Enhanced neuroprotective activity of ophthalmic delivered nerve growth factor conjugated with cell penetrating peptide against optic nerve injury

Aims: Nerve growth factor is a well characterised neurotrophic factor that play a critical role in the survival, growth and differentiation of neurons both in central and peripheral nervous system. However, it is difficult for the conventional exogenous nerve growth factor administration delivery to the central nervous system due to the biological barrier in human bodies.Results: We validated a series of cell penetrating peptides and found that L-PenetraMax significantly enhanced the efficiency of recombinant human nerve growth factor entry into the rat retina. In the optic nerve crush mice model, eye drop administration of recombinant human nerve growth factor alone promoted retinal ganglion cell survival and axon regeneration at high dose, while the combination of recombinant human nerve growth factor with L-PenetraMax significantly enhanced the neuroprotective efficacy at lower dose, thus potentially enhancing the availability of recombinant human nerve growth factor eye drops in patients with optic neuropathy.Conclusions: This study provides the evidence that the noncovalent coadministration of recombinant human nerve growth factor with L-PenetraMax could be a potent strategy for the non-invasive and sustained ocular delivery of therapeutic proteins for improving the optic nerve injury.

RiTe conjugate mediated corneal collagen crosslinking, a novel therapeutic intervention for keratoconus - in vitro and in vivo study

Corneal collagen crosslinking (CXL) is an effective method to halt the disease progression of keratoconus, a progressive corneal dystrophy leading to cone shaped cornea. Despite the efficacy of standard protocol, the concerning step of this procedure is epithelial debridement performed to facilitate the entry of riboflavin drug. Riboflavin, a key molecule in CXL protocol, is a sparsely permeable hydrophilic drug in corneal tissues. The present study has employed cell penetrating peptide (CPP), Tat2, to enhance the penetration of riboflavin molecule, and thereby improve currently followed CXL protocol. This study demonstrates approximately two-fold enhanced uptake of CPP riboflavin conjugate, Tat2riboflavin-5'Phosphate (RiTe conjugate), both in vitro and in vivo. Two different CXL protocols (Epi ON and Epi OFF) have been introduced and implemented in rabbit corneas using RiTe conjugate in the present study. The standard and RiTe conjugate mediated CXL procedures exhibited an equivalent extent of crosslinking in both the methods. Reduced keratocyte loss and no endothelial damage in RiTe conjugate mediated CXL further ascertains the safety of the proposed CXL protocols. Therefore, RiTe conjugate mediated CXL protocols present as potential alternatives to the standard keratoconus treatment in providing equally effective, less invasive and patient compliant treatment modality.

Deconvoluting the Effect of Cell-Penetrating Peptides for Enhanced and Controlled Insertion of Large-Scale DNA Nanopores

DNA nanopores have emerged as powerful tools for molecular sensing, but the efficient insertion of large DNA nanopores into lipid membranes remains challenging. In this study, we investigate the potential of cell-penetrating peptides (CPPs), specifically SynB1 and GALA, to enhance the insertion efficiency of large DNA nanopores. We constructed SynB1- or GALA-functionalized DNA nanopores with an 11 nm inner diameter and visualized and quantified their membrane insertion using a TIRF microscopy-based single-liposome assay. The results demonstrated that incorporating an increasing number of SynB1 or GALA peptides into the DNA nanopore significantly enhanced the membrane perforation. Kinetic analysis revealed that the DNA nanopore scaffold played a role in prearranging the CPPs, which facilitated membrane interaction and pore formation. Notably, the use of pH-responsive GALA peptides allowed highly efficient and pH-controlled insertion of large DNA pores. Furthermore, single-channel recording elucidated that the insertion process of single GALA-modified nanopores into planar lipid bilayers was dynamic, likely forming transient large toroidal pores. Overall, our study highlights the potential of CPPs as insertion enhancers for DNA nanopores, which opens avenues for improved molecule sensing and the controlled release of cargo molecules.

Construction of a versatile fusion protein for targeted therapy and immunotherapy

Antibody (Ab)-based drugs have been widely used in targeted therapies and immunotherapies, leading to significant improvements in tumor therapy. However, the failure of Ab therapy due to the loss of target antigens or Ab modifications that affect its function limits its application. In this study, we expanded the application of antibodies (Abs) by constructing a fusion protein as a versatile tool for Ab-based target cell detection, delivery, and therapy. We first constructed a SpaC Catcher (SpaCC for short) fusion protein that included the C domains of Staphylococcal protein A (SpaC) and the SpyCatcher. SpaCC conjugated with SpyTag-X (S-X) to form the SpaCC-S-X complex, which binds non-covalently to an Ab to form the Ab-SpaCC-S-X protein complex. The "X" can be a variety of small molecules such as fluoresceins, cell-penetrating peptide TAT, Monomethyl auristatin E (MMAE), and DNA. We found that Ab-SpaCC-S-FITC(-TAT) could be used for target cell detection and delivery. Besides, we synthesized the Ab-SpaCC-SN3-MMAE complex by linking Ab with MMAE by SpaCC, which improved the cytotoxicity of small molecule toxins. Moreover, we constructed an Ab-DNA complex by conjugating SpaCC with the aptamer (Ap) and found that Ab-SpaCC-SN3-Ap boosted the tumor-killing function of T-cells by retargeting tumor cells. Thus, we developed a multifunctional tool that could be used for targeted therapies and immunotherapies, providing a cheap and convenient novel drug development strategy.

Cyclohexylalanine-Containing α-Helical Amphipathic Peptide Targets Cardiolipin, Rescuing Mitochondrial Dysfunction in Kidney Injury

Mitochondrial dysfunction is linked to degenerative diseases, resulting from cardiolipin (CL)-induced disruption of cristae structure in the inner mitochondrial membrane (IMM); therefore, preserving cristae and preventing CL remodeling offer effective strategies to maintain mitochondrial function. To identify reactive oxygen species (ROS)-blocking agents against mitochondrial dysfunction, a library of cyclohexylamine-containing cell-penetrating α-helical amphipathic "bundle" peptides were screened. Among these, CMP3013 is selectively bound to abnormal mitochondria, preserving the cristae structure impaired by mitochondria-damaging agents. With a stronger affinity for CL compared with other IMM lipid components, CMP3013 exhibited high selectivity. Consequently, it protected cristae, reduced ROS production, and enhanced adenosine triphosphate (ATP) generation. In mouse models of acute kidney injury, a 1 mg/kg dose of CMP3013 demonstrated remarkable efficacy, highlighting its potential as a therapeutic agent for mitochondrial dysfunction-related disorders. Overall, CMP3013 represents a promising agent for mitigating mitochondrial dysfunction and associated diseases.

Topical Ophthalmic Liposomes Dual-Modified with Penetratin and Hyaluronic Acid for the Noninvasive Treatment of Neovascular Age-Related Macular Degeneration

Introduction

Since intrinsic ocular barrier limits the intraocular penetration of therapeutic protein through eye drops, repeated intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) agents are the standard therapy for neovascular age-related macular degeneration (nAMD), which are highly invasive and may cause particular ocular complications, leading to poor patient compliance.

Methods

Using Penetratin (Pen) as the ocular penetration enhancer and hyaluronic acid (HA) as the retina-targeting ligand, a dual-modified ophthalmic liposome (Penetratin hyaluronic acid-liposome/Conbercept, PenHA-Lip/Conb) eye drop was designed to non-invasively penetrate the ocular barrier and deliver anti-VEGF therapeutic agents to the targeted intraocular tissue.

Results

PenHA-Lip effectively penetrates the ocular barrier and targets the retinal pigment epithelium via corneal and non-corneal pathways. After a single topical administration of conbercept-loaded PenHA-Lip (PenHA-Lip/Conb), the intraocular concentration of conbercept peaked at 18.74 ± 1.09 ng/mL at 4 h, which is 11.55-fold higher than unmodified conbercept. In a laser-induced choroidal neovascularization (CNV) mouse model, PenHA-Lip/Conb eye drops three times daily for seven days inhibited CNV formation and progression without any significant tissue toxicity and achieved an equivalent effect to a single intravitreal conbercept injection.

Conclusion

PenHA-Lip efficiently and safely delivered conbercept to the posterior eye segment and may be a promising noninvasive therapeutic option for nAMD.

