Effect of megazol on Trypanosoma brucei brucei acute and subacute infections in Swiss mice

Rhenium(I) and technetium(I) complexes with megazol derivatives: towards the development of a theranostic platform for Chagas disease

The diagnosis and treatment of Chagas disease (CD) in the chronic phase remains a challenge. With that in mind, a potential theranostic device based on the trypanocidal agent known as megazol and the fac-M(CO)3+ (M = Re or 99mTc) fragment is proposed in the present work. The peripheral structure of megazol (LH,H) was modified to obtain the compounds LR1,R2 (R1 = H, R2 = Me and R1 = R2 = Me), which were used in the syntheses of complexes of composition [ReBr(CO)3LR1,R2]. These compounds were studied by elemental analysis, FTIR, UV-vis, NMR (1H and 13C), HR-ESI-MS, HPLC/UPLC and single-crystal XRD. The trypanocidal activity of the rhenium complexes was evaluated in vitro against the intracellular form of Trypanosoma cruzi. With exception of the [ReBr(CO)3LMe,Me] complex, all compounds are more active than the standard drug, benznidazole (Bzn), while [ReBr(CO)3LH,H] also exhibited a much higher selectivity index. In addition, the interaction of megazol and its ReI complex was evaluated with the T. cruzi Old Yellow Enzyme (TcOYE) by both experimental and computational methods. The data showed that megazol as well as its metal complex exhibited a higher affinity for TcOYE compared to Bzn. Finally, the labelling of megazol with 99mTc was successfully carried out. However, the results indicated that the Re complexes used as standards were not homologous with the 99mTc complexes. Despite this discrepancy, this research suggests that the investigation into Re and 99mTc complexes with megazol could lead to the development of a theranostic device for CD in a near future.

Functionalized Nitroimidazole Scaffold Construction and Their Pharmaceutical Applications: A 1950–2021 Comprehensive Overview

Nitroimidazole represents one of the most essential and unique scaffolds in drug discovery since its discovery in the 1950s. It was K. Maeda in Japan who reported in 1953 the first nitroimidazole as a natural product from Nocardia mesenterica with antibacterial activity, which was later identified as Azomycin 1 (2-nitroimidazole) and remained in focus until now. This natural antibiotic was the starting point for synthesizing numerous analogs and regio-isomers, leading to several life-saving drugs and clinical candidates against a number of diseases, including infections (bacterial, viral, parasitic) and cancers, as well as imaging agents in medicine/diagnosis. In the present decade, the nitroimidazole scaffold has again been given two life-saving drugs (Delamanid and Pretomanid) used to treat MDR (multi-drug resistant) tuberculosis. Keeping in view the highly successful track-record of the nitroimidazole scaffold in providing breakthrough therapeutic drugs, this comprehensive review focuses explicitly on presenting the activity profile and synthetic chemistry of functionalized nitroimidazole (2-, 4- and 5-nitroimidazoles as well as the fused nitroimidazoles) based drugs and leads published from 1950 to 2021. The present review also presents the miscellaneous examples in each class. In addition, the mutagenic profile of nitroimidazole-based drugs and leads and derivatives is also discussed.

Mechanosensitivity of Murine Lung Slowly Adapting Receptors: Minimal Impact of Chemosensory, Serotonergic, and Purinergic Signaling

Murine slowly adapting receptors (SARs) within airway smooth muscle provide volume-related feedback; however, their mechanosensitivity and morphology are incompletely characterized. We explored two aspects of SAR physiology: their inherent static mechanosensitivity and a potential link to pulmonary neuroepithelial bodies (NEBs). SAR mechanosensitivity displays a rate sensitivity linked to speed of inflation; however, to what extent static SAR mechanosensitivity is tuned for the very rapid breathing frequency (B f ) of small mammals (e.g., mouse) is unclear. NEB-associated, morphologically described smooth muscle-associated receptors (SMARs) may be a structural analog for functionally characterized SARs, suggesting functional linkages between SARs and NEBs. We addressed the hypotheses that: (1) rapid murine B f is associated with enhanced in vivo SAR static sensitivity; (2) if SARs and NEBs are functionally linked, stimuli reported to impact NEB function would alter SAR mechanosensitivity. We measured SAR action potential discharge frequency (AP f, action potentials/s) during quasi-static inflation [0-20 cmH2O trans-respiratory pressure (PTR)] in NEB-relevant conditions of hypoxia (FIO2 = 0.1), hypercarbia (FICO2 = 0.1), and pharmacologic intervention (serotonergic 5-HT3 receptor antagonist, Tropisetron, 4.5 mg/kg; P2 purinergic receptor antagonist, Suramin, 50 mg/kg). In all protocols, we obtained: (1) AP f vs. PTR; (2) PTR threshold; and (3) AP f onset at PTR threshold. The murine AP f vs. PTR response comprises high AP f (average maximum AP f: 236.1 ± 11.1 AP/s at 20 cmH2O), a low PTR threshold (mean 2.0 ± 0.1 cmH2O), and a plateau in AP f between 15 and 20 cmH2O. Murine SAR mechanosensitivity (AP f vs. PTR) is up to 60% greater than that reported for larger mammals. Even the maximum difference between intervention and control conditions was minimally impacted by NEB-related alterations: Tropisetron -7.6 ± 1.8% (p = 0.005); Suramin -10.6 ± 1.5% (p = 0.01); hypoxia +9.3 ± 1.9% (p < 0.001); and hypercarbia -6.2 ± 0.9% (p < 0.001). We conclude that the high sensitivity of murine SARs to inflation provides enhanced resolution of operating lung volume, which is aligned with the rapid B f of the mouse. We found minimal evidence supporting a functional link between SARs and NEBs and speculate that the <10% change in SAR mechanosensitivity during altered NEB-related stimuli is not consistent with a meaningful physiologic role.

