Bioengineered Magnetoferritin Nanoprobes for Single-Dose Nuclear-Magnetic Resonance Tumor Imaging

Self-Assembly of Ferritin: Structure, Biological Function and Potential Applications in Nanotechnology

Protein cages are normally formed by the self-assembly of multiple protein subunits and ferritin is a typical example of a protein cage structure. Ferritin is a ubiquitous multi-subunit iron storage protein formed by 24 polypeptide chains that self-assemble into a hollow, roughly spherical protein cage. Ferritin has external and internal diameters of approximately 12 nm and 8 nm, respectively. Functionally, ferritin performs iron sequestration and is highly conserved in evolution. The interior cavity of ferritin provides a unique reaction vessel to carry out reactions separated from the exterior environment. In nature, the cavity is utilized for sequestration of iron and bio-mineralization as a mechanism to render iron inert and safe from the external environment. Material scientists have been inspired by this system and exploited a range of ferritin superfamily proteins as supramolecular templates to encapsulate different carrier molecules ranging from cancer drugs to therapeutic proteins, in addition to using ferritin proteins as well-defined building blocks for fabrication. Besides the interior cavity, the exterior surface and sub-unit interface of ferritin can be modified without affecting ferritin assembly.

Bioengineered H-Ferritin Nanocages for Quantitative Imaging of Vulnerable Plaques in Atherosclerosis

Inflammation and calcification concomitantly drive atherosclerotic plaque progression and rupture and are the compelling targets for identifying plaque vulnerability. However, current imaging modalities for vulnerable atherosclerotic plaques are often limited by inadequate specificity and sensitivity. Here, we show that natural H-ferritin nanocages radiolabeled with technetium-99m (^99mTc-HFn) can identify and accurately localize macrophage-rich, atherosclerotic plaques in living mice using combined SPECT and CT. Focal ^99mTc-HFn uptake was observed in the atherosclerotic plaques with multiple high-risk features of macrophage infiltration, active calcification, positive remodeling, and necrosis on histology and in early active ongoing lesions with intense macrophage infiltration. The uptake of ^99mTc-HFn in plaques enabled quantitative measuring of the dynamic changes of inflammation during plaque progression and anti-inflammation treatment. This strategy lays the foundation of using bioengineered endogenous human ferritin nanocages for the identification of vulnerable and early active plaques as well as potential assessment of anti-inflammation therapy.

Ferritin Nanocarrier Traverses the Blood Brain Barrier and Kills Glioma

Over the last decades, considerable efforts have been put into developing active nanocarrier systems that cross the blood brain barrier (BBB) to treat brain-related diseases such as glioma tumors. However, to date none have been approved for clinical usage. Here, we show that a human H-ferritin (HFn) nanocarrier both successfully crosses the BBB and kills glioma tumor cells. Its principle point of entry is the HFn receptor (transferrin receptor 1), which is overexpressed in both BBB endothelial cells (ECs) and glioma cells. Importantly, we found that HFn enters and exits the BBB via the endosome compartment. In contrast, upon specifically targeting and entering glioma cells, nearly all of the HFn accumulated in the lysosomal compartment, resulting in the killing of glioma tumor cells, with no HFn accumulation in the surrounding healthy brain tissue. Thus, HFn is an ideal nanocarrier for glioma therapy and possesses the potential to serve as a therapeutic approach against a broad range of central nervous system diseases.

Fenobody: A Ferritin-Displayed Nanobody with High Apparent Affinity and Half-Life Extension

Nanobodies consist of a single domain variable fragment of a camelid heavy-chain antibody. Nanobodies have potential applications in biomedical fields because of their simple production procedures and low cost. Occasionally, nanobody clones of interest exhibit low affinities for their target antigens, which, together with their short half-life limit bioanalytical or therapeutic applications. Here, we developed a novel platform we named fenobody, in which a nanobody developed against H5N1 virus is displayed on the surface of ferritin in the form of a 24mer. We constructed a fenobody by substituting the fifth helix of ferritin with the nanobody. TEM analysis showed that nanobodies were displayed on the surface of ferritin in the form of 6 × 4 bundles, and that these clustered nanobodies are flexible for antigen binding in spatial structure. Comparing fenobodies with conventional nanobodies currently used revealed that the antigen binding apparent affinity of anti-H5N1 fenobody was dramatically increased (∼360-fold). Crucially, their half-life extension in a murine model was 10-fold longer than anti-H5N1 nanobody. In addition, we found that our fenobodies are highly expressed in Escherichia coli, and are both soluble and thermo-stable nanocages that self-assemble as 24-polymers. In conclusion, our results demonstrate that fenobodies have unique advantages over currently available systems for apparent affinity enhancement and half-life extension of nanobodies. Our fenobody system presents a suitable platform for various large-scale biotechnological processes and should greatly facilitate the application of nanobody technology in these areas.

