THE ANTIPROLIFERATIVE ACTION OF A MELPHALAN HEXAPEPTIDE WITH COLLAGENASE-CLEAVABLE SITE

Purpose: The objective of the present study was to examine the relevan ce of collagenase in the antitumor action of a melphalan peptide (MHP) with a collagenase-cleavable sequence. The question was addressed as to whether collagenase may act as an activator or a target in the anti proliferative mechanism of MI-IF. Methods: Melphalan was inserted into peptides representing the sequence Pro-Gln-Gly-Ile-Ala.Gly of the col lagenase-cleavable site iii collagens. Changes in growth and collagena se IV activities of HT-1080, HT-29, HT-168, and MCF-7 cell cultures we re investigated. Results: The present investigations provide data indi cating that Pro-Gln-Gly-Ile-Mel-Gly (melphalan hexapeptide, MHP) is a substrate for both bacterial and 72-kDa type IV collagenases and that in this way it can generate Ile-Mel-Gly (melphalan tripeptide. MTP) of higher cytotoxic potency. Indeed, the formation of MTP was detected i n the conditioned medium of HT-1080, a collagenase IV-producing human fibrosarcoma. In a comparison of equimolar concentrations of melphalan and its two peptide derivatives (MHF and MTP), superior antiprolifera tive action of MTP was seen in HT-29, HT-1080, and HT-168 tumor cell c ultures. However, the relatively modest cytostatic actions of MHP were increased when bacterial collagenase was added to the cell cultures. After melphalan treatment, reduced levels of both 92 and 72-kDa type I V collagenases were seen in the HT-1080 cell cultures. However, the re duction of collagenase activity and the cell counts did not run parall el in the MTP-or MHP-treated cultures; indeed, collagenase activity re lated to cell numbers showed an elevated level. Conclusions: As the co nversion of MHP to the more toxic MTP was detected in the presence of collagenases, it is possible that collagenase-directed activation of p rodrugs may be a promising approach for the development of more select ive cytostatic drugs against malignant tumors with high collagenase ac tivities.