Tailoring nanocarriers for intracellular protein delivery

The design and biomedical applications of self-assembled two-dimensional organic biomaterials

Self-assembling 2D organic biomaterials exhibit versatile abilities for structural and functional tailoring, as well as high potential for biomedical applications.

Correlation between polymer architecture and polyion complex micelle stability with proteins in spheroid cancer models as seen by light-sheet microscopy

Polyion complex (PIC) micelles are frequently used as a means to deliver biologics such as proteins.

Programed Assembly of Nucleoprotein Nanoparticles Using DNA and Zinc Fingers for Targeted Protein Delivery

With a growing number of intracellular drug targets and the high efficacy of protein therapeutics, the targeted delivery of active proteins with negligible toxicity is a challenging issue in the field of precision medicine. Herein, a programed assembly of nucleoprotein nanoparticles (NNPs) using DNA and zinc fingers (ZnFs) for targeted protein delivery is presented. Two types of ZnFs with different sequence specificities are genetically fused to a targeting moiety and a protein cargo, respectively. Double-stranded DNA with multiple ZnF-binding sequences is grafted onto inorganic nanoparticles, followed by conjugation with the ZnF-fused proteins, generating the assembly of NNPs with a uniform size distribution and high stability. The approach enables controlled loading of a protein cargo on the NNPs, offering a high cytosolic delivery efficiency and target specificity. The utility and potential of the assembly as a versatile protein delivery vehicle is demonstrated based on their remarkable antitumor activity and target specificity with negligible toxicity in a xenograft mice model.

Cyclic Peptides: Promising Scaffolds for Biopharmaceuticals

To date, small molecules and macromolecules, including antibodies, have been the most pursued substances in drug screening and development efforts. Despite numerous favorable features as a drug, these molecules still have limitations and are not complementary in many regards. Recently, peptide-based chemical structures that lie between these two categories in terms of both structural and functional properties have gained increasing attention as potential alternatives. In particular, peptides in a circular form provide a promising scaffold for the development of a novel drug class owing to their adjustable and expandable ability to bind a wide range of target molecules. In this review, we discuss recent progress in methodologies for peptide cyclization and screening and use of bioactive cyclic peptides in various applications.

Codelivery of a cytotoxin and photosensitiser via a liposomal nanocarrier: a novel strategy for light-triggered cytosolic release

Endosomal entrapment is a key issue for the intracellular delivery of many nano-sized biotherapeutics to their cytosolic or nuclear targets. Photochemical internalisation (PCI) is a novel light-based solution that can be used to trigger the endosomal escape of a range of bioactive agents into the cytosol leading to improved efficacy in pre-clinical and clinical studies. PCI typically depends upon the endolysosomal colocalisation of the bioactive agent with a suitable photosensitiser that is administered separately. In this study we demonstrate that both these components may be combined for codelivery via a novel multifunctional liposomal nanocarrier, with a corresponding increase in the biological efficacy of the encapsulated agent. As proof of concept, we show here that the cytotoxicity of the 30 kDa protein toxin, saporin, in MC28 fibrosarcoma cells is significantly enhanced when delivered via a cell penetrating peptide (CPP)-modified liposome, with the CPP additionally functionalised with a photosensitiser that is targeted to endolysosomal membranes. This innovation opens the way for the efficient delivery of a range of biotherapeutics by the PCI approach, incorporating a clinically proven liposome delivery platform and using bioorthogonal ligation chemistries to append photosensitisers and peptides of choice.

Biomimetic Shells Endow Sub-50 nm Nanoparticles with Ultrahigh Paclitaxel Payloads for Specific and Robust Chemotherapy

Poor loading capacity and nonspecific tumor accumulation of current drug delivery system remain the critical challenges that prevent nanomedicine from maximizing therapeutic efficacy in cancer treatment. Herein, poly(ester amide) polymers composed of cationic and hydrophobic segments were formulated with a paclitaxel/human serum albumin (PTX/HSA) complex, as well as free PTX, to construct a core-shell nanoparticle (NP) platform with the interior simultaneously reserving PTX and PTX/HSA complex, while the exterior absorbing the PTX/HSA complex. Following systematic screening, the optimized NPs, namely, APP1i@e NPs, exhibited small particle size (43.95 nm), maximal PTX loading (42.23%), excellent dynamic stability (at least 1 week), and acid-triggered release. In vitro results showed that after being trafficked through caveolae-mediated endocytosis, APP1i@e NPs successfully escaped from endo-/lysosomes and then rapidly released cargos in the acidic cytosol, which continued to enhance cytotoxicity by mitochondrial control of apoptosis and suppression of microtubule dynamics. Longer circulation time and superior targeting efficiency post-intravenous injection confirmed that surface PEGylation imparted APP1i@e NPs with the ability to control their pharmacokinetics and biodistribution. The biomimetic shell design with HSA, which enlarged PTX stock and improved biosafety, made APP1i@e NPs more suitable for in vivo applications. Furthermore, in vivo safety and efficacy demonstrated that APP1i@e NPs effectively inhibited the growth of ovarian xenograft tumors, whereas significantly avoiding toxic issues associated with PTX. APP1i@e NPs with surface PEG coating and biomimetic HSA design, therefore, may provide a remarkable improvement in the therapeutic index of taxanes used in the clinic.

