Abstract 839: An uncharacterized mechanism of cell death independent of p53 mutation status.
Authors: Bethanie L. Morrison, Elisabeth Russell, Joseph Mitala, Federico Bernal
Journal: Cancer Research (2013)

Abstract Resistance to chemotherapeutic agents is often a rate-limiting event in the treatment of metastatic cancers. Mutations of TP53 or dysfunctions in the p53 pathway are known to play primary roles in the resistance to apoptosis-inducing agents. A stapled alpha-helical p53 peptide (SAH-p53) capable of disrupting the p53-HDM2 and p53-HDMX complexes and restoring p53 function has been found to induce a death response in breast, melanoma and choriocarcinoma cancer cells independent of p53 mutational status. We have recently discovered that the mechanism of death induced by SAH-p53 does not exhibit all of the characteristics of classical apoptosis, necrosis or autophagy independently. The binding of SAH-p53 to HDM2, HDMX, or a yet unidentified target results in a mechanism that leads to the intracellular aggregation of proteins and lipids that are extruded from the cell, resulting in catastrophic damage to the integrity of the cell membrane and culminating in cell death. This type of cell death involves the loss of cytoplasm, generation of phase-clear vacuole-like structures, apparent degradation of cellular membrane components, and the significant release of uniform non-vesicular cellular components. The cellular debris, while yet undefined, displays orange staining with acridine orange as well as accumulation of MitoTracker, suggesting that the debris contains hydrophobic regions. Thus far it has been established that there is a lack of any membrane blebbing, no chromatin condensation, no apoptosis signaling events or typical necrotic bubble formation after treatment with SAH-p53 in cells harboring wild-type p53, mutant p53, or null p53, suggesting an alternative mechanism of cell death. Data suggest the manifestation of early autophagy within 6 hours of SAH-p53 treatment as evidenced by LC3 accumulation, yet this phenotype is lost within 24 hours post-treatment. In addition, the pretreatment of the cells with chloroquine does not inhibit the release of debris and changes in morphology characteristic of SAH-p53 treatment, suggesting that the mechanism of death is independent of classical autophagy. We have begun to uncover the precise mechanism of cell death through the identification and validation of the transcriptional program regulated by SAH-p53 in both wild-type and mutant p53-containing cells via microarray analysis. The complete understanding and characterization of this novel mechanism may be exploited to overcome resistance to apoptosis and thus lead to a more effective way of treating chemotherapy-resistant metastatic cancers. Citation Format: Bethanie L. Morrison, Elisabeth Russell, Joseph Mitala, Federico Bernal. An uncharacterized mechanism of cell death independent of p53 mutation status. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 839. doi:10.1158/1538-7445.AM2013-839