Development of polypeptide-based materials toward messenger RNA delivery

Messenger RNA (mRNA)-based therapeutic agents have demonstrated significant potential in recent times, particularly in the context of the COVID-19 pandemic outbreak. As a promising prophylactic and therapeutic strategy, polypeptide-based mRNA delivery systems attract significant interest because of their low cost, simple preparation, tuneable sizes and morphology, convenient large-scale production, biocompatibility, and biodegradability. In this review, we begin with a brief discussion of the synthesis of polypeptides, followed by a review of commonly used polypeptides in mRNA delivery, including classical polypeptides and cell-penetrating peptides. Then, the challenges against mRNA delivery, including extracellular, intracellular, and clinical barriers, are discussed in detail. Finally, we highlight a range of strategies for polypeptide-based mRNA delivery, offering valuable insights into the advancement of polypeptide-based mRNA carrier development.

Improving combination cancer immunotherapy by manipulating dual immunomodulatory signals with enzyme-triggered, cell-penetrating peptide-mediated biomodulators

Immunosuppressive tumor microenvironments challenge the effectiveness of protein-based biopharmaceuticals in cancer immunotherapy. Reestablishing tumor cell immunogenicity by enhancing calreticulin (CRT) exposure is expected to improve tumor immunotherapy. Given that CRT translocation is inherently modulated by phosphorylated eIF2α, the selective inhibition of protein phosphatase 1 (PP1) emerges as an effective strategy to augment tumor immunogenicity. To harness the PP1-disrupting potential of GADD34-derived motifs and address their limited intracellular delivery, we integrated these sequences into an enzyme-triggered, cell-penetrating peptide-mediated chimeric protein scaffold. This design not only facilitates efficient cytoplasmic delivery of these immunostimulatory motifs to induce "eat-me" signaling, but also provides a versatile platform for combination immunotherapy. Fabrication of biomodulators with cytotoxic BLF1 provides additional "eat-me" signaling through phosphatidylserine exposure or that with an immunomodulatory designed ankyrin repeat protein disables "don't-find-me" signaling by antagonizing PD-L1. Notably, these bifunctional biomodulators exhibit remarkable ability to induce macrophage phagocytosis, dendritic cell maturation, and CD8+ T activation, ultimately substantially inhibiting tumor growth. This study presents a modular genetic coding strategy for PP1-centered therapies that enables seamless integration of immunostimulatory sequences into protein-based anti-tumor cocktail therapies, thereby offering novel alternatives for improving antitumor efficacy.

Dexamethasone phosphate and penetratin co-eluting contact lenses: a strategy to enhance ocular drug permeability

Contact lenses (CLs) have been suggested as drug delivery platforms capable of increasing the drug residence time on the cornea and therefore its bioavailability. However, when targeting the posterior segment of the eye, the drug released from CLs still encounters the barrier effect of the ocular tissues, which considerably reduces the efficacy of administration. This work aims at the development of CLs able to simultaneously deliver an anti-inflammatory drug (dexamethasone sodium phosphate) and a cell-penetrating peptide (penetratin), the latter acting as a drug carrier across the tissues. Hydroxyethyl methacrylate (HEMA)-based hydrogels were functionalized with acrylic acid (AAc) and/or aminopropyl methacrylamide (APMA) to serve as CL materials with increased affinity for the drug and peptide. APMA-functionalized hydrogels sustained the dual release for 8 h, which is compatible with the wearing time of daily CLs. Hydrogels demonstrated suitable light transmittance, swelling capacity and in vitro biocompatibility. The anti-inflammatory activity of the drug was not compromised by the presence of the peptide nor by sterilization. The ocular distribution of the drug after 6 h of CL wearing was evaluated in vivo in rabbits and revealed that the amount of drug in the cornea and aqueous humor significantly increased when the drug was co-delivered with penetratin.

The Current and Promising Oral Delivery Methods for Protein- and Peptide-Based Drugs

Drugs based on peptides and proteins (PPs) have been widely used in medicine, beginning with insulin therapy in patients with diabetes mellitus over a century ago. Although the oral route of drug administration is the preferred one by the vast majority of patients and improves compliance, medications of this kind due to their specific chemical structure are typically delivered parenterally, which ensures optimal bioavailability. In order to overcome issues connected with oral absorption of PPs such as their instability depending on digestive enzymes and pH changes in the gastrointestinal (GI) system on the one hand, but also their limited permeability across physiological barriers (mucus and epithelium) on the other hand, scientists have been strenuously searching for novel delivery methods enabling peptide and protein drugs (PPDs) to be administered enterally. These include utilization of different nanoparticles, transport channels, substances enhancing permeation, chemical modifications, hydrogels, microneedles, microemulsion, proteolytic enzyme inhibitors, and cell-penetrating peptides, all of which are extensively discussed in this review. Furthermore, this article highlights oral PP therapeutics both previously used in therapy and currently available on the medical market.

Topical Application of Cell-Penetrating Peptide Modified Anti-VEGF Drug Alleviated Choroidal Neovascularization in Mice

Background

Age-related macular degeneration (AMD) stands as the foremost cause of irreversible central vision impairment, marked by choroidal neovascularization (CNV). The prevailing clinical approach to AMD treatment relies on intravitreal injections of anti-vascular endothelial growth factor (VEGF) drugs. However, this method is encumbered by diverse complications, prompting exploration of non-invasive alternatives such as ocular administration via eye drops for anti-VEGF therapy.

Methods

Two complexes, 5-FITC-CPP-Ranibizumab (5-FCR) and 5-FITC-CPP-Conbercept (5-FCC), were synthesized by incorporating the anti-VEGF drugs Ranibizumab (RBZ) or Conbercept (CBC) with cell-penetrating peptide (CPP). Circular dichroism spectrum (CD) facilitated complexes characterization. Eye drops was utilized to address laser-induced CNV in mice. Fluorescein fundus angiography (FFA) observe the CNV lesion, while FITC-dextran and IB4 dual fluorescent staining, along with hematoxylin-eosin (HE) staining, assessed in lesion size. Tissue immunofluorescence examined CD31 and VEGF expression in choroidal/retinal pigment epithelial (RPE) tissues. Biocompatibility and biosafety of 5-FCR and 5-FCC was evaluated through histological examination of various organs or cell experiments.

Results

Both 5-FCR and 5-FCC exhibited favorable biocompatibility and safety profiles. VEGF-induced migration of Human umbilical vein endothelial cells (HUVECs) significantly decreased post-5-FCR/5-FCC treatment. Additionally, both complexes suppressed VEGF-induced tube formation in HUVECs. FFA results revealed a significant improvement in retinal exudation in mice. Histological examination unveiled the lesion areas in the 5-FCR and 5-FCC groups showed a significant reduction compared to the control group. Similar outcomes were observed in histological sections of the RPE-choroid-sclera flat mounts.

Conclusion

In this study, utilizing the properties of CPP and two anti-VEGF drugs, we successfully synthesized two complexes, 5-FCR and 5-FCC, through a straightforward approach. Effectively delivering the anti-VEGF drugs to the target area in a non-invasive manner, suppressing the progression of laser-induced CNV. This offers a novel approach for the treatment of wet AMD.

Aflibercept Loaded Eye-Drop Hydrogel Mediated with Cell-Penetrating Peptide for Corneal Neovascularization Treatment

Corneal neovascularization (CoNV) is a major cause of visual impairment worldwide. Currently, available treatment options have limited efficacy and are associated with adverse effects due to biological barriers and clearance mechanisms. To address this challenge, a novel topical delivery system is developed-Gel 2_1&Eylea-an aflibercept-loaded eye-drop hydrogel mediated with cell-penetrating peptide 1. Gel 2_1&Eylea demonstrates superior membrane permeability, increased stability, and prolonged drug retention time on the ocular surface, and thus may improve drug efficacy. In a rabbit CoNV model, Gel 2_1&Eylea significantly reduces the density of neovascularization with no adverse effects on normal corneoscleral limbal vessels, demonstrating high efficacy and biocompatibility. This work identifies a promising treatment for CoNV which has the potential to benefit other ocular neovascular diseases.

Quantitative visualization of myocardial ischemia-reperfusion-induced cardiac lesions via ferroptosis magnetic particle imaging

Myocardial ischemia-reperfusion (MI/R) injury is a complication in vascular reperfusion therapy for MI, occurring in approximately 60% of patients. Ferroptosis is an important process in the development of MI/R cardiac lesions. Transferrin receptor 1 (TfR1), a marker of ferroptosis, corresponds to the changes in MI/R cardiac lesions and is expected to be a biomarker for detecting MI/R-induced ferroptosis. However, the noninvasive in vivo visualization of ferroptosis in MI/R is a big challenge. Thus, this study aimed to develop a novel multimodal imaging platform to identify markers of MI/R cardiac lesions in vivo through targeting TfR1. Methods: Magnetic particle imaging (MPI) modality for ferroptosis based on superparamagnetic cubic-iron oxide nanoparticles (SCIO NPs), named feMPI, has been developed. FeMPI used TfR1 as a typical biomarker. The feMPI probe (SCIO-ICG-CRT-CPPs NPs, CCI NPs) consists of SCIO NPs, TfR1-targeting peptides (CRT), cell-penetrating peptides (CPPs), and indocyanine green (ICG). The specificity and sensitivity of CCI NPs in the MI/R mouse model were evaluated by MPI, magnetic resonance imaging (MRI), and near-infrared (NIR) fluorescent imaging. Results: The intensity of the MPI signal correlates linearly with the percentage of infarct area in MI/R stained by TTC, enabling a quantitative assessment of the extent of cardiac lesions. Notably, these findings are consistent with the standard clinical biochemical indicators in MI/R within the first 24 h. FeMPI detects cardiac injury approximately 48 h prior to the current clinical imaging detection methods of MI/R. Conclusion: The feMPI strategy can be a powerful tool for studying the process of MI/R-induced ferroptosis in vivo, providing clues for molecular imaging and drug development of ferroptosis-related treatments.