2-Amino-1,3,4-thiadiazoles as prospective agents in trypanosomiasis and other parasitoses

Parasitic diseases are a serious public health problem affecting hundreds of millions of people worldwide. African trypanosomiasis, American trypanosomiasis, leishmaniasis, malaria and toxoplasmosis are the main parasitic infections caused by protozoan parasites with over one million deaths each year. Due to old medications and drug resistance worldwide, there is an urgent need for new antiparasitic drugs. 1,3,4-Thiadiazoles have been widely studied for medical applications. The chemical, physical and pharmacokinetic properties recommend 1,3,4-thiadiazole ring as a target in drug development. Many scientific papers report the antiparasitic potential of 2-amino-1,3,4-thiadiazoles. This review presents synthetic 2-amino-1,3,4-thiadiazoles exhibiting antitrypanosomal, antimalarial and antitoxoplasmal activities. Although there are insufficient results to state the quality of 2-amino-1,3,4-thiadiazoles as a new class of antiparasitic agents, many reported derivatives can be considered as lead compounds for drug synthesis and a promise for the future treatment of parasitosis and provide a valid strategy for the development of potent antiparasitic drugs.

In vitro genotoxicity of nitroimidazoles as a tool in the search of new trypanocidal agents

BACKGROUND

Only benznidazole (Bnz) (1) and nifurtimox (Nfx) (2) are licensed for the treatment of Chagas disease although their safety and efficacy profile are far from ideal. Farmanguinhos from Fiocruz has developed seven nitroimidazole compounds (4-10) analogs of megazol (3).

OBJECTIVES

To evaluate whether the genotoxic effect of 3 was abolished in the seven nitroimidazoles (4-10) analogs using the in vitro alkaline comet assay (CA) and the in vitro cytokinesis-block micronucleus assay (CBMN) in whole human blood cells (WHBC) and correlate this effect with their trypanocidal activity using bloodstream trypomastigote forms of Trypanosoma cruzi.

METHODS

The toxicity of 3-10 to WHBC in the in vitro CA was determined using the fluorescein diacetate/ethidium bromide assay. DNA damage in the in vitro CA was evaluated according to tail size in four classes (0-3) and methyl methane-sulfonate (MMS) was used as a positive control. The cytotoxicity of 3-10 to WHBC in the CBMN was measured using the cytokinesis-block proliferation index and the replication index. The number of the micronucleate cells in 2,000 binucleate cells by experimental group was determined. Mitomycin C and N-deacetyl-N-methylcolchicine were used as positive controls.

FINDINGS

Compound 3 showed a significant DNA strand break effect through the in vitro CA and highly significant clastogenic and/or aneugenic effect in the CBMN. Compounds 5, 6, 8, 9 and 10 showed negative results in the CBMN and positive results in the in vitro CA, while the inverse effect was observed for 4 and 7.

MAIN CONCLUSIONS

Compound 10 was the most promising to proceed with the development as a drug candidate in the treatment of Chagas disease showing absence of chromosomal cytogenetic damage and high activity against T. cruzi, about two times higher than 3 and the clinical drug 1.

2-Amino-1,3,4-thiadiazole as a potential scaffold for promising antimicrobial agents

Pathogenic microorganisms are causative agents for different types of serious and even lethal infectious diseases. Despite advancements in medication, bacterial and fungal infections continue to be a growing problem in health care. As more and more bacteria become resistant to antibiotics used in therapy and an increasing number of invasive fungal species become resistant to current antifungal medications, there is considerable interest in the development of new compounds with antimicrobial activity. The compounds containing a heterocyclic ring play an important role among organic compounds with biological activity used as drugs in human and veterinary medicine or as insecticides and pesticides in agriculture. Thiadiazoles belong to the classes of nitrogen-sulfur heterocycles with extensive application as structural units of biologically active molecules and as useful intermediates in medicinal chemistry. The potency of the thiadiazole nucleus is demonstrated by the drugs currently used. 1,3,4-Thiadiazoles and some of their derivatives are extensively studied because of their broad spectrum of pharmacological activities. The aim of this review was to highlight the main antimicrobial properties exhibited by derivatives possessing 2-amino-1,3,4-thiadiazole moiety. Many of the reported 2-amino-1,3,4-thiadiazole derivatives can be considered as lead compounds for drug synthesis, and several of them have demonstrated higher antimicrobial activity in comparison to standard drugs. Furthermore, taking into account the reactivity of the amine group in the derivatization process, 2-amino-1,3,4-thiadiazole moiety may be a good scaffold for future pharmacologically active 1,3,4-thiadiazole derivatives.

