Pep8 to inhibit the Rbm38-eIF4E complex. Importantly, Pep8 alone or together with a low dose of doxorubicin potently induced p53 expression and suppressed colony and tumor sphere formation and xenograft tumors in Rbm38- and p53-dependent manners. Together, we conclude that modulating the Rbm38-eIF4E complex may be explored as a therapeutic strategy for cancers that carry wild-type p53. SIGNIFICANCE: Disruption of the Rbm38-eIF4E complex via synthetic peptides induces wild-type p53 expression, suppresses tumor growth and progression, and may serve as a novel cancer therapeutic strategy.

Multifunctional gene delivery systems with targeting ligand CAGW and charge reversal function for enhanced angiogenesis

A charge reversible polyanion with a targeting peptide was assembled onto binary gene complexes to enhance their endosomal escape and transfection efficiency.

Acid-Induced Activated Cell-Penetrating Peptide-Modified Cholesterol-Conjugated Polyoxyethylene Sorbitol Oleate Mixed Micelles for pH-Triggered Drug Release and Efficient Brain Tumor Targeting Based on a Charge Reversal Mechanism

Glioblastoma multiforme is the most devastating malignant brain tumor in adults. Even with the standard care of therapy, the prognosis remains dismal due to tumor heterogeneity, tumor infiltration, and, more importantly, the restrictive nature of the blood-brain barrier (BBB). To overcome the challenge of effectively delivering therapeutic cargo into the brain, herein a "smart", multifunctional polymeric micelle was developed using a cholesterol-conjugated polyoxyethylene sorbitol oleate. A cell-penetrating peptide, arginine-glycine repeats (RG)₅, was incorporated into the micelles to improve cellular uptake, while a pH-sensitive masking sequence, histidine-glutamic acid repeats (HE)₅, was introduced for charge shielding to minimize nonspecific binding and uptake at physiological pH. Results demonstrated that (RG)₅- and (HE)₅-modified mixed micelles were optimized using this strategy to effectively mask the cationic charges of the activated cell-penetrating peptide (RG)₅ at physiological pH, i.e., limiting internalization, and were selectively triggered in response to a mildly acidic microenvironment in vitro based on a charge reversal mechanism. In vivo results further confirmed that such micelles preferentially accumulated in both brain and tumor tissues in both xenograft and orthotropic glioma mouse models. Furthermore, micelles significantly inhibited tumor growth with limited toxicity to peripheral tissues. The combination of BBB penetration, tumor targeting, potent efficacy, and high tolerance of these micelles strongly suggests that they could be a promising candidate for safe and effective drug delivery to the brain.

Regulation of in vivo behavior of TAT-modified liposome by associated protein corona and avidity to tumor cells

Introduction

PEGylated liposomes are widely used and studied as carriers for chemotherapeutics. While pharmacokinetics of the encapsulated drug is drastically altered resulting in favorable circulation time, improved tumor accumulation, and better manageable or reduced side effects, therapeutic efficacy has been disappointing. Major drawbacks are a failure to reach the tumor cell, limited penetration depth, and impaired uptake by tumor cells.

Materials and methods

Here, we study the implication of HIV-1 transactivator of transcription (TAT)-derived peptides inserted on PEGylated liposomal doxorubicin (PLD) and followed in vitro and in vivo fate. PLDs were installed with 25–400 TAT peptides per liposome without an effect on PLD stability.

Results

While TAT peptides facilitate active endocytosis of the carriers, we observed that these peptides did not promote endosomal escape or enhanced intracellular availability of doxorubicin. Interestingly, incorporation of TAT peptides did not change pharmacokinetics or biodistribution, which we found to result from a dysopsonization of the TAT-modified liposomes by serum proteins. A protein corona (PC) on TAT peptide-modified PLDs shields the active moieties and effectively reduces clearance of the TAT peptide containing nanoparticles. However, intratumoral activity was influenced by the number of TAT peptides present. The best antitumor efficacy was observed with a TAT peptide density of 100, while lower amounts showed results comparable to unmodified PLDs. At 200 TAT peptides, the preparation appeared to be least effective, which likely results from augmented interaction with tumor cells directly upon extravasation.

Conclusion

We conclude that by optimizing TAT-modified PLDs, the occurring PC balances pharmacokinetics and tumor penetration through interference with avidity.

