Platinum-intercalator conjugates: From DNA-targeted cisplatin derivatives to adenine binding complexes as potential modulators of gene regulation

Nuclear DNA is the cellular target for many cancer treatments, and DNA-directed chemotherapies continue to play an important role in drug discovery in the postgenomic era. The majority of DNA-targeted anticancer agents bind through covalent interactions, non-covalent intercalation or groove binding, or hybrid binding modes. The sequence and regiospecificity of these interactions and the resulting structural alterations within the biopolymer play an important role in the mechanism of action of these drugs. DNA-binding proteins and/or DNA-processing enzymes, which also interact with DNA in a sequence- and groove-specific manner, are mediators of the cytotoxic effect produced by these agents. Thus one major goal in the design of new clinical agents of this type is to produce new types of adducts on DNA, which may lead to unprecedented cell kill mechanisms. Platinum-intercalator conjugates are such a class of hybrid agents acting through a dual DNA binding mode. The platinum center (usually a cis-diaminedichloroPt(II) unit) dominates the DNA adduct profiles in the majority of these species-the result of the metal's tendency to form cross-links in runs of consecutive guanine bases in the major groove of DNA. This paradigm has been broken recently for the first time with the design of cytotoxic platinum-acridinylthiourea conjugates, a class of adenine-affinic minor-groove directed agents. This review summarizes major advancements in the chemistry and biology of platinum-intercalators from 1984 to 2004, with emphasis being placed on the interplay between chemical structure, mechanism, of DNA binding, and biological properties.