Bortezomib Is More Effective to Side Population of RPMI8226 Myeloma Cells than Classical Anti-myeloma Agents.

AIM: Cytotoxic chemotherapy-based treatment of multiple myeloma (MM) is not curative, and the disease eventually recurs. This is partially because although currently available anti-MM strategies are effective in targeting the bulk of tumor cells, they do not target the tumor-initiating subpopulation of cancer stem cells. This study investigated the prevalence and biological functions of side population (SP) cells in MM cell lines including RPMI8226, ARH77, MM.1R and IM 9. MATERIALS AND METHODS: Flow cytometry-based Hoechst 33342 staining was used to evaluate the existence of SP cells. In addition, the ability of SP cells to regenerate the original population was determined. RESULTS: The frequency of SP cells was heterogeneous. Most cell lines (ARH77, IM9, and MM.1R) contained fewer than 1% SP cells; however, RPMI8226 contained approximately 10% SP cells. Sorted SP cells showed a higher proliferative ability and clonogenicity than the MP in the RPMI8226 myeloma cell line. The activity of ATP-binding cassette subfamily G member 2 (ABCG2), which is associated with high rates of proliferation, was higher in SP cells. However, the expression of specific surface markers such as cluster of differentiation (CD)138, CD34, CD38, CD19, CD20, and CD27 did not differ between SP and MP cells. Bortezomib was the only agent that significantly affected proliferation of both SP and MP cells. CONCLUSION: Our studies demonstrated that the SP fraction of myeloma cells possessed clonogenic tumor-initiating potential and revealed new mechanisms of action for bortezomib on SP cells.

Src family kinase inhibitor PP2 enhances differentiation of acute promyelocytic leukemia cell line induced by combination of all-trans-retinoic acid and arsenic trioxide.

An all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO) combination yields high-quality remission and survival in newly-diagnosed acute promyelocytic leukemia (APL). For subsequent similar data, NCCN guidelines indicate that ATRA plus ATO is one of the recommended regimens for the treatment of patients with APL. We demonstrated SFK (Src family kinase) inhibitor PP2-enhanced APL cell differentiation when combined with either ATRA or ATO with difference in activation of RA-induced genes. In this study, we investigated whether SFK inhibitor PP2 could enhance the differentiation of NB4 APL cells when combined with ATRA and ATO and the changes in the expression of intercellular adhesion molecule-1 (ICAM-1) derived from the retinoic acid receptor (RAR) target gene. Treatment of NB4 cells with 1 µM of ATRA, 0.5 µM of ATO, or 10 µM of PP2 for 72 h induced expression of CD11b-positive cells by 13.01%, 11.53% or 13.28%, respectively. However, the combination of ATRA and ATO and the combination of three agents (ATRA, ATO, and PP2) led to a significantly higher expression of CD11b-positive cells (30.96% and 63.17%, respectively). The synergistic effect of the combination of three agents was more significant than the combination of ATRA and ATO. These results were confirmed with NBT staining. These effects were not related to apoptosis. Annexin-V-fluorescein staining revealed that a combination of ATRA and ATO and combination of the three agents did not induce apoptosis in NB4 cells. The expression of ICAM-1 markedly increased in cells treated with the combination of the three agents. These findings suggest that the SFK inhibitor can enhance differentiation of APL cells combined with ATRA and ATO. FDA approved SFK inhibitors, such as dasatinib and bosutinib, may be beneficial for the treatment of APL with a combination of ATRA and ATO.

Src Family Kinase Inhibitor PP2 Has Different Effects on All-Trans-Retinoic Acid or Arsenic Trioxide-Induced Differentiation of an Acute Promyelocytic Leukemia Cell Line.

PURPOSE: Leukemic promyelocytes have the unique ability to undergo differentiation after exposure to retinoic acid and both differentiation and apoptosis after exposure to arsenic trioxide (ATO). Recent studies have shown that inhibition of Src family kinases (SFKs) resulted in enhancement of retinoic acid-induced myeloid differentiation. MATERIALS AND METHODS: In this study, we investigated the question of whether the SFK inhibitor PP2 enhanced the differentiation of NB4 cells when combined with ATO as well as when combined with all-trans-retinoic acid (ATRA). In addition, we attempted to determine the difference in retinoic acid-induced gene expression between cells treated with PP2 in combination with ATRA and in combination with ATO. RESULTS: SFK inhibitor PP2 induced significant enhancement of ATRA- or ATO-induced differentiation of NB4 cells. A significantly stronger synergistic effect was observed when PP2 was combined with ATRA than when combined with ATO. Flow cytometric analysis demonstrated a significant increase in CD11b-positive granulocytes up to 60.73% and 31.58%, respectively. These results were confirmed by nitroblue tetrazolium staining. These effects were not related to apoptosis. Results of Annexin-V-fluorescein staining revealed that PP2 combined with ATRA or PP2 combined with ATO did not induce apoptosis in NB4 cells. Retinoic acid-induced gene expression was different in both groups. Intercellular adhesion molecule-1 expression showed a significant increase in cells treated with PP2 in combination with ATRA, whereas cathepsin D expression showed a significant increase in cells treated with PP2 in combination with ATO. CONCLUSION: Our data showed that SFK inhibitor PP2 enhanced acute promyelocytic leukemia cell differentiation when combined with either ATRA or ATO with difference in activation of retinoic acid-induced genes.

