Comparison of recombinant and synthetically formed monoclonal antibody-beta-lactamase conjugates for anticancer prodrug activation

Conjugates of the L49 monoclonal antibody (binds to the p97 antigen on mela nomas and carcinomas) were formed by attaching Enterobacter cloacae beta-la ctamase (bL) to the L49-Fab' fragment using a heterobifunctional cross-link ing reagent or by linking the enzyme to L49-sFv using DNA recombinant techn ology. The conjugates thus formed, L4g-Fab'-bL and L49-sFv-bL, were designe d to activate cephalosporin containing anticancer prodrugs at the surfaces of antigen positive tumor cells. Results from in vitro experiments using tw o lung carcinoma cell lines demonstrated that the conjugates were equally a ctive in effecting the release of phenylenediamine mustard from the cephalo sporin nitrogen mustard prodrug CCM. While treatment with either of the con jugates combined with the maximum tolerated doses of CCM led to cures of es tablished SN12P renal cell carcinoma tumors in nude mice, only the L49-sFv- bL conjugate maintained its ability to do so at 1/4 the maximum tolerated d ose of CCM. L49-sFv-bL was also superior to L49-Fab'-bL in the 1934J renal cell carcinoma tumor model and was shown to be quite active in two in vivo models of human lung carcinoma. These results demonstrate that the recombin ant fusion protein leads to more pronounced therapeutic windows than the ch emical conjugate and is active in an array of human tumor models.