Download Kyung-Hee Chun

Rapamycin, mTOR Inhibitor, Inhibits the Cell Growth and
Proliferation by Mitotic Arrest in Human Gastric Cancer Cells.
Kyung-Hee Chun, Ph.D
Center for Uterine Cancer, National Cancer Center, 809-Madu-1-dong,
Ilsan-gu, Goyang, Geonggi-do, 411-769, Korea
Although decreasing mortality by the improved prognosis, early diagnosis,
surgery and adjuvant therapy, gastric cancer is still the most common and the second
leading cause of cancer-related deaths in northeast Asia, including Korea and Japan.
The only available treatment to cure gastric cancer is detection of early stage disease
and surgical resection. Therefore, improvement of survival rates and treatment is
needed in gastric cancer patients, one of the promising approaches is the development of
novel therapeutic drugs that specifically target molecular regulators of cancer growth
and proliferation. Interestingly, the highly activation of phosphatidylinositol 3-kinase
(PI3K)/Akt (protein kinase B) signaling pathway was reported in tissues of gastric
cancer patients, the inhibition of PI3K/Akt signaling pathway is a good candidate in
gastric cancer treatment. The mammalian target of rapamycin (mTOR), a downstream
effecter of the PI3K/Akt signaling pathway plays the important roles to mediate cell
survival and proliferation, and one of potent mTOR inhibitor, rapamycin has been
underwent clinical trials. However, the exact role of rapamycin in mediating growth
inhibitory effects in gastric cancers is not yet clear.
In this study, it was demonstrated mTOR inhibition by rapamycin on gastric
cancer proliferation with focus on its cell cycle arrest activity. After treatment with
rapamycin in 6 gastric cancer cell lines, AGS, SNU216, and SNU638 cells were most
sensitive by dose- and time- dependent manner. Rapamycin inhibited gastric cancer
cell growth significantly, compared to other cell lines derived cancers that undergo
clinical trial. To elucidate the mechanism by rapamycin in gastric cancers, cell cycle
arrest was detected by PI staining. AGS cells showed G2/M arrest after 1 to 3 day
treatment with rapamycin. However, rapamycin sensitive MCF7 (breast
adenocarcinoma) or H549 (lung adenocarcinoma) was detected G1 arrest and/or
apoptosis instead of G2/M arrest, it was suggested that G2/M arrest by rapamycin is cell
type and/or organ specific manner in gastric cancer. Rapamycin also changed the
expression levels of cell cycle related proteins. Interestingly, p21 expression increased
and sustained until 48 hr after treatment in AGS. The protein expression of p27 and
p53 was not detected in change. Cdc2 and cyclin B1 increased and cdc25c decreased
after treatment. Increasing levels of polo like kinase 1 (PLK1) and aurora A, and
phosphorylated histone H3, which was known mitotic arrest index, also were detected
after rapamycin treatment. It supposed that rapamycin arrests cell cycle in late G2
and/or in mitotic phase. We confirmed that mitotic arrest by rapamycin in AGS cells,
mitotic arresting shaped cells increased almost 25% compared to control, and
phosphorylated histone H3 staining cells were found in rapamycin treated or in
nocodazole treated gastric cancer cells, but not in control cells. Finally, it was detected
by confocal microscope that rapamycin treatment prevented centrosome maturation and
mitotic spindle bypolarity, and resulted in accumulation of aberrant prometaphase cells.
In summary, it was demonstrated that rapamycin inhibits gastric cancer cell
growth by mitotic arrest to accumulate abnormal prometaphase cells. Our results
suggest that rapamycin, clinically useful mTOR inhibitor is promising in the treatment
of gastric cancer and further clinical studies are needed to validate the therapeutic
potential of rapamycin in gastric cancer patients.
Kyung-Hee Chun
1994
Faculty of Pharmacy, Duksung Women’s University Seoul, Korea.
1996
Master, Graduate School of Pharmacy, Duksung Women’s University
Seoul, Korea.
2000
Ph.D., Graduated School of Pharmaceutical Science, Functional biology,
Tokyo university, Tokyo, Japan.
2003
Postdoctoral Fellow, Thoracic Head&Neck Medical Oncology, MD
Anderson Cancer Center, Houston, TX, USA.
2006
Instructor, Thoracic Head&Neck Medical Oncology, MD Anderson
Cancer Center, Houston, TX, USA.
Present
Senior Scientist, Center for gastric cancer, National Cancer Center,
Koyang, Kyonggi, Korea.
Specialty and Present Interest:
Developing new drugs for cell cycle arrest and apoptosis induction.
Phone: 82-31-920-2385; FAX: 82-31-920-2316; E-mail: [email protected]