Abstract 3500: Mitochondrially targeted p53 domains as a stand alone or adjunct to paclitaxel for the treatment of ovarian cancer

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Abstract Although the main function of p53 is a nuclear transcription factor that has important roles in cell cycle arrest, DNA repair, and apoptosis, p53 can directly trigger the intrinsic apoptotic pathway through the mitochondria. p53 has been known to bind to mitochondrial anti-apoptotic proteins (Mcl-1, Bcl-2 and Bcl-XL) and pro-apoptotic proteins (Bak and Bax), which will cause the oligomerization of Bak and Bax. The result is the formation of permeable pores on the mitochondrial outer membrane, which in turn cause the release of cytochrome c and activation of caspase-3. Targeting p53 to the mitochondria is an attractive approach because it can cause a rapid apoptotic response. We have introduced the mitochondrial targeting signal (MTS) from Bak or Bax to the C-terminus of p53 and have shown the superior efficacy of p53-BakMTS and p53-BaxMTS over wtp53 in many human cancer cell lines. We have identified that the DNA binding domain (DBD) of p53 may be the minimal domain of p53 required for apoptosis. Our preliminary data in SKOV-3 ovarian cancer cells also suggests that DBD-BakMTS may work just as well as full length p53-BakMTS. In addition to BakMTS and BaxMTS, attaching pro-apoptotic factors such as Noxa or Bid to p53 has created a chimeric gene construct that show superior cell death activity than wide type p53. Our goal is to use a novel version of p53 directed to the mitochondria as a direct apoptogen to treat ovarian cancer, the most lethal gynecological malignancy with 69% of patients succumbing to this disease. Our next step will be to test these constructs in vivo using the syngeneic ID8 mouse model. To determine the activity of these mitochondrially targeted p53 constructs, TMRE, 7-AAD, and caspase 3/7 assays were performed in many human ovarian cancer cell lines including SKOV-3, OVCAR-3, Kuramochi, and mouse ovarian ID8 cells that have been transfected with our constructs. In all of our cell death and apoptotic assays, p53-Bax-MTS, p53-BakMTS, and p53-Noxa are always superior to wide type p53, regardless of the p53 status of the cells. Furthermore, we have also tested the possibility of combining our p53 constructs with paclitaxel, the current standard of care for ovarian cancer. Our p53 constructs showed a synergistic effect with paclitaxel and was able to reduce its IC5, indicating the possibility of dose-lowering of this highly toxic drug. Our ultimate goal is to use mitochondrially targeted p53 constructs that directly induce apoptosis alone or in combination with other chemotherapy drugs for the treatment of ovarian cancer. Acknowledgements: NIH CA151847 Citation Format: Phong Lu, Carol S. Lim. Mitochondrially targeted p53 domains as a stand alone or adjunct to paclitaxel for the treatment of ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3500.