Denaturation-resistant bifunctional colloidal superstructures assembled via the proteinaceous barnase-barstar interface

It takes Two: Advancing cancer treatment with two-step nanoparticle delivery

The rapid advancement of nanobiotechnology has resulted in the development of numerous targeted nanoformulations and sophisticated nanobiorobots for biomedical applications. Despite the potential of nanostructures to improve drug delivery and therapeutic efficacy, their clinical application is still constrained by insufficient accumulation in tumor tissues. Current methodologies result in only an average of 0.6 % of administered nanoparticles reaching tumors, prompting the development of innovative strategies to improve targeting and influence the pharmacokinetics and pharmacodynamics of drugs. One such approach is two-step targeting, which includes either the concept of tumor pre-targeting with specific recognizing elements or the stimuli-sensitive activation of nanostructures. This review critically evaluates advancements in two-step drug delivery systems utilizing nanobiotechnology for targeted cancer therapy. For instance, two-step delivery based on the pre-targeting concept involves an initial injection of targeting molecules that bind to tumor-specific antigens, followed by the administration of drug-loaded nanocarriers modified with complementary adaptors. This approach enhances nanoparticle accumulation in tumors and improves therapeutic outcomes by increasing interaction avidity and overcoming steric hindrances. We critically assess existing adaptor systems for two-step drug delivery and synthesize findings from various studies demonstrating their efficacy in both in vitro and in vivo settings, while addressing challenges in clinical translation. We also explore future directions for developing novel adaptor systems to enhance two-step delivery mechanisms. This review aims to contribute to optimizing nanobiotechnology in oncology for more effective cancer therapies.

Targeted Two-Step Delivery of Oncotheranostic Nano-PLGA for HER2-Positive Tumor Imaging and Therapy In Vivo: Improved Effectiveness Compared to One-Step Strategy

Therapy for aggressive metastatic breast cancer remains a great challenge for modern biomedicine. Biocompatible polymer nanoparticles have been successfully used in clinic and are seen as a potential solution. Specifically, researchers are exploring the development of chemotherapeutic nanoagents targeting the membrane-associated receptors of cancer cells, such as HER2. However, there are no targeting nanomedications that have been approved for human cancer therapy. Novel strategies are being developed to alter the architecture of agents and optimize their systemic administration. Here, we describe a combination of these approaches, namely, the design of a targeted polymer nanocarrier and a method for its systemic delivery to the tumor site. Namely, PLGA nanocapsules loaded with a diagnostic dye, Nile Blue, and a chemotherapeutic compound, doxorubicin, are used for two-step targeted delivery using the concept of tumor pre-targeting through the barnase/barstar protein “bacterial superglue”. The first pre-targeting component consists of an anti-HER2 scaffold protein, DARPin9_29 fused with barstar, Bs-DARPin9_29, and the second component comprises chemotherapeutic PLGA nanocapsules conjugated to barnase, PLGA-Bn. The efficacy of this system was evaluated in vivo. To this aim, we developed an immunocompetent BALB/c mouse tumor model with a stable expression of human HER2 oncomarkers to test the potential of two-step delivery of oncotheranostic nano-PLGA. In vitro and ex vivo studies confirmed HER2 receptor stable expression in the tumor, making it a feasible tool for HER2-targeted drug evaluation. We demonstrated that two-step delivery was more effective than one-step delivery for both imaging and tumor therapy: two-step delivery had higher imaging capabilities than one-step and a tumor growth inhibition of 94.9% in comparison to 68.4% for the one-step strategy. The barnase*barstar protein pair has been proven to possess excellent biocompatibility, as evidenced by the successful completion of biosafety tests assessing immunogenicity and hemotoxicity. This renders the protein pair a highly versatile tool for pre-targeting tumors with various molecular profiles, thereby enabling the development of personalized medicine.

Genetically Encoded Self-Assembling Protein Nanoparticles for the Targeted Delivery In Vitro and In Vivo

Targeted nanoparticles of different origins are considered as new-generation diagnostic and therapeutic tools. However, there are no targeted drug formulations within the composition of nanoparticles approved by the FDA for use in the clinic, which is associated with the insufficient effectiveness of the developed candidates, the difficulties of their biotechnological production, and inadequate batch-to-batch reproducibility. Targeted protein self-assembling nanoparticles circumvent this problem since proteins are encoded in DNA and the final protein product is produced in only one possible way. We believe that the combination of the endless biomedical potential of protein carriers as nanoparticles and the standardized protein purification protocols will make significant progress in "magic bullet" creation possible, bringing modern biomedicine to a new level. In this review, we are focused on the currently existing platforms for targeted self-assembling protein nanoparticles based on transferrin, lactoferrin, casein, lumazine synthase, albumin, ferritin, and encapsulin proteins, as well as on proteins from magnetosomes and virus-like particles. The applications of these self-assembling proteins for targeted delivery in vitro and in vivo are thoroughly discussed, including bioimaging applications and different therapeutic approaches, such as chemotherapy, gene delivery, and photodynamic and photothermal therapy. A critical assessment of these protein platforms' efficacy in biomedicine is provided and possible problems associated with their further development are described.

