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[Cancer Research 65, 4417-4424, May 15, 2005]
© 2005 American Association for Cancer Research

Experimental Therapeutics, Molecular Targets, and Chemical Biology

1'-Acetoxychavicol Acetate Is a Novel Nuclear Factor {kappa}B Inhibitor with Significant Activity against Multiple Myeloma In vitro and In vivo

Keisuke Ito1, Tomonori Nakazato1, Ming Ji Xian1, Taketo Yamada2, Nobumichi Hozumi3, Akira Murakami4, Hajime Ohigashi4, Yasuo Ikeda1 and Masahiro Kizaki1

1 Division of Hematology, Department of Internal Medicine and 2 Pathology, Keio University School of Medicine, Tokyo, Japan; 3 Institute of Biological Science, Science University of Tokyo, Chiba, Japan; and 4 Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan

Requests for reprints: Masahiro Kizaki, Division of Hematology, Department of Internal Medicine, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan. Phone: 81-3-5363-3785; Fax: 81-3-3353-3515; E-mail: makizaki{at}sc.itc.keio.ac.jp.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
1'-Acetoxychavicol acetate (ACA) is a component of a traditional Asian condiment obtained from the rhizomes of the commonly used ethno-medicinal plant Languas galanga. Here, we show for the first time that ACA dramatically inhibits the cellular growth of human myeloma cells via the inhibition of nuclear factor {kappa}B (NF-{kappa}B) activity. In myeloma cells, cultivation with ACA induced G0-G1 phase cell cycle arrest, followed by apoptosis. Treatment with ACA induced caspase 3, 9, and 8 activities, suggesting that ACA-induced apoptosis in myeloma cells mediates both mitochondrial- and Fas-dependent pathways. Furthermore, we showed that ACA significantly inhibits the serine phosphorylation and degradation of I{kappa}B{alpha}. ACA rapidly decreased the nuclear expression of NF-{kappa}B, but increased the accumulation of cytosol NF-{kappa}B in RPMI8226 cells, indicating that ACA inhibits the translocation of NF-{kappa}B from the cytosol to the nucleus. To evaluate the effects of ACA in vivo, RPMI8226-transplanted NOD/SCID mice were treated with ACA. Tumor weight significantly decreased in the ACA-treated mice compared with the control mice. In conclusion, ACA has an inhibitory effect on NF-{kappa}B, and induces the apoptosis of myeloma cells in vitro and in vivo. ACA, therefore, provides a new biologically based therapy for the treatment of multiple myeloma patients as a novel NF-{kappa}B inhibitor.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
1'-Acetoxychavicol acetate (ACA) is obtained from the rhizomes of Languas galanga (Zingiberaceae), a traditional condiment in Thailand (1). Recent studies have revealed that ACA has potent chemopreventive effects against rat oral carcinomas and inhibits the chemically induced tumor formation and cellular growth of various cancer cells (2–5). More recently, we reported that ACA induces the apoptosis of myeloid leukemia cells in vitro and in vivo, suggesting that ACA has potential as a novel therapeutic agent for the treatment of myeloid leukemia (6). We found that the ACA-induced apoptosis in myeloid leukemic cells was associated with the production of intracellular reactive oxygen species (ROS; ref. 6); however, the exact biological and molecular mechanisms of ACA-induced apoptosis in various cancer cells are still unclear.

Multiple myeloma is a plasma cell malignancy that remains incurable despite the use of conventional and high-dose chemotherapy with hematopoietic stem cell transplantation; therefore, novel therapeutic approaches are urgently needed in clinical settings (7). The understanding that has recently been gained into the biology of myeloma has led to the development of biological treatments, such as thalidomide and bortezomib, which target the myeloma cell and the bone marrow microenvironment. These agents have shown remarkable activity against refractory multiple myeloma in early clinical trials, but prolonged drug exposure may result in the development of de novo drug resistance in some cases (7–9). Therefore, the identification and validation of additional novel targeted therapies to overcome drug resistance and improve patient outcome are needed.

