Novel AGLP-1 albumin fusion protein as a long-lasting agent for type 2 diabetes

Extension of the circulatory half-life of recombinant ecallantide via albumin fusion without loss of anti-kallikrein activity

Ecallantide comprises Kunitz Domain 1 of Tissue Factor Pathway Inhibitor, mutated at seven amino acid positions to inhibit plasma kallikrein (PK). It is used to treat acute hereditary angioedema (HAE). We appended hexahistidine tags to the N- or C-terminus of recombinant Ecallantide (rEcall) and expressed and purified the resulting proteins, with or without fusion to human serum albumin (HSA), using Pichia pastoris. The inhibitory constant (Ki) of rEcall-H6 or H6-rEcall for PK was not increased by albumin fusion. When 125I-labelled rEcall proteins were injected intravenously into mice, the area under the clearance curve (AUC) was significantly increased, 3.4- and 3.6-fold, for fusion proteins H6-rEcall-HSA and HSA-rEcall-H6 versus their unfused counterparts but remained 2- to 3-fold less than that of HSA-H6. The terminal half-life of H6-rEcall-HSA and HSA-H6 did not differ, although that of HSA-rEcall-H6 was significantly shorter than either other protein. Receptor Associated Protein (RAP), a Low-density lipoprotein Receptor-related Protein (LRP1) antagonist, competed H6-rEcall-HSA clearance more effectively than intravenous immunoglobulin (IVIg), a neonatal Fc receptor (FcRn) antagonist. HSA fusion decreases rEcall clearance in vivo, but LRP1-mediated clearance remains more important than FcRn-mediated recycling for rEcall fusion proteins. The properties of H6-rEcall-HSA warrant investigation in a murine model of HAE.

AlbuCatcher for Long-Acting Therapeutics

Therapeutic proteins, pivotal for treating diverse human diseases due to their biocompatibility and high selectivity, often face challenges such as rapid serum clearance, enzymatic degradation, and immune responses. To address these issues and enable prolonged therapeutic efficacy, techniques to extend the serum half-life of therapeutic proteins are crucial. The AlbuCatcher, a conjugate of human serum albumin (HSA) and SpyCatcher, was proposed as a general technique to extend the serum half-life of diverse therapeutic proteins. HSA, the most abundant blood protein, exhibits a long intrinsic half-life through Fc receptor (FcRn)-mediated recycling. The SpyTag/SpyCatcher (ST/SC) system, known for forming irreversible isopeptide bonds, was employed to conjugate HSA and therapeutic proteins. Site-specific HSA conjugation to SC was achieved using an inverse electron-demand Diels-Alder (IEDDA) reaction, minimizing activity loss. Using urate oxidase (Uox) as a model protein with a short half-life, the small ST was fused to generate Uox-ST. Then, HSA-conjugated Uox (Uox-HSA) was successfully prepared via the Uox-ST/AlbuCatcher reaction. In vitro enzyme assays demonstrated that the impact of ST fusion and HSA conjugation on Uox enzymatic activity is negligible. Pharmacokinetics studies in mice revealed that Uox-HSA exhibits a significantly longer serum half-life (about 18 h) compared to Uox-WT (about 2 h). This extended half-life is attributed to FcRn-mediated recycling of HSA-conjugated Uox, demonstrating the effectiveness of the AlbuCatcher strategy in enhancing the pharmacokinetics of therapeutic proteins.

Cathepsin B Processing Is Required for the In Vivo Efficacy of Albumin-Drug Conjugates

