Unique structural properties of DNA interstrand cross-links formed by a new antitumor dinuclear Pt(ii) complex.

The DNA interstrand cross-links of the antitumor drug {[cis-Pt(NH3)2Cl]2(4,4'-methylenedianiline)}2+ (1) play a prevalent role in its antitumor effects. Complex 1 forms DNA long-range interstrand cross-links uniquely in the 3'-3' direction. Conformational distortions induced by these interstrand cross-links in DNA represent a potential structural motif for recognition by high-mobility-group proteins.

Assessment of DNA-binding affinity of cholinesterase reactivators and electrophoretic determination of their effect on topoisomerase I and II activity.

In this paper, we describe the biochemical properties and biological activity of a series of cholinesterase reactivators (symmetrical bisquaternary xylene-linked compounds, K106-K114) with ctDNA. The interaction of the studied derivatives with ctDNA was investigated using UV-Vis, fluorescence, CD and LD spectrometry, and electrophoretic and viscometric methods. The binding constants K were estimated to be in the range 1.05 × 10(5)-5.14 × 10(6) M(-1) and the percentage of hypochromism was found to be 10.64-19.28% (from UV-Vis titration). The used methods indicate that the studied samples are groove binders. Electrophoretic methods proved that the studied compounds clearly influence calf thymus Topo I (at 5 µM concentration, except for compounds K107, K111 and K114 which were effective at higher concentrations) and human Topo II (K110 partially inhibited Topo II effects even at 5 µM concentration) activity.

Comment on "Delivering a photosensitive transplatin prodrug to overcome cisplatin drug resistance" by H. Song, W. Li, R. Qi, L. Yan, X. Jing, M. Zheng and H. Xiao, Chem. Commun., 2015, 51, 11493.

Consistency of literature results with the transformation of trans-diamminedichloridoplatinum(ii) (transplatin) into cis-diammine-dichloridoplatinum(ii) (cisplatin) under UVA irradiation claimed in the article recently published in this journal is questioned on the basis of previous and new experimental data.

Lichen secondary metabolites as DNA-interacting agents.

A series of lichen secondary metabolites (parietin, atranorin, usnic and gyrophoric acid) and their interactions with calf thymus DNA were investigated using molecular biophysics and biochemical methods. The binding constants K were estimated to range from 4.3×10(5) to 2.4×10(7)M(-1) and the percentage of hypochromism was found to be 16-34% (from spectral titration). The results of spectral measurement indicate that the compounds act as effective DNA-interacting agents. Electrophoretic separation studies prove that from all the metabolites tested in this study, only gyrophoric acid exhibited an inhibitory effect on Topo I (25µM).

Sensitisation for cisplatin-induced apoptosis by isothiocyanate E-4IB leads to signalling pathways alterations.

A new synthetic isothiocyanate (ITC) derivative, ethyl 4-isothiocyanatobutanoate (E-4IB), appeared to be an effective modulator of cellular proliferation and potent inducer of apoptosis. In cooperation with cisplatin, this compound exerted synergistic effects in human ovarian carcinoma A2780 cells. In the present study we investigated in more detail E4IB-sensitisation for cisplatin-induced apoptosis. Sequential administration of both cytostatic agents led to increased intracellular platinum accumulation, glutathione level depletion and mitochondrial membrane potential dissipation. These events were accompanied with poly (ADP-ribosyl) polymerase cleavage, stimulation of caspase-3 activity, upregulation of p53, FasL and Gadd45alpha, cyclin B1 downregulation and an increase in mitogen-activated protein kinases JNK, ERK and p38 phosphorylation as well as PI3K level alterations. The presented results might have implications for developing new strategies aimed at therapeutic benefit of natural or synthetic ITCs in cooperation with various anticancer drugs.

Double-check probing of DNA bending and unwinding by XPA-RPA: an architectural function in DNA repair.

