Zwitterionic Polymer Conjugated Glucagon-like Peptide-1 for Prolonged Glycemic Control

Polycarboxybetaine in advanced drug delivery systems: From structure-function relationship to therapeutic applications

Zwitterionic polycarboxybetaines (PCBs), combining quaternary ammonium cations and carboxylate anions in their repeating units, have emerged as promising materials for drug delivery applications. Their exceptional hydration, biocompatibility, and antifouling properties make them attractive alternatives to polyethylene glycol (PEG), particularly given growing concerns about immunogenicity of PEG. PCBs can be functionalized through various methods, including modification of side-chain moieties, adjustment of spacer length between charged groups, and incorporation of responsive elements. When applied to delivery drug, PCBs have been successfully developed into multiple formats including micelles, hydrogels, liposomes, and nanoparticles. Notably, in protein drug delivery, PCBs demonstrate significant advantages such as enhancing protein stability, extending circulation time, improving penetration through biological barriers, and reducing immunogenicity. Despite these promising features, several challenges remain, including complex synthesis requirements, limited mechanical properties, and pending FDA approval as pharmaceutical excipients. This review provides a comprehensive analysis of PCBs from the structure-function relationship, synthesis methods, and applications in drug delivery systems, while examining current limitations and future prospects.

Melanin-Inspired Maleimide Coatings on Various Substrates for Rapid Thiol Functionalization

In this study, a substrate-independent maleimide film is developed that can be formed under mild aqueous conditions (pH 7.4), and which allows rapid and efficient external thiol immobilization onto the coated surfaces. For the coating block, tyrosine-conjugated maleimide (Tyr-Mal) containing a phenolic amine moiety is prepared as a substrate-independent dormant coating precursor, wherein the maleimide component permits a rapid Michael addition reaction with the thiol moiety of interest. By mimicking natural melanogenesis, Tyr-Mal acts as a substrate for tyrosinase under physiological conditions (pH 7.4) to form a melanin-inspired maleimide (Mel-Mal) film on various substrates, including living cell surfaces. The resulting film undergoes a rapid surface reaction (< 30 min) with external thiol groups under mild aqueous conditions. Considering that a typical polydopamine film requires a long reaction time (≈3 h) under alkaline conditions (pH 8.5) to achieve thiol functionalization with low efficiency, the current surface platform demonstrates significant improvements in terms of its reaction kinetics and usability. Moreover, considering that thiol functionalization and surface coating are performed under mild aqueous conditions, it is expected that the developed Mel-Mal film will be a useful tool in the fields of cell surface engineering, microarrays, and high-throughput screening.

Strategies for extending the half-life of biotherapeutics: successes and complications

INTRODUCTION

Engineering of the drug half-life in vivo has become an integral part of modern biopharmaceutical development due to the fact that many proteins/peptides with therapeutic potential are quickly cleared by kidney filtration after injection and, thus, circulate only a few hours in humans (or just minutes in mice).

AREAS COVERED

Looking at the growing list of clinically approved biologics that have been modified for prolonged activity, and also the plethora of such drugs under preclinical and clinical development, it is evident that not one solution fits all needs, owing to the vastly different structural features and functional properties of the pharmacologically active entities. This article provides an overview of established half-life extension strategies, as well as of emerging novel concepts for extending the in vivo stability of biologicals, and their pros and cons.

EXPERT OPINION

Beyond the classical and still dominating technologies for improving drug pharmacokinetics and bioavailability, Fc fusion and PEGylation, various innovative approaches that offer advantages in different respects have entered the clinical stage. While the Fc fusion partner may be gradually superseded by engineered albumin-binding domains, chemical PEGylation may be replaced by biodegradable recombinant amino-acid polymers like PASylation, thus also offering a purely biotechnological manufacturing route.

A De Novo Strategy To Improve Pharmacokinetics of Proteins from mRNA Therapeutics via Zwitterionic Polypeptide Fusion

Achieving therapeutic efficacy in protein replacement therapies requires sustaining pharmacokinetic (PK) profiles, while maintaining the bioactivity of circulating proteins. This is often achieved via PEGylation in protein-based therapies, but it remains challenging for proteins produced in vivo in mRNA-based therapies due to the lack of a suitable post-translational modification method. To address this issue, we integrated a genetically encoded zwitterionic polypeptide, EKP, into mRNA constructs to enhance the PK properties of product proteins. Composed of alternating glutamic acid (E), lysine (K), and proline (P), EKP exhibits unique superhydrophilic properties and low immunogenicity. Our results demonstrate that EKP fusion significantly extends the circulation half-life of proteins expressed from mRNA while preserving their bioactivity using human interferon alpha and Neoleukin-2/15 as examples. This EKP fusion technology offers a new approach to overcoming the current limitations in mRNA therapeutics and has the potential to significantly advance the development of mRNA-based protein replacement therapy.