Tumor Cell Lysate-Based Multifunctional Nanoparticles Facilitate Enhanced mRNA Delivery and Immune Stimulation for Melanoma Gene Therapy

Messenger ribonucleic acid (mRNA)-based gene therapy has great potential for cancer gene therapy. However, the effectiveness of mRNA in cancer therapy needs to be further improved, and the delivery efficiency and instability of mRNA limit the application of mRNA-based products. Both the delivery efficiency can be elevated by cell-penetrating peptide modification, and the immune response can be enhanced by tumor cell lysate stimulation, representing an advantageous strategy to expand the effectiveness of mRNA gene therapy. Therefore, it is vital to exploit a vector that can deliver high-efficiency mRNA with codelivery of tumor cell lysate to induce specific immune responses. We previously reported that DMP cationic nanoparticles, formed by the self-assembly of DOTAP and mPEG-PCL, can deliver different types of nucleic acids. DMP has been successfully applied in gene therapy research for various tumor types. Here, we encapsulated tumor cell lysates with DMP nanoparticles and then modified them with a fused cell-penetrating peptide (TAT-iRGD) to form an MLSV system. The MLSV system was loaded with encoded Bim mRNA, forming the MLSV/Bim complex. The average size of the synthesized MLSV was 191.4 nm, with a potential of 47.8 mV. The MLSV/mRNA complex promotes mRNA absorption through caveolin-mediated endocytosis, with a transfection rate of up to 68.6% in B16 cells. The MLSV system could also induce the maturation and activation of dendritic cells, obviously promoting the expression of CD80, CD86, and MHC-II both in vitro and in vivo. By loading the encoding Bim mRNA, the MLSV/Bim complex can inhibit cell proliferation and tumor growth, with inhibition rates of up to 87.3% in vitro. Similarly, the MLSV/Bim complex can inhibit tumor growth in vivo, with inhibition rates of up to 78.7% in the B16 subcutaneous tumor model and 63.3% in the B16 pulmonary metastatic tumor model. Our results suggest that the MLSV system is an advanced candidate for mRNA-based immunogene therapy.

Synthesis of cell penetrating peptide sterol coupler and its liposome study on S-mRNA

In order to overcome the current LNP-mRNA delivery system's weakness of poor stability and rapid degradation by nuclease, a novel chol-CGYKK molecule and then the new phospholipid liposome were designed and prepared. A solid phase approach synthesized CGYKK and connected it to cholesterol via a disulfide linker to form the desired chol-CGYKK. Four formulated samples with different proportions of excipients were prepared by freeze-drying cationic liposomes and packaged S-mRNA. The stability test shows that after six months at 4 °C, the encapsulation rate of this novel phospholipid liposome was still approximately 90%, which would significantly improve the storage and transportation requirement. Transmission electron microscopy, atomic force microscopy, and scanning electron microscopy indicated that the liposomes were spherical and uniformly dispersed. On comparing the levels of mRNA protein expression of the four formulated samples, the S protein vaccine expression of formulated sample 1 was the highest. Uptake by vector cells for formulated sample 1 showed that compared to Lipo2000, and the transfection efficiency was 66.7%. Furthermore, the safety evaluation of the CGYKK and mRNA vaccine liposomes revealed no toxic effects. The in vivo study demonstrated that this novel mRNA vaccine had an immune response. However, it was still not as good as the LNP group right now, but its excellent physicochemical properties, stability, in vitro biological activity, and in vivo efficacy against SARS-CoV-2 provided new strategies for developing the next generation of mRNA delivery system.

AIE-enabled transfection-free identification and isolation of viable cell subpopulations differing in the level of autophagy

ABBREVIATIONS

3-MA, 3-methyladenine; AIE, aggregation-induced emission; AIEgens, aggregation-induced emission luminogens; ATG5, autophagy related 5; BMDM, bone marrow-derived macrophage; CQ, chloroquine; DiD, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate; DiO, 3,3'-dioctadecyloxacarbocyanine perchlorate; DMSO, dimethyl sulfoxide; d-THP-1, differentiated THP-1; FACS, fluorescence activated cell sorting; FBS, fetal bovine serum; FCCP, carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone; GABARAP, GABA type A receptor-associated protein; GFP, green fluorescent protein; HBSS, Hanks' balanced salt solution; HPLC, high-performance liquid chromatography; HRP, horseradish peroxidase; IL1B, interleukin 1 beta; KT, an AIE probe composed of a cell-penetrating peptide and an AIEgen tetraphenyl ethylene; LC3-II, lipidated LC3; LDH, lactate dehydrogenase; LIR, LC3-interacting region; LKR, engineered molecular probe composed of an LC3-interacting peptide, a cell-penetrating peptide and a non-AIE fluorescent molecule rhodamine; LKT, engineered molecular probe composed of an LC3-interacting peptide, a cell-penetrating peptide and an AIEgen tetraphenyl ethylene; LPS, lipopolysaccharide; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; MEF, mouse embryonic fibroblast; mRFP, monomeric red fluorescent protein; NHS, N-hydroxysuccinimide; NLRP3, NLR family pyrin domain containing 3; PBS, phosphate-buffered saline; PCC, pearson's correlation coefficient; PL, photoluminescence; PMA, phorbol 12-myristate 13-acetate; RAP, rapamycin; RIM, restriction of intramolecular motions; s.e.m., standard error of the mean; SPR, surface plasmon resonance; SQSTM1/p62, sequestosome 1; TAX1BP1, Tax1 binding protein 1; TPE, tetraphenylethylene; TPE-yne, 1-(4-ethynylphenyl)-1,2,2-triphenylethene; Tre, trehalose; u-THP-1: undifferentiated THP-1; UV-Vis, ultraviolet visible.

Nanoplatforms for the Delivery of Nucleic Acids into Plant Cells

Nanocarriers are widely used for efficient delivery of different cargo into mammalian cells; however, delivery into plant cells remains a challenging issue due to physical and mechanical barriers such as the cuticle and cell wall. Here, we discuss recent progress on biodegradable and biosafe nanomaterials that were demonstrated to be applicable to the delivery of nucleic acids into plant cells. This review covers studies the object of which is the plant cell and the cargo for the nanocarrier is either DNA or RNA. The following nanoplatforms that could be potentially used for nucleic acid foliar delivery via spraying are discussed: mesoporous silica nanoparticles, layered double hydroxides (nanoclay), carbon-based materials (carbon dots and single-walled nanotubes), chitosan and, finally, cell-penetrating peptides (CPPs). Hybrid nanomaterials, for example, chitosan- or CPP-functionalized carbon nanotubes, are taken into account. The selected nanocarriers are analyzed according to the following aspects: biosafety, adjustability for the particular cargo and task (e.g., organelle targeting), penetration efficiency and ability to protect nucleic acid from environmental and cellular factors (pH, UV, nucleases, etc.) and to mediate the gradual and timely release of cargo. In addition, we discuss the method of application, experimental system and approaches that are used to assess the efficiency of the tested formulation in the overviewed studies. This review presents recent progress in developing the most promising nanoparticle-based materials that are applicable to both laboratory experiments and field applications.

Carrier peptide interactions with liposome membranes induce reversible clustering by surface adsorption and shape deformation

The cell-penetrating peptide penetratin and its analogues shuffle and penetramax have been used as carrier peptides for oral delivery of therapeutic peptides such as insulin. Their mechanism of action for this purpose is not fully understood but is believed to depend on the interactions of the peptide with the cell membrane. In the present study, peptide-liposome interactions were investigated using advanced biophysical techniques including small-angle neutron scattering and fluorescence lifetime imaging microscopy. Liposomes were used as a model system for the cell membrane. All the investigated carrier peptides induced liposome clustering at a specific peptide/lipid ratio. However, distinctively different types of membrane interactions were observed, as the liposome clustering was irreversible for penetratin, but fully or partly reversible for shuffle and penetramax, respectively. All three peptides were found to adsorb to the surface of the lipid bilayers, while only shuffle and penetramax led to shape deformation of the liposomes. Importantly, the peptide interactions did not disrupt the liposomes under any of the investigated conditions, which is advantageous for their application in drug delivery. This detailed insight on peptide-membrane interactions is important for understanding the mechanism of peptide-based excipients and the influence of peptide sequence modifications.

