Potential role of caspase-3 and -9 in arsenic trioxide-mediated apoptosis in PCI-1 head and neck cancer cells

Lysosomes and Trivalent Arsenic Treatment in Acute Promyelocytic Leukemia

BACKGROUND

Cells from patients with t(15;17) acute promyelocytic leukemia (APL) express the fusion protein between the promyelocytic leukemia protein and retinoic acid receptor alpha (PML/RAR alpha). Patients with APL respond to differentiation therapy with all-trans-retinoic acid, which induces PML/RAR alpha degradation. When resistance to all-trans-retinoic acid develops, an effective treatment is arsenic trioxide (arsenite), which also induces this degradation. We investigated the mechanism of arsenite-induced PML/RAR alpha degradation.

METHODS

NB4-S1 APL cells were treated with clinically relevant concentrations of arsenite. Lysosomes were visualized with a lysosome-specific dye. Lysosomal protein esterase was measured by immunoblot analysis. Lysosomal cathepsin L was detected by immunogold labeling and transmission electron microscopy, and its activity was measured in cytosolic cellular fractions. In vitro degradation assays of PML/RAR alpha in cell lysates were performed with and without protease inhibitors and assessed by immunoblot analysis. Only nonparametric two-sided statistical analyses were used. The nonparametric Wilcoxon test was used for group comparison, and the nonlinear regression technique was used for analysis of dose-response relationship as a function of arsenite concentration.

RESULTS

Arsenite treatment destabilized lysosomes in APL cells. Lysosomal proteases, including cathepsin L, were released from lysosomes 5 minutes to 6 hours after arsenite treatment. PML/RAR alpha was degraded by lysate from arsenite-treated APL cells, and the degradation was inhibited by protease inhibitors. At both 6 and 24 hours, substantially fewer arsenite-treated APL cells, than untreated cells, contained cathepsin L clusters, a reflection of cathepsin L delocalization. Cells with cathepsin L clusters decreased as a function of arsenite concentration at rates of -2.03% (95% confidence interval [CI] = -4.01 to -.045; P = .045) and -2.39% (95% CI = -4.54 to -.024; P = .029) in 6- and 24-hour treatment groups, respectively, per 1.0 microM increase in arsenite concentration. Statistically significantly higher cytosolic cathepsin L activity was detected in lysates of arsenite-treated APL cells than in control lysates. For example, the mean increase in cathepsin activity at 6 hours and 1.0 microM arsenite was 26.3% (95% CI = 3.3% to 33%; P < .001), compared with untreated cells.

CONCLUSIONS

In APL cells, arsenite may cause rapid destabilization of lysosomes.

Cell cycle arrest and apoptotic cell death in cultured human gastric carcinoma cells mediated by arsenic trioxide

AIM: To investigate the effect of arsenic trioxide on human gastric cancer cell line MKN45 with respect to both cytotoxicity and induction of apoptosis in vitro.

METHODS: MKN45 cells were treated with arsenic trioxide (As₂O₃) at the concentration of 1, 5, and 10 µmol/L, respectively, for three successive days. Cell growth and proliferation were observed by cell counting and trypan blue exclusion. Cytotoxicity of As₂O₃ was determined by MTT assay. Morphologic changes were studied with light microscopy. Flow cytometry was used to assay cell DNA distribution and apoptotic cells were confirmed with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and DNA electrophoresis.

RESULTS: The growth of MKN45 cells was significantly inhibited by As₂O₃ which was confirmed by colony-forming assay. After 7 d of culture with various concentrations of As₂O₃, colony-forming capacity of MKN45 cells decreased with As₂O₃ increment in comparison with that of control group. The inhibitory rate of colony-formation was 38.5%, 99.1%, and 99.5% when the concentration of As₂O₃ was 1, 5, and 10 μmol/L in culture medium, respectively. The cell number of a single colony in drug treatment groups was less than that of control group. The cell-killing rate of As₂O₃ to MKN45 cells was both dose- and time-dependent with an IC₅₀ of (11.05±0.25) µmol/L. After incubation in 10 μmol/L As₂O₃ for 24 h, the cell-killing rate was 27.1%, and it was close to 50% after 48 h. The results showed that As₂O₃ induced time- and dose-dependent apoptosis in MKN45 cells, blocked at G2/M phase. The apoptotic peak (sub-G1 phase) appeared and cell apoptotic rate in MKN45 cells was 18.3-32.5% after treatment by 10 μmol/L As₂O₃ for 48 h. The percentage of G2/M cell of the experimental groups was 2.0-5.0 times than that of the control group. Gel electrophoresis of DNA from cells treated with each concentration of As₂O₃ for 48 h revealed a “ladder” pattern, indicating preferential DNA degradation at the internucleosomal, linker DNA sections. TUNEL also demonstrated strand breaks in DNA of MKN45 cells treated with As₂O₃, while control cells showed negative labeling.

CONCLUSION: As₂O₃ can induce apoptosis of human gastric carcinoma cells MKN45, which is the basis of its effectiveness. It shows great potential in the treatment of gastric carcinoma.

