No abstract

MDM2 and MDMX are known as overexpressed oncoproteins in several wild-type p53 cancer cells. The development of potent and dual antagonist peptides for p53-MDM2/X is a continuous challenge. In this study, we intended to investigate the pivotal structural points respecting the development of potent and dual inhibitors of MDM2/X. Correspondingly, MD simulation was performed on the experimentally confirmed peptides, comprising p53, pDI, pDIQ, PMI, and computationally screened mutant pDI and pDIQ. A follow-up secondary structure analysis showed the last three C-terminal residues provide the helicity reservation of peptides bound to MDM2/X. Furthermore, a delicate residue-residue examination displayed Met 11 and Ser12 in the modified peptides contribute significantly to dual inhibition of MDM2/X. Additionally, the peptides_MDM2/X complexes' ΔG binding extracted by the umbrella sampling method were in agreement with the pattern of their experimental affinity values. It was concluded the screened pDI mutants were considered as suitable anti-MDM2/X peptides, and the data obtained could be exploited as the theoretical structure-based guide for rational peptide design. Taking account of results, the suitable C-terminal residues of p53-based peptides especially Met11, and Ser12, as well as higher umbrella sampling, generated ΔG binding to MDM2/X would be considered as the positive structural markers of a promising anti-cancer agent. The mutation of p53 protein is one of the frequent causes of human cancer since it has a key role in numerous cell stability and proliferation functions 1. On the other hand, MDM2 is an oncogene protein that negatively regulates p53 2. MDMX (MDM4) is also a homolog for MDM2 and acts as p53 inhibitor 3. In vivo and in vitro studies have shown the overexpression of both MDM2 and MDMX proteins in several cancer types 4 (e. g. MDMX overexpression up to 92% of AML cases 5). However, their mechanisms of action are slightly different as MDM2 mainly degrades p53 protein using its E3 ubiquitin ligase activity, while MDMX suppresses p53 by decreasing its transactivation activity and increasing MDM2 function 6. Both MDM2 and MDMX (MDM2/X) are significantly overexpressed in cancer cells harboring wild type p53 7,8. As a result, the inhibition of MDM2/X-p53 interaction leads to the restoration of p53 activity and subsequent tumor suppression 9. From the structural point of view, MDM2/X share a similar p53-binding domain of the N-terminal hydrophobic pocket. This site engages hydrophobic bonds with p53 residues of Phe19, Trp23, and Leu26, which leads to the p53 transcriptional activity suppression 10,11. To pharmacologically antagonize the MDM2/X-p53 interaction, several molecules have been developed. In this path, small molecule inhibitors, such as Nutlin-3 were mostly unsuccessful in clinical trials 12. Although its derivative, RG7112, has shown some promising results, its unsuitable inhibition of MDMX was one of the main drawbacks 13-15. Alongside small molecules, some lead peptide sequences have also been...