Metal(triphenylphosphine)-atovaquone Complexes: Synthesis, Antimalarial Activity, and Suppression of Heme Detoxification.

To ascertain the bioinorganic chemistry of metals conjugated with quinones, the complexes [Ag(ATV)(PPh3)2] (1), [Au(ATV)(PPh3)]·2H2O (2), and [Cu(ATV)(PPh3)2] (3) were synthesized by the coordination of the antimalarial naphthoquinone atovaquone (ATV) to the starting materials [Ag(PPh3)2]NO3, [Au(PPh3)Cl], and [Cu(PPh3)2NO3], respectively. These complexes were characterized by analytical and spectroscopical techniques. X-ray diffraction of single crystals precisely confirmed the coordination mode of ATV to the metals, which was monodentate or bidentate, depending on the metal center. Both coordination modes showed high stability in the solid state and in solution. All three complexes showed negative log D values at pH 5, but at pH 7.4, while complex 2 continued to have a negative log D value, complexes 1 and 3 displayed positive values, indicating a more hydrophilic character. ATV and complexes 1-3 could bind to ferriprotoporphyrin IX (FePPIX); however, only complexes 1-3 could inhibit ß-hematin crystal formation. Phenotype-based activity revealed that all three metal complexes are able to inhibit the growth of P. falciparum with potency and selectivity comparable to those of ATV, while the starting materials lack this activity. The outcomes of this chemical design may provide significant insights into structure-activity relationships for the development of new antimalarial agents.

Zinc-clotrimazole complexes are effective against Trichomonas vaginalis.

Trichomonas vaginalis is a protozoan parasite that causes trichomoniasis in humans, the most prevalent non-viral sexually transmitted disease (STD). Imidazole compounds are used for the treatment of trichomoniasis, and metronidazole is the most commonly prescribed. However, these compounds can lead to parasite resistance and unwanted side effects. Therefore, there is a need for an alternative treatment for this disease. Here, we explored the potential of clotrimazole (CTZ) and zinc compounds, as well as CTZ complexed with zinc salts ([1] acetate [Zn(CTZ)2(Ac)2] and [2] a chloride [Zn(CTZ)2Cl2] complexes) against T. vaginalis. We synthesized the zinc complexed CTZ compounds and determined their concentration values that inhibited parasite growth by 50% (IC50). We used scanning and transmission electron microscopy to visualize the ultrastructural alterations induced by CTZ and their zinc complexes. The incubation of the parasites with [Zn(CTZ)2(Ac)2] complex inhibited their growth, yielding an IC50 of 4.9 µm. Moreover, there were changes in the shape of treated parasites, including the formation of surface projections that subsequently detached from the cell, in addition to changes in the hydrogenosomes, endoplasmic reticulum and Golgi complex. We found [Zn(CTZ)2(Ac)2] to be a highly effective compound against T. vaginalis in vitro, suggesting its potential utility as an alternative chemotherapy for trichomoniasis.

Copper(I)-Phosphine Polypyridyl Complexes: Synthesis, Characterization, DNA/HSA Binding Study, and Antiproliferative Activity.

A series of copper(I)-phosphine polypyridyl complexes have been investigated as potential antitumor agents. The complexes [Cu(PPh3)2dpq]NO3 (2), [Cu(PPh3)2dppz]NO3 (3), [Cu(PPh3)2dppa]NO3 (4), and [Cu(PPh3)2dppme]NO3 (5) were synthesized by the reaction of [Cu(PPh3)2NO3] with the respective planar ligand under mild conditions. These copper complexes were fully characterized by elemental analysis, molar conductivity, FAB-MS, and NMR, UV-vis, and IR spectroscopies. Interactions between these copper(I)-phosphine polypyridyl complexes and DNA have been investigated using various spectroscopic techniques and analytical methods, such as UV-vis titrations, thermal denaturation, circular dichroism, viscosity measurements, gel electrophoresis, and competitive fluorescent intercalator displacement assays. The results of our studies suggest that these copper(I) complexes interact with DNA in an intercalative way. Furthermore, their high protein binding affinities toward human serum albumin were determined by fluorescence studies. Additionally, cytotoxicity analyses of all complexes against several tumor cell lines (human breast, MCF-7; human lung, A549; and human prostate, DU-145) and non-tumor cell lines (Chinese hamster lung, V79-4; and human lung, MRC-5) were performed. The results revealed that copper(I)-phosphine polypyridyl complexes are more cytotoxic than the corresponding planar ligand and also showed to be more active than cisplatin. A good correlation was observed between the cytostatic activity and lipophilicity of the copper(I) complexes studied here.

