Cell-permeable. A p53 activator. It strongly activates p53 while selectively inhibiting growth of transformed cells without inducing genotoxicity. It promotes breast cancer cells to undergo apoptosis through activating p53 and inducing expression of proapoptotic genes. Recently, it has been found that activation of p53 by this small molecule is achieved through inhibition of MDMX expression. XI-011 repressed the MDMX promoter, resulting in down-regulation of MDMX mRNA level in MCF-7 cell.