Abstract #4680: Heat shock protein 90 ATPase inhibitors NVP-AUY922 and NVP-BEP800 induce cell apoptosis and disrupt chaperone association with wild-type Bcr-Abl and T315I imatinib mesylate-resistant Bcr-Abl mutant

One of the major causes of drug resistance for chronic myeloid leukemia (CML) therapy is the mutations in the tyrosine kinase domain of Bcr-Abl. The Bcr-Abl protein is an important client protein of heat shock protein 90 (HSP90). We investigated two novel HSP90 ATPase inhibitors, NVP-AUY922 (AUY) and NVP-BEP800 compound (BEP) (Novartis Pharma AG), on wild-type (w-t) Bcr-Abl (32Dp210) and Bcr-Abl mutant imatinib (IM)-resistant cell lines. The MTT results showed that 32Dp210 and five Bcr-Abl mutants (T315I, E255V, E255G, F317L and Y253H) in 32D cells and KBM-5R (CML cell line with T315I mutation) are resistant to IM but sensitive to these two HSP90 inhibitors. The association between HSP90 and Bcr-Abl or mutant Bcr-Abl was significantly inhibited by BEP but only slightly by AUY in both 32Dp210 and T315I Bcr-Abl mutant cells after treatment with either 300 nM BEP or 10 nM AUY compound for 16h. These concentrations were the approximate IC₅₀ as determined by MTT assays. HSP90 protein levels were reduced after treatment with BEP. Tyrosine phosphorylation of Bcr-Abl was decreased in both Bcr-Abl + 32D cells and Bcr-Abl T315I cells in a dose-dependent manner after treatment with BEP or AUY for 16h. The dose of AUY that inhibits phosphorylation of w-t Bcr-Abl (IC₅₀ =20 nM) was much lower than that of mutated Bcr-Abl T315I (IC₅₀ =5 \#956;M).However, the two HSP90 inhibitors have different potency for blocking Bcr-Abl phosphorylation. In 32Dp210 cells, 20 nM AUY efficiently reduced Bcr-Abl phosphorylation compared to the BEP compound (800 nM). In T315I cells, BEP completely inhibited Bcr-Abl phosphorylation at 800 nM while the half inhibition dose of AUY is 5 \#956;M. BEP efficiently induced cell apoptosis in 32Dp210 (IC₅₀ =1 \#956;M) and IM-resistant T315I (IC₅₀ =0.6 \#956;M), E255K (IC₅₀ =0.8 \#956;M) and KBM 5R (IC₅₀ =1.5 \#956;M) cell lines. A dose of 5 µM AUY caused significant apoptosis (90%) in 32Dp210 and E255K cell lines, but exhibited very weak effect on T315I and KBM-5R cell lines even when the dose reached 10 \#956;M. These results showed that w-t Bcr-Abl and mutated Bcr-Abl T315I exhibit different sensitivity to the BEP and AUY compounds. Both HSP90 inhibitors disrupt the association between HSP90 and both w-t Bcr-Abl and the T315I mutant form. Overall, the BEP compound is more potent than the AUY compound in the various Bcr-Abl + cells.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4680.