A cell-penetrating peptide derived from SARS-CoV-2 protein Orf9b allosterically inhibits MARK4 activity and mitigates tau toxicity

Abnormal activation of microtubule affinity-regulating kinase 4 (MARK4) and its phosphorylation of the microtubule-associated protein tau are believed to play a role in the pathogenesis of Alzheimer's disease, and MARK4 inhibition can be a strategy to develop disease-modifying therapy. Here we report the development of a membrane-permeable peptide that inhibits MARK4 activity in an allosteric manner. The SARS-CoV-2-derived protein Orf9b inhibited MARK4-mediated tau phosphorylation in primary neurons and Drosophila. Orf9b inhibited MARK4 activity in an allosteric manner and did not inhibit the activity of MARK2, which is another MARK family member and is closely related to MARK4. Co-expression of Orf9b in the fly retina expressing human tau and MARK4 suppressed phosphorylation of tau at the microtubule-binding repeats and tau-induced neurodegeneration. We identified the minimal sequence of Orf9b required to suppress MARK4 activity and fused it to a cell-permeable sequence (TAT-Orf9b10-18_78-95). Extracellular supplementation of TAT-Orf9b10-18_78-95 inhibited MARK4 activity in primary neurons, and feeding TAT-Orf9b10-18_78-95 to a fly model of tauopathy lowered phospho-tau levels and suppressed neurodegeneration. These results suggest that TAT-Orf9b10-18_78-95 is a unique class of MARK4 inhibitor and can be used to modify tau toxicity.

Engineered phage with cell-penetrating peptides for intracellular bacterial infections

IMPORTANCE

Salmonella infection is a significant threat to global public health, and the increasing prevalence of antibiotic resistance exacerbates the situation. Therefore, finding new and effective ways to combat this pathogen is essential. Phages are natural predators of bacteria and can be used as an alternative to antibiotics to kill specific bacteria, including drug-resistant strains. One significant limitation of using phages as antimicrobial agents is their low cellular uptake, which limits their effectiveness against intracellular bacterial infections. Therefore, finding ways to enhance phage uptake is crucial. Our study provides a straightforward strategy for displaying cell-penetrating peptides on non-model phages, offering a promising novel and effective therapeutic approach for treating intracellular and drug-resistant bacteria. This approach has the potential to address the global challenge of antibiotic resistance and improve public health outcomes.

Fluorophore-Tagged Poly-Lysine RAFT Agents: Controlled Synthesis of Trackable Cell-Penetrating Peptide-Polymers

The conjugation of a fluorophore and a variety of cell-penetrating peptides onto a RAFT agent allowed for the synthesis of polymers of defined sizes with quantifiable cell-uptake. Each peptide-RAFT agent was used to polymerize acrylamide, acrylate, and styrene monomers to form high or low molecular weight polymers (here 50 or 7.5 kDa) with the peptide having no influence on the RAFT agent's control. The incorporation of a single fluorophore per polymer chain allowed cellular analysis of the uptake of the size-specific peptide-polymers via flow cytometry and confocal microscopy. The cell-penetrating peptides had a direct effect on the efficiency of polymer uptake for both high and low molecular weight polymers, demonstrating the versatility of the strategy. These "all-in-one", synthetically accessible RAFT agents allow highly controlled preparation of synthetic peptide-polymer conjugates and subsequent quantification of their delivery into cells.

In vivo direct cell-penetrating peptide mediated protein transduction system in Acyrthosiphon pisum

OBJECTIVE

The principal delivery method for CRISPR-based genome editing in insects is now based on microinjection into single cells or embryos. The direct protein transduction systems cannot be employed in aphids because oogenesis occurs without apparent vitellogenesis. Given the limited timing of injection into the embryonic stage in oviparous aphids, a protein delivery system from the hemolymph to the germline and embryos would be a useful tool for genome editing. This study reports a newly developed direct protein delivery system for aphids using cell-penetrating peptides (CPPs). CPPs are short peptides that translocate across the plasma membrane when bound to cargo proteins.

RESULTS

Penetratin (PEN), a widely conserved CPP among insects, was identified in this study. We used mVenus, a recombinant fluorescent protein, as a visual marker for CPP availability assessments, and fused it with PEN by bacterial protein expression. The mVenus-PEN recombinant proteins were introduced into the hemolymph of adult unwinged Acyrthosiphon pisum females using a nanoinjector. Fluorescence emitted by mVenus-PEN was observed in various tissues, such as the gut, trachea, bacteriocytes, and their progeny. This study shows that PEN can deliver exogenously expressed proteins into tissues in vivo, indicating that CPPs are powerful tools for protein transduction.

Defect Formation and Peptide Permeation across Phospholipid Membranes

Cell penetrating peptides (CPPs) are natural agents that efficiently permeate biological membranes. They are frequently positively charged, which is surprising since membranes pose hydrophobic barriers. In this Perspective, I discuss computations and experiments of a permeation model that couples permeant displacement with a membrane defect. We call the proposed mechanism Defect Assisted by Charge (DAC) and illustrate that it reduces the free energy barrier for translocation. A metastable state at the center of the membrane may be observed due to the charge interactions with the phospholipid head groups at the two leaflets. The combination of experiments and simulations sheds light on the mechanisms of a charged peptide translocation across phospholipid membranes.

Functional small peptides for enhanced protein delivery, solubility, and secretion in microbial biotechnology

In microbial biotechnology, there is a constant demand for functional peptides to give new functionality to engineered proteins to address problems such as direct delivery of functional proteins into bacterial cells, enhanced protein solubility during the expression of recombinant proteins, and efficient protein secretion from bacteria. To tackle these critical issues, we selected three types of functional small peptides: cell-penetrating peptides (CPPs) enable the delivery of diverse cargoes into bacterial cytoplasm for a variety of purposes, protein-solubilizing peptide tags demonstrate remarkable efficiency in solubilizing recombinant proteins without folding interference, and signal peptides play a key role in enabling the secretion of recombinant proteins from bacterial cells. In this review, we introduced these three functional small peptides that offer effective solutions to address emerging problems in microbial biotechnology. Additionally, we summarized various engineering efforts aimed at enhancing the activity and performance of these peptides, thereby providing valuable insights into their potential for further applications.

Utilization of a cell-penetrating peptide-adaptor for delivery of human papillomavirus protein E2 into cervical cancer cells to arrest cell growth and promote cell death

BACKGROUND

Human papillomavirus (HPV) is the causative agent of nearly all forms of cervical cancer, which can arise upon viral integration into the host genome and concurrent loss of viral regulatory gene E2. Gene-based delivery approaches show that E2 reintroduction reduces proliferative capacity and promotes apoptosis in vitro.

AIMS

This work explored if our calcium-dependent protein-based delivery system, TAT-CaM, could deliver functional E2 protein directly into cervical cancer cells to limit proliferative capacity and induce cell death.

MATERIALS AND RESULTS

TAT-CaM and the HPV16 E2 protein containing a CaM-binding sequence (CBS-E2) were expressed and purified from Escherichia coli. Calcium-dependent binding kinetics were verified by biolayer interferometry. Equimolar TAT-CaM:CBS-E2 constructs were delivered into the HPV16+ SiHa cell line and uptake verified by confocal microscopy. Proliferative capacity was measured by MTS assay and cell death was measured by release of lactate dehydrogenase. As a control, human microvascular cells (HMECs) were used. As expected, TAT-CaM bound CBS-E2 with high affinity in the presence of calcium and rapidly disassociated upon its removal. After introduction by TAT-CaM, fluorescently labeled CBS-E2 was detected in cellular interiors by orthogonal projections taken at the depth of the nucleus. In dividing cells, E2 relocalized to regions associated with the mitotic spindle. Cells receiving a daily dose of CBS-E2 for 4 days showed a significant reduction in metabolic activity at low doses and increased cell death at high doses compared to controls. This phenotype was retained for 7 days with no further treatments. When subcultured on day 12, treated cells regained their proliferative capacity.

CONCLUSIONS

Using the TAT-CaM platform, bioactive E2 protein was delivered into living cervical cancer cells, inducing senescence and cell death in a time- and dose-dependent manner. These results suggest that this nucleic acid and virus-free delivery method could be harnessed to develop novel, effective protein therapeutics.