Nuclear factor {kappa}B (NF-{kappa}B), which was originally identified as a B-cell nuclear factor, is required for the proper regulation of B-cell homeostasis (10, 11). NF-{kappa}B is a member of the Rel family of proteins, and is typically a heterodimer composed of p50, p65, and I{kappa}B{alpha} subunits. NF-{kappa}B is constitutively present in the cytosol and is inactivated by its interaction with I{kappa}B family inhibitors. On activation, I{kappa}B{alpha} undergoes phosphorylation and ubiquitination-dependent degradation by the 26S proteosome, leading to translocation of NF-{kappa}B into the nucleus and binding to the specific DNA sequences in the promoter of the target genes, which stimulates their transcription (12–14). The protein products of these genes, including a variety of cytokines, cell adhesion molecules, and chemokines, mediate the regulation of cellular growth in many cells. Recently, it has been reported that NF-{kappa}B is constitutively active in myeloma cells, which contributes to the survival of these cells (15, 16). In addition, it has been reported that myeloma cell adhesion to bone marrow stromal cells induces NF-{kappa}B–dependent up-regulation of the transcription of IL-6, a major growth factor of myeloma cells (17). Tumor necrosis factor (TNF)-{alpha} is secreted into the bone marrow microenvironment and induces NF-{kappa}B–dependent alteration in adhesion molecule expression in both myeloma cells and bone marrow stromal cells, with resulting increased cell adhesion. This confers resistance to myeloma cell apoptosis and also triggers the NF-{kappa}B–dependent secretion of IL-6. These results indicate that NF-{kappa}B is the most important therapeutic target for the treatment of multiple myeloma. Conventional and recent antimyeloma agents, including dexamethasone, thalidomide, proteasome inhibitor PS-341, and arsenic trioxide, inhibit NF-{kappa}B activation (18–21). However, these agents have a multiple number of other biological effects. Therefore, a more specific NF-{kappa}B inhibitor may have clinical benefits and the blockade of its signaling pathway may represent a novel therapeutic strategy for managing multiple myeloma.

Our previous study showed that ACA induces apoptosis through two different pathways in the myeloid leukemia cells: ROS generation and the activation of the Fas-pathway (6). NF-{kappa}B is known to contribute to both the caspase 8 and 9 pathways. In this study, we addressed the molecular mechanisms of the antimyeloma action of ACA, and, quite surprisingly, we found that ACA inhibited the cellular growth of myeloma cells in association with the down-regulation of NF-{kappa}B activity. We further investigated the molecular mechanism of ACA and the possibility of clinically applying it by using in vivo mice model.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Cell cultures. Various human multiple myeloma cell lines, including RPMI8226, U266, and IM-9, were obtained from the Japan Cancer Research Resources Bank (Tokyo, Japan), and were maintained in RPMI 1640 (GIBCO-BRL, Grand Island, NY) with 10% fetal bovine serum (GIBCO-BRL), 100 units/mL penicillin, and 100 mg/mL streptomycin in a humidified atmosphere with 5% CO2. Bone marrow samples from patients with multiple myeloma and healthy donors were obtained according to appropriate Human Protection Committee validation at Keio University School of Medicine (Tokyo, Japan), and with written informed consent. The patients' samples were grown in RPMI 1640 with 15% FBS (Hyclone Laboratories, Logan, MT) under standard culture conditions.

Reagents. ACA (99% purity) was synthesized as previously reported (Fig. 1A; ref. 1). Synthetic (1'R, S')-ACA has an identical suppressive activity to natural (1'S)-ACA, as evaluated by tumor promoter–induced EBV activity (22). ACA was dissolved in DMSO at a stock concentration of 20 mmol/L. Various caspase inhibitors, including Z-VAD-FMK (a pan-caspase inhibitor), DEVD-FMK (a caspase 3 inhibitor), Z-IETD-FMK (a caspase 8 inhibitor), and LEHD-FMK (a caspase 9 inhibitor), were purchased from Calbiochem (La Jolla, CA). TNF-{alpha} was purchased from Sigma Chemical (St. Louis, MO). Phorbol 12-myristate 13-acetate (PMA: synthetic analogue of diacylglycerol) was dissolved in DMSO. The final DMSO concentrations in the medium were not greater than 0.1%. N-Tosyl-L-lysine chloromethyl ketone (TLCK), a serine protease inhibitor, was obtained from Roche (Indianapolis, IN). MG132 (z-Leu-Leu-Leu-aldehyde), a proteasome inhibitor, was purchased from BIOMOL Research Laboratories, Inc. (Plymouth Meeting, PA). For the Fas inhibition assay, antagonistic anti-ZB4 monoclonal antibody was purchased from MBL (Nagoya, Aichi, Japan).



