Survivin silencing sensitizes imatinib-resistant CML cells to the cytotoxic effect of hydroxyurea

Abstract

13119 Background: Imatinib Mesylate (IM), a semi-specific inhibitor of the BCR-ABL tyrosine kinase, is currently the treatment of choice for Chronic Myeloid Leukemia (CML). However, about one third of CML patients treated with IM develop resistance to the drug because of reactivation of BCR-ABL kinase activity. This phenomenon is usually ascribed to the amplification of the BCR-ABL gene or to the selection of leukemic clones harboring point mutations that abrogate IM binding. To identify novel anti-apoptotic signaling pathways employed by BCR-ABL and devise strategies capable of killing IM-resistant CML cells, we investigated the interplay between BCR-ABL and the Inhibitor of Apoptosis Protein Survivin. Methods: Murine hematopoietic cells (32D) transduced with p210 BCR-ABL and human cell lines either positive (K562, KCL22, KYO1 and LAMA84) or negative (HL60) for the BCR-ABL oncoprotein, were analyzed for Survivin expression by western blot before and after IM treatment. Three different pathways (MAPK, PI3K and JAK2/STA3) potentially involved in BCR-ABL-mediated induction of Survivin were studied using inhibitors specific for each signaling cascade. The effect of Survivin on the proliferation and viability of IM-sensitive and IM-resistant CML cells was investigated after silencing Survivin expression with small interfering RNAs. Results: BCR-ABL tyrosine kinase activity induced an over-expression of Survivin in both human and murine hematopoietic cell lines. This over-expression was both at the transcriptional and the translational level and required the JAK2/STAT3 pathway. Survivin silencing by siRNA increased IM cytotoxicity in IM-sensitive cells but failed to restore IM efficacy in IM-resistant cells. However, Survivin silencing sensitized CML cells to the cytotoxic effect of hydroxyurea and enhanced the efficacy of this compound on three different murine cell lines are insensitive to IM because of point mutations in the BCR-ABL kinase domain (Ba/F3p210Y253F, Ba/F3p210D276G and Ba/F3p210T315I). Conclusions: Reduction of Survivin expression improves the efficacy of IM and increases the sensitivity of IM-resistant CML cells to hydroxyurea. Survivin may represent an attractive therapeutic target for both IM-sensitive and IM-resistant CML patients. No significant financial relationships to disclose.