The multiprotein factor composed of XPA and replication protein A (RPA) is an essential subunit of the mammalian nucleotide excision repair system. Although XPA-RPA has been implicated in damage recognition, its activity in the DNA repair pathway remains controversial. By replacing DNA adducts with mispaired bases or non-hybridizing analogues, we found that the weak preference of XPA and RPA for damaged substrates is entirely mediated by indirect readout of DNA helix conformations. Further screening with artificially distorted substrates revealed that XPA binds most efficiently to rigidly bent duplexes but not to single-stranded DNA. Conversely, RPA recognizes single-stranded sites but not backbone bending. Thus, the association of XPA with RPA generates a double-check sensor that detects, simultaneously, backbone and base pair distortion of DNA. The affinity of XPA for sharply bent duplexes, characteristic of architectural proteins, is not compatible with a direct function during recognition of nucleotide lesions. Instead, XPA in conjunction with RPA may constitute a regulatory factor that monitors DNA bending and unwinding to verify the damage-specific localization of repair complexes or control their correct three-dimensional assembly.

Conformation, recognition by high mobility group domain proteins, and nucleotide excision repair of DNA intrastrand cross-links of novel antitumor trinuclear platinum complex BBR3464.

The new antitumor trinuclear platinum compound [(trans-PtCl(NH(3))(2))(2)mu-trans-Pt(NH(3))(2)(H(2)N(CH(2))(6)NH(2))(2)](4+) (designated as BBR3464) is currently in phase II clinical trials. DNA is generally considered the major pharmacological target of platinum drugs. As such it is of considerable interest to understand the patterns of DNA damage. The bifunctional DNA binding of BBR3464 is characterized by the rapid formation of long range intra- and interstrand cross-links. We examined how the structures of the various types of the intrastrand cross-links of BBR3464 affect conformational properties of DNA, and how these adducts are recognized by high mobility group 1 protein and removed from DNA during in vitro nucleotide excision repair reactions. The results have revealed that intrastrand cross-links of BBR3464 create a local conformational distortion, but none of these cross-links results in a stable curvature. In addition, we have observed no recognition of these cross-links by high mobility group 1 proteins, but we have observed effective removal of these adducts from DNA by nucleotide excision repair. These results suggest that the processing of the intrastrand cross-links of BBR3464 in tumor cells sensitive to this drug may not be relevant to its antitumor effects. Hence, polynuclear platinum compounds apparently represent a novel class of platinum anticancer drugs acting by a different mechanism than cisplatin and its analogues.

Different recognition of DNA modified by aatitumor cisplatin and its clinically ineffective trans isomer by tumor suppressor protein p53.

The p53 gene encodes a nuclear phosphoprotein that is biologically activated in response to genotoxic stresses including treatment with anticancer platinum drugs. The DNA binding activity of p53 protein is crucial for its tumor suppressor function. DNA interactions of active wild-type human p53 protein with DNA fragments and oligodeoxyribonucleotide duplexes modified by antitumor cisplatin and its clinically ineffective trans isomer (transplatin) were investigated by using a gel mobility shift assay. It was found that DNA adducts of cisplatin reduced binding affinity of the consensus DNA sequence to p53, whereas transplatin adducts did not. This result was interpreted to mean that the precise steric fit required for the formation and stability of the tetrameric complex of p53 with the consensus sequence cannot be attained, as a consequence of severe conformational perturbations induced in DNA by cisplatin adducts. The results also demonstrate an increase of the binding affinity of p53 to DNA lacking the consensus sequence and modified by cisplatin but not by transplatin. In addition, only major 1,2-GG intrastrand cross-links of cisplatin are responsible for this enhanced binding affinity of p53. The data base on structures of various DNA adducts of cisplatin and transplatin reveals distinctive structural features of 1,2-intrastrand cross-links of cisplatin, suggesting a unique role for this adduct in the binding of p53 to DNA lacking the consensus sequence. The results support the hypothesis that the mechanism of antitumor activity of cisplatin may also be associated with its efficiency to affect the binding affinity of platinated DNA to active p53 protein.

Steric control of DNA interstrand cross-link sites of trans platinum complexes: specificity can be dictated by planar nonleaving groups.

Recent findings that novel trans-dichloroplatinum(II) complexes exhibit antitumor activity violate the classical structure-activity relationships of platinum(II) complexes. These novel "nonclassical" trans platinum complexes also comprise those containing planar aromatic amines. Initial studies have shown that these compounds form a considerable amount of DNA interstrand cross-links (up to approximately 30%) with a rate markedly higher than clinically ineffective transplatin. The present work has shown, using Maxam-Gilbert footprinting, that trans-[PtCl2(NH3)(quinoline)] and trans-[PtCl2(NH3)(thiazole)], representatives of the group of new antitumor trans-dichloroplatinum complexes containing planar amines, preferentially form DNA interstrand cross-links between guanine residues at the 5'-GC-3' sites. Thus, DNA interstrand cross-linking by trans-[PtCl2(NH3)(quinoline)] and trans-[PtCl2(NH3)(thiazole)] is formally equivalent to that by antitumor cisplatin, but different from clinically ineffective transplatin which preferentially forms these adducts between complementary guanine and cytosine residues. This result shows for the first time that simple chemical modification of the structure of an inactive compound alters its DNA binding site into a DNA adduct of an active drug.

Sequence specificity, conformation, and recognition by HMG1 protein of major DNA interstrand cross-links of antitumor dinuclear platinum complexes.

Interactions of high mobility group (HMG) domain proteins with DNA modified by cisplatin plays a role in mechanisms underlying its antitumor activity. A structural motif recognized by HMG domain proteins on cisplatin-modified DNA is a stable, directional bend of the helix axis. In the present work, bending induced in DNA by major adducts of a novel class of antitumor compounds, represented by the formula [¿trans-PtCl(NH(3))(2)¿H(2)N(CH(2))(2-6)NH(2)]Cl(2), was investigated. The oligodeoxyribonucleotide duplexes containing various site-specific interstrand cross-links of these bifunctional dinuclear platinum drugs were purified and characterized by Maxam-Gilbert footprinting, chemical probing, and phasing assay. It was demonstrated that the cross-links of the dinuclear compounds bent the helix much less than those of cisplatin. Gel retardation assay revealed very weak recognition of DNA adducts of dinuclear complexes by HMG1 protein. Hence, the mediation of antitumor properties of dinuclear platinum complexes by HMG domain proteins is unlikely so that polynuclear platinum compounds may represent a novel class of platinum anticancer drugs acting by a different mechanism than cisplatin and its analogues. A further understanding of how polynuclear platinum compounds modify DNA and how these modifications are processed in cells should provide a rational basis for the design of new platinum drugs rather than searching for cisplatin analogues.

Effect of geometric isomerism in dinuclear platinum antitumor complexes on DNA interstrand cross-linking.

The requirement for novel platinum antitumor drugs led to the synthesis of dinuclear bisplatinum complexes. To understand the molecular mechanisms underlying the biological activity of this new class of platinum cytostatics, modifications of natural DNA and synthetic oligodeoxyribonucleotide duplexes by dinuclear bisplatinum complexes with equivalent monofunctional coordination spheres, represented by the general formula [{cis-PtCl(NH(3))(2)}(2)(H(2)N-R-NH(2)](2+) (1,1/c,c), in which R is a linear alkane chain, butane or hexane, were studied by various biochemical and molecular biology methods. The results indicated that the major adducts of 1,1/c,c complexes in DNA ( approximately 90%) were interstrand cross-links preferentially formed between guanine residues. Besides 1,2 interstrand cross-links (between guanine residues in neighboring base pairs), 1,3 or 1,4 interstrand cross-links were also possible. In the latter two long-range adducts, the sites involved in the cross-links were separated by one or two base pairs. 1,2, 1,3, and 1,4 interstrand cross-links were formed with a similar rate and were preferentially oriented in the 5' --> 5' direction. In addition, the DNA adducts of these complexes inhibited DNA transcription in vitro. Thus, the binding of the 1,1/c, c complexes modifies DNA in a way that is distinctly different from the modification by the antitumor drug cisplatin. In addition, there are significant differences between the dinuclear 1,1/c,c and 1,1/t, t isomers. The results of this work are consistent with the hypothesis and support the view that platinum drugs that bind to DNA in a fundamentally different manner can exhibit different biological properties including the spectrum and intensity of antitumor activity. The intracellular DNA binding of the dinuclear compounds is compared to the results presented here. It has been suggested that differences in cross-link structure may be an important factor underlying their different biological efficiencies.

