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Short-chain Pseudopeptide Bombesin Receptor Antagonists with Enhanced Binding Affinities for Pancreatic Acinar and Swiss 3T3 Cells Display Strong Antimitotic Activity
The high inhibitory potency of the previously developed bombesin antagonist [Leu13, ψCH2NHLeu14]bombesin (analogue I) (IC50 values of 30 and 18 nM for inhibition of bombesin-stimulated amylase secretion from guinea pig acinar cells and Swiss 3T3 cell growth, respectively) diminished considerably whe...
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Published in: | The Journal of biological chemistry 1989-09, Vol.264 (25), p.14691-14697 |
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Main Authors: | , , , , , , , , |
Format: | Article |
Language: | English |
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Online Access: | Get full text |
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Summary: | The high inhibitory potency of the previously developed bombesin antagonist [Leu13, ψCH2NHLeu14]bombesin (analogue I) (IC50 values of 30 and 18 nM for inhibition of bombesin-stimulated amylase secretion from guinea pig acinar cells and Swiss 3T3 cell growth, respectively) diminished considerably when shorter chain lengths were examined. For instance, [Leu13, ψCH2NHLeu14]bombesin-(5-14),[Leu13, ψCH2NHLeu14] bombesin-(6-14), and [Leu9, ψCH2NHLeu10]neuromedin C had IC50 values of 150, 150, and 280 nM, respectively. Incorporation of a D-Phe residue at position 6 of [Leu13, ψCH2NHLeu14] bombesin did not significantly change the various biological parameters. However, its presence in [Leu13, ψCH2NHLeu14]bombesin-(6-14) and at position 2 of psi-neuromedin C-(2-10) resulted in about 10-fold increases in potency up to and above that of the original antagonist. For instance, [D-Phe6,Leu13,ψCH2NHLeu14]bombesin-(6-14) and des-Gly1-[D-Phe2,Leu9,ψCH2NHLeu10]neuromedin C exhibited IC50 values of 5 and 28 nM, respectively. Analogues based on the litorin sequence which contains an NH2-terminal pyroglutamic acid residue at the bombesin position 6 equivalent were also quite potent. The ability of various analogues to interact with bombesin receptors on pancreatic acini correlated reasonably well with potencies derived from inhibition of bombesin-stimulated growth of Swiss 3T3 cells. Additional studies of NH2- and COOH-terminal structure-activity relationships resulted in the synthesis of [D-Phe6,Leu13,ψCH2NHPhe14]bombesin-(6-14), which was particularly effective in inhibiting 3T3 cell growth at high picomolar concentrations (IC50 = 0.72 nM and Ki = 3.1 nM for 3T3 cells; IC50 = 7.5 nM and Ki = 9.9 nM for acini). Detailed investigations with one of the most potent antagonists, [D-Phe6,Leu13,ψCH2NHLeu14]bombesin-(6-14) (Ki = 14 nM for acini cells and 7.1 for 3T3 cells), demonstrated that this analogue was a competitive inhibitor of bombesin and that this activity was specific for the bombesin receptor. Thus, inhibitory potencies have been improved generally up to 25 times over previously reported structures; and, given that bombesin itself has a Ki of 1.2 nM for 3T3 cell binding, some of these analogues are extraordinarily high affinity receptor antagonists. They can also be synthesized more readily and offer fewer proteolytic degradation sites than the original pseudopeptide and should be excellent candidates for in vivo studies aimed at inhibition of bombesin-dependent human |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/S0021-9258(18)63753-6 |