Design, synthesis, calorimetry, and crystallographic analysis of 2-alkylaminoethyl-1,1-bisphosphonates as inhibitors of Trypanosoma cruzi farnesyl diphosphate synthase

Linear 2-alkylaminoethyl-1,1-bisphosphonates are effective agents against proliferation of Trypanosoma cruzi , the etiologic agent of American trypanosomiasis (Chagas disease), exhibiting IC(50) values in the nanomolar range against the parasites. This activity is associated with inhibition at the low nanomolar level of the T. cruzi farnesyl diphosphate synthase (TcFPPS). X-ray structures and thermodynamic data of the complexes TcFPPS with five compounds of this family show that the inhibitors bind to the allylic site of the enzyme, with their alkyl chain occupying the cavity that binds the isoprenoid chain of the substrate. The compounds bind to TcFPPS with unfavorable enthalpy compensated by a favorable entropy that results from a delicate balance between two opposing effects: the loss of conformational entropy due to freezing of single bond rotations and the favorable burial of the hydrophobic alkyl chains. The data suggest that introduction of strategically placed double bonds and methyl branches should increase affinity substantially.

1-(Fluoroalkylidene)-1,1-bisphosphonic acids are potent and selective inhibitors of the enzymatic activity of Toxoplasma gondii farnesyl pyrophosphate synthase

α-Fluorinated-1,1-bisphosphonic acids derived from fatty acids were designed, synthesized and biologically evaluated against Trypanosoma cruzi, the etiologic agent of Chagas disease, and against Toxoplasma gondii, the agent responsible for toxoplasmosis, and also towards the target parasitic enzymes farnesyl pyrophosphate synthase of T. cruzi (TcFPPS) and T. gondii (TgFPPS). Interestingly, 1-fluorononylidene-1,1-bisphosphonic acid (compound 43) proved to be an extremely potent inhibitor of the enzymatic activity of TgFPPS at the low nanomolar range, exhibiting an IC(50) of 30 nM. This compound was two-fold more potent than risedronate (IC(50) = 74 nM) that was taken as a positive control. This enzymatic activity was associated with a strong cell growth inhibition against tachyzoites of T. gondii, with an IC(50) value of 2.7 μM.

Synthesis and biological evaluation of new 2-alkylaminoethyl-1,1-bisphosphonic acids against Trypanosoma cruzi and Toxoplasma gondii targeting farnesyl diphosphate synthase

The effect of long-chain 2-alkylaminoethyl-1,1-bisphosphonates against proliferation of the clinically more relevant form of Trypanosoma cruzi, the etiologic agent of American trypanosomiasis (Chagas' disease), and against tachyzoites of Toxoplasma gondii was investigated. Particularly, compound 26 proved to be an extremely potent inhibitor against the intracellular form of T. cruzi, exhibiting IC(50) values at the nanomolar range. This cellular activity was associated with a strong inhibition of the enzymatic activity of T. cruzi farnesyl diphosphate synthase (TcFPPS), which constitutes a valid target for Chagas' disease chemotherapy. Compound 26 was an effective agent against T. cruzi (amastigotes) exhibiting an IC(50) value of 0.67 μM, while this compound showed an IC(50) value of 0.81 μM against the target enzyme TcFPPS. This drug was less effective against the enzymatic activity of T. cruzi solanesyl diphosphate synthase TcSPPS showing an IC(50) value of 3.2 μM. Interestingly, compound 26 was also very effective against T. gondii (tachyzoites) exhibiting IC(50) values of 6.23 μM. This cellular activity was also related to the inhibition of the enzymatic activity towards the target enzyme TgFPPS (IC(50)=0.093 μM) As bisphosphonate-containing compounds are FDA-approved drugs for the treatment of bone resorption disorders, their potential low toxicity makes them good candidates to control different tropical diseases.

