[1382] PU-H71, a HSP90 Inhibitor, Antagonizesstroma-Induced Prosurvival Effects in CLL through Its Inhibition of the B-Cell Receptor Signaling Pathway

Ailin Guo, Shuhua Chen, Pin Lu, Zibo Song, Jiao Ma, Richard R Furman, Morton Coleman, Gabriela Chiosis, Yue Lynn Wang. Weill Cornell Medical College, New York, NY; Memorial Sloan-Kettering Cancer Center, New York, NY

Background: The B-cell receptor (BCR) plays an essential role inthe pathogenesis ofchronic lymphocytic leukemia(CLL) and many components of the BCR signaling pathway are known clients of HSP90. HSP90 is a highly conserved molecular chaperone that ensures the proper folding and stabilization of its clientproteins. In this study, we investigated whether PU-H71 a novel purine-scaffold HSP90 Inhibitorhas anti-tumor activity in CLL by destabilizing BCR signaling pathway constituents.
Design: Fresh CLL cells wereisolatedand cultured ex vivo with or withoutstromal co-culture. Molecular and cellular events were studied in PU-H71-treated and control CLL cells.
Results: Immunoblotting revealed that a significantly higher amount of HSP90 is present in CLL cells than in peripheral blood mononuclear cells (PBMC), suggesting the chaperone may be pathogenically relevant. We found that PU-H71caused the death of CLL cells in a dose and time dependent manner while theviability ofeither PBMC or normal lymphocyteswere not affected.PU-H71 induced apoptosis resulting in CLL cell deathas it caused mitochondrial cytochrome C release and a decrease in the abundance of several anti-apoptotic proteins. Interestingly, PU-H71 has the ability to counteract the prosurvival effects of the stroma and caused apoptosis in CLLcellsco-cultured with stroma. To gain mechanistic insights into how PU-H71 acts, we examined the BCR signaling pathway. We found that the amounts of several key components of the pathway were reduced by PU-H71 treatment. This occurred even in the presence of stromal co-culture.The results suggest that PU-H71 antagonizes the function of HSP90 leading to the destabilization of the BCR signaling transducers.A chemical pull-down experiment revealed the co-existence of the BCR components and HSP90 in the same complex, suggesting these BCR constituents are indeed clients of HSP90 in CLL cells. Further, specific genetic knock-down of the signal transducers by siRNAconfirmedtheirkey roles in mediating the survival of CLL cells.
Conclusions: PU-H71 antagonizes stroma-induced prosurvival effects in CLL through its inhibition of the B-cell receptor signaling pathway. Our results suggest that PU-H71 may serve as a useful therapy against CLL and is worth further clinical development.
Category: Hematopathology

Tuesday, March 5, 2013 9:30 AM

Poster Session III # 159, Tuesday Morning


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