A Review of Protein- and Peptide-Based Chemical Conjugates: Past, Present, and Future

Focus on therapeutic peptides and their delivery

Peptides are bioactive intermediates between small organic molecules and large biological compounds like antibodies or proteins. These compounds play a unique and valuable role as therapeutic agents, owing to their unique biochemical properties and versatility in treating a wide range of diseases such as metabolic disorders, cancer therapy, antimicrobial and anti-inflammatory agents. The global peptide therapeutics market is projected to exceed USD 50 billion by 2024, reflecting the increasing demand and interest in this field. Therapeutic peptides offer an optimal balance of specificity, safety, and molecular size, providing greater precision in targeting specific receptors with fewer off-target effects and reduced toxicity compared to small-organic drugs. Peptides also exhibit enhanced tissue penetration and present simpler, cheaper manufacturing processes with lower immunogenicity. To date, around 100 peptides have attained clinical approval in major markets, with nearly half of these approvals occurring in the past 20 years. This trend highlights the growing importance and therapeutic potential of peptides in modern medicine, explaining the substantial market associated with these treatments. The review presents a detailed comparison of the major parenteral administration modes for therapeutic peptides, specifically subcutaneous and intravenous routes. We highlight how these methods impact the pharmacokinetic profiles of peptides and influence patient outcomes, providing critical insights into the advantages and limitations of each route. Finally, a significant aspect of this review is its focus on innovative drug delivery systems and formulations designed to address the challenges of peptide delivery, namely stability, bioavailability, and therapeutic efficacy.

Modular Calcium-Responsive and CD9-Targeted Phospholipase System Enhancing Endosomal Escape for DNA Delivery

Gene delivery systems must overcome multiple barriers, with endosomal escape representing a prominent obstacle. We have previously shown that a bacterial phospholipase C (PLC) enabled endosomal escape of a non-viral protein-based DNA delivery system termed TFAMoplex. Building upon this, this work introduces a calcium-responsive system designed to enhance endosomal escape through non-covalent capturing of PLC to the TFAMoplex followed by its release within endosomes and nanobody-mediated targeting to the endosomal membrane. This approach leads to improved TFAMoplexes enabling transfection of HeLa cells in full serum with a half maximal effective concentration (EC50) of less than 200 ng DNA per mL serum, using only 5 nM PLC. Particularly, the modular capture, release and targeting system could potentially be adapted to other delivery agents previously constrained by poor endosomal escape. These findings present a promising strategy to achieve efficient endosomal escape, offering prospects for improved delivery of macromolecules, in particular nucleic acids.

Silicon-Based Linkers for Tunable Acid-Sensitive Drug Release from Polymeric Nanoparticles

Active Pharmaceutical Ingredients (APIs) may benefit from a carrier to improve their pharmacokinetic and pharmacodynamic properties. Core-crosslinked polymeric micelles (CCPMs) are carriers for hydrophobic small molecule APIs. In CCPMs, APIs are generally covalently coupled to the core of the micelles by use of a linker, which can be tailored to adjust the release rate of the API. Acid triggered release is promising because of local acidic environment in the tissue of interest, and expected uptake via endocytosis. In the present study, silyl-based linkers were synthesized, and attached to gemcitabine as model API to investigate the tunability of release by introduction of different substituents. Attachment was achieved via an Si ether bond, with the linker coupled to the primary alcohol functionality on gemcitabine. By varying the substituents on the silyl atom, we could vary the release half-life (t1/2) of native gemcitabine from <1 hour->96 hours at pH 5.0 at 37 °C, compared to a t1/2 of 24->240 hours at pH 7.4 at 37 °C, respectively. The steric hinderance caused by substituents contributed to an increase of t1/2 at pH 5.0, as the largest substituents resulted in the slowest release. Extension to other APIs and other carriers is clearly possible.

