Antimalarial Activity of Highly Coordinative Fused Heterocycles Targeting ß-Hematin Crystallization.

The ß-hematin formation is a unique process adopted by Plasmodium sp. to detoxify free heme and represents a validated target to design new effective antimalarials. Most of the ß-hematin inhibitors are mainly based on 4-aminoquinolines, but the parasite has developed diverse defense mechanisms against this type of chemical system. Thus, the identification of other molecular chemical entities targeting the ß-hematin formation pathway is highly needed to evade resistance mechanisms associated with 4-aminoquinolines. Herein, we showed that the highly coordinative character can be a useful tool for the rational design of antimalarial agents targeting ß-hematin crystallization. From a small library consisting of five compound families with recognized antitrypanosomatid activity and coordinative abilities, a group of tetradentate 1,4-disubstituted phthalazin-aryl/heteroarylhydrazinyl derivatives were identified as potential antimalarials. They showed a remarkable curative response against Plasmodium berghei-infected mice with a significant reduction of the parasitemia, which was well correlated with their good inhibitory activities on ß-hematin crystallization (IC50 = 5-7 µM). Their in vitro inhibitory and in vivo responses were comparable to those found for a chloroquine reference. The active compounds showed moderate in vitro toxicity against peritoneal macrophages, a low hemolysis response, and a good in silico ADME profile, identifying compound 2f as a promising antimalarial agent for further experiments. Other less coordinative fused heterocycles exhibited moderate inhibitory responses toward ß-hematin crystallization and modest efficacy against the in vivo model. The complexation ability of the ligands with iron(III) was experimentally and theoretically determined, finding, in general, a good correlation between the complexation ability of the ligand and the inhibitory activity toward ß-hematin crystallization. These findings open new perspectives toward the rational design of antimalarial ß-hematin inhibitors based on the coordinative character as an alternative to the conventional ß-hematin inhibitors.

Synthesis and in silico ADME/Tox profiling studies of heterocyclic hybrids based on chloroquine scaffolds with potential antimalarial activity.

A series of heterocyclic chloroquine hybrids containing either a ß-phenethylamine fragment or a 2-aminoindane moiety were synthesized and screened in vitro as inhibitors of ß-hematin formation and in vivo for their antimalarial activity against chloroquine-sensitive strains of Plasmodium berghei ANKA. Although these new compounds were not found to be more active than chloroquine in vivo, all new compounds significantly reduced heme crystallization with IC50 values < 1 µM. Compounds 12 and 13 were able to inhibit heme crystallization with IC50 values of 0.39 ± 0.09 and 0.48 ± 0.02 µM, respectively, and these values were comparable to that of chloroquine with an IC50 value of 0.18 ± 0.03. It was also determined that the physicochemical and pharmacokinetic properties were moderately favorable after in silico evaluation, derivatives 8 and 10 did not present hepatotoxicity, and the in vitro hemolytic activity against red blood cells was found to be low. Spectral (infrared, nuclear magnetic resonance, and elemental analysis) data for all final compounds were consistent with the proposed structures.

Synthesis of 5H-indeno[1,2-b]pyridine derivatives: Antiproliferative and antimetastatic activities against two human prostate cancer cell lines.

This study describes the direct synthesis of 2-amino-4-(phenylsubstituted)-5H-indeno[1,2-b]pyridine-3-carbonitrile derivatives 5-21, through sequential multicomponent reaction of aromatic aldehydes, malononitrile, and 1-indanone in the presence of ammonium acetate and acetic acid (catalytic). The biological study showed that compound 10 significantly impeded proliferation of the cell lines PC-3, LNCaP, and MatLyLu. The antimetastatic effects of compound 10 could be related with inhibition of MMP9 in the PC-3 and LNCaP human cell lines. On the basis of a study of the structure-activity relationship of these compounds, we propose that the presence of two methoxy groups at positions 6 and 7 of the indeno nucleus and a 4-hydroxy-3-methoxy phenyl substitution pattern at position 4 of the pyridine ring is decisive for these types of molecules to exert very good antiproliferative and antimetastatic activities.

Synthesis, ß-hematin inhibition studies and antimalarial evaluation of new dehydroxy isoquine derivatives against Plasmodium berghei: A promising antimalarial agent.

Many people are affected by Malaria around the world, and the parasite is developing resistance against available drugs. Currently, isoquine and N-tert-butyl isoquine are some of the most promising antimalarial candidates that have already reached Phase I and II clinical trials, respectively. Nevertheless, pharmacodynamic studies have demonstrated that isoquine is highly sensitive to form O-glucuronide metabolite, which may affect its accumulation in tissues. To avoid the O-glucuronide formation and its negative influence in the accumulation process, a series of novel five dehydroxy isoquine derivatives were designed and prepared herein as potential antimalarial agents. By a simple three-step procedure, five dehydroxy isoquines were prepared and subsequently examined on the inhibition of haemozoin formation, the main target of the 4-aminoquinolines. Four derivatives displayed significant inhibitory activities at low IC50 values from 1.66 to 1.86 µM comparable to CQ. On the basis of the results, these four compounds were subsequently tested against Plasmodium berghei ANKA model in mice, showing to be as active as CQ with significant curative responses and parasitemia suppression in mice infected. On the other hand, these four compounds showed an acceptable non specific cytotoxicity on murine peritoneal macrophague and human erythrocyte cells. Thus, the presented data indicate that the dehydroxy isoquines 4b, 4c and 4e constitute promising cost-effective leads for the development of new antiplasmodial targeted at blood-stage malaria parasites.

