A drug conjugate comprising a drug moiety covalently attached to the rest of the drug conjugate, the drug conjugate having formula [D- b - w - g - -] n -Ab wherein: D is a drug moiety having the following formula or a pharmaceutically acceptable salt or ester thereof, wherein: D is covalently attached via a hydroxy group at OR 1, OR 3 or ZH or via a thiol group at ZH, to b if any, or w if any, or to g if any, or; R 1 is selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, -C(=O)R a, -C(=O)OR b and -C(=O)NR c R d; R 2 is hydrogen; R 3 is selected from hydrogen, -C(=O)R a, -C(=O)OR b, and -C(=O)NR c R d; Z is selected from -O- and -S-; R a is selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group; R b is selected from substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group; R c and R d are independently selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl and substituted or unsubstituted heterocyclic group; X and T are extending groups that may be the same or different; each AA is independently an amino acid unit; L is a linker group; w is an integer ranging from 0 to 12; b is an integer of 0 or 1; g is an integer of 0 or 1; Ab is a moiety comprising at least one antigen binding site; and n is the ratio of the group [D- b - w - g - -] to the moiety comprising at least one antigen binding site and is in the range from 1 to 20. D is covalently attached via a hydroxy group at OR 1, OR 3 or ZH or via a thiol group at ZH, to b if any, or w if any, or to g if any, or; R 1 is selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, -C(=O)R a, -C(=O)OR b and -C(=O)NR c R d; R 2 is hydrogen; R 3 is selected from hydrogen, -C(=O)R a, -C(=O)OR b, and -C(=O)NR c R d; Z is selected from -O- and -S-; R a is selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group; R b is selected from substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted heterocyclic group; R c and R d are independently selected from hydrogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted aryl and substituted or unsubstituted heterocyclic group; X and T are extending groups that may be the same or different; each AA is independently an amino acid unit; L is a linker group; w is an integer ranging from 0 to 12; b is an integer of 0 or 1; g is an integer of 0 or 1; Ab is a moiety comprising at least one antigen binding site; and n is the ratio of the group [D- b - w - g - -] to the moiety comprising at least one antigen binding site and is in the range from 1 to 20.