Gonadotropin-Releasing Hormone (GnRH)-Binding Sites in Human Breast Cancer Cell Lines and Inhibitory Effects of GnRH Antagonists*

Abstract

GnRH-binding sites have previously been described in human breast tumors, and a GnRH agonist has been shown to inhibit growth of the MCF-7 human breast cancer cell line. We have investigated the presence of GnRH-binding sites in ZR-75-1, MDA-MB-231, Sk Br 3, MDA-MB-157, and MCF-7 human breast cancer cell lines and the effect of GnRH analogs on the incorporation of [3H]thymidine and 14C-labeled amino acids into DNA and protein. Specific GnRH-binding sites were present in membrane preparations of all five human breast carcinoma cell lines. Studies in three cell lines indicated low affinity (Kd, 1.6-3.0 X 10(-6) M) GnRH binding similar to that reported in human placenta and corpus luteum. In contrast, human pituitary GnRH receptors were of high affinity (Kd, 4.8 X 10(-9) M). Breast carcinoma cell GnRH-binding sites also differed from the pituitary receptor in their inability to discriminate between GnRH and superactive analogs. Binding of a [125I]GnRH analog to ZR-75-1 breast cancer cells and pituitary membranes was affected similarly by various cations. GnRH antagonists rapidly inhibited [3H]thymidine incorporation into DNA (within 3 hr), and this effect was reversible. GnRH antagonists also inhibited cell growth, but only after 6 days. GnRH agonists did not alter either thymidine incorporation or growth. The present observations of low affinity GnRH-binding sites in breast cancer cell lines and inhibitory effects of GnRH antagonists point to the possibility of an autocrine regulatory role of GnRH-like peptides in mammary cells.

Diversity of actions of GnRHs mediated by ligand-induced selective signaling

“…The presence of GnRH receptors in breast cancer tissue [31] and the demonstration of antiproliferative actions of GnRH analogs in breast cancer cell lines [32,47,96] supported this interpretation. Antiproliferative effects of GnRH analogs and the expression of GnRH receptors have now been demonstrated in a number of cell lines of reproductive tract tumors, including prostate, uterine and ovarian cancers, and also in nonreproductive tract tumors [21,43,47,70,73,79].…”

“…15). A number of antagonists of gonadotrope GnRH receptors act as GnRH agonists in the inhibition of tumor cell lines [32,34,44,81,128].…”

Expression of the gene for the receptor of gonadotropin‐releasing hormone in the rat mammary gland

“…Only low-affinity binding could be demonstrated (Fig. 3) failed to demonstrate high-affinity binding of GnRH to noncarcinogenic mammary tissue [21,22]. It was suggested that this discrepancy might be due to activation of some genes as a result of carcinogenic transformation.…”

“…In both reports, the extrapituitary GnRH receptor transcripts were found to have nucleotide sequence identical with that of the pituitary gland. Although GnRH analogs have been demonstrated to exhibit direct effects on growth rate of MCF-7 cells [3,4,24], the affinity and even the detection of specific binding sites for GnRH in this cell line is still a matter of controversy [21,22,24]. Heterogeneity of receptors has been recognized to be an efficient way for obtaining different biological responses to a single hormone stimulation.…”

Complete regression of MX-1 human breast carcinoma xenografts after targeted chemotherapy with a cytotoxic analog of luteinizing hormone-releasing hormone, AN-207

“…3 LH-RH receptors also have been demonstrated in estrogen-independent MXT mouse mammary tumor 5,6 and in many human breast carcinoma cell lines. [7][8][9][10] In the past decade, various cytotoxic LH-RH analogs have been synthesized in our laboratory. 11 These hybrids consisted of various cytotoxic agents linked to LH-RH agonists or antagonists.…”