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Monofunctional platinum complexes offer a promising alternative to cisplatin in cancer chemotherapy, showing a unique mechanism of action. Their ability to induce minor helix distortions effectively inhibits DNA transcription. In our study, we synthesized and characterized three monofunctional Pt(II) complexes with the general formula [Pt(en)(L)Cl]NO 3 , where en = ethylenediamine, and L = pyridine (py), 2-methylpyridine (2-mepy), and 2-phenylpyridine (2-phpy). The hydrolysis rates of [Pt(en)(py)Cl]NO 3 ( 1 ) and [Pt(en)(2-mepy)Cl]NO 3 ( 2 ) decrease with the bulkiness of the auxiliary ligand with k( 1 ) = 2.28 ± 0.15 × 10 -4 s -1 and k( 2 ) = 8.69 ± 0.98 × 10 -5 s -1 at 298 K. The complex [Pt(en)(2-phpy)Cl]Cl ( 3 ) demonstrated distinct behavior. Upon hydrolysis, an equilibrium (K eq = 0.385 mM) between the complexes [Pt(en)(2-phpy)Cl] + and [Pt(en)(2-phpy-H + )] + was observed with no evidence (NMR or HR-ESI-MS) for the presence of the aquated complex [Pt(en)(2-phpy)(H 2 O)] 2+ . Despite the kinetic similarities between phenanthriplatin and ( 2 ), complexes ( 1 ) and ( 2 ) exhibit minimal activity against A549 lung cancer cell line (IC 50 > 100 μΜ), whereas complex ( 3 ) exhibits notable cytotoxicity (IC 50 = 41.11 ± 2.1 μΜ). In examining the DNA binding of ( 1 ) and ( 2 ) to the DNA model guanosine (guo), we validated their binding through guoN7, which led to an increased population of the C3'- endo sugar conformation, as expected. However, we observed that the rapid transition 2 E (C2' -endo ) ↔ 3 E (C3' -endo ), in the case of [Pt(en)(py)(guo)](NO 3 ) 2 ([ 1 -guo]), slows down in the case of [Pt(en)(2-mepy)(guo)](NO 3 ) 2 ([ 2 -guo]), resulting in separate signals for the two conformers in the 1 H NMR spectra. This phenomenon arises from the steric hindrance between the methyl group of pyridine and the sugar moiety of guanosine. Notably, this hindrance is absent in [ 2 -(9-MeG)] (9-MeG = 9-methylguanine), probably due to the absence of a bulky sugar unit in 9-MeG. In the case of ( 3 ), where the bulkiness of the substitution on the pyridine is further increased by a phenyl group, we observed a notable proximity between 9-MeGH8 and the phenyl ring of 2-phpy. Considering that only ( 3 ) exhibited good cytotoxicity against the A549 cancer cell line, it is suggested that auxiliary ligands, L, with an extended aromatic system and proper orientation in complexes of the type cis-[Pt(en)(L)Cl]NO 3 , may enhance the cytotoxic activity of such complexes.

Although the interactions of oligopyridine ruthenium complexes with DNA have been widely studied, the biological activity of similar diruthenium oligopyridine complexes conjugated with peptides has not been investigated. Herein, we report the stepwise synthesis and characterization of diruthenium complexes with the general formula [(L a )Ru(tppz)Ru(L b )] n+ (tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine, L a = 2,2':6',2''-terpyridine or 4-phenyl-2,2':6',2''-terpyridine and L b = 2,2':6',2''-terpyridine-4'-CO(Gly 1 -Gly 2 -Gly 3 -LysCONH 2 ) (5), (6), n = 5; 2,2':6',2''-terpyridine-4'-CO(Gly 1 -Gly 2 -Lys 1 -Lys 2 CONH 2 ) (7), (8), n = 6; 2,2':6',2''-terpyridine-4'-CO(Ahx-Lys 1 Lys 2 CONH 2 ) (9), (10), n = 5, Ahx = 6-aminohexanoic acid). The compounds [(trpy)Ru(tppz)Ru(trpy-CO 2 H)](PF 6 ) 4 , (2)(PF 6 ) 4 , [(ptrpy)Ru(tppz)Ru(trpy-CO 2 H)](PF 6 ) 4 , (3)(PF 6 ) 4 and [(ptrpy)Ru(tppz)Ru(trpy)](PF 6 ) 4 , (4)(PF 6 ) 4 were also characterized by single crystal X-ray methods. Moreover, the interactions of the chloride salts (5), (6) and (4) with the self-complementary dodecanucleotide duplex d(5'-CGCGAATTCGCG-3') 2 were studied by NMR spectroscopic techniques. The results show that complex (4) binds in the central part of the oligonucleotide, from the minor groove through the ligand ptrpy, while the ligand trpy, which was located on the other side of the diruthenium core, does not contribute to the binding. Complex (5) binds similarly, through the ligand ptrpy. However, the induced upfield shifts of the ptrpy proton signals are significantly lower than the corresponding ones in the case of (4), indicating much lower binding affinity. This is clear evidence that the tethered peptide Gly 1 -Gly 2 -Gly 3 -Lys 1 CONH 2 hinders the complex binding, even though it contains groups that are able to assist it (e.g., the positively charged amino group of lysine, the peptidic backbone, the terminal amide). Complex (6) shows a non-specific binding, interacting through electrostatic forces. The chloride salts of (4), (5) and (6) had insignificant effects on the cell cycle distribution and marginal cytotoxicity (IC 50 > 750 μM) against human lung cancer cell lines H1299 and H1437, indicating that their binding to the oligonucleotide is not a sufficient condition for their cytotoxicity.