Granzyme B-loaded, cell-selective penetrating and reduction-responsive polymersomes effectively inhibit progression of orthotopic human lung tumor in vivo

The clinical use of protein therapeutics with intracellular targets is hampered by its in vivo fragility and low cell permeability. Here, we report that cell-selective penetrating and reduction-responsive polymersomes (CPRPs) mediate high-efficiency targeted delivery of granzyme B (GrB) to orthotopic human lung tumor in vivo. Model protein studies using FITC-labeled cytochrome C (FITC-CC) revealed efficient and high protein loading up to 17.2 wt% for CPRPs. FITC-CC-loaded CPRPs exhibited a small size of 82-90 nm, reduction-responsive protein release, as well as greatly enhanced internalization and cytoplasmic protein release in A549 lung cancer cells compared with the non-targeted FITC-CC-loaded RPs control. GrB-loaded CPRPs showed a high potency toward A549 lung cancer cells with a half maximal inhibitory concentration (IC₅₀) of 20.7 nM. Under the same condition, free GrB was essentially non-toxic. Importantly, installing cell-selective penetrating peptide did not alter the circulation time but did enhance tumor accumulation of RPs. Orthotopic A549-Luc lung tumor-bearing nude mice administered with GrB-loaded CPRPs at a dosage of 2.88 nmol GrB equiv./kg showed complete tumor growth inhibition with little body weight loss throughout the treatment period, resulting in significantly improved survival rate over the non-targeted and non-treated controls. These cell-selective penetrating and reduction-responsive polymersomes provide a targeted protein therapy for cancers.

Structural insights into pH-responsive drug release of self-assembling human serum albumin-silk fibroin nanocapsules

Inflammation processes are associated with significant decreases in tissue or lysosomal pH from 7.4 to 4, a fact that argues for the application of pH-responsive drug delivery systems. However, for their design and optimization a full understanding of the release mechanism is crucial. In this study we investigated the pH-depending drug release mechanism and the influence of silk fibroin (SF) concentration and SF degradation degree of human serum albumin (HSA)-SF nanocapsules. Sonochemically produced nanocapsules were investigated regarding particle size, colloidal stability, protein encapsulation, thermal stability and drug loading properties. Particles of the monodisperse phase showed average hydrodynamic radii between 438 and 888 nm as measured by DLS and AFM and a zeta potential of -11.12 ± 3.27 mV. Together with DSC results this indicated the successful production of stable nanocapsules. ATR-FTIR analysis demonstrated that SF had a positive effect on particle formation and stability due to induced beta-sheet formation and enhanced crosslinking. The pH-responsive release was found to depend on the SF concentration. In in-vitro release studies, HSA-SF nanocapsules composed of 50% SF showed an increased pH-responsive release for all tested model substances (Rhodamine B, Crystal Violet and Evans Blue) and methotrexate at the lowered pH of 4.5 to pH 5.4, while HSA capsules without SF did not show any pH-responsive drug release. Mechanistic studies using confocal laser scanning microscopy (CLSM) and small angle X-ray scattering (SAXS) analyses showed that increases in particle porosity and decreases in particle densities are directly linked to pH-responsive release properties. Therefore, the pH-responsive release mechanism was identified as diffusion controlled in a novel and unique approach by linking scattering results with in-vitro studies. Finally, cytotoxicity studies using the human monocytic THP-1 cell line indicated non-toxic behavior of the drug loaded nanocapsules when applied in a concentration of 62.5 µg mL^-1. Based on the obtained release properties of HSA-SF nanocapsules formulations and the results of in-vitro MTT assays, formulations containing 50% SF showed the highest requirements arguing for future in vivo experiments and application in the treatment of inflammatory diseases.

