While development of new therapeutic approaches have contributed to the increase in the complete remission rate for CLL patients, relapses and resistance to re-treatment remain a significant problem. Nevertheless, changes that occur in the biology of CLL upon relapse from front-line therapies provide clues to resistance mechanisms that prevent prolonged complete responses. Our overall strategy is to employ three novel approaches that are each directed at an aspect of the pathophysiology of CLL and the mechanisms associated with resistance. First, a deletion at 11q22-23, the site of the ATM gene, occurs in half of relapsed/refractory patients. Mutation of the residual allele (-50%) inactivates homologous recombinafion (HR) repair of double strand breaks. Because Sapacitabine causes one-ended double strand breaks, cells that lack ATM are selectively sensitized. We will develop assays to identify patients who's CLL lacks ATM function, and initiate a clinical trial of Sapacitabine therapy to test the hypothesis that their disease will be selecfively sensitized. Second, studies in model systems demonstrate that loss of p53 function is a resistance mechanism to cytotoxic therapy. Neariy half of relapsed refractory patients lack p53 funcfion. We postulate that expression of the epigenetically silenced p73 will serve in place of p53 to activate expression of pro-apoptotic proteins. This will be validated in model systems and tested in a clinical trial. Third, a novel mechanism by which the microenvironment sustains CLL cells and increases resistance to chemotherapy appears to act by providing precursors for glutathione. This sustains CLL by neutralizing the destructive action of reactive oxygen species that are innately over-expressed by CLL. By using a small molecule to reduce glutathione we will test this hypothesis to sensitize CLL cells in vitro and in vivo. These investigations will provide mechanism-based rationales for development of combination therapies.

Public Health Relevance

Current first-line therapy for CLL does not target the pathophysiology ofthe disease and is thwarted by resistance mechanisms. This proposal postulates three novel therapeutic approaches aimed at a key genetic lesion, loss of function of a tumor suppressor, and a mechanism of microenvironmental support. Clinical trails are planned to evaluate these strategies in pafients with relapsed/refractory CLL. Successful approaches will be combined with induction therapies to improve overall outcome.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Program Projects (P01)
Project #
2P01CA081534-12A1
Application #
8235346
Study Section
Special Emphasis Panel (ZCA1-RPRB-0 (O1))
Project Start
2011-12-01
Project End
2017-08-31
Budget Start
2012-09-24
Budget End
2013-08-31
Support Year
12
Fiscal Year
2012
Total Cost
$151,641
Indirect Cost
$25,405
Name
University of California San Diego
Department
Type
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
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