1,288 research outputs found
Biological and pharmacological investigations of novel diamidines in animal models of human African trypanosomiasis
No full text"African sleeping sickness, also called human African trypanosomiasis (HAT), results from the infection of humans with either of two protozoan parasites, Trypanosoma brucei gambiense and T. b. rhodesiense. HAT is transmitted by tsetse flies (Glossina spp) and, like the vector, is found exclusively in Africa between the latitudes 14° North and 29° South. A total of 50 million people live in foci where active transmission is possible and are therefore at risk of infection; however, the annual incidence and estimated prevalence currently stand at 7139 and 30 000 cases respectively. When trypanosomes are inoculated into a human host, the resulting clinical disease is classified into a first (early) stage in which trypanosomes are localised within the haemo-lymphatic system and a second (late) stage in which trypanosomes have crossed the blood brain barrier (BBB) and invaded the central nervous system (CNS). Currently, pentamidine and suramin are used to treat the first stage of T. b. gambiense and T. b. rhodesiense HAT, respectively. On the other hand, eflornithine and the nifurtimox eflornithine combination therapy (NECT) are the prefered treatments for second stage T. b. gambiense HAT. The organoarsenic drug melarsoprol may be used for both forms of HAT but is mainly used against T. b. rhodesiense. Clearly, the therapeutic options for HAT are very limited. In addition, available drugs are associated with different levels of toxicity, especially melarsoprol which causes a post treatment reactive encephalopathy (PTRE) in 5-10% of treated patients, up to 50% of PTRE patients may die. There are also reports of high melarsoprol treatment failure rates in some foci and there is a lack of easy to use oral formulations for all the drugs. We have carried out biological and pharmacological investigations of potential new drug candidates in animal models of HAT with the objective of contributing to the development of safe, efficacious and easy to use treatments for HAT. The studies were carried out in the context of a PhD programme at the Swiss TPH/University of Basel and were anchored onto an ongoing diamidines development project of the Consortium for Parasitic Drug Development (CPDD). Vervet monkeys (Chlorocebus [Cercopithecus] aethiops) were the main model for this study. To prepare for the studies in monkeys, one prodrug (DB289) was evaluated in mouse models of first stage HAT. We obtained good activities against different trypanosome isolates, including the one that is used in the monkey model, T. b. rhodesiense KETRI2537. We further evaluated the metabolism of the prodrugs in monkey liver microsomes. In all cases, prodrugs were metabolized to generate expected intermediate and active metabolites, thus allowing us to proceed to test the compounds for safety in un-infected monkeys. We determined that in monkeys: i) diamidine toxicity was dependent on the dose and duration of dosing, ii) the plasma concentrations of active metabolites were potentially therapeutic for HAT, and iii) the dose level at which there were no observed adverse effects (NOAEL). Three prodrugs (DB289, DB844 and DB868) and one active compound (DB829) were subsequently evaluated for efficacy at dose rates that were equal or below NOAEL. In general, the prodrugs were highly active against first stage HAT after oral administration and one prodrug (DB844) had additionally an improved activity (43%) in the second stage monkey HAT model in comparison with pentamidine (0%). The intramuscularly administered parent compound DB829 was fully curative in the second stage HAT model at 2.5 mg/kg x 5 days. Our findings suggest that the two compounds (oral DB868 and intramuscular DB829) should be recommended to enter the regulatory phase of development as potential HAT drugs. Oral DB868 cured the first stage HAT model at a daily dose of 3 mg/kg for 7 days (cumulative dose, CD = 21 mg/kg) compared to a maximum tolerated daily dose of 30 mg/kg for 10 days (CD = 300 mg/kg). The efficacy, safety and pharmacokinetic profiles suggest that this compound would be a useful clinical candidate using an optimal dosing duration of 5-7 days. The second compound, intramuscular DB829, cured the second stage HAT model at a daily dose of 2.5 mg/kg for 5 days and was tolerated at 5 mg/kg for 5 days (CD = 25 mg/kg). Pharmacokinetic analysis indicated the intramuscular administration of DB829 resulted in better systemic bioavailability, thus accounting for the improved efficacy in comparison with oral dosing.
In vitro studies and in vivo evaluation of novel diamidines for 2nd stage sleeping sickness
No full textSummary:
African sleeping sickness is one of the most neglected tropical diseases. Transmitted by the tsetse fly it exclusively occurs in sub-Saharan Africa. It is caused by two different parasite subspecies causing two different forms of African sleeping sickness. Trypanosoma brucei gambiense is prevalent in West and Central Africa while Trypanosoma brucei rhodesiense is prevalent in East and South Africa. Sleeping sickness is classified in two main stages. In the first stage, the parasites reside in the lymph and blood system. In the second stage, the parasites additionally infect the brain. Untreated sleeping sickness is fatal. Drugs are available for this fearsome disease, however, most of them are old and have many drawbacks, such as severe adverse effects, treatment failures and complicated treatment schedules, which is a problem in remote rural areas where the disease primarily occurs.
African sleeping sickness is a communicable disease that can be controlled. In 1998, there were an estimated 300,000 cases. By 2012 the prevalence has decreased to about 30,000, by different control measures such as vector control, improved surveillance and free drug distribution. Elimination seems possible, but safe and effective drugs are needed to reach this goal. One of the current drugs is the diamidine pentamidine which is in use since the early 1940s. However, it works only in patients with first stage disease and it has to be injected.