DNA interactions of new antitumor aminophosphine platinum(II) complexes.

Mechanistic studies are presented of a novel class of aminophosphine platinum(II) complexes as potential anticancer agents. These new agents, which have demonstrated activity against murine and human tumor cells including those resistant to cisplatin are cis-[PtCl2(Me2N(CH2)3PPh2-P)2] (Com1) and cis-[PtCl(C6H11NH(CH2)2PPh2-N,P)(C6H11NH(CH2) 2PPh2-P)] (Com2). We studied modifications of natural and synthetic DNAs in cell-free media by Com1 and Com2 by various biomedical and biophysical methods and compared the results with those obtained when DNA was modified by cisplatin. The results indicated that Com1 and Com2 coordinated to DNA faster than cisplatin. Bifunctional Com1 formed DNA adducts coordinating to single adenine or guanine residues or by forming cross-links between these residues. In comparison with cisplatin, Com1 formed the adducts more frequently at adenine residues and also formed fewer bidentate lesions. The monofunctional Com2 only formed DNA monodentate adducts at guanine residues. In addition, Com1 terminated DNA synthesis in vitro more efficiently than cisplatin whereas Com2 blocked DNA synthesis only slightly. DNA unwinding studies, measurements of circular dichroism spectra, immunochemical analysis, and studies of the B-Z transition in DNA revealed conformational alterations induced by the adducts of Com1, which were distinctly different from those induced by cisplatin. Com2 had little influence on DNA conformation. It is suggested that the activity profile of aminophosphine platinum(II) complexes, which is different from that of cisplatin and related analogs, might be associated with the specific DNA binding properties of this new class of platinum(II) compounds.

DNA modifications by a novel bifunctional trinuclear platinum phase I anticancer agent.

The DNA-binding profile of a novel, trinuclear platinum Phase I clinical agent (BBR3464) is summarized. The structure of BBR3464 is best described as two trans-[PtCl(NH3)2] units linked by a tetra-amine [trans-Pt(NH3)2{H2N(CH2)6NH2}2]2+ unit. The +4 charge of BBR3464, the presence of at least two Pt coordination units capable of binding to DNA, and the consequences of such DNA binding are remarkable departures from the cisplatin structural paradigm. The chemical and biological features argue that the drug should be considered the first clinical representative of an entirely new structural class of DNA-modifying anticancer agents. The high charge on BBR3464 facilitates rapid binding to DNA with a t1/2 of approximately 40 min, significantly faster than the neutral cisplatin. The melting temperature of DNA adducted by BBR3464 increased at low ionic strength but decreased in high salt for the same rb. This unusual behavior is in contrast to that of cisplatin. BBR3464 produces an unwinding angle of 14 degrees in negatively supercoiled pSP73 plasmid DNA, indicative of bifunctional DNA binding. Quantitation of interstrand DNA-DNA cross-linking in plasmid pSP73 DNA linearized by EcoRI indicated approximately 20% of the DNA to be interstrand cross-linked. While this is significantly higher than the value for cisplatin, it is, interestingly, lower than that for dinuclear platinum compounds such as [{trans-PtCl(NH3)2}2H2N(CH2)6NH2]2+ (BBR3005) where interstrand cross-linking efficiency may be as high as 70-90%. Either the presence of charge in the linker backbone or the increased distance between platinating moieties may contribute to this relatively decreased ability of BBR3464 to induce DNA interstrand cross-linking. Fluorescence experiments with ethidium bromide were consistent with the formation of long-range delocalized lesions on DNA produced by BBR3464. The sequence preference for BBR3464 on plasmid DNA was determined to the exact base pair by assaying extension of the polynucleotide by VentR(exo+) DNA polymerase. Strong sequence preference for single dG or d(GG) sites was suggested. The presence of relatively few blocks on DNA in comparison to either cisplatin or BBR3005 was indicative of high sequence selectivity. The following appropriate sequence where stop sites occur was chosen: [sequence: see text] molecular modeling on 1,4 interstrand (G'30 to G33) and 1,5 intrastrand (G33 to G29) cross-links further confirmed the similarity in energy between the two forms of cross-link. Finally, immunochemical analysis confirmed the unique nature of the DNA adducts formed by BBR3464. This analysis showed that antibodies raised to cisplatin-adducted DNA did not recognize DNA modified by BBR3464. In contrast, DNA modified by BBR3464 inhibited the binding of antibodies raised to transplatin-adducted DNA. Thus, the bifunctional binding of BBR3464 contains few similarities to that of cisplatin but may have a subset of adducts recognized as being similar to the transplatinum species. In summary, the results point to a unique profile of DNA binding for BBR3464, strengthening the original hypothesis that modification of DNA binding in manners distinct from that of cisplatin will also lead to a distinct and unique profile of antitumor activity.

