The Efficacy of Dual PI3K and mTOR Inhibitor, NVP-BEZ235 against BCR-ABL Positive Leukemia Cells Include ABL Kinase Domain Mutation in Combination with Nilotinib.

Abstract 3784

Poster Board III-720

Imatinib has shown clinical efficacy against chronic myeloid leukemia (CML) and it is now the standard care fore initial therapy of CML. However, a substantial number of patients are either primary refractory or acquire resistance to imatinib. Mutation in the ABL kinase domain is the principal mechanism of imatinib resistance in patients with BCR-ABL-positive leukemia and this becomes a problematic in clinically. Phosphoinositide 3 kinase (PI3K)/Akt /mammalian target of rapamycin (mTOR) pathway regulates various processes including cell proliferation, survival and anti-apoptosis activity. Moreover, PI3K/Akt/mTOR pathway is desregulated in hematological malignancies and activated by upstream proteins such as BCR-ABL. NVP-BEZ235 is a dual inhibitor of PI3K and mTOR. It has been reported NVP-BEZ235 showed high target specificity and demonstrated antiproliferative activity against tumor. However, the molecular and functional consequences of NVP-BEZ235 against BCR-ABL expressing cells with BCR-ABL kinase domain mutation have not fully known. In this study, we investigated the NVP-BEZ235 efficacy by using the BCR-ABL positive cell line, K562 and murine Ba/F3 cell line which was transfected wild type (Wt) p210 BCR-ABL or imatinib resistant BCR-ABL mutants such as E255K, T315I and primary sample with T315I mutation. 48 hours treatment of NVP-BEZ235 exhibits cell growth inhibition and induced apoptosis against K562 cells in a dose dependent manner. We also found that NVP-BEZ235 potently induced cell growth inhibition of murine Ba/F3 cells ectopically expressing wild type (Wt) p210 and imatinib resistant BCR-ABL mutants such as E255K and T315I mutation. We next examined the intracellular signaling by using these cell lines. We found that phosphorylation of Akt, eukaryotic initiation factor 4-binding protein 1 (4E-BP1) and p70 S6 kinase were decreased after NVP-BEZ235 treatment in a dose dependent manner. However, Mitogen-activated Protein Kinase (MAPK) activation was not reduced after NVP-BEZ235 treatment. Because Abl kinase inhibitor, nilotinib has shown efficacy against imatinib resistant BCR-ABL mutant, we investigated the efficacy between NVP-BEZ235 and nilotinib by using these cell lines. We found that combination of NVP-BEZ235 and nilotinib more potentially cell growth inhibition of K562, Ba/F3 Wt BCR-ABL, BCR-ABL mutations (E255K, T315I) Ba/F3 cells. We found that combination of NVP-BEZ235 and nilotinib more potentially induced apoptosis in 48 hours treatment. Phosphorylation of Akt, 4E-BP-1, S6 kinase was reduced after NVP-BEZ235 and nilotinib treatment in K562 cells. Cyclin D1 and BCL-XL were also decreased. PARP activation was synergistically increased after NVP-BEZ235 and nilotinib treatment. We next examined the affectivity of NVP-BEZ235 and nilotinib by using T315I positive primary sample. We found that NVP-BEZ235 and nilotinib potently induced cell growth inhibition and also increased apoptosis of primary T315I cells in 48 hours treatment. Data from this study suggested that administration of the a dual inhibitor of PI3K and mTOR, NVP-BEZ235 may be a powerful strategy against BCR-ABL mutant cells and enhance cytotoxic effects of nilotinib in those imatinib resistant BCR-ABL mutant cells.