Arylmethylamino Steroids As Antiparasitic Agents
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ARTICLE Received 7 Jun 2016 | Accepted 3 Jan 2017 | Published 17 Feb 2017 DOI: 10.1038/ncomms14478 OPEN Arylmethylamino steroids as antiparasitic agents Reimar Krieg1, Esther Jortzik2, Alice-Anne Goetz3, Ste´phanie Blandin3, Sergio Wittlin4,5, Mourad Elhabiri6, Mahsa Rahbari2, Selbi Nuryyeva6,7, Kerstin Voigt8, Hans-Martin Dahse8, Axel Brakhage8, Svenja Beckmann9, Thomas Quack9, Christoph G. Grevelding9, Anthony B. Pinkerton10,11, Bruno Scho¨necker12, Jeremy Burrows13, Elisabeth Davioud-Charvet6, Stefan Rahlfs2 & Katja Becker2 In search of antiparasitic agents, we here identify arylmethylamino steroids as potent compounds and characterize more than 60 derivatives. The lead compound 1o is fast acting and highly active against intraerythrocytic stages of chloroquine-sensitive and resistant Plasmodium falciparum parasites (IC50 1–5 nM) as well as against gametocytes. In P. berghei- infected mice, oral administration of 1o drastically reduces parasitaemia and cures the animals. Furthermore, 1o efficiently blocks parasite transmission from mice to mosquitoes. The steroid compounds show low cytotoxicity in mammalian cells and do not induce acute toxicity symptoms in mice. Moreover, 1o has a remarkable activity against the blood-feeding trematode parasite Schistosoma mansoni. The steroid and the hydroxyarylmethylamino moieties are essential for antimalarial activity supporting a chelate-based quinone methide mechanism involving metal or haem bioactivation. This study identifies chemical scaffolds that are rapidly internalized into blood-feeding parasites. 1 Institute of Anatomy II, University Hospital Jena, Teichgraben 7, 07743 Jena, Germany. 2 Biochemistry and Molecular Biology, Interdisciplinary Research Centre, Justus Liebig University Giessen, Heinrich Buff Ring 26-32, 35392 Giessen, Germany. 3 Universite´ de Strasbourg, CNRS, Inserm, MIR UPR9022/U963, F-67000 Strasbourg, France. 4 Swiss Tropical and Public Health Institute, Socinstrasse 57, PO Box, 4002 Basel, Switzerland. 5 University of Basel, Petersplatz 1, 4001 Basel, Switzerland. 6 UMR 7509 Centre National de la Recherche Scientifique and University of Strasbourg, European School of Chemistry, Polymers and Materials (ECPM), 25, rue Becquerel, F-67087 Strasbourg, France. 7 New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE. 8 Leibniz Institute for Natural Product Research and Infection Biology-Hans Kno¨ll Institute (HKI), Adolf-Reichwein-Strasse 23, 07745 Jena, Germany. 9 Institute of Parasitology, Biomedical Research Centre, Justus Liebig University Giessen, Schubertstrasse 81, 35392 Giessen, Germany. 10 Conrad Prebys Center for Chemical Genomics, Sanford-Burnham-Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA. 11 Conrad Prebys Center for Chemical Genomics, Sanford-Burnham-Prebys Medical Discovery Institute, 6400 Sanger Road, Orlando, Florida 32827, USA. 12 Institute of Organic and Macromolecular Chemistry, Friedrich Schiller University Jena, Humboldtstrasse 10, 07743 Jena, Germany. 13 Medicines for Malaria Venture, 20 Route de Pre´- Bois, 1215 Geneva 15, Switzerland. Correspondence and requests for materials should be addressed to K.B. (email: [email protected]). NATURE COMMUNICATIONS | 8:14478 | DOI: 10.1038/ncomms14478 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms14478 alaria caused by the unicellular apicomplexan parasite bioavailability whereas the essential hydroxyarylmethylamino Plasmodium still threatens about 3.2 billion people moiety points to a chelate-based quinone methide mechanism Mworldwide. In 2015 there were an estimated 214 million involving metal or haem bioactivation. cases of malaria and 438,000 deaths1. Artemisinin-based combination therapies are the currently recommended Results treatment for uncomplicated P. falciparum malaria1, however, Chemistry. The low molecular weight steroid compounds parasites exhibiting artemisinin-resistance have now been described here are based on a substituted steroidal pharmaco- reported2,3. Thus, the discovery and development of novel phore and represent novel chemical matter14. All compounds are antimalarials and transmission-blocking agents is of global derived from amino steroids with varying constitutions of the importance4,5. Schistosomiasis (bilharzia) ranks second to basic gonane core (series 1–14) and varying functional groups malaria as a parasitosis affecting more than 240 million people R (substitution patterns c, e, g, i, k, m, q, s, u and w, Fig. 1). in the tropics and subtropics6. A vaccine against these parasites is In brief, the compounds were synthesized via condensation of not yet available, and praziquantel (PZQ) is the only commonly amino steroids with arylaldehydes, and subsequent