Synthesis and biological evaluation of 2-alkylaminoethyl-1,1-bisphosphonic acids against Trypanosoma cruzi and Toxoplasma gondii targeting farnesyl diphosphate synthase

The effect of a series of 2-alkylaminoethyl-1,1-bisphosphonic acids against proliferation of the clinically more relevant form of Trypanosoma cruzi, the etiologic agent of American trypanosomiasis (Chagas' disease), and against tachyzoites of Toxoplasma gondii has been studied. Most of these drugs exhibited an extremely potent inhibitory action against the intracellular form of T. cruzi, exhibiting IC(50) values at the low micromolar level. This cellular activity was associated with a strong inhibition of the enzymatic activity of T. cruzi farnesyl diphosphate synthase (TcFPPS), which constitutes a valid target for Chagas' disease chemotherapy. Compound 17 was an effective agent against amastigotes exhibiting an IC(50) value of 0.84 microM, while this compound showed an IC(50) value of 0.49 microM against the target enzyme TcFPPS. Interestingly, compound 19 was very effective against both T. cruzi and T. gondii exhibiting IC(50) values of 4.1 microM and 2.6 microM, respectively. In this case, 19 inhibited at least two different enzymes of T. cruzi (TcFPPS and solanesyl diphosphate synthase (TcSPPS); 1.01 microM and 0.25 microM, respectively), while it inhibited TgFPPS in T. gondii. In general, this family of drugs was less effective against the activity of T. cruzi SPPS and against T. gondii growth in vitro. As bisphosphonate-containing compounds are FDA-approved drugs for the treatment of bone resorption disorders, their potential low toxicity makes them good candidates to control tropical diseases.

Fluorine-containing aryloxyethyl thiocyanate derivatives are potent inhibitors of Trypanosoma cruzi and Toxoplasma gondii proliferation

As a part of our project aimed at developing new safe chemotherapeutic and chemoprophylactic agents against tropical diseases, fluorine-containing drugs structurally related to 4-phenoxyphenoxyethyl thiocyanate (1) were designed, synthesized, and evaluated as antiproliferative agents against Trypanosoma cruzi, the parasite responsible of American trypanosomiasis (Chagas' disease), and Toxoplasma gondii, the etiological agent of toxoplasmosis. This thiocyanate derivative had previously proven to be an effective agent against T. cruzi proliferation. Fluorine-containing thiocyanate derivatives 2 and 3 were threefold more potent than our lead drug 1 against intracellular T. cruzi. The biological evaluation against T. gondii was also very promising. The IC(50) values corresponding to 2 and 3 were at the very low micromolar level against tachyzoites of T. gondii. Both of these drugs are interesting examples of effective antiparasitic agents that have outstanding potential not only as lead drugs but also to be used for further in vivo studies.

Current Status and Progresses Made in Malaria Chemotherapy

Malaria is the most important parasitic disease worldwide, affecting more than 500 million people and causing close to 1 million deaths per annum. This serious fact is mainly attributable to the emergence of drug resistant strains of Plasmodium falciparum. The advances made in malaria chemotherapy based on unique aspects of the biochemistry and physiology of the responsible agents for this disease, parasites of Plasmodium genus, are covered in this review. Increasing resistance to conventional antimalarial drugs constitutes the main drawback for the persistence of this disease. In the present article, a comprehensive analysis of selected molecular targets is depicted in terms of their potential utility as chemotherapeutic agents. Our review focuses on different and important molecular targets for drug design that include proteases that hydrolyze hemoglobin, protein farnesyltransferase, heme detoxification pathway, polyamine pathways, dihydrofolate reductase, artemisinin-based combination therapies (ACTs), etc. Therefore, rational approaches to control malaria targeting metabolic pathways of malaria parasites which are essential for parasites survival are presented.