Cell penetrating peptides: a comparative transport analysis for 474 sequence motifs

Delivering reagents into cells is a key demand in molecular medicine. The vehicle of choice is often cell penetrating peptides (CPPs), which can ferry conjugated cargo across membranes. Although numerous peptides have been shown to promote such uptake events, there has been no comprehensive comparison of individual performance under standardized conditions. We have devised a method to rapidly analyze the ability of a multitude of CPP conjugates to carry a model cargo into HeLa cells. Sequence information for 474 CPPs was collected from literature sources, and the respective peptides were synthesized and modified with carboxyfluorescein (FAM) as model cargo. All candidates were evaluated in an identical uptake test, and transport was quantified using cellular fluorescence intensities. Substantial differences in the ability to carry the fluorophore into the cells were observed, with transport performance differing by a factor of 70 between the best CPP investigated and cargo alone. Strong correlations were observed between uptake efficiency and both sequence length and the presence of positive net charge. A compilation of the 20 top performers with regard to cargo delivery performance and cell compatibility is provided.

Mitochondria and neuroprotection in stroke: Cationic arginine-rich peptides (CARPs) as a novel class of mitochondria-targeted neuroprotective therapeutics

Stroke is the second leading cause of death globally and represents a major cause of devastating long-term disability. Despite sustained efforts to develop clinically effective neuroprotective therapies, presently there is no clinically available neuroprotective agent for stroke. As a central mediator of neurodamaging events in stroke, mitochondria are recognised as a critical neuroprotective target, and as such, provide a focus for developing mitochondrial-targeted therapeutics. In recent years, cationic arginine-rich peptides (CARPs) have been identified as a novel class of neuroprotective agent with several demonstrated mechanisms of action, including their ability to target mitochondria and exert positive effects on the organelle. This review provides an overview on neuronal mitochondrial dysfunction in ischaemic stroke pathophysiology and highlights the potential beneficial effects of CARPs on mitochondria in the ischaemic brain following stroke.

A platform for discovery of functional cell-penetrating peptides for efficient multi-cargo intracellular delivery

Cell penetrating peptides (CPPs) offer great potential to deliver therapeutic molecules to previously inaccessible intracellular targets. However, many CPPs are inefficient and often leave their attached cargo stranded in the cell’s endosome. We report a versatile platform for the isolation of peptides delivering a wide range of cargos into the cytoplasm of cells. We used this screening platform to identify multiple “Phylomer” CPPs, derived from bacterial and viral genomes. These peptides are amenable to conventional sequence optimization and engineering approaches for cell targeting and half-life extension. We demonstrate potent, functional delivery of protein, peptide, and nucleic acid analog cargos into cells using Phylomer CPPs. We validate in vivo activity in the cytoplasm, through successful transport of an oligonucleotide therapeutic fused to a Phylomer CPP in a disease model for Duchenne’s muscular dystrophy. This report thus establishes a discovery platform for identifying novel, functional CPPs to expand the delivery landscape of druggable intracellular targets for biological therapeutics.

pH-responsive Drug Delivery Systems

Acidic microenvironments exist in selected organs, tissues, and subcellular compartments, as well as in many dysregulated pathological states. A continuous effort has been made to harness the unique acidic properties of biological tissues for site-specific delivery of drugs. Various pH-responsive drug delivery systems have been designed and developed with improved spatio-temporal control of payload delivery with enhanced efficacy. This chapter will focus on the recent advances in the development of pH-sensitive materials, mechanisms of payload release, and pH-triggered drug targeting in various biomedical applications.

Preparation and preliminary biological evaluation of 11C-l-SPD

Objective: To explore the method and quality control of [Formula: see text]C radiolabeled [Formula: see text]-SPD ([Formula: see text]-Stepholidine) and biodistribution of [Formula: see text]C-[Formula: see text]-SPD in vivo.

Methods: (1) [Formula: see text]CO2 was produced by CTI RDS III cyclotron, converted [Formula: see text]CO2 to [Formula: see text]C–CH3I by CH3I die-block, and then converted it to [Formula: see text]C-Triflate–CH4, imported [Formula: see text]C-Triflate–CH4 to [Formula: see text]-SPD which was dissolved in Dimethyl sulfoxide [(CH3)2SO], reacted at common temperature and then obtained the product. (2) Take the sample of organs in different times 5, 15, 30, 60, 90[Formula: see text]min after injecting [Formula: see text]C-[Formula: see text]-SPD by vail in mice and measure the radioactive counts per minute (cpm), then the percent injection dose of wet tissue per gram (%ID/g) was calculated.

