Reactivation of cancerogenic p53 mutants by a small molecule APR-246: a structural perspective

The transcription factor p53 is a tumor suppressor that activates DNA repair, cell cycle arrest or apoptosis in response to genotoxic stress. The function of p53 can be compromised by mutations leading to p53 inactivation and thus to cancer development. The majority of these mutations are located at the DNA binding core domain of p53. Among them, six mutational “hotspots” at residues: R175, G245, R248, R249, R273 and R282 were shown to occur at high frequency in human cancer. They can either affect direct p53 binding to DNA: R273H/C, R248Q/W (DNA-contact mutants); or destabilize p53 core domain: R175H, G245S, R249S and R282W (structural mutants).

PRIMA-1 and APR-246/PRIMA-1^MET are small molecules that following conversion into the biologically active compound, methylene quinuclidinone (MQ), reactivate mutant p53 by binding covalently to cysteine residues in the p53 core domain. In our study, we investigate the reactivation mechanisms of mutant p53 by MQ from a high-resolution crystal structures of wild-type p53 and several hotspot mutants bound to MQ in the absence and/or presence of DNA. Our data show that MQ can bind to several cysteine residues located at the surface of the core domain at positions: 124, 182, 229, 275, and 277. A detailed comparison between the structures of specific p53 mutants before and after binding to MQ, reveals the role played by MQ in stabilizing p53 and its interaction with DNA, thus providing a structural framework for the design of new molecules for specific targeting of cysteines in p53 mutants.