Poly(deoxyadenylic-deoxythymidylic acid) damage by radiolytically activated neocarzinostatin

Abstract

The anaerobic reaction of poly(deoxyadenylic-deoxythymidylic acid) with neocarzinostatin activated by the carboxyl radical C.ovrhdot.O2-, an electron donor generated from .gamma.-ray radiolysis of nitrous oxide saturated formate buffer, was characterized. DNA damage includes base release and strand breaks. Few strand breaks are formed prior to alkaline treatment; they bear 3''-phosphoryl termini. Most (66%) of the base release occurs spontaneously. DNA damage is highly (95%) specific for thymidine sites. Neither DNA-drug covalent adduct nor nucleoside 5''-aldehyde, which are major products in the DNA-nicking reaction initiated by mercaptans and O2, is formed in this reaction. The C.ovrhdot.O2--activated neocarzinostatin intermediate is a short-lived free radical able to abstract H atoms from the C-1'' and C-5'' positions of deoxyribose. Attack occurs mostly (68%) at the C-1'' position, producing a lesion whose properties are consistent with those of (oxidized) apyrimidinic sites.