Two-Step Targeted Drug Delivery via Proteinaceous Barnase-Barstar Interface and Doxorubicin-Loaded Nano-PLGA Outperforms One-Step Strategy for Targeted Delivery to HER2-Overexpressing Cells

Nanoparticle-based chemotherapy is considered to be an effective approach to cancer diagnostics and therapy in modern biomedicine. However, efficient tumor targeting remains a great challenge due to the lack of specificity, selectivity, and high dosage of chemotherapeutic drugs required. A two-step targeted drug delivery strategy (DDS), involving cancer cell pre-targeting, first with a first nontoxic module and subsequent targeting with a second complementary toxic module, is a solution for decreasing doses for administration and lowering systemic toxicity. To prove two-step DDS efficiency, we performed a direct comparison of one-step and two-step DDS based on chemotherapy loaded PLGA nanoparticles and barnase*barstar interface. Namely, we developed and thoroughly characterized the two-step targeting strategy of HER2-overexpressing cancer cells. The first targeting block consists of anti-HER2 scaffold polypeptide DARPin9_29 fused with barstar. Barstar exhibits an extremely effective binding to ribonuclease barnase with Kaff = 1014 M-1, thus making the barnase*barstar protein pair one of the strongest known protein*protein complexes. A therapeutic PLGA-based nanocarrier coupled to barnase was used as a second targeting block. The PLGA nanoparticles were loaded with diagnostic dye, Nile Blue, and a chemotherapeutic drug, doxorubicin. We showed that the two-step DDS increases the performance of chemotherapy-loaded nanocarriers: IC50 of doxorubicin delivered via two-step DDS was more than 100 times lower than that for one-step DDS: IC50 = 43 ± 3 nM for two-step DDS vs. IC50 = 4972 ± 1965 nM for one-step DDS. The obtained results demonstrate the significant efficiency of two-step DDS over the classical one-step one. We believe that the obtained data will significantly change the direction of research in developing targeted anti-cancer drugs and promote the creation of new generation cancer treatment strategies.

Barnase-Barstar Pair: Contemporary Application in Cancer Research and Nanotechnology

Barnase is an extracellular ribonuclease secreted by Bacillus amyloliquefaciens that was originally studied as a small stable enzyme with robust folding. The identification of barnase intracellular inhibitor barstar led to the discovery of an incredibly strong protein-protein interaction. Together, barnase and barstar provide a fully genetically encoded toxin-antitoxin pair having an extremely low dissociation constant. Moreover, compared to other dimerization systems, the barnase-barstar module provides the exact one-to-one ratio of the complex components and possesses high stability of each component in a complex and high solubility in aqueous solutions without self-aggregation. The unique properties of barnase and barstar allow the application of this pair for the engineering of different variants of targeted anticancer compounds and cytotoxic supramolecular complexes. Using barnase in suicide gene therapy has also found its niche in anticancer therapy. The application of barnase and barstar in contemporary experimental cancer therapy is reflected in the review.

Barnase encapsulation into submicron porous CaCO3 particles: studies of loading and enzyme activity

The present study focuses on the immobilization of the bacterial ribonuclease barnase (Bn) into submicron porous calcium carbonate (CaCO₃) particles. For encapsulation, we apply adsorption, freezing-induced loading and co-precipitation methods and study the effects of adsorption time, enzyme concentration and anionic polyelectrolytes on the encapsulation efficiency of Bn. We show that the use of negatively charged dextran sulfate (DS) and ribonucleic acid from yeast (RNA) increases the loading capacity (LC) of the enzyme on CaCO₃ particles by about 3-fold as compared to the particles with Bn itself. The ribonuclease (RNase) activity of encapsulated enzyme depends on the LC of the particles and transformation of metastable vaterite to stable calcite, as studied by the assessment of enzyme activities in particles.

