The effects of major DNA intrastrand cross-links of antitumor dinuclear Pt(II) complexes [{trans-PtCl(NH(3))(2)}(2)-μ-{trans-(H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2))}](4+) (1) and [{PtCl(DACH)}(2)-μ-{H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2))}](4+) (2) (DACH is 1,2-diaminocyclohexane) on DNA stability were studied with emphasis on thermodynamic origins of that stability. Oligodeoxyribonucleotide duplexes containing the single 1,2, 1,3, or 1,5 intrastrand cross-links at guanine residues in the central TGGT, TGTGT, or TGTTTGT sequences, respectively, were prepared and analyzed by differential scanning calorimetry. The unfolding of the platinated duplexes was accompanied by unfavorable free energy terms. The efficiency of the cross-links to thermodynamically destabilize the duplex depended on the number of base pairs separating the platinated bases. The trend was 1,5→1,2→1,3 cross-link of 1 and 1,5→1,3→1,2 cross-link of 2. Interestingly, the results showed that the capability of the cross-links to reduce the thermodynamic stability of DNA (ΔG(298)(0)) correlated with the extent of conformational distortions induced in DNA by various types of intrastrand cross-links of 1 or 2 determined by chemical probes of DNA conformation. We also examined the efficiency of the mammalian nucleotide excision repair systems to remove from DNA the intrastrand cross-links of 1 or 2. The efficiency of the excinucleases to remove the cross-links from DNA depended on the length of the cross-link; the trend was identical to that observed for the efficiency of the intrastrand cross-links to thermodynamically destabilize the duplex. Thus, the results are consistent with the thesis that an important factor that determines the susceptibility of the intrastrand cross-links of dinuclear platinum complexes 1 and 2 to be removed from DNA by nucleotide excision repair is the efficiency of these lesions to thermodynamically destabilize DNA.

• MeSH
• Calorimetry, Differential Scanning MeSH
• DNA chemistry   MeSH
• Intercalating Agents chemistry   pharmacology   MeSH
• Nucleic Acid Conformation drug effects   MeSH
• DNA Repair drug effects   MeSH
• Organoplatinum Compounds chemistry   pharmacology   MeSH
• Antineoplastic Agents chemistry   pharmacology   MeSH
• Base Sequence MeSH
• Thermodynamics MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA MeSH
• Intercalating Agents MeSH
• Organoplatinum Compounds MeSH
• Antineoplastic Agents MeSH

A combination of biophysical, biochemical, and computational techniques was used to delineate mechanistic differences between the platinum-acridine hybrid agent [PtCl(en)(L)](NO(3))(2) (complex 1, en = ethane-1,2-diamine, L = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea) and a considerably more potent second-generation analogue containing L' = N-[2-(acridin-9-ylamino)ethyl]-N-methylpropionamidine (complex 2). Calculations at the density functional theory level provide a rationale for the binding preference of both complexes for guanine-N7 and the relatively high level of adenine adducts observed for compound 1. A significant rate enhancement is observed for binding of the amidine-based complex 2 with DNA compared with the thiourea-based prototype 1. Studies conducted with chemical probes and on the bending and unwinding of model duplex DNA suggest that adducts of complex 2 perturb B-form DNA more severely than complex 1, however, without denaturing the double strand and significantly less than cisplatin. Circular and linear dichroism spectroscopies and viscosity measurements suggest that subtle differences exist between the intercalation modes and adduct geometries of the two complexes. The adducts formed by complex 2 most efficiently inhibit transcription of the damaged DNA by RNA polymerase II. Not only do complexes 1 and 2 cause less distortion to DNA than cisplatin, they also do not compromise the thermodynamic stability of the modified duplex. This leads to a decreased or negligible affinity of HMG domain proteins for the adducts formed by either Pt-acridine complex. In a DNA repair synthesis assay the lesions formed by complex 2 were repaired less efficiently than those formed by complex 1. These significant differences in DNA adduct formation, structure, and recognition between the two acridine complexes and cisplatin help to elucidate why compound 2 is highly active in cisplatin-resistant, repair proficient cancer cell lines.

• MeSH
• DNA Adducts chemistry   MeSH
• Acridines chemistry   metabolism   pharmacology   MeSH
• Amidines chemistry   metabolism   pharmacology   MeSH
• DNA, B-Form chemistry   metabolism   MeSH
• Cisplatin analogs & derivatives   chemistry   metabolism   pharmacology   MeSH
• DNA chemistry   metabolism   MeSH
• Transcription, Genetic drug effects   MeSH
• HeLa Cells MeSH
• Intercalating Agents chemistry   metabolism   pharmacology   MeSH
• Kinetics MeSH
• Nucleic Acid Conformation drug effects   MeSH
• Humans MeSH
• DNA Repair drug effects   MeSH
• Organoplatinum Compounds chemistry   metabolism   pharmacology   MeSH
• Protein Isoforms metabolism   MeSH
• HMGB1 Protein metabolism   MeSH
• Antineoplastic Agents chemistry   metabolism   pharmacology   MeSH
• Drug Design MeSH
• Thiourea chemistry   metabolism   pharmacology   MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Comparative Study MeSH
• Names of Substances
• DNA Adducts MeSH
• Acridines MeSH
• Amidines MeSH
• DNA, B-Form MeSH
• Cisplatin MeSH
• DNA MeSH
• Intercalating Agents MeSH
• Organoplatinum Compounds MeSH
• Protein Isoforms MeSH
• HMGB1 Protein MeSH
• Antineoplastic Agents MeSH
• Thiourea MeSH