Near-Infrared Fluorescent Dye-Decorated Nanocages to Form Grenade-like Nanoparticles with Dual Control Release for Photothermal Theranostics and Chemotherapy

Recently, nanoparticles (NPs) have been widely investigated for delivery of anticancer drugs. Here, a dual control drug-release modality was developed that uses naturally occurring protein apoferritin loaded with doxorubicin (DOX) and ADS-780 near-infrared (NIR) fluorescent dye-decorated NPs (ADNIR NPs). ADNIR NPs act as a grenade to detonate the targeted tumor site following laser irradiation (photothermal therapy, PTT) and explode into cluster warheads (apoferritin-loaded DOX nanocages, AF-DOX NCs) that further destroy the tumor cells (chemotherapy). Light was shown to disrupt the grenade-like structure of NPs to release AF-DOX NCs as well as DOX from NCs in low-pH intercellular environments. In vitro and in vivo studies showed that the structure of AF-DOX NCs was disassembled to release DOX, which then killed the cancer cells in organelles with acidic environments. In vivo studies showed that the ADNIR NP-decorated with NIR dye facilitated tracking of the accumulated NPs at the tumor site using an IVIS imaging system. Overall, targeted ADNIR NPs with dual-release mechanisms were developed for use in photothermal theranostic and chemotherapy. This modality has high potential for application in cancer treatment and clinical translation for drug delivery and imaging.

A Self-Targeting, Dual ROS/pH-Responsive Apoferritin Nanocage for Spatiotemporally Controlled Drug Delivery to Breast Cancer

In this study, an intelligent pH and ROS dual-responsive drug delivery system based on an apoferritin (AFt) nanocage was prepared. This therapeutic system can specifically self-target 4T1 breast cancer cells by exploiting L-apoferritin receptor SCARA 5, avoiding the nonspecific binding or aggregation of nanoparticles due to the chemical functionalization for targeting. The characteristics of AFt were utilized for the simultaneous delivery of anticancer drug doxorubicin (DOX) and photosensitizer rose bengal (RB). RB exhibited efficient reactive oxygen species (ROS) generation, which can be applied to photodynamic therapy. Meanwhile, the AFt nanocage was prone to undergoing peptide backbone cleavage when oxidized by ROS. Therefore, by combining the intrinsic pH-responsive property of AFt, the dual ROS/pH-responsive system was developed. The time and location of drug release can be controlled by the combination of internal and external stimulus, which avoids the incomplete drug release under single stimulus response. The drug release rate increased significantly (from 26.1% to 92.0%) under low-pH condition (pH 5.0) and laser irradiation. More DOX from AFt entered the nucleus and killed the tumor cells, and the cell inhibition rate was up to ∼83% (DOX concentration: 5 μg/mL) after 48 h incubation. In addition, the biodistribution and the in vivo antitumor efficacy (within 14 d treatment) of the nanosystem were investigated in 4T1 breast cancer BALB/c mice. The results indicated that the system is a promising therapeutic agent involving ROS/pH dual response, self-targeting, and chemo-photodynamic therapy.

Metal ion assisted interface re-engineering of a ferritin nanocage for enhanced biofunctions and cancer therapy

The bottom-up self-assembly of protein subunits into supramolecular nanoarchitectures is ubiquitously exploited to recapitulate and expand the features of natural proteins to advance nanoscience in medicine. Various chemical and biological re-engineering approaches are available to render diverse functions in the given proteins. They are, unfortunately, capable of compromising protein integrity and stability after extensive modifications. In this study, we introduce a new protein re-engineering method, metal ion assisted interface re-engineering (MAIR), to serve as a robust and universal strategy to extend the functions of self-assembly proteins by boosting structural features to advance their diverse biomedical applications. In particular, the MAIR strategy was applied to a widely used natural protein, ferritin, as a model protein to coordinate with copper ions in its mutagenic artificial metal binding domain. Structure directed rational protein mutagenesis was carried out at the C2 interface amino acid residues of the ferritin subunit for metal ion coordination site optimization. Copper binding at the artificial binding pocket was highly specific over the other divalent ions present in physiological fluids, and the structurally embedded copper ion in turn strengthened the overall protein integrity and stability. In the presence of isotopic copper-64, the interface re-engineered ferritin worked as a chelator-free molecular nanoprobe with an extraordinarily high specific activity to allow PET imaging of tumors in live animals. We also found that the re-engineered ferritin coordinating with copper ions demonstrates high drug loading capacity of a widely used anti-cancer agent, doxorubicin (DOX), to achieve significant drug retention at the tumor site and enhance tumor regression for improved anti-cancer effects. The MAIR approach, thus, exploited the copper ion to facilitate efficient one-step labeling of mutant ferritin derivatives for simultaneous molecular imaging and drug delivery. The reported interface re-engineering strategy provides an unparalleled opportunity to expand protein biofunctions to serve as a new theranostic agent in cancer research.

