Newly Designed Modifier Prolongs the Action of Short-Lived Peptides and Proteins by Allowing Their Binding to Serum Albumin

A Versatile Platform to Generate Prodrugs with Rapid and Precise Albumin Hitchhiking and High Cargo Loading for Tumor-Targeted Chemotherapy

Due to its tumor homing and long serum half-life, albumin is an ideal drug carrier for chemotherapy. For endogenous albumin hitchhiking with high cargo loading, a trimeric albumin-binding domain (ABD), i.e., ABD-Tri is designed by fusing an ABD with high specificity and affinity for albumin to a self-trimerizing domain (Tri) with an additional cysteine residue. ABD-Tri is highly (40 mg L-1 ) expressed as soluble and trimeric proteins in Escherichia coli (E. coli). Once mixed together, ABD-Tri rapidly and specifically forms a stable complex with albumin under physiological conditions without obviously changing its receptor- and cell-binding and tumor-homing properties. Maleimide-modified prodrugs are highly effectively conjugated to ABD-Tri to produce homogenous ABD-Tri-prodrugs with triple cargo loading under physiological conditions by thiol-maleimide click chemistry. Unlike the maleimide moiety, which can only mediate time- and concentration-dependent albumin binding, ABD-Tri mediated fast (within several minutes) albumin binding of drugs even at extremely low concentrations (µg mL-1 ). Compared to maleimide-modified prodrugs, ABD-Tri-prodrugs exhibit better tumor homing and greater in vivo antitumor effect, indicating that conjugation of chemical drug to ABD-Tri outperforms maleimide modification for endogenous albumin hitchhiking. The results demonstrate that ABD-Tri may serve as a novel platform to produce albumin-binding prodrugs with high cargo-loading capacity for tumor-targeted chemotherapy.

Molecular analysis and therapeutic applications of human serum albumin-fatty acid interactions

Human serum albumin (hSA) is the major carrier protein for fatty acids (FAs) in plasma. Its ability to bind multiple FA moieties with moderate to high affinity has inspired the use of FA conjugation as a safe and natural platform to generate long-lasting therapeutics with enhanced pharmacokinetic properties and superior efficacy. In this frame, the choice of the FA is crucial and a comprehensive elucidation of the molecular interactions of FAs with hSA cannot be left out of consideration. To this intent, we report here a comparative analysis of the binding mode of different FA moieties with hSA. The choice among different albumin-binding FAs and how this influence the pharmacokinetics properties of a broad spectrum of therapeutic molecules will be discussed including a critical description of some clinically relevant FA conjugated therapeutics.

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.

Generation of therapeutic protein variants with the human serum albumin binding capacity via site-specific fatty acid conjugation

Extension of the serum half-life is an important issue in developing new therapeutic proteins and expanding applications of existing therapeutic proteins. Conjugation of fatty acid, a natural human serum albumin ligand, to a therapeutic protein/peptide was developed as a technique to extend the serum half-life in vivo by taking advantages of unusually long serum half-life of human serum albumin (HSA). However, for broad applications of fatty acid-conjugation, several issues should be addressed, including a poor solubility of fatty acid and a substantial loss in the therapeutic activity. Therefore, herein we systematically investigate the conditions and components in conjugation of fatty acid to a therapeutic protein resulting in the HSA binding capacity without compromising therapeutic activities. By examining the crystal structure and performing dye conjugation assay, two sites (W160 and D112) of urate oxidase (Uox), a model therapeutic protein, were selected as sites for fatty acid-conjugation. Combination of site-specific incorporation of a clickable p-azido-L-phenylalanine to Uox and strain-promoted azide-alkyne cycloaddition allowed the conjugation of fatty acid (palmitic acid analog) to Uox with the HSA binding capacity and retained enzyme activity. Deoxycholic acid, a strong detergent, greatly enhanced the conjugation yield likely due to the enhanced solubility of palmitic acid analog.

Phenylbutazone, a New Long-Acting Agent that can Improve the Peptide Pharmacokinetic Based on Serum Albumin as a Drug Carrier

As a NPY-2 receptor agonist, PYY24-36- Leu31 is reported to suppress appetite and has a potential in obesity treatment, but its short half-life limits the clinical application. The use of chemical modification to improve interactions with human serum albumin (HSA) is an effective strategy for prolonging the half-lives of peptide analogues. So based on the characteristics that phenylbutazone has a good combination with HSA, we selected a proper linker to link with PYY24-36 -Leu31 to create long-acting and highly biologically active PYY24-36 -Leu31 conjugates, and successfully find a novel, long-acting PYY24-36 -Leu31 conjugate 8 that, when dosed every other day in diet induce obese (DIO) mice for 2 weeks, results in a significant reduction in food intake and body weight and improvement in blood parameter and hepatic steatosis.

Bioconjugation – using selective chemistry to enhance the properties of proteins and peptides as therapeutics and carriers

Both peptide and protein therapeutics are becoming increasingly important for treating a wide range of diseases. Functionalisation of theseviasite-selective chemical modification leads to enhancement of their therapeutic properties.

Site-specific fatty acid-conjugation to prolong protein half-life in vivo

Therapeutic proteins are indispensable in treating numerous human diseases. However, therapeutic proteins often suffer short serum half-life. In order to extend the serum half-life, a natural albumin ligand (a fatty acid) has been conjugated to small therapeutic peptides resulting in a prolonged serum half-life via binding to patients' serum albumin in vivo. However, fatty acid-conjugation has limited applicability due to lack of site-specificity resulting in the heterogeneity of conjugated proteins and a significant loss in pharmaceutical activity. In order to address these issues, we exploited the site-specific fatty acid-conjugation to a permissive site of a protein, using copper-catalyzed alkyne-azide cycloaddition, by linking a fatty acid derivative to p-ethynylphenylalanine incorporated into a protein using an engineered pair of yeast tRNA/aminoacyl tRNA synthetase. As a proof-of-concept, we show that single palmitic acid conjugated to superfolder green fluorescent protein (sfGFP) in a site-specific manner enhanced a protein's albumin-binding in vitro about 20 times and the serum half-life in vivo 5 times when compared to those of the unmodified sfGFP. Furthermore, the fatty acid conjugation did not cause a significant reduction in the fluorescence of sfGFP. Therefore, these results clearly indicate that the site-specific fatty acid-conjugation is a very promising strategy to prolong protein serum half-life in vivo without compromising its folded structure and activity.