
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Departments of Clinical Cancer Prevention [M. L., S. M. L., X-C. X.] and Thoracic/Head & Neck Medical Oncology [R. L.] and Division of Cancer Prevention [R. L., B. L.], University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, and the First Department of Pathology, Hiroshima University, School of Medicine, Hiroshima, Japan [E. T.]
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
12,500 new cases will be diagnosed and
12,200 patients will die of the disease in 1999, which makes this
cancer the seventh leading cause of cancer deaths in men in the United
States (1)
. Epidemiological studies indicate that the
incidence of esophageal adenocarcinoma is increasing in the United
States and in Europe (2, 3, 4, 5)
. The factors underlying this
increase are unknown but may be related to Barretts esophagus, the
presence of which is associated with a 30125-fold increase in the
risk of developing adenocarcinoma of the esophagus (2, 3, 4, 5, 6, 7)
.
The incidence of esophageal cancer differs greatly among racial groups
in the United States; squamous cell carcinoma of the esophagus occurs
five times more frequently in black men than in white men, but
adenocarcinoma of the esophagus occurs more often in whites. The
incidence of esophageal cancer among blacks also is greater at younger
ages (5
, 7)
. Risk factors such as cigarettes and alcohol are significant for both histological types of the cancer in the United States, although higher risk is noted for adenocarcinoma in individuals who have gastroesophageal reflux, which usually results in Barretts esophagus, and who are in the highest decile of body mass index (5 , 7) . In Asian countries, however, especially in northern China, squamous cell carcinoma of the esophagus is dominant, and the risk factors are associated more with nutritional deficiencies and consumption of pickled vegetables (5 , 7) .
The treatment and prognosis of both types of esophageal cancer are quite similar (5) . Surgical resection provides excellent palliation of the neoplasm; however, the rate of cure with esophagectomy alone is only 1020%. Adjuvant therapy at the present time with pre- or postesophagectomy irradiation may improve local-regional control but does not improve survival (8, 9, 10) . Therefore, early identification and new strategies for treatment of esophageal carcinoma are urgently needed. One possible approach is to use NSAIDs3 because recent epidemiological and experimental studies have demonstrated the therapeutic potential of NSAIDs in the chemoprevention of esophageal cancer (11, 12, 13) .
The effects of NSAIDs are thought to be mediated mainly through the inhibition of COXs, which are the key enzymes in the biosynthesis of prostaglandins (prostanoids) through the conversion of arachidonic acid to prostaglandin H2, the precursor of prostanoids (14) . COX-1, the first cloned isozyme, is constitutively expressed in many tissues and is thought to be involved in the homeostasis of various physiological functions; another isozyme, COX-2, is elevated in tumors, including esophageal cancer, and is also inducible by various agents such as growth factors and tumor promoters (14) . Tsujii and DuBois (15) reported that intestinal epithelial cells overexpressing the COX-2 gene exhibited altered adhesion properties and resisted apoptosis. Because these changes were reversed by treatment with NSAIDs, it was suggested that overexpression of COX-2 may be responsible for colorectal carcinogenesis. Other recent studies indicated that apoptosis induced by sulindac metabolites in colorectal cancer cells was independent of COX inhibition or p53 induction (16 , 17) . Most NSAIDs research to date has focused on colon cancer, and the effects of NSAIDs on esophageal cancer cell lines in vitro have not yet been reported. Therefore, we like to investigate their potentials for chemoprevention or therapy of esophageal cancer.
In this study, we tested the effect of aspirin on 10 esophageal cancer cell lines, analyzed the expression of COX-1 and -2 in these cell lines, examined the stimulation of COX-2 by bile acids, and assessed PGE2 production. In addition, we also examined the expression of apoptosis-related genes in these cells.
| Materials and Methods |
|---|
|
|
|---|
Cell Culture and Treatment with Aspirin and Bile Acids.
The above-named cell lines were plated in tissue culture dishes and
grown in DMEM with 10% FBS at 37°C in a humidified atmosphere
of 95% air and 5% CO2. To examine the effect of
aspirin, the cells were plated in regular medium and incubated for
24 h; the medium was then replaced with either control medium or
with medium containing aspirin at 1, 3, or 5 mM. The
aspirin was dissolved in DMSO and diluted into the medium before each
experiment. The medium was completely replaced with fresh medium every
72 h. At the end of the experiment, the cells were fixed with 10%
trichloroacetic acid, stained with 0.4% sulforhodamine B in 1% acetic
acid, and the absorbances were determined using an automated
spectrophotometric plate reader at a single wavelength of 490 nm.
Viability was tested by exclusion of trypan blue (0.1%), and the
percentage of growth inhibition was calculated by the equation: %
control =
(ODt/ODc
x 100; where ODt and
ODc are the absorbances in treated
cultures and control cultures, respectively.
To examine the modulation of COX expression by bile acids, CD and deoxycholate (Sigma Chemical Co., St. Louis, MO) were used to treat the esophageal cancer cells for 12 h at a concentration 400 µM. Cellular proteins were isolated in lysis buffer containing 150 mM NaCl, 1% Triton X-100, 1% sodium deoxycholate, 0.1% SDS, 10 µg/ml phenylmethylsulfonyl fluoride, 30 µg/ml aprotinin, and 50 mM Tris-HCl (pH 8.0). The samples were then put on ice for 60 min and centrifuged at 13,000 rpm for 30 min. Protein concentrations were measured using a Bio-Rad DC kit (Bio-Rad Laboratories, Hercules, CA), according to the manufacturers protocol.
DNA Extraction and Gel Electrophoretic Analysis of DNA
Fragmentation.
Soluble DNA was extracted after a 2-day treatment with 5 mM
aspirin. The cells floating in medium were collected by centrifugation,
and the cells that remained attached to the dish were detached by
scraping. The cells were centrifuged into a pellet and resuspended in
Tris-EDTA buffer (pH 8.0). The plasma membrane of the cell was
lysed in 10 mM Tris-HCl (pH 8.0), 10 mM EDTA,
0.5% Triton X-100 on ice for 15 min. The lysate was centrifuged at
12,000 x g for 15 min to separate soluble (fragmented)
from pellet (intact genomic) DNA. Soluble DNA was treated with RNase A
(50 µg/ml) at 37°C for 1 h, followed by treatment with
proteinase K (100 µg/ml) in 0.5% SDS at 50°C for 2 h. The
residual material was extracted with phenol-chloroform, precipitated in
ethanol, electrophoresed on a 1.8% agarose gel, and stained with
ethidium bromide. The gels were then photographed in the dark using UV
illumination.
TUNEL Assay.
The TUNEL assay was performed with a commercial kit (APO-BRDU Apoptosis
Kit; Phoenix Flow Systems, San Diego, CA). The esophageal cancer cells
were treated with control medium or medium containing 5 mM
aspirin for 2 or 5 days. Both floating and attached cells were
collected, labeled with fluorescein dye, and stained with propidium
iodide according to a protocol provided by the manufacturer. The cells
were then analyzed by flow cytometry using a FACScan flow cytometer
(Epics Profile; Coulter Corp., Hialeah, FL).
Western Blotting.
Samples containing 30 µg of protein extracted from either control or
treated esophageal cancer cells were subjected to gel electrophoresis
in 1014% polyacrylamide slab gels in the presence of SDS (SDS-PAGE).
The proteins were then transferred electrophoretically to a Hybond-C
nitrocellulose membrane (Amersham, Arlington Heights, IL) at 150 V for
1 h at 4°C. The membrane was subsequently immersed in 0.5%
Ponceau S in 1% acetic acid to stain the proteins and to verify that
equal amounts of protein were loaded in each lane and transferred
efficiently. After incubating overnight in a blocking solution
containing 15% bovine skim milk in 10 mM PBS (pH 7.4), the
nitrocellulose membranes were incubated for 3 h with primary
antibodies, i.e., anti-COX-1 from Cayman Chemicals (Ann
Arbor, MI), COX-2 and bcl-2 from Transduction Laboratories
(Lexington, KY), bax and p21 from Oncogene (Cambridge, MA), or
ß-actin from Sigma. The membranes were then washed with PBS buffer to
remove excess unbound antibodies and incubated for 1 h with horse
antimouse or goat antirabbit secondary antibody (Amersham) at 1:2000.
After incubation, the membranes were washed in PBS containing 0.1%
Tween-20, incubated with ECL solution (Amersham) for 12 min, and
exposed to an X-ray film for chemiluminescence.
ELISA Assay of PGE2 Production.
Cells (2 x 104/well) were plated in 24-well
dishes and grown to 80% confluence in DMEM containing 10% FCS. The
medium was then replaced with DMEM containing 1% FCS and vehicle
(DMSO), or aspirin (5 mM), CD (400 µM) or CD
plus aspirin (aspirin pretreatment for 8 h) for 12 h. The
conditioned medium was then collected to determine the production of
PGE2 by a commercial kit (Cayman) according to
the manufacturers protocol.
| Results |
|---|
|
|
|---|
|
|
|
|
|
|
Modulation of bcl-2 by Aspirin.