Cell-Penetrating Peptidic GRP78 Ligand-Conjugated Iron Oxide Magnetic Nanoparticles for Tumor-Targeted Doxorubicin Delivery and Imaging

Although chemotherapy is regarded as an essential option in cancer treatment, it is still far from being perfect. Inadequate tumor drug concentration and systemic toxicity along with broad biodistribution have diminished the utility of chemotherapy. Tumor-targeting peptide-conjugated multifunctional nanoplatforms have emerged as an effective strategy for site-directed tumor tissues in cancer treatment and imaging. Herein, Pep42-targeted iron oxide magnetic nanoparticles (IONPs) functionalized with β-cyclodextrin (ßCD) containing doxorubicin (DOX) (Fe₃O₄-ßCD-Pep42-DOX) were successfully developed. The physical effects of the prepared NPs were characterized by employing various techniques. Transmission electron microscopy (TEM) images disclosed that the developed Fe₃O₄-ßCD-Pep42-DOX nanoplatforms had a spherical morphology and a core-shell structure with a size of nearly 17 nm. Fourier transform infrared (FT-IR) spectroscopy showed that β-cyclodextrin, DOX, and Pep42 molecules were successfully loaded on the IONPs. In vitro cytotoxicity analysis revealed that the fabricated multifunctional Fe₃O₄-ßCD-Pep42 nanoplatforms possessed excellent biosafety toward BT-474, MDA-MB468 (cancerous cells), and MCF10A normal cells, while Fe₃O₄-ßCD-Pep42-DOX exhibited great cancer cell killing ability. The high cellular uptake along with intracellular trafficking of Fe₃O₄-ßCD-Pep42-DOX highlights the usefulness of the Pep42-targeting peptide. In vivo results strongly supported the in vitro results, i.e., significant tumor size reduction was observed by single-dose injection of Fe₃O₄-ßCD-Pep42-DOX into tumor-bearing mice. Interestingly, in vivo MR imaging (MRI) of Fe₃O₄-ßCD-Pep42-DOX revealed T₂ contrast improvement in the tumor cells and therapeutic ability in cancer theranostics. Taken together, these findings provided strong evidence for the potential capability of Fe₃O₄-ßCD-Pep42-DOX as a multifunctional nanoplatform in cancer therapy and imaging and opens up a new avenue of research in this area.

In-Cell Penetration Selection-Mass Spectrometry Produces Noncanonical Peptides for Antisense Delivery

Peptide-mediated delivery of macromolecules in cells has significant potential therapeutic benefits, but no therapy employing cell-penetrating peptides (CPPs) has reached the market after 30 years of investigation due to challenges in the discovery of new, more efficient sequences. Here, we demonstrate a method for in-cell penetration selection-mass spectrometry (in-cell PS-MS) to discover peptides from a synthetic library capable of delivering macromolecule cargo to the cytosol. This method was inspired by recent in vivo selection approaches for cell-surface screening, with an added spatial dimension resulting from subcellular fractionation. A representative peptide discovered in the cytosolic extract, Cyto1a, is nearly 100-fold more active toward antisense phosphorodiamidate morpholino oligomer (PMO) delivery compared to a sequence identified from a whole cell extract, which includes endosomes. Cyto1a is composed of d-residues and two non-α-amino acids, is more stable than its all-l isoform, and is less toxic than known CPPs with comparable activity. Pulse-chase and microscopy experiments revealed that while the PMO-Cyto1a conjugate is likely taken up by endosomes, it can escape to localize to the nucleus without nonspecifically releasing other endosomal components. In-cell PS-MS introduces a means to empirically discover unnatural synthetic peptides for subcellular delivery of therapeutically relevant cargo.

Direct contact-mediated non-viral gene therapy using thermo-sensitive hydrogel-coated dressings

Nanotechnologies are being increasingly applied as systems for peptide and nucleic acid macromolecule drug delivery. However systemic targeting of these, or efficient topical and localized delivery remains an issue. A controlled release system that can be patterned and locally administered such as topically to accessible tissue (skin, eye, intestine) would therefore be transformative in realizing the potential of such strategies. We previously developed a technology termed GAG-binding enhanced transduction (GET) to efficiently deliver a variety of cargoes intracellularly, using GAG-binding peptides to mediate cell targeting, and cell penetrating peptides (CPPs) to promote uptake. Herein we demonstrate that the GET transfection system can be used with the moisturizing thermo-reversible hydrogel Pluronic-F127 (PF127) and methyl cellulose (MC) to mediate site specific and effective intracellular transduction and gene delivery through GET nanoparticles (NPs). We investigated hydrogel formulation and the temperature dependence of delivery, optimizing the delivery system. GET-NPs retain their activity to enhance gene transfer within our formulations, with uptake transferred to cells in direct contact with the therapy-laden hydrogel. By using Azowipe™ material in a bandage approach, we were able to show for the first-time localized gene transfer in vitro on cell monolayers. The ability to simply control localization of gene delivery on millimetre scales using contact-mediated transfer from moisture-providing thermo-reversible hydrogels will facilitate new drug delivery methods. Importantly our technology to site-specifically deliver the activity of novel nanotechnologies and gene therapeutics could be transformative for future regenerative medicine.

Charge-Converting Nanoemulsions as Promising Retinal Drug and Gene Delivery Systems

AIM

This study aimed to develop phosphatase-responsive ζ potential converting nanocarriers utilizing polyphosphate-coated cell-penetrating peptide (CPP)-decorated nanoemulsions (NEs) as a novel gene delivery system to retinal cells.

METHODS

Poly-l-lysine (PLL) was first conjugated with oleylamine (OA) only at its carboxylic end to form the amphiphilic PLL-oleylamine (PLOA) conjugate. Afterward, NEs were loaded with PLOA prior to being coated with tripolyphosphate (TPP) to generate PLOA/TPP NEs. A plasmid containing a reporter gene for green fluorescent protein plasmid (pGFP) was complexed with cationic surfactants forming hydrophobic ion pairs that were loaded in the oily core of NEs. Phosphate removal, ζ potential conversion, and cytotoxicity of the system were evaluated. Cellular uptake and transfection efficiency were investigated in 661W photoreceptor-like cells via microscopic analysis, fluorescence spectroscopy, and flow cytometry.

RESULTS

Dephosphorylation of PLOA/TPP NEs triggered by alkaline phosphatase (ALP) resulted in the exposure of positive amine groups on the surface of NE droplets and a notable conversion of the ζ potential from -22.4 to +8.5 mV. Cellular uptake of PLOA/TPP NEs performed on 661W photoreceptor-like cells showed a 3-fold increase compared to control NEs. Furthermore, PLOA/TPP NEs also showed low cytotoxicity and high transfection efficacy with ∼50% of cells transfected.

CONCLUSIONS

Polyphosphate-coated CPP-decorated NEs triggered by ALP could be a promising nanosystem to efficiently deliver drugs and genetic materials to photoreceptor-like cells and other retinal cells for potential treatments of retinal diseases.

Validation of AAC-11-Derived Peptide Anti-Tumor Activity in a Single Graft Sézary Patient-Derived Xenograft Mouse Model

Sézary syndrome (SS) is an aggressive cutaneous T cell lymphoma with poor prognosis mainly characterized by the expansion of a tumor CD4⁺ T cell clone in both skin and blood. So far, the development of new therapeutic strategies has been hindered by a lack of reproducible in vivo models closely reflecting patients’ clinical features. We developed an SS murine model consisting of the intravenous injection of Sézary patients’ PBMC, together with a mixture of interleukins, in NOD-SCID-gamma mice. Thirty-four to fifty days after injection, mice showed skin disorders similar to that observed in patients, with the detection of epidermis thickening and dermal tumor T cell infiltrates. Although experimental variability was observed, Sézary cells could be tracked in the blood stream, confirming that our model could efficiently exhibit both skin and blood involvement. Using this model, we evaluated the therapeutic potential of RT39, a cell-penetrating peptide derived from the survival protein anti-apoptosis clone 11 (AAC-11), that we previously characterized as specifically inducing apoptosis of Sézary patients’ malignant clone ex vivo. Systemic administration of RT39 led to cutaneous tumor T cells depletion, demonstrating efficient malignant cells’ targeting and a favorable safety profile. These preclinical data confirmed that RT39 might be an innovative therapeutic tool for Sézary syndrome.

BR2 cell penetrating peptide effectively delivers anti-p21Ras scFv to tumor cells with ganglioside expression for therapy of ras-driven tumor

Purpose

Cell membrane penetrating peptide BR2 can bind with ganglioside and introduce foreign drugs into tumor cells. In this study, we employed BR2 to carry the broad-spectrum anti-p21Ras scFv prepared in our laboratory into ganglioside expressing tumor cells for therapy of ras-driven tumors.