The Consortium for Parasitic Drug Development (CPDD) was founded in the year 2000 to find novel diamidines with better characteristics than the existing drugs. We improved oral absorption, which makes it possible to use pills instead of injections, and central nervous system (CNS) penetration. One compound (pafuramidine) has been tested in patients with first stage infections. It was the first compound that cured sleeping sickness orally, which is of great help for rural areas. Unfortunately, pafuramidine caused kidney and liver problems, and it did not cure second stage infections. In the meantime, we have identified superior compounds especially for the second stage.
As described in Chapter 3, two compounds, the prodrugs DB868 and DB844, given orally, cured all mice with CNS infections. However, both prodrugs were too toxic at the high doses required to cure both stages in monkeys. Nevertheless, DB868 is a good candidate drug to cure first stage sleeping sickness by an oral treatment, as demonstrated in mice and monkeys with first stage infections. Chapter 4 shows data of another CNS potent prodrug, DB1227 which was, however, less effective than DB868 in CNS infected mice.
Chapters 3, 7, 8 and 9 deal with two unmasked diamidines, DB829 and 28DAP010, which were highly effective in mice with second stage infections after i.p. injection. This was unexpected since diamidines are rather unlikely to cross the blood brain barrier in sufficient concentrations by diffusion. These two diamidines may penetrate into the brain by specific transporter proteins. The advantage of the two diamidines is that both cure with a short treatment course which could shorten the time of hospitalization of the patients. We have already tested DB829 in monkeys with promising results. It was safe and effective at low doses and a short treatment schedule in monkeys with second stage disease. 28DAP010 seems to be similarly effective as DB829 on both T. brucei subspecies in vitro and in mouse models.
In Chapter 6 we established a new in vitro method to measure the kinetics of drug action on pathogenic protozoa on a real time basis. We exploited the capacity of viable cells to produce heat and measured the heat flow using microcalorimetry. 28DAP010 inhibited the heat production of trypanosome cultures faster than DB829. The parasite clearance time of 28DAP010 was also faster than of DB829 in mice. The required effective treatment duration was still similar in mice with single dose for first stage and 5 days for second stage infections.
Upcoming efficacy studies will reveal if 28DAP010 is as curative in monkeys as DB829 and toxicity studies of 28DAP010 and DB829 side by side will shed light on their toxicity profile. These studies will help to select the better of these two compounds as a clinical drug candidate for the treatment of second stage sleeping sickness. ---------- Zusammenfassung: Die Afrikanische Schlafkrankheit ist eine Tropenkrankheit, welche durch die Tsetsefliege übertragen wird und daher ausschliesslich im tropischen Afrika vorkommt. Sie gehört zu den vernachlässigsten Krankheiten überhaupt und wird deshalb auch “vergessene Seuche“ genannt. Der Erreger ist ein einzelliger Parasit. Es gibt zwei verschiedene Unterarten, die zu etwas unterschiedlichen Schlafkrankheitsformen führen. Ohne wirksame Medikamentenbehandlung sind beide Formen tödlich. Trypanosoma brucei gambiense kommt nur in West- und Zentralafrika vor, während Trypanosoma brucei rhodesiense in Ost- und Südafrika zu finden ist. Der Krankheitsverlauf kann in zwei Stadien unterteilt werden. Im ersten Stadium findet man die Parasiten im Blut- und Lymphsystem und im zweiten Stadium zusätzlich im Gehirn. Zwar gibt es für diese Krankheit Medikamente, jedoch sind die meisten davon veraltet, haben ausgeprägte Nebenwirkungen und sind wegen Rückfällen oder der komplizierten und aufwendigen Behandlung problematisch.
Die Bekämpfung der Afrikanischen Schlafkrankheit ist möglich. 1998 gab es geschätzt etwa 300.000 Krankheitsfälle. Durch verbesserte Überwachung mit anschliessender medizinischer Behandlung der Infizierten, kostenlose Medikamentenverteilung und Vektorkontrolle, liess sich die Krankheit auf etwa 30.000 Krankheitsfälle im Jahr 2012, eindämmen. Für eine Eliminierung sind wirksame und verträgliche Medikamente notwendig. Ein Diamidin, das schon seit den frühen 40-er Jahren eingesetzt wird ist Pentamidin. Es wirkt noch heute, aber nur in Patienten die sich im ersten Stadium befinden, zudem muss es injiziert werden.
Im Jahr 2000 wurde das Konsortium CPDD, für die Entwicklung neuer Wirkstoffe zur Behandlung parasitärer Erkrankungen, vor allem für die Schlafkrankheit, gegründet. Neuartige Diamidine mit verbesserten Eigenschaften wurden gesucht und es war uns möglich, die orale Bioverfügbarkeit und die Bluthirnschrankengängigkeit, chemisch zu verbessern. Pafuramidin, war einer der neuen Wirkstoffe, das erste oral einzunehmende Medikament gegen Schlafkrankheit, das im Menschen getestet wurde. Ein orales Medikament hat grosse Vorteile für diese Krankheit, die hauptsächlich in abgelegenen Gebieten Afrikas vorkommt, wo ein ausgebautes Gesundheitssystem oft fehlt.
