Interaction of dinuclear ruthenium(II) supramolecular cylinders with DNA: sequence-specific binding, unwinding, and photocleavage

Metallosupramolecular chemistry was used to design a new class of synthetic agents, namely, tetracationic supramolecular cylinders, that bind strongly and noncovalently in the major groove of DNA. To gain additional information on interactions of the cylinders with DNA we explored DNA unwinding and sequence-specific binding properties, as well as DNA photonuclease activity of ruthenium(II) metallosupramolecular cylinder [Ru(2)L(3)](4+), where L is a bis-pyridylimine ligand. We found that [Ru(2)L(3)](4+) unwinds negatively supercoiled plasmid DNA and exhibits binding preference to regular alternating purine-pyrimidine sequences in a similar way to the [Fe(2)L(3)](4+) analogue. Photocleavage studies showed that, unlike [Fe(2)L(3)](4+), [Ru(2)L(3)](4+) induces single-strand breaks on irradiation by visible and UVA light and cleaves DNA mainly at guanine residues contained preferentially in regularly alternating purine-pyrimidine nucleotides. As [Ru(2)L(3)](4+) binds and cleaves DNA in a sequence-dependent manner, it may provide a useful tool for basic and applied biology, such as for controlled manipulation of the genome.

Biophysical studies on the stability of DNA intrastrand cross-links of transplatin

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.

DNA interactions of dinuclear RuII arene antitumor complexes in cell-free media

We recently synthesized and characterized water-soluble dinuclear Ru(II) arene complexes, in which two {(eta(6)-p-isopropyltoluene)RuCl[3-(oxo-kappaO)-2-methyl-4-pyridinonato-kappaO(4)]} units were linked by flexible chains of different length [(CH(2))(n) (n=4, 6, 8, 12)]. These new dinuclear ruthenium drugs were found to exert promising cytotoxic effects in human cancer cells. In the present work DNA modifications by these new dinuclear Ru(II) arene compounds, which differed in the length of the linker between the two Ru(II) centers, were examined by biochemical and biophysical methods. The complexes bind DNA forming intrastrand and interstrand cross-links in one DNA molecule in the absence of proteins. An intriguing aspect of the DNA-binding mode of these dinuclear Ru(II) compounds is that they can cross-link two DNA duplexes and also proteins to DNA--a feature not observed for other antitumor ruthenium complexes. Thus, the concept for the design of interhelical and DNA-protein cross-linking agents based on dinuclear Ru(II) arene complexes with sufficiently long linkers between two Ru centers may result in new compounds which exhibit a variety of biological effects and can be also useful in nucleic acids research.

DNA and glutathione interactions in cell-free media of asymmetric platinum(II) complexes cis- and trans-[PtCl2(isopropylamine)(1-methylimidazole)]: relations to their different antitumor effects

The global modification of mammalian and plasmid DNAs by the novel platinum compounds cis-[PtCl(2)(isopropylamine)(1-methylimidazole)] and trans-[PtCl(2)(isopropylamine)(1-methylimidazole)] and the reactivity of these compounds with reduced glutathione (GSH) were investigated in cell-free media using various biochemical and biophysical methods. Earlier cytotoxicity studies had revealed that the replacement of the NH(3) groups in cisplatin by the azole and isopropylamine ligands lowers the activity of cisplatin in both sensitive and resistant cell lines. The results of the present work show that this replacement does not considerably affect the DNA modifications by this drug, recognition of these modifications by HMGB1 protein, their repair, and reactivity of the platinum complex with GSH. These results were interpreted to mean that the reduced activity of this analog of cisplatin in tumor cell lines is due to factors that do not operate at the level of the target DNA. In contrast, earlier studies had shown that the replacement of the NH(3) groups in the clinically ineffective trans isomer (transplatin) by the azole and isopropylamine ligands results in a radical enhancement of its activity in tumor cell lines. Importantly, this replacement also markedly alters the DNA binding mode of transplatin, which is distinctly different from that of cisplatin, but does not affect reactivity with GSH. Hence, the results of the present work are consistent with the view and support the hypothesis systematically tested by us and others that platinum drugs that bind to DNA in a fundamentally different manner from that of conventional cisplatin may have altered pharmacological properties.

