Cell-penetrating mechanism of intracellular targeting albumin: Contribution of macropinocytosis induction and endosomal escape

Beyond the polysaccharide and glycoconjugate vaccines for Streptococcus pneumoniae: Does protein/peptide nanovaccines hold promises?

Streptococcus pneumoniae having almost 98 serotypes and being common cause of acute otitis media, pneumonia, bacteremia, meningitis etc., which results in high mortality and morbidity globally. Although vaccines like PCV-13 and PPV-23 are available, some problems like serotype replacement and poor immunogenicity in children, old age and immunocompromised people has been observed. To overcome these drawbacks protein/peptide-based vaccine can be a good strategy as these provides wide serotype coverage. However, immunogenicity of protein subunit vaccines is lower, that issue can be solved by using adjuvants. Recently nanoparticles as an adjuvant for vaccine delivery being used, which has provided not only good immunogenicity but also improved delivery and efficiency of protein-based vaccines. In this review we have discussed the latest advancement of nanoparticles-based protein/peptide vaccine delivery for Streptococcus pneumoniae.

Albumin pre-opsonized membrane-active iPep nanomedicine potentiates chemo to immunotherapy of cancer

Chemotherapy-conjugated immunotherapy in clinical oncology conceptually resembles the combined effects of cytoreduction and immunostimulation in membrane targeted cell killings mediated by pore-forming proteins or host defense peptides. Of the similar concept, targeting cancer cell membrane using membrane active peptides is a hopeful therapeutic modality but had long been hindered from in vivo application. Here we report an enabling strategy of pre-opsonizing a membrane penetrating Ir-complexed octa-arginine peptide (iPep) with serum albumin via intrinsic amphipathicity-driven bimodal interactions into nanoparticles (NP). We found that NP triggered stress-mediated 4T1 cell oncosis which induced potent immunological activation, surpassing several well-known immunogenic medicines. Vested with albumin-enhanced in vivo tumor targeting specificity and pharmacokinetic properties, NP showed combined chemo to immunotherapies of s. c. tumors in mice, with decreased percentages of MDSC, Treg, M2-like macrophage and improved infiltration of CTLs in tumor site, caused complete regression of 4T1 and CT26 tumors, outperforming clinical medicines. In a challenging orthotopic breast cancer model, boost i. v. injections of NP acted as in situ tumor vaccine that drastically enhanced 4T1-specific cellular and humoral immunities to reverse disease progression. Thus, with combined effects of direct cytoreduction, immune activation and tumor vaccine, iPep-NP presents the promise and potential of a new modality of cancer medicine.

A cascade-responsive nanoplatform with tumor cell-specific drug burst release for chemotherapy

Most of the nanomedicines can reduce the side effects of anti-tumor chemical drugs but do not have good enough therapeutic efficacy, largely due to the sustained drug release profile. It might be a promising alternative strategy to develop a cascade-responsive nanoplatform against tumor with the burst release of chemotherapeutics based on the highly efficient tumor cell targeting delivery. In this work, we constructed innovative nanoparticles (PMP/WPH-NPs) consisting of two functional polymers. PMP contained the MMP-2 enzyme sensitive linker and disulfide bond, which could respond to the tumor-overexpressing enzyme MMP-2 and high-level glutathione. While WPH promoted tumor penetration and acid-responsive drug release by modifying cellular penetrating peptides and polymerizing L-histidine. PMP/WPH-NPs exhibited outstanding features including longer blood circulation time, promoted tumor-specific accumulation, enhanced tumor penetration and efficient escape from lysosomes. Subsequently, the model drug paclitaxel (PTX), widely used in the tumor chemotherapy, was encapsulated into PMP/WPH-NPs via an emulsion solvent evaporation method. Within a short period of time, PTX-PMP/WPH-NP in simulated tumor cellular microenvironment could release 8 times more PTX than that in the physiological environment, demonstrating a good potential in tumor cell-specific burst drug release. In addition, PTX-PMP/WPH-NPs exhibited stronger anti-tumor activity than PTX in vitro and in vivo, which also had good biocompatibility according to the hemolysis assay and H&E staining. In summary, our work has succeeded in designing an original polymeric nanoplatform for programmed burst drug release based on the tailored tumor targeting delivery system. This new approach would facilitate the clinical translation of more anti-tumor nanomedicines. STATEMENT OF SIGNIFICANCE: Biomaterials responsive to the tumor-specific stimulus has conventionally used in the targeted-delivery of anti-tumor drugs. However, the levels of common stimulus are not uniformly distributed and not high enough to effectively trigger drug release. In an effort to achieve a better specific drug release and promote the chemotherapeutic efficacy, we constructed a cascade responsive nanoplatform with tumor cell-specific drug burst release profile. The tailored biomaterial could overcome the bio-barriers in vivo and succeeded in the programmed burst drug release based on the tumor cell-specific delivery of chemotherapeutics.