Method for Screening Sodium Cyanoborohydride for Free Cyanide Content and Its Impact on Bioconjugation Chemistry

Sodium cyanoborohydride (CBH) is commonly used as a mild reducing agent in the reductive amination of aldehydes and free amines. Within the pharmaceutical industry, this reaction is employed in the bioconjugation of proteins and peptides. Free cyanide species such as HCN and NaCN are known residual impurities in CBH that can contribute to the formation of undesired side products including cyanoamines and cyanohydrins. In commercial processes, the potential for bound cyanated species requires an analytical control strategy to monitor and mitigate any risk to human health. Given these concerns, minimization of cyanated side products is of utmost priority and can be achieved through a robust control strategy of quantitative screening of starting materials for free cyanide. Alternative risk mitigation strategies such as purification of bound cyanide containing species to pure species are less effective due to minor chemical differences between the expected product and bound cyanide species. Herein, we present a simple chromatographic assay for the quantitation of free cyanide in the raw material sodium cyanoborohydride. Method development, robustness evaluation, and scientific soundness assessment are reported with excellent linearity, accuracy, precision, and specificity. Additionally, this method was applied for the evaluation of raw material supplied from 10 commercial sources, none of which report a specification for free cyanide within their certificate of analysis. The measured free cyanide from these vendors ranged from 8 to 80 mM concentration, thereby confirming the value of screening these raw materials. Finally, we demonstrate the impact of free cyanide on a model bioconjugation reaction between ornithine and glyceraldehyde.

Design and assessment of lipase-CuO nanoparticle conjugates for enhanced antimicrobial efficacy against clinical pathogens

In the battle against clinical infections particularly the resistant pathogens, the creation of new antimicrobial drugs is essential. This study focuses on synthesis and characterization of Lipase-CuO nanoparticle conjugates in order to investigate their antibacterial efficiency. Lipase enzyme and CuO nanoparticles were synthesized biologically by specific selected fungal strains. Statistical optimization of lipase enzyme was done using a Plackett-Burman design giving two enhancement models for lipase production with increasing in productivity up to 143.43% (2800 U/ml). Copper oxide (CuO) nanoparticles were characterized using visual indication of greenish color formation, UV-vis spectrum analysis which revealed a strong peak at 300 nm. Also, CuO nanoparticles appeared as distinct, well-dispersed spherical particles with average size of 71.035 nm using TEM, while conjugate appears as large protein molecules linked to the nanoparticles. Also, using techniques like energy dispersive X-ray (EDAX) the resultant conjugates formation was confirmed as the elemental analysis approved its formation. The antimicrobial activity of Lipase-CuO nanoparticles conjugates was tested against a range of clinical pathogens. The results demonstrated a significant increase in antimicrobial potency compared to both CuO nanoparticles and lipase alone particularly against E. coli strain NRC B-3703 with remarkable increase of 373.6% and 75% followed by S. aureus with increase of 50 and 42.8%compared to that of individual CuO nanoparticles and lipase enzyme, respectively. These findings suggest that Lipase-CuO nanoparticle conjugates hold great promise as a novel antimicrobial strategy, offering a potential solution to combat bacterial infections, especially those caused by multidrug-resistant strains. The study highlights the importance of nanotechnology in enhancing the efficacy of traditional antimicrobial agents and opens new avenues for targeted antimicrobial therapies.

Heterobifunctional cross-linker with dinitroimidazole and azide modules for protein and oligonucleotide functionalization

Dinitroimidazole (DNIm) was recently identified as a powerful bioconjugation agent that could selectively modify thiol over amine on biomolecules at an ultrahigh speed in an aqueous buffer. However, its derivative containing a DNIm module and a terminal alkyne module failed to construct functional agents bearing a DNIm warhead via the CuAAC reaction. To solve this problem, a heterobifunctional cross-linker was designed and synthesized by linking a DNIm module with an azide module via an oxoaliphatic amido bond spacer arm. Its two modules, DNIm and azide, reacted with a thiol and cyclooctyne, respectively, in an orthogonal way. The cross-linker facilitated the preparation of various functional agents bearing a DNIm warhead via SPAAC reaction and was further applied to protein functionalization (including biotinylation and fluorescence labeling) and oligonucleotide functionalization (including PEGylation, oligonucleotide-peptide and oligonucleotide-protein conjugate). Thus, the cross-linker not only provided convenient access to those functional agents bearing a DNIm warhead but also combined DNIm chemistry with click chemistry of SPAAC to enlarge their respective application range in the bioconjugation field.

