Investigação teórica da formação de complexos de cisplatina com modelos da proteína ATP7A

Abstract

Cisplatin (cis-[Pt(NH3)2(Cl)2]) is known to be an important agent in the fight against various types of cancer, acting on DNA and resulting in distortions in the macromolecular structure that induce the cell to programmed death. With the frequent use of cisplatin, the response of cells is the induction of drug resistance mechanisms, complicating treatment. Numerous studies indicate that cells can absorb and transport cisplatin through the ATP7A and ATP7B transport proteins, which are responsible for the regulation of Cu(I). These proteins are also related to the mechanisms of cellular resistance to the drug due to the intensified flow of cisplatin to the extracellular medium. In this work, DFT calculations with the M06-2X functional and NCI for investigating non-covalent interactions were used throughout mechanistic proposals for the reactions of cis-[Pt(NH3)2(Cl)2] and cis-[Pt(NH3)2(OH2)2]2+ with the active site of the 6th metal-binding domain (Mnk6) of the ATP7A protein, both in the presence and absence of Cu(I) in the protein structure, and in both gas phase and implicit solvation. The results indicated the existence of distinct stages with associative characteristics. In the gas phase, the reaction coordinates suggest greater thermodynamic and kinetic favorability for the diaquo reagent compared to the dichloro; and for the holoprotein form compared to the apoprotein. In the solvated medium, however, the reactions between the diaquo and dichloro forms with the holoprotein site showed barrier energies and free energy changes for the reaction that were remarkably close in the first stage (around 12.3 kcal·mol-1 and 12.0 kcal·mol-1, respectively). In the holoprotein forms, strongly attractive interactions of Cu(I) with Pt(II) were observed, which may impact the reaction rate and stabilization of reagent complexes. Through topological analyses and other observations, the hypothesis is that these are non-covalent interactions, exhibiting in several cases electronic densities greater than those observed for typical hydrogen bonds. NBO calculations also indicated possible charge transfers from S and Cu(I) to Pt(II), concurrently with changes in geometries concerning the metal centers. However, the structural cut of the protein (i.e., the active site) and the failure to obtain IRC results under certain transition states may be considered limiting factors.