Dimerization of a PACAP peptide analogue in DMSO via asparagine and aspartic acid residues

Detection and quantitation of succinimide in intact protein via hydrazine trapping and chemical derivatization

The formation of aspartyl succinimide is a common post-translational modification of protein pharmaceuticals under acidic conditions. We present a method to detect and quantitate succinimide in intact protein via hydrazine trapping and chemical derivatization. Succinimide, which is labile under typical analytical conditions, is first trapped with hydrazine to form stable hydrazide and can be directly analyzed by mass spectrometry. The resulting aspartyl hydrazide can be selectively derivatized by various tags, such as fluorescent rhodamine sulfonyl chloride that absorbs strongly in the visible region (570 nm). Our tagging strategy allows the labeled protein to be analyzed by orthogonal methods, including HPLC-UV-Vis, liquid chromatography mass spectrometry (LC-MS), and SDS-PAGE coupled with fluorescence imaging. A unique advantage of our method is that variants containing succinimide, after derivatization, can be readily resolved via either affinity enrichment or chromatographic separation. This allows further investigation of individual factors in a complex protein mixture that affect succinimide formation. Some additional advantages are imparted by fluorescence labeling including the facile detection of the intact protein without proteolytic digestion to peptides; and high sensitivity, for example, without optimization, 0.41% succinimide was readily detected. As such, our method should be useful for rapid screening, optimization of formulation conditions, and related processes relevant to protein pharmaceuticals.

Structural aspects of gut peptides with therapeutic potential for type 2 diabetes

Gut hormones represent a niche subset of pharmacologically active agents that are rapidly gaining importance in medicine. Due to their exceptional specificity for their receptors, these hormones along with their analogues have attracted considerable pharmaceutical interest for the treatment of human disorders including type 2 diabetes. With the recent advances in the structural biology, a significant amount of structural information for these hormones is now available. This Minireview presents an overview of the structural aspects of these hormones, which have roles in physiological processes such as insulin secretion, as well as a discussion on the relevant structural modifications used to improve these hormones for the treatment of type 2 diabetes.

A mechanism-based kinetic analysis of succinimide-mediated deamidation, racemization, and covalent adduct formation in a model peptide in amorphous lyophiles

The succinimide intermediate generated during deamidation of asparagine-containing peptides and proteins has been implicated as having a role in the formation of multiple types of degradants in addition to hydrolysis products, including racemization products and, more recently, amide-linked, nonreducible protein and peptide aggregates. The formation of alternative degradants may be particularly important in solid-state formulations. This study quantitatively examines the role of the succinimide intermediate in hydrolysis, racemization, and covalent, amide-linked adduct formation in amorphous lyophiles. The degradation of a model peptide, Gly-Phe-L-Asn-Gly, and its L- or D-succinimide intermediates were examined in lyophiles containing hydroxypropyl methylcellulose and varying amounts of excess Gly-Val. Disappearance of the starting reactants and formation of up to 10 degradants were monitored when lyophiles were exposed to either 27°C/40% relative humidity (RH) or 40°C/75 RH using a stability indicating high-performance liquid chromatography method. Terminal degradant profiles were the same when the starting reactant was either Gly-Phe-L-Asn-Gly or its succinimide intermediate. Nucleophilic attack occurred preferentially at the α-carbonyl of the succinimide intermediate at ratios of approximately 2:1 for both water and the N-terminus of Gly-Val as the attacking nucleophiles. A mechanism-based kinetic model analysis indicates that hydrolysis, racemization, and covalent, amide-linked adduct formation all proceed via the succinimide intermediate.

Kinetics and mechanisms of deamidation and covalent amide-linked adduct formation in amorphous lyophiles of a model asparagine-containing Peptide

PURPOSE

Asparagine containing peptides and proteins undergo deamidation via a succinimide intermediate. This study examines the role of the succinimide in the formation of covalent, amide-linked adducts in amorphous peptide formulations.

METHODS

Stability studies of a model peptide, Gly-Phe-L-Asn-Gly, were performed in lyophiles containing an excess of Gly-Val at 'pH' 9.5 and 40°C/40% RH. Reactant disappearance and the formation of ten different degradants were monitored by HPLC. Mechanism-based kinetic models were used to generate rate constants from the concentration vs. time profiles.