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  		Figure 1. Chemical structure of ACA and induction of G0-G1 cell cycle arrest followed by apoptosis in various myeloma cells. A, chemical structure of (1'R, S')-ACA. B and C, various myeloma cell lines [RPMI8226 ({bullet}), U266 ({blacktriangleup}), IM-9 ({blacktriangledown}) and bone marrow mononuclear cells from a healthy donor ({circ})] were treated with various concentrations (0-20 µmol/L) of ACA for 24 hours (B, left) and with 10 µmol/L ACA for various times (0-24 hours; B, right). Cell viability was assessed by trypan blue dye exclusion. Results are expressed as the mean ± SD of three different experiments. C, cell cycle analysis. RPMI8226 cells were treated with 10 µmol/L ACA for the indicated times, and then stained with PI as described in Materials and Methods. The DNA content was analyzed by means of flow cytometry. G0-G1, S, and G2-M indicate the cell phase, and the sub-G1 DNA content refers to the portion of apoptotic cells. Each phase was calculated by using a ModiFIT program. Three duplicate experiments were done with similar results, and the representative data are shown. D, morphologic changes characteristic of apoptosis in RPMI8226 cells. RPMI8226 cells were treated with 10 µmol/L ACA for 3 hours, and cytospin slides were then prepared and stained with Giemsa. Original magnification, x1,000. E, agarose gel electrophoresis demonstrating DNA fragmentation in RPMI8226 cells treated with 10 µmol/L ACA for 3 hours. Preincubation with 20 µmol/L pan-caspase inhibitor, Z-VAD-FMK, inhibited ACA-induced apoptosis.

 
Assays for apoptosis. Apoptosis was determined based on morphologic changes. Apoptotic cells were quantified by annexin V-FITC and propidium iodide (PI) double staining using a staining kit purchased from PharMingen (San Diego, CA). The induction of apoptosis was also detected by DNA fragmentation assay.

Western blot analysis. The cells were collected by centrifugation at 700 x g for 10 minutes, and then the pellets were resuspended in a lysis buffer [1% NP40, 1 mmol/L phenylmethylsulfonyl fluoride, 40 mmol/L Tris-HCl (pH 8.0), 150 mmol/L NaCl] at 4°C for 15 minutes. Mitochondrial and cytosolic fractions were prepared with digitonin-nagarse treatment. Protein concentrations were determined using a protein assay DC system (Bio-Rad, Richmond, CA). Cell lysates (15 µg of protein per lane) were fractionated on 12.5% SDS-polyacrylamide gels before being transferred to the membrane (Immobilon-P membranes, Millipore, Bedford, MA) according to standard protocol. Antibody binding was detected by using the enhanced chemiluminescence kit with hyper-ECL film (Amersham, Buckinghamshire, United Kingdom). The blots were also stained with Coomassie brilliant blue to confirm that equal amounts of protein extract were presented in each lane. The following antibodies were used in this study: anti-Fas (PharMingen); I{kappa}B{alpha}, pSer32-I{kappa}B{alpha} (Cell Signaling Technology, Inc., Beverly, MA); intercellular adhesion molecule 1 (ICAM-1), NF-{kappa}B, FLICE-inhibitory protein (FLIP), X-linked inhibitor of apoptosis protein (XIAP), apoptosis inducing factor (AIF), caspase inhibitory protein-1 (cIAP), and ß-actin (Santa Cruz Biotech, Santa Cruz, CA).

Assays for nuclear factor {kappa}B activity. The DNA binding activity of NF-{kappa}B in the myeloma cells was quantified by ELISA using the Trans-NF-{kappa}B p65 Transcription Factor Assay Kit (Active Motif North America, Carlsbad, CA), according to the instructions of the manufacturer. Briefly, nuclear extracts were prepared and incubated in 96-well plates coated with immobilized oligonucleotide (5'-AGTTGAGGGGACTTTCCCAGGC-3') containing a consensus (5'-GGGACTTTC-3') binding site for the p65 subunit of NF-{kappa}B. NF-{kappa}B binding to the target oligonucleotide was detected by incubation with the primary antibody specific for the activation form of p65 (Active Motif North America), visualized by anti-immunoglobulin G horseradish peroxidase conjugate and Developing Solution, and quantified at 450 nm with a reference wavelength of 655 nm. Background binding, obtained by incubation with a 2-nucleotide mutant oligonucleotide (5'-AGTTGAGGCCACTTTCCCAGGC-3'), was subtracted from the value obtained for binding to the consensus DNA sequence.