Methods

BR2-p21Ras scFv gene was cloned to prokaryotic expression vector and expressed in E. coli BL21, then the fusion protein was purified with HisPur Ni-NTA. The immunoreactivity of the fusion protein with p21Ras was detected by ELISA and western blotting. The membrane-penetrating and immune co-localization with p21Ras of the fusion protein were determined by immunofluorescence. The antitumor activity was investigated using MTT, wound healing, colone formation, and apoptosis assays in vitro.

Results

BR2-p21Ras scFv fusion protein was successfully expressed and purified. We found that the fusion protein could specifically penetrate into human tumor cell lines which express ganglioside including human neuroblastoma cell line SK-N-SH, human colon cancer cell line HCT116 and human glioma cell line U251. After entering tumor cells the fusion protein bonded specifically with p21Ras. In vitro experiments revealed that it could significantly inhibit the proliferation, migration, and colone formation of HCT116, SK-N-SH, and U251 cells and promote the apoptosis of these tumor cells.

Conclusions

BR2-p21Ras scFv can penetrate ganglioside expressing tumor cells and inhibit the growth of ras-driven tumor by binding with p21Ras, and producing an inhibitory effect. It is suggested that BR2-p21Ras scFv is a potential ras-driven tumor therapeutic antibody.

pH-induced insertion of pHLIP into a lipid bilayer: In-situ SEIRAS characterization of a folding intermediate at neutral pH

The pH low insertion peptide (pHLIP) is a pH-sensitive cell penetrating peptide that transforms from an unstructured coil on the membrane surface at pH > 7, to a transmembrane (TM) α-helix at pH < 5. By exploiting this unique property, pHLIP attracts interest as a potential tool for drug delivery and visualisation of acidic tissues produced by various maladies such as cancer, inflammation, hypoxia etc. Even though the structures of initial and end states of pHLIP insertion have been widely accepted, the intermediate structures in between these two states are less clear. Here, we have applied in situ Surface-Enhanced Infrared Absorption spectroscopy to examine the pH-induced insertion and folding processes of pHLIP into a solid-supported lipid bilayer. We show that formation of partially helical structure already takes place at pH only slightly below 7.0, but with the helical axis parallel to the membrane surface. The peptide starts to reorientate its helix from horizontal to vertical direction, accompanied by the insertion into the TM region at pH < 6.2. Further insertion into the TM region of the peptide results in an increase of inherent α-helical structure and complete secondary structure formation at pH 5.3. Analysis of the changes of the carboxylate vibrational bands upon pH titration shows two distinctive groups of aspartates and glutamates with pK_a values of 4.5 and 6.3, respectively. Comparison to the amide bands of the peptide backbone suggests that the latter Asp/Glu groups are directly involved in the conformational changes of pHLIP in the respective intermediate states.

Impact of Cyclization and Methylation on Peptide Penetration through Droplet Interface Bilayers

Cell-penetrating peptides enter cells via diverse mechanisms, such as endocytosis, active transport, or direct translocation. For the design of orally delivered cell-penetrating peptides, it is crucial to know the contribution of these different mechanisms. In particular, the ability of a peptide to translocate through a lipid bilayer remains a key parameter for the delivery of cargos. However, existing approaches used to assess translocation often provide discrepant results probably because they have different sensitivities to the distinct translocation mechanisms. Here, we focus on the passive permeation of a range of hydrophobic cyclic peptides inspired by somatostatin, a somatotropin release-inhibiting factor. Using droplet interface bilayers (DIB), we assess the passive membrane permeability of these peptides and study the impact of the peptide cyclization and backbone methylation on translocation rates. Cyclization systematically improved the permeability of the tested peptides while methylation did not. By studying the interaction of the peptides with the DIB interfaces, we found membrane insertion and peptide intrinsic diffusion to be two independent factors of permeability. Compared to the industrial gold standard Caco-2 and parallel artificial membrane permeability assay (PAMPA) models, DIBs provide intermediate membrane permeability values, closer to Caco-2. Even for conditions where Caco-2 and PAMPA are discrepant, the DIB approach also gives results closer to Caco-2. Thereupon, DIBs represent a robust alternative to the PAMPA approach for predicting the permeability of peptides, even if the latter present extremely small structural differences.

Delivery of antisense oligonucleotides for splice-correction of androgen receptor pre-mRNA in castration-resistant prostate cancer models using cell-penetrating peptides

BACKGROUND

Cell-penetrating peptides (CPPs) are a promising approach for delivering antisense oligonucleotides (AONs) as they form nanosized complexes through noncovalent interactions that show efficient cellular uptake. Previously, we have designed an AON system to correct splicing of the androgen receptor (AR) pre-mRNA, thereby preventing the generation of the splice variant AR-V7 mRNA. AON-mediated knockdown of AR-V7 resulted in inhibition of androgen-independent cell proliferation. In this study, we evaluated the CPP-mediated delivery of this AON into castration-resistant prostate cancer cell line models 22Rv1, DuCaP (dura mater cancer of the prostate), and VCaP (vertebral cancer of the prostate).

METHODS

Nanoparticles (polyplexes) of AONs and CPPs were formed through rapid mixing. The impact of the peptide carrier, the formulation parameters, and cell incubation conditions on cellular uptake of fluorescently labeled AONs were assessed through flow cytometry. The cytotoxic activity of these formulations was measured using the CellTiter-Glo cell viability assay. The effectivity of CPP-mediated delivery of the splice-correcting AON-intronic splicing enhancer (ISE) targeting the ISE in the castration-resistant prostate cancer (CRPC)-derived 22Rv1, DuCaP, and VCaP cells was determined by measuring levels of AR-V7 mRNA normalized to those of the human heterochromatin protein 1 binding protein 3 (HP1BP3). Western blot analysis was used to confirm AR-V7 downregulation at a protein level. The cellular distribution of fluorescently labeled AON delivered by a CPP or a transfection reagent was determined through confocal laser scanning microscopy.

RESULTS

The amphipathic and stearylated CPP PepFect 14 (PF14) showed higher uptake efficiency than arginine-rich CPPs. Through adjustment of formulation parameters, concentration and incubation time, an optimal balance between carrier-associated toxicity and delivery efficiency was found with a formulation consisting of an amino/phosphate ratio of 3, 0.35 μM AON concentration and 30 min incubation time of the cells with polyplexes. Cellular delivery of AON-ISE directed against AR pre-mRNA achieved significant downregulation of AR-V7 by 50%, 37%, and 59% for 22Rv1, DuCaP, and VCaP cells, respectively, and reduced androgen-independent cell proliferation of DuCaP and VCaP cells.

CONCLUSIONS

This proof-of-principle study constitutes the basis for further development of CPP-mediated delivery of AONs for targeted therapy in prostate cancer.

Using nanotechnology to deliver biomolecules from nose to brain - peptides, proteins, monoclonal antibodies and RNA

There is a growing number of biomolecules, including peptides, proteins, monoclonal antibodies and RNA, that could be potentially used for the treatment of central nervous system (CNS) diseases. However, the realization of their potential is being hampered by the extraordinary difficulties these complex biomolecules have to reach the brain in therapeutically meaningful amounts. Nose-to-brain (N-to-B) delivery is now being investigated as a potential option for the direct transport of biomolecules from the nasal cavity to different brain areas. Here, we discuss how different technological approaches enhance this N-to-B transport, with emphasis on those that have shown a potential for clinical translation. We also analyse how the physicochemical properties of nanocarriers and their modification with cell-penetrating peptides (CPPs) and targeting ligands affect their efficacy as N-to-B carriers for biomolecules.

Live Cell Genomics: Cell-Specific Transcriptome Capture in Live Single Cells from Complex Tissues

Analysis of single-cell transcriptomes shows the single-cell heterogeneity between cells within a population which is vital to our understanding of normal function and disease development. To obtain single-cell transcriptome profiling, however, the poly-A RNA must be accurately isolated from the target cell. We developed a single-cell analysis procedure called transcriptome in vivo analysis (TIVA), which will allow accurate characterization of targeted cell-specific transcriptomes from live tissue. This is accomplished using a RNA capture molecule called TIVA tag that captures the transcriptome of selected cells in their natural microenvironment. An important aspect of the TIVA approach is that the tag is delivered into the cytoplasm of live cells using cell-penetrating peptides (CPPs). Once the TIVA tag is in the cellular cytoplasm, it binds to mRNA after photoactivation of the compound. Using CPPs in combination with photoactivation is the first noninvasive access method for accurately isolating single-cell mRNA from live single cells in tissues in their natural microenvironment.