Discovery of a Carbazole-Derived Lead Drug for Human African Trypanosomiasis

The protozoan parasite Trypanosoma brucei causes the fatal illness human African trypanosomiasis (HAT). Standard of care medications currently used to treat HAT have severe limitations, and there is a need to find new chemical entities that are active against infections of T. brucei. Following a "drug repurposing" approach, we tested anti-trypanosomal effects of carbazole-derived compounds called "Curaxins". In vitro screening of 26 compounds revealed 22 with nanomolar potency against axenically cultured bloodstream trypanosomes. In a murine model of HAT, oral administration of compound 1 cured the disease. These studies established 1 as a lead for development of drugs against HAT. Pharmacological time-course studies revealed the primary effect of 1 to be concurrent inhibition of mitosis coupled with aberrant licensing of S-phase entry. Consequently, polyploid trypanosomes containing 8C equivalent of DNA per nucleus and three or four kinetoplasts were produced. These effects of 1 on the trypanosome are reminiscent of "mitotic slippage" or endoreplication observed in some other eukaryotes.

Megazol and its bioisostere 4H-1,2,4-triazole: comparing the trypanocidal, cytotoxic and genotoxic activities and their in vitro and in silico interactions with the Trypanosoma brucei nitroreductase enzyme

Megazol (7) is a 5-nitroimidazole that is highly active against Trypanosoma cruzi and Trypanosoma brucei, as well as drug-resistant forms of trypanosomiasis. Compound 7 is not used clinically due to its mutagenic and genotoxic properties, but has been largely used as a lead compound. Here, we compared the activity of 7 with its 4H-1,2,4-triazole bioisostere (8) in bloodstream forms of T. brucei and T. cruzi and evaluated their activation by T. brucei type I nitroreductase (TbNTR) enzyme. We also analysed the cytotoxic and genotoxic effects of these compounds in whole human blood using Comet and fluorescein diacetate/ethidium bromide assays. Although the only difference between 7 and 8 is the substitution of sulphur (in the thiadiazole in 7) for nitrogen (in the triazole in 8), the results indicated that 8 had poorer antiparasitic activity than 7 and was not genotoxic, whereas 7 presented this effect. The determination of Vmax indicated that although 8 was metabolised more rapidly than 7, it bounds to the TbNTR with better affinity, resulting in equivalent kcat/KM values. Docking assays of 7 and 8 performed within the active site of a homology model of the TbNTR indicating that 8 had greater affinity than 7.

Genotoxicity profile of fexinidazole--a drug candidate in clinical development for human African trypanomiasis (sleeping sickness)

The parasitic disease human African trypanomiasis (HAT), also known as sleeping sickness, is a highly neglected fatal condition endemic in sub-Saharan Africa, which is poorly treated with medicines that are toxic, no longer effective or very difficult to administer. New, safe, effective and easy-to-use treatments are urgently needed. Many nitroimidazoles possess antibacterial and antiprotozoal activity and examples such as tinidazole are used to treat trichomoniasis and guardiasis, but concerns about toxicity including genotoxicity limit their usefulness. Fexinidazole, a 2-substituted 5-nitroimidazole rediscovered by the Drugs for Neglected Diseases initiative (DNDi) after extensive compound mining of public and pharmaceutical company databases, has the potential to become a short-course, safe and effective oral treatment, curing both acute and chronic HAT. This paper describes the genotoxicity profile of fexinidazole and its two active metabolites, the sulfoxide and sulfone derivatives. All the three compounds are mutagenic in the Salmonella/Ames test; however, mutagenicity is either attenuated or lost in Ames Salmonella strains that lack one or more nitroreductase(s). It is known that these enzymes can nitroreduce compounds with low redox potentials, whereas their mammalian cell counterparts cannot, under normal conditions. Fexinidazole and its metabolites have low redox potentials and all mammalian cell assays to detect genetic toxicity, conducted for this study either in vitro (micronucleus test in human lymphocytes) or in vivo (ex vivo unscheduled DNA synthesis in rats; bone marrow micronucleus test in mice), were negative. Thus, fexinidazole does not pose a genotoxic hazard to patients and represents a promising drug candidate for HAT. Fexinidazole is expected to enter Phase II clinical trials in 2012.

Screening of Potential anti-Trypanosoma cruzi Candidates: In Vitro and In Vivo Studies

Chagas disease (CD), caused by the intracellular protozoan Trypanosoma cruzi, is a parasitic illness endemic in Latin America. In the centennial after CD discovery by Carlos Chagas (1909), although it still represents an important public health problem in these affected areas, the existing chemotherapy, based on benznidazole and nifurtimox (both introduced more than four decades ago), is far from being considered ideal due to substantial toxicity, variable effect on different parasite stocks and well-known poor activity on the chronic phase. CD is considered one of the major "neglected" diseases of the world, as commercial incentives are very limited to guarantee investments for developing and discovering novel drugs. In this context, our group has been pursuing, over the last years, the efficacy, selectivity, toxicity, cellular targets and mechanisms of action of new potential anti-T. cruzi candidates screened from an in-house compound library of different research groups in the area of medicinal chemistry. A brief review regarding these studies will be discussed, mainly related to the effect on T. cruzi of (i) diamidines and related compounds, (ii) natural naphthoquinone derivatives, and (iii) megazol derivatives.