Development and applications of enzymatic peptide and protein ligation

Chemical synthesis of complex peptides and proteins continues to play increasingly important roles in industry and academia, where strategies for covalent ligation of two or more peptide fragments to produce longer peptides and proteins in convergent manners have become critical. In recent decades, efficient and site-selective ligation strategies mediated by exploiting the biocatalytic capacity of nature's diverse toolkit (i.e., enzymes) have been widely recognized as a powerful extension of existing chemical strategies. In this review, we present a chronological overview of the development of proteases, transpeptidases, transglutaminases, and ubiquitin ligases. We survey the different properties between the ligation reactions of various enzymes, including the selectivity and efficiency of the reaction, the ligation "scar" left in the product, the type of amide bond formed (natural or isopeptide), the synthetic availability of the reactants, and whether the enzymes are orthogonal to another. This review also describes how the inherent specificity of these enzymes can be exploited for peptide and protein ligation.

Conjugated therapeutic proteins as a treatment for bacteria which trigger cancer development

In recent years, an increasing amount of research has focused on the intricate and complex correlation between bacterial infections and the development of cancer. Some studies even identified specific bacterial species as potential culprits in the initiation of carcinogenesis, which generated a great deal of interest in the creation of innovative therapeutic strategies aimed at addressing both the infection and the subsequent risk of cancer. Among these strategies, there has been a recent emergence of the use of conjugated therapeutic proteins, which represent a highly promising avenue in the field of cancer therapeutics. These proteins offer a dual-targeting approach that seeks to effectively combat both the bacterial infection and the resulting malignancies that may arise because of such infections. This review delves into the landscape of conjugated therapeutic proteins that have been intricately designed with the purpose of specifically targeting bacteria that have been implicated in the induction of cancer.

Polyethylene Glycol-Based Polymer-Drug Conjugates: Novel Design and Synthesis Strategies for Enhanced Therapeutic Efficacy and Targeted Drug Delivery

Due to their potential to enhance therapeutic results and enable targeted drug administration, polymer-drug conjugates that use polyethylene glycol (PEG) as both the polymer and the linker for drug conjugation have attracted much research. This study seeks to investigate recent developments in the design and synthesis of PEG-based polymer-drug conjugates, emphasizing fresh ideas that fill in existing knowledge gaps and satisfy the increasing need for more potent drug delivery methods. Through an extensive review of the existing literature, this study identifies key challenges and proposes innovative strategies for future investigations. The paper presents a comprehensive framework for designing and synthesizing PEG-based polymer-drug conjugates, including rational molecular design, linker selection, conjugation methods, and characterization techniques. To further emphasize the importance and adaptability of PEG-based polymer-drug conjugates, prospective applications are highlighted, including cancer treatment, infectious disorders, and chronic ailments.

Scission-Enhanced Molecular Imaging (SEMI)

Positron emission tomography (PET) imaging methods have advanced our understanding of human biology, while targeted radiotherapeutic drug treatments are now routinely used clinically. The field is expected to grow considerably based on an expanding repertoire of available affinity ligands, radionuclides, conjugation chemistries, and their FDA approvals. With this increasing use, strategies for dose reduction have become of high interest to protect patients from unnecessary and off-target toxicity. Here, we describe a simple and powerful method, scission-enhanced molecular imaging (SEMI). The technique allows for rapid corporeal elimination of radionuclides once imaging or theranostic treatment is completed and relies on "click-to-release" bioorthogonal linkers.

