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 ((125)I-Tyr(4)) BB binding to NCI-H345 SCLC cells with an IC(50)value of 450 nM;
BW2258U89 had an IC(50)value of 17 nM.
BW2258U89 (1 microM) antagonized the ability of 50 nM BB to elevate cytosolic Ca(2+)in NCI-H345 cells, whereas 1 microM (Da)
BW2258U89 did not. One micromolar
BW2258U89 antagonized the increase in NCI-H345 c-fos
mRNA caused by 10 nM BB, whereas 1 microM (Da)
BW2258U89 had little effect. One microM
BW2258U89 inhibited NCI-H345 clonal growth significantly whereas 1 microM (Da)
BW2258U89 did not. These data suggest that an amidated C-terminal is important for antagonism of SCLC GRP receptors by
BW2258U89.