The synthesis, characterization and DNA binding properties of the complex [Ru(terpy)(4,4'-(COLysCONH(2))(2)bpy)Cl](3+) (1) have been studied. Complex (1) hydrolyzes to (2) with a calculated rate constant K(h) = 2.35 ± 0.08 × 10(-4) s(-1) and binds coordinatively to ct-DNA, with a saturation r-value at about 0.1. Stabilization of the ct-DNA helix at low electrolyte (NaClO(4)) concentration (10 mM) and destabilization at higher electrolyte concentrations (50-200 mM) was observed. Circular dichroism studies indicate that the hydrolyzed complex binds to DNA, increasing the unwinding of the DNA helix with an unwinding angle calculated as Φ = 12 ± 2°. The positive LD signal observed at 350 nm indicates some kind of specificity in complex orientation towards the global DNA axis. Complex (2) binds specifically to G4 on the central part of the oligonucleotide duplexes d(CGCGCG)(2) and d(GTCGAC)(2), as evidenced by NMR spectroscopy. Both lysine moieties were found to interact most likely electrostatically with the DNA phosphates, assisting the coordinative binding and increasing the DNA affinity of the complex. Photoinduced DNA cleavage by (2), upon UVA irradiation was observed, but despite its relative high DNA affinity, it was incomplete (~12%).

Diastereomeric oligopyridine-ruthenium(II)-amino acid conjugated complexes of the general formulas Lambda- and Delta-[Ru(bpy)(2)(4,4'(CO(2)Y)(2)-bpy)](2+), where Y = L-AlaCONH(2), L-LysCONH(2), L-HisCONH(2), L-TyrCONH(2)), were synthesized and characterized. Their binding properties with ct-DNA and the oligonucleotide duplex d(5'CGCGCG-3')(2), by means of circular dichroism (CD), NMR spectroscopy and DNA thermal denaturation (T(m)) curves were studied. CD and T(m) data indicate that all diastereomeric complexes bind to the DNA major groove, Delta-diastereomers in a similar manner, while Lambda-diastereomers in dependence of the nature of the amino acid. NMR studies of d(5'CGCGCG-3')(2), and the complexes Delta-1, Delta-2, Lambda-1 and Lambda-2 indicate that Delta-1 and Delta-2 were bound having the ancillary bpy ligands towards the DNA groove, while the corresponding Lambda-1 and Lambda-2 were orientated in a similar way, facing the ligand 4,4'(CO(2)Y)(2)bpy towards the DNA major groove. Photoinduced DNA cleavage was observed in all cases studied, which take place through singlet oxygen production. Delta-4 and Lambda-4 show the lower photoinduced cleavage yield, probably because the singlet oxygen ((1)O(2)) oxidizes not only the DNA phosporodiesteric bonds but the tyrosine's phenolic OH bond as well.

