cytochrome-c-t and Hematologic-Neoplasms

Tocotrienols (Toc3) have been suggested to possess anticancer effects besides antioxidant and antiinflammatory effects. Previous studies have demonstrated that Toc3 induce apoptosis in epithelial carcinoma. However, the effects of Toc3 on malignant hematopoietic cells have not yet been thoroughly investigated. We investigated Toc3-induced apoptosis in human hematological cancer cell lines. α-, δ-, and γ-Toc3 induced concentration-dependent apoptosis, and γ-Toc3 demonstrated more effective induction than the other Toc3 derivatives in HL-60 cells. γ-Toc3 may have induced apoptosis by activation of the caspase cascade, cytochrome c (Cyt.c) release, Bid cleavage, and mitochondorial membrane depolarization in HL-60, NB-4, Raji, and SY-5Y cells. Furthermore, 10-30 μM γ-Toc3 showed cytotoxicity for leukemic cells from various patients regardless of lymphoblastic, myeloblastic, or relapsed leukemia, but the cytotoxic effect was weak in normal mononuclear cells, interestingly. γ-Toc3 may have a role in cancer prevention and potential for treating hematological malignancies.

Topics: Adolescent; Antineoplastic Agents, Phytogenic; Apoptosis; Apoptosis Regulatory Proteins; BH3 Interacting Domain Death Agonist Protein; Bone Marrow Cells; Caspases; Cell Line, Tumor; Cell Nucleus; Cell Proliferation; Cells, Cultured; Child; Child, Preschool; Chromans; Cytochromes c; DNA Fragmentation; Female; Hematologic Neoplasms; Humans; Infant; Leukemia; Male; Membrane Potential, Mitochondrial; Mitochondria; Neoplasm Proteins; Vitamin E

Post-translational modification of Bcl-2 protein has been described in a variety of cell models with effects varying from enhanced to abrogated function. In this study, we demonstrated that Bcl-2 was constitutively phosphorylated in several hematopoietic tumor cell lines and in primary ALL cells. Increased phosphorylation of Bcl-2 protein in the JM1 ALL cell line, achieved by expression of the phosphomimetic Bcl-2 construct S70E, enhanced JM1 cell chemoresistance. In contrast, initiation of JM1 cell apoptosis was coincident with dephosphorylation of Bcl-2 and elevated protein phosphatase 2A activity. S70E expression also diminished tBid-mediated cytochrome c release and blunted chemotherapy-induced activation of caspases-9 and -3 in JM1 cells. To determine whether soluble factors produced by stromal cells in the bone marrow influence phosphorylation of Bcl-2 protein, a panel of recombinant cytokines was evaluated. Of those tested, vascular endothelial growth factor (VEGF) induced phosphorylation of Bcl-2 protein and blunted cytochrome c release during chemotherapy or tBid treatment of ALL cells. In contrast, JM1 cells transfected with S70A, resulting in expression of Bcl-2 protein that cannot be phosphorylated, were not efficiently rescued from apoptosis by VEGF. These observations suggest that optimal protection of leukemic cells by VEGF may require activation of a pathway that includes Bcl-2 phosphorylation.

Topics: Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Burkitt Lymphoma; Caspase 3; Caspase 9; Caspases; Cell Line, Tumor; Cell Survival; Culture Media, Conditioned; Cytochromes c; Gene Expression Regulation, Neoplastic; Hematologic Neoplasms; HL-60 Cells; Humans; Phosphorylation; Proto-Oncogene Proteins c-bcl-2; Stromal Cells; Transfection; Vascular Endothelial Growth Factor A