Enhancing the Therapeutic Efficacy of GLP-1 for Hyperglycemia Treatment: Overcoming Barriers of Oral Gene Therapy with Taurocholic Acid-Conjugated Protamine Sulfate and Calcium Phosphate

Activating the glucagon-like peptide-1 (GLP-1) receptor by oral nucleic acid delivery would be a promising treatment strategy against hyperglycemia due to its various therapeutic actions. However, GLP-1 receptor agonists are effective only in subcutaneous injections because they face multiple barriers due to harsh gastrointestinal tract (GIT) conditions before reaching the site of action. The apical sodium bile acid transporter (ASBT) pathway at the intestinal site could be an attractive target to overcome the problem. Herein, we used our previously established multimodal carrier system utilizing bile salt, protamine sulfate, and calcium phosphate as excipients (PTCA) and the GLP-1 gene as an active ingredient (GENE) to test the effects of different formulation doses against diabetes and obesity. The carrier system demonstrated the ability to protect the GLP-1 model gene encoded within the plasmid at the GIT and transport it via ASBT at the target site. A single oral dose, regardless of quantity, showed the generation of GLP-1 and insulin from the body and maintained the normoglycemic condition by improving insulin sensitivity and blood sugar tolerance for a prolonged period. This oral gene therapy approach shows significantly higher therapeutic efficacy in preclinical studies than currently available US Food and Drug Administration-approved GLP-1 receptor agonists such as semaglutide and liraglutide. Also, a single oral dose of GENE/PTCA is more effective than 20 insulin injections. Our study suggests that oral GENE/PTCA formulation could be a promising alternative to injection-based therapeutics for diabetics, which is effective in long-term treatment and has been found to be highly safe in all aspects of toxicology.

Zwitterionic Polymer: A New Paradigm for Protein Conjugation beyond PEG

To render protein drugs more suitable for clinical treatment, PEGylation has been widely used to ameliorate their inherent deficiencies, such as poor stability, rapid elimination in the bloodstream, and high immunogenicity. While increasingly PEGylated protein drugs have been approved by the FDA, the non-degradability of PEG and the emergence of anti-PEG antibodies after injection raise concerns about their cumulative chronic toxicity and long-term therapeutic efficacy. Zwitterionic polymer, with a unique structure containing equal amounts of positively charged and negatively charged groups, shows a different hydration behavior to PEG, which may be a superior PEG alternative for protein conjugation. In this concept review, a series of features beyond that of PEGylated protein exhibited by protein-zwitterionic polymer conjugate are discussed and some suggestions are presented for their future direction.

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

Over the past few decades, the complexity of molecular entities being advanced for therapeutic purposes has continued to evolve. A main propellent fueling innovation is the perpetual mandate within the pharmaceutical industry to meet the needs of novel disease areas and/or delivery challenges. As new mechanisms of action are uncovered, and as our understanding of existing mechanisms grows, the properties that are required and/or leveraged to enable therapeutic development continue to expand. One rapidly evolving area of interest is that of chemically enhanced peptide and protein therapeutics. While a variety of conjugate molecules such as antibody-drug conjugates, peptide/protein-PEG conjugates, and protein conjugate vaccines are already well established, others, such as antibody-oligonucleotide conjugates and peptide/protein conjugates using non-PEG polymers, are newer to clinical development. This review will evaluate the current development landscape of protein-based chemical conjugates with special attention to considerations such as modulation of pharmacokinetics, safety/tolerability, and entry into difficult to access targets, as well as bioavailability. Furthermore, for the purpose of this review, the types of molecules discussed are divided into two categories: (1) therapeutics that are enhanced by protein or peptide bioconjugation, and (2) protein and peptide therapeutics that require chemical modifications. Overall, the breadth of novel peptide- or protein-based therapeutics moving through the pipeline each year supports a path forward for the pursuit of even more complex therapeutic strategies.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Assessment of Crosslinkers between Peptide Antigen and Carrier Protein for Fusion Peptide-Directed Vaccines against HIV-1