The DNA-binding properties of a number of ruthenium oligopyridine complexes with conjugated amino acids having the general formulae [Ru(terpy)(4-COY-4'-Mebpy)(X)](n)(+), X=NO (n=3), X=Cl (n=1) and NO(2) (n=1) and Y=AlaCONH(2) and TrpCONH(2) are reported. The new complexes were spectroscopically characterized and their DNA-binding properties were studied by means of circular dichroism (CD), (23)Na and (31)P NMR spectroscopy. The results show that the chlorido complexes interact by coordination to the DNA bases with the conjugated amino acid able to provide an additional interaction with the DNA helix. In addition, electrostatic interactions between all studied complexes and the DNA polyanion were observed. The nitro complexes were found to be insignificant, affecting only the (31)P NMR signal, probably due to changes in the hydration sphere of the DNA close to the phosphates.

The interaction of the diastereomeric complexes Lambda-[Ru(bpy)2(m-GHK)]Cl2 and Delta-[Ru(bpy)2(m-GHK)]Cl2 (bpy is 2,2'-bipyridine, GHK is glycine-L-histidine-L-lysine) with the deoxynucleotide duplex d(5'-CGCGATCGCG)2 was studied by means of 1H NMR spectroscopy. At a Delta-isomer to DNA ratio of 1:1, significant shifts for the metal complex are observed, whereas there is negligible effect on the oligonucleotide protons and only one intermolecular nuclear Overhauser effect (NOE) is present at the 2D nuclear Overhauser enhancement spectroscopy spectrum. The 1Eta NMR spectrum at ratio 2:1 is characterized by a slight shift for the Delta-isomer's bpy aromatic protons as well as significant shifts for the decanucleotide G4 H1' and Eta2'', A5 H2, G10 H1', T6 NH and G2 NH protons. Furthermore, at ratio 2:1, 11 intermolecular NOEs are observed. The majority of the NOEs involve the sugar Eta2' and Eta2'' protons sited in the major groove of the decanucleotide. Increasing the Delta-isomer to d(CGCGATCGCG)2 ratio to 5:1 results in noteworthy spectral changes. The Delta-isomer's proton shifts are reduced, whereas significant shifts are observed for the decanucleotide protons, especially the sugar protons, as well as for the exchangeable protons. Interaction is characterized by the presence of only one intermolecular NOE. Furthermore, there is significant broadening of the imino proton signals as the ratio of the Delta-isomer to DNuAlpha increases, which is attributed to the opening of the two strands of the duplex. The Lambda-isomer, on the other hand, approaches the minor groove of the oligonucleotide and interacts only weakly, possibly by electrostatic interactions. Photocleavage studies were also conducted with the plasmid pUC19 and a 158-bp restriction fragment, showing that both diastereomers cleave DNA with similar efficiency, attacking mainly the guanines of the sequence probably by generating active oxygen species.

The complexes of general formulas [RuII(terpy)(4-CO2H-4'-Mebpy)(X)]n+ (X = NO (n = 3) and NO2 (n = 1); 1, 2) and [RuII(terpy)(4-COGHK-4'-Mebpy)(X)] (X = NO (n = 3) and NO2 (n = 1); 3, 4) were synthesized and characterized. The complex [RuII(terpy)(4-CO2-4'-Mebpy)(NO2)]_7.5H2O has also been characterized by X-ray crystallographic studies. It crystallizes in the triclinic system: a = 9.4982(1) A, b = 13.1330(1) A, c = 14.2498(2) A; alpha = 110.5870(6) x bc, beta = 98.4048(5) x bc, gamma = 106.4353(5), P1, Z = 2. The crystal structure reveals an extended hydrogen-bonding network. Two water molecules form strong hydrogen bonds with the nitro and the carboxylic oxygen atoms of two separate units of the complex, resulting in a dimeric unit. The dimers are bridged by a (H2O)15 cluster, consisting of two cyclo-(H2O)6 species, while an exo-H2O(8) connects them. Two more exo-H2O molecules are joined together and connect the cyclo-(H2O)6 units with the H2O(1) of the dimeric unit. It was found that complexes 1 and 3 can be transformed into their nitro derivatives in aqueous media at neutral pH. Photorelease of NO in dry MeCN solutions was observed for complexes 1 and 3. Also, complex 2 partially releases (NO2)- in MeCN upon visible light irradiation. Complex 2 interacts with short fragments (70-300 bp) of calf thymus DNA shortening slightly the apparent polynucleotide length, while the conjugation of the peptide GHK to it (2) affects its DNA-binding mode. The peptide moiety of complex 4 was found to interact with the DNA helix in a synergistic way with the whole complex. Preliminary results of photocleavage of DNA by complex 2 are also reported.

