Tetravalent antibody-drug conjugates and use thereof

An antibody-drug conjugate (ADC) or a pharmaceutically acceptable salt thereof, comprising:

• a tetravalent monoclonal antibody conjugated to a cytotoxic drug by a chemical linker,
• wherein the monoclonal antibody comprises:
• two long chains and four short chains, wherein each of the long chains comprises a first segment and a second segment, the first segment located proximal to the N-terminus of the long chain, and the second segment located proximal to the C-terminus of the long chain, each of the first segment and second segment paring with one of the short chains to form an antigen-binding fragment domain, therefore forming four antigen-binding fragment domains having specificity toward a same antigen;
• and wherein:
• (a) each of the long chains comprises the sequence of SEQ ID NO:1 and each of the short chains comprises the sequence of SEQ ID NO:2;
• or
• (b) each of the long chains comprises the sequence of SEQ ID NO:13 and each of the short chains comprises the sequence of SEQ ID NO:14;
• or
• (c) each of the long chains comprises the sequence of SEQ ID NO:15 and each of the short chains comprises the sequence of SEQ ID NO:16;
• or
• (d) each of the long chains comprises the sequence of SEQ ID NO:17 and each of the short chains comprises the sequence of SEQ ID NO:18;
• or
• (e) each of the long chains comprises the sequence of SEQ ID NO:21 and each of the short chains comprises the sequence of SEQ ID NO:22;
• or
• (f) each of the long chains comprises the sequence of SEQ ID NO:23 and each of the short chains comprises the sequence of SEQ ID NO:24.