DNA interactions of a novel platinum drug, cis-[PtCl(NH3)2(N7-acyclovir)]+.

We synthesized a novel platinum drug, cis-[PtCl(NH3)2(N7-ACV)]+, in which ACV is the antiviral drug acyclovir [a deoxyriboguanosine analogue, 9-(2-hydroxyethoxymethyl)guanine]. This new compound exhibits antiviral efficacy in vitro and exhibits an antitumor activity profile different from that of cisplatin [Metal-Based Drugs 2:249-256 (1995)]. To contribute to understanding the mechanisms underlying biological activity of this new compound, we studied modifications of natural and synthetic DNAs in cell-free media by cis-[PtCl(NH3)2(N7-ACV)]+ by various biochemical and biophysical methods. The results indicated that the major DNA adduct of cis-[PtCl(NH3)2(N7-ACV)]+ was a stable monofunctional adduct at guanine residues. In contrast to DNA adducts of other monodentate and clinically ineffective platinum(II) compounds, the adducts of cis-[PtCl(NH3)2(N7-ACV)]+ terminated in vitro DNA and RNA synthesis. In addition, although DNA adducts of cis-[PtCl(NH3)2(N7-ACV)]+ and cisplatin were different, some properties of DNA modified by either compound were qualitatively similar. Such similarities were not noticed if DNA modifications by other ineffective monofunctional platinum(II) complexes were investigated. Thus, the DNA binding mode of monofunctional cis-[PtCl(NH3)2(N7-ACV)]+ was different from that of other monofunctional but ineffective platinum(II) complexes. It has been suggested that the unique capability of cis-[PtCl(NH3)2(N7-ACV)]+ to modify DNA may be relevant to a distinct antitumor efficiency of this novel drug in comparison with cisplatin. It also has been suggested that at least some aspects of DNA interactions of cis-[PtCl(NH3)2(ACV)]+ revealed in the current study could be exploited in the search for and development of new antiviral platinum complexes containing, as a part of the coordination sphere, antiviral nucleosides.

DNA modifications by antitumor trans-[PtCl2(E-iminoether)2].

