HIGH-AFFINITY BINDING AND DIRECT ANTIPROLIFERATIVE EFFECTS OF LUTEINIZING-HORMONE-RELEASING HORMONE ANALOGS IN HUMAN ENDOMETRIAL CANCER CELL-LINES

Although specific binding sites for LH-releasing hormone (LHRH) and it s analogs have been demonstrated in biopsy samples of human endometria l cancer, their biological significance remains obscure. In this study we evaluated whether binding sites for LHRH are also present in the h uman endometrial cancer cell Lines HEC-1A and Ishikawa and if such sit es could mediate antiproliferative effects of LHRH analogs. Using [I-1 25,D-Trp(6)]LHRH as a ligand, a high affinity/low capacity binding sit e was detected in both lines: HEC-1A line, dissociation constant (K-d) (1) = 5.7 X 10(-9) mol/L, binding capacity (B-max)(1) = 78 fmol/10(6) cells; Ishikawa line, K-d1 = 4.2 X 10(-9) mol/L, B-max1 = 29 fmol/10(6 ) cells. In addition, a second class of low affinity/high capacity bin ding sites for LHRH was demonstrated (HEC-1A line, K-d2 = 1.4 x 10(-6) mol/L, B-max2 = 21 pmol/10(6) cells; Ishikawa, K-d2 = 4 X 10(-6) mol/ L, B-max2 = 32 pmol/10(6) cells). In the presence of 10(-5) mol/L agon ist [D-Trp(6)]LHRH (triptorelin), the proliferation of HEC-1A and Ishi kawa cell lines was significantly reduced to 76+/-2% and 88+/-4% of co ntrols, respectively, after 24 h and to 64+/-2% and 62+/-2%, respectiv ely, after 6 days. Dose-response experiments showed that lower concent rations (10(-9) mol/L) of the agonist decreased the proliferation to 8 0+/-1% for the HEC-1A line and 71+/-2% of controls for the Ishikawa li ne after 6 days. Antiproliferative effects are enhanced by increasing the doses of triptorelin and were maximal in this series of experiment s at 10(-5) mol/L, the proliferation in the HEC-1A line being 62+/-1% and in the Ishikawa line 52+/-2% of controls, respectively. Similar ti me- and dose-dependent antiproliferative effects were obtained in both cell lines with the LHRH antagonist SB-75 (cetrorelix). These data su ggest that LHRH analogs can directly inhibit the proliferation of huma n endometrial cancer cells in vitro. This direct action could be media ted through the high affinity LHRH binding sites.