Inhibition of proteinase-like peptidase activities in serum and tissue from breast cancer patients.

: The inhibitory profiles of several proteinase-like peptidases active on synthetic peptide (MCA) substrates, present in sera and 100,000g supernatants of malignant tissue from patients with breast cancer, have been studied using a series of known inhibitors including epoxysuccinyl peptides (E-64, Ep-475), Z-Phe-Phe-diazomethane, PMSF, iodoacetamide, 1-10-O-phenanthroline, leupeptin, aprotinin, elastatinal and alpha 2-macroglobulin. While in general the inhibition profiles confirmed reported substrate specificities some anomalies were observed. In particular, the serum activities on two cathepsin B substrates were unaffected by specific cysteine proteinase inhibitors and in breast tissue only 20-37% of activity towards these two substrates was apparently due to the presence of endopeptidases. However, the potent inhibition of other proteinase-like activities by the epoxysuccinyl peptides and leupeptin, or similar inhibitors, may be useful agents in the study of methods of combating tumour spread.