New Frontiers in Diagnosis and Therapy of Circulating Tumor Markers in Cerebrospinal Fluid In Vitro and In Vivo

One of the greatest challenges in neuro-oncology is diagnosis and therapy (theranostics) of leptomeningeal metastasis (LM), brain metastasis (BM) and brain tumors (BT), which are associated with poor prognosis in patients. Retrospective analyses suggest that cerebrospinal fluid (CSF) is one of the promising diagnostic targets because CSF passes through central nervous system, harvests tumor-related markers from brain tissue and, then, delivers them into peripheral parts of the human body where CSF can be sampled using minimally invasive and routine clinical procedure. However, limited sensitivity of the established clinical diagnostic cytology in vitro and MRI in vivo together with minimal therapeutic options do not provide patient care at early, potentially treatable, stages of LM, BM and BT. Novel technologies are in demand. This review outlines the advantages, limitations and clinical utility of emerging liquid biopsy in vitro and photoacoustic flow cytometry (PAFC) in vivo for assessment of CSF markers including circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), microRNA (miRNA), proteins, exosomes and emboli. The integration of in vitro and in vivo methods, PAFC-guided theranostics of single CTCs and targeted drug delivery are discussed as future perspectives.

Synthesis of Magnetic Nanoparticles Stabilized by Magnetite-Binding Protein for Targeted Delivery to Cancer Cells

A new method for obtaining biomodified magnetite nanoparticles for targeted delivery to cells was developed. The method is based on the use of the C-terminal fragment of the Mms6 protein, which is involved in the magnetite biomineralization during the synthesis of magnetosomes in magnetotactic bacteria Magnetospirillum magneticum AMB-1, and the barnase*barstar high-affinity protein pair. The Mms6 protein fragment is required for stabilizing magnetite, and the barnase*barstar pair mediates the interaction between nanoparticles and the component for modification. The efficiency of this method was confirmed in the synthesis of magnetite nanoparticles recognizing the HER2/neu tumor marker and in the selective labeling of HER2/neu with these nanoparticles on the surface of cancer cells.

Versatile Platform for Nanoparticle Surface Bioengineering Based on SiO2-Binding Peptide and Proteinaceous Barnase*Barstar Interface

Nanoparticle surface engineering can change its chemical identity to enable surface coupling with functional biomolecules. However, common surface coupling methods such as physical adsorption or chemical conjugation often suffer from the low coupling yield, poorly controllable orientation of biomolecules, and steric hindrance during target binding. These issues limit the application scope of nanostructures for theranostics and personalized medicine. To address these shortfalls, we developed a rapid and versatile method of nanoparticle biomodification. The method is based on a SiO₂-binding peptide that binds to the nanoparticle surface and a protein adaptor system, Barnase*Barstar protein pair, serving as a "molecular glue" between the peptide and the attached biomolecule. The biomodification procedure shortens to several minutes, preserves the orientation and functions of biomolecules, and enables control over the number and ratio of attached molecules. The capabilities of the proposed biomodification platform were demonstrated by coupling different types of nanoparticles with DARPin9.29 and 4D5scFv-molecules that recognize the human epidermal growth factor receptor 2 (HER2/neu) oncomarker-and by subsequent highly selective immunotargeting of the modified nanoparticles to different HER2/neu-overexpressing cancer cells in one-step or two-step (by pretargeting with HER2/neu-recognizing molecule) modes. The method preserved the biological activity of the DARPin9.29 molecules attached to a nanoparticle, whereas the state-of-the-art carbodiimide 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/ N-hydroxysulfosuccinimide method of conjugation led to a complete loss of the functional activity of the DARPin9.29 nanoparticle-protein complex. Moreover, the method allowed surface design of nanoparticles that selectively interacted with antigens in complex biological fluids, such as whole blood. The demonstrated capabilities show this method to be a promising alternative to commonly used chemical conjugation techniques in nanobiotechnology, theranostics, and clinical applications.

Smart multifunctional nanoagents for in situ monitoring of small molecules with a switchable affinity towards biomedical targets

The great diversity of nanomaterials provides ample opportunities for constructing effective agents for biomedical applications ranging from biosensing to drug delivery. Multifunctional nanoagents that combine several features in a single particle are of special interest due to capabilities that substantially exceed those of molecular drugs. An ideal theranostic agent should simultaneously be an advanced biosensor to identify a disease and report the diagnosis and a biomedical actuator to treat the disease. While many approaches were developed to load a nanoparticle with various drugs for actuation of the diseased cells (e.g., to kill them), the nanoparticle-based approaches for the localized biosensing with real-time reporting of the marker concentration severely lag behind. Here, we show a smart in situ nanoparticle-based biosensor/actuator system that dynamically and reversibly changes its structural and optical properties in response to a small molecule marker to allow real-time monitoring of the marker concentration and adjustment of the system ability to bind its biomedical target. Using the synergistic combination of signal readout based on the localized surface plasmon resonance and an original method of fabrication of smart ON/OFF-switchable nanoagents, we demonstrate reversible responsiveness of the system to a model small molecule marker (antibiotic chloramphenicol) in a wide concentration range. The proposed approach can be used for the development of advanced multifunctional nanoagents for theranostic applications.

