Cathepsin B-Labile Dipeptide Linkers for Lysosomal Release of Doxorubicin from Internalizing Immunoconjugates:  Model Studies of Enzymatic Drug Release and Antigen-Specific In Vitro Anticancer Activity

作者：Gene M. Dubowchik, Raymond A. Firestone, Linda Padilla, David Willner, Sandra J. Hofstead, Kathleen Mosure, Jay O. Knipe, Shirley J. Lasch, Pamela A. Trail · 发表于：Bioconjugate Chemistry · 年份：2002 · DOI：10.1021/bc025536j · 被引用次数：553 · 研究领域：Peptidase Inhibition and Analysis、Cell Adhesion Molecules Research、Protease and Inhibitor Mechanisms

The anticancer drug doxorubicin (DOX) has been linked to chimeric BR96, an internalizing monoclonal antibody that binds to a Lewis(y)-related, tumor-associated antigen, through two lysosomally cleavable dipeptides, Phe-Lys and Val-Cit, giving immunoconjugates 72 and 73. A self-immolative p-aminobenzyloxycarbonyl (PABC) spacer between the dipeptides and the DOX was required for rapid and quantitative generation of free drug. DOX release from model substrate Z-Phe-Lys-PABC-DOX 49 was 30-fold faster than from Z-Val-Cit-PABC-DOX 42 with the cysteine protease cathepsin B alone, but rates were identical in a rat liver lysosomal preparation suggesting the participation of more than one enzyme. Conjugates 72 and 73 showed rapid and near quantitative drug release with cathepsin B and in a lysosomal preparation, while demonstrating excellent stability in human plasma. Against tumor cell lines with varying levels of BR96 expression, both conjugates showed potent, antigen-specific cytotoxic activity, suggesting that they will be effective in delivering DOX selectively to antigen-expressing carcinomas.