RESULTS

Deamidation of Gly-Phe-L-Asn-Gly in lyophiles resulted in L- and D-aspartyl and isoaspartyl-containing peptides and four amide-linked adducts between the succinimide and Gly-Val. The kinetic analysis demonstrated competition between water and terminal amino groups in Gly-Val for the succinimide. The extent of covalent adduct formation was dependent on dilution effects due to its second order rate law.

CONCLUSION

The cyclic imide formed during deamidation of asparagine containing peptides in lyophiles can also lead to covalent adducts due to reaction with other neighboring peptides. A reaction model assuming a central role for the succinimide in the formation both hydrolysis products and covalent adducts was quantitatively consistent with the kinetic data. This mechanism may contribute to the presence of covalent, non-reducible aggregates in lyophilized peptide formulations.

Modification of the L1-CAM carboxy-terminus in pancreatic adenocarcinoma cells

The neural cell adhesion molecule L1 has recently been shown to be expressed in pancreatic adenocarcinoma (PDAC) cells. In this report, we demonstrate that L1 is expressed by moderately- to poorly-differentiated PDAC cells in situ, and that L1 expression is a predictor of poor patient survival. In vitro, reduced reactivity of an anti-L1 carboxy-terminus-specific antibody was observed in the more poorly differentiated fast-growing (FG) variant of the COLO357 population, versus its well-differentiated slow-growing (SG) counterpart, even though they express equivalent total L1. The carboxy-terminus of L1 mediates binding to the MAP kinase-regulating protein RanBPM and mutation of T1247/S1248 within this region attenuates the expression of malignancy associated proteins and L1-induced tumorigenicity in mice. Therefore, we reasoned that the differential epitope exposure observed might be indicative of modifications responsible for regulating these events. However, epitope mapping demonstrated that the major determinant of binding was actually N1251; mutation of T1247 and S1248, alone or together, had little effect on C20 binding. Moreover, cluster assays using CD25 ectodomain/L1 cytoplasmic domain chimeras demonstrated the N1251-dependent, RanBPM-independent stimulation of erk phosphorylation in these cells. Reactivity of this antibody also reflects the differential exposure of extracellular epitopes in these COLO357 sublines, consistent with the previous demonstration of L1 ectodomain conformation modulation by intracellular modifications. These data further support a central role for L1 in PDAC, and define a specific role for carboxy-terminal residues including N1251 in the regulation of L1 activity in PDAC cells.

Chemical modification of class II G protein-coupled receptor ligands: frontiers in the development of peptide analogs as neuroendocrine pharmacological therapies

Recent research and clinical data have begun to demonstrate the huge potential therapeutic importance of ligands that modulate the activity of the secretin-like, Class II, G protein-coupled receptors (GPCRs). Ligands that can modulate the activity of these Class II GPCRs may have important clinical roles in the treatment of a wide variety of conditions such as osteoporosis, diabetes, amyotrophic lateral sclerosis and autism spectrum disorders. While these receptors present important new therapeutic targets, the large glycoprotein nature of their cognate ligands poses many problems with respect to therapeutic peptidergic drug design. These native peptides often exhibit poor bioavailability, metabolic instability, poor receptor selectivity and resultant low potencies in vivo. Recently, increased attention has been paid to the structural modification of these peptides to enhance their therapeutic efficacy. Successful modification strategies have included d-amino acid substitutions, selective truncation, and fatty acid acylation of the peptide. Through these and other processes, these novel peptide ligand analogs can demonstrate enhanced receptor subtype selectivity, directed signal transduction pathway activation, resistance to proteolytic degradation, and improved systemic bioavailability. In the future, it is likely, through additional modification strategies such as addition of circulation-stabilizing transferrin moieties, that the therapeutic pharmacopeia of drugs targeted towards Class II secretin-like receptors may rival that of the Class I rhodopsin-like receptors that currently provide the majority of clinically used GPCR-based therapeutics. Currently, Class II-based drugs include synthesized analogs of vasoactive intestinal peptide for type 2 diabetes or parathyroid hormone for osteoporosis.