Advanced Methods for Radiolabeling Multimodality Nanomedicines for SPECT/MRI and PET/MRI

The advent of hybrid cameras that combine MRI with either SPECT or PET has stimulated growing interest in developing multimodality imaging probes. Countless options are available for fusing magnetically active species with positron- or γ-ray-emitting radionuclides. The initial problem is one of choice: which chemical systems are a suitable basis for developing hybrid imaging agents? Any attempt to answer this question must also address how the physical, chemical, and biologic properties of a unified imaging agent can be tailored to ensure that optimum specificity and contrast are achieved simultaneously for both imaging modalities. Nanoparticles have emerged as attractive platforms for building multimodality radiotracers for SPECT/MRI and PET/MRI. A wide variety of nanoparticle constructs have been utilized as radiotracers, but irrespective of the particle class, radiolabeling remains a key step. Classic methods for radiolabeling nanoparticles involve functionalization of the particle surface, core, or coating. These modifications typically rely on using traditional metal ion chelate or prosthetic group chemistries. Though seemingly innocuous, appending nanoparticles with these radiolabeling handles can have dramatic effects on important properties such as particle size, charge, and solubility. In turn, alterations in the chemical and physical properties of the nanoparticle often have a negative impact on their pharmacologic profile. A central challenge in radiolabeling nanoparticles is to identify alternative chemical methods that facilitate the introduction of a radioactive nuclide without detrimental effects on the pharmacokinetic and toxicologic properties of the construct. Efforts to solve this challenge have generated a range of innovative chelate-free radiolabeling methods that exploit intrinsic chemical features of nanoparticles. Here, the chemistry of 9 mechanistically distinct methods for radiolabeling nanoparticles is presented. This discourse illustrates the evolution of nanoparticle radiochemistry from classic approaches to modern chelate-free or intrinsic methods.

Ultrasmall Superparamagnetic Iron Oxide Nanoparticle for T2-Weighted Magnetic Resonance Imaging

A facile method to synthesize ultrasmall-sized supermagnetic iron oxide nanoparticles with good monodispersity and high relaxivity is desired for magnetic resonance imaging (MRI) technology. Herein, we have developed a one-step method to direct the formation of superparamagnetic iron oxide nanoparticle (uBSPIO) using albumin under mild conditions. The resulting uBSPIO possess ultrasmall size (4.78 ± 0.55 nm) and super high MR relaxivity (444.56 ± 8.82 mM^-1 s^-1). After grafted by the luteinizing hormone release hormone peptide (LHRH), the uBSPIO could targeted and accumulated in the tumor site. Finally, the uBSPIOs had good stability and did not induce cytotoxicity in vitro or major organ toxicity in vivo. The uBSPIOs are promising contrast agents for MRI.

Iron oxide nanoclusters for T 1 magnetic resonance imaging of non-human primates

Iron-oxide-based contrast agents for magnetic resonance imaging (MRI) had been clinically approved in the United States and Europe, yet most of these nanoparticle products were discontinued owing to failures to meet rigorous clinical requirements. Significant advances have been made in the synthesis of magnetic nanoparticles and their biomedical applications, but several major challenges remain for their clinical translation, in particular large-scale and reproducible synthesis, systematic toxicity assessment, and their preclinical evaluation in MRI of large animals. Here, we report the results of a toxicity study of iron oxide nanoclusters of uniform size in large animal models, including beagle dogs and the more clinically relevant macaques. We also show that iron oxide nanoclusters can be used as T ₁ MRI contrast agents for high-resolution magnetic resonance angiography in beagle dogs and macaques, and that dynamic MRI enables the detection of cerebral ischaemia in these large animals. Iron oxide nanoclusters show clinical potential as next-generation MRI contrast agents.

