For ADCs, SAR depends not only on the binding properties of the CDRs, but also heavily related to the characteristics of the conjugation site and chemistry, linker, and payload . The comprehensive profiling of AZD8205 biotransformations demonstrated that the critical structural determinant contributing to the design of this ADC was the linker structure that either contained propionyl-PEG8 or caproyl spacers. The linker containing the propionyl-PEG8 spacer resulted in increased thio-succinimide hydrolysis rate (Figure ). While this resulted also in initial increase in deconjugation rate, after approximately 72 hours post-dose the deconjugation rate was reduced by the competing thio-succinimide hydrolysis reaction allowing ADC1 (AZD8205) and ADC4 to effectively maintain a high DAR ratio throughout the dosing period (Figures and). Thus, quantitative biotransformation profiling across time can be an informative tool to assess the impact of various structural components on the ADC in vivo stability.