A protease-based strategy for the controlled release of therapeutic peptides

Peptide GLP-1 receptor agonists: From injection to oral delivery strategies

Peptide glucagon-like peptide-1 receptor agonists (GLP-1RAs) are effective drugs for treating type 2 diabetes (T2DM) and have been proven to benefit the heart and kidney. Apart from oral semaglutide, which does not require injection, other peptide GLP-1RAs need to be subcutaneously administered. However, oral semaglutide also faces significant challenges, such as low bioavailability and frequent gastrointestinal discomfort. Thus, it is imperative that advanced oral strategies for peptide GLP-1RAs need to be explored. This review mainly compares the current advantages and disadvantages of various oral delivery strategies for peptide GLP-1RAs in the developmental stage and discusses the latest research progress of peptide GLP-1RAs, providing a useful guide for the development of new oral peptide GLP-1RA drugs.

Development of a Chimeric Protein BiPPB-mIFNγ-tTβRII for Improving the Anti-Fibrotic Activity in Vivo by Targeting Fibrotic Liver and Dual Inhibiting the TGF-β1/Smad Signaling Pathway

Excessive production of transforming growth factor β1 (TGF-β1) in activated hepatic stellate cells (aHSCs) promotes liver fibrosis by activating the TGF-β1/Smad signaling pathway. Thus, specifically inhibiting the pro-fibrotic activity of TGF-β1 in aHSCs is an ideal strategy for treating liver fibrosis. Overexpression of platelet-derived growth factor β receptor (PDGFβR) has been demonstrated on the surface of aHSCs relative to normal cells in liver fibrosis. Interferon-gamma peptidomimetic (mIFNγ) and truncated TGF-β receptor type II (tTβRII) inhibit the TGF-β1/Smad signaling pathway by different mechanisms. In this study, we designed a chimeric protein by the conjugation of (1) mIFNγ and tTβRII coupled via plasma protease-cleavable linker sequences (FNPKTP) to (2) PDGFβR-recognizing peptide (BiPPB), namely BiPPB-mIFNγ-tTβRII. This novel protein BiPPB-mIFNγ-tTβRII was effectively prepared using Escherichia coli expression system. The active components BiPPB-mIFNγ and tTβRII were slowly released from BiPPB-mIFNγ-tTβRII by hydrolysis using the plasma protease thrombin in vitro. Moreover, BiPPB-mIFNγ-tTβRII highly targeted to fibrotic liver tissues, markedly ameliorated liver morphology and fibrotic responses in chronic liver fibrosis mice by both inhibiting the phosphorylation of Smad2/3 and inducing the expression of Smad7. Meanwhile, BiPPB-mIFNγ-tTβRII markedly reduced the deposition of collagen fibrils and expression of fibrosis-related proteins in acute liver fibrosis mice. Furthermore, BiPPB-mIFNγ-tTβRII showed a good safety performance in both liver fibrosis mice. Taken together, BiPPB-mIFNγ-tTβRII improved the in vivo anti-liver fibrotic activity due to its high fibrotic liver-targeting potential and the dual inhibition of the TGF-β1/Smad signaling pathway, which may be a potential candidate for targeting therapy on liver fibrosis.

Novel XTENylated AWRK6 analog with hypoglycemic activity, and anti-HSV-2 potential in combination with double shRNA

AIMS

To design and evaluate a novel AWRK6 peptide-based long-acting GLP-1 receptor agonist (GLP-1RA) conjugated a recombinant polyethylene glycol mimetic (XTEN protein) with significant therapeutic potential on type 2 diabetes mellitus (T2DM) alone as well as Herpes simplex virus type 2 (HSV-2) infection in combination with double shRNA.

MAIN METHODS

First, four AWRK6 analogs (termed XA-1 to XA-4) were designed and produced by solid phase synthesis strategy. Further surface plasmon resonance (SPR) measurement and in vitro cAMP accumulation assay were performed to detect the GLP-1R binding affinities and GLP-1R activation, respectively. The in vivo efficacy evaluation including pharmacokinetic test, oral glucose tolerance test (OGTT), hypoglycemic duration test and chronic pharmacodynamics study in rodent animals were all carefully performed.

