Date Published: September 27, 2018
Publisher: Public Library of Science
Author(s): Jordan D. Lewicky, Alexandrine L. Martel, Nya L. Fraleigh, Amanda Boraman, Thi M.-D. Nguyen, Peter W. Schiller, Tze Chieh Shiao, René Roy, Hoang-Thanh Le, Maxim Antopolsky.
The therapeutic application of peptide-based drugs is significantly limited by the rapid proteolytic degradation that occurs when in blood. Encapsulation of these peptide structures within a delivery system, such as liposomes, can greatly improve both stability and target delivery. As part of our work focused on novel ambiphilic mannosylated neoglycolipids as targeted drug delivery systems, we have developed a C14-alkyl-mannopyranoside that forms self-assembled monodisperse liposomes. Herein, these glycoliposomes are investigated as a potential method to improve the plasma stability of peptide-based drugs. Reversed phase high-performance liquid chromatography (RP-HPLC) and mass spectrometry (MS) methods were developed to assess the in vitro plasma stability of two structurally diverse peptides, including the kappa opioid receptor selective antagonist dynantin, and the NOD2 innate immune receptor ligand muramyl dipeptide (MDP). The RP-HPLC methods developed were able to resolve the peptides from background plasma contaminants and provided suitable response levels and linearity over an appropriate concentration range. Both compounds were found to be significantly degraded in rat plasma. Increasing degrees of both entrapment and stabilization were noted when dynantin was combined with the C14-alkyl-mannopyranoside in increasing peptide:glycoside ratios. The combination of MDP with the glycolipid also led to peptide entrapment, which greatly improved the plasma stability of the peptide. Overall, the results clearly indicate that the stability of peptide-based structures, which are subject to degradation in plasma, can be greatly improved via entrapment within C14-alkyl-mannopyranoside-bearing glycoliposomes.
Generally, peptides have low toxicity, high specificity and high affinity to their targets, making them interesting molecules for drug development [1–4]. However, the therapeutic potential of peptides is limited due to poor bioavailability, poor absorption through membranes, cleavage by proteolytic enzymes, and rapid elimination by both the reticuloendothelial system and by renal filtration [5–8]. This rapid metabolism and elimination results in an insufficient half-life in vivo for the peptides to reach their therapeutic target.
An optimized reverse phase gradient HPLC method was developed for the analysis of dynantin plasma stability based on the previously reported methods . The method provided excellent results in terms of retention time, peak area reproducibility, detection sensitivity, and resolution between the peptide and the plasma background peaks (S1 Fig). Using this method, a standard curve was generated for dynantin (S2 Fig) which showed consistent linearity over a concentration range appropriate to the intended stability studies (50–800 ng injection mass).
The highly promising therapeutic potential of peptide-based drugs is a product of their broad chemical and biological diversity, high target affinity and specificity, and low degrees of toxicity and tissue accumulation . One of the consequences of the ubiquitous expression of proteolytic enzymes is that the degradation of peptide based drugs starts immediately once in an organism, that which is independent of how the peptide is administered . The administration of peptide based drugs typically occurs by injection or infusion to enable systemic circulation, and in either case, blood will be the first medium the peptide encounters. Proteolytic degradation in blood is typically studied ex vivo by incubating the peptide in serum or plasma which contains all of the same proteases that would be encountered in vivo. This assay has been used as both a predictor of proteolytic lability, and as a tool to assess the efficacy of various strategies aimed at improving stability [7, 9–15]. The results of our study show that the rapid degradation of dynantin and MDP can be improved with ML-C14 glycoliposomal entrapment, confirming our ex vivo plasma stability as a useful and inexpensive tool for the primary assessment of delivery system efficacy in the progression towards in vivo experiments.