Novel prodrugs of alkylating agents derived from 2-fluoro- and 3-fluorobenzoic acids for antibody-directed enzyme prodrug therapy

Abstract

The synthesis of six novel fluorinated potential prodrugs for antibody-directed enzyme prodrug therapy is described. The [2- and 3-fluoro-4-[bis(2-chloroethyl)amino]benzoyl]-L-glutamic acid (9 and 21), their bis(mesyloxy)ethyl derivatives (7 and 19), and their chloroethyl (mesyloxy)-ethyl derivatives (8 and 20) are bifunctional alkylating agents in which the activating effect of the ionized carboxyl function is masked through an amide bond to the glutamic acid residue. These compounds were designed to be activated to their corresponding benzoic acid alkylating agents at a tumor site by prior administration of a monoclonal antibody conjugated to the bacterial enzyme carboxypeptidase G2 (CPG2). The synthesis of the analogous novel parent drugs 2- and 3-fluoro-4-[bis(2-chloroethyl)amino]benzoic acid (12 and 24), their bis(mesyloxy)ethyl derivatives (10 and 22), and their chloroethyl (mesyloxy)ethyl derivatives (11 and 23) is also described. The viability of a colorectal cell line was monitored with the six potential prodrugs in the presence of CPG2 and with the parent drugs alone. Compounds 19-21 demonstrated substantial prodrug activity, with activation by CPG2 leading to cytotoxicities comparable to those of 22-24, respectively. The Km and kcat values for 7-9 and 19-21 were determined for CPG2. All potential prodrugs except 7 proved to be excellent substrates. A comparison of the relative chemical reactivity of the compounds as determined by their half-life measurements showed that the 2-fluoro substituent deactivated while the 3-fluoro substituent activated the alkylating moieties.