KEY FINDINGS

Four XA peptides were synthesized with purity >99%. High binding affinity as well as activation potency of XA-4 for GLP-1R were demonstrated by SPR and cell-based luciferase reporter assay, respectively. Additionally, XA-4 exhibited the long-lasting antidiabetic effects in the multiple OGTTs, hypoglycemic duration test and chronic study in mice. Furthermore, combined treatment of XA-4 and double shRNA (D-shRNA) achieved potent antiviral effects in HSV-2 infected HEK293 cells.

SIGNIFICANCE

XA-4 exhibited promising pharmaceutical potential to be a therapeutic drug for treating T2D, and also held potential to against the HSV-2 infection, which is really an accidental discovery. The strategy of recombinant XTENylation can also be applied to other peptides or small molecules for the development of long-acting therapeutic drugs.

Engineering a protease-based and site-specific PEGylation-based strategy for the controlled release of exenatide

Using the commercially available antidiabetic drug exenatide (exendin-4) as a model peptide, we designed a novel exenatide derivative, termed LEX-1, comprising a 12-mer albumin-binding peptide, a protease-sensitive linker and a native exenatide. In addition, site-specific PEGylation was performed using LEX-1 as a lead sequence to generate four exenatide derivatives (LEX-2 to LEX-5). Moreover, we determined the optimal molecular weight of maleimide-derivatized PEG for the site-specific PEGylation of LEX-1 by an in vitro stability assay and an in vivo hypoglycemic efficacy test. As a result, LEX-3 (PEG10 kDa) exerted enhanced proteolytic stability, rational release rate of free exenatide and the best glucose-stabilizing capability compared with others. In addition, the prolonged hypoglycemic effects of LEX-1 and LEX-3 were demonstrated in type 2 diabetic mice by multiple OGTTs and a hypoglycemic duration test. Furthermore, a pharmacokinetic test was conducted using Sprague Dawley (SD) rats; LEX-3 (PEG10 kDa) showed the best circulating t 1/2 of ∼119.7 h for exenatide release from LEX-3, suggesting that LEX-3 has the potential to be developed into a once-weekly antidiabetic agent. The consecutive 8 week treatment of both LEX-1 and LEX-3 exhibited enhanced beneficial efficacies on body weight gain, cumulative food intake, % fat and hemoglobin A1c (HbA1c) reduction compared with exenatide treatment. Meanwhile, the chronic administration of LEX-1 and LEX-3 also effectively improved the blood biochemical indexes. Our results indicate the enhanced antidiabetic effects of LEX-1 and LEX-3, and our strategy of PEGylation and albumin conjugation can be applied to other bioactive agents.

Engineering an enhanced thrombin-based GLP-1 analog with long-lasting glucose-lowering and efficient weight reduction

Peptides are considered as potent therapeutic drugs primarily due to the exquisite potency and selectivity to targets. However, the development and clinical application of peptide drugs were severely limited by the poor in vivo lifespans. Here, we designed an improved small albumin-binding polypeptide that can associate with human serum albumin (HSA) and liberate the bioactive peptide. Using glucagon-like peptide-1 (GLP-1) as a model, two new long-lasting GLP-1 analogs (termed XTS1 and XTS2) containing an albumin-binding domain, a protease-cleavable linker and a mutated GLP-1(A8Aib) were designed to demonstrate the sustained release of GLP-1 due to the plasma thrombin (TBN) digestion. Two XTS peptides were prepared of high purity (>99%) and accurate molecular weight determined by reversed high-performance liquid chromatography and mass spectrometry, respectively. In vitro measurements of surface plasmon resonance indicated that XTS1 associate with serum albumins of all species with higher affinity compared with XTS2. Metabolic stability of XTS1 in vitro in human plasma was also better than that of XTS2. Protease cleavage assay results of XTS peptides demonstrated the controlled-release of transient GLP-1 from the XTS1 and XTS2 mixture after thrombin-catalyzed hydrolysis. Then the intraperitoneal glucose tolerance test (IPGTT) showed that the glucose-lowering efficacies of XTS1 were in a dosage-dependent manner within the range of 0.1–0.9 mg kg⁻¹. In addition, XTS1 showed similar hypoglycemic intensity and significantly longer action duration compared to Liraglutide in both multiple IPGTTs and hypoglycemic duration test. Apparently extended plasma half-lives of ∼2.3 and ∼3.5 days were observed after a single subcutaneous administration of XTS1 (0.9 mg kg⁻¹) in rats and cynomolgus monkeys, respectively. Furthermore, twice-weekly subcutaneously dosed XTS1 in db/db mice achieved long-term beneficial effects on body weight, hemoglobin A1C (HbA1C) lowering and the function of pancreatic beta cells. These studies support that XTS1 exerts potential as a therapeutic drug for the treatment of T2DM.