A Native CPP from Rattlesnake with Therapeutic and Theranostic Properties

The cell-penetrating peptides (CPPs) are characterized by the ability of internalization into cells in vitro and in vivo, and the ability of these peptides can rely on a high content of positive charges, as it is the case of the native CPP crotamine. Crotamine is a polypeptide of about 42 amino acid residues with high content of basic residues as Arg and Lys. Although most of known CPPs are linear peptides, native crotamine from the venom of a South American rattlesnake has a well-defined 3D structure stabilized by three disulfide bonds which guarantee the exposure of side chains of basic amino acids. This 3D structure also protects this amphipathic polypeptide from the degradation even if administered by oral route, therefore, protecting also the biological activities of crotamine. As several different biological properties of crotamine are dependent of cell penetration, the methods mainly employed for analyzing crotamine properties as anthelminthic and antimalarial activities, antimicrobial and antitumor activities, with a unique selective cytotoxic property against actively proliferating cells, as tumor cells, were chosen based on crotamine ability of internalization mediated by its positive charge. This native cationic polypeptide is also able to efficiently carry, with no need of covalent linkage with the cargo, genetic material into cells in vitro and in vivo, suggesting its use in gene therapy. Moreover, the possibility of decorating gold nanoparticles keeping the ability of transfecting cells was demonstrated. More recently, the ability of crotamine to interfere in animal metabolism, inducing browning of adipose tissue and increasing the energy expenditure, and its application in renal therapy was demonstrated. As crotamine also accumulates specifically in tumor cells in vivo, and the potential utility of crotamine as a theranostic agent was then suggested. Therefore, diverse methodologies employed for the characterization and exploration of the therapeutic applications of this promising native CPP for remediation of several pathogenic conditions are presented here.

Strategies for Peptide-Mediated Cargo Delivery to Human Smooth Muscle Cells

Diseases involving dysfunction of smooth muscle cells present a major health and socioeconomic burden, and have remained stubbornly resistant to standard therapeutic strategies. Examples include many cardiovascular diseases and spontaneous preterm birth, a complication affecting up to 11% of all pregnancies worldwide. This fuels the continued search for new drug delivery strategies to treat these conditions. The use of cell penetrating peptides (CPPs) for this purpose remains a promising, if as yet unrealized, avenue to explore. In part, this may relate to a paucity of studies investigating the application of CPPs as drug delivery vectors to human smooth muscle cells and tissues. We have sought to address this knowledge gap by reporting methods for examining the uptake of different CPP-cargo vectors to human uterine and vascular smooth muscle cells. In particular, we report here (a) that four different CPP-fluorophore conjugates, spanning masses of 1309-3435 Da, and net charges of +2 to +7, can be delivered to human isolated uterine smooth muscle cells without inducing cell toxicity; (b) that the cargo delivered by such CPPs can be fluorescent moieties and/or biologically active peptides; (c) that CPP delivery in a short time frame to native smooth muscle cells in human tissues ex vivo can be achieved. Further exploration of CPPs as tools to facilitate targeted drug delivery to native human smooth muscle tissues will assist in improving our understanding of scientific mechanisms underlying major diseases involving smooth muscle dysfunction as well as facilitating therapeutic investigations.

Improvement of Transfection with PepFects Using Organic and Inorganic Materials

Cell-penetrating peptides (CPPs) are a promising non-viral vector for gene and drug delivery. CPPs exhibit high cell transfection, and are biocompatible. They can be also conjugated with organic and inorganic nanomaterials, such as magnetic nanoparticles (MNPs), graphene oxide (GO), metal-organic frameworks (MOFs), and chitosan. Nanomaterials offered a high specific surface area and provided relatively straightforward methods to be modified with biomolecules including CPPs and oligonucleotides (ONs). Novel nanomaterials conjugates with CPP/ONs complexes are therefore of interest for cell transfection with high efficiency. In this chapter, we described a summary of the non-viral vectors consisting of CPPs and nanomaterials. The book chapter also included a protocol to generate hybrid biomaterials consisting of CPPs and nanoparticles (NPs) for the delivery of oligonucleotides. The conjugation of NPs with CPPs serves as an effective platform for gene therapy with high cell transfection efficiency. The protocol is simple, offers high cell transfection compared to the CPPs-ONs complexes, and can be used for further improvements using external stimuli.

Assessing the Cellular Uptake, Endosomal Escape, and Cytosolic Entry Efficiencies of Cyclic Peptides

Intracellular biologics such as cyclic peptides are an emerging class of macromolecular drugs that are either intrinsically cell permeable or can be effectively delivered into the cell interior to modulate the activity of previously intractable drug targets. They generally enter the mammalian cell by endocytosis mechanisms and are initially localized inside the endosomes. They subsequently escape from the endosomes (and/or lysosomes) into the cytosol with varying efficiencies. In this chapter, we provide the detailed protocol for a flow cytometry-based assay method to quantitate the overall cellular uptake, endosomal escape, and cytosolic entry efficiencies of biomolecules (e.g., linear and cyclic peptides, proteins, and nucleic acids), by using cell-penetrating peptides as an example. The scope of applicability, strengths, and weaknesses of this assay are also discussed.

Delivery of Antibiotics by Cell-Penetrating Peptides to Kill Intracellular Pathogens

In the last decades, the increasing rate of multidrug-resistant bacteria to classical antibiotics has driven research towards identification of other means to fight bacterial infections. In this context, intracellular and/or invasive facultative intracellular bacteria represent a particular problem as common antimicrobials are often not able to reach an effective intracellular concentration. In this regard, cell-penetrating peptides (CPP) can mediate the internalization of previously nonpermeable antimicrobial compounds into the cytoplasm of host cells where they efficiently kill intracellular pathogens. This chapter describes the conjugation of CPPs with antimicrobial agents for the delivery into infected cells. Furthermore, different antimicrobial activity assays will be described including the CPP-mediated delivery of an antimicrobial agent for the treatment of intracellular infections.

Emerging landscape of cell-penetrating peptide-mediated nucleic acid delivery and their utility in imaging, gene-editing, and RNA-sequencing

The safety issues like immunogenicity and unacceptable cancer risk of viral vectors for DNA/mRNA vaccine delivery necessitate the development of non-viral vectors with no toxicity. Among the non-viral strategies, cell-penetrating peptides (CPPs) have been a topic of interest recently because of their ability to cross plasma membranes and facilitate nucleic acids delivery both in vivo and in vitro. In addition to the application in the field of gene vaccine and gene therapy, CPPs based nucleic acids delivery have been proved by its potential application like gene editing, RNA-sequencing, and imaging. Here, we focus on summarizing the recent applications and progress of CPPs-mediated nucleic acids delivery and discuss the current problems and solutions in this field.

Uptake of Cell-Penetrating Peptide RL2 by Human Lung Cancer Cells: Monitoring by Electron Paramagnetic Resonance and Confocal Laser Scanning Microscopy

RL2 is a recombinant analogue of a human κ-casein fragment, capable of penetrating cells and inducing apoptosis of cancer cells with no toxicity to normal cells. The exact mechanism of RL2 penetration into cells remains unknown. In this study, we investigated the mechanism of RL2 penetration into human lung cancer A549 cells by a combination of electron paramagnetic resonance (EPR) spectroscopy and confocal laser scanning microscopy. EPR spectra of A549 cells incubated with RL2 (sRL2) spin-labeled by a highly stable 3-carboxy-2,2,5,5-tetraethylpyrrolidine-1-oxyl radical were found to contain three components, with their contributions changing with time. The combined EPR and confocal-microscopy data allowed us to assign these three forms of sRL2 to the spin-labeled protein sticking to the membrane of the cell and endosomes, to the spin-labeled protein in the cell interior, and to spin labeled short peptides formed in the cell because of protein digestion. EPR spectroscopy enabled us to follow the kinetics of transformations between different forms of the spin-labeled protein at a minimal spin concentration (3-16 μM) in the cell. The prospects of applications of spin-labeled cell-penetrating peptides to EPR imaging, DNP, and magnetic resonance imaging are discussed, as is possible research on an intrinsically disordered protein in the cell by pulsed dipolar EPR spectroscopy.

