The mutation of p53 is implicated in the increased metastatic potential of triple-negative (ER—/PR—/Her2—) breast cancer (TNBC). The low survival rates of advanced metastatic cancer make it critical not only to understand the mechanisms underlying the functional implications of p53 mutations, but also to identify ways to regulate their impact in cancer cell physiology. A common gain-of-function activity of the mutant p53 protein is the enhancement of cell migration and invasion. We have found that a hydrocarbon-stapled p53 transactivation domain peptide (SAH-p53) designed to disrupt the interaction with p53 negative regulators HDM2 and HDMX also has the ability to inhibit the interaction between mutant p53 (mtp53) and HDM2/HDMX. In addition, SAH-p53 was found to inhibit the migration and invasion of MDA-MB-231 cells (mtp53), while exhibiting no alteration in their proliferative ability. The capacity of SAH-p53 to inhibit MDA-MB-231 cell migration was not altered in the absence of HDMX, suggesting an alternative mechanism of action for SAH-p53. The propensity of MDA-MB-231 cells to migrate and invade through Matrigel in response to transforming growth factor b (TGF-β), epidermal growth factor (EGF), hepatocyte growth factor (HGF), and platelet-derived growth factor (PDGF) was decreased by treatment with SAH-p53. Furthermore, increased concentrations of these growth factors displayed a synergistic effect with SAH-p53 in the inhibition of cell migration, suggesting cross-talk between receptor signaling and SAH-p53 activity. This effect was accompanied by an alteration in stress fiber formation and dissolution of focal adhesions. While the knockdown of mutant p53 in MDA-MB-231 cells significantly decreased migration on its own, inhibition of migration by SAH-p53 was not seen in the EGFR/p53-null MDA-MB-157 cells, suggesting a need for either the p53 or EGFR protein for the inhibitory activity of SAH-p53. Moreover, a SAH-p53-induced decrease in the total levels of EGFR and integrin beta1, together with alterations in actin stability, suggests a defect in receptor recycling, a process required for cell migration known to be modulated by an interaction between mutant p53 and p63. These data show that the use of the SAH-p53 peptide provides a novel avenue to study the molecular interactions that drive metastatic behavior originated by p53 gain-of-function mutations.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-03-05.