Effects of 1'-acetoxychavicol acetate in vivo. We have established a human leukemia and multiple myeloma model in an NOD/SCID mouse (23). Briefly, the mice were pretreated with 3 Gy of total body irradiation, which is a sublethal dose that was expected to enhance the acceptance of xenografts. Subsequently, RPMI8226 cells (1 x 107 cells) in their logarithmic growth phase were inoculated s.c. into the NOD/SCID mice (Jackson Laboratory, Bar Harbor, ME). The inoculated RPMI8226 cells formed s.c. tumors at the injection site, and the cells grew rapidly. Seven days after the implantation of the cells, the mice with the transplanted cells were randomly assigned to receive PBS (n = 10) or 3 mg/kg ACA (n = 10) as an i.p. injection once every 3 days for 2 weeks. After 2 weeks of treatment, the mice were sacrificed and dissected to measure the tumor weights. When the mice showed severe wasting, or when the observations were completed, the mice were sacrificed according to the UKCCCR guidelines, and the day of sacrifice was recorded (24).


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Effects of 1'-acetoxychavicol acetate on cellular proliferation of various myeloma cells. We first investigated the effects of ACA on the cellular proliferation of three human multiple myeloma cell lines, including RPMI8226, U266, and IM-9 cells, and fresh samples from patients with multiple myeloma. ACA induced apoptosis of myeloma cell lines, as well as of eight freshly obtained samples from patients with multiple myeloma, but not of normal bone marrow mononuclear cells from a healthy donor, in a dose- and time-dependent manner (Fig. 1B; Table 1). Cultivation with ACA rapidly and strongly increased the population of RPMI8226 myeloma cells in the G0-G1 phase, and then in the sub-G1 phase (Fig. 1C). Apoptosis was assessed in terms of both the morphologic changes and the DNA ladder formation (Fig. 1D and E). Consistent with these results, annexin V–positive cells were increased after incubation with ACA for 3 hours, indicating that the onset of apoptosis had already started to occur after only 3 hours of treatment (data not shown). These results indicate that ACA led to cell cycle arrest at the G0-G1 phase, followed by apoptosis.


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  		Table 1. Clinical characteristics and the effects of ACA on the induction of apoptosis and NF-{kappa}B activity in eight patients with multiple myeloma

 
Effects of 1'-acetoxychavicol acetate on caspase activity. Treatment with 10 µmol/L ACA for 3 hours significantly induced caspase 3, 8, and 9 activities in RPMI8226 cells (Fig. 2A). RPMI8226 cells were treated with 10 µmol/L ACA for 12 hours, either alone or in combination with Z-VAD-FMK (a pan-caspase inhibitor), DEVD-FMK (a caspase 3 inhibitor), Z-IETD-FMK (a caspase 8 inhibitor), or LEHD-CHO (a caspase 9 inhibitor). ACA-induced apoptosis was almost completely blocked by Z-VAD-FMK and by combination of Z-IETD-FMK and LEHD-FMK, although Z-IETD-FMK or LEHD-FMK alone partially inhibited ACA-induced apoptosis in RPMI8226 cells (Fig. 2B). In addition, the preincubation of Z-VAD-FMK inhibited the ACA-induced apoptosis of myeloma cells by means of DNA ladder formation analysis (Fig. 1E). These results suggest that through treatment with ACA, both of the cascades to the caspase 8 and caspase 9 pathways are activated.