Progresses in the field of drug design to combat tropical protozoan parasitic diseases

The progresses made in the field of drug design to combat tropical protozoan parasitic diseases, such as Chagas' disease, leishmaniasis, and sleeping sickness are discussed. This article is focused on different approaches based on unique aspects of parasites biochemistry and physiology, selecting the more promising molecular targets for drug design. In spite of the enormous amount of work on the above features, the chemotherapy for all of these diseases remains unsolved. It is based on old and fairly not specific drugs associated, in several cases, with long-term treatments and severe side effects. Drug resistance and different strains susceptibility are further drawbacks of the existing chemotherapy. In this review article, a thorough analysis of selected molecular targets, mainly those that are significantly different compared with the mammalian host or, even, are not present in mammals would be described in terms of their potencial usefulness for drug design. Therefore, this article covers rational approaches to the chemotherapeutic control of these parasitic infections, such as the progresses in the search for novel metabolic pathways in parasites that may be essential for parasites survival but with no counterpart in the host. Ergosterol biosynthesis is a very interesting example. There are many enzymes involved in this biosynthetic pathway such us squalene synthase, farnesylpyrophosphate synthase, and other enzymes that are able to deplete endogenous sterols will be treated in this article. The enzymes involved in trypanothione biosynthesis, glutathionyl spermidine synthetase and trypanothione synthetase do not have an equivalent in mammals, and therefore it can be predicted low toxicity for compounds that are able to produce highly selective inhibition. Trypanothione reductase (TR), glyceraldehyde-3-phosphate dehydrogenase, dihydrofolate reductase, prenyltransferases, ornithine decarboxylase, etc, will be thoroughly analyzed. The design of specific inhibitors of such metabolic activities as possible means of controlling the parasites without damaging the hosts will be presented. The recent advances in the biochemistry of pathogenic parasites including the discovery of novel organelles will be discussed.

Design, synthesis, and biological evaluation of phosphinopeptides against Trypanosoma cruzi targeting trypanothione biosynthesis

As a part of our project aimed at the search for new safe chemotherapeutic and chemoprophylactic agents against American trypanosomiasis (Chagas's disease), a series of phosphinopeptides structurally related to glutathione was designed, synthesized, and evaluated as antiproliferative agents against the parasite responsible for this disease, the hemoflagellated protozoan Trypanosoma cruzi. The rationale for the synthesis of these compounds was supported on the basis that the presence of the phosphinic acid moiety would mimic the tetrahedral transition state of trypanothione synthase (TryS), a typical C:N ligase, and the molecular target of these drugs. Of the designed compounds, 53 and 54 were potent growth inhibitors against the clinically more relevant form of T. cruzi (amastigotes) growing in myoblasts. The efficacy for these drugs was comparable to that exhibited by the well-known antiparasitic agent WC-9. The simple phosphinopeptide structure found as a pharmacophore in the present study constitutes a starting point for the development of straightforward optimized drugs.

Synthesis and biological evaluation of 1-amino-1,1-bisphosphonates derived from fatty acids against Trypanosoma cruzi targeting farnesyl pyrophosphate synthase

We have investigated the effect of a series of 1-amino-1,1-bisphosphonates derived from fatty acids against proliferation of the clinically more relevant form of Trypanosoma cruzi, the causative agent of American trypanosomiasis (Chagas' disease). Some of these drugs were potent inhibitors against the intracellular form of the parasite, exhibiting IC50 values at low micromolar level. Cellular activity was associated with the inhibition of enzymatic activity of T. cruzi farnesyl pyrophosphate synthase. As bisphosphonate-containing drugs are FDA-approved for the treatment of bone resorption disorders, their potential innocuousness makes them good candidates to control tropical diseases.

Structural determinants of efficacy at A3 adenosine receptors: modification of the ribose moiety