Protein Nanotherapeutics as an Emerging Modality for Cancer Therapy

Protein drugs are a unique and versatile class of biotherapeutics that have not only high biological activity but also superb specificity. This rapidly evolving biotechnology has rendered it possible to produce various proteins in a large scale and reproducible way. Many proteins have demonstrated striking anticancer activities and have emerged as advanced alternatives to cytotoxic chemotherapeutic agents for cancer therapy. The clinical translation of anticancer proteins with intracellular targets is, nevertheless, severely hindered by their fast degradation in vivo, poor cell penetration, and inefficient intracellular transportation. The past few years have witnessed tremendous effort and progress in developing polymeric protein delivery nanosystems, ranging from nanoparticles, nanocapsules, nanogels, micelles, to polymersomes, for the treatment of different tumors such as lung tumors, breast tumors, ovarian cancers, and glioblastoma. These proof-of-concept studies point out that protein nanotherapeutics, with rationally designed nanovehicles, are able to overcome the extracellular barriers, cell membrane barriers, and intracellular barriers, and systemically deliver proteins into targeted cancer cells, resulting in effective cancer protein therapy. Protein nanotherapeutics appear to be a novel modality for safe and efficient cancer treatment.

Versatile Redox-Responsive Polyplexes for the Delivery of Plasmid DNA, Messenger RNA, and CRISPR-Cas9 Genome-Editing Machinery

Gene therapy holds great promise for the treatment of many diseases, but clinical translation of gene therapies has been slowed down by the lack of safe and efficient gene delivery systems. Here, we report two versatile redox-responsive polyplexes (i.e., cross-linked and non-crosslinked) capable of efficiently delivering a variety of negatively charged payloads including plasmid DNA (DNA), messenger RNA, Cas9/sgRNA ribonucleoprotein (RNP), and RNP-donor DNA complexes (S1mplex) without any detectable cytotoxicity. The key component of both types of polyplexes is a cationic poly( N, N'-bis(acryloyl)cystamine- co-triethylenetetramine) polymer [a type of poly( N, N'-bis(acryloyl)cystamine-poly(aminoalkyl)) (PBAP) polymer] containing disulfide bonds in the backbone and bearing imidazole groups. This composition enables efficient encapsulation, cellular uptake, controlled endo/lysosomal escape, and cytosolic unpacking of negatively charged payloads. To further enhance the stability of non-crosslinked PBAP polyplexes, adamantane (AD) and β-cyclodextrin (β-CD) were conjugated to the PBAP-based polymers. The cross-linked PBAP polyplexes formed by host-guest interaction between β-CD and AD were more stable than non-crosslinked PBAP polyplexes in the presence of polyanionic polymers such as serum albumin, suggesting enhanced stability in physiological conditions. Both cross-linked and non-crosslinked polyplexes demonstrated either similar or better transfection and genome-editing efficiencies, and significantly better biocompatibility than Lipofectamine 2000, a commercially available state-of-the-art transfection agent that exhibits cytotoxicity.

Nanocatalyst Complex Can Dephosphorylate Key Proteins in MAPK Pathway for Cancer Therapy

Controlling phosphorylation processes of proteins is a facile way for manipulating cell fates. Herein, a synergistic therapeutic strategy utilizing a near-infrared (NIR)-responsive nanocatalyst (NC) complex is presented, which is comprised of photoactive NC and protein phosphatase 2A (PP2A), to synergistically inhibit hyperphosphorylation of mitogen-activated protein kinase (MAPK) pathway for cancer therapy, as an example of many biological processes this approach can apply to. NIR-triggered release of PP2A specially dephosphorylates and inactivates mitogen-activated protein kinase kinase (MAP2K, also known as MEK) and extracellular regulated protein kinases (ERK) in the MAPK pathway, meanwhile, the NIR-triggered activation of NC decreases the level of intracellular adenosine triphosphate to attenuate protein phosphorylation of MEK and ERK. The synergistic therapeutics effectively suppress melanoma progression by inhibiting hyperphosphorylation of the MAPK pathway. In addition, the nanocatalyst complex reduces the risk of drug-resistance through inhibiting a rebound of RAS-GTP. The NIR-responsive nanocatalyst complex paves a novel way for cancer therapeutics.

Combinatorial library of chalcogen-containing lipidoids for intracellular delivery of genome-editing proteins

Protein based therapeutics with high specificities and low off-target effects are used for transient and accurate manipulation of cell functions. However, developing safe and efficient carriers for intracellular delivery of active therapeutic proteins is a long-standing challenge. Here we report a combinatorial library of chalcogen (O, S, Se) containing lipidoid nanoparticles (LNPs) as efficient nanocarriers for intracellular delivery of negatively supercharged Cre recombinase ((-30)GFP-Cre) and anionic Cas9:single-guide RNA (Cas9:sgRNA) ribonucleoprotein (RNP) for genome editing. The structure-activity relationship between the lipidoids and intracellular protein delivery efficiencies was explored and it was demonstrated that the newly developed LNPs are effective for gene recombination in vivo.

