Drugs with tumor selectivity may have an important benefit in chemotherapies. We have previously shown that Rocaglamide(s), derived from the medicinal plant Aglaia, kills various leukemic cells through the mitochondrial apoptosis pathway with only minor toxicities to normal lymphocytes. Here, we show further that Rocaglamide preferentially promotes activation-induced cell death in malignant T cells by differential regulation of c-FLIP and CD95L expression. Rocaglamide enhances and also prolongs activation-induced JNK activation in malignant T cells leading to downregulation of c-FLIP but upregulation of CD95L expression. We also show that malignant T cells express a significantly higher amount of Bid -the molecular linker that bridges the receptor-mediated to the mitochondria-mediated apoptosis pathway. Conversely, a substantially lower amount of c-FLIP in response to T-cell stimulation compared to normal T cells is observed. This difference may provide a therapeutic window for cancer treatment. The effect of Rocaglamide on sensitization of activation-induced cell death in malignant T cells was further demonstrated in vivo in a mouse model. Our study demonstrates that Rocaglamide may be a potential anticancer drug that simultaneously targets both c-FLIP and CD95L expressions in tumor cells. This study may also provide a new clue to design a more efficient chemotherapy by using a combination of stimuli that engage the receptor-mediated and the mitochondriamediated death pathway. Cell Death and Differentiation (2009) 16, 1289-1299 doi:10.1038/cdd.2009 published online 17 April 2009 Acute lymphocytic leukemia (ALL) comprises approximately 25% of acute leukemia cases, of which two-third occur in children. Although the cure rates of childhood ALL are relatively high (approximately 85%), 1 the cure rates of adult ALL are poor with only 34-57% in patients below the age of 30 years, 15-17% above the age of 50 years and less than 5% over 60 years of age.

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The human T-lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia (ATL). HTLV-1 Tax has been shown to have a prosurvival role in infected T cells by enhancing expression of the Bcl-2 family of antiapoptotic proteins. In this study, we show that the expression of proapoptotic BH3-only proteins Bim (Bcl-2-interacting mediator of cell death) and Bid (BH3-interacting domain death agonist) is diminished in HTLV-1-infected leukemic cells. Using a Tax-inducible system and a transient overexpression approach, we demonstrate that Tax downregulates Bid and Bim expression at the transcriptional level. We show that reinforced expression of Bim and Bid in HTLV-1-infected T-cell lines sensitizes CD95/TRAIL- and anticancer drug-induced apoptosis. Furthermore, we show that Tax suppresses Bid and Bim expression by enhancing hypoxia-inducible factor-1α (HIF-1α) protein expression. siRNA knockdown of HIF-1α or chemical inhibition of the transactivation activity of HIF-1α resulted in an increase in Bid and Bim expression and, consequently, in an increase in CD95/TRAIL- and anticancer drug-induced apoptosis in HTLV-1-infected leukemic T-cell lines. Our study provides evidence that besides upregulation of prosurvival Bcl-2 proteins, Tax may also confer apoptosis resistance to HTLV-1-infected T cells by suppressing the expression of the proapoptotic BH3-only proteins Bim and Bid.