Pafuramidin heilte nur das erste Schlafkrankheitsstadium und dabei wurden Leber- und Nieren-Unverträglichkeiten festgestellt. Während der klinischen Studie testeten wir weitere Diamidine und fanden verbesserte Substanzen, vor allem bezüglich der Wirksamkeit des zweiten Krankheitsstadiums. Kapitel 3 und 4 beschreibt die wirksamsten Moleküle, die das Zweitstadium bei oraler Verabreichung heilten. Diese Moleküle, DB844, DB868, DB1227, aber auch das Pafuramidin sind Medikamenten-vorstufen (Prodrugs). Diese wurden entwickelt, um die orale Aufnahme und Gehirn-gängigkeit zu verbessern. Die aktivsten waren DB868 und DB844 in Mäusen, jedoch zeigten beide Moleküle toxische Wirkungen im Affen ohne dabei ausreichend die Gehirninfektion zu heilen. Dennoch war DB868 im Affenmodell deutlich besser verträglich als Pafuramidin und ist somit ein guter Ersatzkandidat für eine orale Wirkstoffentwicklung fürs erste Stadium.
Unerwartet konnten wir jedoch zwei Diamidine (ohne Vorstufenergänzung) identifizieren, die ebenfalls Mäuse mit Gehirninfektionen heilten. Da Diamidine unter physiologischen Bedingungen protoniert sind, ist es unwahrscheinlich, dass sie durch die Bluthirnschranke diffundieren. Möglicherweise werden sie über spezifische Mechanismen ins Gehirn transportiert. Kapitel 3, 7, 8 und 9 befassen sich mit den beiden aktivsten Diamidinen, DB829 und 28DAP010. Ihre hohe Wirkung und die kurze Behandlungszeit nach parenteraler Verabreichung (i.p. oder i.m) sind vielversprechend. DB829 war gut verträglich und wirksam bei niedrigen Dosen und heilte die infizierten Affen mit dem zweiten Krankheitsstadium bereits bei einer 5-tägigen Behandlung. In vitro und im Mausmodel war 28DAP010 auf beide Trypanosomen Unterarten ähnlich wirksam wie DB829.
Um die Wirkungszeit neuer Substanzen auf Trypanosomen zu testen, entwickelten wir eine neue Methode, die in Kapitel 6 beschrieben wird. Dabei nutzten wir die Eigenschaft der Zellen, Wärme zu produzieren und massen diese mit einem Kalorimeter auf Echtzeit. 28DAP010 reduzierte die Wärmeentwicklung einer Trypanosomenkultur deutlich schneller als DB829. Auch in infizierten Mäusen wirkte 28DAP010 schneller. Die Behandlungsdauer und Dosierung war bei beiden Diamidinen trotzdem vergleichbar. Eine Einzeldosis heilte das erste und eine 5-tägige Behandlung das zweite Stadium in Mäusen.
Weitere Studien sind nötig, um die Wirksamkeit von 28DAP010 im Affenmodel zu überprüfen und die Verträglichkeit beider Diamidine zu analysieren. Diese Ergebnisse werden zeigen, welches der bessere klinische Kandidat für die Behandlung des zweiten Schlafkrankheitsstadiums sein wird
Discovery of antiprotozoal compounds from medicinal plants
No full textTropical parasitic diseases such as malaria, human African trypanosomiasis, chagas disease, and leishmaniasis affect hundreds of millions of people worldwide and have devastating consequences. Current drugs available to treat these diseases have serious drawbacks. New drugs are urgently needed.
Natural products (NPs) play a dominant role in drug discovery for the treatment of human diseases. Particularly, quinine and artemisinin have their origin in nature and have inspired successful drugs for malaria treatment.
In a medium throughput screening, a total of 507 extracts from South African plants were assayed for their antiprotozoal activity against Plasmodium falciparum, Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania donovani. Extracts from Abrus precatorius L. ssp. africanus Verdc. (Fabaceae) and Drypetes gerrardii Hutch. var. gerrardii (Putranjivaceae) inhibited at least one of the parasites at a test concentration considered relevant. With the aim of identifying the compounds responsible for these activities, a HPLC-based activity profiling approach followed by dereplication was applied. Targeted isolation of promising compounds was achieved by a combination of chromatography techniques. Structure elucidation was achieved by HR-ESI-MS and NMR (1H, 13C, COSY, HMBC, HSQC, and NOESY spectroscopy). Absolute configuration was determined by comparison of electronic circular dichroism (ECD) spectra with calculated ECD data.
HPLC-based activity profiling of A. precatorius allowed the identification of abruquinones, as responsible for the trypanocidal activity of the crude extract. A total of ten abruquinones were isolated. Among these were five new compounds. Abruquinone B, I, A, D, K, and L showed remarkable inhibition (0.16 ± 0.060, 0.28 ± 0.051, 0.02 ± 0.003, 0.01 ± 0.001, 0.11 ± 0.053, and 0.02 ± 0.053, respectively) and notable selectivity, expressed as selectivity indices (SIs) which were calculated from cytotoxicity data in L-6 cells (51, 74, 1379, 668, 508, and 374, respectively). These results warrant in vivo assessment of abruquinones.
