Long-Acting Human Growth Hormone Analogue by Noncovalent Albumin Binding

Lipidation-dimerization platform unlocks treatment potential of fibroblast growth factor 21 for non-alcoholic steatohepatitis

Optimizing the druggability of both native and AI-designed bioactive proteins is crucial for realizing their therapeutic potential. A key focus in designing protein-based therapeutics is improving their pharmacokinetic properties. However, a significant challenge is to preserve biological activity while implementing long-acting strategies. Fibroblast growth factor 21 (FGF21), an endogenous hormone with potential as a treatment for non-alcoholic steatohepatitis (NASH), exemplifies this challenge. In this study, we present a novel lipidation-dimerization (LiDi) platform that integrates lipidation with a dimeric form of FGF21 connected by a hydrophilic linker. The lipidation enhances albumin binding, enabling sustained release, while the dimeric structure boosts biological activity. In vivo evaluations of the LiDi FGF21 analogs demonstrated that they offer excellent pharmacokinetic properties and superior efficacy compared to other treatments for NASH. This platform effectively extends the therapeutic half-life of proteins without compromising their activity, substantially broadening the application range of proteins as therapeutics.

Design and Biological Evaluation of the Long-Acting C5-Inhibited Ornithodoros moubata Complement Inhibitor (OmCI) Modified with Fatty Acid

Disorder of complement response is a significant pathogenic factor causing some autoimmune and inflammation diseases. The Ornithodoros moubata Complement Inhibitor (OmCI), a small 17 kDa natural protein, was initially extracted from soft tick salivary glands. The protein was found binding to complement C5 specifically, inhibiting the activation of the complement pathway, which is a successful therapeutic basis of complement-mediated diseases. However, a short half-life due to rapid renal clearance is a common limitation of small proteins for clinical application. In this study, we extended the half-life of OmCI by modifying it with fatty acid, which was a method used to improve the pharmacokinetics of native peptides and proteins. Five OmCI mutants were initially designed, and single-site cysteine mutation was introduced to each of them. After purification, four OmCI mutants were obtained that showed similar in vitro biological activities. Three mutants of them were subsequently coupled with different fatty acids by nucleophilic substitution. In total, 15 modified derivatives were screened and tested for anticomplement activity in vitro. The results showed that coupling with fatty acid would not significantly affect their complement-inhibitory activity (CH50 and AH50). OmCIT90C-CM02 and OmCIT90C-CM05 were validated as the applicable OmCI bioconjugates for further pharmacokinetic assessments, and both showed improved plasma half-life in mice compared with unmodified OmCI (15.86, 17.96 vs 2.57 h). In summary, our data demonstrated that OmCI conjugated with fatty acid could be developed as the potential long-acting C5 complement inhibitor in the clinic.

Site-selective fatty acid chain conjugation of the N-terminus of the recombinant human granulocyte colony-stimulating factor

The clinical application of the recombinant human granulocyte colony-stimulating factor (rhG-CSF) is restricted by its short serum half-life. Herein, site-selective modification of the N-terminus of rhG-CSF with PAL-PEG3-Ph-CHO was used to develop a long-acting rhG-CSF. The optimized conditions for rhG-CSF modification with PAL-PEG3-Ph-CHO were: reaction solvent system of 3% (w/v) Tween 20 and 30 mM NaCNBH3 in acetate buffer (20 mmol/L, pH 5.0), molar ratio of PAL-PEG3-Ph-CHO to rhG-CSF of 6:1, temperature of 20°C, and reaction time of 12 h, consequently, achieving a PAL-PEG3-Ph-rhG-CSF product yield of 70.8%. The reaction mixture was purified via preparative liquid chromatography, yielding the single-modified product PAL-PEG3-Ph-rhG-CSF with a HPLC purity exceeding 95%. The molecular weight of PAL-PEG3-Ph-rhG-CSF was 19297 Da by MALDI-TOF-MS, which was consistent with the theoretical value. The circular dichroism analysis revealed no significant change in its secondary structure compared to unmodified rhG-CSF. The PAL-PEG3-Ph-rhG-CSF retained 82.0% of the in vitro biological activity of unmodified rhG-CSF. The pharmacokinetic analyses showed that the serum half-life of PAL-PEG3-Ph-rhG-CSF was 7.404 ± 0.777 h in mice, 4.08 times longer than unmodified rhG-CSF. Additionally, a single subcutaneous dose of PAL-PEG3-Ph-rhG-CSF presented comparable in vivo efficacy to multiple doses of rhG-CSF. This study demonstrated an efficacious strategy for developing long-acting rhG-CSF drug candidates.