To study the effects of aspirin on apoptosis-related genes, we selected
two cell lines, one expressing high levels of COX-2 (TE-7) and another
one showing no COX-2 protein by Western blotting (TE-1), and then
analyzed the expression of bcl-2, bax, and p21 proteins by Western
blotting. The data showed that aspirin was able to reduce bcl-2 protein
expression after as little as 6 h of treatment (Fig. 6)
, whereas there were no changes in expression of bax (data not shown)
and p21 (Fig. 6)
proteins.
|
| Discussion |
|---|
|
|
|---|
The decreased growth of esophageal cancer cell lines after
treatment with aspirin was associated with induction of
apoptosis, as was evident by both DNA fragmentation and TUNEL assay. In
most cell lines, COX expression seemed to indicate sensitivity to
aspirin. There were, however, exceptions; TE-1 cells, which do not
express COX-1 or COX-2, showed an
50% decrease in cell numbers
after a 7-day treatment with 5 mM aspirin, whereas TE-3
cells, which express both COX-1 and COX-2, were relatively resistant to
aspirin treatment. Previous studies demonstrated that the induction of
apoptosis by NSAIDs was independent of COX inhibition, cell cycle
arrest, or p53 induction (16
, 17)
. This study shows that
aspirin can reduce bcl-2 expression after as little as 6 h of
treatment in two esophageal cancer cell lines tested and that this
effect is independent of COX expression of the cell lines. Sheng
et al. (22)
recently reported that
PGE2 was able to induce bcl-2 expression in colon
cancer cell lines, which can only partially explain the mechanism by
which aspirin induces apoptosis in cancer cells because in this study
aspirin down-regulated bcl-2 expression in TE-1 cells, which do not
express COX-1 or COX-2 and produce only very low levels of
PGE2. Again, two studies did demonstrate that
COX-2-selective analogues could inhibit colon carcinogenesis (23
, 24)
. A different signaling pathway may be involved in the action
of aspirin, which provides insight into the induction of apoptosis by
NSAIDs. For example, aspirin exhibited anti-activator protein activity
and inhibited nuclear factor-
b (25
, 26)
.
Therefore, the mechanisms by which NSAIDs prevent cancer and induce
apoptosis in neoplastic cells are not that simple and need further
study.
Analysis of COX-2 protein in surgical specimens by immunohistochemistry demonstrated that this isozyme is overexpressed in esophageal cancer cells, whereas normal esophageal epithelium expressed no or weak COX-2 (27 , 28) . In this study, COX-2 was overexpressed in 7 of 10 esophageal cell lines. Aspirin was found to inhibit PGE2 production and block bile acid-induced PGE2 production. Bile acids are putative tumor promoters (21) , and PGE2 can induce bcl-2 expression and activate mitogen-activated protein kinase (22) . Another study indicated that PGE2 could reduce the cellular immunoresponse of lymphocytes to phytohemagglutinin stimulation in colon cancer patients (29) . Taken together, the present study and prior evidence suggest that NSAIDs may be used for chemoprevention of esophageal cancer in high-risk populations, although the mechanism by which aspirin induces apoptosis in esophageal cancer needs further investigation.
Nevertheless, the numerous side-effects of aspirin in the gastroenterological tract may prevent patients from long-term use, although the dose used in the present study is clinically achievable. At the present time, a few potent NSAIDs with fewer side-effects are available and indeed are being used in clinical prevention trials for different cancers.
| Acknowledgments |
|---|
| Footnotes |
|---|
1 Supported in part by the Office of Vice
President for Cancer Prevention. ![]()
2 To whom requests for reprints should be
addressed, at the Department of Clinical Cancer Prevention, Box 236,
University of Texas M. D. Anderson Cancer Center, 1515 Holcombe
Boulevard, Houston, TX 77030. Phone: (713) 745-2940; Fax:
(713) 792-0628; E-mail: xxu{at}mdanderson.org ![]()
3 The abbreviations used are: NSAIDs,
non-steroidal anti-inflammatory drugs; COX, cyclooxygenase; FBS, fetal
bovine serum; PGE2, prostaglandin E2; CD,
chenodeoxycholate; TUNEL, terminal deoxynucleotidyl transferase
(Tdt)-mediated nick end labeling. ![]()
Received 10/15/99; revised 2/24/00; accepted 3/20/00.
