Ferritin Nanocages with Biologically Orthogonal Conjugation for Vascular Targeting and Imaging

Ti3C2 Nanosheets Functionalized with Ferritin-Biomimetic Platinum Nanoparticles for Electrochemical Biosensors of Nitrite

Nitrites widely exist in human life and the natural environment, but excessive contents of nitrites will result in adverse effects on the environment and human health; hence, sensitive and stable nitrite detection systems are needed. In this study, we report the synthesis of Ti3C2 nanosheets functionalized with apoferritin (ApoF)-biomimetic platinum (Pt) nanoparticle (Pt@ApoF/Ti3C2) composite materials, which were formed by using ApoF as a template and protein-inspired biomineralization. The formed nanohybrid exhibits excellent electrochemical sensing performance towards nitrite (NaNO2). Specifically, the Pt@ApoF catalyzes the conversion of nitrites into nitrates, converting the chemical signal into an electrical signal. The prepared Pt@ApoF/Ti3C2-based electrochemical NaNO2 biosensors demonstrate a wide detection range of 0.001-9 mM with a low detection limit of 0.425 μM. Additionally, the biosensors possess high selectivity and sensitivity while maintaining a relatively stable electrochemical sensing performance within 7 days, enabling the monitoring of NaNO2 in complex environments. The successful preparation of the Pt@ApoF/Ti3C2 nanohybrid materials provides a new approach for constructing efficient electrochemical biosensors, offering a simple and rapid method for detecting NaNO2 in complex environments.

Enhancing Tumor Immunotherapy by Multivalent Anti-PD-L1 Nanobody Assembled via Ferritin Nanocage

Increasing immunotherapy response rate and durability can lead to significant improvements in cancer care. To address this challenge, a novel multivalent immune checkpoint therapeutic platform is constructed through site-specific ligation of anti-PD-L1 nanobody (Nb) on ferritin (Ftn) nanocage. Nb-Ftn blocks PD-1/PD-L1 interaction and downregulates PD-L1 levels via endocytosis-induced degradation. In addition, the cage structure of Ftn allows encapsulation of indocyanine green (ICG), an FDA-approved dye. Photothermal treatment with Nb-Ftn@ICG induces immunogenic death of tumor cells, which improves systemic immune response via maturation of dendritic cells and enhanced infiltration of T cells. Moreover, Nb-Ftn encapsulation significantly enhances cellular uptake, tumor accumulation and retention of ICG. In vivo assays showed that this nanoplatform ablates the primary tumor, suppresses abscopal tumors and inhibits tumor metastasis, leading to a prolonged survival rate. This work presents a novel strategy for improving cancer immunotherapy using multivalent nanobody-ferritin conjugates as immunological targeting and enhancing carriers.

Engineered protein cages with enhanced extracellular drug release for elevated antitumor efficacy

Human heavy chain ferritin (HFn) protein cage has been explored as a nanocarrier for targeted anticancer drug delivery. Here, we introduced a matrix metalloproteinases (MMPs)-cleavable sequence into the DE loop of HFn, creating an MMP-responsive variant, MR-HFn, for localized and extracellular drug release. The crystal structure of MR-HFn revealed that the addition of the MMPs recognition sequence did not affect the self-assembly of HFn but presented a surface-exposed loop susceptible to MMPs cleavage. Biochemical analysis indicated that this engineered protein cage is responsive to MMPs, enabling the targeted release of encapsulated drugs. To evaluate the therapeutic potential of this engineered protein cage, monosubstituted β-carboxy phthalocyanine zinc (CPZ), a type of photosensitizer, was loaded inside this protein cage. The prepared CPZ@MR-HFn showed higher uptake and stronger phototoxicity in MMPs overexpressed tumor cells, as well as enhanced penetration into multicellular tumor spheroids compared with its counterpart CPZ@HFn in vitro. In vivo, CPZ@MR-HFn displayed a higher tumor inhibitory rate than CPZ@HFn under illumination. These results indicated that MR-HFn is a promising nanocarrier for anticancer drug delivery and the MMP-responsive strategy here can also be adapted for other stimuli.

