SC COBRE in Oxidants, Redox Balance and Stress Signaling
James Chou, PhD
Awarded RO1: Novel lysine deacetylase 6 Hsp domain inhibitors against AML (1R01CA163452-01A1)
Acute myelogenous leukemia (AML) is one of the most common and aggressive forms of acute leukemia affecting 30,000 people per year. Greater than 5 year survival rate still remains around 10-30%, and this depends greatly on the patient’s ability to tolerate the combination of cytotoxic chemotherapies, which suppresses much needed haemopoiesis. The limits of current treatment modalities indicate a need for innovative therapies directed against relevant biological targets in AML to improve the clinical outcome. AML is a heterogeneous disease; recent studies have identified a set of activating kinase mutations in FLT-3, c-Kit, and Ras and constitutively active transcription factors such as STAT5 and chimera MLL relevant to disease outcome. One of the major challenges in treating AML is developing therapies that are capable of affecting multiple biological pathways promoting AML proliferation and survival. Histone deacetylase isozyme 6 (HDAC6) is over-expressed in AML patients and is hypothesized to play a key role in maintaining oncogenic signaling through the regulation of heat-shock protein functions that are critical for AML pathogenesis and survival. HDAC6 is also required for malignant cell transformation both in transformed cells and in vivo. Moreover, HDAC6 knock-out mice have been shown to resist mutagen induced tumors and develop normally, which further underscore the potential of HDAC6 as a better tolerated and less toxic therapeutic target for AML. We have identified novel HDAC6-Hsp domain inhibitors, which preferentially inhibit the HDAC6-Hsp deacetylation domain at low µM concentration and induce Hsp90 acetylation, unlike the canonical hydroxamate HDAC6 inhibitors, tubastatin A and Tubacin. Our overarching hypothesis is that HDAC6-Hsp domain activity promotes AML proliferation and survival by maintaining proper function of multiple heat-shock proteins. Selective HDAC6-Hsp domain inhibition deactivates multiple Hsp activities, attenuates aberrant AML oncogenic signaling, and promotes AML apoptosis. This proposal intends to use multifaceted and innovative approaches to develop novel HDAC6-Hsp domain inhibitors and to investigate the role that HDAC6 plays in the regulation of Hsp activities and apoptosis initiation in AML. In Aim 1, we will refine our HDAC6-Hsp inhibitors through a phylogenetic library synthesis in order to characterize the structure activity relationship of the HDAC6-Hsp domain. In Aim 2, we will investigate the HDAC6-Hsp pathway axis, study HDAC6 dependent Hsp70 regulation, and the roles of Hsp70 acetylation play in apoptosome formation. Finally, we will examine our HDAC6-Hsp deacetylation domain inhibitors in vivo using a physiologically relevant disseminated AML xenograft model. We will determine the efficacy of our lead HDAC6 inhibitor candidates against AML, performing pharmacokinetic and dynamic studies on lead inhibitor candidates, and validate the inhibitor’s ability to influence biomarkers in vivo.
Public Health Relevance Statement:
Acute myelogenous leukemia (AML) is one of the most common and aggressive forms of acute leukemia affecting 30,000 people annually. With an expected increase in American life expectancy, the numbers of AML cases are also expected to increase, as the majority of AML patients are over the age of 60. Little has changed in the standard AML therapies for the last 30 years, and treatments with low cytotoxicity and high therapeutic windows are highly desirable. By studying molecular mechanisms of HDAC6-Hsp domain inhibition and induction of selective AML apoptosis, the development of novel HDAC-Hsp domain inhibitors against AML can be a significant advancement from the current treatment disadvantages.
2011 - 2013
COBRE Project: Novel AML therapy targeting HDAC6 and Hsp90 Chaperone Complex
Abstract: Acute myelogenous leukemia (AML) is one of the most common and aggressive forms of acute leukemia affecting 30,000 people per year. Survival greater than 5 years still remains around 10-30%, and this depends greatly on the patient’s ability to tolerate the combination of cytotoxic chemotherapies, which suppress much needed haemopoiesis. The limits of current treatment modalities indicate a need for innovative therapies directed against relevant biological targets in AML to improve the clinical outcome in AML. Heat-shock protein 90 (Hsp90) and histone deacetylase isozyme 6 (HDAC6) are required for the maintenance of AML oncogenic signaling and stability of oncogenic chimera transcription factors. Hsp90 and HDAC6 are constitutively over-expressed in AML patient blood mononucleocytes and bone marrows. HDAC6 is also required for malignant cell transformation both in transformed cells and in vivo. HDAC6/Hsp90 complex/chaperone activity requires active HDAC6, and inhibition of HDAC6 destabilizes Hsp90 complex and abolish its chaperone function. We have identified a novel class of selective HDAC6/Hsp90 inhibitors, which preferentially inhibit HDAC6 at low µM concentrations and rapidly induce inactive acetylated Hsp90 thereby resulting in Hsp90 client protein depletion. Our overarching hypothesis is that a functional HDAC6/Hsp90 complex is an essential part of AML pathogenesis. The proposal intends to use multifaceted and innovative approaches to develop novel HDAC6/Hsp90 complex inhibitors and to investigate the roles of HDAC6/Hsp90 complex in AML.
Scott Eblen, Ph.D.
Jennifer Isaacs, Ph.D.
Carola Neumann, M.D.