The complex cis-(Cl,Cl)-[RuCl2(terpy)(NO)]Cl (1) has been synthesized by the reaction of [RuCl3(H2O)2(NO)] with terpyridine (terpy) and characterized by various spectroscopic, analytical techniques and using electronic structure calculation (DFT) methods. The cytotoxic activity and the DNA-binding properties of have also been studied using biochemical techniques. The results establish unequivocally that corresponds to a so-called [RuNO]6 species, which readily releases the nitrosyl ligand upon irradiation with a mercury lamp in acetonitrile solution. DFT calculations provided a satisfactory description of structural, bonding, electronic and related properties of the new compound and throw light on the mechanism of the photo-induced NO release. Screening on A2780 (human ovarian carcinoma) cell lines showed significant cytotoxicity with an IC50 value of 0.49 microM. 31P and 23Na NMR spectroscopy along with electrophoretic mobility studies illustrated that complex primarily binds by coordination to DNA without any pi-interaction between the planar terpy ligand and the DNA bases, while weak electrostatic interactions could not be excluded. Studies on the inhibition of the restriction enzymes DraI and SmaI revealed that prefers the guanine and cytosine bases of DNA.

A general method for the synthesis of chloro(polypyridyl)ruthenium conjugated peptide complexes via a solid-phase strategy is described. The method is applied to synthesize two positional isomers of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6). Even though the separation of the isomers was only partially achieved chromatographically, the isomers were unambiguously assigned by NMR spectroscopy. The interactions of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6) with CT-DNA and plasmid DNA, have been studied with various spectroscopic techniques, showing that (i) the complexes coordinatively bind to DNA preferring the bases guanine and cytosine over the bases thymine and adenine after hydrolysis of the coordinated chloride, (ii) electrostatic interactions between the complex cation and the polyanionic DNA chain assist this binding (iii) only in the case of one isomer the peptide does interact further with DNA as evidenced from 31P NMR spectroscopy, (iv) DNA unwinding occurs in all cases with high binding ratio (Ru/base) values (r > 0.3).

Novel full-sandwich (η5-Cp)-Ru-paraphenylene complexes with the general formula [(η5-Cp)nRu(η6-L)](PF6)n where n = 1–3 and L = biphenyl, p-terphenyl and p-quaterphenyl, were synthesized and characterized by means of spectroscopic and analytical techniques. The structures of the complexes [(η5-Cp)Ru(η6-biphenyl)](PF6) (1), [(η5-Cp)Ru(η6-terphenyl)](PF6) (3) and [(η5-Cp)2Ru(η6-terphenyl)](PF6)2 (4) was determined by X-ray single crystal methods. The interaction of the complexes [(η5-Cp)Ru(η6-quaterphenyl)]Cl, (6)Cl, and [(η5-Cp)2Ru(η6-quaterphenyl)]Cl2, (7)Cl2, with the DNA duplex d(5′-CGCGAATTCGCG-3′)2 was studied using NMR techniques. The results showed that both complexes interacted non-specifically with both the minor and major grooves of the helix. Specifically, (6)Cl exhibited partial binding through intercalation between the T7 and T8 bases of the sequence without disrupting the C–G and A–T hydrogen bonds. Fluorometric determination of the complexes' binding constants revealed a significant influence of the number of connected phenyl rings in the paraphenylene ligand (L) on the binding affinity of their complexes with the d(5′-CGCGAATTCGCG-3′)2. The complexes (6)Cl and (7)Cl2 were found to be highly cytotoxic against the A549 lung cancer cell line, with complex (6) being more effective than (7) (IC50 for (6)Cl: 17.45 ± 2.1 μΜ, IC50 for (7)Cl2: 65.83 ± 1.8 μΜ) and with a selectivity index (SI) (SI for (6)Cl: 1.1 and SI for (7)Cl2: 4.8). [ABSTRACT FROM AUTHOR]

