Cytotoxicity evaluation and DNA interaction of RuII-bipy complexes containing coumarin-based ligands.

Although there are various treatment options for cancer, this disease still has caused an increasing number of deaths, demanding more efficient, selective and less harmful drugs. Several classes of ruthenium compounds have been investigated as metallodrugs for cancer, mainly after the entry of imidazolH [trans-RuCl4-(DMSO-S)(imidazole)] (NAMI-A) and indazolH [trans-RuCl4-(Indazol)2] (KP1019) in clinical trials. In this sense, RuII complexes with general formula [Ru(L1-3)(bipy)2]PF6 (1-3) (L1 = ethyl 3-(6-methyl-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L2 = ethyl 3-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L3 = ethyl 3-(8-methoxy-2-oxo-2H-chromen-3-yl)-3-oxopropanoate and bipy = bipyridine) have been synthesized. The crystal structure of 2 revealed that the RuII atom lies on a distorted octahedral geometry with the deprotonated ligand (L2-) coordinated through ß-ketoester group oxygen atoms. In vitro cytotoxic activity of the compounds was evaluated against 4T1 (murine mammary carcinoma) and B16-F10 (murine metastatic melanoma) tumor cells, and the non-tumor cell line BHK-21 (baby hamster kidney). Coordination with RuII resulted in expressive enhancement of cytotoxic activity. The precursors were inactive below 100 µM and the final RuII complexes (1-3) showed IC50 ranging from 2.0 to 12.8 µM; 2 being the most potent compound. DNA interaction studies revealed a greater capacity of the complexes to interact with DNA than the ligands, where, 2 exhibited the highest Kb constant of 2.2 × 104 M-1. Fluorescence investigation demonstrated that 1-3 are capable of quenching the fluorescence emission of the EtdBr-DNA complex up to 40%. Molecular docking showed that the interaction of 1-3 between the DNA base pairs from the coumarin portion was with scores of 67.28, 68.62 and 64.88, respectively, and 75.45 for ellipticine, suggesting an intercalative mode of binding. Our findings show that the RuII complexes are eligible for continuing to be investigated as potential antitumor compounds.

Quinolone-N-acylhydrazone hybrids as potent Zika and Chikungunya virus inhibitors.

This work reports the synthesis of quinolone-N-acylhydrazone hybrids, namely 6-R-N'-(2-hydxoxybenzylidene)-4-oxo-1,4-dihydroquinoline-3-carbohydrazide (R = H: 5a, F: 5b, Cl: 5c and Br: 5d), which exhibited excellent activity against arbovirus Zika (ZIKV) and Chikungunya (CHIKV). In vitro screening towards ZIKV and CHIKV inhibition revealed that all substances have significant antiviral activity, most of them being more potent than standard Ribavirin (5a-d: EC50 = 0.75-0.81 µM, Ribavirin: EC50 = 3.95 µM for ZIKV and 5a-d: 1.16-2.85 µM, Ribavirin: EC50 = 2.42 µM for CHIKV). The quinolone-N-acylhydrazone hybrids were non-toxic against Vero cells, in which compounds 5c and 5d showed the best selectivities (SI = 1410 and 630 against ZIKV and CHIKV, respectively). Antiviral activity was identified by inhibition of viral RNA production in a dose-dependent manner. In the evaluation of the time of addition of the compounds, we observed that 5b and 5c remain with strong effect even in the addition for 12 h after infection. The above results indicate that quinolone-N-acylhydrazones represent a new and promising class to be further investigated as anti-ZIKV and anti-CHIKV agents.

Novel CoIII complexes containing fluorescent coumarin-N-acylhydrazone hybrid ligands: Synthesis, crystal structures, solution studies and DFT calculations.

