Site-directed cysteine coupling of disulfide-containing non-antibody carrier proteins(THIOCAPs)

The development of a new generation of nonantibody protein drug delivery systems requires site-directed conjugation strategies to produce homogeneous,reproducible and scalable nanomedicines.For that,the genetic addition of cysteine residues into solvent-exposed positions allows the thiol-mediated cysteine coupling of therapeutic drugs into protein-based nanocarriers.However,the high reactivity of unpaired cysteine residues usually reduces protein stability,consequently imposing the use of more methodologically demanding purification procedures.This is especially relevant for disulfide-containing nanocarriers,as previously observed in THIOMABs.Moreover,although many protein scaffolds and targeting ligands are also rich in disulfide bridges,the use of these methodologies over emerging non-antibody carrier proteins has been completely neglected.Here,we report the development of a simple and straightforward procedure for a onestep production and site-directed cysteine conjugation of disulfide-containing non-antibody thiolated carrier proteins(THIOCAPs).This method is validated in a fluorescent C-X-C chemokine receptor 4(CXCR4)-targeted multivalent nanocarrier containing two intramolecular disulfide bridges and one reactive cysteine residue strategically placed into a solvent-exposed position(THIO-T22-GFP-H6)for drug conjugation and in a humanized alternative intended for clinical applications(T22-HSNBT-H6).Thus,we produce very stable,homogeneous and fully functional antitumoral nanoconjugates(THIO-T22-GFP-H6-MMAE and T22-HSNBT-H6-MMAE)that selectively eliminate target cancer cells via CXCR4-receptor.Altogether,the developed methodology appears as a powerful tool for the rational engineering of emerging non-antibody,cell-targeted protein nanocarriers that contain disulfide bridges together with a solvent-exposed reactive cysteine(THIOCAP).This should pave the way for the development of a new generation of stable,homogeneous and efficient nanomedicines.

Self-assembling protein nanocarrier for selective delivery of cytotoxic polypeptides to CXCR4^(+) head and neck squamous cell carcinoma tumors

Loco-regional recurrences and distant metastases represent the main cause of head and neck squamous cell carcinoma(HNSCC) mortality. The overexpression of chemokine receptor 4(CXCR4) in HNSCC primary tumors associates with higher risk of developing loco-regional recurrences and distant metastases, thus making CXCR4 an ideal entry pathway for targeted drug delivery. In this context, our group has generated the self-assembling protein nanocarrier T22-GFP-H6, displaying multiple T22 peptidic ligands that specifically target CXCR4. This study aimed to validate T22-GFP-H6 as a suitable nanocarrier to selectively deliver cytotoxic agents to CXCR4^(+)tumors in a HNSCC model. Here we demonstrate that T22-GFP-H6 selectively internalizes in CXCR4^(+)HNSCC cells, achieving a high accumulation in CXCR4^(+)tumors in vivo, while showing negligible nanocarrier distribution in non-tumor bearing organs. Moreover, this T22-empowered nanocarrier can incorporate bacterial toxin domains to generate therapeutic nanotoxins that induce cell death in CXCR4-overexpressing tumors in the absence of histological alterations in normal organs. Altogether, these results show the potential use of this T22-empowered nanocarrier platform to incorporate polypeptidic domains of choice to selectively eliminate CXCR4^(+)cells in HNSCC. Remarkably, to our knowledge, this is the first study testing targeted proteinonly nanoparticles in this cancer type, which may represent a novel treatment approach for HNSCC patients.