DNA interactions of monofunctional organometallic osmium(II) antitumor complexes in cell-free media

This work is the first in-depth study of osmium binding to DNA and confirms the pharmacological activity of a new class of anticancer metallodrugs. We investigated the interactions between the potential biological target DNA and four osmium(II) arene complexes, of the type [(eta 6-arene)Os(LL)Cl]n+, where arene = biphenyl or p-cymene and LL = ethylenediamine, picolinate, or oxinate in an effort to understand their mechanism of action. Most notably we show that these complexes bind to DNA. DNA adducts of the OsII complexes that exhibit promising cytotoxic effects in ovarian tumor cell lines largely distort its conformation. The data are consistent with DNA binding of the complexes containing biphenyl as the arene ligand that involves combined coordination to guanine residues and noncovalent interactions between the arene ligand and DNA. The results also indicate both a mechanism of action and a detoxification mechanism for OsII arene compounds different from those of cisplatin.

DNA binding of dinuclear iron(II) metallosupramolecular cylinders. DNA unwinding and sequence preference

[Fe₂L₃]⁴⁺ (L = C₂₅H₂₀N₄) is a synthetic tetracationic supramolecular cylinder (with a triple helical architecture) that targets the major groove of DNA and can bind to DNA Y-shaped junctions. To explore the DNA-binding mode of [Fe₂L₃]⁴⁺, we examine herein the interactions of pure enantiomers of this cylinder with DNA by biochemical and molecular biology methods. The results have revealed that, in addition to the previously reported bending of DNA, the enantiomers extensively unwind DNA, with the M enantiomer being the more efficient at unwinding, and exhibit preferential binding to regular alternating purine–pyrimidine sequences, with the M enantiomer showing a greater preference. Also, interestingly, the DNA binding of bulky cylinders [Fe₂(L-CF₃)₃]⁴⁺ and [Fe₂(L-Ph)₃]⁴⁺ results in no DNA unwinding and also no sequence preference of their DNA binding was observed. The observation of sequence-preference in the binding of these supramolecular cylinders suggests that a concept based on the use of metallosupramolecular cylinders might result in molecular designs that recognize the genetic code in a sequence-dependent manner with a potential ability to affect the processing of the genetic code.

Electrochemical behaviour of proteins at graphite electrodes. II. Electrooxidation of amino acids

Electrochemical oxidation of L,alpha-amino acids at a paraffin-wax impregnated spectroscopic graphite electrode (WISGE) was studied by means of linear sweep, cyclic, phase-sensitive alternating current and differential pulse voltammetric techniques. It was found that out of the amino acids usually occurring in proteins only tyrosine, tryptophan, histidine, cystine, cysteine and methionine were oxidized at the WISGE. At relatively low concentrations of amino acids (up to ca. 2 x 10(-4) M) the electrode process in which the amino acids are oxidized at the WISGE has the characteristics of an irreversible reaction controlled by diffusion. Coulometric measurements showed that oxidation of tyrosine and tryptophan at the WISGE, i.e. of amino acids which are responsible for the oxidizability of proteins at graphite electrodes, is a two-electron process. At higher concentrations of tyrosine-and tryptophan (above ca. 2 x 10(-4) M) adsorption of the oxidation product of these amino adds was demonstrated.

