Failure to detect gonadotrophin-releasing hormone receptors in human benign and malignant breast tissue and in MCF-7 and MDA-MB-231 cancer cells

Abstract

We have measured the binding of radiolabelled analogues of gonadotrophin-releasing hormone (GnRH) to homogenates of human breast cancer and benign breast tissue, and to MCF-7 and MDA-MB-231 cell lines. Although incubation of breast cancer homogenates with the 125I-labelled GnRH agonist analogues, buserelin [(D-Ser tBU 6)GnRH 1–9 ethylamide] and tryptorelin [(D-Trp 6) GnRH 1–9 ethylamide] appeared to show significant though low, specific GnRH agonist binding in a high proportion of breast cancers ( 32 42 for buserelin; 15 32 for tryptorelin) and benign breast tissues ( 13 16 for buserelin; 10 12 for tryptorelin), after correction for displaceable binding in control assay tubes, GnRH agonist binding to breast tissue was no longer apparent. The lack of specific binding was not due to inactivation of GnRH agonist tracers, as >86% of the unbound tracer was still capable of rebinding to fresh placental membranes after incubation with breast cancer homogenates. GnRH agonist did not bind to MCF-7 and MDA-MB-231 cells, however GnRH agonist tracer inactivation following exposure to these cells was very high. We have shown recently that human placental receptors bound salmon GnRH and chicken GnRH II as well as GnRH agonists, but not other isoforms of GnRH. However, no isoform of GnRH bound significantly to human breast tumour tissue. In summary, we could not confirm the presence of specific GnRH binding sites in homogenates and membranes from human breast tissues in this study. Low levels of apparently specific binding of GnRH agonist tracers could be accounted for entirely by displacement of tracer from assay tubes. Inability to demonstrate specific binding was not due to extensive inactivation of GnRH tracers (although this may be a factor in the failure to demonstrate GnRH binding to MCF-7 and MDA-MB-231 cell lines).