Results: (1) The synthesis time of [Formula: see text]C-[Formula: see text]-SPD was 15 to 20[Formula: see text]min with chemical [Formula: see text]%, and PH values [Formula: see text], radiochemical [Formula: see text]% in 2[Formula: see text]h. All quality criteria of [Formula: see text]C-[Formula: see text]-SPD met the requirements of the positron radio-pharmaceuticals. (2) [Formula: see text]C-[Formula: see text]-SPD was of the characteristic that metabolism was through the liver, and kidney was the main excretory organ, which was [Formula: see text]%ID/g at 5[Formula: see text]min and was decreasing gradually, which was [Formula: see text][Formula: see text]ID/g in liver at 5[Formula: see text]min.

Conclusion: (1) [Formula: see text]C-[Formula: see text]-SPD can be used to further study the animal or human. (2) [Formula: see text]C-[Formula: see text]-SPD could quickly discharge and decrease to the low level from background of issues in vivo.

Blocking TIR Domain Interactions in TLR9 Signaling

Interaction of TLR9 with ligands activates NF-κB, leading to proinflammatory cytokine production. Excessive TLR activation is a pathogenic factor for inflammatory diseases. This study has examined cell-permeating decoy peptides (CPDPs) derived from the TLR9 Toll/IL-1R resistance (TIR) domain. CPDP 9R34, which included AB loop, β-strand B, and N-terminal BB loop residues, inhibited TLR9 signaling most potently. CPDPs derived from α-helices C, D, and E (i.e., 9R6, 9R9, and 9R11) also inhibited TLR9-induced cytokines but were less potent than 9R34. 9R34 did not inhibit TLR2/1, TLR4, or TLR7 signaling. The N-terminal deletion modification of 9R34, 9R34-ΔN, inhibited TLR9 as potently as the full length 9R34. Binding of 9R34-ΔN to TIR domains was studied using cell-based Förster resonance energy transfer/fluorescence lifetime imaging approach. Cy3-labeled 9R34-ΔN dose-dependently decreased fluorescence lifetime of TLR9 TIR-Cerulean (Cer) fusion protein. Cy3-9R34-ΔN also bound TIRAP TIR, albeit with a lesser affinity, but not MyD88 TIR, whereas CPDP from the opposite TIR surface, 9R11, bound both adapters and TLR9. i.p. administration of 9R34-ΔN suppressed oligonucleotide-induced systemic cytokines and lethality in mice. This study identifies a potent, TLR9-specific CPDP that targets both receptor dimerization and adapter recruitment. Location of TIR segments that represent inhibitory CPDPs suggests that TIR domains of TLRs and TLR adapters interact through structurally homologous surfaces within primary receptor complex, leading to formation of a double-stranded, filamentous structure. In the presence of TIRAP and MyD88, primary complex can elongate bidirectionally, from two opposite ends, whereas in TIRAP-deficient cells, elongation is unidirectional, only through the αE side.

Strategies for Enhancing the Permeation of CNS-Active Drugs through the Blood-Brain Barrier: A Review

Background: The blood brain barrier (BBB) is a dynamic and functional structure which poses a vast challenge in the development of drugs acting on the central nervous system (CNS). While most substances are denied BBB crossing, selective penetration of substances mainly occurs through diffusion, carrier mediated transport, or receptor mediated transcytosis. Methods: Strategies in enhancing BBB penetration have been reviewed and summarized in accordance with their type of formulation. Highlights in monoclonal antibodies, peptide-vectors, nanoparticles, and simple prodrugs were included. Conclusion: Nanoparticles and simple prodrugs, for example, can be used for efficient BBB penetration through inhibition of efflux mechanisms, however, monoclonal antibodies are the most promising strategy in BBB penetration. Close follow-up of future development in this area should confirm our expectation.

