Antibody drug conjugate

An antibody-drug conjugate of general formula Ab-(L-U) n, wherein Ab represents an antibody moiety, L represents a linker moiety, U represents a cytotoxic drug moiety, and wherein the antibody-drug conjugate has a structure of formula VII below:

• wherein the Ab represents an antibody moiety comprising a first antigen-binding fragment that binds to ECD4 epitope of HER2 and a second antigen-binding fragment that binds to ECD2 epitope of HER2,
• wherein the first antigen-binding fragment is an scFv and comprises a heavy chain CDR1, a heavy chain CDR2, a heavy chain CDR3, a light chain CDR1, a light chain CDR2 and a light chain CDR3, the heavy chain CDR1, the heavy chain CDR2 and the heavy chain CDR3 comprising amino acid sequences set forth in SEQ ID NOs:
• 43, 28 and 29, respectively, and the light chain CDR1, the light chain CDR2 and the light chain CDR3 comprising amino acid sequences set forth in SEQ ID NOs:
• 30, 31 and 32, respectively,
• the second antigen-binding fragment is an Fab and comprises a heavy chain CDR1, a heavy chain CDR2, a heavy chain CDR3, a light chain CDR1, a light chain CDR2 and a light chain CDR3, the heavy chain CDR1, the heavy chain CDR2 and the heavy chain CDR3 comprising amino acid sequences set forth in SEQ ID NOs:
• 45, 46 and 47, respectively, and the light chain CDR1, the light chain CDR2 and the light chain CDR3 comprising amino acid sequences set forth in SEQ ID NOs:
• 48, 49 and 50, respectively,
• n is an integer or a decimal selected from the group consisting of 1 to 10, and
• R1 and R2 are each independently selected from the group consisting of hydrogen (H) and deuterium (D).