Antagonists of growth hormone-releasing hormone in oncology.
The development of antagonists of growth hormone (GH) - releasing hormone (GH-RH) is reviewed. GH-RH antagonists bind with a high affinity to pituitary receptors for GH-RH and inhibit the release of GH in vitro and in vivo. The main applications of GH-RH antagonists would be for tumor therapy. The antitumor effects of GH-RH antagonists are exerted in part indirectly through the inhibition of the secretion of pituitary GH and the reduction in the levels of hepatic insulin like growth factor (IGF-I). However, principal effects of the GH-RH antagonists are exerted directly on tumors. Antagonists of GH-RH inhibit the proliferation of various cancer cell lines in vitro and suppress in vivo the levels and the expression of mRNA for IGF-I and IGF-II in tumors. In many human cancers, the effects of GH-RH antagonists appear to be due to the blockade of the action of tumoral GH-RH. GH-RH ligand is present in various human cancers indicating that it may be an autocrine/paracrine growth factor. Splice variants (SVs) of GH-RH receptors and pituitary type of GH-RH receptors that might mediate effects of tumoral GH-RH and of GH-RH antagonists were demonstrated in many human cancers. This suggests the presence of a stimulatory loop based on GH-RH and SVs or pituitary type of GH-RH receptors in diverse tumors. It was shown that GH-RH antagonists inhibited the growth of various human cancer lines xenografted into nude mice including mammary, ovarian, endometrial and prostate cancers, small cell lung carcinomas (SCLC) and non-SCLC, renal, pancreatic, gastric and colorectal carcinomas, malignant gliomas, osteosarcomas and Non-Hodgkin's lymphomas. Further development of GH-RH antagonists should lead to potential therapeutic agents for various cancers.
Endocrine, Polypeptide and Cancer Institute, Veterans Affairs Medical Centers, New Orleans, LA 70112, USA. andrew.schally@va.gov
Andrew V
AV
Schally
Jozsef L
JL
Varga
D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D013007:Growth Hormone-Releasing Hormone / Q000037:antagonists & inhibitors*; D006801:Humans; D051379:Mice; D009369:Neoplasms / Q000145:classification / Q000188:drug therapy* / Q000473:pathology
D000970:Antineoplastic Agents; D013007:Growth Hormone-Releasing Hormone