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Advances in Brief |
Second Department of Surgery, Shimane Medical University, Izumo 693, Japan
| ABSTRACT |
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| Introduction |
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| Materials and Methods |
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Immunostaining and RT-PCR for COX-2 Expression.
Expression of COX-2 was checked at the protein and mRNA levels by
immunohistochemistry and RT-PCR, respectively, in all three cell lines
used for this study. Immunohistochemistry was done by the
avidin-biotin-peroxidase complex method as described elsewhere
(4)
. Briefly, cell smears were fixed in 4%
paraformaldehyde, endogenous peroxidase activity was quenched with 3%
H2O2, and nonspecific
binding was blocked by normal rabbit serum. Slides were treated with
mouse anti-human COX-2 antibody (Cayman Chemical, Ann Arbor, MI) at a
1:500 dilution overnight at 4°C. All other steps were done using a
Histofine SAB-PO(R) (Nichirei Corp., Tokyo, Japan) kit according to the
manufacturers instructions. The reaction product was visualized by
3-amino-9-ethylcarbazole (Histofine, Tokyo, Japan).
Counterstaining was done using hematoxylin.
For RT-PCR, total RNA was extracted using the Tri reagent (Molecular Research Center, Inc., Cincinnati, OH) following the manufacturers instructions. RT-PCR was performed as described previously (4) .
Growth Inhibition and MTT Assays.
Approximately 5 x 104 cells were
plated in 60-mm-diameter Petri dishes in triplicate. Cells were allowed
to grow, and after 24 h sulindac (Sigma Chemical Co., St. Louis,
MO) and exisulind (a generous gift from Merck, Rahway, NJ) at various
concentrations (25, 50, and 100 µM) dissolved in DMSO
were added to the treatment dishes. The final concentration of DMSO was
<0.1%. Cells were harvested at definite time intervals by
trypsinization, and aliquots were counted using a hematocytometer. On
day 3, only KYN-2 cells were harvested by trypsinization and were used
for MTT assay (Boehringer Mannheim, Mannheim, Germany). This assay
relies on the ability of viable cells to reduce the tetrazolium salt
MTT metabolically to a purple formazan product, which can be quantified
colorimetrically. One hundred-microliter aliquots of cells were
transferred to triplicate wells of a flat-bottomed 96-well microtiter
plate and treated with 10 µl of MTT for 4 h at 37°C. After
that, 100 µl of solubilization solution were added, and the mixture
was incubated at 37°C for overnight. The solubilized formazan product
was spectrophotometrically quantified using a microtiter plate reader
(EAR 400; FW Slt-Labinstruments, Groedig, Austria) at 550-nm
wavelength. The morphology of the KYN-2 cells both in the sulindac and
control group was checkd by a phase-contrast light microscope.
Cell Cycle Analysis.
The proportion of cells in
G0-G1, S, and
G2-M was determined by flow cytometric analysis
of DNA content (EPICS Elite ESP flow cytometer; Coulter Electronics,
Miami, FL). Cell cycle distribution in KYN2 cells was measured after
24 h of treatment with 100 µM sulindac. In brief,
cell suspension was prepared by trypsinization, and
2 x 106 cells/ml were washed twice with PBS.
The cells were resuspended with 10 ml of 70% ethanol (-20°C),
incubated at 4°C for 4 h, washed twice in PBS, incubated
with RNase (Sigma) at a concentration of 0.25 mg/ml at 37°C for 15
min, followed by treatment with propidium iodide (50 µg/ml), and
incubated for 30 min at 4°C in the dark. DNA histograms were analyzed
using Multicycle AV software (Phoenix, San Diego, CA) to evaluate cell
cycle compartments.
Detection of Apoptosis.
Apoptosis was detected by an annexin V-FITC kit (Immunotech, Marseille,
France) according to the manufacturers instructions. Briefly,
KYN-2 cells were collected by trypsinization after a 72-h treatment,
and the number of cells was adjusted to
1 x 106 cells/ml Cells were washed with ice-cold DMEM
and were centrifuged to collect the cell pellet. Cell pellet was
resuspended in ice-cold binding buffer. After that, annexin V-FITC (10
µl/ml) and PI (10 µl/ml) solutions were added to the cell
suspension and mixed gently. The tube was then incubated for 10 min in
the dark before being analyzed by the flow cytometer. All steps were
carried out on ice. Aliquots of stained cells were smeared onto glass
slides, and morphological changes were examined under a fluorescence
microscope.
Statistical Analysis.