Abruquinones are promising hits due to their strong and selective in vitro inhibition of T. b. rhodesiense, their good compliance with Lipinski’s “rule-of-5” and other molecular properties, as well as their predicted low/moderate toxic potential.
Two different extracts of D. gerrardii showed antiprotozoal activity, and the active constituents were tracked and isolated by HPLC-based activity profiling. The CH2Cl2/MeOH (1:1) stems extract inhibited L. donovani and P. falciparum. The major compound, a new phenanthrenone, showed good in vitro activity (IC50 of 0.9 ? 0.3 mM) and selectivity (SI of 68) against P. falciparum. Based on these promising results, in-vivo studies were conducted. However, the compound was not able to reduce parasitemia in the P. berghei mouse model. A phenanthrenone heterodimer was also isolated and showed in vitro antiplasmodial activity (IC50 of 2.04 ? 0.15 mM and SI of 31). Furthermore, the CH2Cl2/MeOH (1:1) leaves extract displayed trypanocidal properties, and the known saponin putranoside A was isolated and tested against T. b. rhodesiense, (IC50 of 18.0 ? 3.8 mM and a SI of 4).
The phenanthrenone was the most active and selective in vitro inhibitor of P. falciparum, but showed no inhibition in vivo against P. berghei. However, the compound fulfilled Lipinski’s “rule-of-5” and other molecular properties, which indicates a potential to meet requirements of an ideal antimalarial drug such as, oral bioavailability and blood-brain barrier permeability. According to Medicines for Malaria Venture compound progressing criteria, the phenanthrenone complies with some of the features of a validated hit such as sufficient activity against P. falciparum in vitro (? 1 ?M).
Additionally, as part of a project aimed at investigating antiprotozoal European plants Chrysanthemum cynerariifolium (Trevir.) Vis. (Asteraceae), Laurus nobilis L. (Lauraceae), and Eupatorium cannabinum L. (Asteraceae) were studied. A hexane extract of C. cynerariifolium showed promising activity against P. falciparum. Pyrethrins (irregular monoterpenes) were the metabolites responsible for the antiplasmodial activities. Particularly, pyrethrin II and jasmolin II inhibited P. falciparum (IC50 4.0 ? 1.1 ?M and 5.0 ? 0.4 ?M, respectively and SI of 24 and 6, respectively) in vitro. Synthetic pyrethroids were also tested, but they did not show activity.
Finally, as a contribution to the structure activity relationship study of sesquiterpene lactones showing activity against T. b. rhodesiense, costunolide and zaluzanin D were isolated from Laurus nobilis L. (Lauraceae) and eupatoriopicrin from Eupatorium cannabinum L. (Asteraceae). Germacrolides, i.e. costunolide and eupatoriopicrin, showed a higher inhibition (IC50 of 1.3 ? 0.4 mM and 1.2 ± 0.2 mM, respectively) on the protozoon, than the guaianolide zaluzanin D (IC50 of 10.8 mM).
In brief, a total of 22 secondary metabolites were isolated from five species. Among them, seven new compounds were discovered. These compounds belong to the structural classes of isoflavonoids, phenanthrenones, and terpenes such as, sesquiterpene lactones, irregular monoterpenes and triterpenoid saponins. Most of them (15 compounds) exhibited in vitro antiprotozoal activity. The most promising compounds were the abruquinones and the phenanthrenone, which strongly and selectively inhibited T. b. rhodesiense and P. falciparum, respectively. Abruquinones and the phenanthrenone are drug-like compounds with a calculated toxic potential ranging from low to moderate.
ZUSAMMENFASSUNG
Tropische parasitäre Krankheiten wie Malaria, afrikanische Trypanosomiasis (Schlafkrankheit), Chagas-Krankheit und Leishmaniose betreffen Hunderte von Millionen Menschen weltweit und haben verheerenden Folgen. Aktuelle Medikamente, die zur Behandlung dieser Krankheiten zur Verfügung stehen, haben gravierende Nachteile. Neue Medikamente werden dringend benötigt.
Naturstoffe (NP) spielen eine dominierende Rolle in der Wirkstoffforschung für die Behandlung von menschlichen Erkrankungen. So haben Chinin und Artemisin ihren Ursprung in der Natur und führten zu erfolgreichen Medikamenten zur Malariabehandlung.
In einem mittleren Durchsatz-Screening wurden insgesamt 507 Extrakte von südafrikanischen Pflanzen auf ihre Aktivität gegen Protozoen - Plasmodium falciparum, Trypanosoma brucei rhodesiense, Trypanosoma cruzi und Leishmania donovani - getestet. Extrakte von Abrus precatorius L. ssp. africanus Verdc. (Fabaceae) und Drypetes gerrardii Hutch. var. gerrardii (Putranjivaceae) haben mindestens einen der Parasiten in einer als relevant bezeichneten Testkonzentration gehemmt.
Mit dem Ziel die für diese Aktivitäten verantwortlichen Verbindungen zu identifizieren wurde ein Ansatz bestehend aus HPLC-basiertes Aktivitäts-Profiling gefolgt von Dereplikation verwendet. Gezielte Isolierung der vielversprechenden Verbindungen erfolgte durch eine Kombination von Chromatographie-Techniken. Die Strukturaufklärung wurde durch HR-ESI-MS und NMR (1H, 13C, COSY, HMBC, HSQC, und NOESY Spektroskopie) durchgeführt. Die absolute Konfiguration wurde durch den Vergleich der elektronischen Zirkulardichroismus-(ECD)-Spektren mit berechneten ECD-Daten bestimmt.