We have found previously that structural features of adenosine derivatives, particularly at the N6- and 2-positions of adenine, determine the intrinsic efficacy as A3 adenosine receptor (AR) agonists. Here, we have probed this phenomenon with respect to the ribose moiety using a series of ribose-modified adenosine derivatives, examining binding affinity and activation of the human A3 AR expressed in CHO cells. Both 2'- and 3'-hydroxyl groups in the ribose moiety contribute to A3 AR binding and activation, with 2'-OH being more essential. Thus, the 2'-fluoro substitution eliminated both binding and activation, while a 3'-fluoro substitution led to only a partial reduction of potency and efficacy at the A3 AR. A 5'-uronamide group, known to restore full efficacy in other derivatives, failed to fully overcome the diminished efficacy of 3'-fluoro derivatives. The 4'-thio substitution, which generally enhanced A3 AR potency and selectivity, resulted in 5'-CH2OH analogues (10 and 12) which were partial agonists of the A3 AR. Interestingly, the shifting of the N6-(3-iodobenzyl)adenine moiety from the 1'- to 4'-position had a minor influence on A3 AR selectivity, but transformed 15 into a potent antagonist (16) (Ki = 4.3 nM). Compound 16 antagonized human A3 AR agonist-induced inhibition of cyclic AMP with a K(B) value of 3.0 nM. A novel apio analogue (20) of neplanocin A, was a full A3 AR agonist. The affinities of selected, novel analogues at rat ARs were examined, revealing species differences. In summary, critical structural determinants for human A3 AR activation have been identified, which should prove useful for further understanding the mechanism of receptor activation and development of more potent and selective full agonists, partial agonists and antagonists for A3 ARs.

Bisphosphonates derived from fatty acids are potent inhibitors of Trypanosoma cruzi farnesyl pyrophosphate synthase

Studies on the mode of action of a series of bisphosphonates derived from fatty acids, which had previously proved to be potent inhibitors against Trypanosoma cruzi proliferation in in vitro assays, have been performed. Some of these drugs proved to be potent inhibitors against the intracellular form of the parasite, exhibiting IC(50) values at the low micromolar level. As bisphosphonates are FDA clinically approved for treatment of bone resorption disorders, their potential innocuousness makes them good candidates to control tropical diseases.

Mechanism of action of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the causative agent of Chagas' disease

We investigated the molecular basis of the activity of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the etiological agent of Chagas' disease. We found that growth inhibition of T. cruzi epimastigotes induced by this compound was associated with a reduction in the content of the parasite's endogenous sterols due to a specific blockade of their de novo synthesis at the level of squalene synthase.

Design, synthesis, and biological evaluation of aryloxyethyl thiocyanate derivatives against Trypanosoma cruzi

As a continuation of our project aimed at the search for new and safe chemotherapeutic and chemoprophylactic agents against American trypanosomiasis (Chagas' disease), several drugs structurally related to 4-phenoxyphenoxyethyl thiocyanate (4) were designed, synthesized, and evaluated as antiproliferative agents against the parasite responsible for this disease, the hemoflagellated protozoan Trypanosoma cruzi. This thiocyanate derivative was previously shown to be an effective and potent agent against T. cruzi proliferation. Several drugs possessing thiocyanate groups proved to be effective growth inhibitors of T. cruzi growth. Among the designed compounds, it is important to point out the extremely potent activity shown by 11, 23, 38, 53, 90, 99, and 117 against the epimastigote forms of the parasite. All of them exhibited IC(50) values in the low micromolar range, and these values were comparable with those presented by our lead drug 4 and ketokonazole, a well-known antiparasitic agent. The activity displayed by the nitrogen-containing derivative 90 was very promising with IC(50) values of 3.3 microM. Several other thiocyanate derivatives also proved to be very potent inhibitors of the multiplication of T. cruzi epimastigotes, such as compounds 28, 33, 43, 48, 56, 61, 66, 71, 76, and 124. Compound 43 resulted in being a promising drug because it was also very effective against amastigotes, the clinically more relevant form of the parasite. This compound was 3-fold more potent than 4, while 11 showed nearly the same activity as our lead drug against intracellular T. cruzi. It was very surprising that the experimental juvenoid 124, although fairly devoid of activity against epimastigotes, was very effective against intracellular amastigotes growing in myoblasts. The rest of the designed compounds showed a broad degree of inhibitory action, from moderately active drugs to drugs almost devoid of antiparasitic activity. Compound 43 is an interesting example of an effective antichagasic agent that presents excellent prospectives not only as a lead drug but also to be used for further in vivo studies.