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

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

Matrix Metalloproteinase-9-Responsive Nanogels for Proximal Surface Conversion and Activated Cellular Uptake

Here, we have exploited the heightened extracellular concentration of matrix metalloproteinase-9 (MMP-9) to induce surface-conversional properties of nanogels with the aim of tumor-specific enhanced cellular uptake. A modular polymeric nanogel platform was designed and synthesized for facile formulation and validation of MMP-9-mediated dePEGylation and generation of polyamine-type surface characteristics through peptide N-termini. Nanogels containing MMP-9-cleavable motifs and different poly(ethylene glycol) corona lengths (350 and 750 g/mol) were prepared, and enzymatic surface conversional properties were validated by MALDI characterization of cleaved byproducts, fluorescamine assay amine quantification, and zeta potential. The nanogel with a shorter PEG length, mPEG350-NG, exhibited superior surface conversion in response to extracellular concentrations of MMP-9 compared to that of the longer PEG length, mPEG750-NG. Confocal microscopy images of HeLa cells incubated with both fluorescein-labeled nanogels and DiI-encapsulated nanogels demonstrated greater uptake following MMP-9 "activation" for mPEG350-NG compared to its nontreated "passive" mPEG350-NG parent, demonstrating the versatility of such systems to achieve stimuli-responsive uptake in response to cancer-relevant proteases.

Mechanistic insights into the efficacy of cell penetrating peptide-based cancer vaccines

Immunotherapies are increasingly used to treat cancer, with some outstanding results. Immunotherapy modalities include therapeutic vaccination to eliminate cancer cells through the activation of patient’s immune system against tumor-derived antigens. Nevertheless, the full potential of therapeutic vaccination has yet to be demonstrated clinically because many early generation vaccines elicited low-level immune responses targeting only few tumor antigens. Cell penetrating peptides (CPPs) are highly promising tools to advance the field towards clinical success. CPPs efficiently penetrate cell membranes, even when linked to antigenic cargos, which can induce both CD8 and CD4 T-cell responses. Pre-clinical studies demonstrated that targeting multiple tumor antigens, even those considered to be poorly immunogenic, led to tumor regression. Therefore, CPP-based cancer vaccines represent a flexible and powerful means to extend therapeutic vaccination to many cancer indications. Here, we review recent findings in CPP development and discuss their use in next generation immunotherapies.

Organ-based drug delivery

The phenomenal advances in pharmaceutical sciences over the last few decades have led to the development of new therapeutics like peptides, proteins, RNAs, DNAs and highly potent small molecules. Fruitful applications of these therapeutics have been challenged by several anatomical and physiological barriers that limit adequate drug disposition at the site-of-action and by off-target drug distribution to undesired tissues, which together result in the reduced effectiveness and increased side effects of therapeutic agents. As such, the development of drug delivery and targeting systems has been recognised as a cornerstone for future drug development. Research in pharmaceutical sciences is now devoted to tackling delivery challenges through engineering delivery systems that move beyond conventional dosage forms and regimens into state-of-the-art targeted drug delivery tailored toward specific therapeutic needs. Modern drug delivery systems comprise passive and active targeting approaches. While passive targeting relies on the natural course of distribution of drugs or drug carriers in the body, as governed by their physicochemical properties, active targeting often exploits targeting moieties that home preferentially into target tissues. Here, we provide an overview of theories of and approaches to passive and active drug delivery. As the design of drug delivery is dependent on the unique structure of target tissues and organs, we present our discussion in an organ-specific manner with the aim to inspire the development of new strategies for curing disease with high accuracy and efficiency.

Poly-arginine R18 and R18D (D-enantiomer) peptides reduce infarct volume and improves behavioural outcomes following perinatal hypoxic-ischaemic encephalopathy in the P7 rat

We examined the neuroprotective efficacy of the poly-arginine peptide R18 and its D-enantiomer R18D in a perinatal hypoxic-ischaemic (HI) model in P7 Sprague-Dawley rats. R18 and R18D peptides were administered intraperitoneally at doses of 30, 100, 300 or 1000 nmol/kg immediately after HI (8% O₂/92%N₂ for 2.5 h). The previously characterised neuroprotective JNKI-1-TATD peptide at a dose of 1000 nmol/kg was used as a control. Infarct volume and behavioural outcomes were measured 48 h after HI. For the R18 and R18D doses examined, total infarct volume was reduced by 25.93% to 43.80% (P = 0.038 to < 0.001). By comparison, the JNKI-1-TATD reduced lesion volume by 25.27% (P = 0.073). Moreover, R18 and R18D treatment resulted in significant improvements in behavioural outcomes, while with JNKI-1-TATD there was a trend towards improvement. As an insight into the likely mechanism underlying the effects of R18, R18D and JNKI-1-TATD, the peptides were added to cortical neuronal cultures exposed to glutamic acid excitotoxicity, resulting in up to 89, 100 and 71% neuroprotection, respectively, and a dose dependent inhibition of neuronal calcium influx. The study further confirms the neuroprotective properties of poly-arginine peptides, and suggests a potential therapeutic role for R18 and R18D in the treatment of HIE.

