Anti-HER3 antibody-drug conjugate

An antibody-drug conjugate, wherein a linker and an antitumor compound represented by any one of the following formulae and anti-HER3 antibody are connected:

• -(Succinimid-3-yl-N)—CH2CH2CH2CH2CH2—C(═O)-GGFG (SEQ ID NO:
• 585)-NH—CH2CH2CH2—C(═O)-(NH-DX), or
• -(Succinimid-3-yl-N)—CH2CH2CH2CH2CH2—C(═O)-DGGFG (SEQ ID NO:
• 590)-NH—CH2CH2CH2—C(═O)-(NH-DX);
• wherein
• -(Succinimid-3-yl-N)— has a structure represented by the following formula:
• which is connected to the antibody at position 3 thereof and is connected to a methylene group in the linker structure containing this structure on the nitrogen atom at position 1, and (NH-DX) represents a group represented by the following formula:
• wherein the nitrogen atom of the amino group at position 1 is the connecting position.