Estrogen-depleted condition induces apoptosis of rat mammary cancer cells after entering the S-phase of the cell cycle.
To elucidate the relationship of estrogen-depleted condition to apoptosis and tumor regression, 7,12-dimethylbenz[a]anthracene-induced mammary cancers of Sprague-Dawley rats were ovariectomized or treated with the anti-estrogenic agent epitiostanol after which proliferative activity and the incidence of apoptosis were investigated using the nick end labeling method, agarose gel electrophoresis of DNA, electron microscopy, the BrdU-labeling method and mitotic count. Tumor regression was found after 7-day treatment, and apoptosis induced by the agent on the 3rd day was clearly shown in both agarose gel electrophoresis of DNA and electron microscopy, which are two major methods used to judge apoptosis. The incidence of apoptosis revealed by the nick end labeling method reached its maximum, about threefold the control level, on the 3rd day of epitiostanol treatment compared with control tumors (P < 0.01). The incidence of the cells incorporating BrdU reached its maximum of 9.7% on the 2nd day of the treatment, while the incidence in tumors without treatment was 7.5% (P < 0.05). Subsequently, the incidence of apoptosis was reduced after 7-day treatment, and the incidence of BrdU-positive cells was significantly reduced to about 3% after 5-day treatment. The incidence of mitosis did not change until the 3rd day of the treatment and was reduced after 5-day treatment. Similarly, chronological changes of the incidences of BrdU-labeled cells, apoptotic cells and mitosis were observed in the tumors after ovariectomy. BrdU-labeled apoptotic bodies were detected in the tumors on the 3rd day in epitiostanol-treated rats that received a 6-hr bolus of BrdU before sacrifice.(ABSTRACT TRUNCATED AT 250 WORDS)
Watanabe
Y
Y
Department of Pathology, Sapporo Medical University School of Medicine, Japan.
Sawada
N
N
Isomura
H
H
Satoh
H
H
Hirata
K
K
Mori
M
M
D000732:Androstanols / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D004965:Estrogen Antagonists / Q000494:pharmacology; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D016196:S Phase / Q000187:drug effects
D000732:Androstanols; D004965:Estrogen Antagonists; D004967:Estrogens; C002976:epitiostanol