Peptide hormones are an important class of tumor growth factors and are potentially important in the regulation of tumor progression. Our studies of tumor cell enzymes required for processing of precursor prohormones to active peptide hormones are comprised of three parts: A. Biochemistry of peptidyl amidating enzyme complex B. Molecular biology of endo- and exo-protease enzymes C. Effect of inhibiting peptidyl amidating enzyme on cell growth A. Both enzymes (PHM and PGL) required for conversion of glycine-extended prohormones to active amidated peptide hormones are present in endocrine tumor cells. We have shown that there are several different forms of these enzymes present in several lung tumor cell lines, including at least two distinct PHM forms, and one or two forms which appear to be bifunctional PHM/PGL molecules. These different forms have potential importance to regulation of post-translational processing of growth-- stimulatory hormones in tumor cells. B. As there are no good functional assays for differentiating among the families of prohormone endo- and exo- proteases, we are studying these enzymes at the level of mRNA expression. So far, several tumor cell lines have been identified which express different members of the family of processing endoproteases. We are obtaining nucleotide sequence for the mRNAs for the different enzymes to develop probes for in situ hybridization studies of tumor tissue samples, and for early detection of proliferating pre-neoplastic tissues. C. Two classes of inhibitors of peptidyl amidating enzyme have been studied with in vitro growth assays to determine the effect on inhibiting post-translational prohormone processing on tumor cell growth. Inhibitors which chelate copper (an essential cofactor of PHM) inhibit growth of cells expressing PHM. The first irreversible substrate analogue inhibitor of PHM which has been studied is toxic to all cells. Further inhibitors are being evaluated to develop growth inhibitors which are more selective, with the intention of eventual clinical testing of the best agents as cancer intervention agents.
