MDM2 is an important cancer-related protein that induces cancer cell survival and progression through both p53-dependent and -independent signaling pathways. In previous investigations of the p53-independent role of MDM2, we found that the oncoprotein MDM2 can increase the expression of the anti-apoptotic factor XIAP through binding of MDM2's RING domain to the XIAP IRES mRNA, inducing its translational activity. Our preliminary studies for this renewal application demonstrated that when XIAP IRES bound to the MDM2 RING domain protein, MDM2 protein stabilization increased. Based on these findings, we believe that the binding action between XIAP IRES and the RING domain of MDM2 can simultaneously increase expression of XIAP and MDM2, through activation of IRES-dependent translation and by inhibition of protein degradation, respectively. In cancer cells, increased expression of both MDM2 and XIAP may aid cancer progression or resistance to anticancer treatment. Accordingly, we hypothesized that inhibition of this molecular interaction would result in a simultaneous decrease in the expression of both MDM2 and XIAP, leading to not only suppression of the cancer, but a reversal of drug resistance during therapy. The goals of this project are: to identify small molecule inhibitors that can disrupt the MDM2 protein/XIAP IRES interaction, to characterize whether the identified MDM2/XIAP inhibitors are able to induce MDM2 self-ubiquitination and degradation as well as inhibition of XIAP translation, and to ascertain the potential use of the identified inhibitors as new drugs able to treat refractory cancer patients. Specifically, Aim 1 is to perform HTS to select small-molecule compounds that block or disrupt the interaction between XIAP IRES mRNA and the RING domain protein of MDM2;
Aim 2 will investigate how selected MDM2/XIAP inhibitors disrupt that interaction at the molecular level and find the mechanism of action by which the inhibitor targets MDM2 degradation.
For Aim 3, we will examine the effects of MDM2 degradation and inhibition of XIAP translation by selected compounds on cancer cell growth and apoptosis in vitro, plus perform translational studies in animal models to ascertain these identified compounds as clinically viable anticancer drugs. Because a significant number of cancer patients have malignant cells that are overexpressing MDM2 and XIAP and their survival remains poor, we hope our studies will lead directly to the discovery of several useful new drugs to treat these refractory cancer patients.

Public Health Relevance

We found that the interaction between MDM2 protein and XIAP RNA induces XIAP expression and inhibits MDM2 degradation. We believe that blockage of this interaction will bring about an increase in MDM2 degradation and inhibition of XIAP expression. This study will discover small molecule inhibitors that block the interaction between MDM2 protein and XIAP RNA in order to inhibit the characteristic oncologically-associated expression of both MDM2 and XIAP, a novel translational approach in developing targeted cancer treatments.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Basic Mechanisms of Cancer Therapeutics Study Section (BMCT)
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Watson, Joanna M
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Emory University
Schools of Medicine
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Zhang, Hailong; Gu, Lubing; Liu, Tao et al. (2014) Inhibition of MDM2 by nilotinib contributes to cytotoxicity in both Philadelphia-positive and negative acute lymphoblastic leukemia. PLoS One 9:e100960
Li, Jiansha; Gu, Lubing; Zhang, Hailong et al. (2013) Berberine represses DAXX gene transcription and induces cancer cell apoptosis. Lab Invest 93:354-64
Huang, Mei; Zhang, Hailong; Liu, Tao et al. (2013) Triptolide inhibits MDM2 and induces apoptosis in acute lymphoblastic leukemia cells through a p53-independent pathway. Mol Cancer Ther 12:184-94
Zhang, Hailong; He, Jing; Li, Jiansha et al. (2013) Methylation of RASSF1A gene promoter is regulated by p53 and DAXX. FASEB J 27:232-42
Gu, L; Zhang, H; He, J et al. (2012) MDM2 regulates MYCN mRNA stabilization and translation in human neuroblastoma cells. Oncogene 31:1342-53
Zhou, Sheng; Gu, Lubing; He, Jing et al. (2011) MDM2 regulates vascular endothelial growth factor mRNA stabilization in hypoxia. Mol Cell Biol 31:4928-37
He, Jing; Gu, Lubing; Zhang, Hailong et al. (2011) Crosstalk between MYCN and MDM2-p53 signal pathways regulates tumor cell growth and apoptosis in neuroblastoma. Cell Cycle 10:2994-3002
Yang, Lin; Gu, Lubing; Li, Zhuoya et al. (2010) Translation of TRAF1 is regulated by IRES-dependent mechanism and stimulated by vincristine. Nucleic Acids Res 38:4503-13
Zhang, Xiaoling; Gu, Lubing; Li, Jiansha et al. (2010) Degradation of MDM2 by the interaction between berberine and DAXX leads to potent apoptosis in MDM2-overexpressing cancer cells. Cancer Res 70:9895-904
Gu, Lubing; Zhu, Ningxi; Zhang, Hongying et al. (2009) Regulation of XIAP translation and induction by MDM2 following irradiation. Cancer Cell 15:363-75

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