Controlling self-assembling and tumor cell-targeting of protein-only nanoparticles through modular protein engineering

Modular protein engineering is suited to recruit complex and multiple functionalities in single-chain polypeptides. Although still unexplored in a systematic way, it is anticipated that the positioning of functional domains would impact and refine these activities, including the ability to organize as supramolecular entities and to generate multifunctional protein materials. To explore this concept, we have repositioned functional segments in the modular protein T22-GFP-H6 and characterized the resulting alternative fusions. In T22-GFP-H6, the combination of T22 and H6 promotes selfassembling as regular nanoparticles and selective binding and internalization of this material in CXCR4-overexpressing tumor cells, making them appealing as vehicles for selective drug delivery. The results show that the pleiotropic activities are dramatically affected in module-swapped constructs, proving the need of a carboxy terminal positioning of H6 for protein self-assembling, and the accommodation of T22 at the amino terminus as a requisite for CXCR4^+ cell binding and internalization. Furthermore, the failure of self-assembling as regular oligomers reduces cellular penetrability of the fusions while keeping the specificity of the T22-CXCR4 interaction.All these data instruct how multifunctional nanoscale protein carriers can be designed for smart, protein-driven drug delivery, not only for the treatment of CXCR4^+ human neoplasias, but also for the development of anti-HIV drugs and other pathologies in which CXCR4 is a relevant homing marker.

Endosomal escape of protein nanoparticles engineered through humanized histidine-rich peptides

Poly-histidine peptides such as H6(HHHHHH)are used in protein biotechnologies as purification tags,protein-assembling agents and endosomal-escape entities.The pleiotropic properties of such peptides make them appealing to design protein-based smart materials or nanoparticles for imaging or drug delivery to be produced in form of recombinant proteins.However,the clinical applicability of H6-tagged proteins is restricted by the potential immunogenicity of these segments.In this study,we have explored several humanized histidine-rich peptides in tumor-targeted modular proteins,which can specifically bind and be internalized by the target cells through the tumoral marker CXCR4.We were particularly interested in exploring how protein purification,self-assembling and endosomal escape perform in proteins containing the variant histidine-rich tags.Among the tested candidates,the peptide H5 E(HEHEHEHEH)is promising as a good promoter of endosomal escape of the associated fulllength protein upon endosomal internalization.The numerical modelling of cell penetration and endosomal escape of the tested proteins has revealed a negative relationship between the amount of protein internalized into target cells and the efficiency of cytoplasmic release.This fact demonstrates that the His-mediated,proton sponge-based endosomal escape saturates at moderate amounts of internalized protein,a fact that might be critical for the design of protein materials for cytosolic molecular delivery.

Engineering a recombinant chlorotoxin as celltargeted cytotoxic nanoparticles

Cytotoxic proteins have a wide applicability in human therapies, especially in those conditions that require efficient and selective cell killing, such as cancer. Chlorotoxin (CTX) is a small (4 kDa) basic peptide from the venom of the yellow scorpion Leiurus quinquestriatus , which blocks small-conductance chloride channels thus paralyzing the scorpion prey. Being not extremely potent as a cytotoxin (for instance when compared with ribosome-inactivating proteins), it has gained interest as a targeting agent.

The spectrum of building block conformers sustains the biophysical properties of clinically-oriented self-assembling protein nanoparticles

Histidine-rich peptides confer self-assembling properties to recombinant proteins through the supramolecular coordination with divalent cations.This fact allows the cost-effective,large-scale generation of microscopic and macroscopic protein materials with intriguing biomedical properties.Among such materials,resulting from the simple bioproduction of protein building blocks,homomeric nanoparticles are of special value as multivalent interactors and drug carriers.Interestingly,we have here identified that the assembly of a given His-tagged protein might render distinguishable categories of self-assembling protein nanoparticles.This fact has been scrutinized through the nanobody-containing fusion proteins EM1-GFP-H6 and A3C8-GFP-H6,whose biosynthesis results in two distinguishable populations of building blocks.In one of them,the assembling and disassembling is controllable by cations.However,a second population immediately self-assembles upon purification through a non-regulatable pathway,rendering larger nanoparticles with specific biological properties.The structural analyses of both model proteins and nanoparticles revealed important conformational variability in the building blocks.This fact renders different structural and functional categories of the final soft materials resulting from the participation of energetically unstable intermediates in the oligomerization process.These data illustrate the complexity of the Hismediated protein assembling in recombinant proteins but they also offer clues for a better design and refinement of protein-based nanomedicines,which,resulting from biological fabrication,show an architectonic flexibility unusual among biomaterials.