Long Range 1,4 and 1,6-Interstrand Cross-Links Formed by a Trinuclear Platinum Complex. Minor Groove Preassociation Affects Kinetics and Mechanism of Cross-Link Formation as Well as Adduct Structure

• Published in: Journal of the American Chemical Society 2004-02, Vol.126 (7), p.2166-2180
• Main Authors: Hegmans, Alexander, Berners-Price, Susan J, Davies, Murray S, Thomas, Donald S, Humphreys, Anthony S, Farrell, Nicholas
• Format: Article
• Language: English
• Subjects: Antineoplastic Agents - chemistry; Antineoplastic Agents - metabolism; Antineoplastic Agents - pharmacology; Biological and medical sciences; Cross-Linking Reagents - chemistry; Cross-Linking Reagents - metabolism; Cross-Linking Reagents - pharmacology; DNA - chemistry; DNA - drug effects; DNA - metabolism; DNA Adducts - biosynthesis; DNA Adducts - chemistry; General pharmacology; Guanine - chemistry; Guanine - metabolism; Kinetics; Medical sciences; Models, Molecular; Nitrogen Isotopes; Nuclear Magnetic Resonance, Biomolecular; Nucleic Acid Conformation; Oligonucleotides - chemistry; Oligonucleotides - metabolism; Organoplatinum Compounds - chemistry; Organoplatinum Compounds - metabolism; Organoplatinum Compounds - pharmacology; Pharmacology. Drug treatments; Physicochemical properties. Structure-activity relationships
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja036105u

Reported here is a comparison of the kinetics of the stepwise formation of 1,4- and 1,6-GG interstrand cross-links by the trinuclear platinum anticancer compound 15N-[{trans-PtCl(NH3)2}2{μ-trans-Pt(NH3)2(H2N(CH2)6NH2)2}]4+, (1,0,1/t,t,t (1) or BBR3464). The reactions of 15N-1 with the self-complementary 12-mer duplexes 5‘-{d(ATATGTACATAT)2} (I) and 5‘-{d(TATGTATACATA)2} (II) have been studied at 298 K, pH 5.3 by [1H,15N] HSQC 2D NMR spectroscopy. The kinetic profiles for the two reactions are similar. For both sequences initial electrostatic interactions with the DNA are observed for 1 and the monoaqua monochloro species (2) and changes in the chemical shifts of certain DNA 1H resonances are consistent with binding of the central charged {PtN4} linker unit in the minor groove. The pseudo first-order rate constants for the aquation of 1 to 2 in the presence of duplex I (3.94 ± 0.03 × 10-5 s-1), or II (4.17 ± 0.03 × 10-5 s-1) are ca. 40% of the value obtained for aquation of 1 under similar conditions in the absence of DNA. Monofunctional binding to the guanine N7 of the duplex occurs with rate constants of 0.25 ± 0.02 M-1 s-1 (I) and 0.34 ± 0.02 M-1 s-1 (II), respectively. Closure to form the 1,4- or 1,6-interstrand cross-links (5) was treated as direct from 3 with similar rate constants of 4.21 ± 0.06 × 10-5 s-1 (I) and 4.32 ± 0.04 × 10-5 s-1 (II), respectively. Whereas there is only one predominant conformer of the 1,6 cross-link, evidence from both the 1H and [1H,15N] NMR spectra show formation of two distinct conformers of the 1,4 cross-link, which are not interconvertible. Closure to give the major conformer occurs 2.5-fold faster than for the minor conformer. The differences are attributed to the initial preassociation of the central linker of 1 in the minor groove and subsequently during formation of both the monofunctional and bifunctional adducts. For duplex I, molecular models indicate two distinct pathways for the terminal {PtN3Cl} groups to approach and bind the guanine N7 in the major groove with the central linker anchored in the minor groove. To achieve platination of the guanine residues in duplex II the central linker remains in the minor groove but 1 must diffuse off the DNA for covalent binding to occur. Clear evidence for movement of the linker group is seen at the monofunctional binding step from changes of chemical shifts of certain CH2 linker protons as well as the Pt−NH3 and Pt−NH2 groups. Consideration of the 1H and 15N shifts of pe