Cyclic IM-MS reveals Balixafortide's thermal instability and bioactivity loss from topological isomers

Peptide therapeutics, while offering high target specificity and potent bioactivity, are prone to forming topological isomers during synthesis and processing. This often-overlooked microheterogeneity can profoundly impact drug efficacy, structural stability, and in vivo disposition. Current analytical methods struggle to precisely discriminate and quantify these variants, leaving a critical gap in understanding how subtle structural differences translate into significant changes in drug performance, particularly under stress conditions like thermal exposure.

Researchers utilized cyclic ion mobility-mass spectrometry (cIM-MS) as a high-resolution platform to characterize topological isomers in complex peptide mixtures. They employed the lasso peptide Stlassin and the potent CXCR4 antagonist bicyclic peptide Balixafortide as model systems. The capability of cIM-MS to separate peptide topological isomers was systematically evaluated. Accelerated thermal-stability studies were conducted on Balixafortide to assess its behavior under stress. Multiple target-binding assays were then performed to quantify the impact of observed changes on drug efficacy and stability.

The cIM-MS analysis revealed distinct conformational profiles for the model peptides. Stlassin was found to adopt a unique, well-defined conformation, indicating high structural homogeneity. In contrast, Balixafortide populated multiple conformational states, demonstrating significant microheterogeneity. Accelerated thermal-stability studies showed that Balixafortide undergoes rapid topological rearrangement and degradation when subjected to stress conditions. This thermal instability directly led to a compromise in drug efficacy and stability, as demonstrated by subsequent target-binding assays. The study established a clear link between microscopic isomer distributions and macroscopic bioactivity, identifying two primary pathways of thermal inactivation in peptide therapeutics: degradation and conformational reorganization. This highlights how subtle structural variations can scale into biologically meaningful effects, impacting drug performance.

Balixafortide's rapid topological rearrangement and degradation under thermal stress substantially compromised its drug efficacy and stability in target-binding assays.