Conjugate-vaccine immunogens require three components: a carrier protein, an antigen, and a crosslinker, capable of coupling antigen to carrier protein, while preserving both T-cell responses from carrier protein and B-cell responses from antigen. We previously showed that the N-terminal eight residues of the HIV-1 fusion peptide (FP8) as an antigen could prime for broad cross-clade neutralizing responses, that recombinant heavy chain of tetanus toxin (rTTHC) as a carrier protein provided optimal responses, and that choice of crosslinker could impact both antigenicity and immunogenicity. Here, we delve more deeply into the impact of varying the linker between FP8 and rTTHC. In specific, we assessed the physical properties, the antigenicity, and the immunogenicity of conjugates for crosslinkers ranging in spacer-arm length from 1.5 to 95.2 Å, with varying hydrophobicity and crosslinking-functional groups. Conjugates coupled with different degrees of multimerization and peptide-to-rTTHC stoichiometry, but all were well recognized by HIV-fusion-peptide-directed antibodies VRC34.01, VRC34.05, PGT151, and ACS202 except for the conjugate with the longest linker (24-PEGylated SMCC; SM(PEG)24), which had lower affinity for ACS202, as did the conjugate with the shortest linker (succinimidyl iodoacetate; SIA), which also had the lowest peptide-to-rTTHC stoichiometry. Murine immunizations testing seven FP8-rTTHC conjugates elicited fusion-peptide-directed antibody responses, with SIA- and SM(PEG)24-linked conjugates eliciting lower responses than the other five conjugates. After boosting with prefusion-closed envelope trimers from strains BG505 clade A and consensus clade C, trimer-directed antibody-binding responses were lower for the SIA-linked conjugate; elicited neutralizing responses were similar, however, though statistically lower for the SM(PEG)24-linked conjugate, when tested against a strain especially sensitive to fusion-peptide-directed responses. Overall, correlation analyses revealed the immunogenicity of FP8-rTTHC conjugates to be negatively impacted by hydrophilicity and extremes of length or low peptide-carrier stoichiometry, but robust to other linker parameters, with several commonly used crosslinkers yielding statistically indistinguishable serological results.

Peg-Grafted Liposomes for L-Asparaginase Encapsulation

L-asparaginase (ASNase) is an important biological drug used to treat Acute Lymphoblastic Leukemia (ALL). It catalyzes the hydrolysis of L-asparagine (Asn) in the bloodstream and, since ALL cells cannot synthesize Asn, protein synthesis is impaired leading to apoptosis. Despite its therapeutic importance, ASNase treatment is associated to side effects, mainly hypersensitivity and immunogenicity. Furthermore, degradation by plasma proteases and immunogenicity shortens the enzyme half-life. Encapsulation of ASNase in liposomes, nanostructures formed by the self-aggregation of phospholipids, is an attractive alternative to protect the enzyme from plasma proteases and enhance pharmacokinetics profile. In addition, PEGylation might prolong the in vivo circulation of liposomes owing to the spherical shielding conferred by the polyethylene (PEG) corona around the nanostructures. In this paper, ASNase was encapsulated in liposomal formulations composed by 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) containing or not different concentrations of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N [methoxy (polyethylene glycol)-2000] (DSPE-PEG). Nanostructures of approximately 142-202 nm of diameter and polydispersity index (PDI) of 0.069 to 0.190 were obtained and the vesicular shape confirmed by Transmission Electron Microscopy (TEM and cryo-TEM). The encapsulation efficiency (%EE) varied from 10% to 16%. All formulations presented activity in contact with ASNase substrate, indicating the liposomes permeability to Asn and/or enzyme adsorption at the nanostructures' surface; the highest activity was observed for DMPC/DSPE-PEG 10%. Finally, we investigated the activity against the Molt 4 leukemic cell line and found a lower IC50 for the DMPC/DSPE-PEG 10% formulation in comparison to the free enzyme, indicating our system could provide in vivo activity while protecting the enzyme from immune system recognition and proteases degradation.

Advances in oral peptide drug nanoparticles for diabetes mellitus treatment

Peptide drugs play an important role in diabetes mellitus treatment. Oral administration of peptide drugs is a promising strategy for diabetes mellitus because of its convenience and high patient compliance compared to parenteral administration routes. However, there are a series of formidable unfavorable conditions present in the gastrointestinal (GI) tract after oral administration, which result in the low oral bioavailability of these peptide drugs. To overcome these challenges, various nanoparticles (NPs) have been developed to improve the oral absorption of peptide drugs due to their unique in vivo properties and high design flexibility. This review discusses the unfavorable conditions present in the GI tract and provides the corresponding strategies to overcome these challenges. The review provides a comprehensive overview on the NPs that have been constructed for oral peptide drug delivery in diabetes mellitus treatment. Finally, we will discuss the rational application and give some suggestions that can be utilized for the development of oral peptide drug NPs. Our aim is to provide a systemic and comprehensive review of oral peptide drug NPs that can overcome the challenges in GI tract for efficient treatment of diabetes mellitus.

