An efficient liquid chromatography-high resolution mass spectrometry approach for the optimization of the metabolic stability of therapeutic peptides

Collagen derived Gly-Pro-type DPP-IV inhibitory peptides: Structure-activity relationship, inhibition kinetics and inhibition mechanism

Our previous study has demonstrated that both the amino acid at N3 position and peptide length affected the DPP-IV inhibitory activity of Gly-Pro-type peptides. To further elucidate their molecular mechanism, a combined approach of QSAR modeling, enzymatic kinetics and molecular docking was used. Results showed that the QSAR models of Gly-Pro-type tripeptides and Gly-Pro-type peptides containing 3-12 residues were successfully constructed by 5z-scale descriptor with R2 of 0.830 and 0.797, respectively. The lower values of electrophilicity, polarity, and side-chain bulk of amino acid at N3 position caused higher DPP-IV inhibitory activity of Gly-Pro-type peptides. Moreover, an appropriate increase in the length of Gly-Pro-type peptides did not change their competitive inhibition mode, but decreased their inhibition constants (Ki values) and increased interactions with DPP-IV. More importantly, the interactions between the residues at C-terminal of Gly-Pro-type peptides containing 5 ∼ 6 residues with S2 extensive subsites (Ser209, Phe357, Arg358) of DPP-IV increased the interactions of Gly residue at N1 position with the S2 subsites (Glu205, Glu206, Asn710, Arg125, Tyr662) and decreased the acylation level of DPP-IV-peptide complex, and thereby increasing peptides' DPP-IV inhibitory activity.

Fatty acid acylated peptide therapeutics: discovery of omega-n oxidation of the lipid chain as a novel metabolic pathway in preclinical species

We recently described C18 fatty acid acylated peptides as a new class of potent long-lasting single-chain RXFP1 agonists that displayed relaxin-like activities in vivo. Early pharmacokinetics and toxicological studies of these stearic acid acylated peptides revealed a relevant oxidative metabolism occurring in dog and minipig, and also seen at a lower extent in monkey and rat. Mass spectrometry combined to NMR spectroscopy studies revealed that the oxidation occurred, unexpectedly, on the stearic acid chain at ω-1, ω-2 and ω-3 positions. Structure-metabolism relationship studies on acylated analogues with different fatty acids lengths (C15-C20) showed that the extent of oxidation was higher with longer chains. The oxidized metabolites could be generated in vitro using liver microsomes and engineered bacterial CYPs. These systems were correlating poorly with in vivo metabolism observed across species; however, the results suggest that this biotransformation pathway might be catalyzed by some unknown CYP enzymes.

Review on Extraction, Modification, and Synthesis of Natural Peptides and Their Beneficial Effects on Skin

Peptides, functional nutrients with a size between those of large proteins and small amino acids, are easily absorbed by the human body. Therefore, they are seeing increasing use in clinical medicine and have revealed immunomodulatory and anti-inflammatory properties which could make them effective in healing skin wounds. This review sorted and summarized the relevant literature about peptides during the past decade. Recent works on the extraction, modification and synthesis of peptides were reviewed. Importantly, the unique beneficial effects of peptides on the skin were extensively explored, providing ideas for the development and innovation of peptides and laying a knowledge foundation for the clinical application of peptides.

Subcutaneous Catabolism of Peptide Therapeutics: Bioanalytical Approaches and ADME Considerations

Many peptide drugs such as insulin and glucagon-like peptide (GLP-1) analogues are successfully administered subcutaneously (SC). Following SC injection, peptides may undergo catabolism in the SC compartment before entering systemic circulation, which could compromise their bioavailability and in turn affect their efficacy.This review will discuss how both technology and strategy have evolved over the past years to further elucidate peptide SC catabolism.Modern bioanalytical technologies (particularly liquid chromatography-high-resolution mass spectrometry) and bioinformatics platforms for data mining has prompted the development of in silico, in vitro and in vivo tools for characterizing peptide SC catabolism to rapidly address proteolytic liabilities and, ultimately, guide the design of peptides with improved SC bioavailability.More predictive models able to recapitulate the interplay between SC catabolism and other factors driving SC absorption are highly desirable to improve in vitro/in vivo correlations.We envision the routine incorporation of in vitro and in vivo SC catabolism studies in ADME screening funnels to develop more effective peptide drugs for SC delivery.

