Aryl thiosemicarbazones: In vitro and immunomodulatory activities against L. amazonensis.

Leishmaniasis is an infection caused by different species of Leishmania genus. Currently, there is no vaccine available for Leishmania infections in humans and conventional treatments are limited due to side effects. Therefore, the development of new antileishmanial drugs is an urgent need. In present study, we evaluated the cytotoxicity in host cells, leishmanicidal activity and immunomodulatory potential of seven aryl thiosemicarbazones. Host cell cytotoxicity was determined in peritoneal macrophages of BALB/c mouse, antiparasitic activity was determined against promastigotes and amastigotes of WHOM/00LTB 0016 strain of L. amazonensis. Nitric oxide (NO) production, interleukin (IL)-12, IL-10 and TNF-alpha secretion were measured in the supernatant of uninfected and infected macrophage cultures. It was observed that aryl thiosemicarbazones presented in vitro antiparasitic activity against both extracellular and intracellular forms of L. amazonensis. However, unlike Amphotericin B, these compounds displayed low cytotoxicity towards host cells. In addition to observed antiparasitic activity, compounds exhibited modulatory properties in the secretion of cytokines and nitrite content from uninfected stimulated and L. amazonensis-infected macrophages. In conclusion, we demonstrated the in vitro antiparasitic activity against L. amazonensis for aryl thiosemicarbazones, which is possible achieved by Th1 cytokine profile modulation. These findings are potential useful for drug development against cutaneous leishmaniasis.

Desing and synthesis of potent anti-Trypanosoma cruzi agents new thiazoles derivatives which induce apoptotic parasite death.

Chagas disease, caused by the kinetoplastid protozoan parasite Trypanosoma cruzi, remains a relevant cause of illness and premature death and it is estimated that 6 million to 7 million people are infected worldwide. Although chemotherapy options are limited presenting serious problems, such as low efficacy and high toxicity. T. cruzi is susceptible to thiazoles, making this class of compounds appealing for drug development. Previously, thiazoles resulted in an increase in anti-T. cruzi activity in comparison to thiosemicarbazones. Here, we report the structural planning, synthesis and anti-T. cruzi evaluation of new thiazoles derivatives (3a-m and 4a-m), designed from molecular hybridization associated with non-classical bioisosterism. By varying substituents attached to the phenyl and thiazole rings, substituents were observed to retain, enhance or greatly increase their anti-T. cruzi activity, in comparison to the corresponding thiosemicarbazones. In most cases, electron-withdrawing substituents, such as bromine, 3,4-dichloro and nitro groups, greatly increased antiparasitic activity. Specifically, new thiazoles were identified that inhibit the epimastigote proliferation and were toxic for trypomastigotes without affecting macrophages viability. These compounds were also evaluated against cruzain. However, inhibition of this enzyme was not observed, suggesting that the compounds work through another mechanism. In addition, examination of T. cruzi cell death showed that these molecules induce apoptosis. In conclusion, except for compounds 3h and 3k, all thiazoles derivatives evaluated exhibited higher cytotoxic activity against the trypomastigote forms than the reference medicament benznidazole, without affecting macrophages viability. Compounds 4d and 4k were highlights, CC50 = 1.2 e 1.6 µM, respectively. Mechanistically, these compounds do not inhibit the cruzain, but induce T. cruzi cell death by an apoptotic process, being considered a good starting point for the development of new anti-Chagas drug candidates.

New 1,3-thiazole derivatives and their biological and ultrastructural effects on Trypanosoma cruzi.

In previous studies, the compound 3-(bromopropiophenone) thiosemicarbazone was described as a potent anti-Trypanosoma cruzi and cruzain inhibitor. In view to optimize this activity, 1,3-thiazole core was used as building-block strategy to access new lead generation of anti T. cruzi agents. In this way a series of thiazole derivatives were synthesized and most of these derivatives exhibited antiparasitic activity similar to benznidazole (Bzd). Among them, compounds (1c) and (1g) presented better selective index (SI) than Bzd. In addition, compounds showed inhibitory activity against the cruzain protease. As observed by electron microscopy, compound (1c) treatment caused irreversible and specific morphological changes on ultrastructure organization of T. cruzi, demonstrating that this class of compounds is killing parasites.

Conformational restriction of aryl thiosemicarbazones produces potent and selective anti-Trypanosoma cruzi compounds which induce apoptotic parasite death.

