DEVELOPMENT AND ACTIVITIES OF A NEW MELPHALAN PRODRUG DESIGNED FOR TUMOR-SELECTIVE ACTIVATION

The synthesis of C-Mel, a cephalosporin carbamate derivative of the cl inically used alkylating agent melphalan, is described. C-Mel was desi gned as an anticancer nitrogen mustard prodrug that releases melphalan upon tumor-specific activation by targeted beta-lactamase (bL). The K -m and k(cat) values for bL hydrolysis of C-Mel were 218 mu M and 980 s(-1), respectively. In vitro cytotoxicity assays with 3677 human mela noma cells demonstrated that C-Mel was 40-fold less toxic than melphal an and was activated in an immunologically specific manner by L49-sFv- bL, a recombinant fusion protein that binds to the melanotransferrin a ntigen on melanomas and on some carcinomas. L49-sFv-bL in combination with C-Mel led to regressions and cures of established subcutaneous 36 77 tumors in nude mice. The effects were significantly greater than th ose of melphalan, which did not result in any long-term regressions in this tumor model. The therapeutic effects were comparable to those ob tained in mice treated with the previously described L49-sFv-bL/7-(4-c arboxybutanamido)-cephalosporin mustard (CCM) combination. However, C- Mel may be more attractive than CCM for clinical development since the released drug is clinically approved.