Suramin: Effectiveness of analogues reveals structural features that are important for the potent trypanocidal activity of the drug.

Suramin was the first effective drug for the treatment of human African sleeping sickness. Structural analogues of the trypanocide have previously been shown to be potent inhibitors of several enzymes. Therefore, four suramin analogues lacking the methyl group on the intermediate rings and with different regiochemistry of the naphthalenetrisulphonic acid groups and the phenyl rings were tested to establish whether they exhibited improved antiproliferative activity against bloodstream forms of Trypanosomes brucei compared to the parent compound. The four analogues exhibited low trypanocidal activity and weak inhibition of the antitrypanosomal activity of suramin in competition experiments. This indicates that the strong trypanocidal activity of suramin is most likely due to the presence of methyl groups on its intermediate rings and to the specific regiochemistry of naphthalenetrisulphonic acid groups. These two structural features are also likely to be important for the inhibition mechanism of suramin because DNA distribution and nucleus/kinetoplast configuration analyses suggest that the analogues inhibit mitosis while suramin inhibits cytokinesis.

100 years since the publication of the suramin formula.

Suramin was the first drug developed using the approach of medicinal chemistry by the German Bayer company in the 1910s for the treatment of human African sleeping sickness caused by the two subspecies Trypanosoma brucei gambiense and Trypanosoma brucei rhodesienese. However, the drug was politically instrumentalized by the German government in the 1920s in an attempt to regain possession of its former African colonies lost after the First World War. For this reason, the formula of suramin was kept secret for more than 10 years. Eventually, the French pharmacist Ernest Fourneau uncovered the chemical structure of suramin by reverse engineering and published the formula of the drug in 1924. During the Nazi period, suramin became the subject of colonial revisionism, and the development of the drug was portrayed in books and films to promote national socialist propaganda. Ever since its discovery, suramin has also been tested for bioactivity against numerous other infections and diseases. However, sleeping sickness caused by Trypanosoma brucei rhodesiense is the only human disease for which treatment with suramin is currently approved.

Antiparasitic activity of ivermectin: Four decades of research into a "wonder drug".

Parasitic diseases still pose a serious threat to human and animal health, particularly for millions of people and their livelihoods in low-income countries. Therefore, research into the development of effective antiparasitic drugs remains a priority. Ivermectin, a sixteen-membered macrocyclic lactone, exhibits a broad spectrum of antiparasitic activities, which, combined with its low toxicity, has allowed the drug to be widely used in the treatment of parasitic diseases affecting humans and animals. In addition to its licensed use against river blindness and strongyloidiasis in humans, and against roundworm and arthropod infestations in animals, ivermectin is also used "off-label" to treat many other worm-related parasitic diseases, particularly in domestic animals. In addition, several experimental studies indicate that ivermectin displays also potent activity against viruses, bacteria, protozoans, trematodes, and insects. This review article summarizes the last 40 years of research on the antiparasitic effects of ivermectin, and the use of the drug in the treatment of parasitic diseases in humans and animals.

Suramin analogues protect cartilage against osteoarthritic breakdown by increasing levels of tissue inhibitor of metalloproteinases 3 (TIMP-3) in the tissue.

Osteoarthritis is a chronic degenerative joint disease affecting millions of people worldwide, with no disease-modifying drugs currently available to treat the disease. Tissue inhibitor of metalloproteinases 3 (TIMP-3) is a potential therapeutic target in osteoarthritis because of its ability to inhibit the catabolic metalloproteinases that drive joint damage by degrading the cartilage extracellular matrix. We previously found that suramin inhibits cartilage degradation through its ability to block endocytosis and intracellular degradation of TIMP-3 by low-density lipoprotein receptor-related protein 1 (LRP1), and analysis of commercially available suramin analogues indicated the importance of the 1,3,5-trisulfonic acid substitutions on the terminal naphthalene rings for this activity. Here we describe synthesis and structure-activity relationship analysis of additional suramin analogues using ex vivo models of TIMP-3 trafficking and cartilage degradation. This showed that 1,3,6-trisulfonic acid substitution of the terminal naphthalene rings was also effective, and that the protective activity of suramin analogues depended on the presence of a rigid phenyl-containing central region, with para/para substitution of these phenyl rings being most favourable. Truncated analogues lost protective activity. The physicochemical characteristics of suramin and its analogues indicate that approaches such as intra-articular injection would be required to develop them for therapeutic use.