HPLC-basiertes Aktivitäts-Profiling von A. precatorius ermöglichte die Identifizierung von Abruquinonen, als verantwortliche Substanzen für die trypanozide Aktivität des Rohextrakts. Es wurden insgesamt 10 Abruquinone isoliert, darunter fünf neue Verbindungen. Abruquinone B, I, A, D, K und L zeigten bemerkenswerte Hemmung (0.16 ± 0.060, 0.28 ± 0.051, 0.02 ± 0.003, 0.01 ± 0.001, 0.11 ± 0.053, und 0.02 ± 0.053) und beachtenswerte Selektivität, wiedergegeben als Selektivitätsindizes (SIs) die aus der Zytotoxizität in L-6 Zellen (51, 74, 1379, 668, 508, und 374) ermittelt wurden.
Wegen ihrer starken und selektiven in vitro Hemmung von T. b. rhodesiense, ihrer guten Übereinstimmung mit Lipinski’s „5er Regel“ und anderen molekularen Eigenschaften, sowie ihrem niederen/mässigen toxischen Potenzial sind Abruquinone vielversprechende Hits. Deshalb sind weitere Studien notwendig um botanische oder chemische Quellen sicherzustellen und die in-vivo Wirksamkeit dieser Verbindungen zu bestimmen.
Zwei verschiedene Extrakte von D. gerrardii zeigten Aktivität gegen Protozoen. Die aktiven Bestandteile wurden mit Hilfe vom HPLC-basiertem Aktivitäts-Profiling identifiziert und isoliert. Der CH2Cl2/MeOH (1:1) Extrakt aus den Stängeln hemmte L. donovani und P. falciparum. Die Hauptverbindung, ein neues Phenanthrenon, zeigte gute in vitro Aktivität (IC50 von 0.9 ? 0.3 mM) und Selektivität (SI von 68) gegen P. falciparum. Basierend auf diesen vielversprechenden Resultaten wurden in vivo Studien durchgeführt. Allerdings war diese Verbindung nicht in der Lage die Parasitenbelastung im P. berghei Mausmodell zu reduzieren. Es wurde ebenfalls ein Phenanthrenon-Heterodimer isoliert, der in vitro Aktivität gegen Plasmodien (IC50 von 2.04 ? 0.15 mM und SI von 31) aufwies. Ausserdem zeigte der CH2Cl2/MeOH (1:1) Blattextrakt ausgewiesene trypanozidale Eigenschaften. Aus diesem Extrakt wurde das bekannte Saponin Putranoside A isoliert und gegen T. b. rhodesiense, (IC50 von 18.0 ? 3.8 mM und SI von 4) getestet.
Das Phenanthrenon war der aktivste und selektivste in vitro Inhibitor von P. falciparum, zeigte jedoch keine Hemmung in vivo gegen P. berghei. Die Verbindung erfüllte jedoch Lipinski’s „5er Regel“ und andere molekulare Eigenschaften, wie orale Bioverfügbarkeit und Durchlässigkeit der Blut-Hirn-Schranke, was ein mögliches Potenzial aufzeigt den Anforderungen eines idealen Antimalariawirkstoffs gerecht zu werden. Nach „Medicines for Malaria Venture“-Kriterien für die weitere Entwicklung eines Wirkstoffs erfüllt das Phenanthrenon einige der Merkmale eines validierten Hits wie ausreichende in vitro Aktivität gegen P. falciparum (? 1 ?M).
Als weiterer Teil des Projekts wurde die Wirkung von europäischen Heilpflanzen Chrysanthemum cynerariifolium (Trevir.) Vis. (Asteraceae), Laurus nobilis L. (Lauraceae), und Eupatorium cannabinum L. (Asteraceae) gegen Protozoen studiert. Ein Hexan-Extrakt von C. cynerariifolium zeigte vielversprechende Aktivität gegen P. falciparum. Phyrethrine (unregelmässige Monoterpene) waren die Inhaltsstoffe verantwortlich für die antiplasmodiale Aktivität. Besonders Pyrethrin II und Jasmolin II hemmten P. falciparum (IC50 4.0 ? 1.1 ?M und 5.0 ? 0.4 ?M, und SI von 24 und 6) in vitro. Es wurden auch synthetische Pyrethroide getestet, sie zeigten aber keine Aktivität.
Schliesslich, als Beitrag zu den Struktur-Aktivitätsuntersuchungen von Sesquiterpenlactonen mit Aktivität gegen T. b. rhodesiense, wurden Costunolid und Zaluzanin D aus Laurus nobilis L. (Lauraceae) und Eupatoriopicrin aus Eupatorium cannabinum L. (Asteraceae) isoliert. Germacrolides, d.h. Costunolid und Eupatoriopicrin, zeigten eine höhere Hemmung (IC50 von 1.3 ? 0.4 mM und 1.2 ± 0.2 mM) auf Protozoen als das Guaianolid Zaluzanin D (IC50 von 10.8 mM).
