Intercalation Ability of Novel Monofunctional Platinum Anticancer Drugs: A Key Step in Their Biological Action

Phenanthriplatin (PtPPH) is a monovalent platinum(II)-based complex with a large cytotoxicity against cancer cells. Although the aqua-activated drug has been assumed to be the precursor for DNA damage, it is still under debate whether the way in which that metallodrug attacks to DNA is dominated by a direct binding to a guanine base or rather by an intercalated intermediate product. Aiming to capture the mechanism of action of PtPPH, the present contribution used theoretical tools to systematically assess the sequence of all possible mechanisms on drug activation and reactivity, for example, hydrolysis, intercalation, and covalent damage to DNA. Ab initio quantum mechanical (QM) methods, hybrid QM/QM' schemes, and independent gradient model approaches are implemented in an unbiased protocol. The performed simulations show that the cascade of reactions is articulated in three well-defined stages: (i) an early and fast intercalation of the complex between the DNA bases, (ii) a subsequent hydrolysis reaction that leads to the aqua-activated form, and (iii) a final formation of the covalent bond between PtPPH and DNA at a guanine site. The permanent damage to DNA is consequently driven by that latter bond to DNA but with a simultaneous π-π intercalation of the phenanthridine into nucleobases. The impact of the DNA sequence and the lateral backbone was also discussed to provide a more complete picture of the forces that anchor the drug into the double helix.