Synthesis of urea and thiourea derivatives of C20-epi-aminosalinomycin and their activity against Trypanosoma brucei.

Salinomycin (SAL) is a natural polyether ionophore that exhibits a very broad spectrum of biological effects, ranging from anticancer to antiparasitic activities. Our recent studies have shown that the chemical modification of the SAL biomolecule is a fruitful strategy for generating lead compounds for the development of novel antitrypanosomal agents. As a continuation of our program to develop trypanocidal active lead structures, we synthesized a series of 14 novel urea and thiourea analogs of C20-epi-aminosalinomycin (compound 2b). The trypanocidal and cytotoxic activities of the derivatives were assessed with the mammalian life cycle stage of Trypanosoma brucei and human leukemic HL-60 cells, respectively. The most antitrypanosomal compounds were the two thiourea derivatives 4b (C20-n-butylthiourea) and 4d (C20-phenylthiourea) with 50% growth inhibition (GI50) values of 0.18 and 0.22 µM and selectivity indices of 47 and 41, respectively. As potent SAL derivatives have been shown to induce strong cell swelling in bloodstream forms of T. brucei, the effect of compounds 4b and 4d to increase the cell volume of the parasite was also investigated. Interestingly, both derivatives were capable to induce faster cell swelling in bloodstream-form trypanosomes than the reference compound SAL. These findings support the suggestion that C20-epi-aminosalinomycin derivatives are suitable leads in the rational development of new and improved trypanocidal drugs.

Trypanocidal and cell swelling activity of 20-deoxysalinomycin.

The naturally occurring polyether ionophore salinomycin was previously found to display promising anti-proliferative activity against bloodstream forms of Trypanosoma brucei. Here, we report the evaluation of 20-deoxysalinomycin, a naturally occurring homolog to salinomycin, for trypanocidal and cell swelling activity. The concentration of 20-deoxysalinomycin required to reduce the growth rate of bloodstream-form trypanosomes by 50% was determined to be 0.12 µM and found to be 8 times more trypanocidal than that of salinomycin. Moreover, 20-deoxysalinomycin and salinomycin displayed similar cytotoxic activity against human HL-60 cells. Measured as the ratio of cytotoxic to trypanocidal activity, 20-deoxysalinomycin thus exhibits a four-fold higher selectivity compared to salinomycin. The stronger trypanocidal activity of 20-deoxysalinomycin is attributed to an enhanced ability to induce cell swelling in trypanosomes. The findings support 20-deoxysalinomycin as a useful lead in the rational development of new and improved anti-trypanosomal drugs.

Gallic Acid Alkyl Esters: Trypanocidal and Leishmanicidal Activity, and Target Identification via Modeling Studies.

Eight gallic acid alkyl esters (1−8) were synthesized via Fischer esterification and evaluated for their trypanocidal and leishmanicidal activity using bloodstream forms of Trypanosoma brucei and promastigotes of Leishmania major. The general cytotoxicity of the esters was evaluated with human HL-60 cells. The compounds displayed moderate to good trypanocidal but zero to low leishmanicidal activity. Gallic acid esters with alkyl chains of three or four carbon atoms in linear arrangement (propyl (4), butyl (5), and isopentyl (6)) were found to be the most trypanocidal compounds with 50% growth inhibition values of ~3 µM. On the other hand, HL-60 cells were less susceptible to the compounds, thus, resulting in moderate selectivity indices (ratio of cytotoxic to trypanocidal activity) of >20 for the esters 4−6. Modeling studies combining molecular docking and molecular dynamics simulations suggest that the trypanocidal mechanism of action of gallic acid alkyl esters could be related to the inhibition of the T. brucei alternative oxidase. This suggestion is supported by the observation that trypanosomes became immobile within minutes when incubated with the esters in the presence of glycerol as the sole substrate. These results indicate that gallic acid alkyl esters are interesting compounds to be considered for further antitrypanosomal drug development.

