CXCR4(+)-targeted protein nanoparticles produced in the food-grade bacterium Lactococcus lactis

Protein Nanoparticles: Uniting the Power of Proteins with Engineering Design Approaches

Protein nanoparticles, PNPs, have played a long-standing role in food and industrial applications. More recently, their potential in nanomedicine has been more widely pursued. This review summarizes recent trends related to the preparation, application, and chemical construction of nanoparticles that use proteins as major building blocks. A particular focus has been given to emerging trends related to applications in nanomedicine, an area of research where PNPs are poised for major breakthroughs as drug delivery carriers, particle-based therapeutics or for non-viral gene therapy.

Rational engineering of a human GFP-like protein scaffold for humanized targeted nanomedicines

Green fluorescent protein (GFP) is a widely used scaffold for protein-based targeted nanomedicines because of its high biocompatibility, biological neutrality and outstanding structural stability. However, being immunogenicity a major concern in the development of drug carriers, the use of exogenous proteins such as GFP in clinics might be inadequate. Here we report a human nidogen-derived protein (HSNBT), rationally designed to mimic the structural and functional properties of GFP as a scaffold for nanomedicine. For that, a GFP-like β-barrel, containing the G2 domain of the human nidogen, has been rationally engineered to obtain a biologically neutral protein that self-assembles as 10nm-nanoparticles. This scaffold is the basis of a humanized nanoconjugate, where GFP, from the well-characterized protein T22-GFP-H6, has been substituted by the nidogen-derived GFP-like HSNBT protein. The resulting construct T22-HSNBT-H6, is a humanized CXCR4-targeted nanoparticle that selectively delivers conjugated genotoxic Floxuridine into cancer CXCR4+ cells. Indeed, the administration of T22-HSNBT-H6-FdU in a CXCR4-overexpressing colorectal cancer mouse model results in an even more efficient selective antitumoral effect than that shown by its GFP-counterpart, in absence of systemic toxicity. Therefore, the newly developed GFP-like protein scaffold appears as an ideal candidate for the development of humanized protein nanomaterials and successfully supports the tumor-targeted nanoscale drug T22-HSNBT-H6-FdU. STATEMENT OF SIGNIFICANCE: Targeted nanomedicine seeks for humanized and biologically neutral protein carriers as alternative of widely used but immunogenic exogenous protein scaffolds such as green fluorescent protein (GFP). This work reports for the first time the rational engineering of a human homolog of the GFP based in the human nidogen (named HSNBT) that shows full potential to be used in humanized protein-based targeted nanomedicines. This has been demonstrated in T22-HSNBT-H6-FdU, a humanized CXCR4-targeted protein nanoconjugate able to selectively deliver its genotoxic load into cancer cells.

Nanovaccine based on self-assembling nonstructural protein 1 boosts antibody responses to Zika virus

Self-assembling proteins may be generated after the addition of short specific amino acid sequences at both the N- and C-terminal ends. To date, this approach has not been evaluated regarding the impact of self-assembled proteins on the induction of immune responses. In the present study, we report the application of this experimental approach to the immunogenicity of protein antigens by measuring the antibody responses in mice immunized with nanoparticles made with a recombinant form of Zika virus nonstructural protein 1 (∆NS1). The results clearly indicated that ∆NS1-derived nanoparticles (NP-∆NS1) are assembled into a 3-dimensional structure with a high degree of multimerization. While ∆NS1 proved to be a weak immunogen, immunization with NP-∆NS1 enhanced subunit vaccines' immunogenicity with improved longevity in vaccinated mice. Thus, immunization with self-assembled antigens (nanovaccines) represents a new and promising strategy to enhance NS1-specific antibodies' induction based on purified recombinant proteins.

Release of targeted protein nanoparticles from functional bacterial amyloids: A death star-like approach

Sustained release of drug delivery systems (DDS) has the capacity to increase cancer treatment efficiency in terms of drug dosage reduction and subsequent decrease of deleterious side effects. In this regard, many biomaterials are being investigated but none offers morphometric and functional plasticity and versatility comparable to protein-based nanoparticles (pNPs). Here we describe a new DDS by which pNPs are fabricated as bacterial inclusion bodies (IB), that can be easily isolated, subcutaneously injected and used as reservoirs for the sustained release of targeted pNPs. Our approach combines the high performance of pNP, regarding specific cell targeting and biodistribution with the IB supramolecular organization, stability and cost effectiveness. This renders a platform able to provide a sustained source of CXCR4-targeted pNPs that selectively accumulate in tumor cells in a CXCR4⁺ colorectal cancer xenograft model. In addition, the proposed system could be potentially adapted to any other protein construct offering a plethora of possible new therapeutic applications in nanomedicine.

Protein nanoparticles are nontoxic, tuneable cell stressors

Aim: Nanoparticle–cell interactions can promote cell toxicity and stimulate particular behavioral patterns, but cell responses to protein nanomaterials have been poorly studied. Results: By repositioning oligomerization domains in a simple, modular self-assembling protein platform, we have generated closely related but distinguishable homomeric nanoparticles. Composed by building blocks with modular domains arranged in different order, they share amino acid composition. These materials, once exposed to cultured cells, are differentially internalized in absence of toxicity and trigger distinctive cell adaptive responses, monitored by the emission of tubular filopodia and enhanced drug sensitivity. Conclusion: The capability to rapidly modulate such cell responses by conventional protein engineering reveals protein nanoparticles as tuneable, versatile and potent cell stressors for cell-targeted conditioning.