Amide-based prodrugs of spermidine-bridged dinuclear platinum. Synthesis, DNA binding, and biological activity

The chemistry and biology of acetyl-protected spermidine-bridged dinuclear platinum complexes [{ trans-PtCl(NH 3) 2] 2-mu-NH 2(CH 2) 3N(COR)(CH 2) 4NH 2]X 2 (R = H, X = Cl (1,1/t,t-spermidine, BBR3571); R = CH 3 , X = Cl ( 2); R = CH 2 Cl, X = ClO 4 ( 3); R = CF 3 , X = Cl ( 4)) are compared with their carbamate analogues. The compounds are potential prodrugs for the parent compound 1, a highly potent antitumor agent. At pH 6-8 hydrolysis of the blocking group with the release of the "parent" protonated species follows the order 4 > 3 >> 2. For 4, rate constants for the deprotection increase in this pH range. The DNA binding profile of 4 is similar to the Boc derivative, confirming the central influence of charge on DNA binding properties. The differences in cytotoxicity for the protected compounds in ovarian carcinoma cell lines sensitive and resistant to cisplatin cannot completely be explained by spontaneous release of 1,1/t,t-spermidine at physiological pH. Inherent cytotoxicity and cell line specificity may contribute to the observed behavior. The properties of the compounds present them also as possible "second-generation" analogues of the clinically relevant trinuclear complex [{ trans-PtCl(NH 3) 2} 2-mu- trans-Pt(NH 3) 2(NH 2(CH 2) 6NH 2) 2](NO 3) 4, ( 8, BBR3464).

A potent cytotoxic photoactivated platinum complex

We show by x-ray crystallography that the complex trans, trans, trans-[Pt(N(3))(2)(OH)(2)(NH(3))(py)] (1) contains an octahedral Pt(IV) center with almost linear azido ligands. Complex 1 is remarkably stable in the dark, even in the presence of cellular reducing agents such as glutathione, but readily undergoes photoinduced ligand substitution and photoreduction reactions. When 1 is photoactivated in cells, it is highly toxic: 13-80 x more cytotoxic than the Pt(II) anticancer drug cisplatin, and ca. 15 x more cytotoxic toward cisplatin-resistant human ovarian cancer cells. Cisplatin targets DNA, and DNA platination levels induced in HaCaT skin cells by 1 were similar to those of cisplatin. However, cisplatin forms mainly intrastrand cis diguanine cross-links on DNA between neighboring nucleotides, whereas photoactivated complex 1 rapidly forms unusual trans azido/guanine, and then trans diguanine Pt(II) adducts, which are probably mainly intrastrand cross-links between two guanines separated by a third base. DNA interstrand and DNA-protein cross-links were also detected. Importantly, DNA repair synthesis on plasmid DNA platinated by photoactivated 1 was markedly lower than for cisplatin or its isomer transplatin (an inactive complex). Single-cell electrophoresis experiments also demonstrated that the DNA damage is different from that induced by cisplatin or transplatin. Cell death is not solely dependent on activation of the caspase 3 pathway, and, in contrast to cisplatin, p53 protein did not accumulate in cells after photosensitization of 1. The trans diazido Pt(IV) complex 1 therefore has remarkable properties and is a candidate for use in photoactivated cancer chemotherapy.

Biochemical Studies of the Thermal Effects on DNA Modifications by the Antitumor Cisplatin and Their Repair

Using biochemical methods, we have examined the effect of two factors that might play a role in the mechanism of the biological activity of cisplatin at elevated temperatures (>37 degrees C). We show that increased temperatures result in distinct alterations in the modification of the target DNA by cisplatin, and in the repair of these modifications. Our in vitro results support the view that the enhanced DNA-cross-linking efficiency of cisplatin and the lower efficiency of native DNA repair mechanisms at higher temperature play at least a partial role in the potentiation of the antitumor effects of cisplatin under conditions of mild hyperthermia.