Es wurden insgesamt 22 Sekundärmetaboliten aus fünf Arten isoliert, darunter sieben neue Verbindungen. Diese Substanzen gehören zu den Strukturklassen der Isoflavonoide, Phenanthrenone und Terpene einschliesslich Sesquiterpenelactone, unregelmässige Monoterpene und Triterpenoidsaponine. Die meisten von ihnen (15 Verbindungen) zeigten in vitro Aktivität gegen Protozoen. Die vielversprechendsten Verbindungen waren die Abruquinone und das Phenanthrenon, die starke und selektive Hemmung gegen T. b. rhodesiense und P. falciparum zeigten. Abruquinone und das Phenanthrenon sind drug-like Verbindungen mit einem rechnerischen toxischen Potential von gering bis mässig
Screening, identification, structure-activity, and mode of action studies with new antitrypanosomal leads of plant and fungal origin
No full textHuman African trypanosomiasis (HAT) is a neglected disease caused by the protozoan Trypanosoma brucei, which is transmitted during blood-feeding tsetse fly bites. The disease is endemic covering 36 sub-Saharan African countries and mainly impacts poor people living in remote areas, for which satisfactory treatment does not exist. As such, this protozoal disease would never be viewed as viable target market for the pharmaceutical industry. Therefore, it is referred to as a neglected disease. Chemotherapy remains the principal treatment for HAT and is based on four drugs: suramin, pentamidine, melarsoprol, eflornithine, and a recent approved eflornithine-nifurtimox combination. Reported severe side effects (e.g. melarsoprol), treatment failures of up to 25%, administration difficulties, and expensive medication urgently demand for safe, orally administered drugs, that are effective against both stages of HAT. Natural sources like plants and fungi provide a rich biological diversity with unique pharmacophores created by evolution and are therefore potential sources to discover such new drugs.
This thesis describes the search of new natural products (NPs) from nature. Over the last seven years we collected 724 plants and 64 fungi. The material was subsequently extracted and tested in vitro against T. b. rhodesiense, Plasmodium falciparum (the causative agent of malaria), Leishmania donovani (leishmaniasis), and T. cruzi (Chagas disease) to find potential hits. From the total 2151 extracts, 17.9% showed activity of more than 50% at 4.81 µg/mL test concentration against at least one parasite, and 3.4% showed potency of more than 50% at 0.81 µg/mL test concentration, respectively. Overall the plant extracts had six times higher "hit-rates" (15.3%) than the fungi extracts (2.6%), both resulting in high potencies against T. b. rhodesiense and P. falciparum. Yet, with up to 5 millions fungi, which outnumber higher plants by 16:1, the kingdom remains a relatively poorly studied source.
One of the antitrypanosomal hits was a dichloromethane (DCM) extract of the cornflower Centaurea salmantica with a growth inhibition of 61% tested at 4.81 µg/mL against T. b. rhodesiense. HPLC-based activity profiling led to the identification of the sesquiterpene lactone (STL) cynaropicrin (CYN), which was the first plant NP to show in vivo efficacy in T. b. rhodesiense infected mice, treated i.p. at 10 mg/kg/b.i.d. for four consecutive days. Despite of more than 10'000 known STLs is a better understanding of the structural features, which contribute to activity, expedient. The established structure-activity relationship (SAR) study included 18 natural STLs and demonstrated that antitrypanosomal and cytotoxic effect depended on their a,ß-unsaturated enone moieties. Many bioactivities of STLs have been attributed to a nucleophilic Michael-addition of these functional motifs to biological thiols. Considering that trypanosomes depend on their unique trypanothione-based redox system to deal with oxidative stress and to maintain a reducing intracellular milieu and that CYN contains reactive exocyclic a,ß-unsaturated methylenes, we anticipated that the mechanism of action depended on a direct interference with glutathione (GSH) and trypanothione (T(SH)2) in the cells. After 5 min. of CYN's exposure to trypanosomes, the intracellular thiol pool was completely depleted and a GS-CYN-monoadduct as well as a T(S-CYN)2-bisadduct were formed. This led to apoptosis of the trypanosomes over 40 min. linked to phenotype transformations from the typical slender to a stumpy-like form. Additionally, ornithine quantification studies by tandem mass spectroscopy (MS/MS) showed that ornithine decarboxylase (ODC) is a potential secondary target for CYN.
To improve CYN's pharmacokinetic (PK) profile the a,ß-unsaturated exocyclic double bond at the lactone was masked to create an amine prodrug with increased aqueous solubility and reduced unspecific binding to biological thiols. Through subsequent bioactivation the prodrug would be converted back to CYN and it would display a higher concentration on the target side. The lead optimization did not reward any better antitrypanosomal in vivo efficacy after oral application, but the prodrug had an improved in vivo cytotoxic profile. Further PK studies with other orally applied STL amino derivatives are needed to demonstrate if the use of amino STLs as prodrugs is a reasonable approach to improve STLs suitability as antitrypanosomal drug
A novel antimalarial lead compound: in vitro properties and mode of action studies
No full textMalaria remains a major public health problem and the increasing number of resistant
strains underscores the need for new drugs with new modes of action (MOAs).
It was the aim of the present thesis to characterize a novel antimalarial lead compound
with respect to MOA and in vitro properties.
