This invention is directed to prodrugs that can be activated at the preferred
site of action in order to selectively deliver the corresponding therapeutic parent drugs to target cells or to the
target site. This invention will therefore primarily but not exclusively relate to
tumor cells as target cells. More specifically the prodrugs are compounds of the formula V—(W)k—(X)l—A—Z, wherein: V is a specifier; (W)k—(X)l—A is an elongated self-
elimination spacer
system; W and X are each a 1,(4+2n) electronic
cascade spacer, being the same or different; A is either a spacer group of formula (Y)m wherein: Y is a 1,(4+2n) electronic
cascade spacer, or a group of formula U being a cyclization
elimination spacer; Z is a therapeutic
drug; k, l and m are integers from 0 (included) to 5 (included); n is an integer of 0 (included) to 10 (included), with the provisos that: —when A is (Y)m: k+l+m≧1, and if k+l+m=1; —when A is U: k+l≧1.