CID fragmentation, H/D exchange and supermetallization of Barnase-Barstar complex

The barnase-barstar complex is one of the most stable protein-protein complexes and has a very wide range of possible applications. Here we report the use of top-down mass spectrometry for the investigation of the structure of this complex, its ionization via ESI, isolation and fragmentation. It was found that the asymmetry of the resulting charge state distributions of the protein monomer product ions increased as the charge state of the precursor ions increased. For the investigation of the 3D structure of the complex, the gas phase H/D exchange reaction was used. In addition, supermetallized ions of the complex with Zn were produced and investigated. It was observed that an increase in the number of metals bound to the complex results in a change in complex stability and the charge distribution between protein fragment. Analysis of the fragmentation pattern of the supermetallized complex [bn-b* + 5Zn]¹⁰⁺ indicated that this ion is present in different conformations with different charges and Zn distributions. Since Zn cannot migrate, such structures must be formed during ionization.

Smart materials on the way to theranostic nanorobots: Molecular machines and nanomotors, advanced biosensors, and intelligent vehicles for drug delivery

BACKGROUND

Theranostics, a fusion of two key parts of modern medicine - diagnostics and therapy of the organism's disorders, promises to bring the efficacy of medical treatment to a fundamentally new level and to become the basis of personalized medicine. Extrapolating today's progress in the field of smart materials to the long-run prospect, we can imagine future intelligent agents capable of performing complex analysis of different physiological factors inside the living organism and implementing a built-in program thereby triggering a series of therapeutic actions. These agents, by analogy with their macroscopic counterparts, can be called nanorobots. It is quite obscure what these devices are going to look like but they will be more or less based on today's achievements in nanobiotechnology.

SCOPE OF REVIEW

The present Review is an attempt to systematize highly diverse nanomaterials, which may potentially serve as modules for theranostic nanorobotics, e.g., nanomotors, sensing units, and payload carriers.

MAJOR CONCLUSIONS

Biocomputing-based sensing, externally actuated or chemically "fueled" autonomous movement, swarm inter-agent communication behavior are just a few inspiring examples that nanobiotechnology can offer today for construction of truly intelligent drug delivery systems.

GENERAL SIGNIFICANCE

The progress of smart nanomaterials toward fully autonomous drug delivery nanorobots is an exciting prospect for disease treatment. Synergistic combination of the available approaches and their further development may produce intelligent drugs of unmatched functionality.

Synthesis of magnetic silica nanomarkers with controlled physicochemical properties

Magnetic markers which can be detected with an extremely high sensitivity with the method of magnetic particle quantification (MPQ) were synthesized. Using a controlled Stober reaction, a set of magnetic silica markers of different sizes and zeta potentials was obtained. The use of a carboxymethyl dextran polymer to stabilize the magnetite particles during the synthesis made it possible to substantially reduce the detection limit of the obtained construct, which opens up new opportunities for creating effective diagnostic nanoagents.

MPQ-cytometry: a magnetism-based method for quantification of nanoparticle-cell interactions

Precise quantification of interactions between nanoparticles and living cells is among the imperative tasks for research in nanobiotechnology, nanotoxicology and biomedicine. To meet the challenge, a rapid method called MPQ-cytometry is developed, which measures the integral non-linear response produced by magnetically labeled nanoparticles in a cell sample with an original magnetic particle quantification (MPQ) technique. MPQ-cytometry provides a sensitivity limit 0.33 ng of nanoparticles and is devoid of a background signal present in many label-based assays. Each measurement takes only a few seconds, and no complicated sample preparation or data processing is required. The capabilities of the method have been demonstrated by quantification of interactions of iron oxide nanoparticles with eukaryotic cells. The total amount of targeted nanoparticles that specifically recognized the HER2/neu oncomarker on the human cancer cell surface was successfully measured, the specificity of interaction permitting the detection of HER2/neu positive cells in a cell mixture. Moreover, it has been shown that MPQ-cytometry analysis of a HER2/neu-specific iron oxide nanoparticle interaction with six cell lines of different tissue origins quantitatively reflects the HER2/neu status of the cells. High correlation of MPQ-cytometry data with those obtained by three other commonly used in molecular and cell biology methods supports consideration of this method as a prospective alternative for both quantifying cell-bound nanoparticles and estimating the expression level of cell surface antigens. The proposed method does not require expensive sophisticated equipment or highly skilled personnel and it can be easily applied for rapid diagnostics, especially under field conditions.