Materials and methods for delivery of biological drugs

Biological drugs generated via recombinant techniques are uniquely positioned due to their high potency and high selectivity of action. The major drawback of this class of therapeutics, however, is their poor stability upon oral administration and during subsequent circulation. As a result, biological drugs have very low bioavailability and short therapeutic half-lives. Fortunately, tools of chemistry and biotechnology have been developed into an elaborate arsenal, which can be applied to improve the pharmacokinetics of biological drugs. Depot-type release systems are available to achieve sustained release of drugs over time. Conjugation to synthetic or biological polymers affords long circulating formulations. Administration of biological drugs through non-parenteral routes shows excellent performance and the first products have reached the market. This Review presents the main accomplishments in this field and illustrates the materials and methods behind existing and upcoming successful formulations and delivery strategies for biological drugs.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Intracellular delivery of the PTEN protein using cationic lipidoids for cancer therapy

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor, mutated or inactive in a large percentage of human cancers. Restoring PTEN activity in cancer cells through gene therapy has shown to inhibit cell growth and induce apoptosis, particularly in cells with a PTEN deficiency. Gene therapy, however, comes with some inherent risks such as triggering an immune response and permanent off target effects. Nanoparticle assisted protein delivery could mitigate these liabilities while maintaining therapeutic integrity. In this report, we evaluated the use of cationic lipid-like (lipidoid) materials to intracellularly deliver the PTEN protein. We synthesized a small library of cationic lipidoid materials and screened for the delivery of PTEN based on cell viability. The lipidoid material EC16-80 was selected for high efficacy and the subsequent lipidoid-protein complex was characterized using DLS, zeta potential, and TEM. Intracellular delivery of PTEN with EC16-80 to the PTEN deficient prostate cancer cell line PC-3 resulted in a significant decrease in activated AKT and induced apoptosis. Interestingly, delivery of PTEN to PTEN deficient prostate cancer cell lines PC-3 and LNCaP compared to the breast cancer cell line, MCF-7 with endogenous PTEN, resulted in significantly lower IC₅₀ values in PC-3 and LNCaP cells indicating that the treatment is predominantly specific to PTEN-deficient cells. Altogether, these results demonstrate the first intracellular delivery of recombinant PTEN using a synthetic delivery vehicle and highlight the potential of intracellular PTEN protein delivery as a potential targeted cancer therapy.

Spherical Nucleic Acid Nanoparticles: Therapeutic Potential

Spherical nucleic acids (SNAs) are highly oriented, well organized, polyvalent structures of nucleic acids conjugated to hollow or solid core nanoparticles. Because they can transfect many tissue and cell types without toxicity, induce minimum immune response, and penetrate various biological barriers (such as the skin, blood-brain barrier, and blood-tumor barrier), they have become versatile tools for the delivery of nucleic acids, drugs, and proteins for various therapeutic purposes. This article describes the unique structures and properties of SNAs and discusses how these properties enable their application in gene regulation, immunomodulation, and drug and protein delivery. It also summarizes current efforts towards clinical translation of SNAs and provides an expert opinion on remaining challenges to be addressed in the path forward to the clinic.

Antimicrobial peptide encapsulation and sustained release from polymer network particles prepared in supercritical carbon dioxide

Antimicrobial peptide loaded poly(2-hydroxyethyl methacrylate) particles were synthesized in supercritical carbon dioxide via one-pot free-radical dispersion polymerisation of 2-hydroxyethyl methacrylate and a cross-linker. Discrete particles with a well-defined spherical morphology and a diameter as low as 450 nm have been obtained in mild conditions. The encapsulation and release of the peptide were confirmed by antimicrobial tests that demonstrated for the first time a sustained release of the peptide from poly(2-hydroxyethyl methacrylate) microgels prepared by one-pot dispersion polymerization in supercritical carbon dioxide and then dispersed in water.

"Minimalist" Nanovaccine Constituted from Near Whole Antigen for Cancer Immunotherapy

One of the major challenges in vaccine design has been the over dependence on incorporation of abundant adjuvants, which in fact is in violation of the "minimalist" principle. In the present study, a compact nanovaccine derived from a near whole antigen (up to 97 wt %) was developed. The nanovaccine structure was stabilized by free cysteines within each antigen (ovalbumin, OVA), which were tempospatially exposed and heat-driven to form an extensive intermolecular disulfide network. This process enables the engineering of a nanovaccine upon integration of the danger signal (CpG-SH) into the network during the synthetic process. The 50 nm-sized nanovaccine was developed comprising approximately 500 antigen molecules per nanoparticle. The nanovaccine prophylactically protected 70% of mice from tumorigenesis (0% for the control group) in murine B16-OVA melanoma. Significant tumor inhibition was achieved by strongly nanovaccine-induced cytotoxic T lymphocytes. This strategy can be adapted for the future design of vaccine for a minimalist composition in clinical settings.

