Novel allosteric mechanism of p53 activation by small molecules for targeted anticancer therapy

Given the immense significance of p53 restoration for anti-cancer therapy and that p53-activating molecules are in clinical trials, elucidation of the mechanisms of action of p53-activating molecules is of the utmost importance. Here we report a discovery of a novel allosteric modulation of p53 by small molecules, which is an unexpected turn in the p53 story. We identified a structural element involved in allosteric regulation of p53, whose targeting by small molecules RITA, PpIX and licofelone blocks the binding of two p53 inhibitors, MDM2 and MDMX, thereby restoring p53 function. Deletion and mutation analysis followed by molecular modeling and its thorough validation, identified the key p53 residues S33 and S37 targeted by RITA and PpIX. We propose that the binding of small molecules to the identified site in p53 induces a conformational trap preventing p53 from the interaction with MDM2 and MDMX. These results point to a high potential of allosteric activators as targeted drugs. Our study provides a basis for the development of therapeutics with a novel mechanism of action, thus extending the p53 pharmacopeia.