A series of new CoIII complexes of the type [Co(dien)(L1-L3)]ClO4 (1-3), containing fluorescent coumarin-N-acylhydrazonate hybrid ligands, (E)-N'-(1-(7-oxido-2-oxo-2H-chromen-3-yl)ethylidene)-4-R-benzohydrazonate [where R=H (L12-), OCH3 (L22-) or Cl (L32-)], were obtained and isolated in the low spin CoIII configuration. Single-crystal X-ray diffraction showed that the coumarin-N-acylhydrazones act as tridentate ligands in their deprotonated form (L2-). The cation (+1) complexes contain a diethylenetriamine (dien) as auxiliary ligand and their structures were calculated by DFT studies which were also performed for the CoII (S=1/2 and S=3/2) configurations. The LS CoII (S=1/2) concentrated the spin density on the O-Co-O axis while the HS CoII (S=3/2) exhibited a broad spin density distribution around the metallic center. Cyclic voltammetry studies showed that structural modifications made in the L2- ligands caused a slight influence on the electronic density of the metal center, and the E1/2 values for the CoIII/CoII redox couple increased following the electronic effect of the R-substituent, in the order: 2 (R=OCH3)<1 (R=H)<3 (R=Cl). The theoretical redox potentials (E°) of the process CoIII→CoII were calculated for both CoII spin states (S=1/2 and S=3/2) and a better correlation was found for CoIII→CoII (S=1/2), compared with experimental values vs SHE (E°calc=-0.37, -0.36 and -0.32V vs E°exp.=-0.371, -0.406 and -0.358V, for 1-3 respectively). Complexes 1-3 exhibited a very intense absorption band around 470nm, assigned by DFT calculations as π-π* transitions from the delocalized coumarin-N-acylhydrazone system. 1-3 were very stable in MeOH for several days. Likewise, 1-3 were stable in phosphate buffer containing sodium ascorbate after 15h, which was attributed to the high chelate effect and σ-donor ability of the L2- and dien ligands.

New insights into 3-(aminomethyl)naphthoquinones: Evaluation of cytotoxicity, electrochemical behavior and search for structure-activity correlation.

Herein we describe the structure-activity relationship of a large library of Mannich bases (MBs) synthesized from 2-hydroxy-1,4-naphthoquinone. In general, the compounds have shown high to moderate activity against the HL-60 (promyelocytic leukaemia) cell line with IC50=1.1-19.2µM. Our results suggest that the nature of the aryl moiety introduced in the structure of MBs by the aldehyde component is crucial to the cytotoxicity, and although the group originated from the primary amine has a lesser influence, aromatic ones were found to suppress the activity. Thus, MBs derived from salicylaldehydes or 2-pyridinecarboxaldehyde and aliphatic amines are the most active compounds. A satisfactory correlation of the EpIIc versus IC50 (µM) in dimethylsulfoxide was observed. The most cytotoxic MBs (Series a-c, derived from salicylaldehydes) showed the least negative EpIIc values. Noteworthy, however, Series d (derived from 2-pyridinecarboxaldehyde) did not follow this correlation. They exhibited both the lowest IC50 and the most negative EpIIc values, thus suggesting that other factors also influence the cytotoxicity of the MBs, such as lipophilicity, electronic distribution and hydrogen bonding.

Synthetic aminomethylnaphthoquinones inhibit the in vitro replication of bovine herpesvirus 5.

Bovine herpesvirus type 5 (BoHV-5) is an etiologic agent of meningoencephalitis in cattle. The aim of this study was to evaluate the antiviral potential of a series of synthetic Mannich bases derived from lawsone and to investigate at which stage of the BoHV-5 replicative cycle the compounds might be acting. The most potent and selective inhibitor exhibited CC50 and EC50 values of 1867 µM ± 8.3 and 3.8 µM ± 1.2, respectively (ACV: 989 µM ± 2 and 166 µM ± 2, respectively).

Exploring the DNA binding/cleavage, cellular accumulation and topoisomerase inhibition of 2-hydroxy-3-(aminomethyl)-1,4-naphthoquinone Mannich bases and their platinum(II) complexes.

