Enhanced intracellular peptide delivery by multivalent cell-penetrating peptide with bioreducible linkage

Configuration of two cysteine residues in a ring within a stapled Bim peptide affects the secondary structure and apoptotic activity

Many reports have shown that stabilization of secondary structure by stapling functional peptides enhances the intracellular bioactivity. However, no report has discussed the correlation between stabilization and biological activity based on the configuration of amino acid residues used as anchors for stapling. To clarify this, we investigated the helix content and apoptotic efficiency of an apoptosis-inducing peptide, Bim, and four stapled Bim peptides containing stapling-related Cys residues introduced with different configurations within the sequence. The results demonstrated that the configuration of Cys residues in stapled Bim peptides affected the secondary structure and intracellular activity of the peptides, and furthermore, there was a correlation between these latter two variables.

Enhanced Delivery of Biomolecules into Caco2 Cells Based on the Cell-Penetrating Ability of Keratin Peptides

Keratin, as a promising bioresource, possesses significant potential for diverse biological applications due to its favorable biocompatibility, low toxicity, biodegradability, and cell adhesion ability. However, there are few studies on the cell-penetrating ability of keratin peptides (KEPs) for biomolecule delivery. Therefore, this study explored the cell-penetrating ability of KEPs with different molecular weights (Mw) on Caco2 cells using fluorescein-labeled insulin (FITC-INS) as the target intracellular biomolecule. The potential cell-penetrating mechanism was elaborated by combining cellular investigation with the physicochemical characterization of KEPs. The result shows that the KEPs <3 kDa (KEP1) exhibited the highest cell-penetrating ability at 2 mg/mL, allowing efficient delivery of FITC-INS into Caco2 cells without covalent bonding. The cellular uptake mechanism was energy-dependent, mainly involving macropinocytosis. The further fractionation of KEP1 reveals that the most effective components consisted of 8-19 amino acids, including specific hydrophobic peptides (e.g., RVVIEPSPVVV and IIIQPSPVVV), PPII amphipathic peptides (e.g., PPPVVVTFP and FIQPPPVVV), and Cys-rich peptides (e.g., LCAPTPCGPTPL and CLPCRPCGPTPL). Additionally, analysis of the secondary and tertiary structure and amino acid composition illustrated that KEP1 exhibited rich hydrophobic residues and disulfide bonds, which probably contributed to its cell-penetrating ability, as opposed to its small particle size and electrostatic interactions. This study reveals the cell-penetrating ability of KEPs, thus highlighting their potential as biomaterials for noncovalently delivering biomolecules.

A Novel Anti-CD22 scFv.Bim Fusion Protein Effectively Induces Apoptosis in Malignant B cells and Promotes Cytotoxicity

CD22 is a B-cell surface antigen which is highly expressed in cancerous B-cell lineages. Anti-CD22 antibodies are currently under focus as promising biologics against hematologic B-cell malignancies. Herein, we introduce a novel active recombinant anti-CD22 scFv.Bim fusion protein for targeting this cancerous antigen. An expression cassette encoding anti-CD22 scFv.Bim fusion protein was expressed in Pichia pastoris. The binding ability, cytotoxicity, and apoptotic activity of the purified recombinant protein against CD22⁺ Raji cell line were assessed by flow cytometry, microscopy, and MTT assay. Using bioinformatics, the 3D structure of the fusion protein and its interaction with CD22 were assessed. The in vitro binding analysis by immunofluorescence microscopy and flow cytometry demonstrated the specific binding of scFv.Bim to CD22⁺ Raji cells but not to CD22^- Jurkat cells. MTT data and Annexin V/PI flow cytometry analysis confirmed the apoptotic activity of anti-CD22 scFv.Bim against Raji cells but not Jurkat cells. In silico analysis also revealed the satisfactory stereochemical quality of the 3D model and molecular interactions toward CD22. This novel recombinant anti-CD22 scFv.Bim fusion protein could successfully deliver the pro-apoptotic peptide, BIM, to the target cells and thus nominates it as a promising molecule in treating B-cell malignancies.

Redesigning of Cell-Penetrating Peptides to Improve Their Efficacy as a Drug Delivery System

Cell-penetrating peptides (CPP) are promising tools for the transport of a broad range of compounds into cells. Since the discovery of the first members of this peptide family, many other peptides have been identified; nowadays, dozens of these peptides are known. These peptides sometimes have very different chemical–physical properties, but they have similar drawbacks; e.g., non-specific internalization, fast elimination from the body, intracellular/vesicular entrapment. Although our knowledge regarding the mechanism and structure–activity relationship of internalization is growing, the prediction and design of the cell-penetrating properties are challenging. In this review, we focus on the different modifications of well-known CPPs to avoid their drawbacks, as well as how these modifications may increase their internalization and/or change the mechanism of penetration.