Self-assembling toxin-based nanoparticles as self-delivered antitumoral drugs

Loading capacity and drug leakage from vehicles during circulation in blood is a major concern when developing nanoparticle-based cell-targeted cytotoxics. To circumvent this potential issue it would be convenient the engineering of drugs as self-delivered nanoscale entities, devoid of any heterologous carriers. In this context, we have here engineered potent protein toxins, namely segments of the diphtheria toxin and the Pseudomonas aeruginosa exotoxin as self-assembling, self-delivered therapeutic materials targeted to CXCR4⁺ cancer stem cells. The systemic administration of both nanostructured drugs in a colorectal cancer xenograft mouse model promotes efficient and specific local destruction of target tumor tissues and a significant reduction of the tumor volume. This observation strongly supports the concept of intrinsically functional protein nanoparticles, which having a dual role as drug and carrier, are designed to be administered without the assistance of heterologous vehicles.

Improving Biomaterials Imaging for Nanotechnology: Rapid Methods for Protein Localization at Ultrastructural Level

The preparation of biological samples for electron microscopy is material- and time-consuming because it is often based on long protocols that also may produce artifacts. Protein labeling for transmission electron microscopy (TEM) is such an example, taking several days. However, for protein-based nanotechnology, high resolution imaging techniques are unique and crucial tools for studying the spatial distribution of these molecules, either alone or as components of biomaterials. In this paper, we tested two new short methods of immunolocalization for TEM, and compared them with a standard protocol in qualitative and quantitative approaches by using four protein-based nanoparticles. We reported a significant increase of labeling per area of nanoparticle in both new methodologies (H = 19.811; p < 0.001) with all the model antigens tested: GFP (H = 22.115; p < 0.001), MMP-2 (H = 19.579; p < 0.001), MMP-9 (H = 7.567; p < 0.023), and IFN-γ (H = 62.110; p < 0.001). We also found that the most suitable protocol for labeling depends on the nanoparticle's tendency to aggregate. Moreover, the shorter methods reduce artifacts, time (by 30%), residues, and reagents hindering, losing, or altering antigens, and obtaining a significant increase of protein localization (of about 200%). Overall, this study makes a step forward in the development of optimized protocols for the nanoscale localization of peptides and proteins within new biomaterials.

Engineering multifunctional protein nanoparticles by in vitro disassembling and reassembling of heterologous building blocks

The engineering of protein self-assembling at the nanoscale allows the generation of functional and biocompatible materials, which can be produced by easy biological fabrication. The combination of cationic and histidine-rich stretches in fusion proteins promotes oligomerization as stable protein-only regular nanoparticles that are composed by a moderate number of building blocks. Among other applications, these materials are highly appealing as tools in targeted drug delivery once empowered with peptidic ligands of cell surface receptors. In this context, we have dissected here this simple technological platform regarding the controlled disassembling and reassembling of the composing building blocks. By applying high salt and imidazole in combination, nanoparticles are disassembled in a process that is fully reversible upon removal of the disrupting agents. By taking this approach, we accomplish here the in vitro generation of hybrid nanoparticles formed by heterologous building blocks. This fact demonstrates the capability to generate multifunctional and/or multiparatopic or multispecific materials usable in nanomedical applications.

Intrinsic functional and architectonic heterogeneity of tumor-targeted protein nanoparticles

Self-assembling proteins are gaining attention as building blocks for application-tailored nanoscale materials. This is mostly due to the biocompatibility, biodegradability, and functional versatility of peptide chains. Such a potential for adaptability is particularly high in the case of recombinant proteins, which are produced in living cells and are suitable for genetic engineering. However, how the cell factory itself and the particular protein folding machinery influence the architecture and function of the final material is still poorly explored. In this study we have used diverse analytical approaches, including small-angle X-ray scattering (SAXS) and field emission scanning electron microscopy (FESEM) to determine the fine architecture and geometry of recombinant, tumor-targeted protein nanoparticles of interest as drug carriers, constructed on a GFP-based modular scheme. A set of related oligomers were produced in alternative Escherichia coli strains with variant protein folding networks. This resulted in highly regular populations of morphometric types, ranging from 2.4 to 28 nm and from spherical- to rod-shaped materials. These differential geometric species, whose relative proportions were determined by the features of the producing strain, were found associated with particular fluorescence emission, cell penetrability and receptor specificity profiles. Then, nanoparticles with optimal properties could be analytically identified and further isolated from producing cells for use. The cell's protein folding machinery greatly modulates the final geometry reached by the constructs, which in turn defines the key parameters and biological performance of the material.

Technological Microbiology: Development and Applications

Over thousands of years, modernization could be predicted for the use of microorganisms in the production of foods and beverages. However, the current accelerated pace of new food production is due to the rapid incorporation of biotechnological techniques that allow the rapid identification of new molecules and microorganisms or even the genetic improvement of known species. At no other time in history have microorganisms been so present in areas such as agriculture and medicine, except as recognized villains. Currently, however, beneficial microorganisms such as plant growth promoters and phytopathogen controllers are required by various agricultural crops, and many species are being used as biofactories of important pharmacological molecules. The use of biofactories does not end there: microorganisms have been explored for the synthesis of diverse chemicals, fuel molecules, and industrial polymers, and strains environmentally important due to their biodecomposing or biosorption capacity have gained interest in research laboratories and in industrial activities. We call this new microbiology Technological Microbiology, and we believe that complex techniques, such as heterologous expression and metabolic engineering, can be increasingly incorporated into this applied science, allowing the generation of new and improved products and services.