Yeast-derived vacuoles as a novel carrier with enhanced hCMEC/D3 cell monolayer penetration

The blood-brain barrier (BBB) is a brain protection structure that restricts drug delivery from the blood to the central nervous system. Thus, we developed a novel drug carrier using yeast vacuoles to overcome this problem. The purpose of this study was to assess the drug transportability of yeast vacuoles using a human cerebral microvascular endothelial cell line (hCMEC/D3) cell monolayer. Here, we used daunorubicin (DNR) as a microtubule-targeting agent with the ability to disaggregate pre-formed fibrils and prevent Tau fibrillization. An in vitro model was developed by culturing hCMEC/D3 cells on Transwell inserts in EBM-2 endothelial basal medium until the cells formed a monolayer. Next, nano-sized yeast vacuoles were loaded with DNR, and the signals inside and outside the hMEC/D3 cell monolayer were detected using the GloMax^® Explorer fluorometer. DNR penetrated the cell monolayer and was regulated by endocytosis via receptor-mediated macropinocytosis on the surface of the cell. Confocal imaging showed a significant increase in intracellular DNR fluorescence when the cells were treated with the vacuole-encapsulated drug. These results indicate that the drug penetrated the hCMEC/D3 cell monolayer via encapsulation into the vacuoles. Overall, yeast-derived vacuoles are promising candidates as drug carriers to the brain.

Atypical Macropinocytosis Contributes to Malignant Progression: A Review of Recent Evidence in Endometrioid Endometrial Cancer Cells

Simple Summary

A novel type of macropinocytosis has been identified as a trigger for the malignant progression of endometrial cancer. Transiently reducing epithelial barrier homeostasis leads to macropinocytosis by splitting between adjacent cells in endometrioid endometrial cancer. Macropinocytosis causes morphological changes in well-differentiated to poorly differentiated cancer cells. Inhibition of macropinocytosis promotes a persistent dormant state in the intrinsic KRAS-mutated cancer cell line Sawano. This review focuses on the mechanisms of atypical macropinocytosis and its effects on cellular function, and it describes the physiological processes involved in inducing resting conditions in endometrioid endometrial cancer cells.

Abstract

Macropinocytosis is an essential mechanism for the non-specific uptake of extracellular fluids and solutes. In recent years, additional functions have been identified in macropinocytosis, such as the intracellular introduction pathway of drugs, bacterial and viral infection pathways, and nutritional supplement pathway of cancer cells. However, little is known about the changes in cell function after macropinocytosis. Recently, it has been reported that macropinocytosis is essential for endometrial cancer cells to initiate malignant progression in a dormant state. Macropinocytosis is formed by a temporary split of adjacent bicellular junctions of epithelial sheets, rather than from the apical surface or basal membrane, as a result of the transient reduction of tight junction homeostasis. This novel type of macropinocytosis has been suggested to be associated with the malignant pathology of endometriosis and endometrioid endometrial carcinoma. This review outlines the induction of malignant progression of endometrial cancer cells by macropinocytosis based on a new mechanism and the potential preventive mechanism of its malignant progression.

