Notably, trastuzumab-AJICAP-M-MMAE administered at a dose of 5 mg/kg showed significant tumor regression. In prior studies, the minimum effective dose of stochastically conjugated ADCs with a DAR of 4, achieved through native cysteine conjugation, was established at 2.5 mg/kg . To elucidate the different stability characteristics of the two site-specific ADCs, an in vivo pharmacokinetic study was performed using a rat model (Figure ). For the control ADC, discernible detachment of the payload was observed a few days post-administration. In contrast, the AJICAP-M-ADC exhibited a considerably lower rate of payload detachment, as demonstrated by a comparative analysis of the concentration profiles of the total antibody mAb and the total ADC. The present data suggest that the improved stability and minimized payload release of AJICAP-ADCs could significantly enhance their therapeutic efficacy and safety profile, making them advantageous candidates for further exploration of ADC-based treatments.