HIGH-AFFINITY BINDING AND DIRECT ANTIPROLIFERATIVE EFFECTS OF LHRH ANALOGS IN HUMAN OVARIAN-CANCER CELL-LINES

Recently, specific binding sites for luteinizing hormone releasing hor mone (LHRH) and its analogues have been demonstrated in biopsy samples of human epithelial ovarian cancer. Their biological significance rem ained obscure. In this study we ascertained whether such LHRH-binding sites are also present in the human epithelial ovarian cancer cell lin es EFO-21 and EFO-27 and if they could mediate antiproliferative effec ts of LHRH analogues. Using [I-125, D-Trp6]LHRH, a high affinity/low c apacity binding site was detected in both lines: EFO-21 (Kd1 = 1.5 x 1 0(-9) M; binding capacity (Bmax1) = 4.9 fmol/10(6) cells) and EFO-27 ( Kd1 = 1.7 x 10(-9) M; Bmax1 = 3 fmol/10(6) cells). In addition, a seco nd class of low affinity/high capacity binding sites (EFO-21: Kd2 = 7. 5 x 10(-6) M; Bmax2 = 24 pmol/10(6) cells; EFO-27: Kd2 = 4.3 x 10(-6) M; Bmax2 = 14.5 pmol/10(6) cells) was demonstrated. Specific binding o f [I-125, D-Trp6]LHRH was displaced with nearly equal efficiency by un labeled [D-Trp6]LHRH, the LHRH-antagonists SB-75 and Hoe-013, and by n ative LHRH but not by unrelated peptides such as oxytocin and somatost atin. In the presence of 10(-5) M agonist [D-Trp6]LHRH, the proliferat ion of both cell lines was significantly reduced to 77% of controls af ter 24 h and to approx. 60% after 6 days. Lower concentrations (10(-9) M) of the agonist, significantly decreased the proliferation to 87.5% for EFO-21 and 86% for EFO-27 after 6 days. These antiproliferative e ffects were enhanced by increasing doses of [D-Trp6]LHRH and were maxi mal at 10(-5) M (EFO-21: 65.5% of control, EFO-27: 68% of control). Si milar dose-dependent antiproliferative effects were obtained in EFO-21 line with the LHRH-antagonists SB-75 and Hoe-013, while these analogu es had no effects on the proliferation of EFO-27 cells. SB-75 partly a ntagonized the antiproliferative effect of [D-Trp6]LHRH in a dose depe ndent way in the EFO-27 line. These data suggest that LHRH analogues c an directly inhibit the in vitro proliferation of human ovarian cancer cells. This effect might be mediated through the high affinity LHRH b inding sites.