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  		Figure 2. Effects of ACA on caspase and NF-{kappa}B activation. A, RPMI8226 cells were incubated with 10 µmol/L ACA for 3 hours and then analyzed for activation of caspase 3, 8, and 9 by flow cytometry and colorimetric assay. Each caspase activity in the ACA-treated cells was presented as a fold increase of the control cells. B, inhibition of ACA-induced apoptosis in RPMI8226 cells was estimated in a preincubation of Z-VAD-FMK. The cells were preincubated with 20 µmol/L Z-VAD-FMK for 1 hour before the addition of 10 µmol/L ACA. The cell counts were evaluated after 6 hours of incubation. Then, effects of specific caspase inhibitors on ACA-induced apoptosis were examined. The cells were preincubated with each caspase inhibitor [50 µmol/L DEVD-FMK (a caspase 3 inhibitor), 50 µmol/L Z-IETD-FMK (a caspase 8 inhibitor), and 50 µmol/L LEHD-FMK (a caspase 9 inhibitor)] for 1 hour, and then incubated with 10 µmol/L ACA for 6 hours. Cell viability was assessed by trypan blue dye exclusion. Columns, mean of three separate experiments done in triplicate; bars, SD. C, effects of ACA on I{kappa}B{alpha} phosphorylation and the constitutive expression of NF-{kappa}B in myeloma cells. RPMI8226 cells were treated with ACA (10 µmol/L) for the indicated times. Cell lysates (15 µg of protein per lane) were fractionated on 12.5% SDS-polyacrylamide gels and analyzed by Western blotting with antibodies against I{kappa}B{alpha} and pSer32-I{kappa}B{alpha}. Nuclear and cytoplasmic extracts and whole cell lysates were prepared to check the level of NF-{kappa}B by Western blotting. D, ACA down-regulates constitutive NF-{kappa}B activity in myeloma cells in a time-dependent manner. The DNA binding activity of transcriptional factor NF-{kappa}B was quantified in myeloma cells (RPMI8226, U266, and IM-9) pretreated with 10 µmol/L ACA for the indicated times. The DNA binding activity of NF-{kappa}B in the myeloma cells was quantified by ELISA with the use of the Trans-AM NF-{kappa}B p65 Transcription Factor Assay Kit, according to the instruction of the manufacturer. Values (mean ± SD) were normalized for the cellular protein contents. E, ACA decreased the constitutive NF-{kappa}B activity in freshly isolated myeloma cells from two patients, but not in bone marrow mononuclear cells from a healthy donor.

 
1'-Acetoxychavicol acetate inhibits I{kappa}B{alpha} phosphorylation and nuclear factor {kappa}B activation in myeloma cells. ACA significantly inhibited the serine phosphorylation and degradation of I{kappa}B{alpha} in a time-dependent manner (Fig. 2C). Because the phosphorylation of I{kappa}B has been shown to be the primary mechanism of NF-{kappa}B activation, we next examined whether ACA-induced apoptosis is a result of the inhibition of NF-{kappa}B activation. ACA rapidly induced a strong decrease in the NF-{kappa}B expression in the nucleus, whereas the protein accumulated in the cytosol in RPMI8226 cells, indicating that ACA inhibited the translocation of NF-{kappa}B from the cytosol to the nucleus (Fig. 2C). We also confirmed the inhibitory effects of ACA on NF-{kappa}B activation by ELISA in several myeloma cell lines, as well as in primary samples from patients with multiple myeloma, but not in normal cells (Fig. 2D and E; Table 1).

1'-Acetoxychavicol acetate induced the Fas expression and down-regulation of antiapoptotic proteins in RPMI8226 cells. ACA rapidly activated caspase 8, and its specific inhibitor partially inhibited ACA-induced apoptosis in RPMI8226 cells (Fig. 2A). Therefore, we investigated whether or not the Fas-mediated pathway was involved in the ACA-induced apoptosis. The suppression of Fas by an antagonistic anti-Fas antibody (ZB4) dramatically inhibited ACA-induced apoptosis (Fig. 3A). Consistent with these results, the expression of Fas on the plasma membrane was significantly increased immediately after treatment with ACA with the induction of the Fas ligand (FasL; Fig. 3B and data not shown). ACA also rapidly induced the recruitment of caspase 8 to Fas-associated death domain–containing protein, suggesting that ACA induced the formation of death-inducing signaling complex (data not shown). These results indicate that the apoptotic pathway related to Fas/FasL also seems to be involved in ACA-induced apoptosis. Several studies revealed that RPMI8226 cells were resistant to Fas-mediated apoptosis because of higher levels of expression for various antiapoptotic proteins such as FLIP and XIAP. ACA down-regulated the antiapoptotic proteins FLIP and XIAP, but increased the expression of proapoptotic cytosolic AIF (Fig. 3B).



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  		Figure 3. ACA-induced apoptosis in myeloma cells is mediated through the Fas pathway. A, antagonistic anti-Fas antibody (ZB4) blocks ACA-induced apoptosis in RPMI8226 cells. RPMI8226 cells were preincubated for 1 hour in the presence of 500 ng/mL of ZB4 antagonistic anti-Fas antibody, and then treated with 10 µmol/L ACA for 12 hours. Cell viability was assessed by trypan blue dye exclusion (left), and apoptotic cell death was analyzed by annexin V staining (right). Columns, mean of three independent experiments; bars, SD. B, expression of Fas-related proteins in ACA-treated RPMI8226 cells. The cells were treated with 10 µmol/L ACA for the indicated times. Cell lysates (15 µg of protein per lane) were fractionated on 12.5% SDS-polyacrylamide gels and analyzed by Western blotting with antibodies against Fas, FLIP, XIAP, cytosolic AIF (cAIF), and cIAP-1. Reblotting with ß-actin staining showed that equal amounts of protein were presented in each lane (data not shown).