Specific molecular targets to control tropical diseases

Chagas' disease or American trypanosomiasis is considered by the Word Health Organization to be one of the important tropical parasitic diseases worldwide together with malaria and schistosomiasis. The etiologic agent of this illness is the kinetoplastid protozoon Trypanosoma cruzi. The present chemotherapy for the treatment of Chagas' disease remains unsolved. The drugs currently in use are old, ineffective and toxic. Bearing in mind the metabolic differences between the parasite and the mammalian host, some attractive interesting molecular targets for drug design are presented.

Bisphosphonates derived from fatty acids are potent growth inhibitors of Trypanosoma cruzi

We have investigated the effect of a series of bisphosphonates derived from fatty acids against Trypanosoma cruzi proliferation in in vitro assays. Some of these drugs proved to be potent inhibitors against the intracellular form of the parasite exhibiting IC50 values at the low micromolar level. As bisphosphonates are FDA clinically approved for treatment of bone resorption, their potential innocuousness makes them good candidates to control tropical diseases.

Design and synthesis of aryloxyethyl thiocyanate derivatives as potent inhibitors of Trypanosoma cruzi proliferation

As a part of our project directed at the search of new chemotherapeutic agents against American trypanosomiasis (Chagas' disease), several drugs possessing the 4-phenoxyphenoxy skeleton and other closely related structures employing the thiocyanate moiety as polar end group were designed, synthesized, and evaluated as antiproliferative agents against Trypanosoma cruzi, the parasite responsible for this disease. These thiocyanate analogues were envisioned bearing in mind the potent activity shown by 4-phenoxyphenoxyethyl thiocyanate (compound 8) taken as lead drug. This compound had previously proved to be an extremely active growth inhibitor against T. cruzi with IC(50) values ranging from the very low micromolar level in epimastigotes to the low nanomolar level in the intracellular form of the parasite. Of the designed compounds, the ethyl thiocyanate drugs connected to nonpolar skeletons, namely, arylthio, 2,4-dichlorophenoxy, ortho-substituted aryloxy, and 2-methyl-4-phenoxyphenoxy (compounds 15, 34, 47, 52, 72, respectively), were shown to be very potent antireplicative agents against T. cruzi. On the other hand, conformationally restricted analogues as well as branched derivatives at the aliphatic side chain were shown to be moderately active against T. cruzi growth. The biological activity of drugs bearing the thiocyanate group correlated quite well with the activity exhibited by their normal precursors, the tetrahydropyranyl ether derivatives, when bonded to the same nonpolar skeleton. Compounds having the tetrahydropyranyl moeity as polar end were proportionally much less active than sulfur-containing derivatives in all cases. Drugs 47 and 72 also resulted to be very active against the amastigote form of the parasite growing in myoblasts; however, they were slightly less active than the lead drug 8. On the other hand, compounds 34 and 52 were almost devoid of activity against myoblasts. Surprisingly, the dithio derivative 15 was toxic for myoblasts.

Sulphur-containing derivatives structurally related to fenoxycarb are potent growth inhibitors against the intracellular form of Trypanosoma cruzi

Sulphur-containing derivatives structurally related to the insect growth regulator fenoxycarb were shown to be extremely active antiproliferative agents against the amastigote form of Trypanosoma cruzi in in vitro assays. All of these drugs had previously been proved to be remarkably potent growth inhibitors against the epimastigote form of the parasite.

Synthesis of C-5'-nor-dideoxycarbanucleosides structurally related to neplanocin C

Purine carbanucleosides built on a 6-oxabicyclo[3.1.0]hexane template were synthesized from readily available 2-cyclopentenone employing a Mitsunobu reaction to incorporate the base onto the carbocyclic ring. Both adenosine and guanosine analogues exhibited moderate antiviral activity.

Growth inhibitory effect of juvenile hormone analogues on epimastigotes of Trypanosoma cruzi

Several compounds, structurally related to the insect growth regulator Fenoxycarb, exhibited interesting inhibition action to control proliferation of Trypanosoma cruzi, the parasite responsible for Chagas' disease. Some of these drugs were shown to be potent growth inhibitors of this parasite. All of these drugs had previously presented juvenoid activity on several non-related bug species such as Tenebrio molitor, Galleria mellonella, Dysdercus cingulatos, and Pyrrhocoris apterus.