INTERACTIONS OF THE ANTITUMOR AGENTS MITOXANTRONE AND BISANTRENE WITH DEOXYRIBONUCLEIC ACIDS STUDIED BY ELECTRON-MICROSCOPY

  • 1 January 1984
    • journal article
    • research article
    • Vol. 25  (1) , 178-184
Abstract
The interactions of the low cardiotoxic antitumor agents 1,4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)amino]ethyl]amino]-9,10-anthracenedione (mitoxantrone) and 9,10-anthracenedicarboxaldehyde bis[(4,5-dihydro-1H-imidazoyl-2-yl)hydrazone] (bisantrene) with pBR322 and PM2 DNA were examined by EM. Direct evidence was obtained for intercalative binding of both drugs, with mitoxantrone causing a 13% average length increase in pBR322 corresponding to .apprx. 580 drug molecules per circle at saturation and bisantrene causing an 11% increase in length corresponding to .apprx. 480 drug molecules bound per circle. Considerations of the known GC preference for non-nearest neighbor binding of the drugs and inspection of the known sequence of pBR322 suggest that the available intercalation sites are occupied and that additional external electrostatic binding of the cationic drugs also occurs. An apparent difference in behavior of mitoxantrone as compared with that of bisantrene in causing no net increase in length of supercoiled pBR322 was shown to be attributable to an offsetting compaction due to extensive supercoiling by mitoxantrone molecules. This conclusion was confirmed by independent experiments with PM2 convalently closed-circular DNA, both native, negatively supercoiled and relaxed with calf thymus topoisomerase, using ethidium for comparison. Ethidium caused a 21.3 .+-. 3.6% length increase in nicked, open-circular PM2-DNA, or 2100 molecules bound per 10,300 base pairs. Mitoxantrone caused a 16.6% length increase in nicked PM2-DNA equivalent to .apprx. 1700 drug molecules per circle. EM measurements on relaxed PM2-DNA with progressively increasing proportions of mitoxantrone (from 1.4:1 to 14:1 drug molecules per base pair) revealed the onset of formation of lace-like networks of DNA circles linked together. This phenomenon, which is not produced by bisantrene, is attributed to inter-DNA links by the charged side arms of mitoxantrone and is in accord with previous reports that mitoxantrone causes severe compaction and distortion of chromatin. EM examination of the interaction of 6 additional mitoxantrone derivatives, 2 of which produced lace-like DNA networks, revealed strict structural requirements for this phenomenon.

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