Cell-penetrating albumin enhances the sublingual delivery of antigens through macropinocytosis

Innovations in oral immunotherapy have greatly advanced the therapeutic control of allergies. However, these therapeutic effects suffer from the fact that the amount of antigen delivered to antigen-presenting cells is limited given the formulations that are currently available. We recently designed a cell-penetrating albumin and found that this modified albumin enters cells via the induction of macropinocytosis. Herein, we report on a novel system for delivering antigens based on cell-penetrating albumin-inducible macropinocytosis that allows larger amounts of antigens to be delivered to antigen-presenting cells. A treatment with cell-penetrating albumin significantly increased the permeability of ovalbumin (45 kDa) or dextran (2000 kDa) on monolayers derived from human oral squamous carcinoma cells. Flow cytometric analyses showed that the cell-penetrating albumin treatment resulted in a significant elevation in the amount of dextran that was delivered to two types of antigen-presenting cells. Finally, mice that had been sensitized by Japanese cedar pollen extract (JCPE) and cell-penetrating albumin showed a decline in the frequency of nose-rubbing against a subsequent intranasal administration of JCPE. These findings suggest that the sublingual administration of cell-penetrating albumin efficiently delivers antigens to antigen-presenting cells via the induction of macropinocytosis, resulting in an enhancement in the therapeutic effect of sublingual immunotherapy.

Neuronal Glypican4 promotes mossy fiber sprouting through the mTOR pathway after pilocarpine-induced status epilepticus in mice

In temporal lobe epilepsy (TLE), abnormal axon guidance and synapse formation lead to sprouting of mossy fibers in the hippocampus, which is one of the most consistent pathological findings in patients and animal models with TLE. Glypican 4 (Gpc4) belongs to the heparan sulfate proteoglycan family, which play an important role in axon guidance and excitatory synapse formation. However, the role of Gpc4 in the development of mossy fibers sprouting (MFS) and its underlying mechanism remain unknown. Using a pilocarpine-induced mice model of epilepsy, we showed that Gpc4 expression was significantly increased in the stratum granulosum of the dentate gyrus at 1 week after status epilepticus (SE). Using Gpc4 overexpression or Gpc4 shRNA lentivirus to regulate the Gpc4 level in the dentate gyrus, increased or decreased levels of netrin-1, SynI, PSD-95, and Timm score were observed in the dentate gyrus, indicating a crucial role of Gpc4 in modulating the development of functional MFS. The observed effects of Gpc4 on MFS were significantly antagonized when mice were treated with L-leucine or rapamycin, an agonist or antagonist of the mammalian target of rapamycin (mTOR) signal, respectively, demonstrating that mTOR pathway is an essential requirement for Gpc4-regulated MFS. Additionally, the attenuated spontaneous recurrent seizures (SRSs) were observed during chronic stage of the disease by suppressing the Gpc4 expression after SE. Altogether, our findings demonstrate a novel control of neuronal Gpc4 on the development of MFS through the mTOR pathway after pilocarpine-induced SE. Our results also strongly suggest that Gpc4 may serve as a promising target for antiepileptic studies.

Different Approaches to Cyclize a Cell-Penetrating Peptide and to Tether Bioactive Payloads

Cell-penetrating peptides (CPPs) are versatile tools to deliver various molecules into different cell types. The majority of CPPs are usually represented by linear structures, but numerous recent studies demonstrated cyclization to be an effective strategy leading to favorable biological activities. Here we describe two different methods for the side chain and backbone cyclization of CPPs . Furthermore, we highlight straightforward procedures for the covalent coupling of fluorophores or cytotoxic payloads.

In vivo metal-catalyzed SeCT therapy by a proapoptotic peptide

Selective cell tagging (SeCT) therapy is a strategy for labeling a targeted cell with certain chemical moieties via a catalytic chemical transformation in order to elicit a therapeutic effect. Herein, we report a cancer therapy based on targeted cell surface tagging with proapoptotic peptides (Ac-GGKLFG-X; X = reactive group) that induce apoptosis when attached to the cell surface. Using either Au-catalyzed amidation or Ru-catalyzed alkylation, these proapoptotic peptides showed excellent therapeutic effects both in vitro and in vivo. In particular, co-treatment with proapoptotic peptide and the carrier-Ru complex significantly and synergistically inhibited tumor growth and prolonged survival rate of tumor-bearing mice after only a single injection. This is the first report of Ru catalyst application in vivo, and this approach could be used in SeCT for cancer therapy.

