Dxd (Exatecan ADC derivative) is a potent DNA topoisomerase I inhibitor with an IC50 of 0.31 uM for targeting ADCs (DS-8201A). Dxd was cytotoxic to human tumor cell lines KPL-4, NCI-N87 and SK-BR, 3 and the IC50s of MDA-MB-468 was 1.43 NM-4.07 nM, while lgGADC (Dxd as payload) had no inhibitory effect on HER2 expression in the 4 cell lines. DS8201a (Dxd as payload) had a significant inhibitory effect on HER2-positive KPL-4 and NCI cell lines N87 and SK-BRwith IC50 values of 26.8, 25.4 and 6.7 ng/mL, respectively, but had no inhibitory effect on MDA MB-468 (IC50, > 10000 - mL). HRP-anti-DXD-antibody is a conjugation product of HRP and anti-DXD-antibody. It can be used in PK, PD analysis and ELISA.