1-Aryl-4-nitro-1H-imidazoles, a new promising series for the treatment of human African trypanosomiasis

Nitroimidazoles are a well-known class of antibacterial and antiprotozoal drugs but in spite of the widespread clinical and veterinary use of these drugs, this family has been stigmatized in part due to associated genotoxicity problems. Here we report the synthesis, the anti-trypanosomal activity and a structure-activity relationship (SAR) study of a series of about fifty 1-aryl-4-nitro-1H-imidazoles, with an emphasis on selected in vivo active molecules. Compounds 4-nitro-1-{4-(trifluoromethoxy)phenyl}-1H-imidazole and 1-(3,4-dichlorophenyl)-4-nitro-1H-imidazole are curative in mouse models of both acute and chronic African trypanosomiasis when given orally at doses of 25-50 mg/kg for 4 days for the acute infection, and 50-100 mg/kg (bid) for 5 days in the chronic model. While both compounds are bacterial mutagens, activity is lost in strains lacking bacterial specific nitro-reductases. Mammalian nitro-reductases do not reduce nitroaromatic compounds with low redox potentials with same avidity as their bacterial counterparts and these compounds were shown to be devoid of genotoxicity in mammalian cells. Both compounds are promising leads for the treatment of human African trypanosomiasis (HAT or sleeping sickness), including the fatal stage 2 of the disease, for which new treatments are urgently needed.

Fexinidazole--a new oral nitroimidazole drug candidate entering clinical development for the treatment of sleeping sickness

Background

Human African trypanosomiasis (HAT), also known as sleeping sickness, is a fatal parasitic disease caused by trypanosomes. Current treatment options for HAT are scarce, toxic, no longer effective, or very difficult to administer, in particular for the advanced, fatal stage of the disease (stage 2, chronic HAT). New safe, effective and easy-to-use treatments are urgently needed. Here it is shown that fexinidazole, a 2-substituted 5-nitroimidazole rediscovered by the Drugs for Neglected Diseases initiative (DNDi) after extensive compound mining efforts of more than 700 new and existing nitroheterocycles, could be a short-course, safe and effective oral treatment curing both acute and chronic HAT and that could be implemented at the primary health care level. To complete the preclinical development and meet the regulatory requirements before initiating human trials, the anti-parasitic properties and the pharmacokinetic, metabolic and toxicological profile of fexinidazole have been assessed.

Methods and Findings

Standard in vitro and in vivo anti-parasitic activity assays were conducted to assess drug efficacy in experimental models for HAT. In parallel, a full range of preclinical pharmacology and safety studies, as required by international regulatory guidelines before initiating human studies, have been conducted. Fexinidazole is moderately active in vitro against African trypanosomes (IC₅₀ against laboratory strains and recent clinical isolates ranged between 0.16 and 0.93 µg/mL) and oral administration of fexinidazole at doses of 100 mg/kg/day for 4 days or 200 mg/kg/day for 5 days cured mice with acute and chronic infection respectively, the latter being a model for the advanced and fatal stage of the disease when parasites have disseminated into the brain. In laboratory animals, fexinidazole is well absorbed after oral administration and readily distributes throughout the body, including the brain. The absolute bioavailability of oral fexinidazole was 41% in mice, 30% in rats, and 10% in dogs. Furthermore, fexinidazole is rapidly metabolised in vivo to at least two biologically active metabolites (a sulfoxide and a sulfone derivative) that likely account for a significant portion of the therapeutic effect. Key pharmacokinetic parameter after oral absorption in mice for fexinidazole and its sulfoxide and sulfone metabolites are a C_max of 500, 14171 and 13651 ng/mL respectively, and an AUC_0–24 of 424, 45031 and 96286 h.ng/mL respectively. Essentially similar PK profiles were observed in rats and dogs. Toxicology studies (including safety pharmacology and 4-weeks repeated-dose toxicokinetics in rat and dog) have shown that fexinidazole is well tolerated. The No Observed Adverse Event Levels in the 4-weeks repeated dose toxicity studies in rats and dogs was 200 mg/kg/day in both species, with no issues of concern identified for doses up to 800 mg/kg/day. While fexinidazole, like many nitroheterocycles, is mutagenic in the Ames test due to bacterial specific metabolism, it is not genotoxic to mammalian cells in vitro or in vivo as assessed in an in vitro micronucleus test on human lymphocytes, an in vivo mouse bone marrow micronucleus test, and an ex vivo unscheduled DNA synthesis test in rats.

Conclusions

The results of the preclinical pharmacological and safety studies indicate that fexinidazole is a safe and effective oral drug candidate with no untoward effects that would preclude evaluation in man. The drug has entered first-in-human phase I studies in September 2009. Fexinidazole is the first new clinical drug candidate with the potential for treating advanced-stage sleeping sickness in thirty years.