Unlocking nature's arsenal: Nanotechnology for targeted delivery of venom toxins in cancer therapy

AIM

The aim of the present review is to shed light on the nanotechnological approaches adopted to overcome the shortcomings associated with the delivery of venom peptides which possess inherent anti-cancer properties.

BACKGROUND

Venom peptides although have been reported to demonstrate anti-cancer effects, they suffer from several disadvantages such as in vivo instability, off-target adverse effects, limited drug loading and low bioavailability. This review presents a comprehensive compilation of different classes of nanocarriers while underscoring their advantages, disadvantages and potential to carry such peptide molecules for in vivo delivery. It also discusses various nanotechnological aspects such as methods of fabrication, analytical tools to assess these nanoparticulate formulations, modulation of nanocarrier polymer properties to enhance loading capacity, stability and improve their suitability to carry toxic peptide drugs.

CONCLUSION

Nanotechnological approaches bear great potential in delivering venom peptide-based molecules as anticancer agents by enhancing their bioavailability, stability, efficacy as well as offering a spatiotemporal delivery approach. However, the challenges associated with toxicity and biocompatibility of nanocarriers must be duly addressed.

PERSPECTIVES

The everlasting quest for new breakthroughs for safer delivery of venom peptides in human subjects is fuelled by unmet clinical needs in the current landscape of chemotherapy. In addition, exhaustive efforts are required in obtaining and purifying the venom peptides followed by designing and optimizing scale up technologies.

Precision targeting in oncology: The future of conjugated drugs

Coupled drugs, especially antibody-coupled drugs (ADCs), are a hot topic in oncology. As the development of ADCs has progressed, different coupling modes have emerged, inspired by their structural design have emerged. Technological advances have led to interweaving and collision of old and new concepts of coupled drugs, and have even challenged the concepts and techniques of coupled drugs at this stage. For example, antibody-oligonucleotide conjugates are a new class of chimeric biomolecules synthesized by coupling oligonucleotides with monoclonal antibodies through linkers, offering precise targeting and improved pharmacokinetic properties. This study aimed to elucidate the mechanism of action of coupled drugs and their current development status in antitumor therapy to provide better strategies for antitumor therapy.

NSPs: chromogenic linkers for fast, selective, and irreversible cysteine modification

The addition of a sulfhydryl group to water-soluble N-alkyl(o-nitrostyryl)pyridinium ions (NSPs) followed by fast and irreversible cyclization and aromatization results in a stable S-C sp2-bond. The reaction sequence, termed Click & Lock, engages accessible cysteine residues under the formation of N-hydroxy indole pyridinium ions. The accompanying red shift of >70 nm to around 385 nm enables convenient monitoring of the labeling yield by UV-vis spectroscopy at extinction coefficients of ≥2 × 104 M-1 cm-1. The versatility of the linker is demonstrated in the stapling of peptides and the derivatization of proteins, including the modification of reduced trastuzumab with Val-Cit-PAB-MMAE. The high stability of the linker in human plasma, fast reaction rates (k app up to 4.4 M-1 s-1 at 20 °C), high selectivity for cysteine, favorable solubility of the electrophilic moiety and the bathochromic properties of the Click & Lock reaction provide an appealing alternative to existing methods for cysteine conjugation.

PEG modification increases thermostability and inhibitor resistance of Bst DNA polymerase

Polyethylene glycol modification (PEGylation) is a widely used strategy to improve the physicochemical properties of various macromolecules, especially protein drugs. However, its application in enhancing the performance of enzymes for molecular biology remains underexplored. This study explored the PEGylation of Bst DNA polymerase, determining optimal modification reaction conditions. In comparison to the unmodified wild-type counterpart, the modified Bst DNA polymerase exhibited significantly improved activity, thermal stability, and inhibitor tolerance during loop-mediated isothermal amplification. When applied for the detection of Salmonella in crude samples, the modified enzyme demonstrated a notably accelerated reaction rate. Therefore, PEGylation emerges as a viable strategy for refining DNA polymerases, helping in the development of novel molecular diagnostic reagents.

