The invention relates to new functionalized thieno-indole derivatives of formula (I) or (II) which have cytotoxic activity and are useful in treating diseases such as cancer and cellular proliferation disorders. The invention also relates to the use of these functionalized thieno-indole derivatives in the preparation of conjugates. Formula (I) or (II) wherein R1 and R2 taken together form a group (D) or (G): wherein R5 is hydrogen or C1-C4 alkyl R3 and R4 are independently hydrogen, C1-C4 alkyl or C1-C4 hydroxyalkyl n is 0, 1 or 2 each of X is independently &mdashO&mdash, &mdashS&mdash or &mdashNR4&mdash each of Y is independently &mdashCH&boxH or &mdashN&boxH R7 and R8 are independently hydrogen, halogen, hydroxy, C1-C4 alkoxy, cyano, &mdashNHCOOR3, &mdashC(NH)NH2 or &mdashNR3R4 A is &mdashO&mdash, &mdashNH&mdash or &mdashCO&mdash L is null or a conditionally-cleavable moiety W is null or a self-immolative moiety comprising one or more self-immolative groups Z is null or a peptidic, non peptidic or hybrid peptidic and non peptidic linker RM is null or a reactive moiety R6 is a leaving group A1 is null or A L1 is hydrogen or L.