Bifunctional Amine-Tethered Ruthenium(II) Arene Complexes Form Monofunctional Adducts on DNA

The tethered RuII half-sandwich complexes [eta(6):eta(1)-C(6)H(5)(CH(2))(n)NH(2))RuCl(2)] 1 (n = 3) and 2 (n = 2) have been synthesized as potential bifunctional anticancer complexes, and their X-ray crystal structures have been determined. They hydrolyze rapidly in aqueous solution to give predominantly mono-aqua mono-chlorido species. Mono-9EtG adducts, where 9EtG = 9-ethylguanine, form rapidly, but the second 9EtG binds more slowly and more weakly. In the X-ray crystal structure of the di-9EtG adduct [(eta(6):eta(1)-C(6)H(5)(CH(2))(3)NH(2))Ru(9EtG)2](CF(3)SO(3))(2).H(2)O (8.H(2)O), one of the Ru-N7 bonds is significantly longer than the other (2.1588(18) vs 2.101(2) A). The bound guanine bases adopt a head-to-head configuration, stabilized by tether NH2 hydrogen bonding to C6O of 9EtG. The X-ray crystal structure of the dinitrato complex [(eta(6):eta(1)-C(6)H(5)(CH(2))(3)NH(2))Ru(NO(3))(2)] (3) showed both nitrates to be bound to ruthenium. This complex readily rutheniated calf thymus DNA but failed to produce stop sites on pSP73KB plasmid DNA during DNA transcription by an RNA polymerase. This suggested that only monofunctional DNA adducts formed, as did interstrand cross-linking assays. Also, the unwinding angle induced in negatively supercoiled DNA (9 +/- 1 degrees) was less than that induced by cisplatin (13 degrees). These findings may explain why complexes such as 1 and 2 exhibited low cytotoxicities (IC(50) values >100 microM) toward A2780 human ovarian cancer cells.

Conformation of DNA GG intrastrand cross-link of antitumor oxaliplatin and its enantiomeric analog

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.

Reaction of Zn7metallothionein with cis- and trans-[Pt(N-donor)2Cl2] anticancer complexes: trans-Pt(II) complexes retain their N-donor ligands

Intrinsic and acquired resistance are major drawbacks of platinum-based cancer therapy. The protein superfamily of cysteine- and ZnII-rich proteins, metallothioneins (MT), efficiently inactivate these antitumor drugs because of the strong reactivity of platinum compounds with S-donor molecules. In this study the reactions of human Zn7MT-2 with twelve cis/trans-[Pt(N-donor)2Cl2] compounds and [Pt(dien)Cl]Cl, including new generation drugs, were investigated and the products characterized. A comparison of reaction kinetics revealed that trans-PtII compounds react faster with Zn7MT-2 than cis-PtII compounds. The characterization of the products showed that while all ligands in cis-PtII compounds were replaced by cysteine thiolates, trans-PtII compounds retained their N-donor ligands, thus remaining in a potentially active form. These results provide an increased understanding of the role of MT in the acquired resistance to platinum-based anticancer drugs.

Recognition of DNA three-way junctions by metallosupramolecular cylinders: gel electrophoresis studies

The interaction of metallosupramolecular cylinders with DNA three-way junctions has been studied by gel electrophoresis. A recent X-ray crystal structure of a palindromic oligonucleotide forming part of a complex with such a cylinder revealed binding at the heart of a three-way junction structure. The studies reported herein confirm that this is not solely an artefact of crystallisation and reveal that this is a potentially very powerful new mode of DNA recognition with wide scope. The cylinders are much more effective at stabilizing three-way junctions than simple magnesium di-cations or organic or metallo-organic tetra-cations, with the M cylinder enantiomer being more effective than P. The recognition is not restricted to three-way junctions formed from palindromic DNA with a central AT step at the junction; non-palindromic three-way junctions and those with GC steps are also stabilised. The cylinder is also revealed to stabilise other Y-shaped junctions, such as that formed at a fraying point in duplex DNA (for example, a replication fork), and other DNA three-way junction structures, such as those containing unpaired nucleotides, perhaps by opening up this structure to access the central cavity.

