Identification of the active species in deoxyribonucleic acid breakage induced by 4'-(9-acridinylamino)methanesulfon-m-anisidide and copper.

Cyclic voltammetry and UV/VIS spectrometry studies show that 4'-(9-acridinylamino)methanesulfon-m-anisidide (mAMSA) can be oxidized electrochemically to N1-methylsulfonyl-N4-(9-acridinyl)-3-methoxy-2,5-cyclohexadiene-1,4-d iimine (mAQDI) in Tris buffer, pH 7.5. The formal potential of this 2-electron process, as determined by spectroelectrochemical techniques, was 0.141 V versus saturated calomel electrode. Voltammetric data also indicate that an electron transfer reaction between mAMSA and Cu(II) was thermodynamically favored. Two lines of evidence suggest that mAQDI and Cu(I) are the active species in DNA breakage: (1) mAQDI, in the presence of Cu(I), induced both single- and double-strand DNA breakage of the superhelical pDPT275 form I DNA. mAQDI or Cu(I), when used alone, was less effective. (2) The DNA-breaking activity of an mAMSA-Cu(II) mixture was kinetically correlated with the production of both Cu(I) and mAQDI. Thin-layer chromatographic studies showed that mAMSA was oxidized to mAQDI which, in turn, was hydrolyzed. The end product was identified as 9-aminoacridine. When DNA breakage activity was measured as a function of reaction time, a biphasic response was observed. Maximal DNA-breaking activity was obtained upon mixing mAMSA and Cu(II) for 2-4 hr, depending on the concentrations of mAMSA and Cu(II), and was followed by a subsequent decrease in breakage. The decrease appears to be due to the decrease in Cu(I) production and the hydrolysis of mAQDI. These results substantiate the proposed mechanism that DNA breakage induced by mAMSA-Cu(II) involves a rate-limiting electron transfer step to form mAQDI and Cu(I), which are the active species for DNA breakages.