Topoisomerase inhibitors

A compound of formula I:

• wherein:
• A and B are independently N or CH;
• W is N or CH;
• R3 and R4 are each independently H, (C1-C6)alkyl, or substituted (C1-C6)alkyl, or R3 and R4 together are ═O, ═S, ═NH or ═N—R2;
• at least one of Y and Z is aryl(C1-C6)alkanoyl, heteroaryl(C1-C6)alkanoyl, (C1-C6)alkoxycarbonyl, a self-immolative moiety, cascading prodrug moiety or a linker substituted with one or more targeting moieties and the other is hydrogen, (C1-C6)alkyl, substituted (C1-C6)alkyl, (C1-C6)alkanoyl, substituted (C1-C6)alkanoyl, —C(═O)NRcRd, aryl(C1-C6)alkanoyl or heteroaryl(C1-C6)alkanoyl wherein any aryl(C1-C6)alkanoyl or heteroaryl(C1-C6)alkanoyl may be optionally substituted with one or more groups independently selected from halo, cyano, (C1-C6)alkyl, carboxy, NO2, hydroxy, (C1-C6)alkoxy and —NReRf;
• R1 is a —(C1-C6)alkyl optionally substituted with one or more solubilizing groups;
• R2 is (C1-C6)alkyl, substituted (C1-C6)alkyl, aryl or heteroaryl;
• Rc and Rd are each independently H, (C1-C6)alkyl or substituted (C1-C6)alkyl;
• or Rc and Rd together with the nitrogen to which they are attached form a piperazino, pyrrolidino, or piperidino ring, which ring can optionally be substituted with one or more aryl, heteroaryl, or heterocycle;
• and
• Re and Rf are each independently H, (C1-C6)alkyl or substituted (C1-C6)alkyl;
• or Re and Rf together with the nitrogen to which they are attached form a piperazino, pyrrolidino, or piperidino ring, which ring can optionally be substituted with one or more aryl, heteroaryl, or heterocycle;
• or a salt thereof;
• wherein Y is not H when Z is (C1-C6)alkyl;
• and Y is not (C1-C6)alkyl when Z is H.