INTERACTION OF CIS-DIAMMINEDICHLOROPLATINUM(II) WITH PM-2 DNA

Abstract

The interaction of cis-diamminedichloroplatinum(II) (CDDP) [an antineoplastic drug] with PM-2 DNA [a model system for antitumor activity] was studied using 2 techniques: agarose gel electrophoresis of PM-2 DNA conformation isomers after CDDP binding; and viscometric measurement of different forms of CDDP-bound PM-2 DNA. Apparently the DNA isomers interacted differently with CDDP. CDDP induced a decrease of viscosity upon interacting with single-strand broken relaxed circular (Form II) and double-strand broken linear (Form III) PM-2 DNA. These observations are consistent with a DNA shortening effect proposed by Cohen, et al. and Macquet, et al. When covalently closed circular (Form I) PM-2 DNA was used, increasing concentrations of CDDP induced an initial slight increase and then decrease of electrophoretic mobility to the degree that it comigrated with CDDP-bound Form II DNA. Further addition of CDDP restored the electrophoretic mobility of Form I DNA. Corresponding changes in the viscosity of CDDP-bound Form I DNA showed an initial decrease, then an increase, and a final prolonged decrease of viscosity. These effects are similar but not identical to those induced by either DNA intercalators (e.g., ethidium bromide) or certain DNA denaturation agents (e.g., formaldehyde, UV light, alkali trichloroacetate, methylmercuric hydroxide and carbodiimide). Thus, CDDP may induce a DNA superhelix-unwinding process followed either by rewinding or a denaturation process or both. Quantitative analysis of the agarose gel electrophoretic pattern plus sucrose density gradient centrifugation studies also indicated that there was little DNA strand breakage induced by CDDP treatment.