Targeted drug delivery approaches that selectively and preferentially deliver therapeutic agents to specific tissues are of great interest for safer and more effective pharmaceutical treatments. We investigated whether cathepsin B cleavage of a valine-citrulline [VC(S)]-containing linker is required for the release of monomethyl auristatin E (MMAE) from albumin-drug conjugates. In this study, we used an engineered version of human serum albumin, Veltis High Binder II (HBII), which has enhanced binding to the neonatal Fc (fragment crystallizable) receptor (FcRn) to improve drug release upon binding and FcRn-mediated recycling. The linker-payload was conjugated to cysteine 34 of albumin using a carbonylacrylic (caa) reagent which produced homogeneous and plasma stable conjugates that retained FcRn binding. Two caa-linker-MMAE reagents were synthesized─one with a cleavable [VC(S)] linker and one with a noncleavable [VC(R)] linker─to question whether protease-mediated cleavage is needed for MMAE release. Our findings demonstrate that cathepsin B is required to achieve efficient and selective antitumor activity. The conjugates equipped with the cleavable [VC(S)] linker had potent antitumor activity in vivo facilitated by the release of free MMAE upon FcRn binding and internalization. In addition to the pronounced antitumor activity of the albumin conjugates in vivo, we also demonstrated their preferable tumor biodistribution and biocompatibility with no associated toxicity or side effects. These results suggest that the use of engineered albumins with high FcRn binding combined with protease cleavable linkers is an efficient strategy to target delivery of drugs to solid tumors.

Albumin-based drug carrier targeting urokinase receptor for cancer therapy

Urokinase plasminogen activator receptor (uPAR) is a key participant in extracellular proteolysis, tissue remodeling and cell motility. uPAR overexpresses in most solid tumors and several hematologic malignancies, but has low levels on normal tissues, thus is advocated as a molecular target for cancer therapy. One of the obstacles for the evaluation of uPAR targeting agents in preclinical study is the species specificity, where targeting agents for human uPAR  usually not bind to murine uPAR. Here, we develop a targeting agent that binds to both murine and human uPAR. This targeting agent is genetically fused to human serum albumin, a commonly used drug carrier, and the final construct is named as uPAR targeting carrier (uPARTC). uPARTC binds specifically to uPAR-overexpressing 293T/huPAR and 293T/muPAR as demonstrated by flow cytometry. A cytotoxic compound, celastrol, is embedded into uPARTC non-covalently. The resulting macromolecular complex show effective proliferation inhibition on both murine and human uPAR overexpressing cells, and exhibit potent antitumor efficacy on hepatoma H22-bearing mice. This work demonstrates that uPARTC is a promising tumor targeting drug carrier, which address the species-specificity challenge of uPAR targeting agents and can be used to load other cytotoxic compounds.

In vivo degradation forms, anti-degradation strategies, and clinical applications of therapeutic peptides in non-infectious chronic diseases

Current medicinal treatments for diseases comprise largely of two categories: small molecular (chemical) (e.g., aspirin) and larger molecular (peptides/proteins, e.g., insulin) drugs. Whilst both types of therapeutics can effectively treat different diseases, ranging from well-understood (in view of pathogenesis and treatment) examples (e.g., flu), to less-understood chronic diseases (e.g., diabetes), classical small molecule drugs often possess significant side-effects (a major cause of drug withdrawal from market) due to their low- or non-specific targeting. By contrast, therapeutic peptides, which comprise short sequences from naturally occurring peptides/proteins, commonly demonstrate high target specificity, well-characterized modes-of-action, and low or non-toxicity in vivo. Unfortunately, due to their small size, linear permutation, and lack of tertiary structure, peptidic drugs are easily subject to rapid degradation or loss in vivo through chemical and physical routines, thus resulting in a short half-life and reduced therapeutic efficacy, a major drawback that can reduce therapeutic efficiency. However, recent studies demonstrate that the short half-life of peptidic drugs can be significantly extended by various means, including use of enantiomeric or non-natural amino acids (AAs) (e.g., L-AAs replacement with D-AAs), chemical conjugation [e.g., with polyethylene glycol], and encapsulation (e.g., in exosomes). In this context, we provide an overview of the major in vivo degradation forms of small therapeutic peptides in the plasma and anti-degradation strategies. We also update on the progress of small peptide therapeutics that are either currently in clinical trials or are being successfully used in clinical therapies for patients with non-infectious diseases, such as diabetes, multiple sclerosis, and cancer.