Chiral Platinum(II) Complexes Featuring Phosphine and Chloroquine Ligands as Cytotoxic and Monofunctional DNA-Binding Agents.

Chiral molecules in nature are involved in many biological events; their selectivity and specificity make them of great interest for understanding the behavior of bioactive molecules, by providing information about the chiral discrimination. Inspired by these conformational properties, we present the design and synthesis of novel chiral platinum(II) complexes featuring phosphine and chloroquine ligands with the general formula [PtCl(P)2(CQ)]PF6 (where (P)2 = triphenylphosphine (PPh3) (5), 1,3-bis(diphenylphosphine)propane (dppp) (6), 1,4-bis(diphenylphosphine)butane (dppb) (7), 1,1'-bis(diphenylphosphine)ferrocene (dppf) (8), and CQ = chloroquine] and their precursors of the type [PtCl2(P)2] are described. The complexes were characterized by elemental analysis, absorption spectroscopy in the infrared and ultraviolet-visible (UV-vis) regions, multinuclear ((1)H, (13)C, (31)P, (15)N, and (195)Pt) NMR spectroscopy, cyclic voltammetry, and mass spectrometry (in the case of chloroquine complexes). The interactions of the new platinum-chloroquine complexes with both albumin (BSA), using fluorescence spectroscopy, and DNA, by four widely reported methods were also evaluated. These experiments showed that these Pt-CQ complexes interact strongly with DNA and have high affinities for BSA, in contrast to CQ and CQDP (chloroquine diphosphate), which interact weakly with these biomolecules. Additional assays were performed in order to investigate the cytotoxicity of the platinum complexes against two healthy cell lines (mouse fibroblasts (L929) and the Chinese hamster lung (V79-4)) and four tumor cell lines (human breast (MDA-MB-231 and MCF-7), human lung (A549), and human prostate (DU-145)). The results suggest that the Pt-CQ complexes are generally more cytotoxic than the free CQ, showing that they are promising as anticancer drugs.

Magnetic Mesoporous Silica for Targeted Drug Delivery of Chloroquine: Synthesis, Characterization, and In Vitro Evaluation.

Malaria is a dangerous tropical disease, with high morbidity in developing countries. The responsible parasite has developed resistance to the existing drugs; therefore, new drug delivery systems are being studied to increase efficacy by targeting hemozoin, a parasite paramagnetic metabolite. Herein, magnetic mesoporous silica (magMCM) was synthesized using iron oxide particles dispersed in the silica structure for magnetically driven behavior. The X-ray diffractogram (XRD) and Mössbauer spectra show patterns corresponding to magnetite and maghemite. Furthermore, Mössbauer spectroscopy revealed superparamagnetic behavior, attributed to single magnetic domains in particles smaller than 10 nm. Even in the presence of iron oxide particles, the hexagonal structure of MCM is clearly identified in XRD (low-angle region) and the channels are visible in TEM images. The drug chloroquine (CQ) was encapsulated by incipient wetness impregnation (magMCM-CQ). The N2 adsorption-desorption isotherms show that CQ molecules were encapsulated in the pores, without completely filling the mesopores. BET surface area values were 630 m2 g-1 (magMCM) and 467 m2 g-1 (magMCM-CQ). Encapsulated CQ exhibited rapid delivery (99% in 3 h) in buffer medium and improved solubility compared to the non-encapsulated drug, attributed to CQ encapsulation in amorphous form. The biocompatibility assessment of magMCM, magMCM-CQ, and CQ against MRC5 non-tumoral lung fibroblasts using the MTT assay after 24 h revealed no toxicity associated with magMCM. On the other hand, the non-encapsulated CQ and magMCM-CQ exhibited comparable dose-response activity, indicating a similar cytotoxic effect.

