Bisphosphonates inhibit the growth of Trypanosoma brucei, Trypanosoma cruzi, Leishmania donovani, Toxoplasma gondii, and Plasmodium falciparum: a potential route to chemotherapy

We have investigated the effects in vitro of a series of bisphosphonates on the proliferation of Trypanosoma cruzi, Trypanosoma brucei rhodesiense, Leishmania donovani, Toxoplasma gondii, and Plasmodium falciparum. The results show that nitrogen-containing bisphosphonates of the type used in bone resorption therapy have significant activity against parasites, with the aromatic species having in some cases nanomolar or low-micromolar IC(50) activity values against parasite replication (e.g. o-risedronate, IC(50) = 220 nM for T. brucei rhodesiense; risedronate, IC(50) = 490 nM for T. gondii). In T. cruzi, the nitrogen-containing bisphosphonate risedronate is shown to inhibit sterol biosynthesis at a pre-squalene level, most likely by inhibiting farnesylpyrophosphate synthase. Bisphosphonates therefore appear to have potential in treating parasitic protozoan diseases.     

Antiparasitic and antimicrobial indolizidines from the leaves of Prosopis glandulosa var. glandulosa

A new indolizidine alkaloid, named Δ1,?-juliprosopine (1), together with previously known indolizidine analogs (2- 6), was isolated from the leaves of Prosopis glandulosa var. glandulosa, collected from Nevada, USA; while two other known indolizidines, juliprosopine (6) and juliprosine (7), were isolated from P. glandulosa leaves collected in Texas, USA. The structures of compound 1 and 7 were determined using a combination of NMR and MS techniques. Compound 7 exhibited potent antiplasmodial activity against Plasmodium falciparum D6 and W2 strains with IC (50) values of 170 and 150 ng/mL, respectively, while 1 was found to be less active (IC?? values 560 and 600?ng/mL, respectively). Both compounds were devoid of VERO cells toxicity up to a concentration of 23?800?ng/mL. The antileishmanial activity of indolizidines was evaluated against Leishmania donovani promastigotes, axenic amastigotes, and amastigotes in THP1 macrophage cultures. When tested against macrophage cultures, the tertiary bases (1, 3, 6) were found to be more potent than quaternary salts (2, 5, 7), displaying IC?? values between 0.8-1.7?μg/mL and 3.1-6.0?μg/mL, respectively. In addition, compound 7 showed potent antifungal activity against Cryptococcus neoformans and antibacterial activity against Mycobacterium intracellulare, while 1 was potent only against C. neoformans and weakly active against other organisms.     

Antiplasmodial and antitrypanosomal activity of tanshinone-type diterpenoids from Salvia miltiorrhiza

In a medium throughput screen of 880 plant and fungal extracts for antiprotozoal activity, a dichloromethane extract of Salvia miltiorrhiza roots was active against both Trypanosoma brucei rhodesiense and Plasmodium falciparum. With HPLC-based activity profiling in combination with on- and off-line spectroscopic methods (PDA, -MS (n), HR-MS, microprobe NMR), the active compounds were identified as tanshinone-type diterpenoids. Subsequent isolation and structure elucidation yielded the known substances miltirone (1), tanshinone II?a (2), 1,2 dihydrotanshinquinone (3), methylenetanshinquinone (4), 1-oxomiltirone (5), 11-hydroxymiltiodiol (6), tanshinone I (7), methyltanshinonate (8), and cryptotanshinone (9). The IC??s of the compounds were determined against the two parasites and rat myoblast (L6) cells. They ranged from 4.1?μM to over 30?μM against P. falciparum K1 strain with selectivity indices (SI) from 0.3 to 1.9. IC??s against T. brucei rhodesiense STIB 900 were from 0.5?μM (1,?4) to over 30?μM, and 4 showed the greatest selective activity with an SI of 24.     

