A. Myers, Scott B. Cohen, N. J. Tom
Jul 1, 1995
Citations
0
Influential Citations
24
Citations
Journal
Journal of the American Chemical Society
Abstract
Dynemicin A (1) is a potent natural antitumor agent that is capable of cleaving double-stranded DNA in the presence of a reducing cofactor such as glutathione (GSH) or NADPH. The first step in the proposed cleavage mechanism involves reduction of the anthraquinone,' a functional group that is unique to 1 among the enediyne antibiotiw2 The anthraquinone is also believed to serve as a DNA-binding element by intercalation into the base stack, while the (a-enediyne bridge is positioned in the minor gr00ve.l~3~ Another unusual feature of 1, as a DNA-binding molecule, is that it bears a negative charge at physiological pH, by virtue of its carboxylate group. All other members of the enediyne antibiotic family are positively charged at neutral pH, as is common for molecules that bind to the DNA p~lyanion .~ By studying the DNA-binding and -cleaving properties of 1 and synthetic analogs of 1 we show that the E-ring hydroxyl groups are beneficial for binding and propose that the carboxylate group of 1 plays a critical role in the DNAcleavage process by destabilizing the DNA-drug complex. A rationale for this finding and mechanistic detail for the dynamic process of DNA cleavage by dynemicin A (1) and analogs are presented. We have recently developed a convergent synthetic route to enantiomerically pure dynemicin A (1) that has also provided access to dynemicin A methyl ester (3), dynemicin A-ring analog 5, and the corresponding dideoxy compounds 2,4, and 6.5 Each of the molecular pairs 1 and 2, 3 and 4, and 5 and 6 varies only in the presence or absence of the E-ring hydroxyl groups, whereas pair 1 and 3 and pair 2 and 4 are related as carboxylate and (charge-neutral) methyl ester. Compounds 5 and 6 may also be viewed simply as charge-neutral A-ring analogs of 1 and 2, respectively. Equilibrium constants for the binding of compounds 1-6 to double-stranded calf thymus DNA were determined by equilibrium dialysis in aqueous tris buffer solution (30 mM, pH 7.5; NaCl, 50 mM) at 25 "C using a dialysis membrane with molecular weight cutoff 12 000-14 000. The binding constants span a range of 4 orders of magnitude, from 6 x lo2 M-' for dideoxydynemicin A (2, weakest binding) to 8 x lo6 M-' for dynemicin A methyl ester (3, tightest binding, Figure 1). Comparison of binding constants for structure pairs 1 and 2, 3