Fluorinated amphiphilic Poly(β-Amino ester) nanoparticle for highly efficient and specific delivery of nucleic acids to the Lung capillary endothelium

Endothelial cell dysfunction occurs in a variety of acute and chronic pulmonary diseases including pulmonary hypertension, viral and bacterial pneumonia, bronchopulmonary dysplasia, and congenital lung diseases such as alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). To correct endothelial dysfunction, there is a critical need for the development of nanoparticle systems that can deliver drugs and nucleic acids to endothelial cells with high efficiency and precision. While several nanoparticle delivery systems targeting endothelial cells have been recently developed, none of them are specific to lung endothelial cells without targeting other organs in the body. In the present study, we successfully solved this problem by developing non-toxic poly(β-amino) ester (PBAE) nanoparticles with specific structure design and fluorinated modification for high efficiency and specific delivery of nucleic acids to the pulmonary endothelial cells. After intravenous administration, the PBAE nanoparticles were capable of delivering non-integrating DNA plasmids to lung microvascular endothelial cells but not to other lung cell types. IVIS whole body imaging and flow cytometry demonstrated that DNA plasmid were functional in the lung endothelial cells but not in endothelial cells of other organs. Fluorination of PBAE was required for lung endothelial cell-specific targeting. Hematologic analysis and liver and kidney metabolic panels demonstrated the lack of toxicity in experimental mice. Thus, fluorinated PBAE nanoparticles can be an ideal vehicle for gene therapy targeting lung microvascular endothelium in pulmonary vascular disorders.

Ferritin nanocages as efficient nanocarriers and promising platforms for COVID-19 and other vaccines development

BACKGROUND

The development of safe and effective vaccines against SARS-CoV-2 and other viruses with high antigenic drift is of crucial importance to public health. Ferritin is a well characterized and ubiquitous iron storage protein that has emerged not only as a useful nanoreactor and nanocarrier, but more recently as an efficient platform for vaccine development.

SCOPE OF REVIEW

This review discusses ferritin structure-function properties, self-assembly, and novel bioengineering strategies such as interior cavity and exterior surface modifications for cargo encapsulation and delivery. It also discusses the use of ferritin as a scaffold for biomedical applications, especially for vaccine development against influenza, Epstein-Barr, HIV, hepatitis-C, Lyme disease, and respiratory viruses such as SARS-CoV-2. The use of ferritin for the synthesis of mosaic vaccines to deliver a cocktail of antigens that elicit broad immune protection against different viral variants is also explored.

MAJOR CONCLUSIONS

The remarkable stability, biocompatibility, surface functionalization, and self-assembly properties of ferritin nanoparticles make them very attractive platforms for a wide range of biomedical applications, including the development of vaccines. Strong immune responses have been observed in pre-clinical studies against a wide range of pathogens and have led to the exploration of ferritin nanoparticles-based vaccines in multiple phase I clinical trials.

GENERAL SIGNIFICANCE

The broad protective antibody response of ferritin nanoparticles-based vaccines demonstrates the usefulness of ferritin as a highly promising and effective approaches for vaccine development.

Ferritin-based nanomedicine for disease treatment

Ferritin is an endogenous protein which is self-assembled by 24 subunits into a highly uniform nanocage structure. Due to the drug-encapsulating ability in the hollow inner cavity and abundant modification sites on the outer surface, ferritin nanocage has been demonstrated great potential to become a multi-functional nanomedicine platform. Its good biocompatibility, low toxicity and immunogenicity, intrinsic tumor-targeting ability, high stability, low cost and massive production, together make ferritin nanocage stand out from other nanocarriers. In this review, we summarized ferritin-based nanomedicine in field of disease diagnosis, treatment and prevention. The different types of drugs to be loaded in ferritin, as well as drug-loading methods were classified. The strategies for site-specific and non-specific functional modification of ferritin were investigated, then the application of ferritin for disease imaging, drug delivery and vaccine development were discussed. Finally, the challenges restricting the clinical translation of ferritin-based nanomedicines were analyzed.

Protein-based nanocages for vaccine development

Protein nanocages have attracted considerable attention in various fields of nanomedicine due to their intrinsic properties, including biocompatibility, biodegradability, high structural stability, and ease of modification of their surfaces and inner cavities. In vaccine development, these protein nanocages are suited for efficient targeting to and retention in the lymph nodes and can enhance immunogenicity through various mechanisms, including excellent uptake by antigen-presenting cells and crosslinking with multiple B cell receptors. This review highlights the superiority of protein nanocages as antigen delivery carriers based on their physiological and immunological properties such as biodistribution, immunogenicity, stability, and multifunctionality. With a focus on design, we discuss the utilization and efficacy of protein nanocages such as virus-like particles, caged proteins, and artificial caged proteins against cancer and infectious diseases such as coronavirus disease 2019 (COVID-19). In addition, we summarize available knowledge on the protein nanocages that are currently used in clinical trials and provide a general outlook on conventional distribution techniques and hurdles faced, particularly for therapeutic cancer vaccines.

