Molecular Modeling Investigation of Folic Acid Conjugation to MDM2 Inhibitors for Enhanced Cellular Uptake and Target Binding.

The activation of tumor suppressor p53 protein through inhibition of its interaction with the oncogenic Murine Double Minute 2 (MDM2) protein presents a novel therapeutic strategy against cancer. Accordingly, several small-molecule inhibitors have been developed that mimic three hydrophobic groups of p53 involved in p53-MDM2 binding and thus block the p53-binding pocket on MDM2. Interestingly, presence of a fourth, solvent-exposed hydrophilic moiety in these MDM2 inhibitors is shown to enhance their binding to MDM2 by protecting the inhibitor-MDM2 binding interface from surrounding solvent. In this context, we hypothesized that vitamin folic acid (FA) may prove to be suitable as the hydrophilic cover for enhancing activity of present MDM2 inhibitors. The proposed conjugation of FA to MDM2 inhibitors may also lead to their enhanced and selective uptake by cancer cells, owing to significantly higher expression of the FA receptors on cancer cells compared to normal cells. Therefore, based on our novel hypothesis we designed FA-conjugated MDM2 inhibitors and investigated their binding with MDM2 protein as well as the FA receptor. Specifically, a molecular modeling approach combining flexible receptor docking and molecular mechanics energy minimization calculations revealed highly favorable interactions of FA-conjugated MDM2 inhibitors with both MDM2 protein and the FA receptor as compared to native crystal ligands. Furthermore, these binding interactions were found to be stable using 50,000 ps molecular dynamics simulations. In summary, the newly-designed molecules of this kind, with better MDM2 target binding and enhanced cellular uptake potential, may prove highly useful against cancer and thus warrant further experimental investigations.

Prospective virtual screening for novel p53-MDM2 inhibitors using ultrafast shape recognition.

The p53 protein, known as the guardian of genome, is mutated or deleted in approximately 50 % of human tumors. In the rest of the cancers, p53 is expressed in its wild-type form, but its function is inhibited by direct binding with the murine double minute 2 (MDM2) protein. Therefore, inhibition of the p53-MDM2 interaction, leading to the activation of tumor suppressor p53 protein presents a fundamentally novel therapeutic strategy against several types of cancers. The present study utilized ultrafast shape recognition (USR), a virtual screening technique based on ligand-receptor 3D shape complementarity, to screen DrugBank database for novel p53-MDM2 inhibitors. Specifically, using 3D shape of one of the most potent crystal ligands of MDM2, MI-63, as the query molecule, six compounds were identified as potential p53-MDM2 inhibitors. These six USR hits were then subjected to molecular modeling investigations through flexible receptor docking followed by comparative binding energy analysis. These studies suggested a potential role of the USR-selected molecules as p53-MDM2 inhibitors. This was further supported by experimental tests showing that the treatment of human colon tumor cells with the top USR hit, telmisartan, led to a dose-dependent cell growth inhibition in a p53-dependent manner. It is noteworthy that telmisartan has a long history of safe human use as an approved anti-hypertension drug and thus may present an immediate clinical potential as a cancer therapeutic. Furthermore, it could also serve as a structurally-novel lead molecule for the development of more potent, small-molecule p53-MDM2 inhibitors against variety of cancers. Importantly, the present study demonstrates that the adopted USR-based virtual screening protocol is a useful tool for hit identification in the domain of small molecule p53-MDM2 inhibitors.