The lead compound, ACT-AM, inhibited in vitro proliferation of all tested P. falciparum
strains, irrespective of their drug resistance properties, with IC50 values in the low singledigit
nanomolar range. ACT-AM was further shown to equally and rapidly affect all
asexual blood stages of the parasite. The novel molecule is therefore comparable to the
most efficacious registered antimalarial drugs in terms of in vitro activity.
To investigate the MOA of ACT-AM, a chemical derivative of the compound able to
form covalent bonds upon UV activation was utilized. This advantageous UV-dependent
system was adapted and implemented for P. falciparum- notably for the use in intact cells
and proved to be appropriate for various biochemical methods including pull-down
experiments, fluorescent imaging and Far Western blotting. Pull-down experiments
revealed numerous target candidates, three of which were shown to interact with ACTAM
in vitro, namely MDR (multidrug resistance protein), ENT4 (equilibrative nucleoside
transporter 4) and CRT (chloroquine resistance transporter). These proteins could
represent actual targets or might confer resistance to the compound.
Microarray and hematin interaction studies suggested that ACT-AM has an MOA distinct
from that of several registered antimalarials, a factor that bodes well for possible
combination therapies.
The promising in vitro activity of the compound and the indication of a novel MOA
emphasize the potential of ACT-AM or analogues of the same chemical class as
therapeutic agents for the treatment of malaria
New drugs against trypanosomatid parasites : rediscovery of fexinidazole
No full textNeglected tropical diseases (NTDs) are a group of communicable diseases mostly affecting people in developing countries. These diseases are responsible for a major part of the global morbidity, mortality and poverty. There is no doubt that the well-being of people in the developing world can only be improved if the NTDs are controlled. An important tool for disease control is the drug treatment. The few available drugs are unsatisfactory because of the limited efficacy, adverse effects and the high price. Chagas disease, leishmaniasis and human African trypanosomiasis belong to this group of NTDs. They are caused by infections with protozoa of the family Trypanosomatidae. For these three diseases new drugs are urgently needed.
By definition there is no commercial market for drugs against NTDs. Drug research and development (R&D) for NTDs is mainly driven by the public sector, the so-called product development partnerships (PDPs). Drug R&D is a very long (10-15 years), risky and therefore expensive process. Three different series of compounds (agrochemicals, marketed drugs and nitro-heterocyclic compounds) were tested for their antiparasitic effects, with the aim to identify new lead compounds or even clinical candidates against leishmaniasis, sleeping sickness, and Chagas disease.
Agrochemicals are used worldwide on a large scale in food production. They undergo a rigorous toxicological testing prior to launch. Over 600 compounds were screened for their antiparasitic activity. Agrochemicals are not optimized for use in mammals, yet a significant number of molecules were found with good and selective in vitro activity. Some of them showed also efficacy in the corresponding rodent model. These results indicate that agrochemicals can provide very interesting starting structures for drug research against parasitic diseases.
Drugs or drug-like compounds are an ideal starting point for antiparasitic drug discovery, because very often pharmacokinetic and toxicological data are available. A number of drugs, including antibiotics, antivirals, antifungals, and anti-psychotics were assayed for antiparasitic activity. Some of the drugs tested showed selective antiparasitic activity. These compounds can be regarded as new lead structures and should be further investigated.
Nitroheterocycles belong to a well- known class of compounds with the stigma of being mutagenic or genotoxic. Over 700 compounds, mainly nitroimidazoles, have been systematically tested for their antiparasitic activity, and their pharmacokinetics and mutagenicity was investigated. A number of effective, non-mutagenic and non- genotoxic compounds was identified. So fexinidazole was rediscovered, a drug that had been in clinical development already in the 70’s as a broad-spectrum antimicrobial drug. Fexinidazole is rapidly metabolized to fexinidazole-sulfoxide and -sulfone. The parent compound and the two principle metabolites showed in vitro trypanocidal activity against all (sensitive and resistant) tested T. brucei strains (IC50 of 0.2 - 0.9 ug / ml). Fexinidazole cured the first stage mouse model with a 4-day oral treatment of 100 mg/kg/day and the 2nd stage mouse model with a 5-day oral treatment of 200 mg/kg/day. The two metabolites are mainly responsible for the good efficacy in animal models. Both reach very high concentrations in blood and brain tissue. Fexinidazole has successfully completed preclinical development and Phase I clinical trials and is currently in a clinical phase II / III study.
With the approach of phenotypic screening of compounds that have been developed for other purposes, new leads for drug R&D against Chagas’ disease, leishmaniasis and human African trypanosomiasis were identified.
Fexinidazole is the first drug candidate in clinical Phase II / III trials since decades. It would be the first oral drug for the treatment of stage 1 and 2 of human African sleeping sickness. If fexinidazole overcomes all obstacles, this would be a major breakthrough in the fight against African sleeping sickness. With a well tolerated, orally active drug like Fexinidazole the elimination of sleeping sickness seems finally tangible
Discovery of natural antiprotozoals from medicinal plants Saussurea costus and Carica papaya
No full textMedicinal plants have been an important source for the discovery of therapeutic agents for infectious diseases. In order to explore their potential an appropriate selection of plant species is important. In our attempt to find hits targeting antiprotozoal diseases, we utilized an extract library setting, and ethnomedicinal information. A library of 1800 plant and fungal extracts was screened for in vitro effects against Trypanosoma brucei rhodesiense STIB 900 strain and Plasmodium falciparum K1 strain. The ethyl acetate extract of Saussurea costus roots, and the methanolic extract of Carica papaya leaves were selected for further studies. HPLC-based activity profiling enabled the localization and identification of the active constituents of these plants extracts. Sensitive hyphenated analytical methods such as HPLC-PDA-ESI-TOF-MS and microprobe NMR were used for structure elucidation of the isolated compounds. X-ray crystallography was used in combination with electronic circular dichroism to determine the absolute configuration of selected compounds.