Lipid Nanoparticles for Nucleic Acid Delivery to Endothelial Cells

Endothelial cells play critical roles in circulatory homeostasis and are also the gateway to the major organs of the body. Dysfunction, injury, and gene expression profiles of these cells can cause, or are caused by, prevalent chronic diseases such as diabetes, cardiovascular disease, and cancer. Modulation of gene expression within endothelial cells could therefore be therapeutically strategic in treating longstanding disease challenges. Lipid nanoparticles (LNP) have emerged as potent, scalable, and tunable carrier systems for delivering nucleic acids, making them attractive vehicles for gene delivery to endothelial cells. Here, we discuss the functions of endothelial cells and highlight some receptors that are upregulated during health and disease. Examples and applications of DNA, mRNA, circRNA, saRNA, siRNA, shRNA, miRNA, and ASO delivery to endothelial cells and their targets are reviewed, as well as LNP composition and morphology, formulation strategies, target proteins, and biomechanical factors that modulate endothelial cell targeting. Finally, we discuss FDA-approved LNPs as well as LNPs that have been tested in clinical trials and their challenges, and provide some perspectives as to how to surmount those challenges.

Nucleic Acid Delivery to the Vascular Endothelium

This Review examines the state-of-the-art in the delivery of nucleic acid therapies that are directed to the vascular endothelium. First, we review the most important homeostatic functions and properties of the vascular endothelium and summarize the nucleic acid tools that are currently available for gene therapy and nucleic acid delivery. Second, we consider the opportunities available with the endothelium as a therapeutic target and the experimental models that exist to evaluate the potential of those opportunities. Finally, we review the progress to date from investigations that are directly targeting the vascular endothelium: for vascular disease, for peri-transplant therapy, for angiogenic therapies, for pulmonary endothelial disease, and for the blood-brain barrier, ending with a summary of the future outlook in this field.

Engineering Self-Assembling Protein Nanoparticles for Therapeutic Delivery

Despite remarkable advances over the past several decades, many therapeutic nanomaterials fail to overcome major in vivo delivery barriers. Controlling immunogenicity, optimizing biodistribution, and engineering environmental responsiveness are key outstanding delivery problems for most nanotherapeutics. However, notable exceptions exist including some lipid and polymeric nanoparticles, some virus-based nanoparticles, and nanoparticle vaccines where immunogenicity is desired. Self-assembling protein nanoparticles offer a powerful blend of modularity and precise designability to the field, and have the potential to solve many of the major barriers to delivery. In this review, we provide a brief overview of key designable features of protein nanoparticles and their implications for therapeutic delivery applications. We anticipate that protein nanoparticles will rapidly grow in their prevalence and impact as clinically relevant delivery platforms.

Protein Cages Engineered for Interaction-Driven Selective Encapsulation of Biomolecules

Hollow protein cages have become attractive drug delivery vehicles with high biocompatibility and precise functional/structural manipulability. However, difficulties in effective cargo loading inside the cages have been limiting further development of protein cage-based drug carriers. Here, we developed a specific interaction-driven encapsulation and cellular delivery strategy for various biomolecules by engineering a porous protein cage. The computationally designed hyperstable mi3 protein cage was circularly permuted to fuse the cancer targeting RGD tripeptide to the cage surface and SpyTag (ST), which forms a covalent bond with SpyCatcher (SC), to the cage inner cavity. SC-fused proteins with different sizes and charges could be stably and actively encapsulated in the engineered nanocage via the ST/SC reaction. Cargo protein encapsulation inside the cage was directly confirmed by cryo-electron microscopy (EM) structure determination. In addition, SC-fused monomeric avidin was added to the nanocage to encapsulate various biotinylated (nonprotein) cargos such as oligonucleotides and the anticancer drug doxorubicin. All cargo molecules loaded onto the engineered mi3 were effectively delivered to cells. This work introduces a highly versatile cargo loading/delivery strategy, where loading/delivery interactions, cargo molecules, and cell targeting moieties can be further varied for optimal cellular drug delivery.