Design of Membrane Active Peptides Considering Multi-Objective Optimization for Biomedical Application

A multitude of membrane active peptides exists that divides into subclasses, such as cell penetrating peptides (CPPs) capable to enter eukaryotic cells or antimicrobial peptides (AMPs) able to interact with prokaryotic cell envelops. Peptide membrane interactions arise from unique sequence motifs of the peptides that account for particular physicochemical properties. Membrane active peptides are mainly cationic, often primary or secondary amphipathic, and they interact with membranes depending on the composition of the bilayer lipids. Sequences of these peptides consist of short 5–30 amino acid sections derived from natural proteins or synthetic sources. Membrane active peptides can be designed using computational methods or can be identified in screenings of combinatorial libraries. This review focuses on strategies that were successfully applied to the design and optimization of membrane active peptides with respect to the fact that diverse features of successful peptide candidates are prerequisites for biomedical application. Not only membrane activity but also degradation stability in biological environments, propensity to induce resistances, and advantageous toxicological properties are crucial parameters that have to be considered in attempts to design useful membrane active peptides. Reliable assay systems to access the different biological characteristics of numerous membrane active peptides are essential tools for multi-objective peptide optimization.

Comparison of different protein precipitation and solid-phase extraction protocols for the study of the catabolism of peptide drugs by LC-HRMS

LC-HRMS-based identification of the products of peptide catabolism is the key to drive the design of more stable compounds. Because the catabolite of a given peptide can be very different from the parent compound and from other catabolites in terms of physicochemical properties, it can be challenging to develop an analytical method that allows recovery and detection of the parent and all parent-related catabolites. The aim of this study was to investigate how the recovery and the matrix effect of peptidic drugs and their catabolites are affected by different protein precipitation (PP) and solid-phase extraction (SPE) protocols. To this purpose, four model peptides representative of different classes (somatostatin, GLP-2, human insulin and liraglutide) were digested with trypsin and chymotrypsin to simulate proteolytic catabolism. The resulting mixtures of the parent peptides and their proteolytic products covering a wide range of relative hydrophobicity (H_R ) and isoelectric points (pI) were spiked in human plasma and underwent different PP and SPE protocols. Recovery and matrix effect were measured for each peptide and its catabolites. PP with three volumes of ACN or EtOH yielded the highest overall recoveries (more than 50% for the four parent peptides and all their catabolites) among all the tested PP and SPE protocols. Mixed-mode anion exchange (MAX) was the only SPE sorbent among the five tested that allowed to extract all the peptides with recoveries more than 20%. Matrix effect was generally lower with SPE. Overall, it was observed that peptides with either high hydrophilicity (e.g., somatostatin catabolites) or hydrophobicity (GLP-2 and lipidated liraglutide catabolites) had a much narrower choice of PP solvent or SPE protocol. Simulation of catabolism using recombinant enzymes together with in silico calculation of the H_R and the pI of potential proteolysis products is recommended to select the optimal extraction conditions for the study of peptide catabolism.

In Vitro Metabolic Stability of a Casein-Derived Dipeptidyl Peptidase-IV (DPP-IV) Inhibitory Peptide VPYPQ and Its Controlled Release from Casein by Enzymatic Hydrolysis

The aim of this study was to investigate the dipeptidyl peptidase-IV (DPP-IV) inhibition and metabolic stability of a casein-derived peptide Val-Pro-Tyr-Pro-Gln (VPYPQ) and its fragments as well as their release from casein following hydrolysis. Results showed that VPYPQ was the most potent DPP-IV inhibitory peptide among them with an IC₅₀ value of 41.45 μM. This might be due to its two internal Pro residues at positions 2 and 4. Moreover, VPYPQ was resistant to hydrolysis by gastrointestinal enzymes and was relatively more stable to hydrolysis by DPP-IV and peptidases in plasma compared with its fragments. Additionally, oral administration of VPYPQ at a dose of 90 μmol/kg body weight could reduce the postprandial blood glucose levels in mice. More importantly, VPYPQ could be released efficiently from casein following hydrolysis by a combination of papain and in vitro digestion, reaching up to 3211.15 μg/g. Therefore, VPYPQ was a promising casein-derived DPP-IV inhibitor.

Octreotide Conjugates for Tumor Targeting and Imaging

Tumor targeting has emerged as an advantageous approach to improving the efficacy and safety of cytotoxic agents or radiolabeled ligands that do not preferentially accumulate in the tumor tissue. The somatostatin receptors (SSTRs) belong to the G-protein-coupled receptor superfamily and they are overexpressed in many neuroendocrine tumors (NETs). SSTRs can be efficiently targeted with octreotide, a cyclic octapeptide that is derived from native somatostatin. The conjugation of cargoes to octreotide represents an attractive approach for effective tumor targeting. In this study, we conjugated octreotide to cryptophycin, which is a highly cytotoxic depsipeptide, through the protease cleavable Val-Cit dipeptide linker using two different self-immolative moieties. The biological activity was investigated in vitro and the self-immolative part largely influenced the stability of the conjugates. Replacement of cryptophycin by the infrared cyanine dye Cy5.5 was exploited to elucidate the tumor targeting properties of the conjugates in vitro and in vivo. The compound efficiently and selectively internalized in cells overexpressing SSTR2 and accumulated in xenografts for a prolonged time. Our results on the in vivo properties indicate that octreotide may serve as an efficient delivery vehicle for tumor targeting.