Growth hormone receptor agonists and antagonists: From protein expression and purification to long-acting formulations

Recombinant human growth hormone (rhGH) and GH receptor antagonists (GHAs) are used clinically to treat a range of disorders associated with GH deficiency or hypersecretion, respectively. However, these biotherapeutics can be difficult and expensive to manufacture with multiple challenges from recombinant protein generation through to the development of long-acting formulations required to improve the circulating half-life of the drug. In this review, we summarize methodologies and approaches used for making and purifying recombinant GH and GHA proteins, and strategies to improve pharmacokinetic and pharmacodynamic properties, including PEGylation and fusion proteins. Therapeutics that are in clinical use or are currently under development are also discussed.

Silica-collagen nanoformulations with extended human growth hormone release

Growth hormone deficiency has been treated by the daily administration of recombinant human growth hormone (hGH) for decades. Patient compliance to this treatment is generally incomplete due to challenges including dose frequency and lack of perceived benefits. This stimulates the research on new formulations to reduce the number of periodic administrations. In this study silica nanoparticles and silica-collagen nanocomposites were evaluated for hGH loading and release. Bare nanoparticles showed higher hGH adsorption capacity than thiol- and isobutyl-bearing particles of similar diameters. Monitoring of bound protein conformation changes indicated hGH structure retention when adsorbed on bare silica nanoparticles and suggested no alterations on protein activity. Protein-loaded particles incorporated into collagen matrices (silica-collagen nanocomposites) showed a progressive protein release profile different from the observed for hGH-loaded silica nanoparticles and hGH-loaded collagen matrices. While both the collagen and the silica nanoparticle systems reached a 100 % release after 4 and 7 days respectively, silica-collagen nanocomposites showed a bi-phasic prolonged hGH release reaching approximately an 80 % after 15 days. These findings suggest that biocompatible silica-collagen nanocomposites could be used as vehicles for the prolonged delivery of hGH which could lead to a potential reduction in the number of periodic administrations.

Derivatization with fatty acids in peptide and protein drug discovery

Peptides and proteins are widely used to treat a range of medical conditions; however, they often have to be injected and their effects are short-lived. These shortcomings of the native structure can be addressed by molecular engineering, but this is a complex undertaking. A molecular engineering technology initially applied to insulin - and which has now been successfully applied to several biopharmaceuticals - entails the derivatization of peptides and proteins with fatty acids. Various protraction mechanisms are enabled by the specific characteristics and positions of the attached fatty acid. Furthermore, the technology can ensure a long half-life following oral administration of peptide drugs, can alter the distribution of peptides and may hold potential for tissue targeting. Due to the inherent safety and well-defined chemical nature of the fatty acids, this technology provides a versatile approach to peptide and protein drug discovery.

Structure identification of circulating metabolites from somapacitan, a long-acting growth hormone derivative, and pharmacokinetics after single and multiple subcutaneous dosing in rats

Somapacitan is a growth hormone derivative approved for once-weekly treatment of growth hormone deficiency in adults and currently in clinical development for once-weekly dosing in children. The purpose of this study was to obtain non-clinical data from rats to support the safety evaluation of the most abundant metabolites of somapacitan in humans. The aims were to identify somapacitan metabolites and their relative proportions in rat plasma, identify the structure of abundant metabolites and measure the systemic metabolite exposure at the no-observed-adverse-effect level in the rat. After a single dose of radiolabelled somapacitan and analysis by high-performance liquid chromatography with radiochemical detection, seven somapacitan-related metabolites were detected in plasma from male rats, of which six were seen in plasma from female rats. The three most abundant metabolites (M1, M2 and M3) were structurally identified from liquid chromatography and mass spectrometry data, and a fourth metabolite (P1) was characterised from its specific retention time (lacking retention to the stationary phase) in plasma analysis with reversed-phase liquid chromatography and radiochemical detection. The metabolites were products from proteolysis of the peptide backbone in somapacitan. A deamidation product of the M1 metabolite (M1B) was also identified. Following multiple, twice-weekly dosing for 4 weeks, somapacitan was the principal plasma component up to 36 h after dosing. After 36 h, metabolites M1+M1B were the most abundant plasma components. Pharmacokinetic models were developed for somapacitan and metabolite P1 and used for steady-state assessment in the rat. Comparison of our data generated from rats with data from the parallel human study demonstrated that the most abundant metabolites were present in rats at higher levels than in humans. This study has provided non-clinical safety data that contribute to an overall safety assessment of somapacitan.

