The new RuII chloroquine complexes [Ru(η6-arene)(CQ)Cl2] (CQ = chloroquine; arene = p-cymene 1, benzene 2), [Ru(η6-p-cymene)(CQ)(H2O)2][BF4]2 (3), [Ru(η6-p-cymene)(CQ)(en)][PF6]2 (en = ethylenediamine) (4), and [Ru(η6-p-cymene)(η6-CQDP)][BF4]2 (5, CQDP = chloroquine diphosphate) have been synthesized and characterized by use of a combination of NMR and FTIR spectroscopy with DFT calculations. Each complex is formed as a single coordination isomer: in compounds 1–4 chloroquine binds to ruthenium in the η1-N mode through the quinoline nitrogen atom whereas in complex 5 an unprecedented η6 bonding through the carbocyclic ring is observed. Compounds 1, 2, 3, and 5 are active against CQ-resistant (Dd2, K1 and W2) and CQ-sensitive (FcB1, PFB, F32 and 3D7) malaria parasites (Plasmodium falciparum); importantly, the potency of these complexes against resistant parasites is consistently higher than that of the standard drug chloroquine diphosphate. Complexes 1 and 5 also inhibit the growth of colon cancer cells, independently of the p53 status and of liposarcoma tumor cell lines with the latter showing increased sensitivity, especially to complex 1 (IC50 8 µM); this is significant because this type of tumor does not respond to currently employed chemotherapies.

A series of organometallic ruthenium(II) complexes containing iminophosphorane ligands have been synthesized and characterized. Cationic compounds with chloride as counterion are soluble in water (70–100 mg/mL). Most compounds (especially highly water-soluble 2) are more cytotoxic to a number of human cancer cell lines than cisplatin. Initial mechanistic studies indicate that the cell death type for these compounds is mainly through canonical or caspase-dependent apoptosis, nondependent on p53, and that the compounds do not interact with DNA or inhibit protease cathepsin B. In vivo experiments of 2 on MDA-MB-231 xenografts in NOD.CB17-Prkdc SCID/J mice showed an impressive tumor reduction (shrinkage) of 56% after 28 days of treatment (14 doses of 5 mg/kg every other day) with low systemic toxicity. Pharmacokinetic studies showed a quick absorption of 2 in plasma with preferential accumulation in the breast tumor tissues when compared to kidney and liver, which may explain its high efficacy in vivo.

New stable cationic organogold(III) complexes containing the 'pincer' iminophosphorane ligand (2-C 6 H 4 -PPh 2 =NPh) have been prepared by reaction of the previously described [Au{κ 2 -C,N-C 6 H 4 (PPh 2 =N(C 6 H 5 )-2}Cl 2 ] 1 and a combination of sodium or silver salts and appropriate ligands. The presence of the P atom in the PR 3 fragment has been used as a "spectroscopic marker" to study the in vitro stability (and oxidation state) of the new organogold complexes in solvents like DMSO and water. Compounds with dithiocarbamato ligands and water-soluble phosphines of the general type [Au{κ 2 -C,NC 6 H 4 (PPh 2 =N(C 6 H 5 )-2}(S 2 CN-R 2 )]PF 6 (R = Me 2; Bz 3) and [Au{κ 2 -C,N-C 6 H 4 (PPh 2 =N(C 6 H 5 )-2}(PR 3 ) n Cl]PF 6 (PR 3 = P{Cp(m-C 6 H 4 -SO 3 Na) 2 } n = 1 4, n = 2 TPA {1,3,5-triaza-7-phosphaadamantane} 5) have been synthesized and characterized in solution and in the solid state (the crystal structure of 2 has been determined by X-ray diffraction studies). Complexes 1-5 have been tested as potential anticancer agents and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and Jurkat-T acute lymphoblastic leukemia cells. Compounds 2 and 3 are quite cytotoxic for these two cell lines. There is a preferential induction of apoptosis in HeLa cells after treatment with 1-5. However in the case of the more cytotoxic complex (2), cell death is activated due to both apoptosis and necrosis. The interactions of 1-5 with Calf Thymus DNA have been evaluated by Thermal Denaturation methods. All these complexes show no or little (electrostatic) interaction with DNA. The interaction of 2 with two model proteins (cytochrome c and thioredoxin reductase) has been analyzed by spectroscopic methods (vis-UV and fluorescence). Compound 2 manifests a high reactivity toward both proteins. The mechanistic implications of these results are discussed here.

