Inhibition of growth of human malignant glioblastoma in nude mice by antagonists of bombesin/gastrin-releasing peptide

The effects of antagonists of bombesin/gastrin-releasing peptide (GRP) on t he growth of human malignant glioblastoma cell line U-87MG xenografted into nude mice were evaluated. Nude mice bearing s.c. implanted U-87MG tumors w ere treated with bombesin/GRP antagonists RC-3095 and RC-3940-II. RC-3095 a nd RC-3940-II administered s.c. at a dose of 20 mu g/day for 4 weeks decrea sed the volume of U-87MG xenografts by 60 and 74%, respectively, compared w ith controls. RT-PCR analysis showed that U-87MG xenografts expressed mRNA for bombesin receptor subtype (BRS)-1 (GRP receptor) and BRS-2 (neuromedin- B receptor), but the mRNA for GRP ligand was not detected in U-87MG cells s uggesting that GRP may stimulate the growth of U-87MG glioblastomas by a pa racrine mechanism. The levels of mRNA for c-fos oncogene mere decreased by 30-40% in U-87MG tumors treated with RC-3095 or RC-3940-II. In U-373MG glio blastoma cells, which also express BRS-1, and U-87MG cells, cultured in vit ro, GRP(14-27) induced the expression of c-fos mRNA, and some c-jun mRNA, i n a time-dependent manner with the maximal effect occurring 2 h after the s timulation and a return to basal levels after 8 h. Antagonist RC-3940-II in hibited the stimulation of c-fos by GRP(14-27), Our results indicate that a ntagonists of bombesin/GRP inhibit the growth of U-87MG glioblastomas by a mechanism that may involve the downregulation of c-fos oncogene.