The Role of BCL-2 Family Members in Acute Kidney Injury

B-cell lymphoma 2 (BCL-2) family proteins gather at the biologic cross-roads of renal cell survival: the outer mitochondrial membrane. Despite shared sequence and structural features, members of this conserved protein family constantly antagonize each other in a life-and-death battle. BCL-2 members innocently reside within renal cells until activated or de-activated by physiologic stresses caused by common nephrotoxins, transient ischemia, or acute glomerulonephritis. Recent experimental data not only illuminate the intricate mechanisms of apoptosis, the most familiar form of BCL-2-mediated cell death, but emphasizes their newfound roles in necrosis, necroptosis, membrane pore transition regulated necrosis, and other forms of acute cell demise. A major paradigm shift in non-cell death roles of the BCL-2 family has occurred. BCL-2 proteins also regulate critical daily renal cell housekeeping functions including cell metabolism, autophagy (an effective means for recycling cell components), mitochondrial morphology (organelle fission and fusion), as well as mitochondrial biogenesis. This article considers new concepts in the biochemical and structural regulation of BCL-2 proteins that contribute to membrane pore permeabilization, a universal feature of cell death. Despite these advances, persistent BCL-2 family mysteries continue to challenge cell biologists. Given their interface with many intracellular functions, it is likely that BCL-2 proteins determine cell viability under many pathologic circumstances relevant to the nephrologist and, as a consequence, represent an ideal therapeutic target.

An opportunistic route to success: Towards a change of paradigm to fully exploit the potential of cell-penetrating peptides

About 25years ago it was demonstrated that certain peptides possess the ability to cross the plasma membrane. This led to the development of cell-penetrating peptides (CPPs) as vectors to mediate the cellular entry of (macro-)molecules that do not show cell entry by themselves. Nonetheless, in spite of an early bloom of promising pre-clinical studies, not a single CPP-based drug has been approved, yet. It is a paradigm in CPP research that the peptides are taken up by virtually all cells. In exploratory research and early preclinical development, this assumption guides the choice of the therapeutic target. However, while this indiscriminatory uptake may be the case for tissue culture experiments, in an organism this is clearly not the case. Biodistribution analyses demonstrate that CPPs only target a very limited number of cells and many tissues are hardly reached at all. Here, we review biodistribution analyses of CPPs and CPP-based drug delivery systems. Based on this analysis we propose a paradigm change towards a more opportunistic approach in CPP research. The application of CPPs should focus on those pathophysiologies for which the relevant target cells have been shown to be reached in vivo.

A New Noncanonical Anionic Peptide That Translocates a Cellular Blood-Brain Barrier Model

The capacity to transport therapeutic molecules across the blood–brain barrier (BBB) represents a breakthrough in the development of tools for the treatment of many central nervous system (CNS)-associated diseases. The BBB, while being protective against infectious agents, hinders the brain uptake of many drugs. Hence, finding safe shuttles able to overcome the BBB is of utmost importance. Herein, we identify a new BBB-translocating peptide with unique properties. For years it was thought that cationic sequences were mandatory for a cell-penetrating peptide (CPP) to achieve cellular internalization. Despite being anionic at physiological pH, PepNeg (sequence (SGTQEEY) is an efficient BBB translocator that is able to carry a large cargo (27 kDa), while maintaining BBB integrity. In addition, PepNeg is able to use two distinct methods of translocation, energy-dependent and -independent, suggesting that direct penetration might occur when low concentrations of peptide are presented to cells. The discovery of this new anionic trans-BBB peptide allows the development of new delivery systems to the CNS and contributes to the need to rethink the role of electrostatic attraction in BBB-translocation.