Peptides are considered as potent therapeutic drugs primarily due to the exquisite potency and selectivity to targets.

Fusion of Lysostaphin to an Albumin Binding Domain Prolongs Its Half-Life and Bactericidal Activity in the Systemic Circulation

Antibacterial lysins are promising proteins that are active against both antibiotic-susceptible and antibiotic-resistant bacterial strains. However, a major limitation of antibacterial lysins is their fast elimination from systemic circulation. PEGylation increases the plasma half-life of lysins but renders them inactive. Here we report the construction of a fusion protein of lysostaphin, a potent anti-staphylococcal lysin, and an albumin-binding domain from streptococcal protein G. The resulting fusion protein was less active than the parent enzyme lysostaphin, but it still retained significant antibacterial activity even when bound to serum albumin. The terminal half-life of the fusion protein in rats was five-fold greater than that of lysostaphin (7.4 vs. 1.5 h), and the area under the curve increased more than 115 times. Most importantly, this increase in systemic circulation time compensated for the decrease in activity. The plasma from rats that received an injection of the fusion protein retained bactericidal activity for up to 7 h, while plasma from rats that received plain lysostaphin lacked any detectable activity after 4 h. To the best of our knowledge, this is the first report of an antibacterial lysin with both improved pharmacokinetic parameters and prolonged bactericidal activity in the systemic circulation.

Improvements in chemical carriers of proteins and peptides

The successful intracellular delivery of biologically active proteins and peptides plays an important role for therapeutic applications. Indeed, protein/peptide delivery could overcome some problems of gene therapy, for example, controlling the expression levels and the integration of transgene into the host cell genome. Thus, protein/peptide drug delivery showed a promising and safe approach for treatment of cancer and infectious diseases. Due to the unique physical and chemical properties of proteins, their production (e.g., isolation, purification & formulation) and delivery represented significant challenges in pharmaceutical studies. Modification in the structural moieties of these protein/peptide drugs could improve their solubility, stability, crystallinity, lipophilicity, enzymatic susceptibility and targetability, and subsequently, therapies and cures against various diseases. Using the structural modification of protein/peptide, their delivery provided overall higher success rates including high specificity, high activity, bioreactivity and safety. Recently, biotechnological and pharmaceutical companies have tried to find novel techniques for the modifications and improve delivery systems/carriers. However, each carrier has its own benefits and drawbacks, and an appropriate carrier is often established by the physicochemical properties of protein or peptide, the ideal route of injection, and clinical characteristics of therapy. In this review, an attempt was made to give an overview on the chemical carriers for proteins and peptides as well as the recent advances in this field.

Engineering a novel protease-based Exendin-4 derivative for type 2 antidiabetic therapeutics