Reversible Chemical Modification of Antibody Effector Function Mitigates Unwanted Systemic Immune Activation

Antibody effector functions including antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) are mediated through the interaction of the antibody Fc region with Fcγ receptors present on immune cells. Several approaches have been used to modulate antibody Fc-Fcγ interactions with the goal of driving an effective antitumor immune response, including Fc point mutations and glycan modifications. However, robust antibody-Fcγ engagement and immune cell binding of Fc-enhanced antibodies in the periphery can lead to the unwanted induction of systemic cytokine release and other dose-limiting infusion-related reactions. Creating a balance between effective engagement of Fcγ receptors that can induce antitumor activity without incurring systemic immune activation is an ongoing challenge in the field of antibody and immuno-oncology therapeutics. Herein, we describe a method for the reversible chemical modulation of antibody-Fcγ interactions using simple poly(ethylene glycol) (PEG) linkers conjugated to antibody interchain disulfides with maleimide attachments. This method enables dosing of a therapeutic with muted Fcγ engagement that is restored in vivo in a time-dependent manner. The technology was applied to an effector function enhanced agonist CD40 antibody, SEA-CD40, and experiments demonstrate significant reductions in Fc-induced immune activation in vitro and in mice and nonhuman primates despite showing retained efficacy and improved pharmacokinetics compared to the parent antibody. We foresee that this simple, modular system can be rapidly applied to antibodies that suffer from systemic immune activation due to peripheral FcγR binding immediately upon infusion.

Sortase A-Based Post-translational Modifications on Encapsulin Nanocompartments

Protein-based encapsulin nanocompartments, known for their well-defined structures and versatile functionalities, present promising opportunities in the fields of biotechnology and nanomedicine. In this investigation, we effectively developed a sortase A-mediated protein ligation system in Escherichia coli to site-specifically attach target proteins to encapsulin, both internally and on its surfaces without any further in vitro steps. We explored the potential applications of fusing sortase enzyme and a protease for post-translational ligation of encapsulin to a green fluorescent protein and anti-CD3 scFv. Our results demonstrated that this system could attach other proteins to the nanoparticles' exterior surfaces without adversely affecting their folding and assembly processes. Additionally, this system enabled the attachment of proteins inside encapsulins which varied shapes and sizes of the nanoparticles due to cargo overload. This research developed an alternative enzymatic ligation method for engineering encapsulin nanoparticles to facilitate the conjugation process.

Study of uricase-polynorbornene conjugates derived from grafting-from ring-opening metathesis polymerization

PEGylation has been the 'gold standard' in bioconjugation due to its ability to improve the pharmacokinetics and pharmacodynamics of native proteins. However, growing clinical evidence of hypersensitivity reactions to PEG due to pre-existing anti-PEG antibodies in healthy humans have raised concerns. Advancements in controlled polymerization techniques and conjugation chemistries have paved the way for the development of protein-polymer conjugates that can circumvent these adverse reactions while retaining the benefits of such modifications. Herein, we show the development of polynorbornene based bioconjugates of therapeutically relevant urate oxidase (UO) enzymes used in the treatment of gout synthesized by grafting-from ring-opening metathesis polymerization (ROMP). Notably, these conjugates exhibit comparable levels of bioactivity to PEGylated UO and demonstrate increased stability across varying temperatures and pH conditions. Immune recognition of conjugates by anti-UO antibodies reveal low protein immunogenicity following the conjugation process. Additionally, UO conjugates employing zwitterionic polynorbornene successfully avoid recognition by anti-PEG antibodies, further highlighting a potential replacement for PEG.