The trinuclear BBR3464 ([{trans-PtCl(NH(3))(2)}(2)µ-(trans-Pt(NH(3))(2)(H(2)N(CH(2))(6)NH(2))(2))](4+)) belongs to the polynuclear class of platinum-based anticancer agents. DNA adducts of this complex differ significantly in structure and type from those of clinically used mononuclear platinum complexes, especially, long-range (Pt, Pt) intrastrand and interstrand cross-links are formed in both 5'-5' and 3'-3' orientations. We show employing short oligonucleotide duplexes containing single, site-specific cross-links of BBR3464 and gel electrophoresis that in contrast to major DNA adducts of clinically used platinum complexes, under physiological conditions the coordination bonds between platinum and N7 of G residues involved in the cross-links of BBR3464 can be cleaved. This cleavage may lead to the linkage isomerization reactions between this metallodrug and double-helical DNA. Differential scanning calorimetry of duplexes containing single, site-specific cross-links of BBR3464 reveals that one of the driving forces that leads to the lability of DNA cross-links of this metallodrug is a difference between the thermodynamic destabilization induced by the cross-link and by the adduct into which it could isomerize. The rearrangements may proceed in the way that cross-links originally formed in one strand of DNA can spontaneously translocate from one DNA strand to its complementary counterpart, which may evoke walking of the platinum complex on DNA molecule.

• MeSH
• DNA Adducts chemistry   MeSH
• Calorimetry, Differential Scanning MeSH
• DNA chemistry   MeSH
• Organoplatinum Compounds chemistry   MeSH
• Antineoplastic Agents chemistry   MeSH
• Cross-Linking Reagents chemistry   MeSH
• Thermodynamics MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• BBR 3464 MeSH Browser
• DNA MeSH
• Organoplatinum Compounds MeSH
• Antineoplastic Agents MeSH
• Cross-Linking Reagents MeSH

Clinically ineffective transplatin [trans-diamminedichloridoplatinum(II)] is used in the studies of the structure-pharmacological activity relationship of platinum compounds. In addition, a number of transplatin analogs exhibit promising toxic effects in several tumor cell lines including those resistant to conventional antitumor cisplatin. Moreover, transplatin-modified oligonucleotides have been shown to be effective modulators of gene expression. Owing to these facts and because DNA is also considered the major pharmacological target of platinum complexes, interactions between transplatin and DNA are of great interest. We examined, using biophysical and biochemical methods, the stability of 1,3-GNG intrastrand cross-links (CLs) formed by transplatin in short synthetic oligodeoxyribonucleotide duplexes and natural double-helical DNA. We have found that transplatin forms in double-helical DNA 1,3-GNG intrastrand CLs, but their stability depends on the sequence context. In some sequences the 1,3-GNG intrastrand CLs formed by transplatin in double-helical DNA readily rearrange into interstrand CLs. On the other hand, in a number of other sequences these intrastrand CLs are relatively stable. We show that the stability of 1,3-GNG intrastrand CLs of transplatin correlates with the extent of conformational distortion and thermodynamic destabilization induced in double-helical DNA by this adduct.

• MeSH
• Biophysical Phenomena * MeSH
• Cisplatin metabolism   MeSH
• DNA chemistry   genetics   metabolism   MeSH
• Calorimetry MeSH
• Nucleic Acid Conformation MeSH
• Oligodeoxyribonucleotides chemistry   genetics   metabolism   MeSH
• Cross-Linking Reagents metabolism   MeSH
• Base Sequence MeSH
• Thermodynamics MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cisplatin MeSH
• DNA MeSH
• Oligodeoxyribonucleotides MeSH
• Cross-Linking Reagents MeSH
• transplatin MeSH Browser

Downstream processes that discriminate between DNA adducts of a third generation platinum antitumor drug oxaliplatin and conventional cisplatin are believed to be responsible for the differences in their biological effects. These different biological effects are explained by the ability of oxaliplatin to form DNA adducts more efficient in their biological effects. In this work conformation, recognition by HMG domain protein and DNA polymerization across the major 1,2-GG intrastrand cross-link formed by cisplatin and oxaliplatin in three sequence contexts were compared with the aid of biophysical and biochemical methods. The following major differences in the properties of the cross-links of oxaliplatin and cisplatin were found: i), the formation of the cross-link by oxaliplatin is more deleterious energetically in all three sequence contexts; ii), the cross-link of oxaliplatin bends DNA slightly but systematically less in all sequence contexts tested; iii), the affinity of HMG domain protein to the cross-link of oxaliplatin is considerably lower independent of the sequence context; and iv), the Klenow fragment of DNA polymerase I pauses considerably more at the cross-link of oxaliplatin in all sequence contexts tested. We have also demonstrated that the chirality at the carrier ligand of oxaliplatin can affect its biological effects.

