Antagonists of growth hormone-releasing hormone (GH-RH) inhibit in vivo proliferation of experimental pancreatic cancers and decrease IGF-II levels in tumours.
Insulin-like growth factors (IGF-I and IGF-II) are implicated in the pathogenesis of pancreatic carcinoma. Antagonists of growth hormone-releasing hormone (GH-RH) suppress the GH-RH-GH-IGF-I axis and also act directly on tumours to reduce production of IGF-I or II. The aim of this study was to investigate the effects of two potent GH-RH antagonists in two experimental models of pancreatic cancer. Syrian golden hamsters with nitrosamine-induced pancreatic tumours were treated with 10 micrograms/day of GH-RH antagonist MZ-4-71 for 60 days. The therapy reduced the number of tumorous animals, decreased the weight of tumorous pancreata by 55%, and lowered AgNOR numbers in tumour cells. In two other experiments, GH-RH antagonists MZ-4-71 and MZ-5-156 significantly inhibited growth of SW-1990 human pancreatic cancers xenografted into nude mice, as shown by a reduction in tumour volume and tumour weights, and a decrease in AgNORs in cancer cells. IGF-I levels in serum and in pancreatic cancer tissue remained unchanged after therapy, suggesting that an effect on IGF-I is not involved in tumour inhibition. In contrast, IGF-II concentrations in tumours were significantly reduced by 50-60% after treatment with the GH-RH antagonists as compared with controls. In vitro studies showed that the concentration of IGF-II in the culture medium was increased after seeding of SW-1990 cells, indicating that this pancreatic cancer cell line produced and released IGF-II. This finding was also supported by the expression of IGF-II mRNA in the SW-1990 cells. Addition of 3 x 10(-6) M of GH-RH antagonist MZ-5-156 to the reduced-serum medium decreased cell proliferation, IGF-II mRNA expression in the cells and IGF-II concentration in the medium. Our findings indicate that inhibitory effects of GH-RH antagonists on the growth of experimental pancreatic cancers, may result from a decrease in the production and concentration of IGF-II in the tumours.
Szepeshazi
K
K
Endocrine, Polypeptide and Cancer Institute, Veterans Affairs Medical Center, New Orleans, LA 70146, USA.
Schally
A V
AV
Groot
K
K
Armatis
P
P
Hebert
F
F
Halmos
G
G
D000818:Animals; D002455:Cell Division; D006224:Cricetinae; D004354:Drug Screening Assays, Antitumor; D005260:Female; D013006:Growth Hormone / Q000097:blood; D013007:Growth Hormone-Releasing Hormone / Q000037:antagonists & inhibitors*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D008297:Male; D008647:Mesocricetus; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000378:metabolism*; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000517:prevention & control*; D017337:Sermorelin / Q000031:analogs & derivatives* / Q000494:pharmacology
C095215:MZ 4-71; C106656:MZ 5-156; D009363:Neoplasm Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017337:Sermorelin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone