Drug conjugates of formula [D-(X)b-(AA)w-(L)-]n-Ab wherein: D is a drug moiety having the following formula (I) or a pharmaceutically acceptable salt, ester, solvate, tautomer or stereoisomer thereof, wherein: A is selected from (II) and (III) R1, R2 and R3 is H, ORa, OCORa, OCO&mdash；ORa, alkyl, alkenyl, alkynyl, etc； R3&prime； is, CORa, COORa, CONRaRb, etc； each of R4 to R10 and R12 is alkyl, alkenyl or alkynyl； R11 is H, CORa, COORa, alkyl, alkenyl or alkynyl, or R11 and R12+N+C atoms to which they are attached may form a heterocyclic group； each of R13 and R14 is H, CORa, COORa, alkyl, alkenyl or alkynyl； each Ra and Rb is H, alkyl, alkenyl, alkynyl, etc.； each dotted line represents an optional additional bond； X is an extending group； AA is an amino acid unit； L is a linker group； w is 0 to 12； b is 0 or 1； A bis a moiety comprising at least one antigen binding site, and n is the ratio of the group [D-(X)b-(AA)w-(L)-] to the moiety comprising at least one antigen binding site and is in the range from 1 to 20, are useful in the treatment of cancer.
