Comparison of structural effects in 1,4 DNA-DNA interstrand cross-links formed by dinuclear and trinuclear platinum complexes.

The novel anticancer drug ([[trans-PtCl(NH(3))(2)](2)-mu-[trans-Pt(NH(3))(2)(NH(2)(CH(2))(6)NH(2))(2)]](NO(3))(4)) (BBR3464, 1,0,1/t,t,t, TPC) forms a 1,4-interstrand cross-linked adduct with the self-complementary DNA octamer 5'-d(ATG*TACAT)(2)-3', with the two platinum atoms coordinated in the major groove at N7 positions of guanines four base pairs apart on opposite DNA strands [Y. Qu, N.J. Scarsdale, M.-C. Tran, N. Farrell, J. Biol. Inorg. Chem. 8 (2003) 19-28]. The structure of the identical cross-link formed by the dinuclear [[trans-PtCl(NH(3))(2)](2)-mu-NH(2)(CH(2))(6)NH(2)]](NO(3))(2) (BBR3005, 1,1/t,t, DPC) was examined for comparison. The adduct was characterized and analyzed by MS, UV and NMR spectroscopy. NMR analysis of the adduct shows platination of the unique guanine residues. The strong H8/H1' intraresidue cross-peaks observed for all purine residues (A1, G3, A5 and A7) are consistent with a syn-conformation of the nucleoside unit in all cases. Thus, the structure resembles closely that formed by the trinuclear compound. Further confirmation of this similarity comes from the increase in melting temperature (66 degrees for DPC, 60 degrees for TPC, 22 degrees for free oligonucleotide). Since DNA is the principal target in vivo for these Pt cross-linking agents, the unique structural perturbations induced by these cross-links may be related to the increased cytotoxicity and antitumor activity of polynuclear platinum compounds as compared to cisplatin (cis-DDP). The similarity in the structures suggests opportunities to "deliver" the cross-link in a more efficient manner than the current clinically tested drug.

Cooperative effects in long-range 1,4 DNA-DNA interstrand cross-links formed by polynuclear platinum complexes: an unexpected syn orientation of adenine bases outside the binding sites.

The novel phase II anticancer drug BBR3464 ([[ trans-PtCl(NH(3))(2)](2)- micro -[ trans-Pt(NH(3))(2)(NH(2)(CH(2))(6)NH(2))(2)]](NO(3))(4)) forms a 1,4-interstrand cross-link adduct with the self-complementary DNA octamer 5'-d(ATG*TACAT)(2)-3', with the two platinum atoms coordinated in the major groove at the N7 positions of guanines that are four base pairs apart on opposite DNA strands. The "central" tetraamine linker [ trans-H(2)N(CH(2))(6)NH(2)Pt(NH(3))(2)NH(2)(CH(2))(6)NH(2)] was located in or close to the minor groove. The adduct was characterized and analyzed by MS, UV and NMR spectroscopy. NMR analysis of the adduct shows strong H8/H1' intraresidue crosspeaks observed for the A1 and A7 resonances, consistent with a syn conformation for these bases which is usually not observed for adenine residues and bases not directly involved in the cross-link in oligonucleotides. The strong intraresidue H8/H1' crosspeak is also observed for G3. Examination of the structure thus reveals unusual cooperative effects unique to this class of anticancer drugs and is the first demonstration of cooperative effects in solution for an anticancer drug. The significant characteristic of the structure is the lack of severe DNA distortion such as a kink, directed bend or significant unwinding of the helices which are characteristic for DNA adducts of mononuclear complexes. This may contribute to the lack of protein recognition of the cross-link by HMG-domain proteins, a biological consequence significantly different from that of mononuclear complexes such as cisplatin. Since DNA is the principal target in vivo for these Pt cross-linking agents, the unique structural perturbations induced by BBR3464 cross-links are likely related to its increased cytotoxicity and antitumor activity as compared to cisplatin ( cis-DDP).