Strategies for Multienzyme Assemblies

Proteins are not designed to be standalone entities and must coordinate their collective action for optimum performance. Nature has developed through evolution the ability to co-localize the functional partners of a cascade enzymatic reaction in order to ensure efficient exchange of intermediates. Inspired by these natural designs, synthetic scaffolds have been created to enhance the overall biological pathway performance. In this chapter, we describe several DNA- and protein-based scaffold approaches to assemble artificial enzyme cascades for a wide range of applications. We highlight the key benefits and drawbacks of these approaches to provide insights on how to choose the appropriate scaffold for different cascade systems.

Design of a Superpositively Charged Enzyme: Human Carbonic Anhydrase II Variant with Ferritin Encapsulation and Immobilization

Supercharged proteins exhibit high solubility and other desirable properties, but no engineered superpositively charged enzymes have previously been made. Superpositively charged variants of proteins such as green fluorescent protein have been efficiently encapsulated within Archaeoglobus fulgidus thermophilic ferritin (AfFtn). Encapsulation by supramolecular ferritin can yield systems with a variety of sequestered cargo. To advance applications in enzymology and green chemistry, we sought a general method for supercharging an enzyme that retains activity and is compatible with AfFtn encapsulation. The zinc metalloenzyme human carbonic anhydrase II (hCAII) is an attractive encapsulation target based on its hydrolytic activity and physiologic conversion of carbon dioxide to bicarbonate. A computationally designed variant of hCAII contains positively charged residues substituted at 19 sites on the protein's surface, resulting in a shift of the putative net charge from -1 to +21. This designed hCAII(+21) exhibits encapsulation within AfFtn without the need for fusion partners or additional reagents. The hCAII(+21) variant retains esterase activity comparable to the wild type and spontaneously templates the assembly of AfFtn 24mers around itself. The AfFtn-hCAII(+21) host-guest complex exhibits both greater activity and thermal stability when compared to hCAII(+21). Upon immobilization on a solid support, AfFtn-hCAII(+21) retains enzymatic activity and exhibits an enhancement of activity at elevated temperatures.

Protein-Based Nanoparticles for the Imaging and Treatment of Solid Tumors: The Case of Ferritin Nanocages, a Narrative Review

Protein nanocages have been studied extensively, due to their unique architecture, exceptional biocompatibility and highly customization capabilities. In particular, ferritin nanocages (FNs) have been employed for the delivery of a vast array of molecules, ranging from chemotherapeutics to imaging agents, among others. One of the main favorable characteristics of FNs is their intrinsic targeting efficiency toward the Transferrin Receptor 1, which is overexpressed in many tumors. Furthermore, genetic manipulation can be employed to introduce novel variants that are able to improve the loading capacity, targeting capabilities and bio-availability of this versatile drug delivery system. In this review, we discuss the main characteristics of FN and the most recent applications of this promising nanotechnology in the field of oncology with a particular emphasis on the imaging and treatment of solid tumors.

Functionalizing Ferritin Nanoparticles for Vaccine Development

In the last decade, the interest in ferritin-based vaccines has been increasing due to their safety and immunogenicity. Candidates against a wide range of pathogens are now on Phase I clinical trials namely for influenza, Epstein-Barr, and SARS-CoV-2 viruses. Manufacturing challenges related to particle heterogeneity, improper folding of fused antigens, and antigen interference with intersubunit interactions still need to be overcome. In addition, protocols need to be standardized so that the production bioprocess becomes reproducible, allowing ferritin-based therapeutics to become readily available. In this review, the building blocks that enable the formulation of ferritin-based vaccines at an experimental stage, including design, production, and purification are presented. Novel bioengineering strategies of functionalizing ferritin nanoparticles based on modular assembly, allowing the challenges associated with genetic fusion to be circumvented, are discussed. Distinct up/down-stream approaches to produce ferritin-based vaccines and their impact on production yield and vaccine efficacy are compared. Finally, ferritin nanoparticles currently used in vaccine development and clinical trials are summarized.

