COORDINATION OF INTERSTRAND CROSS-LINKS BETWEEN POLYDEOXYGUANYLIC ACID AND POLYDEOXYCYTIDYLIC ACID BY CIS-DIAMMINEDICHLOROPLATINUM(II)

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  • 1 January 1983
    • journal article
    • research article
    • Vol. 43  (10) , 4799-4804
Abstract
Cisplatin [cis-diamminedichloroplatinum(II)] has been shown to create interstrand DNA cross-links by several methods. These experiments were performed to determine if cisplatin coordinates cross-links between poly(dG) and poly(dC). After incubation at pH 7.2 with cisplatin at various Pt/base nucleotide ratios, ri, for 3 days at 20.degree. C, poly(dG).cntdot.poly(dC) was centrifuged in alkaline cesium sulfate for 3 days at 35,000 rpm. Untreated samples resulted in a low-density poly(dC) peak and a high-density poly(dG) peak, as identified by the UV absorption spectrum. The density gradient profiles of cisplatin-treated poly(dG).cntdot.poly(dC) had an additional hybrid-density peak the area of which increased with the dose (ri) as the areas under the poly(dC) and poly(dG) peaks diminished. With increasing ri, the densities of both the poly(dG) and hybrid peaks increased, while that of the poly(dC) peak remained unchanged. Similarly, the amount of bound Pt in the poly(dG) and hybrid-density peaks increased with ri, while no Pt could be detected in the poly(dC) peak. Therefore, cisplatin appears to react first with the poly(dG), followed by a 2nd reaction with the poly(dC) strand to form the interstrand cross-links that are necessary for the formation of the hybrid-density bands. Based on the intercept of the percent cross-linked poly(dG).cntdot.poly (dC) vs. ri curve with the abscissa, the minimum amount of cisplatin or the threshold amount of cisplatin required to observe cross-links was ri = 0.017. When multiplied by the MW of the poly(dG).cntdot.poly(dC) used, this was equivalent to 1 cross-link/15 molecules of bound Pt. Based on the amount of bound drug, the frequency of cross-links per Pt reaction was calculated to range from 1 of 50 to 67 reactions. Due to limitations in the sensitivity of the Pt assay and to a progressively lower recovery of the cross-linked material at lower ri values, it was not possible to calculate the cross-linking efficiency based on the amount of bound drug for ri values .ltoreq. 0.025. The monofunctional analog, [diethylenetriaminechloroplatinum] chloride, did not cause a hybrid peak to form. These studies demonstrate that cisplatin coordinates interstrand cross-links between poly(dG) and poly(dC).

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