Correlation between Protonation of Tailor-Made Polypiperazines and Endosomal Escape for Cytosolic Protein Delivery

Responsive polymers, which become protonated at decreasing pH, are considered a milestone in the development of synthetic cell entry vectors. Exact correlations between their properties and their ability to escape the endosome, however, often remain elusive due to hydrophobic interactions or limitations in the design of water-soluble materials with suitable basicity. Here, we present a series of well-defined, hydrophilic polypiperazines, where systematic variation of the amino moiety facilitates an unprecedented fine-tuning of the basicity or pK_a value within the physiologically relevant range (pH 6-7.4). Coincubation of HEK 293T cells with various probes, including small fluorophores or functioning proteins, revealed a rapid increase of endosomal release for polymers with pK_a values above 6.5 or 7 in serum-free or serum-containing media, respectively. Similarly, cytotoxic effects became severe at increased pK_a values (>7). Although the window for effective transport appears narrow, the discovered correlations offer a principal guideline for the design of effective polymers for endosomal escape.

Macropinocytosis as a cell entry route for peptide-functionalized and bystander nanoparticles

Endocytic pathways provide the primary route for therapeutic and diagnostic nanoparticles (NPs) to enter cells and subcellular compartments. A better understanding of these cell entry processes will not only aid in nanomaterial applications but also broaden our knowledge of cell biology. Among the endocytic routes, macropinocytosis has unique characteristics for engulfing NPs and other large cargo, yet its molecular machinery and involvement in NP uptake are far less characterized relative to other pathways. In this review, we summarize the current knowledge on the macropinocytic machinery, and its involvement in NP internalization. Particularly, we differentiate ligand (specifically peptide)-functionalized and unfunctionalized NPs (bystander NPs). While most of previous research focused on ligand-functionalized NPs, we showcase here a synergistic effect between these two NP types during their cell entry through receptor-mediated macropinocytosis. The regulation of NP uptake efficiency by extracellular amino acids is also highlighted in the context of interconnections between macropinocytosis and metabolic signaling. These discussions may fuel future research interests in improving NP internalization through this pathway, and open a new avenue to study the interplay among endocytosis, metabolism and nanomedicine.

Hydrocarbon staple constructing highly efficient α-helix cell-penetrating peptides for intracellular cargo delivery

The effects of all-hydrocarbon cross-linking on the cell-penetrating properties of Tat were systematically investigated. These stapled cell-penetrating peptides were designed to exhibit a cationic secondary amphipathic profile. We found that the hydrophobicity and helical conformation of these hydrocarbon staple peptides correlate well with their cellular uptake efficiency. Our results also revealed that higher affinity to heparan sulfate of the rigid stapled Tat peptides correlated well with the higher cellular uptake compared with non-stapled Tat peptides with flexible charge display. Notably, the stapled Tat peptides showed increased endosomal escape, high proteolytic stability, and low cytotoxicity. Therefore, they present a potent system for the intracellular transport of bioactive cargos.

Membrane Trafficking and Subcellular Drug Targeting Pathways

The movement of micro and macro molecules into and within a cell significantly governs several of their pharmacokinetic and pharmacodynamic parameters, thus regulating the cellular response to exogenous and endogenous stimuli. Trafficking of various pharmacological agents and other bioactive molecules throughout and within the cell is necessary for the fidelity of the cells but has been poorly investigated. Novel strategies against cancer and microbial infections need a deeper understanding of membrane as well as subcellular trafficking pathways and essentially regulate several aspects of the initiation and spread of anti-microbial and anti-cancer drug resistance. Furthermore, in order to avail the maximum possible bioavailability and therapeutic efficacy and to restrict the unwanted toxicity of pharmacological bioactives, these sometimes need to be functionalized with targeting ligands to regulate the subcellular trafficking and to enhance the localization. In the recent past the scenario drug targeting has primarily focused on targeting tissue components and cell vicinities, however, it is the membranous and subcellular trafficking system that directs the molecules to plausible locations. The effectiveness of the delivery platforms largely depends on their physicochemical nature, intracellular barriers, and biodistribution of the drugs, pharmacokinetics and pharmacodynamic paradigms. Most subcellular organelles possess some peculiar characteristics by which membranous and subcellular targeting can be manipulated, such as negative transmembrane potential in mitochondria, intraluminal delta pH in a lysosome, and many others. Many specialized methods, which positively promote the subcellular targeting and restrict the off-targeting of the bioactive molecules, exist. Recent advancements in designing the carrier molecules enable the handling of membrane trafficking to facilitate the delivery of active compounds to subcellular localizations. This review aims to cover membrane trafficking pathways which promote the delivery of the active molecule in to the subcellular locations, the associated pathways of the subcellular drug delivery system, and the role of the carrier system in drug delivery techniques.