This article describes the preclinical profile of fexinidazole, a new drug candidate with the potential to become a novel, oral, safe and effective short-course treatment for curing both stage 1 and 2 human African trypanosomiasis and replace the old and highly problematic treatment modalities available today. Fexinidazole is orally available and rapidly metabolized in two metabolites having equivalent biological activity to the parent and contributing significantly to the in vivo efficacy in animal models of both stage 1 and 2 HAT. Animal toxicology studies indicate that fexinidazole has an excellent safety profile, with no particular issues identified. Fexinidazole is a 5-nitroimidazole and, whilst it is Ames-positive, it is devoid of any genetic toxicity in mammalian cells and therefore does not pose a genotoxic risk for use in man. Fexinidazole, which was rediscovered through a process of compound mining, is the first new drug candidate for stage 2 HAT having entered clinical trials in thirty years, and has the potential to revolutionize therapy of this fatal disease at a cost that is acceptable in the endemic regions.

In vitro and in vivo activities of 1,3,4-thiadiazole-2-arylhydrazone derivatives of megazol against Trypanosoma cruzi

From a series of 1,3,4-thiadiazole-2-arylhydrazone derivatives of megazol screened in vitro against Trypanosoma cruzi, eight (S1 to S8) were selected for in vivo screening by single-dose oral administration (200 mg/kg of body weight) to infected mice at 5 days postinfection (dpi). Based on significant decreases in both parasitemia levels and mortality rates, S2 and S3 were selected for further assays. Despite having no in vivo effect, S1 was included since it was 2-fold more potent against trypomastigotes than megazol in vitro. Trypomastigotes treated with S1, S2, or S3 showed alterations of the flagellar structure and of the nuclear envelope. When assayed on intracellular amastigotes, the selectivity index (SI) for macrophages was in the range of >27 to >63 and for cardiac cells was >32 for S1 and >48 for megazol. In noninfected mice, S1 did not alter the levels of glutamic oxalacetic transaminase (GOT), glutamate pyruvate transaminase (GPT), or urea. S2 led to an increase in GOT, S3 to increases in GOT and GPT, and megazol to an increase in GOT. Infected mice were treated with each derivative at 50 and 100 mg/kg from dpi 6 to 15: S1 did not interfere with the course of infection or reduce the number of inflammatory foci in the cardiac tissue, S2 led to a significant decrease of parasitemia, and S3 decreased mortality. There was no direct correlation between the in vitro effect on trypomastigotes and amastigotes and the results of the treatment in experimental models, as S1 showed a high potency in vitro while, in two different schemes of in vivo treatment, no decrease of parasitemia or mortality was observed.

Inhibition of growth of Leishmania donovani promastigotes by newly synthesized 1,3,4-thiadiazole analogs

Leishmania donovani, the causative agent of visceral leishmaniasis, is transmitted by sand flies and replicates intracellularly in their mammalian host cells. The emergence of drug-resistant strains has hampered efforts to control the spread of the disease worldwide. Forty-four 1,3,4-thiadiazole derivatives and related compounds were tested in vitro for possible anti-leishmanial activity against the promastigotes of L. donovani. Micromolar concentrations of these agents were used to study the inhibition of multiplication of L. donovani promastigotes. Seven compounds were identified with potential antigrowth agents of the parasite. Compound 4a was the most active at 50 μM followed by compound 3a. These compounds could prove useful as a future alternative for the control of visceral leishmaniasis.

Simultaneous determination of seven nitroimidazole residues in meat by using HPLC-UV detection with solid-phase extraction

A method was developed for the determination of the seven nitroimidazoles including metronidazole (MNZ), ronidazole (RNZ), dimetridazole (DMZ), tinidazole (TNZ), ornidazole (ONZ), secnidazole (SNZ) and the common metabolite of RNZ and hydroxydimetridazole (DMOHZ) in poultry and pork muscles by high-performance liquid chromatography (HPLC) with ultraviolet detection (UV). After extraction with ethyl acetate and evaporation, the nitroimidazoles were redissolved in ethyl acetate and purified using strong cation exchange (SCX) solid-phase extraction (SPE) column. The HPLC separation was carried through on a C(18) bonded silica column with a deionized water-methanol-acetonitrile mobile phase using a gradient elution procedure. The limit of detection of all the seven nitroimidazoles was 0.2 microg/kg. The recoveries of the seven nitroimidazoles for chicken, pork and bacon samples spiked with 1-20 microg/kg were in the range of 71.4-99.5%. The linearity is satisfactory with a correlation coefficient of >0.998 at concentrations ranging from 0.7 to 60 microg/kg. The relative standard deviations of 10 measurements for spiked chicken, pork and bacon samples at the concentration of 1 and 20 microg/kg were in the range of 6.2-13.9% and 4.0-8.7%, respectively. The intra-day precision (n=5) for nitroimidazoles residues in chicken spiked at 20 microg/kg is 6.9%, and the inter-day precision for 5 days (n=25) is 11%. The method is capable of identifying nitroimidazole residues at > or =0.7 microg/kg levels and was applied in the determination of nitroimidazole residues in meat sample.