Eight new ruthenium complexes of clotrimazole (CTZ) with high antiparasitic activity have been synthesized, cis,fac-[RuIICl2(DMSO)3(CTZ)] (1), cis,cis,trans-[RuIICl2(DMSO)2(CTZ)2] (2), Na[RuIIICl4(DMSO)(CTZ)] (3) and Na[trans-RuIIICl4(CTZ)2] (4), [RuII(η6-p-cymene)Cl2(CTZ)] (5), [RuII(η6-p-cymene)(bipy)(CTZ)][BF4]2 (6), [RuII(η6-p-cymene)(en)(CTZ)][BF4]2 (7) and [RuII(η6-p-cymene)(acac)(CTZ)][BF4] (8) (bipy = bipyridine; en = ethlylenediamine; acac = acetylacetonate). The crystal structures of compounds 4-8 are described. Complexes 1-8 are active against promastigotes of Leishmania major and epimastigotes of Trypanosoma cruzi. Most notably complex 5 increases the activity of CTZ by factors of 110 and 58 against L. major and T. cruzi, with no appreciable toxicity to human osteoblasts, resulting in nanomolar and low micromolar lethal doses and therapeutic indexes of 500 and 75, respectively. In a high-content imaging assay on L. major infected intraperitoneal mice macrophages, complex 5 showed significant inhibition on the proliferation of intracellular amastigotes (IC70 = 29 nM), while complex 8 displayed some effect at a higher concentration (IC40 = 1 μM).

In our ongoing search for new metal-based chemotherapeutic agents against leishmaniasis and Chagas disease, six new ruthenium-ketoconazole (Ru-KTZ) complexes have been synthesized and characterized, including two octahedral coordination complexes cis-fac-[RuIICl2(DMSO)3(KTZ)] (1) and cis-[RuIICl2(bipy)(DMSO)(KTZ)] (2), and four organometallic compounds [RuII(η6-p-cymene)Cl2(KTZ)] (3), [RuII(η6-p-cymene)(en)(KTZ)][BF4]2 (4), [RuII(η6-p-cymene)(bipy)(KTZ)][BF4]2 (5), and [RuII(η6-p-cymene)(acac)(KTZ)][BF4] (6); the crystal structure of (3) is described. The central hypothesis of our work is that combining a bioactive compound like KTZ and a metal in a single molecule results in a synergy that can translate into improved activity and/or selectivity against parasites. In agreement with this hypothesis, complexation of KTZ to RuII in compounds 3-5 produces a marked enhancement of the activity toward promastigotes and intracellular amastigotes of Leishmania major, when compared with uncomplexed KTZ, or with similar Ru compounds not containing KTZ. Importantly, the selective toxicity of compounds 3-5 toward the leishmania parasites, in relation to human fibroblasts and osteoblasts, or murine macrophages, is also superior to those of the individual constituents of the drug. When tested against Trypanosoma cruzi epimastigotes, some of the organometallic complexes displayed an activity and selectivity comparable to that of free KTZ. A dual-target mechanism is suggested to account for the antiparasitic properties of these complexes.