Low-dose combinations of LBH589 and TRAIL can overcome TRAIL-resistance in colon cancer cell lines.

BACKGROUND: Despite the considerable advances in the treatment of colorectal cancer, substantial changes in treatment strategies are required to overcome the problems of drug resistance and toxicity. MATERIALS AND METHODS: Combinations of Pan-deacetylase inhibitor LBH589 and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) were studied in three colon cancer cell lines, HCT116, colo205, and HT29 (HCT116 and colo205 are TRAIL sensitive, whereas HT29 is TRAIL resistant). RESULTS: It was found that TRAIL-induced cytotoxicity was enhanced by LBH589 cotreatment in the TRAIL-sensitive cell lines, and in the TRAIL-resistant HT29 cell line. The cytotoxicity of low-dose TRAIL plus LBH589 was found to be comparable to that of high-dose TRAIL plus LBH589. Additionally, TRAIL and LBH589 were significantly less toxic to normal UCB mononuclear cells than to the three colon cancer cell lines examined. CONCLUSION: LBH589 enhances TRAIL-induced apoptosis in human colon cancer cell lines, especially those resistant to TRAIL-induced apoptosis.

Up-regulation of the DR5 expression by proteasome inhibitor MG132 augments TRAIL-induced apoptosis in soft tissue sarcoma cell lines.

PURPOSE: Current chemotherapeutics for treating locally advanced or metastatic soft tissue sarcomas (STS) are limited. Accordingly, the present in vitro study was conducted to evaluate the effects of treatment of STS cells with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) applied as a single agent or in combination with a proteasome inhibitor, MG132. MATERIALS AND METHODS: Sensitivity to TRAIL and activity of TRAIL-induced apoptotic pathways were analyzed in four STS cell lines: HTB-82 (rhabdomyosarcoma), HT-1080 (fibrosarcoma), HTB-93 (synovial sarcoma), and HTB-94 (chondrosarcoma). Reduction of the dye dimethylthiazolyl 2,5 diphenyltetrazolium bromide (MTT) was used to evaluate cytotoxic activity; western blots were used to evaluate TRAIL-induced apoptosis. RESULTS: TRAIL induced apoptosis in HTB-93 cells, but had little effect in HTB-82, HT-1080, or HTB-94 cells. Expression of TRAIL receptor-1 and -2 did not correlate with sensitivity to TRAIL. Co-incubation of cells with TRAIL and a proteasome inhibitor, MG132, augmented the apoptotic effect of TRAIL in both TRAIL-sensitive and TRAIL-resistant cells. This effect was due to up-regulation of TRAIL receptors and members of the pro-apoptotic BCL-2 family by MG132. CONCLUSION: These data show that combining TRAIL with MG132 enhances apoptosis and overcomes TRAIL resistance. This restoration of TRAIL sensitivity occurs through an increase in the expression of death receptor 5 and of pro-apoptotic BCL-2 family members such as BAX.

Sulindac enhances arsenic trioxide-mediated apoptosis by inhibition of NF-kappaB in HCT116 colon cancer cells.

To study whether the apoptotic effect of arsenic trioxide (As2O3) on colon cancer cells could be enhanced by the addition of sulindac, HCT116 cells were treated with As2O3 (1, 5, 10 microM) and sulindac (0.5 mM), either alone or in combination. As2O3 alone slightly inhibited the growth of HCT116 cells, whereas the combination of As2O3 and sulindac reduced cell growth by 30-40%. Annexin V staining indicated that the synergistic effect of the combination was mediated through increased apoptosis. We examined whether the combination of As2O3 and sulindac on apoptosis is mediated by inhibition of the NF-kappaB pathway in HCT116 colon cancer cells. Western blot analysis showed that the level of nuclear NF-kappaB (p65) was not changed significantly by As2O3 or sulindac treatment alone, while the level of nuclear NF-kappaB (p65) was drastically decreased in the combination treatment by inhibiting the phosphorylation and the degradation of IkappaB-alpha. These results suggest that sulindac enhances apoptosis when combined with As2O3 by inhibiting NF-kappaB activation mediated through the blocking of phosphorylation and degradation of IkappaB-alpha.