Mycoplasma agalactiae Vaccines: Current Status, Hurdles, and Opportunities Due to Advances in Pathogenicity Studies

Contagious agalactia (CA) is a serious multietiological disease whose classic etiological agent is Mycoplasma agalactiae and which causes high morbidity and mortality rates in infected herds. CA is classified as a notifiable disease by the World Organization for Animal Health due to its significant worldwide economic impact on livestock, primarily involving goat and sheep farms. The emergence of atypical symptoms and strains of M. agalactiae in wildlife ungulates reestablishes its highly plastic genome and is also of great epidemiological significance. Antimicrobial therapy is the main form of control, although several factors, such as intrinsic antibiotic resistance and the selection of resistant strains, must be considered. Available vaccines are few and mostly inefficient. The virulence and pathogenicity mechanisms of M. agalactiae mainly rely on surface molecules that have direct contact with the host. Because of this, they are essential for the development of vaccines. This review highlights the currently available vaccines and their limitations and the development of new vaccine possibilities, especially considering the challenge of antigenic variation and dynamic genome in this microorganism.

Diligent Design Enables Antibody-ASO Conjugates with Optimal Pharmacokinetic Properties

Antisense-oligonucleotides (ASOs) are a promising drug modality for the treatment of neurological disorders, but the currently established route of administration via intrathecal delivery is a major limitation to its broader clinical application. An attractive alternative is the conjugation of the ASO to an antibody that facilitates access to the central nervous system (CNS) after peripheral application and target engagement at the blood-brain barrier, followed by transcytosis. Here, we show that the diligent conjugate design of Brainshuttle-ASO conjugates is the key to generating promising delivery vehicles and thereby establishing design principles to create optimized molecules with drug-like properties. An innovative site-specific transglutaminase-based conjugation technology was chosen and optimized in a stepwise process to identify the best-suited conjugation site, tags, reaction conditions, and linker design. The overall conjugation performance was found to be specifically governed by the choice of buffer conditions and the structure of the linker. The combination of the peptide tags YRYRQ and RYESK was chosen, showing high conjugation fidelity. Elaborate conjugate analysis revealed that one leading differentiating factor was hydrophobicity. The increase of hydrophobicity by the ASO payload could be mitigated by the appropriate choice of conjugation site and the heavy chain position 297 proved to be the most optimal. Evaluating the properties of the linker suggested a short bicyclo[6.1.0]nonyne (BCN) unit as best suited with regards to conjugation performance and potency. Promising in vitro activity and in vivo pharmacokinetic behavior of optimized Brainshuttle-ASO conjugates, based on a microtubule-associated protein tau (MAPT) targeting oligonucleotide, suggest that such designs have the potential to serve as a blueprint for peripherally delivered ASO-based drugs for the CNS in the future.

Site-Selective Functionalized PD-1 Mutant for a Modular Immunological Activity against Cancer Cells

Targeting immune checkpoints is a well-established strategy in cancer therapy, and antibodies blocking PD-1/PD-L1 interactions to restore the immunological activity against cancer cells have been clinically validated. High-affinity mutants of the PD-1 ectodomain have recently been proposed as an alternative to antibodies to target PD-L1 on cancer cells, shedding new light on this research area. In this dynamic scenario, the PD-1 mutant, here reported, largely expands the chemical space of nonantibody and nonsmall-molecule inhibitor therapeutics that can be used to target cancer cells overexpressing PD-L1 receptors. The polyethylene glycol moieties and the immune response-stimulating carbohydrates, used as site-selective tags, represent the proof of concept for future applications.

