Specificity of esterases and structure of prodrug esters. II. Hydrolytic regeneration behavior of 5-fluoro-2'-deoxyuridine (FUdR) from 3',5'-diesters of FUdR with rat tissue homogenates and plasma in relation to their antitumor activity.

Abstract

The bioactivation characteristics of 3', 5'-diesters of 5-fluoro-2'-deoxyuridine (FUdR) esterified with saturated aliphatic acids, including acetic, propionic, butyric, hexanoic, octanoic, decanoic, dodecanoic and trimethylacetic acids, were studied by using rat tissue homogenates and plasma. The susceptibility of the esters to hydrolysis by the biological media increased as the acyl promoiety was lengthened up to octanoyl. Further elongation resulted in decreasing susceptibility. Antitumor activity against L1210 of the esters with a longer chain or branched acyl group administered intraperitoneally and orally to tumor-bearing mice was also examined. Both the antitumor activity and the therapeutic index (ILSmax/ILS30) of the esters improved as the acyl promoiety was lengthened from octanoyl to dodecanoyl. These results suggested that the higher antitumor activities of longer alkyl chain diesters of FUdR are due to their slow rates of FUdR regeneration with esterases.