MUSTARD PRODRUGS FOR ACTIVATION BY ESCHERICHIA-COLI NITROREDUCTASE INGENE-DIRECTED ENZYME PRODRUG THERAPY

Twenty nitrogen mustard analogues derived from 5-(aziridin-1-yl)-2,4-d initrobenzamide (CB 1954, 1) were evaluated as candidate prodrugs for gene-directed enzyme prodrug therapy (GDEPT) in Chinese hamster V79 ce ll lines engineered to express Escherichia coli nitroreductase(NR). St ructural variations within the series included the use of N-dihydroxyp ropyl and (N-dimethylamino)ethyl carboxamide side chains, the use of c hloro, bromo, mesyl, and iodo leaving groups on the mustards, and regi oisomeric changes. The compounds were assayed for cytotoxicity (IC50) with the NR-expressing and controls of non-NR-expressing cell lines. T he proportion of NR-expressing cells required in a mixture for nonexpr essing cells to experience 50% of their cytotoxicity (termed the TE(50 )) was used to assess the compounds' ability to induce a bystander eff ect. This study suggests that -[N,N-bis(2-bromoethyl)amino]-2,4-dinitr obenzamide (8), 5-[N,N-bis(2-iodoethyl)amino]-2,4-dinitrobenzamide (9) , -[N,N-bis(2-bromoethyl)amino]-3,5-dinitrobenzamide (13), and 2-[N,N- bis(2-iodoethyl)amino]-3,5-dinitrobenzamide (14) showed considerable i mprovements over 1, exhibiting greater potency, higher IC50 ratios, an d lower TE(50)s, and are thus superior prodrugs to 1 for GDEPT.