The ethyl acetate extract of S. costus roots potently inhibited the growth of T. b. rhodesiense in vitro. HPLC-based activity profiling led to the identification of four sesquiterpene lactones. Three structurally related sesquiterpene lactones that originated from different sources were also investigated. All compounds exhibited profound activity against T. b. rhodesiense with IC50 values between 0.8 – 21.9 µM. Cytotoxicity was tested on rat myoblast L-6 cells, where IC50 values of 1.6 to 19.4 µM were observed, and provided selectivity indices (SI) between 0.5 and 6.5. The most active compounds in this study were the germacranolides costunolide, parthenolide, and eupatoriopicrin.
The leaves of the Indonesian ethnomedicinal plant C. papaya are a known antimalarial remedy. So far, the active principles have not been investigated from a phytochemical and pharmacological point of view. HPLC-based activity profiling of the methanolic extract from C. papaya leaves against P. falciparum led to the discovery of five alkaloids and four flavonol glycosides. All compounds exhibited in vitro antimalarial activity against P. falciparum K1 strain, albeit to varying degrees. Three dimeric alkaloids showed potent activity with IC50 values ranging from 0.2 to 1.8 µM, and SI from 24.2 to 107.5. The isolated flavonol glycosides were less active, with IC50 values between 13.2 – 16.8 µM, and selectivity indices of more than 9. Lower activity was observed for the two monomeric alkaloids (IC50 = 77 µM). Carpaine (IC50 of 0.2 µM; SI of 107.5) was the most interesting compound in this study and was, hence, selected for further evaluation of its in vivo pharmacological properties using a 4-day suppressive assay on mice. However, only a reduction of parasitemia by 11.9% was observed. With the aid of X-ray crystallography and ECD calculation, the absolute configuration for carpaine was established as 1S,11R,13S,14S,24R,26S. Carpaine represents a new scaffold for anti-plasmodial drugs. An analysis of carpaine content by means of UPLC-MS/MS was pursued with 28 leaf samples from Indonesia and one from India. The carpaine content varied from 0.02 to 0.31%
Synthesis and evaluation of antiparasitic activities of new 4-[5-(4-phenoxyphenyl)-2H-pyrazol-3-yl]morpholine derivatives
No full textA series of new 4-[5-(4-phenoxyphenyl)-2H-pyrazol-3-yl]morpholine derivatives, prepared by two synthetic routes, were in vitro assayed against three Trypanosoma strains, Leishmania donovani, and Plasmodium falciparum K1. Seven out of 17 compounds showed moderate to very good activity against blood stage T. b. rhodesiense, with 10 and 17 exhibiting highest potency (IC 50 of 1.0 and 1.1 μM. respectively). Interestingly, the β-diketone precursors 1-3 had good antitrypanosomal activity toward the insect stage, with IC50 values of 1.0-3.4 μM. Among different compounds with moderate activity against T. cruzi, compound 17 showed the lowest IC50 value of 9.5 μM; thus, the series seemed to act selectively toward the different Trypanosoma parasites. Eight compounds were moderately active against L. donovani, with 2, 3, and 12 being the most promising ones (IC50 values of 2.3-5.2 μM), whereas compound 14 was the only derivative with good activity against P. falciparum (IC50 of 3.7 μM). © 2007 American Chemical Society
In pursuit of natural product leads: Synthesis and biological evaluation of 2-[3-hydroxy-2-[(3-hydroxypyridine-2-carbonyl)amino]phenyl]benzoxazole-4- carboxylic acid (A-33853) and its analogues: Discovery of N-(2-benzoxazol-2- ylphenyl)benzamides as novel antileishmanial chemotypes
No full textThe first synthesis and biological evaluation of antibiotic 31 (A-33853) and its analogues are reported. Initial screening for inhibition of L. donovani, T. b. rhodesiense, T. cruzi, and P. falciparum cultures followed by determination of IC50 in L. donovani and cytotoxicity on L6 cells revealed 31 to be 3-fold more active than miltefosine, a known antileishmanial drug. Compounds 14, 15, and 25 selectively inhibited L. donovani at nanomolar concentrations and showed much lower cytotoxicity. © 2008 American Chemical Society
Author Correction: Local Josephson vortex generation and manipulation with a Magnetic Force Microscope (Nature Communications, (2019), 10, 1, (4009), 10.1038/s41467-019-11924-0)
No full text© 2019, The Author(s). The original version of this Article contained an error in the spelling of the author Christophe Brun, which was incorrectly given as Chritophe Brun. Additionally this Article omitted from the author list the seventh author Nickolay Lebedev, who is from the ‘Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia’. These errors have now been corrected in both the PDF and HTML versions of the Article
- …