Chagas disease, caused by Trypanosoma cruzi, is a life-threatening infection leading to approximately 12,000 deaths per year. T. cruzi is susceptible to thiosemicarbazones, making this class of compounds appealing for drug development. Previously, the homologation of aryl thiosemicarbazones resulted in an increase in anti-T. cruzi activity in comparison to aryl thiosemicarbazones without a spacer group. Here, we report the structural planning, synthesis and anti-T. cruzi evaluation of new aryl thiosemicarbazones (9a-x), designed as more conformationally restricted compounds. By varying substituents attached to the phenyl ring, substituents were observed to retain, enhance or greatly increase the anti-T. cruzi activity, in comparison to the nonsubstituted derivative. In most cases, hydrophobic and bulky substituents, such as bromo, biphenyl and phenoxyl groups, greatly increased antiparasitic activity. Specifically, thiosemicarbazones were identified that inhibit the epimastigote proliferation and were toxic for trypomastigotes without affecting mouse splenocytes viability. The most potent anti-T. cruzi thiosemicarbazones were evaluated against cruzain. However, inhibition of this enzyme was not observed, suggesting that the compounds work through another mechanism. In addition, examination of T. cruzi cell death showed that these thiosemicarbazones induce apoptosis. In conclusion, the structural design executed within the series of aryl thiosemicarbazones (9a-x) led to the identification of new potent anti-T. cruzi agents, such as compounds (9h) and (9r), which greatly inhibited epimastigote proliferation, and demonstrated a toxicity for trypomastigotes, but not for splenocytes. Mechanistically, these compounds do not inhibit the cruzain, but induce T. cruzi cell death by an apoptotic process.

Evaluation of the anti-Schistosoma mansoni activity of thiosemicarbazones and thiazoles.

Schistosomiasis is a chronic and debilitating disease caused by a trematode of the genus Schistosoma and affects over 207 million people. Chemotherapy is the only immediate recourse for minimizing the prevalence of this disease and involves predominately the administration of a single drug, praziquantel (PZQ). Although PZQ has proven efficacy, there is a recognized need to develop new drugs as schistosomicides since studies have shown that repeated use of this drug in areas of endemicity may cause a temporary reduction in susceptibility in isolates of Schistosoma mansoni. Hydrazones, thiosemicarbazones, phthalimides, and thiazoles are thus regarded as privileged structures used for a broad spectrum of activities and are potential candidates for sources of new drug prototypes. The present study determined the in vitro schistosomicidal activity of 10 molecules containing these structures. During the assays, parameters such motility and mortality, oviposition, morphological changes in the tegument, cytotoxicity, and immunomodulatory activity caused by these compounds were evaluated. The results showed that compounds formed of thiazole and phthalimide led to higher mortality of worms, with a significant decline in motility, inhibition of pairing and oviposition, and a mortality rate of 100% starting from 144 h of exposure. These compounds also stimulated the production of nitric oxide and tumor necrosis factor alpha (TNF-α), thereby demonstrating the presence of immunomodulatory activity. The phthalyl thiazole LpQM-45 caused significant ultrastructural alterations, with destruction of the tegument in both male and female worms. According to the present study, phthalyl thiazole compounds possess antischistosomal activities and should form the basis for future experimental and clinical trials.

Structural design, synthesis and structure-activity relationships of thiazolidinones with enhanced anti-Trypanosoma cruzi activity.

Pharmacological treatment of Chagas disease is based on benznidazole, which displays poor efficacy when administered during the chronic phase of infection. Therefore, the development of new therapeutic options is needed. This study reports on the structural design and synthesis of a new class of anti-Trypanosoma cruzi thiazolidinones (4 a-p). (2-[2-Phenoxy-1-(4-bromophenyl)ethylidene)hydrazono]-5-ethylthiazolidin-4-one (4 h) and (2-[2-phenoxy-1-(4-phenylphenyl)ethylidene)hydrazono]-5-ethylthiazolidin-4-one (4 l) were the most potent compounds, resulting in reduced epimastigote proliferation and were toxic for trypomastigotes at concentrations below 10 µM, while they did not display host cell toxicity up to 200 µM. Thiazolidinone 4 h was able to reduce the in vitro parasite burden and the blood parasitemia in mice with similar potency to benznidazole. More importantly, T. cruzi infection reduction was achieved without exhibiting mouse toxicity. Regarding the molecular mechanism of action, these thiazolidinones did not inhibit cruzain activity, which is the major trypanosomal protease. However, investigating the cellular mechanism of action, thiazolidinones altered Golgi complex and endoplasmic reticulum (ER) morphology, produced atypical cytosolic vacuoles, as well as induced necrotic parasite death. This structural design employed for the new anti-T. cruzi thiazolidinones (4 a-p) led to the identification of compounds with enhanced potency and selectivity compared to first-generation thiazolidinones. These compounds did not inhibit cruzain activity, but exhibited strong antiparasitic activity by acting as parasiticidal agents and inducing a necrotic parasite cell death.