To develop an effective long-acting antidiabetic agent, we designed a novel Exendin-4 derivative (termed LEx4) containing an albumin-binding domain (ABD), a protease-cleavable linker and a native Exendin-4. Here, we present the LEx4 with balanced glucoregulatory activity and prolonged in vivo activity. As a first step, the LEx4 with purity more than 99% was prepared. Microscale thermophoresis (MST) results demonstrated that LEx4 associates with rat and monkey serum albumin with high-affinity (K_a = 1.26 × 10⁶ M^-1 and 1.52 × 10⁶ M^-1, respectively). Then the stability test in vitro showed the enhanced antiproteolytic ability of LEx4 in rat and human plasma compared to native Exendin-4. Oral glucose tolerance test (OGTT) in type 2 diabetic mice showed the glucose-lowering efficacy of LEx4 was clearly dosage-dependent within 25-250 nmol/kg. In addition, the protracted antidiabetic effects of LEx4 were further confirmed by both multiple OGTTs and hypoglycemic efficacies test in type 2 diabetic mice. In Sprague Dawley (SD) rats, LEx4 also showed 3.3-fold longer elimination half-life (t_1/2) than native Exendin-4. Furthermore, once daily injection of LEx4 to db/db mice achieved long-term beneficial effects on body weight, blood biochemical values, glucose tolerance and pancreatic tissue. We believe LEx4 has superior pharmaceutical potential as a therapeutic drug to against type-2 diabetes mellitus (T2DM) based on these results. This strategy of albumin binding is also applicable to other bioactive peptides for development of long-acting therapeutic drugs.

Novel delivery systems for improving the clinical use of peptides

Peptides have long been recognized as a promising group of therapeutic substances to treat various diseases. Delivery systems for peptides have been under development since the discovery of insulin for the treatment of diabetes. The challenge of using peptides as drugs arises from their poor bioavailability resulting from the low permeability of biological membranes and their instability. Currently, subcutaneous injection is clinically the most common administration route for peptides. This route is cost-effective and suitable for self-administration, and the development of appropriate dosing equipment has made performing the repeated injections relatively easy; however, only few clinical subcutaneous peptide delivery systems provide sustained peptide release. As a result, frequent injections are needed, which may cause discomfort and additional risks resulting from a poor administration technique. Controlled peptide delivery systems, able to provide required therapeutic plasma concentrations over an extended period, are needed to increase peptide safety and patient compliancy. In this review, we summarize the current peptidergic drugs, future developments, and parenteral peptide delivery systems. Special emphasis is given to porous silicon, a novel material in peptide delivery. Biodegradable and biocompatible porous silicon possesses some unique properties, such as the ability to carry exceptional high peptide payloads and to modify peptide release extensively. We have successfully developed porous silicon as a carrier material for improved parenteral peptide delivery. Nanotechnology, with its different delivery systems, will enable better use of peptides in several therapeutic applications in the near future.

Slow-release RGD-peptide hydrogel monoliths

We report on the formation of hydrogel monoliths formed by functionalized peptide Fmoc-RGD (Fmoc: fluorenylmethoxycarbonyl) containing the RGD cell adhesion tripeptide motif. The monolith is stable in water for nearly 40 days. The gel monoliths present a rigid porous structure consisting of a network of peptide fibers. The RGD-decorated peptide fibers have a β-sheet secondary structure. We prove that Fmoc-RGD monoliths can be used to release and encapsulate material, including model hydrophilic dyes and drug compounds. We provide the first insight into the correlation between the absorption and release kinetics of this new material and show that both processes take place over similar time scales.

A highly parallel method for synthesizing DNA repeats enables the discovery of 'smart' protein polymers

Robust high-throughput synthesis methods are needed to expand the repertoire of repetitive protein-polymers for different applications. To address this need, we developed a new method, overlap extension rolling circle amplification (OERCA), for the highly parallel synthesis of genes encoding repetitive protein-polymers. OERCA involves a single PCR-type reaction for the rolling circle amplification of a circular DNA template and simultaneous overlap extension by thermal cycling. We characterized the variables that control OERCA and demonstrated its superiority over existing methods, its robustness, high-throughput and versatility by synthesizing variants of elastin-like polypeptides (ELPs) and protease-responsive polymers of glucagon-like peptide-1 analogues. Despite the GC-rich, highly repetitive sequences of ELPs, we synthesized remarkably large genes without recursive ligation. OERCA also enabled us to discover 'smart' biopolymers that exhibit fully reversible thermally responsive behaviour. This powerful strategy generates libraries of repetitive genes over a wide and tunable range of molecular weights in a 'one-pot' parallel format.