SUPPRESSION OF SUBSTANCE-P BIOSYNTHESIS IN SENSORY NEURONS OF DORSAL-ROOT GANGLION BY PRODRUG ESTERS OF POTENT PEPTIDYLGLYCINE ALPHA-AMIDATING MONOOXYGENASE INHIBITORS

Substance P as well as many other neuropeptides are synthesized as gly cine-extended precursors and converted to the biologically active C-te rminal amides by posttranslational modification. The final step of pos ttranslational processing is catalyzed by peptidylglycine alpha-amidat ing monooxygenase (PAM), In a previous study, N-substituted homocystei ne analogs were found to be potent inhibitors of PAM partially purifie d from conditioned medium of cultured rat medullary thyroid carcinoma CA-77 cells, These compounds, however, were only modest inhibitors of substance P production in cultured dorsal root ganglion cells, possibl y because of poor cell penetration, Several ester derivatives of hydro cinnamoyl-phenylalanyl-homocysteine, one of the most potent PAM inhibi tors, were prepared to increase the intracellular accessibility of the se compounds, drocinnamoyl-phenylalanyl-(S-benzoyl-homocysteine) benzy l ester was identified as the most potent compound, inhibiting substan ce P biosynthesis in dorsal root ganglion cells with an IC50 of 2 mu M . Inhibition of PAM resulted in a concomitant increase in the glycine- extended substance p (substance P-Gly) precursor peptide. In the prese nce of 3 mu M benzyl ester derivative, the intracellular substance P-G ly level was 2.4-fold higher while the substance P level was 2.1-fold lower than the corresponding peptides in control cells. These results suggest that PAM inhibition represents an effective method for suppres sion of substance P biosynthesis and, therefore, may have therapeutic utility in conditions associated with elevated substance P levels. Fur thermore, PAM inhibition may also prove useful in decreasing other ami dated peptides.