STABILITY OF ADRIAMYCIN-INDUCED DNA-ADDUCTS AND INTERSTRAND CROSS-LINKS

The stability of adriamycin-induced DNA adducts and interstrand crossl inks was measured at 37 degrees C by three independent procedures. The loss of [C-14]-labelled adducts was described by two first-order deca ys with half-lives of 7.4 h (60% amplitude) and 39 h (40%). The loss o f the drug chromophore also exhibited a biphasic character, with half- lives of 6 h (65%) and similar to 150 h (35%). The decay of transcript ional blockages at an isolated, apparent interstrand GpC crosslinking site was described by two first-order processes, with half-lives of 3 h (65%) and 40 h (35%), whereas the decay of transcriptional blockages at an isolated guanine residue (apparent site of monoadduct) was comp letely described by a first-order decay with a half-life of 5.3 h. The loss of interstrand crosslinks was measured using a gel electrophores is assay, and the decay was characterised by a single first-order proc ess with a half-life of 4.7 h. Collectively, these values serve to def ine a model of the interstrand crosslink with unstable sites of attach ment at both ends of the crosslink, with half-lives at either end bein g similar to 5 and 40 h. The adducts exhibited increasing lability wit h increasing pH, and were particularly unstable at pH 12, with a half- life of similar to 0.5 h. The adducts were also heat labile, with an o verall melting temperature of 67 degrees C (10 min exposure) and this was also the thermal lability measured at three individual adduct site s probed by lambda exonuclease.