A novel bombesin receptor antagonist (2258U89), potently inhibits bombesin evoked release of gastrointestinal hormones from rats and dogs, in vitro and in vivo

Several bombesin-receptor antagonists are available that inhibit secretory and growth effects of bombesin, in vitro. In the present study, we examined the effects of a new class of bombesin receptor antagonists (modified GRP(15-27) peptides, with d-Pro²⁶ and d-Ala²⁴ moieties), on bombesin mediated effects, in vivo and in vitro. Of the 10 different compounds tested, BW-10 or 2258U89 ([de-NH₂)Phe¹⁹,d-Ala²⁴,d-Pro²⁶Ψ(CH₂NH)Phe²⁷]-GRP(19-27)) was most potent towards inhibiting bombesin binding to rat pancreatic acinar cancer cells with an ID₅₀ of 0.5 nM. BW-10 (1 and 10 nM) significantly inhibited the gastrin response to 1 nM bombesin, from isolated rat stomach, in vitro, in a dose-dependent fashion. BW-10 (10-100 nmol/kg) was equally effective at significantly inhibiting bombesin evoked gastrin release in anesthetized rats, in vivo. [d-Phe⁶]Bombesin(6-13)-propylamide (BIM), a member of another class of antagonists, reported previously to be the most potent antagonist, in vitro, on the other hand, enhanced bombesin provoked gastrin release in rats. The antagonistic effects of BIM, in vivo, may thus be more selective. Intravenous infusion of BW-10 (10 nmol/kg/h) partially depressed gastrin and pancreatic polypeptide and completely abolished insulin released in response to bombesin, in conscious dogs. These results suggest that BW-10 functions as one of the most potent bombesin receptor antagonists, in vitro and in vivo, which could potentially be used as a therapeutic compound in treatment of some human diseases.