Trimethyl-1, 2-dioxetane induced lesions in DNA: photo-induced pyrimidine dimers detected by T4 UV-endonuclease, local denaturation, and interstrand cross-linking

The chemiluminescent energy derived from the thermal (37°C) decomposition of micromolar concentrations of trimethyl-1, 2-dioxetane induces lesions in topo- isomerase relaxed PM2-CCC-DNA including photodimerization of adjacent pyrimidme bases, local denaturation and interstrand cross-linking. The lesions were detected and quantified using ethidium binding assays in conjunction with repair enzymes. Lesions of the type which give rise to local denaturation were detected usmg the enzyme endonuclsase S r The pyrimidine dimers were determined using T4 UV-endonuclease and represent about 86% of those causing local topological distortions. The effects of the trimethyl-1, 2-dioxetane parallel those of photoactivated acetone i mplicating a photoexcited carbonyl fragment. An estimate is made that about one in three excited fragments is capable of inducing pyrimidine dimer formation. Trimethyl-1,2-dioxetane also produces a concentration-dependent interstrand cross-linking of DNA, amounting to about 44% at 5 /iM drug concentrations. This latter lession is similar to the reported UV-induced cross-linking of DNA and again suggests a chemically produced photo-induced process.