Organometallic ruthenium(II) complexes of the general formula [Ru(eta6-p-cymene)Cl2(L)] and [Ru(eta6-p-cymene)Cl(L)2][BPh4] with modified phenoxazine- and anthracene-based multidrug resistance (MDR) modulator ligands (L) have been synthesized, spectroscopically characterized, and evaluated in vitro for their cytotoxic and MDR reverting properties in comparison with the free ligands. For an anthracene-based ligand, coordination to a ruthenium(II) arene fragment led to significant improvement of cytotoxicity as well as Pgp inhibition activity. A similar, but weaker effect was also observed when using a benzimidazole-phenoxazine derivative as Pgp inhibitor. The most active compound in terms of both Pgp inhibition and cytotoxicity is [Ru(eta6-p-cymene)Cl2(L)], where L is an anthracene-based ligand. Studies show that it induces cell death via inhibition of DNA synthesis. Moreover, because the complex is fluorescent, its uptake in cells was studied, and relative to the free anthracene-based ligand, uptake of the complex is accelerated and accumulation of the complex in the cell nucleus is observed.

Ten complexes of general formula [Ru(eta6-arene)Cl2(L)], [Ru(eta6-arene)Cl(L)2][X], and [Ru(eta6-arene)(L)3][X]2 (eta6-arene = benzene, p-cymene; L = imidazole, benzimidazole, N-methylimidazole, N-butylimidazole, N-vinylimidazole, N-benzoylimidazole; X = Cl, BF4, BPh4) have been prepared and characterized by spectroscopy. The structures of five representative compounds have been established in the solid state by single-crystal X-ray diffraction. All the new compounds were assessed by the same in vitro screening assays applied to [imidazole-H][trans-RuCl4(DMSO)(imidazole)] (NAMI-A) and [Ru(eta6-arene)Cl2(1,3,5-triaza-7-phosphaadamantane)] (RAPTA) compounds. It was found that the new compounds show essentially the same order of cytotoxicity as the RAPTA compounds toward cancer cells. Several of the compounds were selective toward cancer cells in that they were less (or not) cytotoxic toward nontumorigenic cells that are used to model healthy human cells. Thus, two of the compounds, [Ru(eta6-p-cymene)Cl(vinylimid)2][Cl] (vinylimid = N-vinylimidazole) and [Ru(eta6-benzene)(mimid)3][BF4]2 (mimid = N-methylimidazole), have been selected for a more detailed in vivo evaluation.

bUpon the screening of 16 antiproliferative compounds against Toxoplasma gondii and Neospora caninum, two hydrolytically stable ruthenium complexes (compounds 16 and 18) exhibited 50% inhibitory concentrations of 18.7 and 41.1 nM (T. gondii) and 6.7 and 11.3 nM (N. caninum). To achieve parasiticidal activity with compound 16, long-term treatment (22 to 27 days at 80 to 160 nM) was required. Transmission electron microscopy demonstrated the rapid impact on and ultrastructural alterations in both parasites. These preliminary findings suggest that the potential of ruthenium-based compounds should thus be further exploited.T oxoplasma gondii and Neospora caninum are cyst-forming apicomplexan parasites that infect a wide range of hosts. In an immunocompetent host, infection with either parasite does not cause disease (1-3). N. caninum has emerged as one of the most important infectious causes of bovine abortion (4-6). In contrast, T. gondii causes toxoplasmosis in humans and many animal species, either in chronically infected individuals during a decrease in immunoreactivity or if a seronegative mother acquires a primary infection during pregnancy, leading to abortion or serious fetal abnormalities (7-9). Toxoplasmosis treatment is based on only a few chemotherapeutics with considerable adverse effects (10, 11). In Neospora-seropositive cattle, pregnancy and the associated immunomodulation are already sufficient to cause recrudescence, fetal damage, and abortion (2-6). Chemotherapy has been considered a promising option if effective drugs can be identified (12, 13). Several compounds were investigated in vitro (14-16), but only a few were evaluated in small-animal models (14,(17)(18)(19)(20)(21)(22)(23)(24).We have evaluated compounds originally synthesized as anticancer drugs. Currently used metal complexes (25-31) exhibit considerable toxicity. This has stimulated the interest in other compounds with more acceptable toxicity, such as ruthenium complexes (32-36). Effects of ruthenium compounds on some bacteria and parasites have been studied (37-46). "Classical ruthenium complexes" contain heteroatom ligands (e.g., azole derivatives), and NAMI-A and KP-1019 have been evaluated in phase I clinical trials for cancer treatment (47-49). Organometallic complexes are defined by at least one metal-carbon bond. The 6 -arene ruthenium(II) phosphite complexes 5, 6, 12, and 15 to 18 were characterized earlier (50), while [Ru( 6 -p-cymene)(bipyridine)Cl][Cl] 11 was synthesized as shown previously (51). Based on our experiences in the design of selective inhibitors of CYP11B2 (53) and CYP11B1 (54), the pyridine-based compounds 4, 7 to 10, and 14 were from a small in-house library of CYP enzyme inhibitors. 2,2=-Bipyridine 3 was obtained from Joachim W. Heinicke, Ernst Moritz Arndt University of Greifswald, Greifswald, Germany. The cytotoxic lipophilic imidazolium salt 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride 3 was synthesized as described previously (54-56). The arylimidamide DB745 2 (23) was kindly provided by David Bo...