A versatile insertion point on albumin to accommodate peptides and maintain their activities

Genetic fusion of human serum albumin to peptides is an important strategy to enhance the plasma half-life of the peptide. An inherent challenge of such method is the reduction of specific activity of the cargo peptides upon connecting at N- or C-termini of albumin. Here, we report a finding that residue 363-364 of albumin can be inserted with a peptide while maintaining the peptide activities. We insert a peptide inhibitor into this site, and at the N-terminus of albumin, for comparison. The chimeric protein displays potent inhibition (IC₅₀ value of 30 nM) to its target (uPAR), but not the N-terminally fused construct. We also study the chimera of HSA with a cyclic peptide inhibitor of murine urokinase-type plasminogen activator grafted at either the internal site or the N-terminus. The internally peptide-grafted protein possesses a much more potent inhibition compared to the N-terminally located fusion (IC₅₀ value of 32 nM vs 19 μM). We further demonstrate that such internal fusion does not affect albumin expression, secondary structure, and inherent drug binding activity. Thus, this work identifies a versatile insertion point inside albumin for maintaining fusion peptide activity, and opens a new avenue to expand the applications of albumin fusion technology.

A review of existing strategies for designing long-acting parenteral formulations: Focus on underlying mechanisms, and future perspectives

The need for long-term treatments of chronic diseases has motivated the widespread development of long-acting parenteral formulations (LAPFs) with the aim of improving drug pharmacokinetics and therapeutic efficacy. LAPFs have been proven to extend the half-life of therapeutics, as well as to improve patient adherence; consequently, this enhances the outcome of therapy positively. Over past decades, considerable progress has been made in designing effective LAPFs in both preclinical and clinical settings. Here we review the latest advances of LAPFs in preclinical and clinical stages, focusing on the strategies and underlying mechanisms for achieving long acting. Existing strategies are classified into manipulation of in vivo clearance and manipulation of drug release from delivery systems, respectively. And the current challenges and prospects of each strategy are discussed. In addition, we also briefly discuss the design principles of LAPFs and provide future perspectives of the rational design of more effective LAPFs for their further clinical translation.

A supramolecular nanocarrier for efficient cancer imaging and therapy by targeting at matriptase

Human serum albumin (HSA), a versatile protein carrier for endogenous and exogenous compounds, is a proven macromolecule to form nanoparticles for drug delivery. To render HSA carrier specificity toward tumors, we designed a recombinant HSA protein fused with Kunitz domain 1 (KD1) of hepatocyte growth factor activator inhibitor type 1, which targets to matriptase, a type II transmembrane serine protease overexpressed on tumor cell surface. The carrier was thus named matriptase targeting carrier (MTC). In this study, we showed that MTC displayed the same inhibitory potency as the KD1 againast matriptase, demonstrating the HSA fusion did not affect the KD1 targeting potency. For tumor optical imaging and ablation, MTC was prepared as nanoparticle drug carrier by a novel method via denaturation and refolding to incorporate photosensitizer, CPZ. This matriptase targeting nanoparticles, CPZ:MTC@NPs, showed high specificity and cytotoxicity for matriptase-overexpressing cancer cells in vitro. In tumor-bearing mice, CPZ:MTC@NPs demonstrated selective accumulation and high retention in matriptase-overexpressing tumor. Under illumination, the nanoparticles significantly reduced tumor volumes (79.6%) as compared to saline control. These findings showed that this supramolecular nanocarrier, a new type of tumor targeting self-assembly nanoparticle, had potential as a highly efficient tumor targeting drug carrier for imaging and therapy.

Expression and characterization of albumin fusion protein canine IFNγ-CSA in baculovirus-insect cell expression system

In this study, canine IFNγ was fused by a flexible linker with canine serum albumin to construct the fusion protein IFNγ-CSA for the purpose to design a long-acting canine IFNγ. The fusion protein was successfully expressed in baculovirus-infected Sf9 insect cells and was purified by salting-out and ion exchange chromatography. The IFNγ-CSA fusion possessed potent anti-viral assay against vesicular stomatitis virus in cultured cells. IFNγ-CSA was also stable at 37 °C up to 72 h compared with 8 h for IFNγ alone. In vivo pharmacokinetics demonstrated a significantly longer half-life for IFNγ-CSA (15.42 h) than for canine reIFNγ (1.51 h) in KM mice. These results indicate that IFNγ-CSA expression in the baculovirus system was successful and provide a promising long-acting cytokine for veterinary clinical applications.