IONP-doped nanoparticles for highly effective NIR-controlled drug release and combination tumor therapy

Despite advances in controlled drug delivery, drug delivery systems (DDSs) with controlled activated drug release and high spatial and temporal resolution are still required. Theranostic nanomedicine is capable of diagnosis, therapy, and monitoring the delivery and distribution of drug molecules and has received growing interest. In this study, a near-infrared light-controlled “off–on” DDS with magnetic resonance imaging and magnetic targeting properties was developed using a hybrid nanoplatform (carbon nanotubes [CNTs]-iron oxide nanoparticle). Doxorubicin (DOX) and distearoyl-sn-glycero-3-phosphoethanolamine-PEG were adsorbed onto CNTs-iron oxide nanoparticle, and then to avoid the unexpected drug release during circulation, 1-myristyl alcohol was used to encapsulate the CNTs–drug complex. Herein, multifunctional DOX-loaded nanoparticles (NPs) with “off–on” state were developed. DOX-NPs showed an obvious “off–on” effect (temperature increase, drug release) controlled by near-infrared light in vitro and in vivo. In the in vivo and in vitro studies, DOX-NPs exhibited excellent magnetic resonance imaging ability, magnetic targeting property, high biosafety, and high antitumor combined therapeutic efficacy (hyperthermia combined with chemotherapy). These results highlight the great potential of DOX-NPs in the treatment of cancer.

Imaging-guided synergetic therapy of orthotopic transplantation tumor by superselectively arterial administration of microwave-induced microcapsules

It is an ambitious target to improve overall Hepatocellular Carcinoma therapeutic effects. Recently, MW ablation has emerged as a powerful thermal ablation technique, affording favorable survival with excellent local tumor control. To achieve better therapeutic effects of MW ablation, MW sensitizers are prepared for enhanced MW ablation to preferentially heat tumor territory. However, it is still not practicable for treatment of the orthotopic transplantation tumor. Herein, biocompatible and degradable methoxy poly(ethylene glycol)-poly(lactic-co-glycolic acid) (mPEG-PLGA) microcapsules with hierarchical structure have been designed for microwave-induced tumor therapy. Chemical drug doxorubicin hydrochloride (DOX·HCl), microwave (MW) sensitizers and CT imaging contrast MoS₂ nanosheets and MR imaging contrast Fe₃O₄ nanoparticles are co-incorporated into the microcapsules. In vitro/vivo MR/CT dual-modal imaging results prove the potential application for guiding synergetic therapy and predicting post-therapy tumor progression in the orthotopic transplantation tumor model. After blocking the tumor-feeding arteries, these microcapsules not only exclude the cooling effect by cutting off the blood flow but also enhance MW heating conversion at tumor site. The focused MW heating makes microcapsules mollescent or ruptured and releases DOX·HCl from the microcapsules, achieving the controlled release of drugs for chemical therapy. Compared with MW ablation, 29.4% increase of necrosis diameter of normal liver in rabbit is obtained under MW ablation combined with transcatheter arterial blocking, and the average size of necrosis and inhibition rate of VX-2 liver orthotopic transplantation tumor in rabbit has increased by 129.33% and 73.46%. Moreover, it is proved that the superselectively arterial administration of the as-prepared microcapsules has no recognizable toxicity on the animals. Therefore, this research provides a novel strategy for the construction of MW-induced microcapsules for orthotopic transplantation tumor ablation with the properties of MW sensitizing, superselective arterial blocking, control release and enhanced accumulation of DOX·HCl, and MR/CT dual-modal imaging, which exhibits great potential applications in the field of HCC therapy.

Functional ferritin nanoparticles for biomedical applications

Ferritin, a major iron storage protein with a hollow interior cavity, has been reported recently to play many important roles in biomedical and bioengineering applications. Owing to the unique architecture and surface properties, ferritin nanoparticles offer favorable characteristics and can be either genetically or chemically modified to impart functionalities to their surfaces, and therapeutics or probes can be encapsulated in their interiors by controlled and reversible assembly/disassembly. There has been an outburst of interest regarding the employment of functional ferritin nanoparticles in nanomedicine. This review will highlight the recent advances in ferritin nanoparticles for drug delivery, bioassay, and molecular imaging with a particular focus on their biomedical applications.

Engineered ferritin nanocages as natural contrast agents in magnetic resonance imaging

Here we report the development of a “natural” MRI contrast agent with tunable Fe loading and a magnetic core for magnetic resonance imaging.