 
Effects of 1'-acetoxychavicol acetate on tumor necrosis factor {alpha}–induced sequelae in myeloma cells. TNF-{alpha} is known to activate NF-{kappa}B and have a small stimulatory effect on myeloma cell proliferation (25). However, TNF-{alpha} triggers death-receptor–mediated apoptosis in myeloma cells treated with the NF-{kappa}B inhibitor in association with the down-regulation of expression of cIAP-1. In our study, the stimulatory effect of TNF-{alpha} on the NF-{kappa}B DNA binding activity was completely inhibited by the treatment with 5 µmol/L ACA (Fig. 4A). TNF-{alpha}–induced apoptosis in RPMI8226 cells cotreated with a nontoxic concentration of ACA (5 µmol/L) corresponded to NF-{kappa}B inactivation (Fig. 4B). In addition, the treatment with TNF-{alpha} slightly up-regulated the expression of well-known NF-{kappa}B target molecules, the FLIP and XIAP proteins (Fig. 4C). In contrast, cotreatment with ACA and TNF-{alpha} strongly inhibited the induction of these proteins (Fig. 4C). In addition, ACA decreased the levels of another NF-{kappa}B target gene, the adhesion molecule ICAM, in TNF-{alpha}–treated RPMI8226 cells (Fig. 4C). These data further suggest that NF-{kappa}B is an important molecule for the regulation of myeloma cell adhesion and for the interaction of myeloma cells in the bone marrow microenvironment.



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  		Figure 4. Effects of ACA on TNF-{alpha}–induced NF-{kappa}B activity and its sequelae in myeloma cells. RPMI8226 cells were treated with 50 ng/mL TNF-{alpha} for 12 hours, and then the cells were incubated with a nontoxic dose (5 µmol/L) of ACA for 3 hours. A, the DNA binding activity of NF-{kappa}B in the myeloma cells was quantified by ELISA with the use of the Trans-AM NF-{kappa}B p65 Transcription Factor Assay Kit. A nontoxic dose of ACA significantly inhibited the stimulatory effect of TNF-{alpha} on the NF-{kappa}B DNA binding activity (P < 0.001). B, the induction of apoptosis was examined by annexin V/PI double staining. Representative of three duplicate experiments. C, ACA inhibited the TNF-{alpha}–induced FLIP, XIAP, and ICAM-1 expressions on myeloma cells. RPMI8226 cells were incubated with 10 µmol/L ACA with or without 50 ng/mL TNF-{alpha} for 12 hours, and then cell lysates (15 µg of protein per lane) were fractionated on 12.5% SDS-polyacrylamide gels and analyzed by Western blotting. D, RPMI8226 cells were treated with 20 µg/mL PMA for 1 hour, and the cells were then incubated with 10 µmol/L ACA for 6 hours. Induction of apoptosis was examined by annexin V/PI double staining. E, RPMI8226 cells were treated with a nontoxic dose (5 µmol/L) of ACA and/or low-dose TLCL (5 µmol/L) for 24 hours. The assays for the caspase 8 activity (left) were analyzed by flow cytometry analysis, and the NF-{kappa}B activity (right) was evaluated by ELISA. Columns, mean of three separate experiments done in triplicate; bars, SD. F, RPMI8226 cells were treated with a nontoxic dose (5 µmol/L) of ACA with low dose (5 µmol/L) of MG132 for 24 hours. Neither agent alone in this concentration affected the cellular growth of RPMI8226 cells. The assays for the caspase 8 activity (left) were analyzed by flow cytometry analysis, and the NF-{kappa}B activity (right) was evaluated by ELISA. Columns, mean of three separate experiments done in triplicate; bars, SD.