•Oral administration of peptide drugs is a promising strategy for diabetes mellitus treatment

•A series of formidable unfavorable conditions in gastrointestinal tract result in the low oral bioavailability of peptide drugs

•Nanoparticles can improve the oral bioavailability of peptide drugs

Sequence Effect of Peptide-Based Materials on Delivering Interferon-α (IFN-α): A Molecular Dynamic Perspective

Peptide-based biomaterials exhibit great potentials in developing drug delivery platforms due to their biocompatibility and biodegradability beyond poly(ethylene glycol). How different amino acids in peptides used for delivery play their roles is still unclear at the microscopic level. This work compared the assembly behaviors of a series of peptides around interferon-α (IFN-α). Through all-atom molecular simulations, the sequence effect of peptides on delivering interferon-α was quantitively characterized. The hydrophobic elastin-like peptide (VPGAG)_n preferred to self-aggregate into dense clusters, rather than encapsulate IFN-α. The hydrophilic zwitterionic peptides with repeating unit "KE" tended to phase-separate from IFN-α in the mixture. In contrast, peptides with a hybrid sequence, i.e., (VPKEG)_n, exhibited the highest contact preference, and the formed protective shell endowed IFN-α with better thermal stability and stealth property and achieved a subtle balance between protecting IFN-α and subsequent releasing. Further energy decomposition analysis revealed that the positively charged Lys contributed most to the binding affinity while the negatively charged Glu contributed most to the hydrophilic property of peptide-based materials. In summary, this article reveals why peptides composed of repeating hydrophobic and charged residues could be a potential choice for delivering therapeutic proteins in the form of solution.

Zwitterionic polymers in drug delivery: A review

Developments of novel drug delivery vehicles are sought-after to augment the therapeutic effectiveness of standard drugs. An urgency to design novel drug delivery vehicles that are sustainable, biocompatible, have minimized cytotoxicity, no immunogenicity, high stability, long circulation time, and are capable of averting recognition by the immune system is perceived. In this pursuit for an ideal candidate for drug delivery vehicles, zwitterionic materials have come up as fulfilling almost all these expectations. This comprehensive review is presenting the progress made by zwitterionic polymeric architectures as prospective sustainable drug delivery vehicles. Zwitterionic polymers with varied architecture such as appending protein conjugates, nanoparticles, surface coatings, liposomes, hydrogels, etc, used to fabricate drug delivery vehicles are reviewed here. A brief introduction of zwitterionic polymers and their application as reliable drug delivery vehicles, such as zwitterionic polymer-protein conjugates, zwitterionic polymer-based drug nanocarriers, and stimulus-responsive zwitterionic polymers are discussed in this discourse. The prospects shown by zwitterionic architecture suggest the tremendous potential for them in this domain. This critical review will encourage the researchers working in this area and boost the development and commercialization of such devices to benefit the healthcare fraternity.

Molecular simulation of zwitterionic polypeptides on protecting glucagon-like peptide-1 (GLP-1)

Owing to their anti-fouling properties, zwitterionic polypeptides demonstrate great advantage on protecting protein drugs. When conjugated to glucagon-like peptide-1 (GLP-1), a drug for type-II diabetes, zwitterionic polypeptides confer better pharmacokinetics than uncharged counterparts. However, its microscopic mechanism is still unclear due to the complicated conformational space. To address this challenge, this work explored the interaction modes of GLP-1 with the unconnected repeat units, instead of the full-length polypeptides. The three repeat units are two zwitterionic pentapeptides VPKEG and VPREG, and one uncharged control VPGAG. Our molecular simulations revealed that the helical conformation of GLP-1 was stabilized by adding 40 polypeptides. Both VPGAG and VPREG formed dense packing shells around GLP-1, but the driving forces were hydrophobic and electrostatic interactions, respectively. In contrast, the packing shell composed of VPKEG was most loose, while could still stabilize GLP-1. The moderate electrostatic interactions endowed VPKEG an anti-fouling property, thereby avoiding non-specific interaction with other amino acids. The strong electrostatic interactions exerted by arginine promoted atomic contacts between VPREG and other residues, making it as "hydrophobic" as VPGAG. In summary, the combination of hydrophobic and moderate electrostatic interactions in VPKEG brings about a subtle balance between stabilizing GLP-1 and avoiding non-specific interaction.