Abstract
14541 Background: Bone marrow stroma-derived factor-1 (SDF-1, CXCL12) binds and activates the chemokine receptor CXCR4, which regulates the trafficking and mobilization of normal and leukemic hematopoietic cells. CXCR4 signaling thorough AKT and c-Raf also promotes survival and decreases sensitivity of AML cells to anti-leukemia agents. Both CXCL12 and CXCR4 are overexpressed and confer poor prognosis in AML. Treatment with the CXCR4 antagonist AMD3100 sensitizes AML cells to anti-leukemia drugs. We determined the effect of panobinostat (P) and/or FC-131 (a new generation CXCR4 inverse agonist) on CXCR4 expression and signaling in cultured and primary AML cells. Methods: Following treatment of human AML OCI-AML3, HL-60, and Jurkat cells, as well as primary AML cells with P (10 to 50 nM) and/or FC-131 (10 nM) with our without 10 nM of CXCL12, cell surface expression of CXCR4 and apoptosis (Annexin V/PI staining) were determined by flow cytometry. Intracellular protein levels of CXCR4, p-AKT, p-ERK1/2, heat shock protein (hsp) 70 and hsp90 were determined by immunoblot (IB) analyses. Binding of CXCR4 to hsp90 and hsp70, as well as CXCR4 acetylation, were determined by immunoprecipitation (IP)/IB analyses. Results: Treatment with P depleted the intracellular and surface expression of CXCR4 in the presence or absence of CXCL12. P induced acetylation of hsp90 and decreased its binding to CXCR4. P also induced acetylation and increased membrane binding of CXCR4 to hsp70. P promoted degradation of CXCR4 by the proteasome. Treatment with P alone also decreased p-AKT and p-ERK1/2. Co- treatment with P markedly attenuated the phosphorylation (p) of AKT and ERK1/2 induced by CXCL12, casuing apoptosis of up to 50% of cultured and primary AML cells. Co-treatment with P and FC-131 caused greater depletion of CXCR4, p-AKT and p-ERK1/2 levels, and synergistically induced apoptosis of the cultured AML cells (combination indices of < 1.0, utilizing isobologram analysis). Conclusions: CXCR4 is chaperoned by hsp90, and treatment with P depletes CXCR4 levels and signaling in AML cells. The novel combination of FC-131 and P is synergistically active and its in vivo ant-AML efficacy is currently under evaluation. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Novartis Institute for Biomedical Research Inc. Novartis Institute for Biomedical Research Inc. Merck & Co., Novartis, Novartis Institute for Biomedical Research Inc.
Published Version
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