Anthranoid compounds with antiprotozoal activity from Vismia orientalis

A phytochemical investigation of the 80% ethanolic extract of stem bark of Vismia orientalis Engl. (Guttiferae or Clusiaceae), a plant used in traditional medicine in Tanzania, resulted in the isolation and spectroscopic characterisation of 3-geranyloxy-6-methyl-1,8-dihydroxyanthraquinone, emodin, vismione D and bianthrone A1. Vismione D exhibited a broad range of antiprotozoal activities against Trypanosoma brucei rhodesiense and T. cruzi (IC50 < 10 micrograms/mL), Leishmania donovani (IC50 0.37 micrograms/mL) and Plasmodium falciparum strain K1 (IC50 1.0 microgram/mL). However, it was also slightly cytotoxic against human L6 cells (IC50 4.1 micrograms/mL). Emodin showed antileishmanial activity (IC50 2.0 micrograms/mL), while its IC50 against L6 cells was 20.3 micrograms/mL. Other antiprotozoal activities observed for emodin against both Trypanosoma species and P. falciparum, for bianthrone A1 against T. b. rhodesiense and P. falciparum, and for 3-geranyloxy-6-methyl-1,8-dihydroxyanthraquinone against T. b. rhodesiense, L. donovani and P. falciparum were in the range of 10 to 50 micrograms/mL. None of the compounds showed antibacterial or antiviral (including also HIV) activity.     

9β-hydroxyparthenolide esters from Inula montbretiana and their antiprotozoal activity

In continuation of ongoing studies on the potential of natural products as antiprotozoal leads or drugs, it was found that the CH?Cl? extract obtained from the flowering aerial parts of Inula montbretiana DC. (Asteraceae, tribe Inuleae) displays antiprotozoal activity, especially against Trypanosoma brucei rhodesiense (IC??: 3.38?μg/mL). Isolation of the possible active constituents led to the identification of six sesquiterpene lactones, all esters of 9 β-hydroxyparthenolide. Two isolates, namely, 9 β-(3',4'-epoxy-3'-methylpentanoyloxy)-parthenolide and 9 β-(3'-oxo-2'-methylbutanoyloxy)-parthenolide, represented diastereomeric mixtures differing only in the configuration within the acyl moieties. According to in vitro test results, the mixture of esters with diastereomeric 3,4-epoxy-3-methylpentanoic acid was the most active constituent against Trypanosoma brucei rhodesiense (IC??: 0.26?μg/mL) and was less cytotoxic against rat skeletal myoblasts (L6 cell line) with a selectivity index of about 9. The mixture of diastereomeric 2-methyl-3-oxobutyric acid esters was the most potent against Plasmodium falciparum (IC??: 1.48?μg/mL) and displayed a selectivity index of about 35.     

Synthesis and evaluation of antiparasitic activities of new 4-[5-(4-phenoxyphenyl)-2H-pyrazol-3-yl]morpholine derivatives

A 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 (IC50 of 1.0 and 1.1 microM, respectively). Interestingly, the beta-diketone precursors 1-3 had good antitrypanosomal activity toward the insect stage, with IC50 values of 1.0-3.4 microM. Among different compounds with moderate activity against T. cruzi, compound 17 showed the lowest IC50 value of 9.5 microM; 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 microM), whereas compound 14 was the only derivative with good activity against P. falciparum (IC50 of 3.7 microM).     

Synthesis, biological evaluation, and structure-activity relationships of N-benzoyl-2-hydroxybenzamides as agents active against P. falciparum (K1 strain), Trypanosomes, and Leishmania

In our efforts to identify novel chemical scaffolds for the development of new antiprotozoal drugs, a compound library was screened against Toxoplasma gondii tachyzoites with activity discovered for N-(4-ethylbenzoyl)-2-hydroxybenzamide 1a against T. gondii as described elsewhere. Synthesis of a compound set was guided by T. gondii SAR with 1r found to be superior for T. gondii , also active against Thai and Sierra Leone strains of Plasmodium falciparum , and with superior ADMET properties as described elsewhere. Herein, synthesis methods and details of the chemical analysis of the compounds in this series are described. Further, this series of N-benzoyl-2-hydroxybenzamides was repurposed for testing against four other protozoan parasites: Trypanosoma brucei rhodesiense , Trypanosoma cruzi , Leishmania donovani , and P. falciparum (K1 isolate). Structure-activity analyses led to the identification of compounds in this set with excellent antileishmanial activity (compound 1d). Overall, compound 1r was the best and had activity 21-fold superior to that of the standard antimalarial drug chloroquine against the K1 P. falciparum isolate.     