Advance in oral delivery systems for therapeutic protein

Oral delivery is the most common method of drug administration with high safety and good compliance for patients. However, delivering therapeutic proteins to the target site via oral route involves tremendous challenge due to unfavourable conditions like biochemical barrier, mucus barrier and epithelial barriers. According to the functional differences of various protein drug delivery systems, the recent advances in pH responsive polymer-based drug delivery system, mucoadhesive polymer-based drug delivery system, absorption enhancers-based drug delivery system and composite polymer-based delivery system all were briefly summarised in this review, which not only clarified the clinic potential of these novel drug delivery systems, but also described the way for increasing oral bioavailability of therapeutic protein.

Drug nanorods are potential new nanocarriers for intracellular protein delivery

Protein therapeutics are increasingly important for the treatment of many diseases; however, intracellular protein delivery remains a considerable challenge. To address this challenge, drug nanorods have emerged as new nanocarriers for enhanced intracellular protein delivery via bypassing endo-lysosomes, which was called a “drug-delivering-drug platform”.

An autonomous tumor-targeted nanoprodrug for reactive oxygen species-activatable dual-cytochrome c/doxorubicin antitumor therapy

The precise tumor cell-specific delivery of therapeutic proteins and the elimination of side effects associated with routine chemotherapeutic agents are two current critical considerations for tumor therapy. In this study, we report a reactive oxygen species (ROS)-activated yolk-shell nanoplatform for the tumor-specific co-delivery of cytochrome c (Cyt c) prodrug and doxorubicin, in which the bioactivity of Cyt c could be restored by the intracellular ROS-trigger and readily initiate the sequential doxorubicin release. The DOX-loaded lactobionic acid-modified yolk-shell mesoporous silica nanoparticles were first encapsulated with 4-nitrophenyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl carbonate (NBC)-modified Cyt c via boronic ester linkages, and functionalized again with lactobionic acid to further shield Cyt c and confer the selective tumor targeting against liver cancer cells. The key feature in this design is that by taking advantage of the boronic ester linkage, the cytotoxicity of Cyt c capped on the nanoparticle could be temporarily deactivated during blood transportation and rapidly restored upon exposure to the ROS-rich microenvironment within liver cancer cells, thereby simultaneously achieving the protein therapy and stimuli-responsive doxorubicin release. This study presents a novel strategy for the development of tumor-sensitive co-delivery nanoplatforms.

Supramolecularly Engineered Circular Bivalent Aptamer for Enhanced Functional Protein Delivery

Circular bivalent aptamers (cb-apt) comprise an emerging class of chemically engineered aptamers with substantially improved stability and molecular recognition ability. Its therapeutic application, however, is challenged by the lack of functional modules to control the interactions of cb-apt with therapeutics. We present the design of a β-cyclodextrin-modified cb-apt (cb-apt-βCD) and its supramolecular interaction with molecular therapeutics via host-guest chemistry for targeted intracellular delivery. The supramolecular ensemble exhibits high serum stability and enhanced intracellular delivery efficiency compared to a monomeric aptamer. The cb-apt-βCD ensemble delivers green fluorescent protein into targeted cells with efficiency as high as 80%, or cytotoxic saporin to efficiently inhibit tumor cell growth. The strategy of conjugating βCD to cb-apt, and subsequently modulating the supramolecular chemistry of cb-apt-βCD, provides a general platform to expand and diversify the function of aptamers, enabling new biological and therapeutic applications.

Drug-delivering-drug platform-mediated potent protein therapeutics via a non-endo-lysosomal route

Protein therapeutics is playing an increasingly critical role in treatment of human diseases. However, current vectors are captured by the digestive endo-lysosomal system, which results in an extremely low fraction (<2%) of protein being released in the cytoplasm. This paper reports a drug-delivering-drug platform (HA-PNPplex, 200 nm) for potent intracellular delivery of protein and combined treatment of cancer.

Methods: The platform was prepared by loading functional protein on pure drug nanoparticles (PNPs) followed by hyaluronic acid coating and was characterized by dynamic light scattering, transmission electron microscopy, and gel electrophoresis. In vitro, cellular uptake, trafficking, and cytotoxicity were evaluated by flow cytometry and confocal laser microscopy. Protein expression was assayed by western blot. In vivo, blood circulation and biodistribution were studied using a fluorescence imaging system, antitumor efficacy was assessed in a caspase 3-deficient tumor model, and biocompatibility was determined by comparison of hemolytic activity and proinflammatory cytokines and tissue histology.

Results: HA-PNPplex delivered the functional protein, caspase 3, to cells via bypassing endo-lysosomes and raised the caspase-3 level 6.5-fold in caspase 3-deficient cells. Promoted tumor accumulation (1.5-fold) and penetration were exhibited, demonstrating a high tumor-targeting ability of HA-PNPplex. HA-PNPplex rendered a 7-fold increase in caspase 3 in tumor and allowed for a 100% tumor growth inhibition and >60% apoptosis, implying significant antitumor activities.