Site-selective post-modification of short α/γ hybrid foldamers: a powerful approach for molecular diversification towards biomedical applications

The extensive research work in the exhilarating area of foldamers (artificial oligomers possessing well-defined conformation in solution) has shown them to be promising candidates in biomedical research and materials science. The post-modification approach is successful in peptides, proteins, and polymers to modulate their functions. To the best of our knowledge, site-selective post-modification of a foldamer affording molecules with different pendant functional groups within a molecular scaffold has not yet been reported. We demonstrate for the first time that late-stage site-selective functionalization of short hybrid oligomers is an efficient approach to afford molecules with diverse functional groups. In this article, we report the design and synthesis of hybrid peptides with repeating units of leucine (Leu) and 5-amino salicylic acid (ASA), regioselective post-modification, conformational analyses (based on solution-state NMR, circular dichroism and computational studies) and morphological studies of the peptide nanostructures. As a proof-of-concept, we demonstrate the applications of differently modified peptides as drug delivery agents, imaging probes, and anticancer agents. The novel feature of the work is that the difference in reactivity of two phenolic OH groups in short biomimetic peptides was utilized to achieve site-selective post-modification. It is challenging to apply the same approach to short α-peptides having a poor folding tendency, and their post-functionalization may considerably affect their conformation.

Therapeutic Oligonucleotides: An Outlook on Chemical Strategies to Improve Endosomal Trafficking

The potential of oligonucleotide therapeutics is undeniable as more than 15 drugs have been approved to treat various diseases in the liver, central nervous system (CNS), and muscles. However, achieving effective delivery of oligonucleotide therapeutics to specific tissues still remains a major challenge, limiting their widespread use. Chemical modifications play a crucial role to overcome biological barriers to enable efficient oligonucleotide delivery to the tissues/cells of interest. They provide oligonucleotide metabolic stability and confer favourable pharmacokinetic/pharmacodynamic properties. This review focuses on the various chemical approaches implicated in mitigating the delivery problem of oligonucleotides and their limitations. It highlights the importance of linkers in designing oligonucleotide conjugates and discusses their potential role in escaping the endosomal barrier, a bottleneck in the development of oligonucleotide therapeutics.

Iron-Gallic Acid Peptide Nanoparticles as a Versatile Platform for Cellular Delivery with Synergistic ROS Enhancement Effect

Cytosolic delivery of peptides is of great interest owing to their biological functions, which could be utilized for therapeutic applications. However, their susceptibility to enzymatic degradation and multiple cellular barriers generally hinders their clinical application. Integration into nanoparticles, which can enhance the stability and membrane permeability of bioactive peptides, is a promising strategy to overcome extracellular and intracellular obstacles. Herein, we present a versatile platform for the cellular delivery of various cargo peptides by integration into metallo-peptidic coordination nanoparticles. Both termini of cargo peptides were conjugated with gallic acid (GA) to assemble GA-modified peptides into nanostructures upon coordination of Fe(III). Initial pre-complexation of Fe(III) by poly-(vinylpolypyrrolidon) (PVP) as a template favored the formation of nanoparticles, which are able to deliver the peptides into cells efficiently. Iron-gallic acid peptide nanoparticles (IGPNs) are stable in water and are supposed to generate reactive oxygen species (ROS) from endogenous H₂O₂ in cells via the Fenton reaction. The strategy was successfully applied to an exemplary set of peptide sequences varying in length (1-7 amino acids) and charge (negative, neutral, positive). To confirm the capability of transporting bioactive cargos into cells, pro-apoptotic peptides were integrated into IGPNs, which demonstrated potent killing of human cervix carcinoma HeLa and murine neuroblastoma N2a cells at a 10 µM peptide concentration via the complementary mechanisms of peptide-triggered apoptosis and Fe(III)-mediated ROS generation. This study demonstrates the establishment of IGPNs as a novel and versatile platform for the assembly of peptides into nanoparticles, which can be used for cellular delivery of bioactive peptides combined with intrinsic ROS generation.

Chemically Enhanced Peptide and Protein Therapeutics

Proteins and peptides are on the rise as therapeutic agents and represent a higher percentage of approved drugs each year: 24% in 2021 vs [...]