Discovery of a Long-Acting Parathyroid Hormone 1-34 Analogue to Treat Hypoparathyroidism

Hypoparathyroidism (HP) is a rare disease with clinical manifestations of hypocalcemia and hyperphosphatemia, resulting from deficient or absent parathyroid hormone (PTH) secretion. Conventional treatment for patients with HP involves extensive calcium and vitamin D supplementation. In 2015, PTH1-84 was approved by the United States Food and Drug Administration as an adjunct for HP patients who cannot be well-controlled on conventional treatment. However, PTH1-84 therapy requires a daily injection, leading to poor patient compliance. The purpose of this study was to develop a long-acting PTH1-34 analogue by increasing its affinity to albumin. Three PTH1-34 variants were generated by substituting two of the three lysine (Lys) residues with arginine, reserving a single Lys as the modification site in each sequence. A series of side chains, containing fatty acid, deoxycholic acid, or biotin groups, were synthesized to modify these PTH1-34 variants by using a solid-liquid phase synthesis approach. In vitro bioactivity and albumin affinity tests were used to screen these new PTH1-34 analogues. Finally, Lys27-AAPC was selected from 69 synthesized analogues as a candidate therapeutic compound because it retained potency and exhibited a high albumin-binding capacity. In pharmacodynamic experiments, Lys27-AAPC demonstrated enhanced and prolonged efficacy in serum calcium elevating relative to PTH1-84. Moreover, a lyophilized powder for injection containing Lys27-AAPC was developed for further testing and represented a potential long-acting HP treatment.

Synthesis of a Novel PTH1–34 Analog with Increased Human Serum Albumin Affinity

Parathyroid hormone (PTH)1–34 is an effective peptide drug for osteoporosis therapy. However, the half-life of PTH1–34 in vivo is short, leading to the need for frequent injections of this drug during its treatment. To prolong the half-life of PTH1–34, a novel PTH1–34 analog was generated based on fatty acid generation, and its synthesis process included recombinant protein expression, side-chain modification, and peptide decoration. The PTH1–34 variant was expressed in Escherichia coli, with a single Lys (position 27) retained as a modification site. The side chain, –AEEA-γGlu-C18 diacid, was synthesized using 2-chlorotrityl chloride resin as a solid support, and then was conjugated to the PTH1-34 variant to form PTH-Lys27-AGC. Reversed-phase chromatography confirmed a high final purity (>98%) of the target compound; in vitro bioactivity tests showed that PTH-1 receptor potency of PTH-Lys27-AGC was comparable to that of the native PTH1–34. A competitive human serum albumin binding test demonstrated a high albumin affinity of PTH-Lys27-AGC in comparison to PTH1–34. In summary, we developed a novel PTH1–34 analog, PTH-Lys27-AGC, which may be a long-acting agent for osteoporosis treatment in the future.

The Minimal Effect of Linker Length for Fatty Acid Conjugation to a Small Protein on the Serum Half-Life Extension

Conjugation of serum albumin or one of its ligands (such as fatty acid) has been an effective strategy to prolong the serum half-lives of drugs via neonatal Fc receptor (FcRn)–mediated recycling of albumin. So far, fatty acid (FA) has been effective in prolonging the serum half-lives for therapeutic peptides and small proteins, but not for large therapeutic proteins. Very recently, it was reported a large protein conjugated to FA competes with the binding of FcRn with serum albumin, leading to limited serum half-life extension, because primary FA binding sites in serum albumin partially overlap with FcRn binding sites. In order to prevent such competition, longer linkers between FA and the large proteins were required. Herein, we hypothesized that small proteins do not cause substantial competition for FcRn binding to albumin, resulting in the extended serum half-life. Using a small protein (28 kDa), we investigated whether the intramolecular distance in FA-protein conjugate affects the FcRn binding with albumin and serum half-life using linkers with varying lengths. Unlike with the FA-conjugated large protein, all FA-conjugated small proteins with different linkers exhibited comparable the FcRn binding to albumin and extended serum half-life.

