DNA damaging anticancer agents induce arrest at various checkpoints throughout the cell cycle. This protective mechanism allows cells time to repair damage before progressing. UCN-01 (7-hydroxy-staurosporine) was identified as a potent inhibitor of the DNA damage-induced S and G2 arrest, thereby causing a marked enhancement in cell killing. UCN-01-mediated abrogation of normal cells is prevented by the p53 tumor suppressor protein. Thus, UCN-01 may selectively enhance chemotherapy in the tumor while sparing normal tissue. However, some p53-defective tumors are also resistant to UCN-01, while some p53-wildtype tumors are sensitive. This leads to the major question in this proposal: what are the determinants of response to checkpoint inhibitors? Aim 1 will focus on p53-defective tumor cell lines and investigate the role of Chk1 (inhibited by UCN-01) and other checkpoint kinases in arresting cell cycle progression. The response of various cell lines to different checkpoint inhibitors will be assessed. Three resistant tumor cell models will be analyzed for alternate kinases that explain their resistance to Chk1 and Chk2 inhibitors;candidate kinases include hSAD1, PLK3, MAPKAPK2 and JNK. To confirm the role of each kinase in checkpoint regulation, cell lines will be generated in which the kinase expression is prevented by siRNA.
Aim 2 will address the question as to why some p53-wildtype tumors retain sensitivity to Chk1 inhibitors despite the fact that non-tumorigenic lines are resistant. Recent results demonstrate that p53 regulates the checkpoint through both gene activation (p21waf1) and repression (cyclin B) and that regulation of both of these proteins is defective in UCN-01-sensitive p53 wildtype tumors;p21 fails to be induced during S phase arrest, while cyclin B fails to be repressed during G2 arrest. The transcriptional and post-translational regulation of these two proteins will be studied and contributors to their differential regulation assessed. Experimental approaches will include dissection of the pathways through promoter analysis and chromatin immunoprecipitation assays. As novel checkpoint inhibitors enter clinical trial, the results of these studies will provide a basis upon which to stratify patients and thereby enhance the probability of developing a successful therapeutic regimen. For those tumors in which a response is not indicated, these experiments will likely identify alternate targets for drug discovery.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA117874-03
Application #
7629019
Study Section
Developmental Therapeutics Study Section (DT)
Program Officer
Arya, Suresh
Project Start
2007-08-10
Project End
2012-05-31
Budget Start
2009-06-01
Budget End
2010-05-31
Support Year
3
Fiscal Year
2009
Total Cost
$303,810
Indirect Cost
Name
Dartmouth College
Department
Pharmacology
Type
Schools of Medicine
DUNS #
041027822
City
Hanover
State
NH
Country
United States
Zip Code
03755
Eastman, Alan (2017) Improving anticancer drug development begins with cell culture: misinformation perpetrated by the misuse of cytotoxicity assays. Oncotarget 8:8854-8866
Sakurikar, Nandini; Eastman, Alan (2016) Critical reanalysis of the methods that discriminate the activity of CDK2 from CDK1. Cell Cycle 15:1184-8
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Sakurikar, Nandini; Eastman, Alan (2015) Will targeting Chk1 have a role in the future of cancer therapy? J Clin Oncol 33:1075-7
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Thompson, Ruth; Eastman, Alan (2013) The cancer therapeutic potential of Chk1 inhibitors: how mechanistic studies impact on clinical trial design. Br J Clin Pharmacol 76:358-69
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Chang, Li-Ju; Eastman, Alan (2012) Differential regulation of p21 (waf1) protein half-life by DNA damage and Nutlin-3 in p53 wild-type tumors and its therapeutic implications. Cancer Biol Ther 13:1047-57

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