Trypanocidal nitroimidazole derivatives: Relationships among chemical structure and genotoxic activity

Human American trypanosomiasis is resurgent in Latin Americans, and new drugs are urgently required as current medications suffer from a number of drawbacks. Some nitroheterocycles have been demonstrated to exert a potent activity against trypanosomes. However, host toxicity issues halted their development as trypanocides. As part of the efforts to develop new compounds in order to treat parasitic infections, it is important to define their structure-activity relationship. In this study, 5-nitromegazol and two of its analogues, 4-nitromegazol, and 1-methyl-5-nitro-2-imidazolecarboxaldehyde 5-nitroimidazole-thiosemicarbazone, were tested and compared for in vitro induction of DNA damage in human leukocytes by the comet assay, performed at different pHs to better identify the types of damage. Specific oxidatively generated damage to DNA was also measured by using the comet assay with endonucleases. DNA damage was found in 5-nitromegazol-treated cells: oxidative stress appeared as the main source of DNA damage. 4-Nitromegazol did not produce any significant effect, thus confirming that 4-nitroimidazoles isomers have no important biological activity. The 5-nitroimidazole-thiosemicarbazone induced DNA damage with a higher efficiency than 5-nitromegazol. The central role in the reduction process played by the acidic hydrazine proton present in the thiosemicarbazone group but not in the cyclic (thiadiazole) form can contribute to rationalise our results. Given its versatility, thiosemicarbazone moiety could be involved in different reactions with nitrogenous bases (nucleophilic and/or electrophilic attacks).

The vervet monkey (Chlorocebus aethiops) as an experimental model for Trypanosoma brucei gambiense human African trypanosomiasis: a clinical, biological and pathological study

It has long been known that the vervet monkey, Chlorocebus (C.) aethiops, can be infected with Trypanosoma rhodesiense, but this model has not been described for T. gambiense. In this study, we report the development of such a model for human African trypanosomiasis. Twelve vervet monkeys infected with T. gambiense developed chronic disease. The duration of the disease ranged between 23 and 612 days (median 89 days) in five untreated animals. Trypanosomes were detected in the blood within the first 10 days post-infection and in the cerebrospinal fluid, with a median delay of 120 days (n = 4, range 28-348 days). Clinical changes included loss of weight, adenopathy, and in some cases eyelid oedema and lethargy. Haematological alterations included decreases in haemoglobin level and transitory decreases in platelet count. Biological modifications included increased gamma globulins and total proteins and decreased albumin. Pathological features of the infection were presence of Mott's cells, inflammatory infiltration of either mononuclear cells or lymphocytes and plasma cells in the brain parenchyma, and astrocytosis. These observations indicate that the development of the disease in vervet monkeys is similar to human T. gambiense infection. We conclude that C. aethiops is a promising experimental primate model for the study of T. gambiense trypanosomiasis.

A plethora of targets, a paucity of drugs: progress towards the development of novel chemotherapies for human African trypanosomiasis

Human African trypanosomiasis is a major health problem in large regions of Africa. Current chemotherapeutic options are limited and far from ideal. A diverse range of drug targets has been identified and validated in trypanosomes. These include several organelles (glycosomes, acidocalcisomes, kinetoplast) that are not represented in the mammalian host and biochemical pathways that differ significantly from host counterparts (carbohydrate metabolism, protein and lipid modification, response to oxidative stress, cell cycle). However, there has been little progress in developing novel drugs. Pharmaceutical companies are unwilling to invest in the development of drugs for a market that comprises some of the worlds poorest people. This review highlights some of the most attractive drug targets in trypanosomes.

In vitro and in vivo chromosomal aberrations induced by megazol

With the re-emergence of Human African Trypanosomiasis (HAT) on the one hand, which are increasingly resistant to current therapies, and the stage-dependent effectiveness or even the prohibitive cost of these therapies on the other hand, megazol, a 5-nitroimidazole thiadiazole highly active against various trypanosomal species, was assessed for its genotoxic potential. Very little information has become available until now. Two batches of megazol were provided by two different suppliers: Far-Manguinhos, a part of the Fiocruz foundation, under the Brazilian Minister of Health, and Delphia, a French company. These two batches, obtained by different synthetic routes, were studied by means of the in vitro micronucleus assay on L5178Y mouse lymphoma cells, in its microscale version. Both batches of magazol displayed a strong genotoxic activity in this screening assay. A second batch from Delphia was then investigated by use of two tests, i.e. the in vitro metaphase analysis with human lymphocytes and the in vivo micronucleus test in rat bone-marrow. Megazol was shown to be a potent inducer of in vitro and in vivo chromosomal aberrations. Although megazol is a potent trypanocidal agent and is orally bio-available, its toxicity dictates that it should not be developed further for the treatment of HAT and Chagas disease. All development work has therefore been discontinued.

Trypanocidal activity of melamine-based nitroheterocycles

A series of nitroheterocyclic compounds were designed with linkages to melamine or benzamidine groups that are known substrates of the P2 aminopurine and other transporters in African trypanosomes of the brucei group. Several compounds showed in vitro trypanotoxicity with 50% inhibitory concentrations in the submicromolar range. Although most compounds interacted with the P2 transporter, as judged by their ability to inhibit adenosine transport via this carrier, uptake through this route was not necessary for activity since TbAT1-null mutant parasites, deficient in this transporter, retained sensitivity to these drugs. One compound, a melamine-linked nitrofuran, also showed pronounced activity against parasites in mice. Studies into the mode of action of this compound indicated that neither reductive, nor oxidative, stress were related to its trypanocidal activity ruling out a genotoxic effect in T. brucei, distinguishing it from some other, mammalian cell toxic, trypanocidal nitroheterocycles.