Cytotoxic and antimicrobial activities of aporphine alkaloids isolated from Stephania venosa (Blume) Spreng

The cytotoxic activity of five alkaloids, namely 4,5-dioxo-dehydrocrebanine (1), dehydrocrebanine (2), crebanine (3), oxostephanine (4), and thailandine (5) isolated from the tuber and leaves of Stephania venosa (Blume) Spreng was investigated. Thailandine showed the strongest activity against lung carcinoma cells (A549) (IC50 of 0.30?μg/mL) with very low cytotoxicity against normal embryonic lung cells (MRC-5). Thailandine also demonstrated strong activity against Plasmodium falciparum, K1 strain (IC50 of 20?ng/mL), and Mycobacterium tuberculosis H(37)Ra (MIC of 6.25?μg/mL) as well as gram-positive bacteria such as Streptococcus pneumoniae and Staphylococcus aureus. Oxostephanine exhibited strong activity against breast cancer (BC) and acute lymphoblastic leukemia cells (MOLT-3) with an IC50 of 0.24 and 0.71?μg/mL, respectively, and exhibited very low cytotoxicity against MRC-5 cells. Dehydrocrebanine demonstrated strong activity against promyelocytic leukemia cells (HL-60) with an IC50 of 2.14?μg/mL whereas crebanine showed weak activity against cancer cell lines. However, both of them showed cytotoxicity against MRC-5 cells.     

Synthesis and in vitro antiprotozoal activity of bisbenzofuran cations

Forty three cationic bisbenzofurans were synthesized either by interaction of o-hydroxyaldehydes with alpha-halogenated ketones followed by intramolecular ring closure or by a copper- or palladium-mediated heteroannulation of substituted o-iodophenols with terminal acetylenes. In vitro antiprotozoal activities of compounds 1-43 against Trypanosoma brucei rhodesiense, Plasmodium falciparum, and Leishmania donovani and cytotoxicity against mammalian cells were influenced by the position and the type of cationic substituents as well as the length of the carbon linker between aromatic moieties. One bisamidine displayed an antitrypanosomal efficacy comparable to that of pentamidine and melarsoprol. Twenty two compounds were more potent than pentamidine and seven dications were more effective than artemisinin against P. falciparum. Eight bisbenzofurans displayed activity against L. donovani superior to that of pentamidine. Overall, bisamidines connected by two-carbon linkers exhibited the highest efficacies against T. b. rhodesiense, P. falciparum, and L. donovani.     

Antimicrobial, antimalarial, and antileishmanial activities of mono- and bis-quaternary pyridinium compounds

Pyridinium-based oxime compounds have been utilized worldwide as antidotes following exposure to anticholinesterase agents. In the event of combined chemical and biological incident, it is of vital importance to know the ability of antidotes to provide additional protection against biological threats. This paper reports results of in vitro antimicrobial and antiprotozoal activities of a series of quaternary pyridinium oximes against a number of lower pathogenicity BSL-1 and 2 agents. In general, our compound panel had little to no antimicrobial action except for thiophene- and benzothiophene-substituted monoquaternary pyridinium compounds 21 and 24 that showed moderate antibacterial activity against Staphylococcus aureus and methicillin-resistant S. aureus with IC(50) values ranging from 12.2 to 17.7 μg/mL. Compounds 21 and 24 also exhibited antileishmanial activity against Leishmania donovani with IC(50) values of 19 and 18 μg/mL, respectively. Another monoquaternary pyridinium compound with a bromobutyl side chain 17 showed antimalarial activity against both a chloroquine sensitive and resistant strains of Plasmodium falciparum with IC(50) values of 3.7 and 4.0 μg/mL, respectively. None of the bisquaternary pyridinium compounds showed antimicrobial or antiprotozoal activity. None of the compounds showed cytotoxic effects toward mammalian kidney fibroblasts. Results of this study indicate that the pyridinium compounds, some of which are already in use as antidotes, do not have significant antimicrobial and antiprotozoal activities and cannot be relied upon for additional protection in the event of combined chemical-biological incident.     

