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Journal of Cancer Research and Clinical Oncology logoLink to Journal of Cancer Research and Clinical Oncology
. 1994 Sep;120(9):519–528. doi: 10.1007/BF01221028

Bombesin antagonists inhibit in vitro and in vivo growth of human gastric cancer and binding of bombesin to its receptors

Yunfeng Qin 1,2, Gabor Halmos 1,2, Ren-Zhi Cai 1,2, Balazs Szoke 1,2, Tibor Ertl 1,2, Andrew V Schally 1,2,✉
PMCID: PMC12201039  PMID: 8045917

Abstract

We investigated the effect of bombesin/gastrinreleasing peptide (GRP) antagonist RC-3095 and other analogs on the growth of Hs746T human gastric cancer cells implanted in nude mice or culturedin vitro and on the binding of bombesin to its receptors. Nude mice bearing xenografts of the Hs746T cell line received s.c. injections of RC-3095 (10 μg twice daily) or the vehicle (control) for 21 days. Administration of antagonist RC-3095 inhibited the growth of Hs746T tumors. Treatment with RC-3095 produced a significant decrease in tumor volume, prolonged the tumor volume doubling time from 3.6 days to 5.1 days, and decreased the tumor growth rate by 76.9%. The tumor growth delay time in mice treated with RC-3095 was 2.8 days. Treatment with RC-3095 also decreased the final tumor weight by 88.3% and reduced DNA and protein contents in tumors by 91.5% and 89.5%, respectively, as compared to controls. The presence of specific receptors for bombesin/GRP was investigated on the crude membranes of implanted tumors of Hs746T cells. Saturation binding assays showed that the binding of [125I-Tyr4]bombesin to the membranes was saturable and reversible. Scatchard analysis indicated the presence of a single class of binding sites with a high affinity (K d=0.24±0.07 nM) and a low binding capacity (B max=57.0±0.9 fmol/mg protein). In displacement studies, the binding of [125I-Tyr4]bombesin was inhibited in a dose-dependent manner by unlabelled bombesin(1-14), [Tyr4]-bombesin and GRP(14-27), but not by structurally unrelated peptides. Synthetic bombesin/GRP antagonists RC-3095, RC-3110, and RC-3950-II were all able to inhibit effectively the binding of [125I-Tyr4]bombesin to the membranes of Hs746T cells. RC-3950-II showed a higher binding affinity for bombesin receptors than RC-3095 or RC-3110. Addition of the non-hydrolyzable guanine-nucleotide analog GTP [S] to the binding buffer caused a significant reduction in the amount of [125I-Tyr4]bombesin bound to the cells, indicating that the bombesin receptor is coupled to a G-protein. In cell cultures, bombesin significantly stimulated the growth of Hs746T cellsin vitro as shown by an increase in the uptake of [3H]thymidine. Bombesin antagonist RC-3095 could effectively inhibit the bombesinstimulated growth of Hs746T cells in cultures. These observations suggest that bombesin/GRP may act as growth factors through specific receptors present on the membranes of Hs746T cells. Bombesin/GRP antagonists appear to nullify the effects of bombesin/GRP and may be useful for the treatment of gastric cancers.

Key words: Bombesin, gastrin-releasing peptide, bombesin receptor, bombesin antagonist, gastric carcinoma

Abbreviations

BN

bombesin

GRP

gastrin-releasing peptide

LHRF

hitemizing-hormone-releasing harmone

GHRH

growth hormone-releasing hormone

Tac

thiazolidine-4-carboxylic acid

GTP[S]

guanosine 5′[γ-thio]triphosphate

G-protein

guanine-nucleotide-binding regulatory protein

SCLC

small-cell lung cancer

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