 
Activation of protein kinase C by phorbol 12-myristate 13-acetate protects cells from 1'-acetoxychavicol acetate–induced apoptosis. PMA is a tumor promoter phorbol ester recognized to be a general activator of protein kinase C (PKC; ref. 26). PMA is also known to be an NF-{kappa}B activator mediated by the induction of the nuclear translocation of NF-{kappa}B (27). A number of previous studies have reported that the activation of PKC by PMA suppresses death receptor–mediated apoptosis through the activation of NF-{kappa}B (28). In our study, pretreatment with PMA dramatically attenuated ACA-induced apoptosis by the treatment with ACA (Fig. 4D). In addition, pretreatment with PMA abrogated ACA-mediated caspase 8 activation and NF-{kappa}B inactivation in myeloma cells (data not shown). TLCK, a serine protease inhibitor, is known to sensitize Fas-mediated apoptosis, even in cells resistant to Fas-induced apoptosis. Several reports have also shown that TLCK can inhibit NF-{kappa}B activity by blocking PKC (29, 30). Low-dose TLCK (5 µmol/L) dramatically enhanced the apoptosis of low-dose ACA (5 µmol/L)–treated RPMI8226 cells with the activation of caspase 8 and NF-{kappa}B inactivation (Fig. 4E). These results also suggest that the ACA-induced apoptosis was mediated through NF-{kappa}B inactivation. In addition, low-dose MG132 (5 µmol/L), an excellent proteasome inhibitor, synergistically enhanced ACA-induced apoptosis with caspase 8 activation and NF-{kappa}B inactivation (Fig. 4F), strongly supporting that ACA induces the apoptosis of multiple myeloma cells through NF-{kappa}B inactivation.

Effects of 1'-acetoxychavicol acetate in vivo. Our in vitro data prompted us to examine whether the effects of ACA are equally valid in vivo. Tumor weight decreased in the mice that were injected with ACA (mean weight: 0.04 ± 0.06 g in the ACA-treated group versus 0.63 ± 0.29 g in the control group; Fig. 5A and B). During treatment, the ACA-treated mice appeared healthy. In addition, pathologic analysis at autopsy revealed no ACA-induced tissue changes in any of the organs. These results suggest that ACA had no toxic effects on the mice throughout the treatment.



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  		Figure 5. ACA-induced apoptosis of myeloma cells in vivo using NOD/SCID mice model. RPMI8226 cells (1 x 107) were inoculated s.c. into NOD/SCID mice. Seven days after transplantation, PBS (control; n = 10) or ACA (3 mg/kg; n = 10) was given i.p. once every 3 days for 2 weeks. After 2 weeks of treatment, the mice were sacrificed, and the tumor weights measured. A, tumors in both the control (upper) and ACA-treated (lower) mice at autopsy. B, ACA significantly decreased the tumor weights in the ACA-treated mice compared with the controls (P < 0.001).

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
In this study, we showed for the first time that ACA, a traditional Asian condiment, induces the apoptosis of human multiple myeloma cell lines as well as of freshly obtained samples from patients with multiple myeloma through inhibition of NF-{kappa}B activity. Furthermore, ACA exhibited in vivo antimyeloma activity in NOD/SCID mice with no side effects. In addition, ACA did not affect the cellular growth of bone marrow cells from healthy volunteers.

Multiple myeloma is an incurable hematologic malignancy of plasma cells, despite advances in conventional chemotherapy or high-dose chemotherapy with stem cell transplantation (7–9). Therefore, novel therapeutic approaches are urgently needed in clinical settings. The recent understanding that has been gained into the biology of myeloma has led to the development of biological treatments, such as thalidomide and bortezomib, which target the myeloma cells and the bone marrow microenvironment (8, 31). In early clinical trials, these agents have shown remarkable activities against refractory multiple myeloma, but prolonged drug exposure may result in the development of de novo drug resistance (32, 33). Therefore, the identification and validation of additional novel targeted therapies for patients with multiple myeloma are needed. The transcription factor NF-{kappa}B has been identified as a critical component of several signal transduction pathways (34). NF-{kappa}B is an important transcription factor because of its ability to protect cells from apoptosis (35–37). Consequently, NF-{kappa}B has emerged as a therapeutic target in a variety of neoplasias, and the NF-{kappa}B inhibitor induces apoptosis in myeloma cells (37). In the present study, we investigated the effects of ACA on NF-{kappa}B activity in myeloma cells in vitro and in vivo, and found for the first time that ACA inhibited NF-{kappa}B activity in multiple myeloma cell lines and patient cells, but not in normal cells. ACA also sensitized myeloma cells to TNF-{alpha} and had a synergistic proapoptotic effect with NF-{kappa}B inhibitors, MG-132 and TLCK. In contrast, an excellent NF-{kappa}B activator, PMA, dramatically abrogated ACA-induced apoptosis. These results provide the framework for targeting NF-{kappa}B inhibition by treatment with ACA in multiple myeloma therapy.