Plasma kinetics and efficacy of oral megazol treatment in Trypanosoma brucei brucei-infected sheep

Experimentally infected sheep have been previously developed as an animal model of trypanosomosis. We used this model to test the efficacy of megazol on eleven Trypanosoma brucei brucei-infected sheep. When parasites were found in blood on day 11 post-infection, megazol was orally administered at a single dose of 40 or 80mg/kg. After a transient aparasitaemic period, all animals except two relapsed starting at day 2 post-treatment, which were considerated as cured on day 150 post-treatment and showed no relapse after a follow-up period of 270 days. In order to understand the high failure of megazol treatment to cure animals, a kinetic study was carried out. Plasma concentrations of megazol determined, by reverse-phase high-performance liquid chromatography at 8h post-treatment in these animals, were lowered, suggesting slow megazol absorption, except in cured animals. However, megazol plasma profiles in uninfected sheep after a single oral dose of megazol showed a fast megazol lowered absorption associated with a short plasma half-life of drug. Inter-individual variation of megazol pharmacokinetic properties was also observed. These findings suggested that the high failure rates of megazol treatment were related to poor drug availability after oral administration in sheep. In conclusion, megazol could cure sheep with T. b. brucei infection but oral administration was not an effective route.

Megazol combined with suramin improves a new diagnosis index of the early meningo-encephalitic phase of experimental African trypanosomiasis

In human African trypanosomiasis (HAT), the parasites invade the central nervous system (CNS), leading to the development of meningo-encephalitis and an irreversible demyelinating process, which kills the patient unless specific treatment is undertaken. Among the experimental trypanocides, the nitroimidazole derivative megazol alone at optimal doses does not cure late-stage disease tested in mouse models, however the combination of suramin and megazol is able to cure infected mice without CNS involvement. We recently developed an experimental model of HAT with a sharp decrease in both the food intake and the body weight which may constitute an effective index of the early meningo-encephalitic phase. Using this model, we tested this hypothesis by the exclusive effectiveness of a megazol and suramin combination treatment to eliminate CNS trypanosomes. Sprague-Dawley rats were infected with Trypanosoma brucei brucei AnTat 1.1E. Food intake and body weight were measured daily from the day of infection to death. Haematocrit was measured twice a week. Treatment consisted of 20 mg suramin per kg body weight administered intraperitoneally (i.p.) alone, or three daily doses (80 mg/kg) of megazol given per os, or suramin (20 mg/kg, i.p.) followed 24 h later by three daily doses (80 mg/kg) of megazol given per os. Treatment was followed by an increase in daily body weight and food intake similar to those of the control animals, 2 weeks after treatment. The anaemia developed after infection is also cleared as shown by the haematocrit measurements. The rats treated with megazol alone died about 29 days after treatment and those treated with suramin, after about 26 days. Seven months later, no signs of relapse were seen in 10 of 12 rats treated with the therapeutic combination, indicating that this chemotherapy regimen was curative. The results support our previous finding, i.e. the decrease in body weight may constitute a diagnosis index of the early meningo-encephalitic phase.

Activity of megazol, a trypanocidal nitroimidazole, is associated with DNA damage

DNA damage associated with the trypanocidal activity of megazol [2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazole] was shown in experiments in which DNA repair-deficient RAD51(-/-) Trypanosoma brucei mutants were found to be hypersensitive to the drug. Parasites resistant to megazol were selected and showed modest cross-resistance to other trypanocides, although neither drug efflux nor changes to intracellular thiols correlated with resistance.

Treatment perspectives for human African trypanosomiasis

Human African trypanosomiasis (HAT), or sleeping sickness, is currently on the rise. HAT develops in two stages, the first involving the hemolymphatic system, and the second, the neurological system. Left untreated, HAT is invariably fatal. There have been no therapeutic advances in more than 40 years. Stage 1 can be treated with pentamidine and suramin, but stage 2 can only be treated with melarsoprol, a toxic arsenic derivative that has a 2-12% incidence of fatal side-effects (encephalopathy). Eflornithine has never achieved widespread use because it is difficult to administer under field conditions. Nifurtimox has been used successfully in the treatment of American trypanosomiasis, or Chagas disease, but only in small studies or as a compassionate use treatment. There is little research and development for new drugs in this area: only one prodrug is in the clinical development phase, a pentamidine analog that offers hope for the replacement of injectable pentamidine with an orally administered drug. Current efforts appear to be focused on reevaluating older drugs. A course of treatment with melarsoprol for 10 days at 2.2 mg/kg/day is now in the multicenter evaluation phase. Orally administered eflornithine is also slated for reevaluation. In addition, studies of drug combinations are recommended to determine possible combined or synergistic effects and find ways to reduce toxicity.

Trypanosoma cruzi: effect and mode of action of nitroimidazole and nitrofuran derivatives

With the aim of determining the actual target(s) of nitro-group bearing compounds considered as possible leads for the development of drugs against Chagas' disease, we studied in parallel nitrofurans and nitroimidazoles. We investigated nine representative compounds for the following properties: efficacy on different Trypanosoma cruzi strains, redox cyclers, inhibition of respiration, production of corresponding nitroso derivatives and intracellular thiol scavengers. Our results indicate that nifurtimox and related compounds act as redox cyclers, whereas the most active in the series, the 5-nitroimidazole megazol essentially acts as thiol scavenger particularly for trypanothione, the cofactor for trypanothione reductase, an essential enzyme in the detoxification process.