Scuticociliatosis caused by Philasterides dicentrarchi.

The ciliate Philasterides dicentrarchi has been previously identified as a new agent of scuticociliatosis in marine fish. The parasite can cause high mortalities in fish reared on farms or kept in aquariums. P. dicentrarchi is usually a free-living protozoan but can become an opportunistic histophagous parasite causing rapid lethal systemic infections in cultured fish. This review provides information about the morphology and biology of the scuticociliate P. dicentrarchi, as well as information about the pathological and immunological reactions of the host in response to the infection with the parasite. The epidemiology and the control strategies of the disease are also reviewed.

Synthesis and evaluation of antibacterial and trypanocidal activity of derivatives of monensin A.

The synthesis and biological evaluation of eleven derivatives of the natural polyether ionophore monensin A (MON), modified at the C-26 position, is presented. Eight urethane and three ester derivatives were tested for their antimicrobial activity against different strains of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa. In addition, their antiparasitic activity was also evaluated with bloodstream forms of Trypanosoma brucei. The majority of the modified ionophores were active against a variety of Gram-positive bacterial strains, including methicillin-resistant S. epidermidis, and showed better antibacterial activity than the unmodified MON. The phenyl urethane derivative of MON exhibited the most promising antibacterial activity of all tested compounds, with minimal inhibitory concentration values of 0.25-0.50 µg/ml. In contrast, none of the MON derivatives displayed higher antitrypanosomal activity than the unmodified ionophore.

Should the enzyme name 'rhodesain' be discontinued?

Rhodesain is the generic name for the cathepsin L-like peptidase of Trypanosoma brucei rhodesiense. The term rhodesain was derived from the subspecies epithet rhodesiense which itself originated form Rhodesia, a historical region in southern Africa named after the 19th century British imperialist and white supremacist Cecil Rhodes. This tainting could be grounds for discontinuing the name, however, there are also scientific grounds. Specifically, protein sequence comparisons and frequency-based difference profiling reveal that rhodesain is essentially identical (99.87-98.44%) to the cathepsin L-like peptidases of both T. b. brucei and T. b. gambiense. Accordingly, and based on a previously proposed terminology for kinetoplastid C1 peptidases (Caffrey and Steverding, 2009), we suggest the use of the formal term, TbrCATL, to denote the cathepsin L-like peptidases of the T. brucei subspecies. The earlier and informal term, 'brucipain', could also be used.

Decolonising Parasitology: The Case of Trypanosoma brucei rhodesiense.

Trypanosoma brucei rhodesiense was named after Rhodesia which, in turn, was named after the British imperialist and white supremacist Cecil Rhodes. In the light of the Black Lives Matter movement and contemporary consciousness of postcolonial legacy, it seems opportune to reconsider the subspecies name. Pros and cons of renaming T. b. rhodesiense are discussed.

Trypanosoma brucei transferrin receptor: Functional replacement of the GPI anchor with a transmembrane domain.

The transferrin receptor of Trypanosoma brucei (TbTfR) is a heterodimer of a glycosylphosphatidylinositol (GPI)-anchored ESAG6 subunit and an ESAG7 subunit. To investigate whether the GPI-anchor is essential for the function of the TbTfR, an ESAG6 with a transmembrane domain instead of a GPI-anchor (ESAG6tmd) was inducibly expressed in bloodstream form trypanosomes. It is shown that the ESAG6tmd is able to dimerise with ESAG7 to form a TbTfR that can bind transferrin. Fractionation experiments clearly demonstrated that the transmembrane-anchored TbTfR is exclusively associated with the membrane fraction. No difference in the uptake of transferrin was observed between trypanosomes inducibly expressing a transmembrane-anchored TbTfR and trypanosomes inducibly expressing a GPI-anchored TbTfR. Differences in glycosylation pattern of ESAG6tmd and native ESAG6 may indicate different intracellular trafficking of transmembrane- and GPI-anchored TbTfRs. The findings suggest that the GPI-anchor is not essential for the function of the TbTfR in bloodstream forms of T. brucei.

Singly and doubly modified analogues of C20-epi-salinomycin: A new group of antiparasitic agents against Trypanosoma brucei.