Conclusions: This platform gains cellular entry without entrapment in the endo-lysosomes and enables efficient intracellular protein delivery and resultant profound cancer treatment. This platform, with extremely high drug-loading, is a valuable platform for combined cancer therapy with small-molecule drugs and proteins. More importantly, this work offers a robust and safe approach for protein therapeutics and intracellular delivery of other functional peptides, as well as gene-based therapy.

Protein delivery into cells using inorganic nanoparticle-protein supramolecular assemblies

The delivery of proteins into cells is a potential game changer for a wide array of therapeutic purposes, including cancer therapy, immunomodulation and treatment of inherited diseases. In this review, we present recently developed nanoassemblies for protein delivery that utilize strategies that range from direct assembly, encapsulation and composite formation. We will discuss factors that affect the efficacy of nanoassemblies for delivery from the perspective of both nanoparticles and proteins. Challenges in the field, particularly achieving effective cytosolar protein delivery through endosomal escape or evasion are discussed.

Self-Assembly of Extracellular Vesicle-like Metal-Organic Framework Nanoparticles for Protection and Intracellular Delivery of Biofunctional Proteins

The intracellular delivery of biofunctional enzymes or therapeutic proteins through systemic administration is of great importance in therapeutic intervention of various diseases. However, current strategies face substantial challenges owing to various biological barriers, including susceptibility to protein degradation and denaturation, poor cellular uptake, and low transduction efficiency into the cytosol. Here, we developed a biomimetic nanoparticle platform for systemic and intracellular delivery of proteins. Through a biocompatible strategy, guest proteins are caged in the matrix of metal-organic frameworks (MOFs) with high efficiency (up to ∼94%) and high loading content up to ∼50 times those achieved by surface conjunction, and the nanoparticles were further decorated with the extracellular vesicle (EV) membrane with an efficiency as high as ∼97%. In vitro and in vivo study manifests that the EV-like nanoparticles can not only protect proteins against protease digestion and evade the immune system clearance but also selectively target homotypic tumor sites and promote tumor cell uptake and autonomous release of the guest protein after internalization. Assisted by biomimetic nanoparticles, intracellular delivery of the bioactive therapeutic protein gelonin significantly inhibits the tumor growth in vivo and increased 14-fold the therapeutic efficacy. Together, our work not only proposes a new concept to construct a biomimetic nanoplatform but also provides a new solution for systemic and intracellular delivery of protein.

Recombinant Spider Silk Hydrogels for Sustained Release of Biologicals

Therapeutic biologics (i.e., proteins) have been widely recognized for the treatment, prevention, and cure of a variety of human diseases and syndromes. However, design of novel protein-delivery systems to achieve a nontoxic, constant, and efficient delivery with minimal doses of therapeutic biologics is still challenging. Here, recombinant spider silk-based materials are employed as a delivery system for the administration of therapeutic biologicals. Hydrogels made of the recombinant spider silk protein eADF4(C16) were used to encapsulate the model biologicals BSA, HRP, and LYS by direct loading or through diffusion, and their release was studied. Release of model biologicals from eADF4(C16) hydrogels is in part dependent on the electrostatic interaction between the biological and the recombinant spider silk protein variant used. In addition, tailoring the pore sizes of eADF4(C16) hydrogels strongly influenced the release kinetics. In a second approach, a particles-in-hydrogel system was used, showing a prolonged release in comparison with that of plain hydrogels (from days to week). The particle-enforced spider silk hydrogels are injectable and can be 3D printed. These initial studies indicate the potential of recombinant spider silk proteins to design novel injectable hydrogels that are suitable for delivering therapeutic biologics.

Hierarchical Nanoassemblies-Assisted Combinational Delivery of Cytotoxic Protein and Antibiotic for Cancer Treatment

Protein therapeutics hold increasing interest with the promise of revolutionizing the cancer treatment by virtue of a potent specific activity and reduced adverse effects. Nonetheless, the therapeutic efficacy of anticancer proteins is highly compromised by multiple successive physiological barriers to protein delivery. In addition, concurrent elimination of bulk tumor cells and highly tumorigenic cancer stem-like cells (CSCs) as a promising strategy has been evidenced to significantly improve cancer therapy. Here we show that a hierarchically assembled nanocomposite can self-adaptively transform its particulate property in response to endogenous tumor-associated signals to overcome the sequential barriers and achieve an enhanced antitumor efficacy by killing CSCs and bulk tumor cells synchronously. The nanoassemblies preferentially accumulate in tumors and dissociate under tumor microenvironmental acidity accompanied by the extracellular release of small-sized ribonuclease A (RNase A)-encapsulated nanocapsule (R-rNC) and small-molecule anti-CSC doxycycline (Doc), which exhibit increased tumor penetration and intracellular accumulation. The endocytosed R-rNC rapidly releases RNase A within both CSCs and tumor cells at intracellular reductive conditions, causing cell death by catalyzing RNA degradation, while Doc eradicates CSCs by inhibiting the mitochondrial biogenesis. The hierarchical assemblies show enhanced cytotoxicity on the CSC-enriched MDA-MB-231 mammospheres and an enhanced antitumor efficacy on the xenograft tumor mouse model.

