Further insights of selenium-containing analogues of WC-9 against Trypanosoma cruzi.

As a continuation of our project aimed at searching for new chemotherapeutic agents against American trypanosomiasis (Chagas disease), new selenocyanate derivatives were designed, synthesized and biologically evaluated against the clinically more relevant dividing form of Trypanosoma cruzi, the etiologic agent of this illness. In addition, in order to establish the role of each part of the selenocyanate moiety, different derivatives, in which the selenium atom or the cyano group were absent, were conceived, synthesized and biologically evaluated. In addition, in order to study the optimal position of the terminal phenoxy group, new regioisomers of WC-9 were synthesized and evaluated against T. cruzi. Finally, the resolution of a racemic mixture of a very potent conformationally rigid analogue of WC-9 was accomplished and further tested as growth inhibitors of T. cruzi proliferation. The results provide further insight into the role of the selenocyanate group in its antiparasitic activity.

Selenium-containing analogues of WC-9 are extremely potent inhibitors of Trypanosoma cruzi proliferation.

The obligate intracellular parasite, Trypanosoma cruzi is the etiologic agent of Chagas disease or American trypanosomiasis, which is the most prevalent parasitic disease in the Americas. The present chemotherapy to control this illness is still deficient particularly in the chronic stage of the disease. The ergosterol biosynthesis pathway has received much attention as a molecular target for the development of new drugs for Chagas disease. Especially, inhibitors of the enzymatic activity of squalene synthase were shown to be effective compounds on T. cruzi proliferation in in vitro assays. In the present study we designed, synthesized and evaluated the effect of a number of isosteric analogues of WC-9 (4-phenoxyphenoxyethyl thiocyanate), a known squalene synthase inhibitor, on T. cruzi growth in tissue culture cells. The selenium-containing derivatives turned out to be extremely potent inhibitors of T. cruzi growth. Certainly, 3-phenoxyphenoxyethyl, 4-phenoxyphenoxyethyl, 4-(3-fluorophenoxy)phenoxyethyl, 3-(3-fluorophenoxy)phenoxyethyl selenocyanates and (±)-5-phenoxy-2-(selenocyanatomethyl)-2,3-dihydrobenzofuran arose as relevant members of this family of compounds, which exhibited effective ED50 values of 0.084 µM, 0.11 µM, 0.083, µM, 0.085, and 0.075 µM, respectively. The results indicate that compounds bearing the selenocyanate moiety are at least two orders of magnitude more potent than the corresponding skeleton counterpart bearing the thiocyanate group. Surprisingly, these compounds exhibited excellent selectively index values ranging from 900 to 1800 making these molecules promising candidates as antiparasitic agents.

Antiparasitic Activity of Sulfur- and Fluorine-Containing Bisphosphonates against Trypanosomatids and Apicomplexan Parasites.

Based on crystallographic data of the complexes 2-alkyl(amino)ethyl-1,1-bisphosphonates-Trypanosoma cruzi farnesyl diphosphate synthase, some linear 1,1-bisphosphonic acids and other closely related derivatives were designed, synthesized and biologically evaluated against T. cruzi, the responsible agent of Chagas disease and against Toxoplasma gondii, the etiologic agent of toxoplasmosis and also towards the target enzymes farnesyl pyrophosphate synthase of T. cruzi (TcFPPS) and T gondii (TgFPPS), respectively. The isoprenoid-containing 1,1-bisphosphonates exhibited modest antiparasitic activity, whereas the linear α-fluoro-2-alkyl(amino)ethyl-1,1-bisphosphonates were unexpectedly devoid of antiparasitic activity. In spite of not presenting efficient antiparasitic activity, these data turned out to be very important to establish a structural activity relationship.

In Vitro and In Vivo Activities of Sulfur-Containing Linear Bisphosphonates against Apicomplexan Parasites.