Several chlorido and amino Pt(2+) complexes of 2-hydroxy-3-(aminomethyl)-1,4-naphthoquinone Mannich bases HL exhibiting moderate to high cytotoxicity against cancer cell lines were studied in order to investigate their modes of DNA binding, in vitro DNA strand breaks, mechanism of topoisomerase (Topo I) inhibition and cellular accumulation. DNA model base studies have shown that complex 1a [Pt(HL1)Cl(2)] was capable of binding covalently to 9-ethylguanine (9-EtG) and 5'-GMP. (1)H NMR and mass spectrometry studies have shown that both chlorides were substituted by 9-EtG ligands, whereas 5'-GMP was able to replace only one chlorido ligand, due to steric hindrance. The chlorido Pt(2+) complexes [Pt(HL)Cl(2)] highly accumulate in prostate (PC-3) and melanoma (MDA-MB-435) cell lines, being able to induce DNA strand breaks in vitro and inhibit Topo I by a catalytic mode. On the other hand, the free 2-hydroxy-3-(aminomethyl)-1,4-naphthoquinones HL and the amino Pt(2+) complexes [Pt(L(-))(NH(3))(2)]NO(3) neither cause DNA strand breakage nor exhibit strong DNA interaction, nevertheless the latter were also found to be catalytic inhibitors of Topo I at 100µM. Thus, coordination of the Mannich bases HL to the "PtCl(2)" fragment substantially affects the chemical and biophysical properties of the pro-ligands, leading to an improvement of their DNA binding properties and generating compounds that cleave DNA and catalytically inhibit Topo I. Finally, the high cytotoxicity exhibited by the free (uncomplexed) 2-hydroxy-3-(aminomethyl)-1,4-naphthoquinones might be associated with their decomposition in solution, which is not observed for the Pt(2+) complexes.

Novel zinc(II) and copper(II) complexes of a Mannich base derived from lawsone: Synthesis, single crystal X-ray analysis, ab initio density functional theory calculations and vibrational analysis.

Zinc(II) and copper(II) complexes of a tridentate Mannich base L1 derived from 2-hydroxy-1,4-naphthoquinone, pyridinecarboxyaldehyde and 2-aminomethylpyridine, [ZnL1Cl(2)]·H(2)O 1 and [CuL1Cl(2)]·2H(2)O 2, have been synthesized and fully characterized. The structure of complex 1 has been elucidated by a single crystal X-ray diffraction study: the zinc atom is pentacoordinate and the coordination geometry is a distorted square base pyramid, with a geometric structural parameter τ equal to 0.149. Vibrational spectroscopy and ab initio DFT calculations of both compounds have confirmed that the two complexes exhibit similar structures. Full assignment of the vibrational spectra was also supported by careful analysis of the distorted geometries generated by the normal modes.

Novel platinum(II) complexes of 3-(aminomethyl)naphthoquinone Mannich bases: synthesis, crystal structure and cytotoxic activities.

The first examples of platinum(II) complexes of 3-(aminomethyl)naphthoquinone Mannich bases have been synthesised and their crystal structures are described. Neutral and charged complexes have been obtained, fully characterised and their cytotoxic activities have also been investigated. 3-[(R(1)-amino)(pyridin-2-yl)methyl]-2-hydroxy-1,4-naphthoquinones (R(1) = n-Bu, HL1; Bn, HL2; furfuryl, HL3; n-heptyl, HL4 and n-decyl, HL5) coordinate to platinum(II) through the two nitrogen atoms. The neutral complexes cis-[Pt(HL)Cl(2)] 1a-5a are analogous to cisplatin with the bidentate ligand HL and two chlorine atoms occupying cis positions. In the charged complexes cis-[Pt(L(-))(NH(3))(2)]NO(3)1b-5b the deprotonated form of the ligand L(-) also coordinates via the nitrogen atoms, and the other two positions around the platinum(II) ion are completed with NH(3) ligands. The cytotoxic activities of all compounds have been tested for six different cancer cell lines: MDA-MB-435 (melanoma), HL-60 (promyelocytic leukaemia), HCT-8 (colon), SF-295 (brain), OVCAR-8 (ovary) and PC-3 (prostate). Proligands HL4 and HL5 have exhibited high activity against HL-60 (IC(50) = 1.9 and 3.8 µmol L(-1), respectively), HCT-8 (IC(50) = 1.6 and 1.7 µmol L(-1), respectively) and SF-295 (IC(50) = 1.1 and 1.7 µmol L(-1), respectively). The chlorido complexes 1a-5a have shown high to moderate cytotoxic activities, complex 4a (R(1) = n-heptyl) being more active than proligand HL4 against melanoma (IC(50) = 6.4 and > 40 µmol L(-1), respectively) and more active than cisplatin against all tested cell lines. Among the amine charged complexes only 4b and 5b have exhibited significant cytotoxic activity against the tested cell lines, although they were only moderately active against the PC-3 cell line (IC(50) = 29.9 and 15.6 µmol L(-1), respectively). In general the compounds with the longest carbon chains (R(1) = n-heptyl and n-decyl) have exhibited the highest activities.