Histochemical determination of stereoselectivity of esterases in normal pancreas and pancreatic tubular adenocarcinoma of hamsters.

Esterases in normal hamster pancreas and pancreatic tubular adenocarcinoma of ductal origin induced by N-nitrosobis(2-oxopropyl)amine were stained in cryostat sections with mixtures of a diazonium salt (fast blue RR) and with each of the enantiomers of alpha-naphthyl N-methoxycarbonylalaninate, N-methoxycarbonylvalinate, and N-acetylprolinate. Azo coupling of alpha-naphthol formed by enzymatic hydrolysis with the diazonium salt gives an azo dye that indicates the presence and amount of the enzyme activity in situ. Comparison between the color intensities obtained with each of the enantiomers of a chiral alpha-naphthyl ester shows the stereoselectivity, or enantiomeric preference, of the enzyme. Esterases in acinar cells of the normal pancreas showed slight stereoselectivity for N-methoxycarbonylalaninate, while esterases in fat cells scattered throughout the exocrine pancreas showed high stereoselectivity for (R)-N-acetylprolinate. These esterase activities were not found in the tumor, but another prominent esterase activity with high stereoselectivity for (S)-N-methoxycarbonylvalinate was found. Similar results were obtained by staining after polyacrylamide gel electrophoresis showing that the bands of esterases in the adenocarcinoma stained only with the S enantiomer of the N-methoxycarbonylvalinate. The present method is a valuable tool for designing anticancer prodrugs that are activated by tumor-specific esterases.