Molecular engineering solutions for therapeutic peptide delivery

Proteins and their interactions in and out of cells must be well-orchestrated for the healthy functioning and regulation of the body. Even the slightest disharmony can cause diseases. Therapeutic peptides are short amino acid sequences (generally considered <50 amino acids) that can naturally mimic the binding interfaces between proteins and thus, influence protein-protein interactions. Because of their fidelity of binding, peptides are a promising next generation of personalized medicines to reinstate biological harmony. Peptides as a group are highly selective, relatively safe, and biocompatible. However, they are also vulnerable to many in vivo pharmacologic barriers limiting their clinical translation. Current advances in molecular, chemical, and nanoparticle engineering are helping to overcome these previously insurmountable obstacles and improve the future of peptides as active and highly selective therapeutics. In this review, we focus on self-assembled vehicles as nanoparticles to carry and protect therapeutic peptides through this journey, and deliver them to the desired tissue.

ARMMs as a versatile platform for intracellular delivery of macromolecules

Majority of disease-modifying therapeutic targets are restricted to the intracellular space and are therefore not druggable using existing biologic modalities. The ability to efficiently deliver macromolecules inside target cells or tissues would greatly expand the current landscape of therapeutic targets for future generations of biologic drugs, but remains challenging. Here we report the use of extracellular vesicles, known as arrestin domain containing protein 1 [ARRDC1]-mediated microvesicles (ARMMs), for packaging and intracellular delivery of a myriad of macromolecules, including the tumor suppressor p53 protein, RNAs, and the genome-editing CRISPR-Cas9/guide RNA complex. We demonstrate selective recruitment of these macromolecules into ARMMs. When delivered intracellularly via ARMMs, these macromolecules are biologically active in recipient cells. P53 delivered via ARMMs induces DNA damage-dependent apoptosis in multiple tissues in mice. Together, our results provide proof-of-principle demonstration that ARMMs represent a highly versatile platform for packaging and intracellular delivery of therapeutic macromolecules.

One of the challenges of biologic drug therapy is delivery into target cells and tissues. Here the authors present ARMMs (arrestin domain containing protein 1 mediated microvesicles) as a versatile platform for packaging and delivery of a myriad of molecules, including p53, RNAs and CRISPR-Cas9.

Transduction Methods for Cytosolic Delivery of Proteins and Bioconjugates into Living Cells

The human organism and its constituting cells rely on interplay between multiple proteins exerting specific functions. Progress in molecular biotechnologies has facilitated the production of recombinant proteins. When administrated to patients, recombinant proteins can provide important healthcare benefits. To date, most therapeutic proteins must act from the extracellular environment, with their targets being secreted modulators or extracellular receptors. This is because proteins cannot passively diffuse across the plasma membrane into the cytosol. To expand the scope of action of proteins for cytosolic targets (representing more than 40% of the genome) effective methods assisting protein cytosolic entry are being developed. To date, direct protein delivery is extremely tedious and inefficient in cultured cells, even more so in animal models of pathology. Novel techniques are changing this limitation, as recently developed in vitro methods can robustly convey large amount of proteins into cell cultures. Moreover, advances in protein formulation or protein conjugates are slowly, but surely demonstrating efficiency for targeted cytosolic entry of functional protein in vivo in tumor xenograft models. In this review, various methods and recently developed techniques for protein transport into cells are summarized. They are put into perspective to address the challenges encountered during delivery.

Intra-tumoral delivery of functional ID4 protein via PCL/maltodextrin nano-particle inhibits prostate cancer growth

ID4, a helix loop helix transcriptional regulator has emerged as a tumor suppressor in prostate cancer. Epigenetic silencing of ID4 promotes prostate cancer whereas ectopic expression in prostate cancer cell lines blocks cancer phenotype. To directly investigate the anti-tumor property, full length human recombinant ID4 encapsulated in biodegradable Polycaprolactone/Maltodextrin (PCL-MD) nano-carrier was delivered to LNCaP cells in which the native ID4 was stably silenced (LNCaP(-)ID4). The cellular uptake of ID4 resulted in increased apoptosis, decreased proliferation and colony formation. Intratumoral delivery of PCL-MD ID4 into growing LNCaP(-)ID4 tumors in SCID mice significantly reduced the tumor volume compared to the tumors treated with chemotherapeutic Docetaxel. The study supports the feasibility of using nano-carrier encapsulated ID4 protein as a therapeutic. Mechanistically, ID4 may assimilate multiple regulatory pathways for example epigenetic re-programming, integration of multiple AR co-regulators or signaling pathways resulting in tumor suppressor activity of ID4.

