| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 2005: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
The therapeutic approach to leukemia is based on chemotherapy, but the side effects of the drugs used and various complications are sometimes fatal. Recently, molecular-targeted therapy is pay attention in the clinical setting ; therefore, we have sought out new agents to establish the more non-invasive therapy for the patients with leukemia
We have reported that reactive oxygen species (ROS) are key mediators of apoptosis induced by a green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG). EGCG rapidly induced apoptosis in MPO-positive, but not MPO-negative leukemia cell lines as well as fresh samples from AML. Pre-incubation of MPO-positive leukemic cells with the MPO-specific inhibitor, 4-aminobenzoic acid hydrazide (ABAH), and the heme biosynthesis inhibitor, succinylacetone (ScAc), resulted in inhibition of the ROS production and induction of apoptosis following addition of EGCG. To investigate the role of MPO in EGCG-induced apoptosis, we transfected the full length MPO cDNA
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and empty vector into MPO-negative K562 cells. In contrast to control cells, MPO transfected cells enhanced MPO activity and ROS production, and sensitized EGCG-resistant K562 cells to apoptosis induced by ROS-producing agents. In addition, an enzymatically inactive MPO mutant expressing K562 (K562/H502A) cells could not respond to EGCG, suggesting that MPO is important for determining the sensitivity to EGCG-induced oxidative stress. Further, it is noteworthy that the fluorescence intensity of both APF-and HPF-loaded myeloid leukemic cells significantly increased upon stimulation with EGCG suggesting that EGCG generated highly toxic ROS in MPO-positive leukemic cells. Taken together, these observations indicate that highly toxic ROS such as hydroxyl radical generated via the H_2O_2/MPO/halide system induce apoptosis, and that such ROS may be the direct mediators of oxidative stress-induced apoptosis in MPO-positive leukemic cells. Gene expression profiling with Affimetrix gene chips demonstrated HIF-1α and its down-stream genes (RTP801,EGR-1,BNIP3, and VEGF), that were up-regulated, suggesting that HIF-1α pathways will be important for ROS-mediated apoptosis. Less
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