Polyether ionophores, with >120 molecules belonging to this group, represent a class of naturally-occurring compounds that exhibit a broad range of pharmacological properties, including promising activity towards a variety of parasites. In this context, salinomycin (SAL) seems to be interesting, as this ionophore has been found to be active against parasites that are responsible for a number of human and animal diseases. On the other hand, less explored is the investigation into the anti-parasitic activity of SAL derivatives. Recently, we identified C1 amides and esters of SAL and its analogue, C20-oxosalinomycin, as promising structures for trypanocidal drug candidates. In search for novel compounds effective against African trypanosomes, the synthetic access to a completely new series of C20-epi-salinomycin (compound 2) analogues is described in this paper. This series includes products obtained via derivatisation of either the C1 carboxyl or the C20 hydroxyl of 2, but also C1/C20 double modified derivatives. The anti-trypanosomal activity as well as the cytotoxic activity of these analogues were evaluated with bloodstream forms of T. brucei and human myeloid HL-60 cells, respectively. It was found that the C20 single modified derivatives 8, 12, and 18 (C20 decanoate, C20 ethyl carbonate, and C20 allophanate of 2, respectively) were the most active compounds in selectively targeting bloodstream-form trypanosomes, with 50% growth inhibition (GI50) values of 0.027-0.043 µM and selectivity indices of 165-353. These results indicate that modification at the C20 position of C20-epi-salinomycin 2 can provide semi-synthetic products with enhanced trypanocidal activity that could be of great value for the development of new drugs to treat African trypanosomiasis.

The spreading of parasites by human migratory activities.

The global spread of parasites is unquestionably linked with human activities. Migration in all its different forms played a major role in the introduction of parasites into new areas. In ancient times, mass migrations were the main causes for the spread of parasites while in the recent past and present, emigration, immigration, displacement, external and internal migration, and labor migration were the reasons for the dispersal of parasites. With the advent of seagoing ships, long-distance trading became another important mode of spreading parasites. This review summarizes the spread of parasites using notable examples. In addition, the different hypotheses explaining the arrival of Plasmodium vivax and soil-transmitted helminths in pre-Columbian America are also discussed.

Trypanocidal and leishmanicidal activity of six limonoids.

Six limonoids [kotschyienone A and B (1, 2), 7-deacetylgedunin (3), 7-deacetyl-7-oxogedunin (4), andirobin (5) and methyl angolensate (6)] were investigated for their trypanocidal and leishmanicidal activities using bloodstream forms of Trypanosoma brucei and promastigotes of Leishmania major. Whereas all compounds showed anti-trypanosomal activity, only compounds 1-4 displayed anti-leishmanial activity. The 50% growth inhibition (GI50) values for the trypanocidal and leishmanicidal activity of the compounds ranged between 2.5 and 14.9 µM. Kotschyienone A (1) was found to be the most active compound with a minimal inhibition concentration (MIC) value of 10 µM and GI50 values between 2.5 and 2.9 µM. Only compounds 1 and 3 showed moderate cytotoxicity against HL-60 cells with MIC and GI50 values of 100 µM and 31.5-46.2 µM, respectively. Compound 1 was also found to show activity against intracellular amastigotes of L. major with a GI50 value of 1.5 µM. The results suggest that limonoids have potential as drug candidates for the development of new treatments against trypanosomiasis and leishmaniasis.

Cytotoxic Activity of LCS-1 is not Only due to Inhibition of SOD1.

BACKGROUND: The cytotoxic activity of the pyridazin-3-one derivative LCS-1 was previously suggested to be due to the inhibition of superoxide dismutase 1 (SOD1). However, no direct evidence was provided that LCS-1 inhibits SOD1 within cells. METHODS: In this study, we investigated the cytotoxic activity of LCS-1 against bloodstream forms of Trypanosoma brucei, a protozoan parasite that does not express copper/zinc-containing SOD1, but an iron-containing superoxide dismutase (FeSOD). RESULTS: At 250 µM, LCS-1 did not inhibit the activity of FeSOD in cell lysates of bloodstream forms of T. brucei, confirming that the compound is a specific inhibitor of SOD1. However, LCS-1 displayed substantial trypanocidal activity with a minimum inhibitory concentration of 10 µM and a half-maximal effective concentration of 1.36 µM, indicating that the cytotoxic action of the compound cannot solely be due to inhibition of SOD1. CONCLUSION: The results of this study is an important finding as it shows that LCS-1 has more than one cytotoxic mode of action.