Synthesis and in vitro antiprotozoal activities of water-soluble, inexpensive 3,7-bis(dialkylamino)phenoxazin-5-ium derivatives

3,7-Bis(dialkylamino)phenoxazinium salts were synthesized and evaluated for in vitro activities against Plasmodium falciparum, Trypanosoma cruzi, T. brucei rhodesiense, and Leishmania donovani. Notably, the compounds showed potent antiprotozoal activities, especially against P. falciparum and T. cruzi. The compounds with alkyl side chains less than three carbons in length possessed good activities with high selective indices.     

Synthesis and structure-activity relationships of parasiticidal thiosemicarbazone cysteine protease inhibitors against Plasmodium falciparum, Trypanosoma brucei, and Trypanosoma cruzi

We have synthesized a library of thiosemicarbazones and screened them against three parasitic cysteine proteases, cruzain, falcipain-2, and rhodesain, and against the respective parasite sources of these three proteases, Trypanosoma cruzi, Plasmodium falciparum, and Trypanosoma brucei. The screens identified compounds that were effective against the enzymes and the parasites but also some compounds that were parasiticidal despite a lack of activity against the proteases. Several compounds were effective in killing all tested parasites. These promising lead compounds were tested for general toxicity in mice, and only one produced observable toxicity after 62 h. Our results suggest that thiosemicarbazones represent validated drug leads that kill several species of protozoan parasites through the inhibition of cysteine proteases as well as other novel targets.     

Synthesis and in vitro protozoocidal evaluation of novel diazabicyclic tropolone derivatives

The synthesis and in vitro antiparasitic activity of twenty-seven novel diazabicycles based on tropolone ethers is presented. The compounds can be readily prepared by means of a high-yielding hetero Diels-Alder reaction using simple and readily available starting materials. Several of the new diazabicycles have in vitro activities against Trypanosoma cruzi, Leishmania donovani, Trypanosoma brucei rhodesiense, and chloroquine-resistant Plasmodium falciparum that are comparable or superior to those of currently employed protozoocidal agents.     

Synthesis and evaluation of novel 7-trifluoromethyl-4-(4-substituted anilino)quinolines as antiparasitic and antineoplastic agents

Several novel derivatives bearing the 7-trifluoromethyl-4-(4-substituted anilino)-quinoline skeleton were synthesized and evaluated for their in vitro activity against the blood streaming form of the parasites Trypanosoma brucei rhodesiense, the trypomastigotes of Trypanosoma cruzi cultured in rat skeletal myoblasts, the amastigotes form of Leishmania donovani, Plasmodium falciparum (K1 strain) infected erythrocyte suspension, as well as their toxicity towards rat skeletal L-6 cells. In addition, three of the synthesized compounds were tested for their in vitro antitumor activity towards 60 human tumor cell lines by the National Cancer Institute (NCI). Compound 1-(4-[[7-(trifluoromethyl)quinolin-4-yl]amino]phenyl)ethan-1-one thiosemicarbazone 23 exhibited potential activity against T. b. rhodesiense, T. cruzi and P. falciparum with IC50's of 0.278, 0.85 and 0.417 microgram/ml, respectively. These values are even more valuable since this compound was clearly non-toxic (cytotoxicity IC50 > 90 micrograms/ml), leading to in vitro therapeutic indices of > 323, > 106 and > 216, respectively. Meanwhile, compound N-[4-[5-(4-chlorophenyl)-4,5-dihydroisoxazol-3-yl]phenyl]-7-(trifluoromethyl) quinolin-4-amine 21 showed broad spectrum antitumor activity with full panel median growth inhibition GI50 (MG-MID) of 1.95 mumol and total growth inhibition TGI (MG-MID) of 6.87 mumol, respectively. Compound 23 represents a very good prospective as a lead compound able to combat three tropical diseases at a time. However, the pattern for the antitumor activity did not parallel any of the antiparasitic ones, indicating that non-common mechanisms of action may exist among these activities.     