DNA interactions of new cytotoxic tetrafunctional dinuclear platinum complex trans,trans-[{PtCl2(NH3)}2(piperazine)]

A new tetrafunctional dinuclear platinum complex trans,trans-[{PtCl2(NH3)}2(piperazine)] with sterically rigid linking group was designed, synthesized and characterized. In this novel molecule, the DNA-binding features of two classes of the platinum compounds with proven antitumor activity are combined, namely trans oriented bifunctional mononuclear platinum complexes with a heterocyclic ligand and polynuclear platinum complexes. DNA-binding mode of this new complex was analyzed by various methods of molecular biology and biophysics. The complex coordinates DNA in a unique way and interstrand and intrastrand cross-links are the predominant lesions formed in DNA in cell-free media and in absence of proteins. An intriguing aspect of trans,trans-[{PtCl2(NH3)}2(piperazine)] is that, using a semi-rigid linker, interstrand cross-linking is diminished relative to other dinuclear platinum complexes with flexible linking groups and lesions that span several base pairs, such as tri- and tetrafunctional adducts, become unlikely. In addition, in contrast to the inability of trans,trans-[{PtCl2(NH3)}2(piperazine)] to cross-link two DNA duplexes, the results of the present work convincingly demonstrate that this dinuclear platinum complex forms specific DNA lesions which can efficiently cross-link proteins to DNA. The results substantiate the view that trans,trans-[{PtCl2(NH3)}2(piperazine)] or its analogues could be used as a tool for studies of DNA properties and their interactions or as a potential antitumor agent. The latter view is also corroborated by the observation that trans,trans-[{PtCl2(NH3)}2(piperazine)] is a more effective cytotoxic agent than cisplatin against human tumor ovarian cell lines.

Dual triggering of DNA binding and fluorescence via photoactivation of a dinuclear ruthenium(II) arene complex

The dinuclear RuII arene complexes [{(eta6-arene)RuCl}2(mu-2,3-dpp)](PF6)2, arene=indan (1), benzene (2), p-cymene (3), or hexamethylbenzene (4) and 2,3-dpp=2,3-bis(2-pyridyl)pyrazine, have been synthesized and characterized. Upon irradiation with UVA light, complexes 1 and 2 readily underwent arene loss, while complexes 3 and 4 did not. The photochemistry of 1 was studied in detail. In the X-ray structure of [{(eta6-indan)RuCl}2(mu-2,3-dpp)](PF6)2 (1), 2,3-dpp bridges two RuII centers 6.8529(6) A apart. In water, aquation of 1 in the dark occurs with replacement of chloride with biexponential kinetics and decay constants of 100+/-1 min-1 and 580+/-11 min-1. This aquation was suppressed by 0.1 M NaCl. UV or visible irradiation of 1 in aqueous or methanolic solution led to arene loss. The fluorescence of the unbound arene is approximately 40 times greater than when it is complexed. Irradiation of 1 also had a significant effect on its interactions with DNA. The DNA binding of 1 is increased after irradiation. The non-irradiated form of 1 preferentially formed DNA adducts that only weakly blocked RNA polymerase, while irradiation of 1 transformed the adducts into stronger blocks for RNA polymerase. The efficiency of irradiated 1 to form DNA interstrand cross-links was slightly greater than that of cisplatin in both 10 mM NaClO4 and 0.1 M NaCl. In contrast, the interstrand cross-linking efficiency of non-irradiated 1 in 10 mM NaClO4 was relatively low. An intermediate amount of cross-linking was observed when the sample of DNA already modified by non-irradiated 1 was irradiated. DNA unwinding measurements supported the conclusion that both mono- and bifunctional adducts with DNA can form. These results show that photoactivation of dinuclear RuII arene complexes can simultaneously produce a highly reactive ruthenium species that can bind to DNA and a fluorescent marker (the free arene). Importantly, the mechanism of photoreactivity is also independent of oxygen. These complexes, therefore, have the potential to combine both photoinduced cell death and fluorescence imaging of the location and efficiency of the photoactivation process.

