Gastrin-releasing peptide (GRP), a member of the bombesin family of peptides, 
has been shown to have mitogenic activity in small cell lung carcinoma (SCLC), 
and to be produced by SCLC in an autocrine fashion. In this report, we 
demonstrate that both GRP and another member of the bombesin family of peptides, 
neuromedin B (NMB), are also autocrine growth factors for non-small cell lung 
carcinoma (NSCLC). Using the reverse transcription-polymerase chain reaction 
(RT-PCR), we have detected mRNA for the neuromedin B receptor (NMBR) in all 14 
of the NSCLC cell lines examined. GRP receptor (GRPR) mRNA was also expressed in 
the majority of NSCLC cell lines (nine of 14). By immunoblotting using SDS-PAGE 
gradient gels fixed in trichloroacetic acid, GRP and NMB were found in fractions 
of culture medium that had been purified by high pressure liquid chromatography 
(HPLC) from NSCLC cell lines. NMB was detected in the conditioned medium of 
seven of nine cell lines and GRP in seven of nine cell lines; both peptides were 
produced in six cell lines. In four of the cell lines where both peptides were 
produced, the relative amount of NMB secreted into the medium was 7-15 times 
that of GRP; in the other two cases, the relative amounts of GRP and NMB were 
equivalent. Cultured human bronchial epithelial (HBE) cells expressed the GRPR 
and NMBR but did not produce either peptide. A subline of A549 cells that was 
adapted to grow in serum-free and growth factor-free conditions, termed 
A549-R(0), secreted both bombesin-like peptides (BLPs) into the culture medium. 
Using either a colony-forming assay or a BrDU incorporation assay, both NMB and 
GRP were found to be mitogens for three NSCLC cell lines that express mRNA for 
BLP receptors and secrete BLPs, regardless of which peptide and/or receptor 
subtype was detected. The monoclonal antibody 2A11, which preferentially 
recognizes GRP, was able to block the in vitro proliferative response to GRP in 
the BrDU incorporation assay, and partially blocked the response to NMB. The 
2A11 antibody could only partially block the in vivo growth of cell lines that 
showed proliferative responses to BLPs. 2A11 antibody was more effective against 
the 239T cell line, which secreted a low amount of GRP into the medium (0.6 nM), 
compared to the 201T cell line, which secreted a higher amount of both GRP and 
NMB (4.2 nM and 36.6 nM, respectively). These results suggest that both NMB and 
GRP are autocrine growth factors for NSCLC, but that the production of NMB and 
expression of the NMBR may be more prominent than the production of GRP and 
expression of the GRP receptor. If BLP ligand-receptor systems are to be 
targeted therapeutically in NSCLC, it will be necessary to inhibit both NMB and 
GRP.