New Fluorocarbon conjugates to increase metabolic stability of GPCR peptides: Design, synthesis, physicochemical and biological characterizations – FLUOROPEP

During the last decade, peptides have gained a wide range of applications in medicine. Indeed, more than 60 US Food and Drug Administration (FDA)-approved peptide medicines are on the market and this is expected to grow significantly, with approximately 140 peptide drugs currently in clinical trials and more than 500 therapeutic peptides in preclinical development. In addition, out of the 390 non-olfactory G protein coupled receptors (GPCRs) identified in the genome, 290 have only peptides as ligands (no small organic compounds). However, these peptides are often not directly suitable for use as convenient pharmacological tools or novel therapeutics because they display generally short circulating plasma half-life.

Currently, the techniques developed for half-life extension are generally based on the modification of the native peptide backbone (non-natural amino-acids, lactam bridges, stapling, cyclization) which is a long process. The incorporation of Polyethylene glycol (PEG) into peptides has also been used to limit glomerular filtration and thereby increase plasma half-life by limiting the elimination of peptides. However, because of increased safety and tolerability concerns related to the use of PEG as a component of an injectable therapeutic, PEGylation has become a less preferred choice. Another approach is based on the binding of the peptide to the circulating protein albumin used as a vehicle by peptide acylation with hydrocarbon tail as seen in the GLP-1 agonist (Luraglutide). Nevertheless the presence of the hydrocarbon tail makes the peptide much less selective for its target with potential enhanced toxicity.

In the FLUOROPEP project, we propose a multidisciplinary research program (organic chemistry, physicochemistry, biophysics, biology) which aims at developing an unprecedented, innovative and convenient approach to improve circulating plasma half-life of endogenous peptides, taking GPCRs peptidic ligands as model system. The strategy adopted in our project relies in the incorporation of a fluorocarbon-chain (F-chain) into N-terminal or C-terminal part of the peptide sequence to force the native peptide to self-organize in aqueous solution. As a consequence, the supramolecular organization should result in the decrease of enzymatic peptides degradation and the enhancement of its in vivo plasma half-life stability. F-chains have unique properties, very different from those of hydrocarbon chains. In particular, they are more stable, stiffer, hydrophobic and significantly more lipophobic which increases their specificity and their bioavailability. In addition, F-chains are biologically inert molecules with no intrinsic immuno-stimulatory activity or immunogenicity. Thereby, fluorocarbons have already been used for various medical applications, including blood substitutes (fluorocarbon emulsions) or more recently as synthetic vaccine (fluoropeptides) demonstrating their absence of toxicity in human.

Three GPCR peptides that were previously reported for in vivo unstability will be selected as models: apelin, oxytocin and spexin. The physicochemical and the in vitro and in vivo pharmacology of the resulting fluoropeptides will be fully investigated. The preliminary data demonstrate that the incorporation of a fluorocarbon-chain on apeline peptide enables not only to maintain its pharmacological properties towards APJ receptor but also greatly increases its human plasma half-life and in vivo efficacy.

To date, such a strategy has never been evaluated for therapeutic peptides with targets located in the systemic and/or central nervous system. The FLUOROPEP project should open the route to a convenient, safe and general approach to greatly increase the half-life stability of peptides for their in vivo evaluation as pharmacological tools and/or therapeutic agents.