Anti-HER2 antibody-drug conjugate and application thereof

An antibody-drug conjugate or a pharmaceutically acceptable salt thereof, wherein the structure of the antibody-drug conjugate is as shown in formula I:

• Ab-(L-D)n I
• wherein:
• Ab is an antibody, wherein the antibody is pertuzumab;
• L is a linker connecting the antibody and the drug;
• wherein L has a structure of L-1:
• wherein L21 is a linker moiety independently selected from the group consisting of Val-Cit, —(CH2)n-, —(CH2CH2O)n-, Ala-Ala-Asn, and a combination thereof, and the wavy line indicates the connection position with antibody
• D is a small molecule drug that inhibits tumor cells, and the structure of D is as shown in formula II:
• wherein in formula II, Y is O or NH, and the wavy line indicates the connection position with L,
• X is CH2N3 or
• n is an average number of coupled drugs in the antibody-drug, and n is from 1.8 to 2;
• the dash marks represent bonds;
• wherein the light chain constant region of the antibody comprises a EKH motif and the drug molecule is linked to a lysine (K) residue of the motif.