Synthesis and antiprotozoal activity of cationic 2-phenylbenzofurans

A series of cationically substituted 2-phenylbenzofurans 1- 49 have been synthesized, and their in vitro antiprotozoal properties against Trypanosoma brucei rhodesiense, Plasmodium falciparum, and Leishmania donovani, as well as cytotoxicity against mammalian cells, have been evaluated. Eight dications exhibited antitrypanosomal activities comparable to that of pentamidine and melarsoprol. Twenty-six compounds were more active than pentamidine, and seven dications demonstrated increased activities against P. falciparum than artemisinin. Five congeners were more active against L. donovani than pentamidine. Introduction of methoxy or hydroxy groups in the 7- and/or 2'-position afforded derivatives that were highly selective against T. b. rhodesiense, P. falciparum, and L. donovani. Fourteen 2-phenylbenzofurans displayed excellent in vivo efficacies in the acute mouse model of trypanosomiasis, curing 3/4 or 4/4 animals at 4 x 5 mg/kg. Diamidine 1 and di( N-isopropyl)amidine 45, administered at 4 x 1 mg/kg, exhibited potency comparable to that of melarsoprol, providing 3/4 and 2/4 cures, respectively.     

Antimalarial, antitrypanosomal, and antileishmanial activities and cytotoxicity of bis(9-amino-6-chloro-2-methoxyacridines): influence of the linker

Forty bis(9-amino-6-chloro-2-methoxyacridines), in which acridine moieties are joined by alkanediamines, polyamines, or polyamines substituted by a side chain, were synthesized and tested for their in vitro activity upon the erythrocytic stage of Plasmodium falciparum, trypomastigote stage of Trypanosoma brucei, and amastigote stage of Trypanosoma cruzi and Leishmania infantum as well as for their cytotoxic effects upon MRC-5 cells. Results clearly showed the importance of the nature of the linker and of its side chain for antiparasitic activity, cytotoxicity, and cellular localization. Among several compounds devoid of cytotoxic effects at 25 microM upon MRC-5 cells, one displayed IC(50) values ranging from 8 to 18 nM against different P. falciparum strains while three others totally inhibited T. brucei at 1.56 microM.     

Psilostachyin C: a natural compound with trypanocidal activity

In this study, the antiprotozoal activity of the sesquiterpene lactone psilostachyin C was investigated. This natural compound was isolated from Ambrosia scabra by bioassay-guided fractionation and was identified by spectroscopic techniques. Psilostachyin C exerted in vitro trypanocidal activity against Trypanosoma cruzi epimastigotes, trypomastigotes and amastigotes, with 50% inhibitory concentration (IC(50)) values of 0.6, 3.5 and 0.9 μg/mL, respectively, and displayed less cytotoxicity against mammalian cells, with a 50% cytotoxic concentration (CC(50)) of 87.5 μg/mL. Interestingly, this compound induced ultrastructural alterations, as seen by transmission electron microscopy, in which vacuolisation and a structural appearance resembling multivesicular bodies were observed even at a concentration as low as 0.2 μg/mL. In an in vivo assay, a significant reduction in the number of circulating parasites was found in T. cruzi-infected mice treated with psilostachyin C for 5 days compared with untreated mice (7.4 ± 1.2 × 10(5)parasites/mL vs. 12.8 ± 2.0 × 10(5)parasites/mL) at the peak of parasitaemia. According to these results, psilostachyin C may be considered a promising template for the design of novel trypanocidal agents. In addition, psilostachyin C inhibited the growth of Leishmania mexicana and Leishmania amazonensis promastigotes (IC(50)=1.2 μg/mL and 1.5 μg/mL, respectively).     