Tissue Distribution and Receptor Activation by Somapacitan, a Long Acting Growth Hormone Derivative

Somapacitan is a long-acting, once-weekly, albumin-binding growth hormone (GH) derivative. The reversible albumin-binding properties leads to prolonged circulation half-life. Here, we investigated and compared somapacitan with human GH on downstream receptor signaling in primary hepatocytes and hepatocellular models and using isothermal titration calorimetry to characterize receptor binding of somapacitan in the presence or absence of human serum albumin (HSA). With non-invasive fluorescence imaging we quantitatively visualize and compare the temporal distribution and examine the tissue-specific growth hormone receptor (GHR) activation at distribution sites. We found that signaling kinetics were slightly more rapid and intense for GH compared with somapacitan. Receptor binding isotherms were characterized by a high and a low affinity interaction site with or without HSA. Using in vivo optical imaging we found prolonged systemically biodistribution of somapacitan compared with GH, which correlated with plasma pharmacokinetics. Ex vivo mouse organ analysis revealed that the temporal fluorescent intensity in livers dosed with somapacitan was significantly increased compared with GH-dosed livers and correlated with the degree of downstream GHR activation. Finally, we show that fluorescent-labeled analogs distributed to the hypertrophic zone in the epiphysis of proximal tibia of hypophysectomized rats and that somapacitan and GH activate the GHR signaling in epiphyseal tissues.

The Use and Abuse of Growth Hormone in Sports

GH is banned by the World Anti-Doping Agency as a performance-enhancing anabolic agent. Doping with GH likely began in the early 1980s and became more prevalent with the advent of recombinant technology well before any scientific evidence of benefit. The expectation that GH improves physical function stems from its anabolic and lipolytic properties. Athletic performance depends on muscle strength and the energy required to power muscle function. In recreational athletes, GH selectively improves anaerobic sprint capacity but has not been proven to significantly enhance muscle strength, power, or maximum rate of oxygen consumption. GH is secreted as a family of isoform peptides in a pulsatile manner reflecting intermittent secretion and rapid clearance. Its anabolic actions are largely mediated by IGF-I, which stimulates whole-body protein synthesis, including skeletal muscle and collagen proteins. Two methods have been validated for detecting GH abuse in athletes. The first (the isoform method) is based on distinguishing pure recombinant 22-kDa GH from the heterogeneous isoforms secreted from the pituitary. The second (the marker method) is based on measuring blood levels of GH-responsive proteins, specifically IGF-I and the N-terminal propeptide of type III collagen (P-III-NP). Only a handful of athletes have been caught since the implementation of GH doping tests in 2004. The low rate likely reflects the limitation of in-competition testing using current methods. Improved detection rates may be achieved by more out-of-competition testing, introducing athletes' biological passports, and the development of novel methods. Governance, operational, technical, and political factors influence the effectiveness of an anti-doping program.

A review of lipidation in the development of advanced protein and peptide therapeutics

The use of biologics (peptide and protein based drugs) has increased significantly over the past few decades. However, their development has been limited by their short half-life, immunogenicity and low membrane permeability, restricting most therapies to extracellular targets and administration by injection. Lipidation is a clinically-proven post-translational modification that has shown great promise to address these issues: improving half-life, reducing immunogenicity and enabling intracellular uptake and delivery across epithelia. Despite its great potential, lipidation remains an underutilized strategy in the clinical translation of lead biologics. We review how lipidation can overcome common challenges in biologics development as well as highlight gaps in our understanding of the effect of lipidation on therapeutic efficacy, where increased research and development efforts may lead to next-generation drugs.

Non-covalent hitchhiking on endogenous carriers as a protraction mechanism for antiviral macromolecular prodrugs

Albumin is a highly successful tool of drug delivery providing drastically extended body and blood residence time for the associated cargo, but it only traffics single drug copies at a time. In turn, macromolecular prodrugs (MP) are advantaged in carrying a high drug payload but offering only a modest extension of residence time to the conjugated drugs. In this work, we engineer MP to contain terminal groups that bind to albumin via non-covalent association and reveal that this facile measure affords a significant protraction for the associated polymers. This methodology is applied to MP of acyclovir, a successful drug against herpes simplex virus infection but with poor pharmacokinetics. Resulting albumin-affine MP were efficacious agents against herpes simplex virus type 2 (HSV-2) both in vitro and in vivo. In the latter case, sub-cutaneous administration of MP resulted in local (vaginal) antiviral effects and a systemic protection. Presented benefits of non-covalent association with albumin are readily transferrable to a wide variety of MP in development for drug delivery as anticancer, anti-inflammatory, and anti-viral measures.