Building Stable MMP2-Responsive Multifunctional Polymeric Micelles by an All-in-One Polymer-Lipid Conjugate for Tumor-Targeted Intracellular Drug Delivery

In this study, we described an "all-in-one" polymer-lipid conjugate (PEG2k-ppTAT-PEG1k-PE) that could self-assemble to matrix metalloproteinase 2 (MMP2)-sensitive multifunctional micelles. The assembled micelles had several key features, including a protective long chain poly(ethylene glycol) (PEG2k) (the outer shell), an MMP2-sensitive peptide linker (pp) (the tumor-targeting middle layer), a trans-activating transcriptional activator (TAT) peptide (the cell-penetrating middle layer), and a stable PEG1k-PE micelle for drug loading (the inner core). In the absence of MMP2, the PEG2k-ppTAT-PEG1k-PE micelles were intact and showed low bioactivity due to the surface-anchored PEG2k, whereas in the presence of MMP2, the pp was cleaved, resulting in the PEG2k deshielding and exposure of the previously hidden TAT for enhanced intracellular drug delivery. Even if completely cleaved by MMP2, the remaining PEG1k-PE micelles were stable and the micelles' particle size and drug release were not significantly influenced. The paclitaxel (PTX)-loaded PEG2k-ppTAT-PEG1k-PE micelles showed significant MMP2-dependent cellular uptake, tumor penetration, and anticancer activity in various cancer cells and three-dimensional multicellular spheroids. Because of the enhanced intracellular drug accumulation, these multifunctional micelles were able to sensitize the drug-resistant cancer cells and their spheroids to PTX treatments. Furthermore, in vivo tumor uptake and retention data indicated that the PEG2k-ppTAT-PEG1k-PE micelles could dramatically increase the residence time of their payloads in the tumor.

Novel Peptides Derived from Dengue Virus Capsid Protein Translocate Reversibly the Blood-Brain Barrier through a Receptor-Free Mechanism

The delivery of therapeutic molecules to the central nervous system is hampered by poor delivery across the blood-brain barrier (BBB). Several strategies have been proposed to enhance transport into the brain, including invasive techniques and receptor-mediated transport (RMT). Both approaches have several drawbacks, such as BBB disruption, receptor saturation, and off-target effects, raising safety issues. Herein, we show that specific domains of Dengue virus type 2 capsid protein (DEN2C) can be used as trans-BBB peptide vectors. Their mechanism of translocation is receptor-independent and consistent with adsorptive-mediated transport (AMT). One peptide in particular, named PepH3, reaches equilibrium distribution concentrations across the BBB in less than 24 h in a cellular in vitro assay. Importantly, in vivo biodistribution data with radiolabeled peptide derivatives show high brain penetration. In addition, there is fast clearance from the brain and high levels of excretion, showing that PepH3 is a very good candidate to be used as a peptide shuttle taking cargo in and out of the brain.

Design and Proof of Programmed 5-Aminolevulinic Acid Prodrug Nanocarriers for Targeted Photodynamic Cancer Therapy

5-Aminolevulinic acid (ALA), the precursor of photosensitizer protoporphyrin IX (PpIX), is a U.S. FDA-approved photodynamic therapeutic agent. However, realizing efficient delivery of ALA is still a big challenge as it is hydrophilic and cannot be recognized and selectively accumulated in tumor cells. In this study, matrix metalloproteinase-2 (MMP-2) and pH dual-sensitive ALA prodrug nanocarriers were constructed as a programmed delivery strategy for the targeted delivery of ALA. The nanocarriers were prepared by the co-modification of gold nanoparticles (AuNPs) with hydrazone-linked ALA and MMP-2-activatable cell-penetrating peptides (CPPs). Cationic CPP RRRRRRRR (R8) was shielded by zwitterionic stealth peptide EKEKEKEKEKEKEKEKEKEK (EK10) via MMP-2 substrate peptide PLGLAG. The zwitterionic stealth peptide EK10 is designed to endow ALA prodrug nanocarriers with strong antifouling ability and prolonged circulation time. Upon arriving at the tumor tissue, the shielded cationic CPP R8 can be activated by tumor-microenvironment-overexpressed MMP-2, which enabled enhanced cellular uptake of ALA. The results of drug loading and release, cellular uptake, PpIX generation and accumulation, photodynamic cytotoxicity, and photodynamic tumor inhibition demonstrated that such tumor-microenvironment-sensitive ALA prodrug nanocarriers could be considered as potential candidates for targeted photodynamic cancer therapy.