We tested a series of sulfur-containing linear bisphosphonates against Toxoplasma gondii, the etiologic agent of toxoplasmosis. The most potent compound (compound 22; 1-[(n-decylsulfonyl)ethyl]-1,1-bisphosphonic acid) is a sulfone-containing compound, which had a 50% effective concentration (EC50) of 0.11 ± 0.02 µM against intracellular tachyzoites. The compound showed low toxicity when tested in tissue culture with a selectivity index of >2,000. Compound 22 also showed high activity in vivo in a toxoplasmosis mouse model. The compound inhibited the Toxoplasma farnesyl diphosphate synthase (TgFPPS), but the concentration needed to inhibit 50% of the enzymatic activity (IC50) was higher than the concentration that inhibited 50% of growth. We tested compound 22 against two other apicomplexan parasites, Plasmodium falciparum (EC50 of 0.6 ± 0.01 µM), the agent of malaria, and Cryptosporidium parvum (EC50 of ∼65 µM), the agent of cryptosporidiosis. Our results suggest that compound 22 is an excellent novel compound that could lead to the development of potent agents against apicomplexan parasites.

Activity of Fluorine-Containing Analogues of WC-9 and Structurally Related Analogues against Two Intracellular Parasites: Trypanosoma cruzi and Toxoplasma gondii.

Two obligate intracellular parasites, Trypanosoma cruzi, the agent of Chagas disease, and Toxoplasma gondii, an agent of toxoplasmosis, upregulate the mevalonate pathway of their host cells upon infection, which suggests that this host pathway could be a potential drug target. In this work, a number of compounds structurally related to WC-9 (4-phenoxyphenoxyethyl thiocyanate), a known squalene synthase inhibitor, were designed, synthesized, and evaluated for their effect on T. cruzi and T. gondii growth in tissue culture cells. Two fluorine-containing derivatives, the 3-(3-fluorophenoxy)- and 3-(4-fluorophenoxy)phenoxyethyl thiocyanates, exhibited half-maximal effective concentration (EC50 ) values of 1.6 and 4.9 µm, respectively, against tachyzoites of T. gondii, whereas they showed similar potency to WC-9 against intracellular T. cruzi (EC50 values of 5.4 and 5.7 µm, respectively). In addition, 2-[3- (phenoxy)phenoxyethylthio]ethyl-1,1-bisphosphonate, which is a hybrid inhibitor containing 3-phenoxyphenoxy and bisphosphonate groups, has activity against T. gondii proliferation at sub-micromolar levels (EC50 =0.7 µm), which suggests a combined inhibitory effect of the two functional groups.

Aryloxyethyl Thiocyanates Are Potent Growth Inhibitors of Trypanosoma cruzi and Toxoplasma gondii.

As a part of our project aimed at searching for new safe chemotherapeutic agents against parasitic diseases, several compounds structurally related to the antiparasitic agent WC-9 (4-phenoxyphenoxyethyl thiocyanate), which were modified at the terminal phenyl ring, were designed, synthesized, and evaluated as growth inhibitors against Trypanosoma cruzi, the etiological agent of Chagas disease, and Toxoplasma gondii, the parasite responsible of toxoplasmosis. Most of the synthetic analogues exhibited similar antiparasitic activity and were slightly more potent than our lead WC-9. For example, two trifluoromethylated derivatives exhibited ED50 values of 10.0 and 9.2 µM against intracellular T. cruzi, whereas they showed potent action against tachyzoites of T. gondii (ED50 values of 1.6 and 1.9 µM against T. gondii). In addition, analogues of WC-9 in which the terminal aryl group is in the meta position with respect to the alkyl chain bearing the thiocyanate group showed potent inhibitory action against both T. cruzi and T. gondii at the very low micromolar range, which suggests that a para-phenyl substitution pattern is not necessary for biological activity.

Design, synthesis and biological evaluation of WC-9 analogs as antiparasitic agents.

As a part of our project pointed at the search of new safe chemotherapeutic and chemoprophylactic agents against parasitic diseases, several compounds structurally related to 4-phenoxyphenoxyethyl thiocyanate (WC-9), which were modified at the terminal aromatic ring, 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. Most of the synthetic analogs exhibited similar antiparasitic activity being slightly more potent than the reference compound WC-9. For example, the nitro derivative 13 showed an ED50 value of 5.2 µM. Interestingly, the regioisomer of WC-9, compound 36 showed similar inhibitory action than WC-9 indicating that para-phenyl substitution pattern is not necessarily required for biological activity. The biological evaluation against T. gondii was also very promising. The ED50 values corresponding for 13, 36 and 37 were at the very low micromolar level against tachyzoites of T. gondii.