[Targeted Delivery of Quantum Dots to HER2-Expressing Tumor Using Recombinant Antibodies]

Targeted delivery of semiconductor quantum dots (Q Ds) to tumors overexpressing HER2 cancer marker has been. demonstrated on immunocompromised mice bearing human breast cancer xenografts. To obtain targeted QDs complexes we applied the approach based on the use of protein adaptor system, RNAase barnase and its inhibitor barstar. Specific binding to target cancer marker was achieved through bivalent fusion protein containing two fragments of4D5scFv recombinant antibody and a fragment of barnase. QDs were conjugated to barstar, and final assembly of targeted complexes was obtained through non-covalent specific interaction of barstar, attached to QD, and barnase, that is part of the recombinant targeting protein. The efficient delivery of QDs to HER2-expressing tumor demonstrates the possibilities and prospects of the approach for targeted delivery of nanoparticles to cancer cells in vivo as the way to improve the efficiency of diagnosis and promote development of therapies based on the use of nanoparticles.

Nanoparticles Self-Assembly Driven by High Affinity Repeat Protein Pairing

Proteins are the most specific yet versatile biological self-assembling agents with a rich chemistry. Nevertheless, the design of new proteins with recognition capacities is still in its infancy and has seldom been exploited for the self-assembly of functional inorganic nanoparticles. Here, we report on the protein-directed assembly of gold nanoparticles using purpose-designed artificial repeat proteins having a rigid but modular 3D architecture. αRep protein pairs are selected for their high mutual affinity from a library of 10(9) variants. Their conjugation onto gold nanoparticles drives the massive colloidal assembly of free-standing, one-particle thick films. When the average number of proteins per nanoparticle is lowered, the extent of self-assembly is limited to oligomeric particle clusters. Finally, we demonstrate that the aggregates are reversibly disassembled by an excess of one free protein. Our approach could be optimized for applications in biosensing, cell targeting, or functional nanomaterials engineering.

A comprehensive study of interactions between lectins and glycoproteins for the development of effective theranostic nanoagents

A comprehensive study of the interactions between lectins and glycoproteins possessing different glycosylation profiles in the composition of nanoparticles was carried out in order to find specifically interacting protein pairs for the creation of novel classes of multifunctional nanoagets that based on protein-assisted selfassembly. We obtained information about specific interactions of certain lectins with selected glycoproteins as well as about the ability of certain monosaccharides to competitively inhibit binding of glycoproteins with lectins. These protein-mediated interactions may be involved in the formulation of self-assembled nanoparticles for therapy and diagnostics of various diseases.

Biocomputing based on particle disassembly

Nanoparticles with biocomputing capabilities could potentially be used to create sophisticated robotic devices with a variety of biomedical applications, including intelligent sensors and theranostic agents. DNA/RNA-based computing techniques have already been developed that can offer a complete set of Boolean logic functions and have been used, for example, to analyse cells and deliver molecular payloads. However, the computing potential of particle-based systems remains relatively unexplored. Here, we show that almost any type of nanoparticle or microparticle can be transformed into autonomous biocomputing structures that are capable of implementing a functionally complete set of Boolean logic gates (YES, NOT, AND and OR) and binding to a target as result of a computation. The logic-gating functionality is incorporated into self-assembled particle/biomolecule interfaces (demonstrated here with proteins) and the logic gating is achieved through input-induced disassembly of the structures. To illustrate the capabilities of the approach, we show that the structures can be used for logic-gated cell targeting and advanced immunoassays.

Reaction-based and single fluorescent emitter decorated ratiometric nanoprobe to detect hydrogen peroxide

A novel reaction-based cross-linked polymeric nanoprobe with a self-calibrating ratiometric fluorescence readout to selectively detect H2O2 is reported. The polymeric nanoprobe is fabricated by using hydrophobic H2O2-reactive boronic ester groups, crosslinker units, and environmentally sensitive 3-hydroxyflavone fluorophores through a miniemulsion polymerization. On treatment with H2O2, the boronic esters in the polymer are cleaved to form hydrophilic alcohols and subsequently lead to a hydrophobic-hydrophilic transition. Covalently linked 3-hydroxyflavones manifest the change in polarity as a ratiometric transition from green to blue, accompanied by a 500-fold increase in volume. Furthermore, this nanoprobe has been used for ratiometric sensing of glucose by monitoring the H2O2 generated during the oxidation of glucose by glucose oxidase, and thus successfully distinguished between normal and pathological levels of glucose.