A minimum of three experiments measuring the growth inhibition was
performed, and the mean of the inhibitory effect was expressed as
percent inhibition calculated as (number of treated cells/number of
control cells x 100. Pairwise group comparisons between
different groups were done using the unpaired Students t
test. Significant differences were assumed when the chance of
differences arising from a sampling error was <1 in 20
(i.e., P < 0.05).
| Results |
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| Discussion |
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All of the three cell lines used in this study had different differentiation statuses, with HepG2 and Huh-7 being well differentiated (9) and KYN-2 being less differentiated (10) . Koga et al. (8) reported that COX-2 is involved in early stages of HCC carcinogenesis and is expressed frequently in well-differentiated carcinomas. However, in this study, irrespective of their differentiation status, all three cell lines expressed COX-2 both at the protein and mRNA levels. Supplementation of culture medium with both sulindac and its irreversible oxidative form exisulind at comparable concentrations produced a concentration-dependent growth-inhibitory effect. A growing body of evidence suggests that exisulind induces apoptosis in various tumor cell lines and inhibits chemically induced colonic (11) and mammary carcinogenesis (2) . In these reports the authors concluded, and we concur with them, that the antineoplastic effect of sulindac may be irrespective of its inhibitory effect on COX enzymes and prostaglandin biosynthesis. It is worth mentioning that a comparable growth-inhibitory effect of sulindac could be achievable at a much lower concentration (100 µM) in HCC cell lines than in other cell lines, because sulindac had a significant inhibitory effect at 100 µM in HCC cell lines, whereas in pancreatic and colon cancer cell lines it was 200 and 400 µM, respectively (4 , 7) . Sulindac is a prodrug and is metabolized to sulindac sulfide by the gut flora and in the liver before it exerts its effect on COX enzymes (12) . It might be possible that HCC cell lines efficiently converted sulindac to its sulfide form for effectivity at a relatively lower concentration.
Although the exact mechanism for the antineoplastic effect of NSAIDs
has yet to be delineated, the antiproliferative effect and/or induction
of apoptosis have been attributed to this antineoplastic effect. The
antiproliferative effect of NSAIDs by quiescence of the cell cycle has
been questioned by several authors, but most of them agree regarding
the proapoptotic effect of NSAIDs. In a recent report, Elder et
al. (13)
demonstrated that NS-398, a new generation
of NSAID had no effect on cell cycle distribution in a colon carcinoma
cell line, whereas Piazza et al. (14)
showed
that sulindac produced G1 arrest in proliferating
colon carcinoma cell lines. In this study, we found that both cell
cycle arrest and apoptosis contributed to the growth-inhibitory effect
of sulindac in HCC cell lines. In the preconfluent state, sulindac
produced significant cell cycle arrest in
G0-G1 as early evidence of
an antineoplastic effect; however, this was not time dependent, because
the cells emerged from the arrest and entered into S-phase. In
contrast, the rate of apoptosis increased uniformly in a time-dependent
manner and reached a maximum of 66.5% at 48 h of sulindac
treatment, which was followed by a maximum growth inhibition at 72 h of treatment (Fig. 4)
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Several mechanisms have been proposed affecting the molecular pathways
regulating the cellular proliferation and apoptosis by the NSAIDs,
although the key mechanism still remains a dilemma. Only a few of these
mechanisms are related to their capability to inhibit COX, and most of
them are COX independent, including modulation of ras signal
transduction (15)
, mitogen-activated protein kinase
activation (16)
, nuclear factor
B activation
(17)
, cyclin expression (7)
, activation of
the sphingomyelin-ceramide pathway (18)
, and p53
expression (14)
. In this study, we used two
well-differentiated HCC cell lines of differentially mutated
p53 and ras genes with an N-ras
mutation at codon 61 position 2 in the HepG2 cell line, and a
p53 point mutation resulted in the amino acid changes of
cysteine for tyrosine at codon 220 in the Huh-7 cell line (9
, 19)
. Sulindac was equally effective in both of these cell lines
and produced similar growth inhibition, indicating that neither of
these pathways is crucial for the antineoplastic effect of sulindac.
HCC is the leading cancer in men in Taiwan and is one of the most common causes of malignancy-related death in Africa and Asia (20) . Despite an enthusiastic effort to diagnose the disease at an early stage, the prognosis is still dismal, thus implying that emphasis should be given on preventive measures. Unfortunately, to date, there is no effective preventive measure in this highly malignant disease. Both viral infection and chemical carcinogens are thought to be responsible for the development of HCC, with distinct preceding steps of premalignant lesions in the vicinity of cirrhotic liver. Epidemiological studies have shown a 4050% reduction in mortality rates from colon cancer in patients receiving NSAID therapy (21) . It is worth mentioning that the results of this study might create a new avenue for the chemoprevention of HCC by the new generations of NSAID therapy. In the late 1970s, Hial et al. (22) demonstrated that COX-dependent NSAIDs exerted an antiproliferative effect on a rat hepatoma cell line. For long-term chemoprevention, the COX-dependent NSAIDs are not suitable because of their deleterious effect on gastrointestinal functions. Therefore, the new generation of COX-independent NSAIDs such as exisulind and COX-2-specific inhibitors might be suitable for HCC chemoprevention. However, before recommending these drugs as routine prophylaxis, further studies regarding the safety profile of these drugs and identification of cohorts at high risk for subsequent development of HCC should be conducted.
| FOOTNOTES |
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1 To whom requests for reprints should be
addressed. Phone: (81) 853-202-235; Fax: (81) 853-202-229; E-mail: rahman{at}shimane-med.ac.jp ![]()
2 The abbreviations used are: NSAID, nonsteroidal
anti-inflammatory drug; HCC, hepatocellular carcinoma; COX-2,
cyclooxegenase-2; RT, reverse transcription; MTT,
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide; PI,
propidium iodide. ![]()
Received 11/24/99. Accepted 3/ 3/00.
| REFERENCES |
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