Characterization of receptors for growth hormone-releasing hormone in human osteosarcomas and Ewing's sarcomas.
Antagonists of growth hormone-releasing hormone (GH-RH) inhibit growth of various human cancers including osteosarcomas and Ewing's sarcomas, xenografted into nude mice or cultured in vitro. The antiproliferative effect of GH-RH antagonists could be mediated, in part, through the splice variants (SVs) of receptors for GH-RH which have been found in several human cancers and cancer cell lines. In this study we investigated the expression of SVs of GH-RH receptors and the binding characteristics of these receptor isoforms in MNNG/HOS human osteosarcoma and SK-ES-1 human Ewing's sarcoma grown in nude mice. RT-PCR revealed the presence of mRNA for SVs of GH-RH receptors in both human malignant bone cancer models. Using ligand competition assays with 125I-labeled GH-RH antagonist JV-1-42, we demonstrated in MNNG/HOS and SK-ES-1 tumors the presence of specific high affinity binding sites for GH-RH (Kd=5.83 nM and Kd=2.76 nM) with a maximal binding capacity (Bmax) of 552.1 fmol/mg protein and 371.9 fmol/mg protein, respectively. We also investigated the effect of GH-RH antagonist JV-1-38, administered s.c. at a dose of 20 microg twice daily for 4 weeks on the gene expression, affinity and concentration of receptors for GH-RH in MNNG/HOS human osteosarcomas xenografted into nude mice. Treatment with JV-1-38 did not affect the expression and binding characteristics of GH-RH receptors. High affinity binding of JV-1-38 to GH-RH receptors on MNNG/HOS tumors was characterized by an IC50 value of 1.04 nM. The presence of GH-RH receptors in human bone tumors provides a rationale for new approaches to the therapy of this malignancy based on GH-RH antagonists.
Halmos
Gabor
G
Department of Biopharmacy, University of Debrecen, School of Pharmacy, H-4032 Debrecen, Hungary. halmos@king.pharmacol.dote.hu
Schally
Andrew V
AV
Bernardino
Andrea L F
AL
Varga
Jozsef L
JL
D000818:Animals; D045744:Cell Line, Tumor; D013007:Growth Hormone-Releasing Hormone / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D051379:Mice; D009368:Neoplasm Transplantation; D012516:Osteosarcoma / Q000378:metabolism*; D011485:Protein Binding; D018013:Receptors, Neuropeptide / Q000737:chemistry*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000737:chemistry*; D012512:Sarcoma, Ewing / Q000378:metabolism*
D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D013007:Growth Hormone-Releasing Hormone; C048250:somatotropin releasing hormone receptor