Recent findings that an analogue of clinically ineffective transplatin, trans-[PtCl2(E-iminoether)2], exhibits antitumor activity has helped reevaluation of the empirical structure-antitumor activity relationship generally accepted for platinum(II) complexes. According to this relationship, only the cis geometry of leaving ligands in the bifunctional platinum(II) complexes, should be therapeutically active. Global modifications of natural DNAs in cell-free media by trans-[PtCl2(E-iminoether)2] were studied through various molecular biophysical methods and compared with modifications by cis-[PtCl2(E-iminoether)2], transplatin, cisplatin, and monofunctional chlorodiethylenetriamineplatinum(II) chloride. Thus, the results of this study have extended our recent finding, indicating that the prevalent lesion occurring in double-helical DNA on its modification by trans-[PtCl2(E-iminoether)2] is a monofunctional adduct at guanine residues. The modification by trans-[PtCl2(E-iminoether)2] has been found to induce local distortions in DNA, which have a character differing fundamentally from those induced by both clinically ineffective or antitumor platinum complexes tested in this study. The different character of alterations induced in DNA by the adducts of trans-[PtCl2(E-iminoether)2] and transplatin has been suggested to be relevant to the unexpected observation that the new complex with leaving chloride groups in trans position exhibits antitumor efficacy. In addition, the results support the idea that platinum drugs that bind to DNA in a manner fundamentally different from that of cisplatin can exhibit altered biological properties, including differing spectra and intensities of antitumor activity.

DNA interactions of bifunctional dinuclear platinum(II) antitumor agents.

Modifications of natural DNA in a cell-free medium by dinuclear bisplatinum complexes with equivalent coordination spheres, represented by the general formula [¿trans-PtCl(NH3)2¿2(H2N-R-NH2)]2+, where R is a propane or hexane, were studied by various methods of biochemical analysis or molecular biophysics. These methods include binding studies by means of differential-pulse polarography, measurements of melting curves with the aid of absorption spectrophotometry, measurements of CD spectra, ELISA with specific antibodies that recognize DNA modified by platinum complexes, interstrand cross-linking assay employing gel electrophoresis under denaturing conditions and mapping of DNA adducts by means of transcription assays. The results indicated that the major adduct of [¿trans-PtCl(NH3)2¿2(H2N-R-NH2)]2+ in DNA was an interstrand cross-link which was formed with a relatively short half-time (approximately 1 h). At least some types of these interstrand cross-links induced local denaturational changes in the DNA. The results of analyses of interactions of [¿trans-PtCl(NH3)2¿2(H2N-R-NH2)]2+ with linear DNA at relatively higher levels of the modification could be interpreted to mean that these dinuclear platinum complexes were also capable of intrastrand-cross-link formation between adjacent base residues in DNA. However, these intrastrand adducts of [¿trans-PtCl(NH3)2¿2(H2N-R-NH2)]2+ distorted DNA conformation in a way different from the DNA intrastrand adducts of cisplatin. In addition, the DNA adducts of the dinuclear platinum complexes inhibited DNA transcription in vitro. The length of the aliphatic linker chain affected the DNA-binding mode of [¿trans-PtCl(NH3)2¿2(H2N-R-NH2)]2+ and the resulting conformational changes in DNA. The extensive analysis of DNA interactions with [¿trans-PtCl(NH3)2¿2(H2N-R-NH2)]2+ described in this communication has provided further experimental support for previous suggestions [Farrell, N. (1991) in Platinum and other metal coordination compounds in cancer chemotherapy (Howell, S. B., ed.) pp. 81-91, Plenum Press, New York] that the binding of the dinuclear platinum complexes modifies DNA in a way that is different from the modification by antitumor cisplatin. Thus, the results of this work are consistent with the hypothesis that platinum drugs that bind to DNA in a manner fundamentally different from that of cisplatin can exhibit altered biological properties, including a different spectrum and intensity of antitumor activity.

Site-specific d(GpG) intrastrand cross-links formed by dinuclear platinum complexes. Bending and NMR studies.

