ONCOLOGY REPORTS 27: 87-93, 2012
Abstract. Progesterone has a potential protective effect
against ovarian carcinoma induced by estrogen. Progesterone
is also known to cause apoptosis while tamoxifen induces
growth arrest. Therefore, we attempted to determine whether
combined treatment with progesterone and tamoxifen
has a synergistic effect on anti-cancer activity. Although
progesterone is known to cause apoptosis while tamoxifen
induces growth arrest in many cancer cells, the detailed action
of progesterone and tamoxifen and the anticancer effect of
combined treatment have not been tested in ovarian cancer
cells. Therefore, we tested the growth and apoptosis activity
of progesterone and tamoxifen and the anticancer effect of
combined treatment of progesterone and tamoxifen in ovarian
cancer cells. Ovarian cancer cells, PA-1, were treated with
progesterone, tamoxifen, or a combination of progesterone
and tamoxifen. The anti-cancer effects were investigated by
use of flow cytometry, terminal deoxynucleotidyl transferase
dUTP nick end labeling (TUNEL) assay, DNA fragmentation
analysis, and Western blot analysis. We found that 100 µM
progesterone induced typical apoptosis in PA-1 cells.
Treatment of PA-1 cells with 10 µM tamoxifen resulted in
an increase in the levels of p21, p27, p16 and phospho-pRb,
indicating typical G1 arrest. Co-treatment of PA-1 cells with
100 µM progesterone and 10 µM tamoxifen resulted in typical
apoptosis, similar to that induced by treatment with 100 µM
progesterone alone. These results indicate that progesterone
caused apoptosis and tamoxifen induced G1 arrest. Combined
treatment with tamoxifen and progesterone caused apoptosis
similar to that induced by treatment with progesterone alone
and had no additional anti-cancer effect in ovarian cancer cells.
Ovarian carcinoma is one of the most common fatal gyneco-
logic malignancies and is characterized by an insidious onset
and a lack of early specific symptoms. About two-thirds of
patients with ovarian carcinoma usually present with advanced
ovarian carcinoma and have widespread tumor dissemination.
Unfortunately, the most effective strategy for the management
of ovarian carcinoma is yet to be determined. Although Taxol
and platinum-based combination chemotherapy is a standard
treatment for ovarian carcinoma and has achieved a high
response rate, its success is limited by the development of drug
resistance (1). Therefore, it is important to explore alternative
treatment modalities that have favorable cost benefit ratios in
terms of toxicity and do not lead to the development of drug
resistance or disease relapse.
It has been reported that estrogen and progesterone are
involved in the etiology and long-term survival of patients with
ovarian carcinoma. In 1963, Long and Evans (2) suggested for
the first time that ovarian carcinoma might be sensitive to
hormones. According to their report, the use of diethylstilbes-
trol in 14 patients with advanced ovarian carcinoma led to a
partial response in 4 (28%) patients. The incidence of ovarian
carcinoma is increased among women after menopause
because of lower levels of sex steroids. Estrogen replacement
therapy in postmenopausal women does not reduce the risk
of ovarian carcinoma. However, the risk may be reduced by
use of combination-type oral contraceptives, which contain
estrogen and a high dose of progesterone. Recent studies
have reported the presence of estrogen, progesterone, and
androgen receptors in varying concentrations and combina-
tions in ovarian carcinoma (3). According to the results of
many studies, although estrogen is proposed to facilitate the
induction of ovarian carcinoma, progesterone has a potential
protective effect (4,5). Progesterone has strong effects on
Effect of combined treatment with progesterone and tamoxifen
on the growth and apoptosis of human ovarian cancer cells
JI-YOUNG LEE3, JONG-YEON SHIN4, HYUN-SEOK KIM5, JEE-IN HEO1,2, YOON-JUNG KHO2,
HONG-JUN KANG6, SEONG-HOON PARK1,5 and JAE-YONG LEE1,2
1Department of Biochemistry and 2Institute of Natural Medicine, College of Medicine, Hallym University, Chuncheon,
Gangwon-do 200-702, Republic of Korea; 3Department of Obstetrics and Gynecology, Sisters of Charity Hospital,
State University of New York at Buffalo, Buffalo, NY 14214, USA; 4Genomic Medicine Institute, Medical Research
Center, Seoul National University, Seoul, Republic of Korea; 5Molecular Radiation Oncology, Radiation Oncology Branch,
Center for Cancer Research, NCI, NIH, Bethesda, MD 20892; 6Genetic Disease Research Section,
NIDDK, National Institutes of Health, Building 10, Room 9D11, Bethesda, MD 20892, USA
Received June 9, 2011; Accepted July 28, 2011
Correspondence to: Dr Jae-Yong Lee, Department of Biochem-
istry, College of Medicine, Hallym University, 1 Okcheon-dong,
Chuncheon, Gangwon-do 200-702, Republic of Korea
Key words: ovarian cancer cell line, progesterone, tamoxifen,
apoptosis, growth arrest
ONCOLOGY REPORTS 27: 87-93, 2012
did not happen. Currently, we do not have an answer as to why
One plausible explanation is the following. It has been
proposed that the binding of p53 to specific p53 response
elements differs greatly. Low-affinity sites appear to be
associated with growth arrest-related genes, while high-
affinity sites are more related to proapoptotic genes (16,17).
Ubiquitination of p53 in response to mild damage is known to
be associated with growth arrest-related genes, and acetylated
and phosphorylated p53 proteins activate proapoptotic genes
in response to severe damage. In addition, p53-interacting
proteins like HZF interact directly with the p53 DNA-binding
domain to activate p21 while proapoptotic genes are attenu-
ated. In contrast, CAS is associated with p53 on the promoters
of several proapoptotic genes. This relieves the inhibitory
H3K27 methylation within the transcribed region of those
genes, thereby increasing their transcription and facilitating
apoptosis (18,19). Therefore, tamoxifen treatment appears
to cause mild damage in which p53 induces growth arrest
whereas progesterone treatment causes severe damage, which
results in apoptosis. Combined treatment seems to induce a
severe form of damage, resulting in apoptosis similar to the
case of progesterone treatment.
We still do not know the detailed mechanism of how p53
decides between growth arrest and apoptosis in PA-1 cells
subjected to these treatments. Combined treatment is used in
many therapeutic cancer regimes since it sometimes results in
synergistic effects on cancer. Some cell death-inducing agents
that induce the death of cancer cells via different pathways
will exert a synergistic effect. Even combined treatment with
apoptosis-inducing agents will be advantageous if the two
agents involve different apoptosis pathways. However, the
combination of an anti-cancer medicine that induces growth
arrest and another that induces apoptosis may not be recom-
mended as the combination will not have an advantageous
effect. Further detailed characterization of the mechanisms
of action of these medicines in p53-deleted or p53-mutated
ovarian cancer cells may provide a better understanding of
these treatment methods.
This study was supported by Priority Research Centers Program
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education, Science and Technology
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