Anti-plasmodial and anti-leishmanial activity of conformationally restricted pentamidine congeners

A library of 52 pentamidine congeners in which the flexible pentyldioxy linker in pentamidine was replaced with various restricted linkers was tested for in-vitro activity against two Plasmodium falciparum strains and Leishmania donovani. The tested compounds were generally more effective against P. falciparum than L. donovani. The most active compounds against the chloroquine-sensitive (D6, Sierra Leone) and -resistant (W2, Indochina) strains of P. falciparum were bisbenzamidines linked with a 1,4-piperazinediyl or 1, 4-homopiperazinediyl moiety, with IC50 values (50% inhibitory concentration, inhibiting parasite growth by 50% in relation to drug-free control) as low as 7 nM based on the parasite lactate dehydrogenase assay. Seven piperazine-linked bisbenzamidines substituted at the amidinium nitrogens with a linear alkyl group of 3-6 carbons (22, 25, 27, 31) or cycloalkyl group of 4, 6 or 7 carbons (26, 32, 34) were more potent (IC50<40 nM) than chloroquine or pentamidine as anti-plasmodial agents. The most active anti-leishmanial agents were 4,4'-[1,4-phenylenebis(methyleneoxy)]bisbenzenecarboximidamide (2, IC50 approximately 0.290 microM) and 1,4-bis[4-(1H-benzimidazol-2-yl)phenyl] piperazine (44, IC50 approximately 0.410 microM), which were 10- and 7-fold more potent than pentamidine (IC50 approximately 2.90 microM). Several of the more active anti-plasmodial agents (e.g. 2, 31, 33, 36-38) were also potent anti-leishmanial agents, indicating broad antiprotozoal properties. However, a number of analogues that showed potent anti-plasmodial activity (1, 18, 21, 22, 25-28, 32, 43, 45) were not significantly active against the Leishmania parasite. This indicates differential modes of anti-plasmodial and anti-leishmanial actions for this class of compounds. These compounds provide important structure-activity relationship data for the design of improved chemotherapeutic agents against parasitic infections.     

In-vitro antileishmanial and trypanocidal activities of arsonoliposomes and preliminary in-vivo distribution in BALB/c mice

We have studied the antiprotozoal activity of some recently prepared and characterized arsonoliposome formulations. Plain arsonoliposomes and phosphatidylcholine arsonoliposomes prepared with palmitoyl- (C16) or lauroyl-(C12) acyl side chain arsonolipids showed in-vitro antileishmanial activity after a 72-h incubation period against wild-type promastigote forms of Leishmania donovani. The IC50 values ranged from 0.40 to 11.6 microM arsonolipid. Interestingly, all preparations tested were found to be significantly more potent against amphotericin B- or miltefosine-resistant promastigote forms of L. donovani, with IC50 values ranging between 0.21- and 2.33 microM arsonolipid. When tested in-vitro against Trypanosoma brucei brucei, all arsonoliposome formulations were found to have anti-trypanosomal activity after a 24-h incubation period. The fact that the corresponding arsonolipids (dissolved in dimethyl sulfoxide) were found not to be potent against the Leishmania promastigotes or the trypanosomes tested suggested that the formation of liposomes possibly influenced the mode of interaction between the active lipid and the parasites modulating their potency. In addition, a preliminary in-vivo study in BALB/c mice was performed for the initial evaluation of the biodistribution of arsonoliposomes. The accumulation of arsenic in the BALB/c mouse liver in relatively high amounts was an additional advantage of this approach for anti-protozoal therapy, especially for visceral leishmaniasis where parasites are located mainly in the liver.     

Evaluation of azasterols as anti-parasitics

In this article, the design and synthesis of some novel azasterols is described, followed by their evaluation against Trypanosoma brucei rhodesiense, T. cruzi, Leishmania donovani, and Plasmodium falciparum, the causative agents of human African trypanosomiasis, Chagas disease, leishmaniasis, and malaria, respectively. Some of the compounds showed anti-parasitic activity. In particular, a number of compounds appeared to very potently inhibit the growth of the blood stream form T. b. rhodesiense, with one compound giving an IC50 value of 12 nM. Clear structure activity relationships could be discerned. These compounds represent important leads for further optimization. Azasterols have previously been shown to inhibit sterol biosynthesis in T. cruzi and L. donovani by the inhibition of the enzyme sterol 24-methyltransferase. However, in this case, none of the compounds showed inhibition of the enzyme. Therefore, these compounds have an unknown mode of action.