The novel platinum drugs [{trans-PtCl(NH3)2}2H2N(CH2)nNH2]2+ (1,1/t,t) are currently undergoing preclinical development. The bifunctional DNA binding of these agents allows comparison with that of cisplatin [Farrell et al. (1995) Biochemistry, 34, 15480]. The major DNA lesion of cisplatin, the 1,2-d(GpG) intrastrand adduct, produces a rigid, directed bend 30-35 degrees into the major groove of DNA. We have now completed a structural analysis of the corresponding adduct formed with the dinuclear complexes. Gel retardation assays on 15-22 bp oligonucleotides containing a central d(TG*G*T) site show that the (Pt,Pt)-intrastrand adducts result in a flexible nondirectional bend. This bend is essentially independent of chain length (n = 2, 4, 6). Chemical reactivity assays indicated a hypersensitivity of the thymine 5' to the adduct and an enhanced sensitivity of the 3'-thymine to OsO4. 2D 1H NMR studies on a d(TG1G2T) adduct of [{trans-PtCl(NH3)2}2H2N(CH2)6NH2]2+ have delineated the structural features responsible for these observations. In contrast to the cisplatin adduct, which displays a 100% N-type sugar of the 5'-G and an anti base conformation of the platinated bases in both solid state and solution, the dinuclear adduct does not display the typical N-type sugar pucker. The base orientations are anti (5'-T), anti (G1), anti/syn (G2), and anti (3'-T) while the sugar conformations are N, S/N, N, and S, respectively. The 5'-T remains stacked with its guanine neighbor while the 3'-T becomes unstacked, a reverse of the situation observed for cis-DDP.

Correlation between cytotoxicity and DNA binding of polypyridyl ruthenium complexes.

The cytotoxicity of chloropolypyridyl ruthenium complexes of structural formulas [Ru(terpy)-(bpy)Cl]Cl, cis-[Ru(bpy)2Cl2], and mer-[Ru(terpy)Cl3] (terpy = 2,2':6'2"-terpyridine, bpy = 2,2'-bipyridyl) has been studied in murine and human tumor cell lines. The results show that mer-[Ru(terpy)Cl3] exhibits a remarkably higher cytotoxicity than the other complexes. Moreover, investigations of antitumor activity in a standard tumor screen have revealed the highest efficiency for mer-[Ru(terpy)Cl3]. In a cell-free medium, the ruthenium complexes coordinate to DNA preferentially at guanine residues. The resulting adducts can terminate DNA synthesis by thermostable VentR DNA polymerase. The reactivity of the complexes to DNA, their efficiency to unwind closed, negatively supercoiled DNA, and a sequence preference of their DNA adducts (studied by means of replication mapping) do not show a correlation with biological activity. On the other hand, the cytotoxic mer-[Ru(terpy)Cl3] exhibits a significant DNA interstrand cross-linking, in contrast to the inactive complexes which exhibit no such efficacy. The results point to a potential new class of metal-based antitumor compounds acting by a mechanism involving DNA interstrand cross-linking.

Recognition of DNA interstrand cross-links of cis-diamminedichloroplatinum(II) and its trans isomer by DNA-binding proteins.

Recognition and processing by cellular proteins of DNA modified by platinum complexes have been suggested to be relevant to the mechanism of their antitumor activity. Platinum complexes form on DNA various mono- and bifunctional adducts. It has already been described by other authors that intrastrand cross-links formed on DNA by antitumor cis-diamminedichloroplatinum(II) (cisplatin) between neighboring purine residues are recognized by several DNA-binding proteins. In contrast, these proteins do not recognize the intrastrand cross-links formed on DNA by cisplatin or its clinically ineffective trans isomer (transplatin) between nonadjacent base residues. An eventuality heretofore not addressed is that DNA interstrand cross-links (ICLs) of platinum compounds may be recognized by and bound to DNA-binding proteins. DNA probes of 110 base pairs (bp) were constructed containing five equally spaced ICLs of cisplatin or transplatin. These ICLs were formed at specific sites at which these adducts are preferentially formed in natural DNA. Gel electrophoresis mobility shift and competition assays with these probes were used to investigate the specific recognition and binding of the calf thymus HMG1 protein to the DNA ICLs of both platinum isomers. The ICL of antitumor cisplatin was recognized by and bound to the HMG1 protein with a similar affinity as the 1,2-intrastrand d(GpG) cross-link of this drug. The protein binding to the ICL is selective for the DNA modification by cisplatin, but not by chemotherapeutically inactive transplatin.(ABSTRACT TRUNCATED AT 250 WORDS)