19-Nor-1,25(OH)2D2(a Novel, Noncalcemic Vitamin D Analogue), Combined with Arsenic Trioxide, Has Potent Antitumor Activity against Myeloid Leukemia

Recently, we reported that a novel, noncalcemic vitamin D analogue (19-nor-1,25(OH)2D2; paricalcitol) had anticancer activity. In this study, we explored if paricalcitol enhanced anticancer effects of other clinically useful drugs in vitro against a large variety of cancer cells. Paricalcitol, when combined with As2O3, showed a markedly enhanced antiproliferative effect against acute myeloid leukemia (AML) cells. This combination induced monocytic differentiation of NB-4 acute promyelocytic leukemia (APL) cells and HL-60 AML cells and caused both to undergo apoptosis associated with down-regulation of Bcl-2 and Bcl-x(L). Paricalcitol induced monocytic differentiation of U937 AML cells, which was partially blocked by inducing expression of APL-related PML-retinoic acid receptor alpha (RARalpha) chimeric protein in the U937 cells containing a Zn2+-inducible expression vector coding for this fusion protein (PR9 cells). Exposure to As2O3 decreased levels of PML-RARalpha in PR9 cells, and the combination of paricalcitol and As2O3 enhanced their monocytic differentiation in parallel with the As2O3-mediated decrease of PML-RARalpha. Furthermore, As2O3 increased the transcriptional activity of paricalcitol probably by increasing intracellular levels of paricalcitol by decreasing the function of the mitochondrial enzyme 25-hydroxyvitamin D3-24-hydroxylase, which functions to metabolize the active vitamin D in cells. In summary, the combination of paricalcitol and As2O3 potently decreased growth and induced differentiation and apoptosis of AML cells. This probably occurred by As2O3 decreasing levels of both the repressive PML-RARalpha fusion protein and the vitamin D metabolizing protein, 25-hydroxyvitamin D3-24-hydroxylase, resulting in increased activity of paricalcitol. The combination of both of these Food and Drug Administration-approved drugs should be considered for treatment of all-trans retinoic acid-resistant APL patients as well as those with other types of AML.

Morphological and functional changes of mitochondria in apoptotic esophageal carcinoma cells induced by arsenic trioxide

AIM: To demonstrate that mitochondrial morphological and functional changes are an important intermediate link in the course of apoptosis in esophageal carcinoma cells induced by As₂O₃.

METHODS: The esophageal carcinoma cell line SHEEC1, established in our laboratory, was cultured in 199 growth medium, supplemented with 100 mL·L^-1 calf serum and 3 μmol·L^-1 As₂O₃ ( the same below). After 2, 4, 6, 12, 24 h of drug adding, the SHEEC1 cells were collected for light-and electron-microscopic examination. The mitochondria were labeled by Rhodamine fluorescence probe and the fluorescence intensity of the mitochondria was measured by flow cytometer and cytofluorimetric analysis. Further, the mitochondrial transmembrane potential (MTP, ∆Ψ m) change was also calculated.

RESULTS: The mitochondrial morphological change after adding As₂O₃ could be divided into three stages. In the early-stage (2-6 h) after adding As₂O₃, an adaptive proliferation of mitochondria appeared; in the mid-stage (6-12 h) a degenerative change was observed; and in the late-stage (12-24 h) the mitochondria swelled with outer membrane broken down and then cells death with apoptotic changes of nucleus. The functional change of the mitochondria indicated by fluorescent intensity, which reflected the MTP status of mitochondria, was in accordance with morphological change of the mitochondria. The fluorescent intensity increased at early-stage, declined in mid-stage and decreased to the lowest in the late-stage. 24 h after As₂O₃ adding, the cell nucleus showed typical apoptotic changes.

CONCLUSION: Under the inducement of As₂O₃, the early apoptotic changes of SHEEC1 cells were the apparent morphological and functional changes of mitochondria, afterwards the nucleus changes followed. It is considered that changes of mitochondria are an important intermediate link in the course of apoptosis of esophageal carcinoma cells induced by As₂O₃.

Nitric oxide and calcium ions in apoptotic esophageal carcinoma cells induced by arsenite

AIM: To Quantitatively analyze the nitri oxide (NO) and Ca²⁺ in apoptosis of esophageal carcinoma cells induced by arsenic trioxide (As₂O₃).

METHODS: The cell line SHEEC1, a malignant esophageal epithelial cell induced by HPV in synergy with TPA in our laboratory, was cultured in a serum-free medium and treated with As₂O₃. Before and after administration of As₂O₃, NO production in cultured medium was detected quantitatively using the Griess Colorimetric method. Intracellular Ca²⁺ was labeled by using the fluorescent dye Fluo3-AM and detected under confocal laser scanning microscope (CLSM), which was able to acquire data in real-time enabling Ca²⁺ dynamics of individual cells in vitro. The apoptotic cells were examined under electron microscopy.

RESULTS: Intracellular concentration of Ca²⁺ increased from 1.00 units to 1.09-1.38 units of fluorescent intensity at As₂O₃ treatment and NO products subsequently released from As₂O₃-treated cells increased from 0.98-1.00 × 10^-2μmol·L^-1 up to 1.48-1.52 × 10^-2μmol·L^-1 and maintained in a high level continuously. Finally apoptosis of cells occurred, chromatin being agglutinated, cells shrunk, nuclei became round and mitochondria swelled.

CONCLUSION: Ca²⁺ and NO increased with cell damage and apoptosis in cells treated by As₂O₃. The Ca²⁺ is an initial messenger to the apoptotic pathway. To investigate Ca²⁺ and NO will be a new direction for studying the apoptotic signaling messenger of the esophageal carcinoma cells induced by As₂O₃.