Peptide-based strategies for enhanced cell uptake, transcellular transport, and circulation: Mechanisms and challenges

Peptides are emerging as a new tool in drug and gene delivery. Peptide-drug conjugates and peptide-modified drug delivery systems provide new opportunities to avoid macrophage recognition and subsequent phagocytosis, cross endothelial and epithelial barriers, and enter the cytoplasm of target cells. Peptides are relatively small, low-cost, and are stable in a wide range of biological conditions. In this review, we summarize recent work in designing peptides to enhance penetration of biological barriers, increase cell uptake, and avoid the immune system. We highlight recent successes and contradictory results, and outline common emerging concepts and design rules. The development of sequence-structure-function relationships and standard protocols for benchmarking will be a key to progress in the field.

Blocking peptides and molecular mimicry as treatment for kidney disease

Protein mimotopes, or blocking peptides, are small therapeutic peptides that prevent protein-protein interactions by selectively mimicking a native binding domain. Inexpensive technology facilitates straightforward design and production of blocking peptides in sufficient quantities to allow preventive and therapeutic trials in both in vitro and in vivo experimental disease models. The kidney is an ideal peptide target, since small molecules undergo rapid filtration and efficient bulk absorption by tubular epithelial cells. Because the half-life of peptides is markedly prolonged in the kidneys compared with the bloodstream, blocking peptides are an attractive tool for treating diverse renal diseases, including ischemia, proteinuric states, such as membranous nephropathy and focal and segmental glomerulosclerosis, and renal cell carcinoma. Therapeutic peptides represent one of the fastest-growing reagent classes for novel drug development in human disease, partly because of their ease of administration, high binding affinity, and minimal off-target effects. This review introduces the concepts of blocking peptide design, production, and administration and highlights the potential use of therapeutic peptides to prevent or treat specific renal diseases.

Functionalized cell nucleus-penetrating peptide combined with doxorubicin for synergistic treatment of glioma

Clinical application of cell-penetrating peptides (CPPs) in cancer therapy is greatly restricted due to lack of tissue selectivity and tumor-targeting ability. CB5005, a rationally designed CPP that targets and inhibits intracellular NF-κB activation, is constituted by a unique membrane-permeable sequence (CB5005M) cascading to a NF-κB nuclear localization sequence (CB5005N). In vitro cellular evaluation confirmed that CB5005 was effectively taken up by brain capillary endothelial cell bEnd.3 and glioma cells U87. The intracellular localization analysis further demonstrated that CB5005 could not only penetrate into the cells but also enter into their nuclei. More interestingly, CB5005 permeated deeply into the tumor spheroids of U87 cell. In vivo imaging illustrated that the fluorescence-labeled CB5005 distributed itself into the brain and accumulated at the tumor site after intravenous injection. Given the important role of over expressed NF-κB in tumor growth and development, we further investigated CB5005 for its potential in treatment of glioma. When combined administration in vitro with doxorubicin (DOX), CB5005 exhibited a synergistic effect in killing U87 cells. In a nude mice xenograft model, CB5005 inhibited the growth of tumor when applied alone, and displayed a synergistic anti-tumor effect with DOX. In conclusion, CB5005 functioned simultaneously as a cell penetrating peptide and a tumor growth inhibitor, therefore can work as a potential synergist for chemotherapy of human tumor.

STATEMENT OF SIGNIFICANCE

Clinical application of cell-penetrating peptides in cancer therapy is restricted due to lack of tissue selectivity and tumor-targeting ability. In this manuscript, we reported a rationally designed peptide, named CB5005, which had an attractive capability of translocation into the cell nucleus and blocking nuclear translocation of endogenous NF-κB protein. CB5005 had unique affinity with brain and glioma, and could rapidly accumulate in these tissues after intravenous injection. Furthermore, CB5005 showed a synergistic effect on inhibiting gliomas when administrated with doxorubicin. This is the first literature report on this multi-functionalized peptide, which can work as a potential synergist for chemotherapy of tumor. This work should be of general interest to scientists in the fields of biomaterials, biology, pharmacy, and oncology.