Understanding the chemical stability of peptidomimetic therapeutics using high-resolution mass spectrometry: a study of terlipressin and its degradation products.

Terlipressin, a synthetic 12-amino acid peptidomimetic of vasopressin, is a critical therapeutic agent for hepatorenal syndrome and oesophageal variceal hemorrhage. The inherent susceptibility of therapeutic peptides to hydrolytic and oxidative degradation necessitates thorough stability profiling. Conformational changes in the peptide, arising from hydrolysis and oxidative degradation, can hinder effective target binding and thereby diminish its capacity to elicit intended downstream effects, leading to reduced efficacy. For synthetic peptides, the most relevant stability testing principles are derived from the parent International Council for Harmonisation (ICH) stability testing guidelines Q1A(R2) and Q5C [1,2]. This study investigated the intrinsic degradation pathways of terlipressin under systematically varied stress conditions, including acidic, basic, neutral, and oxidative (H₂O₂) exposure at room temperature. Terlipressin exhibited sensitivity across all tested conditions, yielding a total of eleven distinct degradation products (DPs). To facilitate the separation of these DPs, a gradient reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed utilizing an XSelect® CSH™ C18 (130 Å, 2.5 µm, 4.6 × 150 mm) column. The analytical assay method was validated according to ICH Q2(R1) guidelines. The intramolecular disulfide linkage between two cysteine residues presented a challenge for DP characterization. To address this, a chemical reduction strategy employing dithiothreitol (DTT) was integrated with ultra-high performance liquid chromatography-high resolution tandem mass spectrometry (UHPLC-HRMS/MS). This approach enabled the successful elucidation of the eleven DPs, revealing modifications such as truncation, deamidation, acetylation, and oxidation. The characterized fragmentation patterns and identified degradation products provide fundamental insights into the stability behavior of disulfide-containing therapeutic peptides, directly contributing to rational formulation design and development.