N'-Formyl-2-(5-nitrothiophen-2-yl)benzothiazole-6-carbohydrazide as a potential anti-tumour agent for prostate cancer in experimental studies.

OBJECTIVES: Benzothiazoles (BZTs) represent organic compounds with different biological actions. In this study we aimed to investigate ten newly synthesized BZT derivatives as potential anti-tumour agents against prostate cancer in vitro and in vivo. METHODS: The cytotoxic effect of these compounds was screened on the human prostate cancer cell lines PC-3 and LNCaP. The most effective compound, N'-formyl-2-(5-nitrothiophen-2-yl)benzothiazole-6-carbohydrazide, was further characterized regarding its dose- and time-dependent effects on cell viability and proliferation (XTT test) as well as on adhesion and spreading (real-time cell analyzer xCelligence), migration (scratch-wound repair assay) and invasion (Boyden chamber) of the cells. This BZT derivative was also tested as an inhibitor of angiogenesis (chicken chorioallantoic membrane assay), clonogenic activity (soft agar) and matrix metalloproteinase 9 (gelatin zymography). KEY FINDINGS: N'-Formyl-2-(5-nitrothiophen-2-yl)benzothiazole-6-carbohydrazide significantly inhibited all tested properties of the prostate cancer cell lines and showed low toxic in vitro and in vivo effects. The in vitro anti-tumour activity of this compound was confirmed by the in vivo effects on PC-3 xenografts in nude mice. Tumour growth was decreased in treated compared with untreated mice. CONCLUSIONS: These results suggest the potential capacity of BZTs and in particular N'-formyl-2-(5-nitrothiophen-2-yl)benzothiazole-6-carbohydrazide as anti-tumour agents for the treatment of prostate cancer.

Potential antitumour and pro-oxidative effects of (E)-methyl 2-(7-chloroquinolin-4-ylthio)-3-(4-hydroxyphenyl) acrylate (QNACR).

CONTEXT: Characterization of the pro-oxidant activity of QNACR. OBJECTIVES: Reactive oxygen species (ROS) induce cellular damage and represent unique opportunities to kill malignant cells. In this study, we synthesized and evaluated the new compound, (E)-methyl 2-(7-chloroquinolin-4-ylthio)-3-(4-hydroxyphenyl) acrylate (QNACR) as potential pro-oxidative agent against breast cancer. METHODS: Oxidative stress biomarkers such as ROS, thiobarbuturic acid reactive species (TBARs) and different antioxidant enzyme activities were determined in cell lysates. RESULTS: QNACR showed cytotoxic and more selective effects to tumour MCF7 cells (IC50 < 25 µM) compared to antitumour controls, inducing ROS and TBARs parallel to inhibitions of catalase (CAT), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). Longer exposures to QNACR triggered adaptive effects increasing the overall activities of CAT, glutathione reductase, G6PDH and 6PGDH, but eventually the adaptation changes faded and cells died. CONCLUSION: QNACR led to remarkable modifications in the oxidative status of tumour cells, proposing this compound as potential alternative for antitumour therapy.

Cytotoxic effects of N'-formyl-2-(5-nitrothiophen-2-yl) benzothiazole-6-carbohydrazide in human breast tumor cells by induction of oxidative stress.

Chemically active molecules, such as reactive oxygen species (ROS), are prone to induce cellular damage by oxidative stress and this could be exploited as a strategy to kill malignant cells. In this study, we evaluated the antitumor activity of a new compound, N'-formyl-2-(5-nitrothiophen-2-yl)benzothiazole-6-carbohydrazide (FBZC) by assessing its pro-oxidant effects on breast cancer in vitro. Oxidative stress, generated by FBZC, was characterized by measuring reactive species and antioxidant enzymes and markers. Results showed that the cytotoxic effects of FBZC on MCF7 breast cancer cells (half inhibitory concentration of 5.4 µg/ml), were partially reversed by the addition of regular antioxidants. FBZC induced ROS and lipid peroxidation, together with a significant inhibition of superoxide dismutase, glutathione reductase and total glutathione levels as well as increases in catalase and glutathione-S-transferase activities, in an acute fast response. Thus, the antitumor effects of FBZC could be related to oxidative deregulation due to a combination of induction of ROS generation and inhibition of key antioxidant enzymes.

Effect of quinolinyl acrylate derivatives on prostate cancer in vitro and in vivo.