Three new ruthenium complexes with bidentate chloroquine analogue ligands, [Ru(η6-cym)(L1)Cl]Cl (1, cym = p-cymene, L1 = N-(2-((pyridin-2-yl)methylamino)ethyl)-7-chloroquinolin-4-amine), [Ru(η6-cym)(L2)Cl]Cl (2, L2 = N-(2-((1-methyl-1H-imidazol-2-yl)methylamino)ethyl)-7-chloroquinolin-4-amine) and [Ru(η6-cym)(L3)Cl] (3, L3 = N-(2-((2-hydroxyphenyl)methylimino)ethyl)-7-chloroquinolin-4-amine) have been synthesized and characterized. In addition, the X-ray crystal structure of 2 is reported. The antimalarial activity of complexes 1–3 and ligands L1, L2 and L3, as well as the compound N-(2-(bis((pyridin-2-yl)methyl)amino)ethyl)-7-chloroquinolin-4-amine (L4), against chloroquine sensitive and chloroquine resistant Plasmodium falciparum malaria strains was evaluated. While 1 and 2 are less active than the corresponding ligands, 3 exhibits high antimalarial activity. The chloroquine analogue L2 also shows good activity against both the choloroquine sensitive and the chloroquine resistant strains. Heme aggregation inhibition activity (HAIA) at an aqueous buffer/n-octanol interface (HAIR50) and lipophilicity (D, as measured by water/n-octanol distribution coefficients) have been measured for all ligands and metal complexes. A direct correlation between the D and HAIR50 properties cannot be made because of the relative structural diversity of the complexes, but it may be noted that these properties are enhanced upon complexation of the inactive ligand L3 to ruthenium, to give a metal complex (3) with promising antimalarial activity.

We have measured water/n-octanol partition coefficients, pKa values, heme binding constants, and heme aggregation inhibition activity of a series of ruthenium–πarene–chloroquine (CQ) complexes recently reported to be active against CQ-resistant strains of Plasmodium falciparum. Measurements of heme aggregation inhibition activity of the metal complexes near water/n-octanol interfaces qualitatively predict their superior antiplasmodial action against resistant parasites, in relation to CQ; we conclude that this modified method may be a better predictor of antimalarial potency than standard tests in aqueous acidic buffer. Some interesting tendencies emerge from our data, indicating that the antiplasmodial activity is related to a balance of effects associated with the lipophilicity, basicity, and structural details of the compounds studied.

The mechanism of antimalarial action of the ruthenium-chloroquine complex [RuCl 2 (CQ)] 2 (1), previously shown by us to be active in vitro against CQ-resistant strains of Plasmodium falciparum and in vivo against P. berghei, has been investigated. The complex is rapidly hydrolyzed in aqueous solution to [RuCl(OH 2 ) 3 (CQ)] 2 [Cl] 2 , which is probably the active species. This compound binds to hematin in solution and inhibits aggregation to β-hematin at pH ∼ 5 to a slightly lower extent than chloroquine diphosphate; more importantly, the heme aggregation inhibition activity of complex 1 is significantly higher than that of CQ when measured at the interface of noctanol-aqueous acetate buffer mixtures under acidic conditions modeling the food vacuole of the parasite. Partition coefficient measurements confirmed that complex 1 is considerably more lipophilic than CQ in n-octanol-water mixtures at pH ∼ 5. This suggests that the principal target of complex 1 is the heme aggregation process, which has recently been reported to be fast and spontaneous at or near water-lipid interfaces. The enhanced antimalarial activity of complex 1 is thus probably due to a higher effective concentration of the drug at or near the interface compared with that of CQ, which accumulates strongly in the aqueous regions of the vacuole under those conditions. Furthermore, the activity of complex 1 against CQ-resistant strains of P. falciparum is probably related to its greater lipophilicity, in line with previous reports indicating a lowered ability of the mutated transmembrane transporter PfCRT to promote the efflux of highly lipophilic drugs. The metal complex also interacts with DNA by intercalation, to a comparable extent and in a similar manner to uncomplexed CQ and therefore DNA binding does not appear to be an important part of the mechanism of antimalarial action in this case.