The long-term objective of this project is to apply the mechanistic insights of the interaction between Rac GTPase of the Rho family and their regulatory proteins, the Dbl family guanine nucleotide exchange factors (GEFs) in particular, to the design of novel approaches to target deregulated Rac activities in human diseases such as cancer. The GEF-Rac signaling axis lies in the crossroads of many signaling events initiated by growth factors, cytokines, stress, and adhesion molecules. Their functional interaction leads to the activation of Rac and a variety of Rac-mediated physiological responses including actin and microtubule cytoskeletal reorganization, adhesion, migration, and proliferation. In the last funding period, we have studied the structure-function relationship of Rac1 in regard of its interaction with GEFs and effectors, and have succeeded in deriving structural and kinetic information of several functional interactions involving Rac1. Further, we have studied the role of Rac1 by a conditional gene targeting approach in mice to reveal several cell functions of Rac1 that could not have been discovered by conventional means. Last, we have discovered a first generation small molecule inhibitor, NSC23766, that is effective in targeting Rac in vitro and in vivo, and have utilized it to study a number of physiological and pathological functions of Rac GTPases ranging from hematopoietic stem cell mobilization, platelet regulation, to schwannoma phenotype reversion. In this proposal, we will (1) pursue structure-function based rational design and improvement of Rac-targeting small molecule inhibitors by screening and medicinal chemistry based on the newly resolved Rac1-NSC23766 crystal structure, and (2) apply the Rac-targeting small molecule inhibitors to leukemia stem cell mobilization from their bone marrow niche in a chronical myeloid leukemia mouse model. These mechanism-based studies of small molecule inhibitor design and pre-clinical validation in a novel pathologic context will not only provide an improved generation of Rac GTPase inhibitors for a wide range of usage in cancer research, but also will implicate an innovative avenue of application in mobilizing leukemia stem cells from their microenvironment, which can be utilized as an important regiment in combinatory therapy for effective eradication of cancer.

Public Health Relevance

Rac GTPases have emerged as potential anti-cancer therapeutic targets by recent studies. The proposed work will pursue structure-based design of new chemical inhibitors of Rac GTPases by translating the mechanistic information obtained from the decade-long biochemical, structural, cell biological, and animal studies of Rac GTPases for anti-cancer therapy. Further, the proposed work will help establish a novel therapeutic concept that targeting Rac in leukemia stem cells could result in their mobilization from the niche. Our studies will raise a new possibility for future combinatory therapy in cancer research.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Drug Discovery and Molecular Pharmacology Study Section (DMP)
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Mufson, R Allan
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Cincinnati Children's Hospital Medical Center
United States
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Lin, Yuan; Zheng, Yi (2015) Approaches of targeting Rho GTPases in cancer drug discovery. Expert Opin Drug Discov 10:991-1010
Chang, Kyung Hee; Nayak, Ramesh C; Roy, Swarnava et al. (2015) Vasculopathy-associated hyperangiotensinemia mobilizes haematopoietic stem cells/progenitors through endothelial AT?R and cytoskeletal dysregulation. Nat Commun 6:5914
Zandvakili, Inuk; Davis, Ashley Kuenzi; Hu, Guodong et al. (2015) Loss of RhoA Exacerbates, Rather Than Dampens, Oncogenic K-Ras Induced Lung Adenoma Formation in Mice. PLoS One 10:e0127923
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Liu, Ming; Bi, Feng; Zhou, Xuan et al. (2012) Rho GTPase regulation by miRNAs and covalent modifications. Trends Cell Biol 22:365-73
Konstantinidis, Diamantis G; Pushkaran, Suvarnamala; Johnson, James F et al. (2012) Signaling and cytoskeletal requirements in erythroblast enucleation. Blood 119:6118-27
Bosco, Emily E; Kumar, Sachin; Marchioni, Filippo et al. (2012) Rational design of small molecule inhibitors targeting the Rac GTPase-p67(phox) signaling axis in inflammation. Chem Biol 19:228-42
Akunuru, S; James Zhai, Q; Zheng, Y (2012) Non-small cell lung cancer stem/progenitor cells are enriched in multiple distinct phenotypic subpopulations and exhibit plasticity. Cell Death Dis 3:e352

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