Peptide-Conjugated Nano Delivery Systems for Therapy and Diagnosis of Cancer

Peptides are strings of approximately 2-50 amino acids, which have gained huge attention for theranostic applications in cancer research due to their various advantages including better biosafety, customizability, convenient process of synthesis, targeting ability via recognizing biological receptors on cancer cells, and better ability to penetrate cell membranes. The conjugation of peptides to the various nano delivery systems (NDS) has been found to provide an added benefit toward targeted delivery for cancer therapy. Moreover, the simultaneous delivery of peptide-conjugated NDS and nano probes has shown potential for the diagnosis of the malignant progression of cancer. In this review, various barriers hindering the targeting capacity of NDS are addressed, and various approaches for conjugating peptides and NDS have been discussed. Moreover, major peptide-based functionalized NDS targeting cancer-specific receptors have been considered, including the conjugation of peptides with extracellular vesicles, which are biological nanovesicles with promising ability for therapy and the diagnosis of cancer.

Minimization of apoptosis-inducing CPP-Bim peptide

Pro-apoptotic peptides may be promising agents for cancer therapy owing to their ability to induce apoptosis in cancer cells. TatBim, a fusion peptide of Tat cell-penetrating peptide (CPP) and the BH3 domain derived from Bim apoptosis-inducing protein, is a pro-apoptotic peptide. In this study, based on the TatBim sequence, we attempted to minimize the CPP-Bim peptide while retaining apoptosis-inducing activity. The CPP and Bim parts were systematically shortened, and the pro-apoptotic activities of the shortened peptides were examined. We obtained TatBim-N1C2 and R8Bim-N1C2 as minimized peptides with efficient apoptotic activity. These peptides may have potential applications in future biomedical studies, such as cancer therapeutics.

Peptide Spiders: Peptide-Polymer Conjugates to Traffic Nucleic Acids

Therapeutic nucleic acids hold great promise for the treatment of genetic diseases, yet the delivery of this highly charged macromolecular drug remains a challenge in the field. Peptides are promising agents to mediate nucleic acid delivery because they can encode a biological function to overcome the trafficking barriers. Electrostatic nanocomplexes of nucleic acid and peptides can achieve effective delivery, but the balance between their stability and biological function must be finely tuned. In this work, we explore two peptide building blocks that have been studied in the literature: targeting ligands and intracellular trafficking peptides. We grafted these peptides on a polyethylene glycol (PEG) backbone with eight sites for substitution to create so-called "peptide spiders". These conjugates achieve stability via the well-known hydrophilic shielding effect of PEG. In addition, the coordination of peptide building blocks into multimers may create new biological properties, such as the well-known phenomena of increased binding avidity with multivalent ligands. In this work, we linked two trafficking peptides to the PEG backbone using either nonreducible or reducible chemistries and investigated the ability of these materials to carry silencing RNAs into mammalian cells. We then investigated these nanomaterials for their pharmacokinetic properties and silencing of undruggable targets in a mouse model of cancer. While reducible linkages were more potent at silencing in vitro, this effect was reversed when applied in the context of living animals. This work offers an insight into peptide-based delivery materials and investigates peptide-polymer linkages.

Fine-tuning bispecific therapeutics

Bispecific therapeutics target two distinct antigens simultaneously and provide novel functionalities that are not attainable with single monospecific molecules or combinations of them. The unique potential of bispecific therapeutics is driving extensive efforts to discover synergistic dual targets, design molecular formats to integrate bispecific elements, and accelerate successful clinical translation. In particular, the past decade has witnessed a boom in the design and development of bispecific antibody formats with more than 100 collections to date. Despite the remarkable progress that has been made to expand the number of formats, qualitative fine-tuning of bispecific formats is needed to achieve optimal dual-target engagement based on understanding of the spatiotemporal interdependence of the two physically linked binding specificities and the complex target biology associated with bispecific approaches. This review provides insights into the design parameters - including affinity, valency, and geometry - that need to be considered at an early stage of development in order to take the best advantage of bispecific therapeutics.

Poly(ethylene glycol) shell-sheddable TAT-modified core cross-linked nano-micelles: TAT-enhanced cellular uptake and lysosomal pH-triggered doxorubicin release