High-throughput screening identifies novel agents eliciting hypersensitivity in Fanconi pathway-deficient cancer cells

Inactivation of the Fanconi anemia (FA) pathway occurs in diverse human tumors among the general population and renders those tumors hypersensitive to DNA interstrand-cross-linking (ICL) agents. The identification of novel agents to which FA pathway-deficient cells were hypersensitive could provide new therapeutic opportunities and improve our molecular understanding of the FA genes. Using high-throughput screening, we assessed the growth of isogenic human cancer cells that differed only in the presence or absence of single FA genes upon treatment with 880 active drugs and 40,000 diverse compounds. We identified several compounds to which FA pathway-deficient cells were more sensitive than FA pathway-proficient cells, including two groups of structurally related compounds. We further investigated the compound eliciting the strongest effect, termed 80136342. Its mechanism of action was distinct from that of ICL agents; 80136342 did not cause increased chromosomal aberrations, enhanced FANCD2 monoubiquitination, H2AX phosphorylation, p53 activation, or ICL induction. Similar to ICL agents, however, 80136342 caused a pronounced G(2) arrest in FA pathway-deficient cells. When applied in combination with ICL agents, 80136342 had at least additive toxic effects, excluding interferences on ICL-induced toxicity and facilitating a combinational application. Finally, we identified one particular methyl group necessary for the effects of 80136342 on FA-deficient cells. In conclusion, using high-throughput screening in an isogenic human FA cancer model, we explored a novel approach to identify agents eliciting hypersensitivity in FA pathway-deficient cells. We discovered several attractive candidates to serve as lead compounds for evaluating structure-activity relationships and developing therapeutics selectively targeting FA pathway-deficient tumors.

Mechanism of the formation of DNA-protein cross-links by antitumor cisplatin

DNA–protein cross-links are formed by various DNA-damaging agents including antitumor platinum drugs. The natures of these ternary DNA–Pt–protein complexes (DPCLs) can be inferred, yet much remains to be learned about their structures and mechanisms of formation. We investigated the origin of these DPCLs and their cellular processing on molecular level using gel electrophoresis shift assay. We show that in cell-free media cisplatin [cis-diamminedichloridoplatinum(II)] forms DPCLs more effectively than ineffective transplatin [trans-diamminedichloridoplatinum(II)]. Mechanisms of transformation of individual types of plain DNA adducts of the platinum complexes into the DPCLs in the presence of several DNA-binding proteins have been also investigated. The DPCLs are formed by the transformation of DNA monofunctional and intrastrand cross-links of cisplatin. In contrast, interstrand cross-links of cisplatin and monofunctional adducts of transplatin are stable in presence of the proteins. The DPCLs formed by cisplatin inhibit DNA polymerization or removal of these ternary lesions from DNA by nucleotide excision repair system more effectively than plain DNA intrastrand or monofunctional adducts. Thus, the bulky DNA–protein cross-links formed by cisplatin represent a more distinct and persisting structural motif recognized by the components of downstream cellular systems processing DNA damage considerably differently than the plain DNA adducts of this metallodrug.

Raman spectroscopy of DNA modified by intrastrand cross-links of antitumor cisplatin

Raman spectroscopy was employed to characterize the perturbations to DNA conformation induced in DNA by two different intrastrand adducts of antitumor cis-diamminedichloroplatinum(II) (cisplatin), namely by its 1,2-GG or 1,3-GTG intrastrand cross-links. We examined short deoxyribooligonucleotide duplexes containing single, site-specific cross-link by Raman spectroscopy and assigned the spectral alterations to conformational changes induced in DNA by 1,2-GG or 1,3-GTG intrastrand CLs determined earlier by other biochemical and biophysical methods. The results confirmed significant perturbations to the B-form DNA backbone due to the intrastrand lesions and that several nucleotides changed their conformation from C2'-endo to C3'-endo. Evidence for a partial transition from B- to A-form was found in several regions of the Raman spectra as well. The spectra also confirmed the different and more extensive distortion induced in B-DNA by 1,3-GTG in comparison with 1,2-GG intrastrand CLs, consistent with their already known high resolution structures. The results of the present work demonstrate that Raman spectroscopy represents a suitable tool to provide insights into structural factors involved in the mechanisms underlying antitumor effects of platinum drugs.