Adult T-cell leukemia-lymphoma (ATL) is a chemo-resistant malignancy. Heat shock protein 90 (HSP90) is involved in folding and functions as a chaperone for multiple client proteins, many of which are important in tumorigenesis. The HSP90 inhibitor 17-AAG, derived from geldanamycin, has potent antitumor activity against ATL. However, geldanamycin derivatives have several limitations, including poor solubility, formulation difficulties, and severe hepatotoxicity in clinical settings, which have prompted development of second generation synthetic HSP90 inhibitors including NVP-AUY922 (AUY922), a second generation isoxazole-based non-geldanamycin HSP90 inhibitor that inhibits the ATPase activity of HSP90. AUY922 has shown nanomolar efficacy against a wide range of human cancer cells in vitro and also inhibits progression of a variety of tumors in vivo. Phase I/II studies of AUY922 with advanced solid tumors and hematological malignancies are presently underway. Here, we studied the effects of AUY922 on ATL in vitro and in vivo.
We initially analyzed the effects of AUY922 (Novartis Pharmaceuticals) on survival of ATL-derived cell lines (KK1, SO4, LM-Y1, KOB, ST1) and HTLV-I-infected T-cell lines (MT2, HuT102). Cells cultured with various concentrations of AUY922 for 72 hours showed survival suppression in a dose-dependent manner in MTS assay findings. The concentrations of AUY922 required to inhibit cell survival by 50% (IC50) varied from 12.5 to 25.0 nM. We also found that the inhibitory effect of AUY was superior to that of 17-AAG. We further assessed AUY922-induced cell survival inhibition with peripheral blood mononuclear cells (PBMCs) obtained from patients with ATL and healthy donors. AUY922 induced apparent cell survival suppression in primary ATL cells, but not in normal PBMCs, while FACS analysis revealed that AUY922 induced cell-cycle arrest and apoptosis in these cell lines. Interestingly, AUY922 induced down-regulation of PIM kinases, which was confirmed by DNA microarray, qRT-PCR, and WB analysis results. Furthermore, SGI-1776, a PIM kinase inhibitor, successfully induced cell survival suppression in ATL and HTLV-1 infected cell lines in both dose- and cell-dependent manners. To elucidate the molecular mechanisms of cytotoxicity, we also examined the expressions of several client proteins using WB analysis. AUY922 treatment led to strong up-regulation of HSP70, a surrogate marker of HSP90 inhibition, and a dose-dependent decrease of HSP90 client proteins associated with cell survival, proliferation, and cell cycle in the G1 phase, including p-Akt, Akt, IκBα, IKKα, IKKβ, IKKγ, Cdk4, Cdk6, and survivin. In a xenograft model created with C.B-17/Icr-SCID mice, intraperitoneal administration of the vehicle or AUY922 was given after injection of HuT102 cells. In the control mice, bulky tumors grew within 4 weeks, whereas daily administrations of AUY922 significantly impaired tumor growth.
Together, our findings suggest that AUY922 may be an effective therapeutic agent for ATL and PIM kinases are a novel therapeutic target.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.