Outgoing from an etomidate-based design concept, we succeeded in the development of a series of highly active and selective inhibitors of CYP11B1, the key enzyme of cortisol biosynthesis, as potential drugs for the treatment of Cushing's syndrome and related diseases. Thus, compound 33 (IC 50 = 152 nM) is the first CYP11B1 inhibitor showing a rather good selectivity toward the most important steroidogenic CYP enzymes aldosterone synthase (CYP11B2), the androgen-forming CYP17, and aromatase (estrogen synthase, CYP19). KEYWORDS Cushing's syndrome, steroid hormone biosynthesis, steroid-11β-hydroxylase, CYP11B1 inhibitor, CYP17, CYP19, CYP11B2, etomidate I t is well-known that steroid hormones are essential for a large number of vitally important physiological processes. However, they are also associated with life-threatening diseases. Application of hormone receptor antagonists or biosynthesis inhibitors are regarded as therapeutic methods of choice. The biosynthetic pathways contain several established and potential drug targets. In the last decades, aromatase (CYP19) inhibitors were developed and continuously improved. 1-4 Nowadays, second and third generation inhibitors are used as first line therapeutics for hormonedependent breast cancer. 5 Some 15 years ago, the first selective androgen synthase (CYP17) inhibitors were described, [6][7][8] and recently, their benefits for the treatment of castration refractory prostate cancer were demonstrated. 9 Research was not only focused on the formation of steroid hormones in their endocrine glands but also on their activation in the target cell. Inhibition of steroid 5R-reductase is clinically well-established for androgen-dependent diseases. 10-13 Experimental results with hydroxysteroid dehydrogenase (HSD) inhibitors are very encouraging for estrogen-and glucocorticoid-dependent diseases. [14][15][16][17][18] Until some years ago, selective inhibitors of mineralo-and glucocorticoids were not in the focus of research efforts. This was due to the fact that the sequence identity between aldosterone synthase (CYP11B2) and cortisol synthase (steroid-11β-hydroxylase, CYP11B1) is very high (93%), 19 and it was considered impossible to obtain selective inhibitors of one enzyme versus the other. Recently, however, we have been able to demonstrate that it is possible to selectively inhibit CYP11B2. [20][21][22][23][24] Further structural optimizations resulted in in vivo active compounds with selectivity factors (sfs) reaching 1000 with regard to CYP11B1. 25,26 They could be candidates for the treatment of hyperaldosteronism, congestive heart failure, and myocardial fibrosis. Although there is a high medical need for drugs interfering with excessive glucocorticoid formation resulting in Cushing's syndrome, there are only a few inhibitors of CYP11B1 described so far. 27 Because of their unselective action, their application is associated with severe side effects: The CYP19 inhibitor aminoglutethimide, metyrapone, the antimycotics ketoconazole and fluconazole, and the h...

A series of compounds of general formula [Ru(η 6 -p-cymene) (R 2 acac)(PTA)][X] (R 2 acac = Me 2 acac, tBu 2 acac, Ph 2 acac, Me 2 acac-Cl; PTA = 1,3,5-triaza-7-phosphaadamantane; X = BPh 4 , BF 4 ), and the precursor to the Me 2 acac-Cl derivative [Ru(η 6 -p-cymene)(Me 2 acac-Cl)Cl], have been prepared and characterised spectroscopically. Five of the compounds have also been characterised in the solid state by X-ray crystallography. The tetrafluoroborate salts are water-soluble, quite

Two series of η(6)-areneruthenium(II) phosphite complexes were prepared, characterized, and evaluated in vitro for their toxic potential against Echinococcus multilocularis metacestodes. Neutral complexes of general formula [(η(6)-p-cymene)RuCl(2){P(OR)(3)}] (R = Et, (i)Pr, Ph) with two easily exchangable chloride ligands showed only minor toxicity, whereas the substitution of these moieties against a β-diketonate (2,2,6,6-tetramethylheptanedionate) ligand led to hydrolytically stable complex salts of type [(η(6)-p-cymene)Ru(β-diketonate){P(OR)(3)}][BF(4)] (R = Et, (i)Pr, Ph) with comparable in vitro toxicity (50% PGI release at c = 1.4 - 4.7 μM) to the reference drug nitazoxanide (50% PGI release at c = 1.2 μM). In addition, the latter complexes were highly toxic against rat hepatoma cells (IC(50) = 0.40-2.0 μM) and less toxic against human foreskin fibroblasts (IC(50) = 1.1-2.9 μM) and Vero cells (IC(50) = 1.2-8.9 μM). The measured cytotoxicities against mammalian cells are, to the best of our knowledge, among the highest ever observed for ruthenium-based complexes. In conclusion, complex salts of type [(η(6)-p-cymene)Ru(β-diketonate){P(OR)(3)}][BF(4)] might be interesting candidates for further development toward anthelmintic drugs and/or highly cytotoxic metal compounds.

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