Insulin-like growth factor-II participates in the biphasic effect of a gonadotropin-releasing hormone agonist on ovarian cancer cell growth

Abstract

Objective: To examine the involvement of insulin-like growth factors (IGFs) in growth regulation of an ovarian cancer cell line and to investigate whether the GnRH agonist tryptorelin might influence a potential autocrine or paracrine loop involving IGFs.

Design: In vitro, prospective, randomized controlled study.

Setting: In vitro experiments at the Section of Gynecologic Oncology, Surgery Branch, National Cancer Institute.

Patient(s): None. Human ovarian adenocarcinoma cell line IGROV-1.

Intervention(s): The proliferative effect of tryptorelin on IGROV-1 cells was analyzed by using the MTT (93-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide) colorimetric assay. The ribonuclease protection assay was used to investigate whether an autocrine pathway involving IGF-I or IGF-II might participate in the growth of these cells. The expression of GnRH receptor was assessed by the 125I-GnRH binding assay.

Main outcome measure(s): Changes in cell growth and expression of IGF-I and IGF-II messenger RNA (mRNA).

Result(s): Tryptorelin exhibited a bimodal, dose- and time-dependent effect on IGROV-1 cells when compared with untreated control cells: Cellular proliferation was enhanced during the first 24 hours of exposure, but longer incubations resulted in growth inhibition. The mitogenic effect of tryptorelin was inhibited when cells were co-incubated with either IGF binding protein-5 (IGFBP-5) or anti-IGF-II antibody, which can both bind to IGF-II and neutralize it. Insulin-like growth factor-I mRNA was not detected in IGROV-1 cells. However, IGF-II transcripts were detected after incubation with tryptorelin for 12 hours, but thereafter, no mRNA was observed, even after prolonged exposure. Binding analysis revealed a specific, high-affinity GnRH binding site.

Conclusion(s): These data suggest that tryptorelin exerts a bimodal growth effect on ovarian cancer cells by a mechanism involving the autocrine production of IGF-II. The effect of tryptorelin on IGF-II gene transcription in these ovarian cancer cells appears to mirror the desensitizing effects of prolonged GnRH exposure on pituitary gonadotropin production.