• MeSH
• DNA Adducts chemistry   ultrastructure   MeSH
• Guanine chemistry   MeSH
• Nucleic Acid Conformation MeSH
• Organoplatinum Compounds chemistry   MeSH
• Oxaliplatin MeSH
• Base Pairing MeSH
• Antineoplastic Agents chemistry   MeSH
• Cross-Linking Reagents MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• Guanine MeSH
• Organoplatinum Compounds MeSH
• Oxaliplatin MeSH
• Antineoplastic Agents MeSH
• Cross-Linking Reagents MeSH

Effects of adducts of [PtCl(NH3)3]Cl or chlorodiethylenetriamineplatinum(II) on DNA stability were studied with emphasis on thermodynamic origins of that stability. Oligodeoxyribonucleotide duplexes (15-bp) containing the single, site-specific monofunctional adduct at G-residues of the central sequences TGT/ACA or 5'-AGT/5'-ACT were prepared and analyzed by differential scanning calorimetry, temperature-dependent ultraviolet absorption and circular dichroism. The unfolding of the platinated duplexes was accompanied by relatively small unfavorable free energy terms. This destabilization was enthalpic in origin. On the other hand, a relatively large reduction of melting temperature (T(m)) was observed as a consequence of the monofunctional adduct in the TGT sequence, whereas T(m) due to the adduct in the AGT sequence was reduced only slightly. We also examined the efficiency of the mammalian nucleotide excision repair system to remove from DNA the monofunctional adducts and found that these lesions were not recognized by this repair system. Thus, rather thermodynamic than thermal characterization of DNA adducts of monofunctional platinum compounds is a property implicated in the modulation of downstream effects such as protein recognition and repair.

• MeSH
• DNA Adducts analysis   chemistry   MeSH
• Nucleic Acid Denaturation MeSH
• DNA analysis   chemistry   MeSH
• Kinetics MeSH
• DNA Repair * MeSH
• Platinum analysis   chemistry   MeSH
• Energy Transfer MeSH
• Temperature MeSH
• Thermodynamics MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• DNA MeSH
• Platinum MeSH

Bifunctional polynuclear platinum compounds represent a novel class of metal-based antitumor drugs which are currently undergoing preclinical development. A typical agent is [(trans-PtCl(NH(3))(2))(2)H(2)N(CH(2))(4)NH(2)]Cl(2) (1,1/t,t), which coordinates to bases in DNA and forms various types of covalent crosslinks. It also forms a 1,2-d(GpG) intrastrand adduct, the equivalent of the major DNA lesion of 'classical' cisplatin. In the present study differential scanning calorimetry and spectroscopic techniques were employed to characterize the influence of this crosslink on the thermal stability and energetics of 20 bp DNA duplexes site-specifically modified by 1,1/t,t. Thermal denaturation data revealed that the crosslink of 1,1/t,t reduced thermal and thermodynamical stability of the duplex noticeably more than that of 'classical' cisplatin. The energetic consequences of the intrastrand crosslink at the d(GG) site are discussed in relation to the structural distortions induced by this adduct in DNA and to its recognition and binding by HMG domain proteins. It has been suggested that the results of the present work are consistent with different DNA binding modes of cisplatin and polynuclear bifunctional DNA-binding drugs, which might be relevant to their distinct biological effectiveness.

• MeSH
• DNA Adducts chemistry   genetics   metabolism   MeSH
• Circular Dichroism MeSH
• Cisplatin metabolism   MeSH
• Nucleic Acid Denaturation MeSH
• Calorimetry, Differential Scanning MeSH
• DNA-Binding Proteins chemistry   metabolism   MeSH
• Entropy MeSH
• Guanine metabolism   MeSH
• Mutagenesis, Site-Directed * MeSH
• Oligodeoxyribonucleotides chemistry   genetics   metabolism   MeSH
• Platinum chemistry   metabolism   MeSH
• High Mobility Group Proteins chemistry   metabolism   MeSH
• Antineoplastic Agents chemistry   metabolism   MeSH
• Cross-Linking Reagents chemistry   metabolism   MeSH
• Base Sequence MeSH
• Spectrophotometry, Ultraviolet MeSH
• Temperature MeSH
• Protein Structure, Tertiary MeSH
• Thermodynamics MeSH
• Binding Sites MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• Cisplatin MeSH
• DNA-Binding Proteins MeSH
• Guanine MeSH
• Oligodeoxyribonucleotides MeSH
• Platinum MeSH
• High Mobility Group Proteins MeSH
• Antineoplastic Agents MeSH
• Cross-Linking Reagents MeSH