Quaternary Amine-Induced Peptide Degradation via Cyclization

Aspects of complexity in quality and safety assessment of peptide therapeutics and peptide-related impurities. A regulatory perspective

In recent years, a number of therapeutic peptides have been authorized in the EU market, and several others are in the clinical development phase or under assessment for full dossier or generic applications. Quality and safety guidelines specific to peptides are limited, and some aspects have to be considered. In particular, concerns relate to the analytical investigation for impurities and the toxicological assessment of these substances. The guidelines and the compendial pharmacopoeias provide certain references but that may be questionable if interpreted according to whether therapeutic peptides are considered chemical or biological entities, large or small. The characterization of peptide-related impurities cannot follow the small molecule approach but should consider aspects closely linked to the complex mechanisms of action that these large molecules can exert in the human body. Although direct genotoxic mechanisms cannot be excluded, hazardous interactions on biological systems cannot be ruled out, as in the case of natural peptide toxins and their specific interactions with cellular or membrane targets. From a regulatory perspective, only after specific risk identification and characterization should an equally specific safety threshold in relation to potential toxicity be defined.

Peptides derivatized with bicyclic quaternary ammonium ionization tags. Sequencing via tandem mass spectrometry

Improving the sensitivity of detection and fragmentation of peptides to provide reliable sequencing of peptides is an important goal of mass spectrometric analysis. Peptides derivatized by bicyclic quaternary ammonium ionization tags: 1-azabicyclo[2.2.2]octane (ABCO) or 1,4-diazabicyclo[2.2.2]octane (DABCO), are characterized by an increased detection sensitivity in electrospray ionization mass spectrometry (ESI-MS) and longer retention times on the reverse-phase (RP) chromatography columns. The improvement of the detection limit was observed even for peptides dissolved in 10 mM NaCl. Collision-induced dissociation tandem mass spectrometry of quaternary ammonium salts derivatives of peptides showed dominant a- and b-type ions, allowing facile sequencing of peptides. The bicyclic ionization tags are stable in collision-induced dissociation experiments, and the resulted fragmentation pattern is not significantly influenced by either acidic or basic amino acid residues in the peptide sequence. Obtained results indicate the general usefulness of the bicyclic quaternary ammonium ionization tags for ESI-MS/MS sequencing of peptides.