Ferritin nanocage: A promising and designable multi-module platform for constructing dynamic nanoassembly-based drug nanocarrier

Ferritin has been widely recognized as an ideal drug delivery vehicle owing to its unique cage-like structure. Coupled with intrinsic targeting ability and excellent biosafety, ferritin-based drug delivery system, recently coined as ferritin drug carrier (FDC), has sparked great interest among researchers and shown promising application potential in the biomedical field. However, the flexibility and accuracy of traditional FDCs are limited when facing with complex disease microenvironments. To meet the fast-growing requirements for precision medicine, ferritin can serve as a designable multi-module platform to fabricate smarter FDC, which we introduce here as dynamic nanoassembly-based ferritin drug carrier (DNFDC). Compared to conventional FDC, DNFDCs directly integrate required functions into their nanostructure, which can achieve dynamic transformation upon stimuli to specifically activate and exert therapeutic functions at targeted sites. In this review, we summarize the superior characteristics of ferritin that contribute to the on-demand design of DNFDC and outline the current advances in DNFDC. Moreover, the potential research directions and challenges are also discussed here. Hopefully, this review may inspire the future development of DNFDC.

ERK-Peptide-Inhibitor-Modified Ferritin Enhanced the Therapeutic Effects of Paclitaxel in Cancer Cells and Spheroids

Rational design of a drug delivery system with enhanced therapeutic potency is critical for efficient tumor chemotherapy. Many protein-based drug delivery platforms have been designed to deliver drugs to target sites and improve the therapeutic efficacy. In this study, paclitaxel (PTX) molecules were encapsulated within an apoferritin nanocage-based drug delivery system with the modification of an extracellular-signal-regulated kinase (ERK) peptide inhibitor at the C-terminus of ferritin (HERK). Apoferritin is an endogenous nano-sized spherical protein which has the ability to specially bind to a majority of tumor cells via interacting with transferrin receptor 1. The ERK peptide inhibitor is a peptide which can disrupt the interaction of MEK with ERK in the mitogen-activated protein kinase/ERK pathway. By combining the targeted delivery effect of ferritin and the inhibitory effect of the ERK peptide inhibitor, the newly fabricated ferritin carrier nanoparticle HERK could still be taken up by tumor cells, and it displayed higher cell cytotoxicity than the parent ferritin. After loading with PTX, HERK-PTX displayed a favorable anticancer effect in human breast cancer cells MDA-MB-231 and lung carcinoma cells A549. The remarkable inhibitory effect on MDA-MB-231 tumor spheroids was also identified. These results indicated that the constructed HERK nanocarrier is a promising multi-functional drug delivery vehicle to enhance the therapeutic effect of drugs in cancer therapy.

Engineering bionanoparticles for improved biosensing and bioimaging

The importance of bioimaging and biosensing has been clear with the onset of the COVID-19 pandemic. In addition to viral detection, detection of tumors, glucose levels, and microbes is necessary for improved disease treatment and prevention. Bionanoparticles, such as extracellular vesicles and protein nanoparticles, are ideal platforms for biosensing and bioimaging applications because of their propensity for high density surface functionalization and large loading capacity. Scaffolding large numbers of sensing modules and detection modules onto bionanoparticles allows for enhanced analyte affinity and specificity as well as signal amplification for highly sensitive detection even at low analyte concentrations. Here we demonstrate the potential of bionanoparticles for bioimaging and biosensing by highlighting recent examples in literature that utilize protein nanoparticles and extracellular vesicles to generate highly sensitive detection devices with impressive signal amplification.

Kinetics of Ferritin Self-Assembly by Laser Light Scattering: Impact of Subunit Concentration, pH, and Ionic Strength

Ferritins, the cellular iron repositories, are self-assembled, hollow spherical nanocage proteins composed of 24 subunits. The self-assembly process in ferritin generates the electrostatic gradient to rapidly sequester Fe(II) ions, thereby minimizing its toxicity (Fenton reaction). Although the factors that drive self-assembly and control its kinetics are little investigated, its inherent reversibility has been utilized for cellular imaging and targeted drug delivery. The current work tracks the kinetics of ferritin self-assembly by laser light scattering and investigates the factors that influence the process. The formation of partially structured subunit-monomers/dimers, at pH ≤ 1.5, serves as the starting material for the self-assembly, which upon increasing the pH exhibits biphasic behavior (a rapid assembly process coupled with subunit folding followed by a slower reassembly/reorganization process) and completes within 10 min. The ferritin self-assembly accelerated with subunit concentration and ionic strength (t_1/2 decreases in both the cases) but slowed down with the pH of the medium from 5.5 to 7.5 (t_1/2 increases). These findings would help to regulate the ferritin self-assembly to enhance the loading/unloading of drugs/nanomaterials for exploiting it as a nanocarrier and nanoreactor.