| References |
|---|
|
|
|---|
716 knockout mice by inhibition of cyclooxygenase 2 (COX-2). Cell, 87: 803-809, 1996.[Medline]
B by sodium salicylate and aspirin. Science (Washington DC), 265: 956-959, 1994.This article has been cited by other articles:
![]() |
L. A. Anderson, B. T. Johnston, R.G. P. Watson, S. J. Murphy, H. R. Ferguson, H. Comber, J. McGuigan, J. V. Reynolds, and L. J. Murray Nonsteroidal Anti-inflammatory Drugs and the Esophageal Inflammation-Metaplasia-Adenocarcinoma Sequence. Cancer Res., May 1, 2006; 66(9): 4975 - 4982. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. H.-X. Xia, S. T. Zhang, S. K. Lam, M. C.-M. Lin, H. F. Kung, and B. C.-Y. Wong Expression of macrophage migration inhibitory factor in esophageal squamous cell carcinoma and effects of bile acids and NSAIDs Carcinogenesis, January 1, 2005; 26(1): 11 - 15. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. D. Basu, L. B. Pathangey, T. L. Tinder, M. LaGioia, S. J. Gendler, and P. Mukherjee Cyclooxygenase-2 Inhibitor Induces Apoptosis in Breast Cancer Cells in an In vivo Model of Spontaneous Metastatic Breast Cancer Mol. Cancer Res., November 1, 2004; 2(11): 632 - 642. [Abstract] [Full Text] [PDF] |
||||
![]() |
O. N. Tucker, A. J. Dannenberg, E. K. Yang, and T. J. Fahey III Bile acids induce cyclooxygenase-2 expression in human pancreatic cancer cell lines Carcinogenesis, March 1, 2004; 25(3): 419 - 423. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. E. Castelao, R. D. Bart III, C. A. DiPerna, E. M. Sievers, and R. M. Bremner Lung cancer and cyclooxygenase-2 Ann. Thorac. Surg., October 1, 2003; 76(4): 1327 - 1335. [Abstract] [Full Text] [PDF] |
||||
![]() |
X. Chen, N. Li, S. Wang, J. Hong, M. Fang, J. Yousselfson, P. Yang, R. A. Newman, R. A. Lubet, and C. S. Yang Aberrant arachidonic acid metabolism in esophageal adenocarcinogenesis, and the effects of sulindac, nordihydroguaiaretic acid, and {alpha}-difluoromethylornithine on tumorigenesis in a rat surgical model Carcinogenesis, December 1, 2002; 23(12): 2095 - 2102. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. L. Vaughan, A. R. Kristal, P. L. Blount, D. S. Levine, P. C. Galipeau, L. J. Prevo, C. A. Sanchez, P. S. Rabinovitch, and B. J. Reid Nonsteroidal Anti-inflammatory Drug Use, Body Mass Index, and Anthropometry in Relation to Genetic and Flow Cytometric Abnormalities in Barrett's Esophagus Cancer Epidemiol. Biomarkers Prev., August 1, 2002; 11(8): 745 - 752. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. S. Carlton, R. Gopalakrishnan, A. Gupta, B. W. Liston, S. Habib, M. A. Morse, and G. D. Stoner Piroxicam Is an Ineffective Inhibitor of N-Nitrosomethylbenzylamine-induced Tumorigenesis in the Rat Esophagus Cancer Res., August 1, 2002; 62(15): 4376 - 4382. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. J. Thun, S. J. Henley, and C. Patrono Nonsteroidal Anti-inflammatory Drugs as Anticancer Agents: Mechanistic, Pharmacologic, and Clinical Issues J Natl Cancer Inst, February 20, 2002; 94(4): 252 - 266. [Abstract] [Full Text] [PDF] |
||||
![]() |
I. Shureiqi, X. Xu, D. Chen, R. Lotan, J. S. Morris, S. M. Fischer, and S. M. Lippman Nonsteroidal Anti-Inflammatory Drugs Induce Apoptosis in Esophageal Cancer Cells by Restoring 15-Lipoxygenase-1 Expression Cancer Res., June 1, 2001; 61(12): 4879 - 4884. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Li, X. Wu, and X.-C. Xu Induction of Apoptosis in Colon Cancer Cells by Cyclooxygenase-2 Inhibitor NS398 through a Cytochrome c-dependent Pathway Clin. Cancer Res., April 1, 2001; 7(4): 1010 - 1016. [Abstract] [Full Text] |
||||
![]() |
W. K. Hong, M. R. Spitz, and S. M. Lippman Cancer Chemoprevention in the 21st Century: Genetics, Risk Modeling, and Molecular Targets J. Clin. Oncol., November 1, 2000; 18(90001): 9s - 18. [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |