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Open Access Research

The anti-myeloma activity of a novel purine scaffold HSP90 inhibitor PU-H71 is via inhibition of both HSP90A and HSP90B1

Saad Z Usmani1*, Robert D Bona2, Gabriela Chiosis3 and Zihai Li4*

Author Affiliations

1 Myeloma Institute for Research & Therapy, University of Arkansas for Medical Sciences, Little Rock, AR, USA

2 Carole and Ray Neag Comprehensive Cancer Center, Lea's Center for Hematologic Disorders, University of Connecticut Health Center, Farmington, CT, USA

3 Department of Molecular Pharmacology & Chemistry, Memorial Sloan Kettering Cancer Center, New York, NY, USA

4 Department of Immunobiology & Cancer Immunology, Hollings Cancer Center, Medical University of South Carolina, Charleston, SC, USA

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Journal of Hematology & Oncology 2010, 3:40  doi:10.1186/1756-8722-3-40

Published: 26 October 2010

Abstract

Background

Heat shock protein 90 (HSP90) inhibitors have emerged as a promising class of anti-cancer drugs in both solid and hematologic malignancies. The HSP90 family includes the cytosolic HSP90 (HSP90AA1), the ER paralogue gp96 (HSP90B1) and the mitochondrial member TRAP1 (HSP90L). We evaluated the in vitro anti-tumor activity and mechanism of action of PU-H71, a novel purine scaffold HSP90 inhibitor in human multiple myeloma cell lines.

Methods

Multiple human myeloma cell lines including cells that are resistant to corticosteroids and bortezimab were treated with PU-H71, followed by analysis of cell viability, cell cycle progression and apoptosis, by flow cytometry and caspase 3 immunoblot. Induction of unfolded protein response was studied by XBP-1 s immunoblot. The role of gp96 was further assessed by small hairpin RNA knockdown of gp96 before treatment with PU-H71.

Results

PU-H71 has potent in vitro anti-myeloma activity in both drug-sensitive and drug-resistant cell lines. PU-H71 activates the unfolded protein response and induces caspase-dependent apoptosis. The stable gp96 knockdown human myeloma cell line was found to be more resistant to PU-H71 and other HSP90 inhibitors including 17-AAG and 17-DMAG, even though these cells are more sensitive to conventional anti-myeloma drugs.

Conclusion

We conclude that PU-H71 is a promising drug for the treatment of myeloma. Our finding further suggests that PU-H71 and the geldanamycin analogues work in part by inhibiting the endoplasmic reticulum gp96 along with the cytosolic HSP90.