RPMI8226, U266, and IM-9 cells used in this study were relatively resistant to the NF-{kappa}B inhibitors (38) because these cells constitutively expressed higher levels of various antiapoptotic molecules including FLIP, cIAP-1, XIAP, and survivin. ACA decreased the levels of these proteins in myeloma cells. The inhibition of NF-{kappa}B stimulates caspase 9–dependent apoptosis through the reduction of XIAP and caspase 8–dependent apoptosis mediated through the decrease in FLIP. In our study, ACA activated both cascades to the caspase 8 and caspase 9 pathways in association with NF-{kappa}B inactivation, suggesting that ACA has a strong potential for inhibiting the proliferation of myeloma cells through various apoptotic signaling pathways.

The induction of NF-{kappa}B with the related up-regulation of adhesion molecules, including CD54 (ICAM-1) and CD106 (VCAM-1), has been shown in TNF-{alpha}–stimulated myeloma cell lines and bone marrow stromal cells (25, 39). In addition, myeloma cell adhesion to fibronectin mediates an antiapoptotic effect against chemotherapeutic agents (40, 41). In this study, ACA inhibited the TNF-{alpha}–induced up-regulation of the adhesion molecule ICAM-1 expression in RPMI8226 cells, suggesting that ACA may also modulate myeloma cell adhesion to stromal cells in the bone marrow. Several studies have revealed that the inhibition of NF-{kappa}B abrogates the induction of IL-6 secretion in bone marrow stromal cells and the proliferation of adherent myeloma cells (25, 39). The ACA-mediated inhibition of adhesion molecule expression, the abrogation of protection against apoptosis conferred by myeloma cells by binding to bone marrow stromal cells, and the blockade of cytokine secretion in the bone marrow milieu provide a further rationale for targeting NF-{kappa}B in novel therapies for multiple myeloma.

Finally, ACA had a synergistic proapoptotic effect with the NF-{kappa}B inhibitors MG132 and TLCK, and the NF-{kappa}B activator PMA inhibited ACA-induced apoptosis, suggesting that ACA induced apoptosis through the inhibition of NF-{kappa}B activity. The blockade of NF-{kappa}B signaling may represent a novel therapeutic strategy in multiple myeloma (7–9, 31, 32). Because NF-{kappa}B activity mediates survival and drug resistance in myeloma cells, the down-regulation of its activity by ACA, as recently observed with proteasome inhibitors (20), could also contribute to its antimyeloma activity. Our finding that ACA down-regulates the constitutive activity of NF-{kappa}B in myeloma cells further suggests that it may have combined antimyeloma activity with conventional or novel therapies that also target NF-{kappa}B.

In clinical settings, the therapeutic approach to multiple myeloma is basically chemotherapy, but severe side effects, complications, and resistance are major problems. In particular, the side effects of anticancer drugs can be fatal in elderly patients or immunocompromised patients. ACA, which is a component of a traditional Thai condiment, is a natural compound which seems to be safer than current chemotherapeutic drugs. ACA remarkably inhibited the cellular growth of myeloma cells from patients by the induction of apoptosis, whereas the same dose of ACA did not affect the cellular growth of cells from healthy volunteers, indicating that the effects of ACA are specific to malignant cells. We also showed the anticancer effects of ACA in vivo with no toxic effects. The Fas receptor is constitutively expressed in the liver; therefore, the liver might be very sensitive to Fas-induced apoptosis, and mice treated with an agonistic anti-CD95 antibody died from hepatic failure caused by the generalized apoptosis of hepatocytes (42). However, we could not observe any organ damage in vivo in our study. These results strongly indicate that it might be possible to develop ACA as a new potent anticancer agent for the management of multiple myeloma and as a novel therapeutic agent that can replace the more cytotoxic agents currently used to treat patients with multiple myeloma.


   Acknowledgments
 
Grant support: Ministry of Education, Culture, Sports, Science and Technology of Japan (M. Kizaki), and a grant from the Mitsubishi Pharma Research Foundation (M. Kizaki).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

We thank Kaori Saito for her excellent technical assistance.

Received 1/13/05. Accepted 3/ 8/05.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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