Quinolines and acrylates are chemical compounds which were previously described as potential antitumor agents. In this study, a series of seven new quinolinyl acrylate derivatives were synthesized and evaluated against human prostate cancer cells PC-3 and LNCaP in vitro and in vivo. The most effective compound (E)-methyl 2-(7-chloroquinolin-4-ylthio)-3-(4 hydroxyphenyl) acrylate reduced the viability in both cell lines in a time- and dose-dependent manner. Inhibitory effects were also observed on the adhesion, migration, and invasion of the prostate cancer cells as well as on the neoangiogenesis, clonogenic and MMP-9 activity. The effect in vivo was studied in PC-3 xenografts in nude mice. The results were concordant with the in vitro effects and showed decreased tumor growth in treated animals compared to controls. The study suggests the multi-target efficacy of the quinolinyl derivate against human prostate cancer cells and supports its potential therapeutic usefulness.

Synthesis and antimalarial activities of optically active labdane-type diterpenes.

An efficient method for the synthesis of optically active labdane-type diterpenes from (+)-manool 8 is described. We prepared the natural labdane-type diterpene 5 via key intermediate peroxide 9, and synthetic hydroxybutenolides 6 and 7 via a furan photosensitised oxygenation reaction of labdafuran (14). Compounds 5, 6, 7 and 9 were evaluated as inhibitors of the beta-haematin formation and globin proteolysis, and then were assayed in a malarial murine model. Compound 9 was the most promising compound, showing a positive correlation between in vitro and in vivo activities.

Effect of dequalinium on the oxidative stress in Plasmodium berghei-infected erythrocytes.

The bisquinoline drug dequalinium (DQ) has demonstrated remarkable activity against some infection diseases, including malaria. Oxidative stress represents a biochemical target for potential antimalarials. In this work, we have tested the ability of this compound to modify the oxidative status in Plasmodium berghei-infected erythrocytes. After hemolysis, activities of superoxide dismutase (SOD), catalase (CAT), glutathione cycle, and dehydrogenase enzymes were investigated. The activity of glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGLD) in infected cells were diminished by this drug compared to controls (300% and 80% approximately, respectively), while glutathione peroxidase (GPx), glutathione transferase (GST), and glutathione levels were also lowered. As a compensatory response, we could appreciate an increase of SOD activity (20% approximately) in infected cells treated with DQ; however, catalase was not affected by the compound. Lipid peroxidation was also decreased by this drug, protecting the cells from the hemolysis caused by the infection. In conclusion, oxidative stress represents a biochemical event which is modulated by DQ, interfering with the antioxidant regular activities in P. berghei infection.

Synthesis and antimalarial activity of pyrazolo and pyrimido benzothiazine dioxide derivatives.

A series of phenylsubstituted pyrazolo and pyrimido benzothiazine dioxide derivatives were synthesized and investigated for their abilities to inhibit beta-hematin formation, hemoglobin hydrolysis and in vivo for their antimalarial efficacy in rodent Plasmodium berghei. Compounds 3-amino-7-chloro-9-(2'-methylphenyl)-1,9-dihydro-pyrazolo-[4,3-b]benzothiazine 4,4-dioxide 2b and 2,4-diamino-8-chloro-10H-phenyl-pyrimido-[5,4-b]benzothiazine 5,5-dioxide 3a were the most promising as inhibitors of hemoglobin hydrolysis, however, their effect as inhibitors of beta-hematin formation was marginal, except for compound 3-amino-7-chloro-9-(3'-chlorophenyl)-1,9dihydro-pyrazolo-[4,3-b]benzothiazine 4,4-dioxide 2g. The most active compound to emerge from the in vitro and in vivo murine studies was 2b, suggesting an antimalarial activity via inhibition of hemoglobin hydrolysis, however, not as efficient as chloroquine.

Synthesis and antimalarial activity of E-2-quinolinylbenzocycloalcanones.

A series of E-2-quinolinylbenzocycloalcanones 5-21 were prepared and evaluated for their activity to inhibit beta-hematin formation and the hydrolysis of hemoglobin in vitro. Positive compounds for both assays were also tested for their efficacy in rodent Plasmodium berghei. Compounds 6, 16, 19, and 20, were the most promising. Inhibition of beta-hematin formation was minimal when a hydrogen or methoxy groups were present on the position 8 of the quinoline and position 4' of the indanone ring as it appeared for compounds 5, 7-15, 17, 18, and 21, and greatest with compounds (52%) and (90%) with a substitution of methoxy on position 6 and 7 or methyl on position 8 of the quinoline nucleus and methoxy or methyl groups on position 4' of the indanone. The most active compound to emerge from this study is 2-chloro-8-methyl-3-[(4'-methoxy-1'-indanoyl)-2'-methyliden]-quinoline 20 effective as antimalarial that target beta-hematin formation and the inhibition of the hydrolysis of hemoglobin in vitro together with a good survival in a murine malaria model, which should help delay the rapid onset of resistance to drugs acting at only a single site. Results with these assays suggest that quinolinylbenzocycloalcanones exert their antimalarial activity via multiple mechanisms.