Copper (I)-Chloroquine Complexes: Interactions with DNA and Ferriprotoporphyrin, Inhibition of ß-Hematin Formation and Relation to Antimalarial Activity.

A new Cu(I)-chloroquine (CQ) complex [Cu(CQ)(PPh3)2]NO3 (1) was synthesized and characterized, and its mechanism of action studied concomitant with the previously reported complex [Cu(CQ)2]Cl (2). These copper (I) coordination compounds can be considered as potential antimalarial agents because they show better inhibition of the CQ-resistant strain in in vitro studies than CQ alone. In comparison with other metal-CQ complexes, only the gold complex was similar to (1), i.e., more active than CQ against both CQ-susceptible (3D7) and CQ-resistant strains (W2). These two copper (I)-compounds also demonstrated higher antiplasmodial activity against W2 than other copper complexes reported to date. This suggests that the incorporation of the copper metal center enhanced the biological activity of CQ. To better understand their significant growth inhibition of the Plasmodium falciparum parasite, the interaction with two essential molecular targets for the survival and proliferation of the malarial parasite were studied. These were the ferriprotoporphyrin group and the DNA, both important targets for current antimalarial drugs at the asexual erythrocytic stages. Both compounds (1,2) exhibited significant interactions with these targets. In particular, interactions with the DNA were dominated by the intercalator properties of the CQ ligand but may have also been affected by the presence of copper. Overall, these compounds were better parasitic inhibitors than chloroquine diphosphate (CQDP) alone or other previously reported metal-CQ complexes such as platinum, ruthenium and gold.

Promising fluconazole based zinc(II) and copper(II) coordination polymers against Chagas disease.

A series of new transition metal coordination polymers, [Zn(Ac)2(FLZ)2]n (1), [Zn(FLZ)2(Cl)2]n (2), {[Zn(FLZ)2](NO3)2}n (3), [Cu(FLZ)2(CH3COO)4]n (4), {[Cu(FLZ)2Cl2]}n (5) and {[Cu(FLZ)2](NO3)2}n (6), were synthesized by the reaction of fluconazole (FLZ) with the respective zinc or copper salts under mild conditions. The molecular structure of these compounds was elucidated by several analytical and spectroscopy techniques such as elemental analyses, 1H and 13C{1H} nuclear magnetic resonance, electronic paramagnetic resonance, and infrared spectroscopy. Single-crystal X-ray diffraction confirmed the structure of the compounds 2, 4, 5 and 6 in solid state. The antichagasic activity of these compounds was evaluated against different forms of Trypanosoma cruzi. Compound 2 exhibited the highest activity against intracellular amastigotes. The ultrastructural changes in epimastigotes and intracellular amastigotes were investigated. These promising biological results demonstrated that the zinc or copper coordination polymers can form very active anti-parasitic compounds. The resulting compounds are more effective than the free azole drug and, consequently, great candidates for the treatment of Chagas disease.

Studies of Potency and Efficacy of an Optimized Artemisinin-Quinoline Hybrid against Multiple Stages of the Plasmodium Life Cycle.

A recently developed artemisinin-quinoline hybrid, named 163A, has been shown to display potent activity against the asexual blood stage of Plasmodium, the malaria parasite. In this study, we determined its in vitro cytotoxicity to mammalian cells, its potency to suppress P. berghei hepatic infection and to decrease the viability of P. falciparum gametocytes, in addition to determining whether the drug exhibits efficacy of a P. berghei infection in mice. This hybrid compound has a low level of cytotoxicity to mammalian cells and, conversely, a high level of selectivity. It is potent in the prevention of hepatic stage development as well as in killing gametocytes, denoting a potential blockage of malaria transmission. The hybrid presents a potent inhibitory activity for beta-hematin crystal formation, in which subsequent assays revealed that its endoperoxide component undergoes bioactivation by reductive reaction with ferrous heme towards the formation of heme-drug adducts; in parallel, the 7-chloroquinoline component has binding affinity for ferric hemin. Both structural components of the hybrid co-operate to enhance the inhibition of beta-hematin, and this bitopic ligand property is essential for arresting the growth of asexual blood parasites. We demonstrated the in vivo efficacy of the hybrid as an erythrocytic schizonticide agent in comparison to a chloroquine/artemisinin combination therapy. Collectively, the findings suggest that the bitopic property of the hybrid is highly operative on heme detoxification suppression, and this provides compelling evidence for explaining the action of the hybrid on the asexual blood stage. For sporozoite and gametocyte stages, the hybrid conserves the potency typically observed for endoperoxide drugs, and this is possibly achieved due to the redox chemistry of endoperoxide components with ferrous heme.