Ferritin as a Platform for Creating Antiviral Mosaic Nanocages: Prospects for Treating COVID-19

Infectious diseases are a continues threat to human health and the economy worldwide. The latest example is the global pandemic of COVID-19 caused by SARS-CoV-2. Antibody therapy and vaccines are promising approaches to treat the disease; however, they have bottlenecks: they might have low efficacy or narrow breadth due to the continuous emergence of new strains of the virus or antibodies could cause antibody-dependent enhancement (ADE) of infection. To address these bottlenecks, I propose the use of 24-meric ferritin for the synthesis of mosaic nanocages to deliver a cocktail of antibodies or nanobodies alone or in combination with another therapeutic, like a nucleotide analogue, to mimic the viral entry process and deceive the virus, or to develop mosaic vaccines. I argue that available data showing the effectiveness of ferritin-antibody conjugates in targeting specific cells and ferritin-haemagglutinin nanocages in developing influenza vaccines strongly support my proposals.

An Apoferritin-Hemagglutinin Conjugate Vaccine with Encapsulated Nucleoprotein Antigen Peptide from Influenza Virus Confers Enhanced Cross Protection

Naturally occurring self-assembling ferritin nanoparticles have become widely appreciated for vaccine design. In this study, an apoferritin (AFt) nanocage was used as a carrier to construct a biomimetic influenza vaccine by encapsulating a conserved internal nucleoprotein (NP) antigen peptide inside the nanocage, followed by chemically conjugating the surface antigen hemagglutinin (HA) protein on the outer surface of the AFt. Benefiting from the excellent thermal stability and thermallyassociated structural flexibility of the AFt nanocages, a novel temperature shift based encapsulation process was proposed and proved efficient for encapsulation of the NP peptides. On average, about 18 NPs were encapsulated and 1.6 HA antigens were conjugated in each of the HA-AFt+NP dual-antigen influenza vaccines. Upon immunization in mice, the HA-AFt+NP vaccine elicited both HA and NP-specific antibodies, and conferred complete protection against a lethal infection of both homologous PR8 H1N1 and heterologous A/FM/1/47 (FM1, H1N1) strains, while the HA-AFt conjugate vaccine without encapsulated NP antigen only conferred 60% protection against the FM1 H1N1 viral challenge. The potential cross-protective effect of the HA-AFt+NP vaccine was further demonstrated by significant specific hemagglutination inhibition (HAI) titers in serum of the immunized mice against heterologous A/Hong Kong/4801/2014 (H3N2) viral strain, which was about 3-fold of that induced by HA antigen and 2-fold of the HA-AFt conjugate vaccine. This biomimetic HA-AFt+NP conjugate vaccine, therefore, may represent a new strategy for developing a potential universal influenza vaccine without the need of any adjuvant, and further broaden the application of AFt nanocages in the areas of vaccine development and delivery system.

Targeting drug delivery in the vascular system: Focus on endothelium

The bloodstream is the main transporting pathway for drug delivery systems (DDS) from the site of administration to the intended site of action. In many cases, components of the vascular system represent therapeutic targets. Endothelial cells, which line the luminal surface of the vasculature, play a tripartite role of the key target, barrier, or victim of nanomedicines in the bloodstream. Circulating DDS may accumulate in the vascular areas of interest and in off-target areas via mechanisms bypassing specific molecular recognition, but using ligands of specific vascular determinant molecules enables a degree of precision, efficacy, and specificity of delivery unattainable by non-affinity DDS. Three decades of research efforts have focused on specific vascular targeting, which have yielded a multitude of DDS, many of which are currently undergoing a translational phase of development for biomedical applications, including interventions in the cardiovascular, pulmonary, and central nervous systems, regulation of endothelial functions, host defense, and permeation of vascular barriers. We discuss the design of endothelial-targeted nanocarriers, factors underlying their interactions with cells and tissues, and describe examples of their investigational use in models of acute vascular inflammation with an eye on translational challenges.