Novel cyclic peptides facilitating transcellular blood-brain barrier transport of macromolecules in vitro and in vivo

Brain delivery of nanoparticles and macromolecular drugs depends on blood-brain barrier (BBB)-permeable carriers. In this study, we searched for cyclic heptapeptides facilitating BBB permeation of M13 phages by phage library screening using a transcellular permeability assay with hCMEC/D3 cell monolayers, a human BBB model. The M13 phage, which is larger than macromolecular drugs and nanoparticles, served as a model macromolecule. The screen identified cyclic heptapeptide SLSHSPQ (SLS) as a human BBB-permeable peptide. The SLS-displaying phage (SLS-phage) exhibited improved permeation across the cell monolayer of monkey and rat BBB co-culture models. The SLS-phage internalized into hCMEC/D3 cells via macropinocytosis and externalized via the exosome excretion pathway. SLS-phage distribution into brain parenchyma was observed in mice after intravenous administration. Moreover, liposome permeated across the BBB as cyclic SLS peptide conjugates. In conclusion, the cyclic SLS heptapeptide is a novel carrier candidate for brain delivery of macromolecular drugs and nanoparticles.

Cell Penetrating Peptide: Sequence-Based Computational Prediction for Intercellular Delivery of Arginine Deiminase

Background:

Cell-Penetrating Peptides (CPPs), a family of short peptides, are broadly used as the carrier in the delivery of drugs and different therapeutic agents. Thanks to the existence of valuable databases, computational screening of the experimentally validated CPPs can help the researchers to select more effective CPPs for the intercellular delivery of therapeutic proteins. Arginine deiminase of Mycoplasma hominis, an arginine-degrading enzyme, is currently in the clinical trial for treating several arginine auxotrophic cancers. However, some tumor cells have developed resistance to ADI treatment. The ADI resistance arises from the over-expression of argininosuccinate synthetase 1 enzyme, which is involved in arginine synthesis. Intracellular delivery of ADI into tumor cells is suggested as an efficient approach to overcome the aforesaid drawback.

Objective:

In this study, in-silico tools were used for evaluating the experimentally validated CPPs to select the best CPP candidates for the intracellular delivery of ADI.

Results:

In this regard, 150 CPPs of protein cargo available at CPPsite were retrieved and evaluated by the CellPPD server. The best CPP candidates for the intracellular delivery of ADI were selected based on stability and antigenicity of the ADI-CPP fusion form. The conjugated forms of ADI with each of the three CPPs including EGFP-hcT (9-32), EGFP-ppTG20, and F(SG)4TP10 were stable and nonantigenic; thus, these sequences were introduced as the best CPP candidates for the intracellular delivery of ADI. In addition, the proposed CPPs had appropriate positive charge and lengths for an efficient cellular uptake.

Conclusion:

These three introduced CPPs not only are appropriate for the intracellular delivery of ADI, but also can overcome the limitation of its therapeutic application, including short half-life and antigenicity.

Editorial focus: understanding off-target effects as the key to successful RNAi therapy

With the first RNA interference (RNAi) drug (ONPATTRO (patisiran)) on the market, we witness the RNAi therapy field reaching a critical turning point, when further improvements in drug candidate design and delivery pipelines should enable fast delivery of novel life changing treatments to patients. Nevertheless, ignoring parallel development of RNAi dedicated in vitro pharmacological profiling aiming to identify undesirable off-target activity may slow down or halt progress in the RNAi field. Since academic research is currently fueling the RNAi development pipeline with new therapeutic options, the objective of this article is to briefly summarize the basics of RNAi therapy, as well as to discuss how to translate basic research into better understanding of related drug candidate safety profiles early in the process.