Effects of geometric isomerism and anions on the kinetics and mechanism of the stepwise formation of long-range DNA interstrand cross-links by dinuclear platinum antitumor complexes.
Reported herein is a detailed study of the kinetics and mechanism of formation of a 1,4-GG interstrand cross-link by the dinuclear platinum anticancer compound [15N][{cis-PtCl(NH3)2}2{mu-NH2(CH2)6NH2}]2+ (1,1/c,c (1)). The reaction of [15N]1 with 5'-{d(ATATGTACATAT)2} (I) has been studied by [1H,15N] HSQC NMR spectroscopy in the presence of different concentrations of phosphate. In contrast with the geometric trans isomer (1,1/t,t), there was no evidence for an electrostatic preassociation of 1,1/c,c with the polyanionic DNA surface, and the pseudo-first-order rate constant for the aquation of [(15)N]1 was actually slightly higher (rather than lower) than that in the absence of DNA. When phosphate is absent, the overall rate of formation of the cross-link is quite similar for the two geometric isomers, occurring slightly faster for 1,1/t,t. A major difference in the DNA binding pathways is the observation of phosphate-bound intermediates only in the case of 1,1/c,c. 15 mM phosphate causes a dramatic slowing in the overall rate of formation of DNA interstrand cross-links due to both the slow formation and slow closure of the phosphate-bound monofunctional adduct. A comparison of the molecular models of the bifunctional adducts of the two isomers shows that helical distortion is minimal and globally the structures of the 1,4 interstrand cross-links are quite similar. The effect of carrier ligand was investigated by similar studies of the ethylenediamine derivative [15N]1-en. A pKa value of 5.43 was determined for the [15N]1,1/c,c-en diaquated species. The rate of reaction of [15N]1-en with duplex I is similar to that of 1,1/c,c and the overall conformation of the final adduct appears to be similar. The significance of these results to the development of "second-generation" polynuclear platinum clinical candidates based on the 1,1/c,c chelate (dach) series is discussed.
School of Biomedical, Biomolecular & Chemical Sciences, University of Western Australia, Crawley, WA, Australia.
Junyong
J
Zhang
Donald S
DS
Thomas
Susan J
SJ
Berners-Price
Nicholas
N
Farrell
D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D001483:Base Sequence; D003432:Cross-Linking Reagents / Q000737:chemistry* / Q000494:pharmacology*; D004247:DNA / Q000737:chemistry* / Q000235:genetics; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009944:Organoplatinum Compounds / Q000737:chemistry* / Q000494:pharmacology*; D010710:Phosphates / Q000737:chemistry; D013237:Stereoisomerism
D000970:Antineoplastic Agents; D003432:Cross-Linking Reagents; D008024:Ligands; D009944:Organoplatinum Compounds; D010710:Phosphates; C503895:bis(diamminechloroplatinum(II))(mu-1,6-hexanediamine); D004247:DNA