Binding and biologic characterization of recombinant human serum albumin-eTGFBR2 fusion protein expressed in CHO cells

Transforming growth factor-β1 (TGF-β1) signaling is involved in cell metabolism, growth, differentiation, carcinoma invasion and fibrosis development, which suggests TGF-β1 can be treated as a therapeutic target extensively. Because TGF-β1 receptor type α(TGFBR2) is the directed and essential mediator for TGF-β1 signals, the extracellular domain of TGFBR2 (eTGFBR2), binding partner for TGF-β1, has been produced in a series of expression systems to inhibit TGF-β1 signaling. However, eTGFBR2 is unstable with a short half-life predominantly because of enzymatic degradation and kidney clearance. In this study, a fusion protein consisting of human eTGFBR2 fused at the C-terminal of human serum albumin (HSA) was stably and highly expressed in Chinese Hamster Ovary (CHO) cells. The high and stable expression sub-clones with Ig kappa signal peptide were selected by Western blot analysis and used for suspension culture. After fed-batch culture over 8 d, the expression level of HSA-eTGFBR2 reached 180 mg/L. The fusion protein was then purified from culture medium using a 2-step chromatographic procedure that resulted in 39% recovery rate. The TGF-β1 binding assay revealed that HSA-eTGFBR2 could bind to TGF-β1 with the affinity constant (K_D of 1.42 × 10^-8 M) as determined by the ForteBio Octet System. In addition, our data suggested that HSA-eTGFBR2 exhibited a TGF-β1 neutralizing activity and maintained a long-term activity more than eTGFBR2. It concluded that the overexpressing CHO cell line supplied sufficient recombinant human HSA-eTGFBR2 for further research and other applications.

Tat-ATOX1 inhibits streptozotocin-induced cell death in pancreatic RINm5F cells and attenuates diabetes in a mouse model

Antioxidant 1 (ATOX1) functions as an antioxidant against hydrogen peroxide and superoxide, and therefore may play a significant role in many human diseases, including diabetes mellitus (DM). In the present study, we examined the protective effects of Tat-ATOX1 protein on streptozotocin (STZ)-exposed pancreatic insulinoma cells (RINm5F) and in a mouse model of STZ-induced diabetes using western blot analysis, immunofluorescence staining and MTT assay, as well as histological and biochemical analysis. Purified Tat-ATOX1 protein was efficiently transduced into RINm5F cells in a dose- and time-dependent manner. Additionally, Tat-ATOX1 protein markedly inhibited reactive oxygen species (ROS) production, DNA damage and the activation of Akt and mitogen activated protein kinases (MAPKs) in STZ-exposed RINm5F cells. In addition, Tat-ATOX1 protein transduced into mice pancreatic tissues and significantly decreased blood glucose and hemoglobin A1c (HbA1c) levels as well as the body weight changes in a model of STZ-induced diabetes. These results indicate that transduced Tat-ATOX1 protein protects pancreatic β-cells by inhibiting STZ-induced cellular toxicity in vitro and in vivo. Based on these findings, we suggest that Tat-ATOX1 protein has potential applications as a therapeutic agent for oxidative stress-induced diseases including DM.

Fusion Proteins for Half-Life Extension of Biologics as a Strategy to Make Biobetters

The purpose of making a "biobetter" biologic is to improve on the salient characteristics of a known biologic for which there is, minimally, clinical proof of concept or, maximally, marketed product data. There already are several examples in which second-generation or biobetter biologics have been generated by improving the pharmacokinetic properties of an innovative drug, including Neulasta(®) [a PEGylated, longer-half-life version of Neupogen(®) (filgrastim)] and Aranesp(®) [a longer-half-life version of Epogen(®) (epoetin-α)]. This review describes the use of protein fusion technologies such as Fc fusion proteins, fusion to human serum albumin, fusion to carboxy-terminal peptide, and other polypeptide fusion approaches to make biobetter drugs with more desirable pharmacokinetic profiles.

A platform for efficient, thiol-stable conjugation to albumin's native single accessible cysteine

Herein we report the use of bromomaleimides for the construction of stable albumin conjugates via conjugation to its native, single accessible, cysteine followed by hydrolysis. Advantages over the classical maleimide approach are highlighted in terms of quantitative hydrolysis and absence of undesirable retro-Michael deconjugation.