DNA Nanotechnology-Enabled Drug Delivery Systems

Over the past decade, we have seen rapid advances in applying nanotechnology in biomedical areas including bioimaging, biodetection, and drug delivery. As an emerging field, DNA nanotechnology offers simple yet powerful design techniques for self-assembly of nanostructures with unique advantages and high potential in enhancing drug targeting and reducing drug toxicity. Various sequence programming and optimization approaches have been developed to design DNA nanostructures with precisely engineered, controllable size, shape, surface chemistry, and function. Potent anticancer drug molecules, including Doxorubicin and CpG oligonucleotides, have been successfully loaded on DNA nanostructures to increase their cell uptake efficiency. These advances have implicated the bright future of DNA nanotechnology-enabled nanomedicine. In this review, we begin with the origin of DNA nanotechnology, followed by summarizing state-of-the-art strategies for the construction of DNA nanostructures and drug payloads delivered by DNA nanovehicles. Further, we discuss the cellular fates of DNA nanostructures as well as challenges and opportunities for DNA nanostructure-based drug delivery.

Highly Efficient Intracellular Protein Delivery by Cationic Polyethyleneimine-Modified Gelatin Nanoparticles

Intracellular protein delivery may provide a safe and non-genome integrated strategy for targeting abnormal or specific cells for applications in cell reprogramming therapy. Thus, highly efficient intracellular functional protein delivery would be beneficial for protein drug discovery. In this study, we generated a cationic polyethyleneimine (PEI)-modified gelatin nanoparticle and evaluated its intracellular protein delivery ability in vitro and in vivo. The experimental results showed that the PEI-modified gelatin nanoparticle had a zeta potential of approximately +60 mV and the particle size was approximately 135 nm. The particle was stable at different biological pH values and temperatures and high protein loading efficiency was observed. The fluorescent image results revealed that large numbers of particles were taken up into the mammalian cells and escaped from the endosomes into the cytoplasm. In a mouse C26 cell-xenograft cancer model, particles accumulated in cancer cells. In conclusion, the PEI-modified gelatin particle may provide a biodegradable and highly efficient protein delivery system for use in regenerative medicine and cancer therapy.

Preoccupation of Empty Carriers Decreases Endo-/Lysosome Escape and Reduces the Protein Delivery Efficiency of Mesoporous Silica Nanoparticles

Endo-/lysosome escape is a major challenge in nanoparticle-based protein delivery for cancer therapy. To enhance the endo-/lysosomal escape and increase the efficacy of protein delivery, current strategies mainly focus on destroying endo-/lysosomes by employing modified nanoparticles, such as pH-sensitive polyplexes, cell-penetrating peptides, and photosensitive molecules. Herein, we hypothesize that pretreatment with empty nanocarriers might make endo-/lysosomes occupied and affect the endo/lysosomal escape of protein subsequently delivery by nanocarriers. We first treated breast carcinoma MDA-MB-231 cells with a high concentration of empty nanocarriers, mesoporous silica nanoparticles (MSN), to occupy the endo-/lysosome. After 2 h, we treated the cells with a lower concentration of fluorescein isothiocyanate-labeled MSN (MSN-FITC) and investigated the intracellular spatial and temporal distribution of MSN-FITC and their colocalization with endo-/lysosomes. We discovered the preoccupation of endo-/lysosomes by the empty nanocarriers did exist, mainly through changing the spatial distribution of the subsequently introduced nanocarriers. Furthermore, for the protein delivery, we observed reduced MSN-saporin delivery after endo-/lysosome preoccupation by MSN empty carriers. A similar result is observed for the delivery of cytochrome C by MSN but not for the small-molecule anticancer drug doxorubicin. The results show that the empty nanocarriers inhibit the endo-/lysosome intracellular trafficking process and decrease the endo-/lysosome escape of proteins subsequently delivered by the nanocarriers. This new discovered phenomenon of declined endo-/lysosome escape after endo-/lysosome preoccupation indicates that repeated treatment by nanomaterials with low protein-loading capacity may not yield a good cancer therapeutic effect. Therefore, it provides a new insightful perspective on the role of nanomaterial carriers in intracellular protein delivery.

Cellular delivery of enzyme-loaded DNA origami

In this communication, we show that active enzymes can be delivered into HEK293 cells in vitro when they are attached to tubular DNA origami nanostructures. We use bioluminescent enzymes as a cargo and monitor their activity from a cell lysate. The results show that the enzymes stay intact and retain their activity in the transfection process. The method is highly modular, which makes it a compelling candidate for a great variety of delivery applications.