A purine nucleoside analog includes a pyrido[2,3-d]pyrimidine or a pyrimido[4,5-d]pyrimidine and further has a sugar moiety that is optionally modified at the C2', C3', C4' and/or C5' position. Particularly contemplated compounds also include prodrug forms of the purine nucleoside analogs, and both purine nucleoside analogs and the corresponding prodrugs are employed in the reduction of growth of neoplastic cells.