Abstract
1′-acetoxychavicol acetate (ACA) is a component of traditional Asian condiment, obtained from rhizomes of the commonly used ethno-medicinal plant Languas galanga (Zingiberacetate). Recent extensive studies revealed that ACA has potent chemopreventive effects against various tumors. More recently, we have reported that ACA induces apoptosis of myeloid leukemic cells via mitochondrial- and Fas-mediated dual pathway. The transcription factor NF-κB confers significant survival potential in myeloma cells; therefore, it has emerged as a therapeutic target for the treatment of multiple myeloma. Multiple myeloma is an incurable hematological disorders, which has been fatal outcome despite of high dose chemotherapy with stem cell transplantation; therefore, a novel biologically based therapeutic approach is desired. In this study, we investigated the effects of ACA on myeloma cells in vitro and in vivo, and further examined the molecular mechanisms of ACA-induced apoptosis in myeloma cells. ACA dramatically inhibited cellular growth of various human myeloma cell lines (RPMI8226, U266, IM9, and HS-Sultan) as well as freshly isolated myeloma cells from patients, but not normal bone marrow cells, in a dose (0-20 μM)- and time (0-24 h)-dependent manner. Cultivation with 10 μM ACA rapidly increased the population of cells in the G0/G1 phase with a reduction of cells in the S phase, and a strong induction of apoptosis was shown by the appearance of a hypodiploid DNA peak with sub-G1 DNA content 3 h after treatment. Treatment with ACA induced both caspase-3, -9, and caspase-8 activities, suggesting that ACA-induced apoptosis in myeloma cells mediates both mitochondrial- and Fas-dependent pathways. Furthermore, we investigated the effects of ACA on NF-κB activity in myeloma cells, and were able to demonstrate that ACA significantly inhibited serine phosphorylation and degradation of IκBα in a time-dependent manner. ACA rapidly decreased the nuclear expression of NF-κB, but increased the accumulation of cytosol NF-κB in RPMI8226 cells, indicating that ACA inhibits translocation of NF-κB from the cytosol to the nucleus. In addition, we also confirmed the inhibitory effects of ACA on NF-κB activation by ELISA in myeloma cell lines and fresh samples. ACA had a synergistic proapoptotic effect with another NF-κB inhibitor, MG-132 and TLCK. In contrast, NF-κB activator, PMA, dramatically abrogated ACA-induced apoptosis in myeloma cells. These in vitro studies prompted us to examine whether the effects of ACA are equally valid in vivo. To evaluate the effects of ACA in vivo, RPMI8226-transplanted NOD/SCID mice were treated with ACA. Tumor weight decreased in the mice that were injected ACA (mean weight: 0.04±0.06 g in the ACA-treated group vs. 0.63±0.29 g in the control group; p<0.01). During the treatment, ACA-treated mice appeared healthy, and pathological analysis at autopsy revealed no ACA-induced tissue changes in any of the organ, indicating that ACA might be developed as a new potent anti-cancer agent for the management of multiple myeloma. In conclusion, ACA has an inhibitory activity of NF-κB, and induces apoptosis of myeloma cells in vitro and in vivo. Therefore, ACA provides the new biologically based therapy for the treatment of multiple myeloma patients as a novel NF-κB inhibitor.
Dickkopf-1 (DKK1) is a widely expressed and potent tumor-associated antigen in multiple myeloma