Induction of Spontaneous Liposome Adsorption by Exogenous Surface Modification with Cell-Penetrating Peptide-Conjugated Lipids

The use of amphiphilic molecules such as poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) enables incorporation into liposome surfaces by exogenous addition as a result of the self-assembly with lipids. This technique can be applicable for manipulation of both liposomes and cells. In this study, we aimed to characterize Tat peptide (YGRKKRRQRRR)-conjugated PEG-lipids when used to exogenously surface modify liposomes (size: ca. 100 nm). We earlier reported that cells, which were surface modified with Tat peptides conjugated to PEG-lipids could attach spontaneously to material surfaces without any chemical modification. Here, we synthesized different types of Tat-PEG-lipids by combining PEG of different molecular weights (5 and 40 kDa) with different lipids with three acyl chains (myristoyl, palmitoyl, and stearoyl, respectively) and then studied the spontaneous adsorption of modified liposomes onto a substrate surface induced by the different Tat-PEG-lipids. The amount of adsorbed liposomes strongly depended on the number of incorporated Tat-PEG-lipid moieties: a decrease in both the PEG and the acyl chain lengths led to adsorption of higher amounts of liposomes. Furthermore, when a collagenase-cleavable amino acid sequence was inserted between the Tat sequence and the PEG segment, adsorbed liposomes could be harvested from the substrate by collagenase treatment with no difference in desorption efficiency between the different Tat-PEG-lipids. Thus, Tat-PEG-lipid can be a suitable tool for the manipulation of liposomes and cells.

Usefulness of cell-penetrating peptides and penetration accelerating sequence for nose-to-brain delivery of glucagon-like peptide-2

Neuropeptides are expected as therapeutic drug candidates for central nervous system (CNS) disorders. Intracerebroventricular (i.c.v.) administration of glucagon-like peptide-2 (GLP-2) has an antidepressant-like effect not only in depression model mice but also in treatment-resistant depression model mice. However, because i.c.v. administration is very invasive, research is progressing on brain delivery using intranasal administration as a non-invasive method. After intranasal administration of the drug, there are two routes to the brain. That of direct delivery from the paracellular route of olfactory epithelium to the brain via the olfactory bulb has been studied, and that of systemic absorption via the paracellular route of respiratory epithelium has been put to practical use. The high degree of vascularization and permeability of the nasal mucosa enables drug delivery via the paracellular route that leads to systemic delivery. Therefore, suppressing systemic absorption may increase drug delivery to brain, so we focused on the transcellular route. We created a GLP-2 derivative by adding cell-penetrating peptides (CPP) and penetration accelerating sequences (PAS), which are reported to provide efficient intracellular uptake, to GLP-2. However, to deliver GLP-2 by the transcellular route, GLP-2 must not only be taken up into cells but also move out of the cells. We investigated in vitro and in vivo function of PAS-CPP-GLP-2 to enable the translocation of GLP-2 directly from the nose to the brain. Derivatization of PAS-CPP-GLP-2 prevented its degradation. In the evaluation of intracellular dynamics, PAS-CPP-GLP-2 enhanced cellular uptake by macropinocytosis with CPP and promoted escape from endosomal vesicles by PAS. This study also showed that PAS-CPP-GLP-2 can move out of cells. Furthermore, only this PAS-CPP-GLP-2 showed an antidepression-like effect within 20 min of intranasal administration. Intranasal administered PAS-CPP-GLP-2 surprisingly showed the effect at the same dose with i.c.v. administration, but intravenous administered PAS-CPP-GLP-2 did not show the effect. These results suggested that PAS-CPP-GLP-2 can be efficiently delivered from the nose to the CNS and show a pharmacological effect, demonstrating the usefulness of PAS and CPP for nose-to-brain delivery of GLP-2.

Insight of Synergistic Effect between CPP and Cargo on the Facilitation Mechanisms of R7-PTX Translocation: Experiments and Molecular Simulations

In our previous study, a novel cell penetrating peptide (CPP) R7 (Arg-Arg-Arg-Arg-Arg-Trp-Trp, RRRRRWW) has been developed to help cellular internalization of paclitaxel (PTX) through the non-covalent interaction with CPP. However, the facilitation mechanism of R7 mediated PTX translocation is not clear. Here the uptake pathways of R7 and R7-PTX were investigated by in vitro test and molecular simulations. In vitro experiments reveal that both R7 and R7-PTX complex translocate through the direct translocation and clathrin mediated endocytosis and associate with the macropinocytosis pathway at high CPP concentration. The translocation of R7(0.1 mM)-PTX complex further involves the lipid raft/caveolae mediated endocytosis. The simulation results show that the synergistic effect between R7 and PTX not only changes the penetration energy barrier but also activates the macropinocytosis and lipid raft/caveolae mediated pathway, resulting in the improvement in the translocation. The presence of heparin also improves the R7 and R7-PTX translocation. These studies provide a theoretical basis for understanding PTX delivery facilitated by the synergistic effect between CPP and cargo and paves a way for CPP design.

Endosome-escaping micelle complexes dually equipped with cell-penetrating and endosome-disrupting peptides for efficient DNA delivery into intact plants

The delivery of DNA to plants is crucial for enhancing their ability to produce valuable compounds and adapt to climate change. Peptides can provide a versatile tool for delivering DNA to a specific target organelle in various plant species without the use of specialized equipment. However, peptide-mediated DNA delivery suffers from endosomal entrapment and subsequent vacuolar degradation of the DNA cargo, which leads to poor transfection efficiency. To overcome the lack of a reliable approach for bypassing vacuolar degradation in plants, we herein present an endosome-escaping micelle. The micelle surface is dually modified with cell-penetrating (CPP) and endosome-disrupting peptides (EDP) and the core is composed of plasmid DNA condensed with cationic peptides. Due to the functions of CPP and EDP, the dual peptide-modified micelles efficiently undergo endocytic internalization and escape from endosomes to the cytosol, thereby achieving significantly enhanced transfection of intact plants with negligible cytotoxicity. The present study offers a robust strategy for efficient intracellular DNA delivery to plants without vacuolar degradation, and can facilitate plant bioengineering for diverse biotechnological applications.

Cell penetrating peptide TAT-functionalized liposomes for efficient ophthalmic delivery of flurbiprofen: Penetration and its underlying mechanism, retention, anti-inflammation and biocompatibility

In treating eye diseases, topical administration on the ocular surface is the most convenient and acceptable route. However, the intraocular efficiency of non-invasive drug delivery systems is still considerably hampered by the eye's defense barriers. In this work, cell-penetrating peptide TAT-functionalized, flurbiprofen-loaded liposomes (TAT-FB-Lip) were designed to enable transcorneal drug delivery and prolong ocular surface retention. The corneal penetration-promoting properties of TAT-functionalized liposomes (TAT-Lip) were confirmed in vitro using a corneal permeability assay and the HCE-T cell sphere model and in vivo by aqueous humor pharmacokinetics assessment. TAT-Lip induced an increase in intracellular calcium ion concentration and membrane potential depolarization. F-actin images of HCE-T cells treated with TAT-Lip show the tight junctions between cells partly opened. The cellular internalization pathway mainly depended on the electrostatic interaction between TAT-Lip and the cell membrane, and there is a certain degree of energy dependence. The pharmacokinetics of flurbiprofen in tears demonstrated TAT-Lip could reduce the drug loss rate. Moreover, the anti-inflammatory effect of TAT-FB-Lip was enhanced by markedly suppressing PGE₂, IL-6, and TNF-α production in tears and aqueous humor in a rabbit conjunctivitis model. In conclusion, this work demonstrates that TAT-Lip is an effective ocular drug carrier system that facilitates transcorneal delivery.

Intracellular delivery of immunoglobulin G at nanomolar concentrations with domain Z-fused multimeric α-helical cell penetrating peptides

A new vehicle is designed for the intracellular delivery of antibodies at nanomolar concentrations by combination of domain Z, a small affibody with strong binding affinity to Fc regions of immunoglobulin G (IgG), and the multimers of LK sequences, α-helical cell penetrating peptides (CPP) with powerful cell penetrating activities. Domain Z and multimeric LK are fused together to form LK-domain Z proteins. The LK-domain Z can bind with IgG at a specific ratio at nanomolar concentrations by simple mixing. The IgG/LK-domain Z complexes can successfully penetrate live cells at nanomolar concentration and the delivery efficiency is strongly dependent upon the concentrations of IgG/LK-domain Z complex as well as the species and subclasses of IgGs. The IgG/LK-domain Z complexes penetrate cells via ATP-dependent endocytosis pathway and the majority of delivered IgG seems to escape endosome to cytosol. Remarkably, the delivered IgGs are able to control the targeted intracellular signaling pathway as shown in the down-regulation of pro-survival genes by the delivery of anti-NF-κB using an LK-domain Z vehicle with a cathepsin B-cleavable linker between the LK sequence and domain Z. The simple but very efficient intracellular delivery method of antibodies at nanomolar concentrations is expected to facilitate profound understanding of cell mechanisms and development of new future therapeutics on the basis of intracellular antibodies.