Direct effects of luteinizing hormone-releasing hormone agonists and antagonists on MCF-7 mammary cancer cells.
The binding of luteinizing hormone-releasing hormone (LH-RH) analogues to the human mammary tumor cell line MCF-7 and their effect on the cell proliferation was studied to elucidate their direct action on estrogen-dependent mammary tumors. The growth rate of these cells was doubled by the addition of 1 nM estradiol to cells maintained in an estrogen-deficient medium. Although the basal growth rate was only slightly inhibited by the LH-RH antagonist [Ac-D-Nal(2)1,D-Phe(pCl)2,D-Pal(3)3,D-Cit6,D-Ala10]LH-RH (SB-75), the estrogen-stimulated growth was completely abolished by the antagonist. In contrast, the LH-RH agonist buserelin stimulated cell growth in estrogen-deficient medium, whereas it had no effect in the presence of estrogen. 125I-labeled buserelin was used for the measurement of LH-RH receptors on MCF-7 cells. A Scatchard plot analysis of buserelin-specific binding revealed a nonlinear plot, which suggested the presence of one high-affinity binding site with a Kd of 1.4 +/- 1.0 nM and the remaining sites with low affinity (Kd = 1.3 +/- 1.0 microM). The binding of 125I-labeled buserelin was displaced equally well by unlabeled buserelin and by the LH-RH antagonist SB-75, suggesting that both analogues are bound to the same receptor. When parallel experiments were performed with 125I-labeled SB-75, the binding was displaced by unlabeled SB-75 and other antagonists, but only partially displaced by unlabeled buserelin. The results suggest that in these mammary tumor cells there is a LH-RH antagonist binding site that is not recognizable by LH-RH agonists. This hypothesis was tested by measuring cell growth in the presence of both agonists and antagonists. It was found that SB-75 inhibited the stimulation of growth by buserelin, but buserelin did not prevent the inhibition by the antagonist of the estrogen-dependent growth. These results suggest that antagonists directly inhibit mammary tumor growth, not only by competing with LH-RH high-affinity receptors, but also by other mechanisms mediated by low-affinity antagonist binding sites.
Segal-Abramson
T
T
Clinical Biochemistry Department, Faculty of Health Sciences, Soroka Medical Center, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Kitroser
H
H
Levy
J
J
Schally
A V
AV
Sharoni
Y
Y
D000970:Antineoplastic Agents / Q000494:pharmacology; D001943:Breast Neoplasms; D002064:Buserelin / Q000378:metabolism / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D011966:Receptors, LHRH / Q000378:metabolism*; D017329:Triptorelin Pamoate
D000970:Antineoplastic Agents; D011966:Receptors, LHRH; D017329:Triptorelin Pamoate; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; C062876:cetrorelix; D002064:Buserelin