Reductive Desulfuration as an Important Tool in Detection of Small Molecule Modifications to Payload of Antibody Drug Conjugates.

A high resolution accurate mass LC-MS method was developed to facilitate the characterization of a subset of antibody drug conjugate (ADC) biotherapeutics, where the payload is linked to the antibody by a thioether bond. Desulfuration of the thioether linker was optimized for release of the payload to take advantage of the high resolution and high mass accuracy of the Orbitrap to characterize metabolism of the payload. Two model ADCs, trastuzumab emtansine (T-DM1) and SigmaMAb dansyl-cadavarine-SMCC (SigmaMAb ADC mimic) were selected for optimization of the desulfuration reaction as a function of reaction time, pH, organic solvent, and chaotropic reagents (urea, guanidine HCl) by monitoring the yield of released desulfurated DM1 from T-DM1 and desulfurated dansyl-cadaverine-SMCC from SigmaMAb ADC mimic, respectively. The optimized desulfuration technique was successfully applied to enable characterization of the ADC following its incubation in hepatocytes, liver microsomes, and buffers, as illustrated by the identification of a hydrolyzed thiosuccinimide ring of SigmaMAb ADC mimic following incubation in buffer for 48 h. The results from this study demonstrate that the chemical cleavage of thioether bond by desulfuration is simple, efficient, and specific. This technique is useful in characterization of metabolism on the payload of ADC to provide guidance for improvement of its biopharmaceutical profile. This is the first report on characterization of modification to payload of ADC following desulfuration.