We investigated the direct effects of
LH-releasing hormone (
LH-RH) antagonist,
Cetrorelix, on the growth of HTOA human
epithelial ovarian cancer cell line. RT-PCR revealed the expression of
mRNA for
LH-RH and its receptor in HTOA cells.
Cetrorelix, at concentrations between 10(-9) and 10(-5) M, exerted a dose-dependent antiproliferative action on HTOA cells, as measured by
5-bromo-2'-deoxyuridine incorporation into
DNA. Flow cytometric analysis indicated that
Cetrorelix,
at 10(-5) M, arrested cell cycle in HTOA cells, at G1 phase, after 24 h of treatment. Western blot analysis of
cell cycle-regulatory proteins demonstrated that treatment with
Cetrorelix (10(-5) M) for 24 h did not change the steady-state levels of
cyclin D1,
cyclin E, and
cyclin-dependent kinase (Cdk)4 but decreased the levels of
cyclin A and Cdk2. The
protein levels of p21 (a Cdk inhibitor) and p53 (a suppressor of
tumor cell growth and a positive regulator for p21 expression) were increased by
Cetrorelix, but the levels of p27 (a Cdk inhibitor) did not change significantly. Flow cytometric analysis and terminal
deoxynucleotidyltransferase-mediated
deoxyuridine 5-triphosphate nick end labeling staining demonstrated that
Cetrorelix (10(-5) M) induced apoptosis in HTOA cells. In conclusion,
Cetrorelix directly inhibits the proliferation of human
epithelial ovarian cancer cells through mechanisms mediated by
LH-RH receptor and involving multiple events in cell cycle progression, including G1 phase cell cycle arrest coupled with down-regulation of
cyclin A-Cdk2 complex levels, presumably attributable to an up-regulation of p53 and p21
protein levels and apoptosis.