A novel platinum complex containing a piplartine derivative exhibits enhanced cytotoxicity, causes oxidative stress and triggers apoptotic cell death by ERK/p38 pathway in human acute promyelocytic leukemia HL-60 cells.

Piplartine (piperlongumine) is a plant-derived compound found in some Piper species that became a novel potential antineoplastic agent. In the present study, we synthesized a novel platinum complex containing a piplartine derivative cis-[PtCl(PIP-OH)(PPh3)2]PF6 (where, PIP-OH = piplartine demethylated derivative; and PPh3 = triphenylphosphine) with enhanced cytotoxicity in different cancer cells, and investigated its apoptotic action in human promyelocytic leukemia HL-60 cells. The structure of PIP-OH ligand was characterized by X-ray crystallographic analysis and the resulting platinum complex was characterized by infrared, molar conductance measurements, elemental analysis and NMR experiments. We found that the complex is more potent than piplartine in a panel of cancer cell lines. Apoptotic cell morphology, increased internucleosomal DNA fragmentation, without cell membrane permeability, loss of the mitochondrial transmembrane potential, increased phosphatidylserine externalization and caspase-3 activation were observed in complex-treated HL-60 cells. Treatment with the complex also caused a marked increase in the production of reactive oxygen species (ROS), and the pretreatment with N-acetyl-L-cysteine, an antioxidant, reduced the complex-induced apoptosis, indicating activation of ROS-mediated apoptosis pathway. Important, pretreatment with a p38 MAPK inhibitor (PD 169316) and MEK inhibitor (U-0126), known to inhibit ERK1/2 activation, also prevented the complex-induced apoptosis. The complex did not induce DNA intercalation in cell-free DNA assays. In conclusion, the complex exhibits more potent cytotoxicity than piplartine in a panel of different cancer cells and triggers ROS/ERK/p38-mediated apoptosis in HL-60 cells.

Platinum(ii)-chloroquine complexes are antimalarial agents against blood and liver stages by impairing mitochondrial function.

Chloroquine is an antimalarial agent with strong activity against the blood stage of Plasmodium infection, but with low activity against the parasite's liver stage. In addition, the resistance to chloroquine limits its clinical use. The discovery of new molecules possessing multistage activity and overcoming drug resistance is needed. One possible strategy to achieve this lies in combining antimalarial quinolones with the pharmacological effects of transition metals. We investigated the antimalarial activity of four platinum(ii) complexes composed of chloroquine and phosphine ligands, denoted as WV-90, WV-92, WV-93 and WV-94. In comparison with chloroquine, the complexes were less potent against the chloroquine-sensitive 3D7 strain but they were as active as chloroquine in inhibiting the chloroquine-resistant W2 strain of P. falciparum. Regarding selectivity, the complexes WV-90 and WV-93 displayed higher indexes. Unlike chloroquine, the complexes act as irreversible parasiticidal agents against trophozoites and the WV-93 complex displayed activity against the hepatic stage of P. berghei. The in vivo suppression activity against P. berghei in the Peters 4 day test displayed by the complexes was similar to that of chloroquine. However, the efficacy in an established P. berghei infection in the Thompson test was superior for the WV-93 complex compared to chloroquine. The complexes' antimalarial mechanism of action is initiated by inhibiting the hemozoin formation. While chloroquine efficiently inhibits hemozoin, parasites treated with the platinum complexes display residual hemozoin crystals. This is explained since the interaction of the platinum complexes with ferriprotoporphyrin is weaker than that of chloroquine. However, the complexes caused a loss of mitochondrial integrity and subsequent reduction in mitochondrial activity, and their effects on mitochondria were more pronounced than those in the chloroquine-treated parasites. The dual effect of the platinum complexes may explain their activity against the hemozoin-lacking parasites (hepatic stage), where chloroquine has no activity. Our findings indicate that the platinum(ii)-chloroquine complexes are multifunctional antimalarial compounds and reinforce the importance of metal complexes in antimalarial drug discovery.

