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
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- 作者：Alexander Hegmans ; Susan J. Berners-Price ; Murray S. Davies ; Donald S. Thomas ; Anthony S. Humphreys ; and Nicholas Farrell
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：February 25, 2004
- 年：2004
- 卷：126
- 期：7
- 页码：2166 - 2180
- 全文大小：401K
- 年卷期：v.126,no.7(February 25, 2004)
- ISSN：1520-5126
文摘
Reported here is a comparison of the kinetics of the stepwise formation of 1,4- and 1,6-GGinterstrand cross-links by the trinuclear platinum anticancer compound 15N-[{trans-PtCl(NH3)2}2{
f">-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-complementary12-mer duplexes 5'-{d(ATATGTACATAT)2} (I) and 5'-{d(TATGTATACATA)2} (II) have been studied at298 K, pH 5.3 by [1H,15N] HSQC 2D NMR spectroscopy. The kinetic profiles for the two reactions aresimilar. For both sequences initial electrostatic interactions with the DNA are observed for 1 and themonoaqua monochloro species (2) and changes in the chemical shifts of certain DNA 1H resonances areconsistent 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 theabsence of DNA. Monofunctional binding to the guanine N7 of the duplex occurs with rate constants of0.25 ± 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-interstrandcross-links (5) was treated as direct from 3 with similar rate constants of 4.21 ± 0.06 × 10-5 s-1 (I) and4.32 ± 0.04 × 10-5 s-1 (II), respectively. Whereas there is only one predominant conformer of the 1,6cross-link, evidence from both the 1H and [1H,15N] NMR spectra show formation of two distinct conformersof the 1,4 cross-link, which are not interconvertible. Closure to give the major conformer occurs 2.5-foldfaster than for the minor conformer. The differences are attributed to the initial preassociation of the centrallinker of 1 in the minor groove and subsequently during formation of both the monofunctional and bifunctionaladducts. For duplex I, molecular models indicate two distinct pathways for the terminal {PtN3Cl} groups toapproach 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 groovebut 1 must diffuse off the DNA for covalent binding to occur. Clear evidence for movement of the linkergroup is seen at the monofunctional binding step from changes of chemical shifts of certain CH2 linkerprotons as well as the Pt-NH3 and Pt-NH2 groups. Consideration of the 1H and 15N shifts of peaks in thePt-NH2 region show that for both the 1,4 and 1,6 interstrand cross-links there is a gradual and irreversibletransformation from an initially formed conformer(s) to product conformer(s) in which the amine protons ofthe two bound {PtN3} groups exist in a number of different environments. The behavior is similar to thatobserved for the 1,4-interstrand cross-link of the dinuclear 1,1/t,t compound. The potential significance ofpreassociation in determining kinetics of formation and structure of the adducts is discussed. Theconformational flexibility of the cross-links is discussed in relation to their biological processing, especiallyprotein recognition and repair, which are critical determinants of the cytotoxicity of these unique DNA-binding agents.
f">-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-complementary12-mer duplexes 5'-{d(ATATGTACATAT)2} (I) and 5'-{d(TATGTATACATA)2} (II) have been studied at298 K, pH 5.3 by [1H,15N] HSQC 2D NMR spectroscopy. The kinetic profiles for the two reactions aresimilar. For both sequences initial electrostatic interactions with the DNA are observed for 1 and themonoaqua monochloro species (2) and changes in the chemical shifts of certain DNA 1H resonances areconsistent 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 theabsence of DNA. Monofunctional binding to the guanine N7 of the duplex occurs with rate constants of0.25 ± 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-interstrandcross-links (5) was treated as direct from 3 with similar rate constants of 4.21 ± 0.06 × 10-5 s-1 (I) and4.32 ± 0.04 × 10-5 s-1 (II), respectively. Whereas there is only one predominant conformer of the 1,6cross-link, evidence from both the 1H and [1H,15N] NMR spectra show formation of two distinct conformersof the 1,4 cross-link, which are not interconvertible. Closure to give the major conformer occurs 2.5-foldfaster than for the minor conformer. The differences are attributed to the initial preassociation of the centrallinker of 1 in the minor groove and subsequently during formation of both the monofunctional and bifunctionaladducts. For duplex I, molecular models indicate two distinct pathways for the terminal {PtN3Cl} groups toapproach 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 groovebut 1 must diffuse off the DNA for covalent binding to occur. Clear evidence for movement of the linkergroup is seen at the monofunctional binding step from changes of chemical shifts of certain CH2 linkerprotons as well as the Pt-NH3 and Pt-NH2 groups. Consideration of the 1H and 15N shifts of peaks in thePt-NH2 region show that for both the 1,4 and 1,6 interstrand cross-links there is a gradual and irreversibletransformation from an initially formed conformer(s) to product conformer(s) in which the amine protons ofthe two bound {PtN3} groups exist in a number of different environments. The behavior is similar to thatobserved for the 1,4-interstrand cross-link of the dinuclear 1,1/t,t compound. The potential significance ofpreassociation in determining kinetics of formation and structure of the adducts is discussed. Theconformational flexibility of the cross-links is discussed in relation to their biological processing, especiallyprotein recognition and repair, which are critical determinants of the cytotoxicity of these unique DNA-binding agents.