Hepatocyte-like cells from human mesenchymal stem cells engrafted in regenerating rat liver tracked with in vivo magnetic resonance imaging.

Cell transplantation using hepatocytes derived from stem cells has been regarded as a possible alternative treatment for various hepatic disorders. Recently, mesenchymal stem cells (MSCs) from the bone marrow have shown the potential to differentiate into hepatocytes in in vitro and in vivo conditions. Noninvasive imaging techniques allowing in vivo assessment of the location of cells are of great value for experimental studies in which these cells are transplanted. We labeled human mesenchymal stem cells (hMSCs) with green fluorescence protein (GFP) and superparamagnetic iron oxide (SPIO) using a transfection agent (GenePORTER). Cellular labeling was evaluated with magnetic resonance (MR) imaging of labeled suspensions, and Prussian blue staining for iron assessment. hMSCs labeled with SPIO and GFP were injected into the portal veins of immunosuppressed, hepatic-damaged rats. MR imaging findings were compared histologically. To identify the differentiation of hMSCs into hepatocytes and to trace the hepatocytes with molecular imaging, we observed the potential of SPIO and GFP double-labeled hMSCs to differentiate into hepatocyte-like cells in the regenerating rat liver. Serial MR imaging showed the possible detection of transplanted cells in the early period of transplantation. Our results indicate that magnetic labeling of hMSCs with SPIO may enable cellular MR imaging and tracking in experimental in vivo settings.

Magnetic resonance evaluation of human mesenchymal stem cells in corpus cavernosa of rats and rabbits.

AIM: To investigate whether the biological process of superparamagnetic iron oxide (SPIO)-labeled human mesenchymal stem cells (hMSCs) may be monitored non-invasively by using in vivo magnetic resonance (MR) imaging with conventional 1.5-T system examinations in corpus cavernosa of rats and rabbits. METHODS: The labeling efficiency and viability of SPIO-labeled hMSCs were examined with Prussian blue and Tripan blue, respectively. After SPIO-labeled hMSCs were transplanted to the corpus cavernosa of rats and rabbits, serial T2-weighted MR images were taken and histological examinations were carried out over a 4-week period. RESULTS: hMSCs loaded with SPIO compared to unlabeled cells had a similar viability. For SPIO-labeled hMSCs more than 1 X 10 (5) concentration in vitro, MR images showed a decrease in signal intensity. MR signal intensity at the areas of SPIO-labeled hMSCs in the rat and rabbit corpus cavernosa decreased and was confined locally. After injection of SPIO-labeled hMSCs into the corpus cavernosum, MR imaging demonstrated that hMSCs could be seen for at least 12 weeks after injection. The presence of iron was confirmed with Prussian blue staining in histological sections. CONCLUSION: SPIO-labeled hMSCs in corpus cavernosa of rats and rabbits can be evaluated non-invasively by molecular MR imaging. Our findings suggest that MR imaging has the ability to test the long-term therapeutic potential of hMSCs in animals in the setting of erectile dysfunction.

Effect of Arsenic Trioxide in TRAIL (Tumor Necrosis Factor-related Apoptosis Inducing Ligand)-Mediated Apoptosis in Multiple Myeloma Cell Lines.

PURPOSE: The potential therapeutic application of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), in the treatment of multiple myeloma (MM), was recently proposed. However, there have been some problems with the use of TRAIL, due to the appearance of TRAIL-resistant cells in MM. The effect of arsenic trioxide (As2O3) on the rate of apoptosis induced by TRAIL was evaluated in MM cells. MATERIALS AND METHODS: Using TRAIL-sensitive (RPMI- 8226) and TRAIL-resistant (ARH-77 and IM-9) MM cell lines, the cell viability, induction of apoptosis, and change in the caspases were examined after treatment with TRAIL alone, or in combination with various concentrations of As2O3. RESULTS: Incubating the cell lines with As2O3 augmented the TRAIL-induced apoptosis in the MM cell lines, according to the As2O3 concentration. Apoptosis was mediated through caspase activation. When TRAIL was used alone, caspase8 was activated in the RPMI-8226 cell lines, but not in the ARH-77 and IM-9 cell lines. When As2O3 was added to TRAIL, caspase-9 was activated in the ARH-77 and IM-9 cells. CONCLUSION: The use of As2O3, in combination with TRAIL, would help enhance the level of TRAIL-induced apoptosis, and overcome the TRAIL-resistance, in MM cells.