TP53 is a tumour suppressor gene that is mutated in about half of human cancers1 and is often associated with poor therapeutic responses1. P53 protein encoded by TP53 is a transcription factor that regulates the expression of target genes that control various cellular processes, including apoptotic cell death, cellular senescence, cell cycle arrest, coordination of DNA repair and adaptation of metabolism2. p53 can be activated in response to diverse stimuli, such as oncogene expression, DNA damage and oxidative stress. The loss or mutation of TP53 leads to uncontrolled cell proliferation and survival and consequently the formation of tumours2. In mouse models, reinstatement of WT p53 induces cellular senescence or apoptosis of malignant cells without detrimental effects on normal tissues3,4. Therefore, restoring WT p53 function is a potential strategy to treat p53-mutant cancers.
PRIMA-1 (precursor of APR-246) is a compound reported to specifically kill mutant p53-expressing cancer cells both in vitro and in vivo5. APR-246 is a pro-drug that is converted inside cells to the active compound methylene quinuclidinone6. APR-246 is reported to restore WT conformation, DNA-binding and transcriptional transactivation to mutant p53 proteins, leading to the suppression of tumour growth by inducing p53-dependent apoptosis5. Currently, it is under clinical investigation in several malignancies6. However, its mechanism of action is debated, with a report APR-246 alters mitochondrial metabolism in cancer cells and induces ferroptosis, an iron-dependent cell death7. Furthermore, there is evidence that p53 mutation status is not predictive of response to APR-2466. Work from our group using diverse p53 mutated tumour cell lines in which mutant p53 was removed using CRISPR has indicated that APR-246 kills cells independently of their p53 status. We hypothesise that APR-246 induces cell death independent of mutant TP53 through various cellular pathways. We will identify factors that contribute to the resistance to APR-246-induced killing of cancer cells by performing genome-wide CRISPR knockout screens in cancer cell lines. This will inform how APR-246 kills cancer cells.
References
1 Hollstein, M., Sidransky, D., Vogelstein, B. & Harris, C. C. p53 mutations in human cancers. Science 253, 49-53 (1991).
2 Aubrey, B. J., Kelly, G. L., Janic, A., Herold, M. J. & Strasser, A. How does p53 induce apoptosis and how does this relate to p53-mediated tumour suppression? Cell Death Differ 25, 104-113, doi:10.1038/cdd.2017.169 (2018).
3 Ventura, A. et al. Restoration of p53 function leads to tumour regression in vivo. Nature 445, 661-665, doi:10.1038/nature05541 (2007).
4 Xue, W. et al. Senescence and tumour clearance is triggered by p53 restoration in murine liver carcinomas. Nature 445, 656-660, doi:10.1038/nature05529 (2007).
5 Bykov, V. J. et al. Restoration of the tumor suppressor function to mutant p53 by a low-molecular-weight compound. Nat Med 8, 282-288, doi:10.1038/nm0302-282 (2002).
6 Fujihara, K. M. et al. SLC7A11 Is a Superior Determinant of APR-246 (Eprenetapopt) Response than TP53 Mutation Status. Mol Cancer Ther 20, 1858-1867, doi:10.1158/1535-7163.MCT-21-0067 (2021).
7 Fujihara, K. M. et al. Genome-wide CRISPR screens reveal APR-246 (Eprenetapopt) triggers ferroptosis and inhibits iron-sulfur cluster biogenesis. bioRxiv, doi:https://doi.org/10.1101/2020.11.29.398867 (2020).