Specific antibody drug conjugates (ADCs) having KSP inhibitors

An antibody-drug conjugate (ADC) of formula (I):

• or a salt, a solvate, or a salt of the solvate thereof;
• wherein:
• n is 1 to 8;
• AK is an anti-CD123 antibody comprising a variable region of the heavy chain (VH) comprising the variable CDR1 sequence of the heavy chain (H-CDR1), as shown by SEQ ID NO:
• 12, the variable CDR2 sequence of the heavy chain (H CDR2), as shown by SEQ ID NO:
• 13 and the variable CDR3 sequence of the heavy chain (H-CDR3), as shown by SEQ ID NO:
• 14, and a variable region of the light chain (VL) comprising the variable CDR1 sequence of the light chain (L CDR1), as shown by SEQ ID NO:
• 16, the variable CDR2 sequence of the light chain (L-CDR2), as shown by SEQ ID NO:
• 17 and the variable CDR3 sequence of the light chain (L-CDR3), as shown by SEQ ID NO:
• 18, or is an antigen-binding fragment thereof, wherein the antibody or the antigen-binding fragment thereof is attached via a sulfur atom of a cysteine side group.