Anticancer drugs: a detailed computational analysis of "non classical" compounds mechanism of action

Abstract

Metal containing drugs have attracted an enormous deal of interest for their use in cancer therapy. Transition metal compounds’ richness offers extraordinary opportunities for the design of anticancer compounds, possessing pharmacokinetic properties inaccessible to purely organic compounds. The most successful and evident proof of their pivotal role is represented by cisplatin that, together with its carboplatin and oxaliplatin derivatives, continues to be routinely used worldwide in clinical practice. However, it is well known that the use of such drugs for fighting cancer is accompanied by severe side effects and intrinsic or acquired resistance that drastically limit their successful action. Therefore, decades of research efforts have been devoted to the search and the synthesis of safer and more effective and selective agents, either containing platinum or alternative metals, acting with similar or different mechanisms. In order to accomplish this aim is of decisive importance the elucidation of the mechanism of action of the drugs. Molecular simulations, or in silico experiments, are able to provide detailed information at atomistic resolution, rarely accessible to experiments, that can complement laboratory experiments. The increasing accuracy of computational approaches and the growing performance of computer performance, allow to properly describe reaction paths and involved molecular orbitals, calculate electronic properties, simulate spectra without any limitation except those connected with the adopted level of theory and compuatational protocol. The main aim of the present work was the detailed investigation, in the framework of the Density Functional Theory, of the mechanism of action of “non classical” platinum and transition metal non-platinum compounds, for some of them in collaboration with experimentalists, and the rationalization of their behaviors. In the next paragraphs all the studied systems will be shortly described together with the motivations that have prompted us to study such systems. Both “non classical” platinum(IV) prodrugs, non-platinum drugs and photoactivatable Pt(II) and Pt(IV) complexes have been examined. In the development of new platinum-based anticancer drugs, is of great interest the emerging class of "dual action" Pt(IV) prodrugs that, undergoing a reductive elimination process, which is the key step for their activation, are able to release the active Pt(II) complexes and bioactive axial ligands that together lead to cell death. Indeed, the two axial ligands, in turn, can be chosen to possess physico-chemical and biopharmaceutical properties or even facilitate the incorporation into a drug delivery system. According to the research lines mentioned above, the use of drug delivery systems has also grown, and many different strategies have been examined to encapsulate platinum drugs within macromolecules, including macrocyclic species, which are responsible for creating supramolecular host-guest structures. The encapsulation slows down and prevents the drug degradation by proteins and peptides. One of the most widely studied class of synthetic supramolecular macrocycles are Calix[n]arenes (CX), whose property, as molecular hosts and delivery systems, are of increasing interest. Photodynamic Therapy (PDT) is a non-toxic therapeutic technique, clinically approved and minimally invasive, used for the treatment of several types of cancers based on the generation of reactive oxygen species (ROS), that acts as cytotoxic agents. In PDT applications three components are required: a photosensitizer (PS), a light of a specific wavelength and tissue oxygen. A promising approach to increase the effectiveness of anticancer therapy is the combination of multimodal treatment methods into a single system. Recently, a strategy has been proposed providing the possibility to combine the classical Pt-based chemotherapy with photodynamic therapy (PDT) treatment. This approach involves the functionalization of a photosensitizer (PS) with a therapeutic drug such as cisplatin-like compounds.