NaBH - used drug for treatment, justifying the fear of upcoming 4 7 reduction of obtained Schiff-bases furnished the desired resistance . compounds in high yields. The synthesis could also be carried In connection with our work on steroids as chiral ligands for 8 out as a one-pot procedure without isolation of Schiff-bases. This metal ions we became interested in the biological activity of is especially beneficial in case of cis-configured amino alcohols steroid compounds. In general, steroids possess a conformation (series 5, 8, 11 and 14) where reaction with aldehydes leads to of their lipophilic framework, which allows the placement rapidly exchanging tautomeric Schiff-based/oxazoline equilibria. of substituents in well-defined spatial environments and Complete synthetic details can be found in Supplementary conformational freedom. Also, there is a great structural Note 1, 1H and 13C NMR spectra of the most relevant variability of the tetracyclic framework, including estratrienes, compounds are provided in Supplementary Figs 1–6. androstanes, and cholestanes. In addition, ring junctions (5a/5b,14a/14b and so on) can differ considerably. Functional groups can be attached at up to 27 positions in the framework Activity against Plasmodium falciparum blood stages in vitro. or on side chains, and advances in synthetic chemistry over The activity of the steroid compounds was tested against the asexual the last several years have made accessing many of these blood stages of the malaria parasite P. falciparum (strain 3D7) in derivatives possible. In addition to their use in pharmaceuticals, the 3H-hypoxanthine incorporation assay. As shown in Table 1, the there has also been growing interest in the use of steroid compounds are highly active against red blood cell stages of P. derivatives as rigid homochiral model compounds, for example, falciparum with IC50 values in the nanomolar range. The most biomimetics, or as templates for chemo-, regio- and active compound 1o had an IC50 value of 4.1±1.6 nM on 3D7 stereoselective investigation. Thus, one approach to discover (n ¼ 6), (± indicates s.d. throughout the manuscript, unless new biologically active compounds is to combine a steroid otherwise stated) which is comparable to the in vitro activity of skeleton with structural elements possessing appropriate clinically employed antimalarials such as chloroquine (IC50 ¼ 8.6 biological activities. nM) and artemisinin (IC50 ¼ 17.3 nM) using the same methods Interestingly, during a screening program for potential (72 h 3H-hypoxanthine incorporation assay)15. The second most antiprotozoal drugs, the naturally occurring steroid 3b-amino- active compound 2o showed an IC50 value of 6.6±2.1 nM (n ¼ 4) 22,26-epiminocholest-5-ene (sarachine) from the leaves of Saraca on 3D7 (for data on all compounds tested, please see punctate, had been isolated as a hit. Despite its simple Supplementary Table 1). Notably, the compounds were found to substitution patterns, it was reported to exhibit activity against be more active against chloroquine-resistant parasites as tested for the malaria parasite Plasmodium falciparum9, and a series of the P. falciparum strain Dd2: 1o:1.0±0.9 nM (n ¼ 4); 2o: amino steroids having side chains similar to that of sarachine 2.0±1.2 nM (n ¼ 4); chloroquine: 90.2 nM; artemisinin: 20.4 nM were prepared from deoxycholic acid as the starting material10. (ref. 15) (Supplementary Fig. 7). A similar phenomenon has been To this end, the most active derivative of this series contained reported for other antimalarial compounds as diverse as 8- a chloroquinoline moiety in the side chain, which might be aminoquinolines and amadantine. The underlying mechanism of contributing to biological activity. The advantage of employing this very promising activity of the steroid compounds deserves hydrophobic steroid units is their membrane permeability, paving further attention. the way for biologically active hybrid molecules. On the basis of To assess the rapidity of growth inhibition induced by the 16 this knowledge o-pyridiniumalkyl ethers of steroidal phenols steroid compounds, the so-called IC50 speed assay was were synthesized and indeed the combination of the hydrophobic conducted for compound 1o on P. falciparum NF54 (Fig. 2a,b). steroid moiety with a hydrophilic group (ferrocenylmethylamino In this assay, a comparison of IC50 values, which are obtained group, N-alkyl-pyridinium groups)11,12 led to compounds side-by-side after 72, 48, and 24 h of compound incubation, is with antimicrobial activity. In continuation of this work, the carried out (the 72 h assay is the standard IC50 assay otherwise 3-methoxy-estra-1,3,5(10)-triene unit was combined with the used in our study). For compound 1o, no significant IC50 shifts o-hydroxybenzylamino