Factors affecting DNA-DNA interstrand cross-links in the antiparallel 3'-3' sense: a comparison with the 5'-5'...

Reported herein is a study of the unusual 3'-3' 1,4-GG interstrand cross-link (IXL) formation in duplex DNA by a series of polynuclear platinum anticancer complexes. To examine the effect of possible preassociation through charge and hydrogen-bonding effects the closely related compounds [{trans-PtCl(NH(3))(2)}(2)(mu-trans-Pt(NH(3))(2){NH(2)(CH(2))(6)NH(2)}(2))](4+) (BBR3464, 1), [{trans-PtCl(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (BBR3005, 2), [{trans-PtCl(NH(3))(2)}(2)(mu-H(2)N(CH(2))(3)NH(2)(CH(2))(4))](3+) (BBR3571, 3) and [{trans-PtCl(NH(3))(2)}(2){mu-H(2)N(CH(2))(3)-N(COCF(3))(CH(2))(4)}](2+) (BBR3571-COCF(3), 4) were studied. Two different molecular biology approaches were used to investigate the effect of DNA template upon IXL formation in synthetic 20-base-pair duplexes. In the "hybridisation directed" method the monofunctionally adducted top strands were hybridised with their complementary 5'-end labelled strands; after 24 h the efficiency of interstrand cross-linking in the 5'-5' direction was slightly higher than in the 3'-3' direction. The second method involved "postsynthetic modification" of the intact duplex; significantly less cross-linking was observed, but again a slight preference for the 5'-5' duplex was present. 2D [(1)H, (15)N] HSQC NMR spectroscopy studies of the reaction of [(15)N]-1 with the sequence 5'-d{TATACATGTATA}(2) allowed direct comparison of the stepwise formation of the 3'-3' IXL with the previously studied 5'-5' IXL on the analogous sequence 5'-d(ATATGTACATAT)(2). Whereas the preassociation and aquation steps were similar, differences were evident at the monofunctional binding step. The reaction did not yield a single distinct 3'-3' 1,4-GG IXL, but numerous cross-linked adducts formed. Similar results were found for the reaction with the dinuclear [(15)N]-2. Molecular dynamics simulations for the 3'-3' IXLs formed by both 1 and 2 showed a highly distorted structure with evident fraying of the end base pairs and considerable widening of the minor groove.