Synthesis and Biological Evaluation of RGD⁻Cryptophycin Conjugates for Targeted Drug Delivery

Cryptophycins are potent tubulin polymerization inhibitors with picomolar antiproliferative potency in vitro and activity against multidrug-resistant (MDR) cancer cells. Because of neurotoxic side effects and limited efficacy in vivo, cryptophycin-52 failed as a clinical candidate in cancer treatment. However, this class of compounds has emerged as attractive payloads for tumor-targeting applications. In this study, cryptophycin was conjugated to the cyclopeptide c(RGDfK), targeting integrin αvβ₃, across the protease-cleavable Val-Cit linker and two different self-immolative spacers. Plasma metabolic stability studies in vitro showed that our selected payload displays an improved stability compared to the parent compound, while the stability of the conjugates is strongly influenced by the self-immolative moiety. Cathepsin B cleavage assays revealed that modifications in the linker lead to different drug release profiles. Antiproliferative effects of Arg-Gly-Asp (RGD)⁻cryptophycin conjugates were evaluated on M21 and M21-L human melanoma cell lines. The low nanomolar in vitro activity of the novel conjugates was associated with inferior selectivity for cell lines with different integrin αvβ₃ expression levels. To elucidate the drug delivery process, cryptophycin was replaced by an infrared dye and the obtained conjugates were studied by confocal microscopy.

Evaluating prodrug characteristics of a novel anticoagulant fusion protein neorudin, a prodrug targeting release of hirudin variant 2-Lys47 at the thrombosis site, by means of in vitro pharmacokinetics

Recombinant neorudin (EPR-hirudin, EH), a low-bleeding anticoagulant fusion protein, is an inactive prodrug designed to be converted to the active metabolite, hirudin variant 2-Lys47 (HV2), locally at the thrombus site by FXa and/or FXIa, following activation of the coagulation system. Our aim was to evaluate the prodrug characteristics of EH by comparing the biotransformation of EH and HV2 in biological matrices, including rat blood, liver, and kidney homogenates, demonstrating the cleavage of EH to HV2 by FXa and FXIa, and comparing the conversion of EH to HV2 between fresh whole blood and whole-blood clot homogenate, using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS). Both EH and HV2 were stable in blood and unstable in the liver and kidney homogenates. Eight EH metabolites and eight HV2 metabolites identified as N-terminal fragments were found in the liver and kidney. C-terminal proteolysis is therefore the major metabolic pathway, with serine/cysteine carboxypeptidases and metallocarboxypeptidases being responsible for the degradation of EH and HV2 in the liver and kidney, respectively. EH was cleaved to release HV2 by FXIa. Higher levels of HV2 were produced from EH in the whole-blood clot homogenate, in which the coagulation system was activated compared with those in fresh whole blood. In conclusion, the metabolism of EH and HV2 shares the same cleavage pattern, and EH is transformed into HV2 when the coagulation system is activated, where FXIa is a specific enzyme. Our in vitro study revealed the anticipated prodrug characteristics of EH newly designed as an inactive prodrug of hirudin.

Smart biomaterials: Surfaces functionalized with proteolytically stable osteoblast-adhesive peptides

Engineered scaffolds for bone tissue regeneration are designed to promote cell adhesion, growth, proliferation and differentiation. Recently, covalent and selective functionalization of glass and titanium surfaces with an adhesive peptide (HVP) mapped on [351-359] sequence of human Vitronectin allowed to selectively increase osteoblast attachment and adhesion strength in in vitro assays, and to promote osseointegration in in vivo studies. For the first time to our knowledge, in this study we investigated the resistance of adhesion sequences to proteolytic digestion: HVP was completely cleaved after 5 h. In order to overcome the enzymatic degradation of the native peptide under physiological conditions we synthetized three analogues of HVP sequence. A retro-inverted peptide D-2HVP, composed of D amino acids, was completely stable in serum-containing medium. In addition, glass surfaces functionalized with D-2HVP increased human osteoblast adhesion as compared to the native peptide and maintained deposition of calcium. Interestingly, D-2HVP increased expression of IBSP, VTN and SPP1 genes as compared to HVP functionalized surfaces. Total internal reflection fluorescence microscope analysis showed cells with numerous filopodia spread on D-2HVP-functionalized surfaces. Therefore, the D-2HVP sequence is proposed as new osteoblast adhesive peptide with increased bioactivity and high proteolytic resistance.