This study aimed to develop sheddable polyethylene glycol (PEG) shells with TAT-modified core cross-linked nanomicelles as drug-delivery carriers of doxorubicin (DOX) to establish a programmed response against the tumor microenvironment, enhanced endocytosis, and lysosomal pH-triggered DOX release. First, poly(L-succinimide) (PSI) underwent a ring-opening reaction with ethylenediamine to generate poly(N-(2-aminoethyl)-l-aspartamide) (P(ae-Asp)). Next, the thiolytic cleavable PEG, 3,4-dihydroxyphenylacetic acid, and TAT were grafted onto P(ae-Asp) to synthesize the amphiphilic graft copolymer of mPEG-SS-g-P(ae-Asp)-MCA-DA-TAT. In aqueous solution, the amphiphilic polymer self-assembled into nanomicelles, encapsulating DOX into the hydrophobic core of micelles. TAT was shielded by the PEG corona during circulation to avoid non-specific transmembrane interaction with normal cells, while the tumor redox environment-responsive shedding of PEG could expose TAT to promote internalization of tumor cells. In order to improve the stability of nanomicelles and achieve pH-triggered drug release, a core cross-linking strategy based on the coordination of catechol and Fe³⁺ was adopted. In vitro studies demonstrated that core cross-linked nanomicelles maintained the nanostructure in 100 times dilution in pH 7.4 phosphate-buffered saline (PBS). Moreover, DOX release from DOX-loaded core cross-linked nanomicelles (DOX-TAT-CCLMs) was favored at simulated lysosomal conditions over simulated plasma conditions, indicating that these nanomicelles demonstrate characteristics of pH-triggered DOX release. The TAT modification considerably enhanced the mean fluorescence intensity of the nanomicelles endocytosed by MCF-7/ADR cells by 8 times, compared with DOX·HCl after 8 h of incubation. Notably, the IC₅₀ value of nanomicelles (11.61 ± 0.95 μg/mL) was nearly 4 times lower than that of DOX·HCl against MCF-7/ADR cells, implying that the nanomicelles could overcome drug resistance observed in MCF-7/ADR cells. Furthermore, the DOX-TAT-CCLMs reported superior tumor growth suppression in a 4T1 tumor-bearing mouse model. Thus, the redox- and pH- stimuli stepwise-responsive novel nanomicelles fabricated from the mPEG-SS-g-P(ae-Asp)-MCA-DA-TAT graft copolymer exhibited multifunctionality and displayed great potential for drug delivery.

Higher Order Architecture of Designer Peptides Forms Bioinspired 10 nm siRNA Delivery System

The higher-order architecture observed in biological systems, like viruses, is very effective in nucleic acid transport. The replications of this system has been attempted with both synthetic and naturally occurring polymers with mixed results. Here we describe a peptide/siRNA quaternary complex that functions as an siRNA delivery system. The rational design of a peptide assembly is inspired by the viral capsids, but not derived from them. We selected the collagen peptide (COL) to provide the structural stability and the folding framework, and hybridize it with the cell penetrating peptide (CPP) that allows for effective penetration of biological barriers. The peptide/siRNA quaternary complex forms stoichiometric, 10 nm nanoparticles, that show fast cellular uptake (<30 min), effective siRNA release, and gene silencing. The complex provides capsid-like protection for siRNA against nucleases without being immunostimulatory, or cytotoxic. Our data suggests that delivery vehicles based on synthetic quaternary structures that exhibit higher-order architecture may be effective in improving delivery and release of nucleic acid cargo.

Cell-penetrating peptide: a means of breaking through the physiological barriers of different tissues and organs

The selective infiltration of cell membranes and tissue barriers often blocks the entry of most active molecules. This natural defense mechanism prevents the invasion of exogenous substances and limits the therapeutic value of most available molecules. Therefore, it is particularly important to find appropriate ways of membrane translocation and therapeutic agent delivery to its target site. Cell penetrating peptides (CPPs) are a group of short peptides harnessed in this condition, possessing a significant capacity for membrane transduction and could be exploited to transfer various biologically active cargoes into the cells. Since their discovery, CPPs have been employed for delivery of a wide variety of therapeutic molecules to treat various disorders including cranial nerve involvement, ocular inflammation, myocardial ischemia, dermatosis and cancer. The promising results of CPPs-derived therapeutics in various tumor models demonstrated a potential and worthwhile scope of CPPs in chemotherapy. This review describes the detailed description of CPPs and CPPs-assisted molecular delivery against various tissues and organs disorders. An emphasis is focused on summarizing the novel insights and achievements of CPPs in surmounting the natural membrane barriers during the last 5 years.

Multifunctional Vector for Delivery of Genome Editing Plasmid Targeting β-Catenin to Remodulate Cancer Cell Properties

Accurate and efficient delivery of genome editing plasmids to targeted cells is of critical importance in genome editing. Herein, we prepared a multifunctional delivery vector with a combination of ligand-mediated selectivity and peptide-mediated transmembrane function to effectively deliver plasmids to targeted cancerous cells. In the delivery system, the clustered regularly interspaced short palindromic repeat-associated Cas9 nuclease (CRISPR-Cas9) plasmid is combined with protamine with membrane and nuclear translocating activities and co-precipitated with CaCO₃, which is further decorated by AS1411-functionalized carboxymethyl chitosan and cell penetrating peptide (TAT)-functionalized carboxymethyl chitosan. The AS1411-mediated tumor cell/nuclear targeting and TAT-induced enhanced endocytosis result in obviously increased cellular uptake and nuclear transport. As a result, the CRISPR-Cas9 plasmid can be efficiently delivered to cancer cell nuclei to mediate genome editing, resulting in an efficacious knockout of CTNNB1 gene encoding β-catenin. More importantly, downregulation of β-catenin could effectively prevent its enrichment in nuclei and then significantly downregulate the expression of proteins, such as vimentin, Snail, MMP-2, MMP-9, CD44, Nanog, and Oct4 to prevent tumor progression and metastasis. The edited cancerous cells exhibit favorable remodulated properties including inhibited growth, suppressed migration and invasion, and reduced cancer stemness.