The metabolism of BW2258U89, a GRP receptor antagonist

BW2258U89 is a gastrin releasing peptide (GRP) receptor antagonist which inhibits the proliferation of the neuroendocrine tumor small cell lung cancer (SCLC). Here the biological activity of BW2258U89 and its metabolite were investigated. Using mass spectroscopy (LC-ESI/MS) techniques, three major peaks for BW2258U89 were observed with mass/charge (m/z) ratios of 1081.6, 541.4 and 361.4. After metabolism by mouse plasma enzymes, the major product had a m/z ratio of 1082.5, 541.9 and 361.8 suggesting that BW2258U89 was deamidated. Deamidated (Da) BW2258U89 was synthesized and it inhibited (125I-Tyr4) BB binding to NCI-H345 SCLC cells with an IC50value of 450nM; BW2258U89 had an IC50value of 17nM. BW2258U89 (1μ M) antagonized the ability of 50nM BB to elevate cytosolic Ca2+in NCI-H345 cells, whereas 1μ M (Da) BW2258U89 did not. One micromolar BW2258U89 antagonized the increase in NCI-H345 c-fos mRNA caused by 10nM BB, whereas 1μ M (Da) BW2258U89 had little effect. One μ M BW2258U89 inhibited NCI-H345 clonal growth significantly whereas 1μ M (Da) BW2258U89 did not. These data suggest that an amidated C-terminal is important for antagonism of SCLC GRP receptors by BW2258U89.