Cancer has been the leading cause of disease-related deaths in human beings, yet, its major non-surgery treatments have been chemotherapy and radiotherapy, both of which are quite toxic and cause severe side effects. Also, the survival rates of cancer patients have had little improvement. Thus, it still remains remarkably important, though challenging, to develop more potent and specific molecule-targeted therapies. The inactivation of the most important tumor suppressor p53 is one highly cancer-related molecular alteration, as its gene is mutated in ~50% of all types of human cancers while its activity or leve is often markedly reduced in the remaining 50% of cancers that harbor wild type TP53. The p53 deactivation is primarily due to the negative feedback regulation by its two chief suppressors, MDM2 and MDMX, which are over expressed in cancers and form a complex that mediates p53 ubiquitination and degradation as well as inhibits p53 activity directly. This negative regulation s further facilitated by SIRT1, which is highly expressed in some cancers, as the deacetylation of p53 by this deacetylase favors MDM2/MDMX-mediated ubiquitination of this protein. Thus, re-activation of p53 in cancers by targeting SIRT1 can be utilized to screen small molecules for the development of an anti-cancer therapy. Indeed, our recent work has identified a small molecule named Inauhzin (INZ) that inhibits the activity of SIRT1 and induces p53 acetylation, level and activity, leading to p53-dependent apoptosis and senescence in p53-containing human lung and colon cancer cells and suppressing the growth of xenograft lung and colon tumors. Our further studying INZ surprisingly reveals another target, IMPDH2, which is also highly expressed in human cancers. Our previous study shows that inhibition of this enzyme causes ribosomal stress by reducing the level of nucleostemin (NS), which is essential for rRNA processing. Consistent with this, INZ also binds to IMPDH2 and reduces NS levels, leading to the activation of the ribosomal stress-p53 pathway. In light of these interesting findings, I hypothesize that INZ can activate p53 by simultaneously targeting SIRT1 and IMPDH2 and thus eliminate cancer cells via a p53-dependent mechanism. We will test this hypothesis by addressing two specific aims. 1. To determine if INZ induces ribosomal stress and activates p53 by inhibiting IMPDH2 and downregulating NS. Since we have recently reported that INZ inhibits SIRT1 activity, here in this aim we will determine if INZ targets IMPDH2 by verifying INZ as a specific inhibitor of IMPDH2, consolidating if inhibition of IMPDH2 by INZ reduces NS levels and induces consequent ribosomal stress, and determining if RPL11 and RPL5 are critical for INZ-induced p53 activation. 2. To determine the role of INZ-14, a more potent INZ analog, in p53 activation and tumor suppression. In this aim, we will test our newly synthesized INZ derivatives, particularly potent INZ-14, by further modifying it, characterizing it in our established biochemical, cellular and animal tumor model systems, and testing the cooperative effect of INZ-14 with doxorubicin or ?-irradiation in xenograft and orthotopic tumor model systems.

Public Health Relevance

Cancer is a leading killer of disease-bearing patients in all human beings, yet for decades, anti-cancer treatments have been traditional chemotherapy and radiotherapy with little improvement of survival rate in general, and thus, developing molecule-targeted anti-cancer therapies still remains significant and challenging. The recent identification of a novel small molecule named Inauhzin (INZ) that can activate the tumor suppressor p53 by specifically targeting two cancer-relevant protein molecules in this laboratory lays a solid foundation for the proposed projects in this application;Hence, the completion of these projects will unearth a potent anti-cancer drug candidate that would significantly contribute to Public Health in the country and in the world, as cancer remains as the top cause of human deaths.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
5R01CA172468-03
Application #
8717615
Study Section
Drug Discovery and Molecular Pharmacology Study Section (DMP)
Program Officer
Watson, Joanna M
Project Start
Project End
Budget Start
Budget End
Support Year
3
Fiscal Year
2014
Total Cost
Indirect Cost
Name
Tulane University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
City
New Orleans
State
LA
Country
United States
Zip Code
70118
Lo, D; Zhang, Y; Dai, M-S et al. (2015) Nucleostemin stabilizes ARF by inhibiting the ubiquitin ligase ULF. Oncogene 34:1688-97
He, Guifen; Zhang, Yi-Wei; Lee, Jun-Ho et al. (2014) AMP-activated protein kinase induces p53 by phosphorylating MDMX and inhibiting its activity. Mol Cell Biol 34:148-57
Zhang, Qi; Zeng, Shelya X; Lu, Hua (2014) Targeting p53-MDM2-MDMX loop for cancer therapy. Subcell Biochem 85:281-319
Zhang, Qi; Zhou, Xiang; Wu, RuiZhi et al. (2014) The role of IMP dehydrogenase 2 in Inauhzin-induced ribosomal stress. Elife 3:
Liao, Jun-Ming; Cao, Bo; Zhou, Xiang et al. (2014) New insights into p53 functions through its target microRNAs. J Mol Cell Biol 6:206-13
Zhan, Yang; Cao, Bo; Qi, Yanfeng et al. (2013) Methylselenol prodrug enhances MDV3100 efficacy for treatment of castration-resistant prostate cancer. Int J Cancer 133:2225-33
Liao, Jun-Ming; Zhang, Yu; Liao, Wenjuan et al. (2013) I*B kinase * (IKK*) inhibits p63 isoform ýý (TAp63ýý) transcriptional activity. J Biol Chem 288:18184-93
Zhang, Qi; Lu, Hua (2013) Identification of small molecules affecting p53-MDM2/MDMX interaction by fluorescence polarization. Methods Mol Biol 962:95-111
Zhang, Yiwei; Zhang, Qi; Zeng, Shelya X et al. (2013) Inauhzin sensitizes p53-dependent cytotoxicity and tumor suppression of chemotherapeutic agents. Neoplasia 15:523-34
Zhou, Xiang; Hao, Qian; Liao, Jun-Ming et al. (2013) Ribosomal protein S14 negatively regulates c-Myc activity. J Biol Chem 288:21793-801