Organometallic ciprofloxacin conjugates with dual action: synthesis, characterization, and antimicrobial and cytotoxicity studies.

The synthesis, characterization and biological activity of six bioorganometallic conjugates of ciprofloxacin with ferrocenyl, ruthenocenyl and cymantrenyl entities are described. Their antimicrobial activities were investigated against Gram-positive bacteria, Gram-negative bacteria and bloodstream forms of Trypanosoma brucei. Furthermore, the morphological changes of bacterial cells upon treatment with the conjugates were examined by scanning electron microscopy. In addition, the cytotoxicity of the conjugates against tumor and normal mammalian cells was also investigated. The results showed that conjugation of an organometallic moiety can significantly enhance the antimicrobial activity of the antibiotic ciprofloxacin drug. It was found that N-alkyl cymantrenyl and ruthenocenyl ciprofloxacin conjugates were the most effective derivatives although other conjugates also showed significant antimicrobial activity. The increase in the antimicrobial activity was most likely due to two independent mechanisms of action. The first mechanism is due to the bacterial topoisomerase inhibitory activity of ciprofloxacin while the second mechanism can be attributed to the generation of reactive oxygen species caused by the organometallic moiety. The presence of two modes of action enables the conjugates to kill bacteria in their stationary growth phase and to overcome the drug resistance of S. aureus strains. In addition, the conjugates showed promising selectivity toward bacterial and parasitic cells over mammalian cells.

Trypanosoma brucei: Inhibition of cathepsin L is sufficient to kill bloodstream forms.

The lysosomal cysteine protease activity of Trypanosoma brucei comprises a cathepsin B enzyme (TbCATB) and a cathepsin L enzyme (TbCATL). Inhibition of the cysteine protease activity is lethal to bloodstream-form trypanosomes but it was not entirely clear which of the two enzymes are essential for survival of the parasites. Here we show that the vinyl sulfone compound LU-102 selectively inhibits TbCATL without affecting TbCATB and the proteasomal trypsin-like activity within trypanosomes. Therefore, the trypanocidal activity displayed by LU-102 can be attributed solely to the inhibition of TbCATL demonstrating that this enzyme is essential to the survival of T. brucei.

Anti-trypanosomal activity of doubly modified salinomycin derivatives.

As a group of biologically active compounds, polyether antibiotics (ionophores) show a broad spectrum of interesting pharmacological properties, ranging from anti-bacterial to anti-cancer activities. There is increasing evidence that ionophores, including salinomycin (SAL), and their semi-synthetic analogues are promising candidates for the development of drugs against parasitic diseases. Our previous studies have shown that esterification and amidation of the C1 carboxylate moiety of SAL provides compounds with potent activity against Trypanosoma brucei, protozoan parasites responsible for African trypanosomiasis. In this paper, we present the synthetic pathways, crystal structures and anti-trypanosomal activity of C1 esters, amides and hydroxamic acid conjugates of SAL, its C20-oxo and propargylamine analogues as well novel C1/C20 doubly modified derivatives. Evaluation of the trypanocidal and cytotoxic activity using bloodstream forms of T. brucei and human myeloid HL-60 cells revealed that the single-modified C20-oxo and propargylamine precursor molecules 10 and 16 were the most anti-trypanosomal and selective compounds with 50% growth inhibition (GI50) values of 0.037 and 0.035 µM, and selectivity indices of 252 and 300, respectively. Also the salicylhydroxamic acid conjugate of SAL (compound 9) as well as benzhydroxamic acid and salicylhydroxamic acid conjugates of 10 (compounds 11 and 12) showed promising trypanocidal activities with GI50 values between 0.032 and 0.035 µM but less favorable selectivities. The findings confirm that modification of SAL can result in derivatives with improved trypanocidal activity that might be interesting lead compounds for further anti-trypanosomal drug development.