Abstract 5298: Finding new molecules to bypass the tumor suppressor gene TP53 and restore cell cycle checkpoint control

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Abstract The tumor suppressor gene, tumor protein 53 (TP53), has been shown to be mutated in more than half of all human cancer cases. p53 controls the G1/S phase checkpoint of the mitotic cell cycle, protecting the fidelity of DNA and inducing apoptosis in cells with irreparable DNA damage. Mutations in TP53, which are often missense mutations that interfere with p53 DNA binding activity or protein folding, result in protein inactivation and loss of checkpoint control, allowing cells with potentially oncogenic mutations to survive and proliferate. TP53 mutations have been shown to enhance tumor progression, increase metastatic potential, and mediate chemotherapy resistance. Because of the importance of p53 in cancer, many studies have aimed to identify small molecules that can “reactivate” mutated p53 protein in cell culture, although this has met with little success thus far. The aim of this research is to identify the extent to which the effects of non-functioning p53 can be completely bypassed, and cell cycle checkpoint restored, using already-established FDA approved compounds in a zebrafish model of p53 loss. Zebrafish were genetically engineered to have their entire TP53 locus removed using TALEN (Transcription activator-like effector nuclease), rendering them unable to produce the p53 protein. p53 deficient and wild-type zebrafish larvae were then subjected to gamma-irradiation to induce DNA damage. An apoptotic cell staining assay was then performed to allow for the qualitative and quantitative analysis of apoptosis levels throughout the larvae. As expected, TP53 null fish had significantly less apoptotic cells than control after DNA damage. We are in the process of testing 770 FDA approved compounds for their effects in inducing an apoptotic response in p53 null larvae after gamma-irradiation. Positive hits will be carried forward to human cancer cells with TP53 mutation, and the mechanism of action of the drug will be determined using biochemical approaches. These results could identify novel pathways that work in concert with p53 and will allow us to harness new mechanisms of DNA damage induced apoptosis to kill cancer cells. Repurposing FDA-approved drugs can also rapidly translate to clinical benefit in a wide number of cancers driven by TP53 mutation. Citation Format: Henry Moore, Jessica Blackburn. Finding new molecules to bypass the tumor suppressor gene TP53 and restore cell cycle checkpoint control [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5298.