Ru(II)/clotrimazole/diphenylphosphine/bipyridine complexes: Interaction with DNA, BSA and biological potential against tumor cell lines and Mycobacterium tuberculosis.

Three ruthenium complexes [RuCl(CTZ)(bipy)(P-P)]PF6 [P-P=1,2-bis(diphenylphosphino)ethane (dppe-1), 1,4-bis(diphenylphosphino)butane (dppb-2) and 1,1'-bis(diphenylphosphino)ferrocene (dppf-3), bipy=2,2'-bipiridine and clotrimazole (CTZ) 1-[(2-chlorophenyl)diphenylmethyl]-1H-imidazole] were synthesized. These complexes were characterized by a combination of elemental analysis, molar conductivity, infrared and UV-vis spectroscopy, 1H, 13C{1H} and 31P{1H} nuclear magnetic resonance techniques, cyclic voltammetry and mass spectroscopy. Bovine serum albumin binding constants, which were in the range of 1.30-36.00×104M-1, and thermodynamic parameters suggest spontaneous interactions with this protein by electrostatic forces due to the positive charge of the complexes. DNA interactions studied by spectroscopic titration, viscosity measurements, gel electrophoresis, circular dichroism, ethidium bromide displacement and reactions with guanosine and guanosine monophosphate indicated the DNA binding affinity primarily through non-covalent interactions. All complexes 1-3 were tested against the human carcinoma cell lines MCF-7 (breast), A549 (lung) and DU-145 (prostate) presenting promising IC50 values, between 0.50 and 14.00µM, in some cases lower than the IC50 for the reference drug (cisplatin). The antimicrobial activity assays of the complexes provided evidence that they are potential agents against mycobacterial infections, specifically against Mycobacterium tuberculosis H37Rv.

Cytotoxicity of Ru(II) piano-stool complexes with chloroquine and chelating ligands against breast and lung tumor cells: Interactions with DNA and BSA.

The synthesis and spectroscopic characterization of nine π-arene piano-stool ruthenium (II) complexes with aromatic dinitrogen chelating ligands or containing chloroquine (CQ), are described in this study: [Ru(η(6)-C10H14)(phen)Cl]PF6 (1), [Ru(η(6)-C10H14)(dphphen)Cl]PF6 (2), [Ru(η(6)-C10H14)(bipy)Cl]PF6 (3), [Ru(η(6)-C10H14)(dmebipy)Cl]PF6 (4) and [Ru(η(6)-C10H14)(bdutbipy)Cl]PF6 (5), [Ru(η(6)-C10H14)(phen)CQ](PF6)2 (6), [Ru(η(6)-C10H14)(dphphen)CQ](PF6)2 (7), [Ru(η(6)-C10H14)(bipy)CQ](PF6)2 (8), [Ru(η(6)-C10H14)(dmebipy)CQ](PF6)2 (9): [1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (dphphen), 2,2'-bipyridine (bipy), 5,5'-dimethyl-2,2'-bipyridine (dmebipy), and 4,4'-di-t-butyl-2,2'-bipyridine (dbutbipy)]. The solid state structures of five ruthenium complexes (1-5) were determined by X-ray crystallography. Electrochemical experiments were performed by cyclic voltammetry to estimate the redox potential of the Ru(II)/Ru(III) couple in each case. Their interactions with DNA and BSA, and activity against four cell lines (L929, A549, MDA-MB-231 and MCF-7) were evaluated. Compounds 2, 6 through 9, interact with DNA which was comparable to the one observed for free chloroquine. The results of fluorescence titration revealed that these complexes strongly quenched the intrinsic fluorescence of BSA following a static quenching procedure. Binding constants (Kb) and the number of binding sites (n~1) were calculated using modified Stern-Volmer equations. The thermodynamic parameters ΔG at different temperatures were calculated and subsequently the values of ΔH and ΔS were also calculated, which revealed that hydrophobic and electrostatic interactions play a major role in the BSA-complex association. The MTT assay results indicated that complexes 2, 5 and 7 showed cytostatic effects at appreciably lower concentrations than those needed for cisplatin, chloroquine and doxorubicin.