Nanobody-Ferritin Conjugate for Targeted Photodynamic Therapy

Ferritin is an iron-storage protein nanocage that is assembled from 24 subunits. The hollow cavity of ferritin enables its encapsulation of various therapeutic agents; therefore, ferritin has been intensively investigated for drug delivery. The use of antibody-ferritin conjugates provides an effective approach for targeted drug delivery. However, the complicated preparation and limited protein stability hamper wide applications of this system. Herein, we designed a novel nanobody-ferritin platform (Nb-Ftn) for targeted drug delivery. The site-specific conjugation between nanobody and ferritin is achieved by transglutaminase-catalyzed protein ligation. This ligation strategy allows the Nb conjugation after drug loading in ferritin, which avoids deactivation of the nanobody under the harsh pH environment required for drug encapsulation. To verify the tumor targeting of this Nb-Ftn platform, a photodynamic reagent, manganese phthalocyanine (MnPc), was loaded into the ferritin cavity, and an anti-EGFR nanobody was conjugated to the surface of the ferritin. The ferritin nanocage can encapsulate about 82 MnPc molecules. This MnPc@Nb-Ftn conjugate can be efficiently internalized by EGFR positive A431 cancer cells, but not by EGFR negative MCF-7 cells. Upon 730 nm laser irradiation, MnPc@Nb-Ftn selectively killed EGFR positive A431 cells by generating reactive oxygen species (ROS), whereas no obvious damage was observed on MCF-7 cells. Given that ferritin can be used for encapsulation of various therapeutic agents, this work provides a strategy for facile construction of nanobody-ferritin for targeted drug delivery.

Ferritin: A Platform for MRI Contrast Agents Delivery

The search for high relaxivities and increased specificity continues to be central to the development of paramagnetic contrast agents for magnetic resonance imaging (MRI). Ferritin, due to its unique surface properties, architecture, and biocompatibility, has emerged as a natural nanocage that can potentially help to reach both these goals. This review aims to highlight recent advances in the use of ferritin as a nanoplatform for the delivery of metal-based MRI contrast agents (containing Gd3+, Mn2+, or Fe2O3) alone or in combination with active molecules used for therapeutic purposes. The collected results unequivocally show that the use of ferritin for contrast agent delivery leads to more accurate imaging of cancer cells and a significantly improved targeted therapy.

Spatially controlled assembly of affinity ligand and enzyme cargo enables targeting ferritin nanocarriers to caveolae

One of the goals of nanomedicine is targeted delivery of therapeutic enzymes to the sub-cellular compartments where their action is needed. Endothelial caveolae-derived endosomes represent an important yet challenging destination for targeting, in part due to smaller size of the entry aperture of caveolae (ca. 30-50 nm). Here, we designed modular, multi-molecular, ferritin-based nanocarriers with uniform size (20 nm diameter) for easy drug-loading and targeted delivery of enzymatic cargo to these specific vesicles. These nanocarriers targeted to caveolar Plasmalemmal Vesicle-Associated Protein (Plvap) deliver superoxide dismutase (SOD) into endosomes in endothelial cells, the specific site of influx of superoxide mediating by such pro-inflammatory signaling as some cytokines and lipopolysaccharide (LPS). Cell studies showed efficient internalization of Plvap-targeted SOD-loaded nanocarriers followed by dissociation from caveolin-containing vesicles and intracellular transport to endosomes. The nanocarriers had a profound protective anti-inflammatory effect in an animal model of LPS-induced inflammation, in agreement with the characteristics of their endothelial uptake and intracellular transport, indicating that these novel, targeted nanocarriers provide an advantageous platform for caveolae-dependent delivery of biotherapeutics.

Bioengineering Strategies for Protein-Based Nanoparticles

In recent years, the practical application of protein-based nanoparticles (PNPs) has expanded rapidly into areas like drug delivery, vaccine development, and biocatalysis. PNPs possess unique features that make them attractive as potential platforms for a variety of nanobiotechnological applications. They self-assemble from multiple protein subunits into hollow monodisperse structures; they are highly stable, biocompatible, and biodegradable; and their external components and encapsulation properties can be readily manipulated by chemical or genetic strategies. Moreover, their complex and perfect symmetry have motivated researchers to mimic their properties in order to create de novo protein assemblies. This review focuses on recent advances in the bioengineering and bioconjugation of PNPs and the implementation of synthetic biology concepts to exploit and enhance PNP's intrinsic properties and to impart them with novel functionalities.