The novel binuclear η6-arene-Ru(II) complexes with the general formula {[(η6-cym)Ru(L)]2(μ-BL)}(PF6)4, and their corresponding water soluble {[(η6-cym)Ru(L)]2(μ-BL)}Cl4, where cym = p-cymene, L = 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen), BL = 4,4′-bipyridine (BL-1), 1,2-bis(4-pyridyl)ethane (BL-2) and 1,3-bis(4-pyridyl)propane (BL-3), were synthesized and characterized. The structure of {[(η6-cym)Ru(phen)]2(μ-BL-1)}(PF6)4 was determined by X-ray single crystal methods. The interaction of {[(η6-cym)Ru(phen)]2(μ-BL-i)}Cl4 (i = 1, 2, 3; (4), (5) and (6) correspondingly) with the DNA duplex d(5′-CGCGAATTCGCG-3′)2 was studied by means of NMR techniques and fluorescence titrations. The results show that complex (4) binds with a Kb = 12.133 × 103 M−1 through both intercalation and groove binding, while (5) and (6) are groove binders (Kb = 2.333 × 103 M−1 and Kb = 3.336 × 103 M−1 correspondingly). Comparison with the mononuclear complex [(η6-cym)Ru(phen)(py)]2+ reveals that it binds to the d(5′-CGCGAATTCGCG-3′)2 with a Kb value two orders of magnitude lower than (4) (Kb = 0.158 × 103 M−1), indicating that for the binuclear complexes both ruthenium moieties participate in the binding. The complexes were found to be cytotoxic against the A2780 and A2780 res. cancer cell line with a selectivity index (SI) in the range of 3.0–5.9. [ABSTRACT FROM AUTHOR]

The interaction of the diastereomeric complexes Λ-[Ru(bpy)2(m-GHK)]Cl2 and Δ-[Ru(bpy)2(m-GHK)]Cl2 (bpy is 2,2′-bipyridine, GHK is glycine– l-histidine– l-lysine) with the deoxynucleotide duplex d(5′-CGCGATCGCG)2 was studied by means of 1H NMR spectroscopy. At a Δ-isomer to DNA ratio of 1:1, significant shifts for the metal complex are observed, whereas there is negligible effect on the oligonucleotide protons and only one intermolecular nuclear Overhauser effect (NOE) is present at the 2D nuclear Overhauser enhancement spectroscopy spectrum. The 1Η NMR spectrum at ratio 2:1 is characterized by a slight shift for the Δ-isomer’s bpy aromatic protons as well as significant shifts for the decanucleotide G4 H1′ and Η2″, A5 H2, G10 H1′, T6 NH and G2 NH protons. Furthermore, at ratio 2:1, 11 intermolecular NOEs are observed. The majority of the NOEs involve the sugar Η2′ and Η2″ protons sited in the major groove of the decanucleotide. Increasing the Δ-isomer to d(CGCGATCGCG)2 ratio to 5:1 results in noteworthy spectral changes. The Δ-isomer’s proton shifts are reduced, whereas significant shifts are observed for the decanucleotide protons, especially the sugar protons, as well as for the exchangeable protons. Interaction is characterized by the presence of only one intermolecular NOE. Furthermore, there is significant broadening of the imino proton signals as the ratio of the Δ-isomer to DΝΑ increases, which is attributed to the opening of the two strands of the duplex. The Λ-isomer, on the other hand, approaches the minor groove of the oligonucleotide and interacts only weakly, possibly by electrostatic interactions. Photocleavage studies were also conducted with the plasmid pUC19 and a 158-bp restriction fragment, showing that both diastereomers cleave DNA with similar efficiency, attacking mainly the guanines of the sequence probably by generating active oxygen species. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of the enantiomeric complexes Λ- and Δ-[Ru(bpy)2(pbmz)](PF6)2 (bpy=2,2′-bipyridine, pbmz=2-(2′-pyridyl)benzimidazole) with the DNA duplex d(CGCGAATTCGCG)2 was investigated by means of 2D NMR techniques. The synthesis of the enantiomers was based on the optically pure complexes Λ- and Δ-[Ru(bpy)2(py)2]2+ and were characterized by CD and NMR spectroscopy. NMR data indicate that both enantiomers bind weakly to the oligonucleotide, approaching from the minor groove at the centre of the helix. The perturbation of the B-DNA conformation is minor with an apparent absence of enantioselectivity. Molecular modelling calculations in conjunction with the NOE data support the suggestion that more than one binding modes are present. The imidazole amine group of the pbmz ligand is probably hydrogen bonded to the DNA phosphodiesteric backbone at the AATT step, and this may provide an explanation for the diminished enantioselectivity observed. [Copyright &y& Elsevier]