Synthesis and biological activity of nitro heterocycles analogous to megazol, a trypanocidal lead

As part of our efforts to develop new compounds aimed at the therapy of parasitic infections, we synthesized and assayed analogues of a lead compound megazol, 5-(1-methyl-5-nitro-1H-2-imidazolyl)-1,3,4-thiadiazol-2-amine, CAS no. 19622-55-0), in vitro. We first developed a new route for the synthesis of megazol. Subsequently several structural changes were introduced, including substitutions on the two rings of the basic nucleus, replacement of the thiadiazole by an oxadiazole, replacement of the nitroimidazole part by a nitrofurane or a nitrothiophene, and substitutions on the exocyclic nitrogen atom for evaluation of an improved import by the glucose or the purine transporters. Assays of the series of compounds on the protozoan parasites Trypanosoma brucei, Trypanosoma cruzi, and Leishmania donovani, as either extracellular cells or infected macrophages, indicated that megazol was more active than the derivatives. Megazol was then evaluated on primates infected with Trypanosoma brucei gambiense, including late-stage central nervous system infections in combination with suramin. Full recovery was observed in five monkeys in the study with no relapse of parasitemia within a 2 year follow-up. Because there is a lack of efficacious treatments for sleeping sickness in Africa and Chagas disease in South America, megazol is proposed as a potential alternative. The mutagenicity of this compound is at present being reevaluated, and metabolism is also under investigation prior to possible further developments.

New drugs for the treatment of human African trypanosomiasis: research and development

Chemotherapy of human African trypanosomiasis is problematic because of the high frequency of severe adverse events, the long duration and high cost of treatment, and an increasing number of treatment-refractory cases. New cost-efficient, easy-to-use drugs are urgently needed. Whereas basic research on potential drug targets is anchored in academia, the complex, highly regulated and very expensive process of preclinical and clinical drug development is almost exclusively in the hands of pharmaceutical companies. Jennifer Keiser, August Stich and Christian Burri here review, from the angle of industrial drug research and development, the past ten years of research activities at different stages of the development of trypanocidal drugs, and assess future prospects. The absence of compounds in clinical development Phases I-III indicates no new drugs will become available in the next few years.

Uptake of the nitroimidazole drug megazol by African trypanosomes

Megazol, CL 64,855 (2-amino-5-[1-methyl-5-nitro-2-imidazolyl]-1,3, 4-thiazole) has been shown to be extremely effective in clearing experimental infections of African trypanosomes. An unusual amino-purine transporter termed P2, implicated in the transport of both the diamidine and melaminophenyl arsenical classes of drug in Trypanosoma brucei, recognised chemical groups on compounds which are also present on megazol. Megazol interacted with this carrier protein, as judged by its ability to inhibit P2 adenosine transport and to abrogate in vitro arsenical-induced lysis in a dose-dependent manner. However, parasites resistant to melaminophenyl arsenical and diamidine drugs due to lack of the P2 transporter showed no resistance to megazol. This is because passive diffusion represented the major route of entry. Initial rates of uptake were not saturable within the limit of megazol's solubility and did not conform to thermodynamic precepts compatible with carrier-mediated uptake. Adenosine and other P2 transporter substrates, even at high concentration, had little impact on megazol uptake. Uptake was biphasic, with a very rapid equilibration across the membrane followed by a slower accumulation over time. The equilibration phase represented a simple passive diffusion, with the subsequent uptake probably being due to metabolism of the drug.

Enzymatic reduction studies of nitroheterocycles

The nitroimidazole derivative Megazol is a highly active compound used against several strains of Trypanosoma cruzi, the causative agent of Chagas' disease (American trypanomiasis). With the aim of gaining an insight into the probable mode of action, the interaction of Megazol with different redox enzymes was studied in comparison to that of Nifurtimox and Metronidazole. The three nitroaromatic compounds are reduced by L-lactate cytochrome c-reductase, adrenodoxin reductase, and NADPH:cytochrome P-450 reductase (EC 1.6.2.4), the efficiencies of the enzymatic reductions being roughly related to the reduction potentials of these pseudo-substrates. As the enzyme responsible for the reduction of Megazol within the parasite has not yet been identified, the nitroimidazole was assayed with T. cruzi lipoamide dehydrogenase and trypanothione reductase. Megazol did not inhibit the physiological reactions but proved to be a weak substrate of both flavoenzymes. The single electron reduction of the compound by NADPH:cytochrome P-450 reductase, by rat liver as well as by trypanosome microsomes was confirmed by ESR experiments. As shown here, Megazol interferes with the oxygen metabolism of the parasite, but its extra activity when compared to Nifurtimox may be related to other features not yet identified.

Simple high-performance liquid chromatographic method to analyse megazol in human and rat plasma

A simple and sensitive high-performance liquid chromatographic method has been developed to measure megazol in human plasma. The method was optimized and validated according to the Washington Concensus Conference on the Validation of Analytical Methods (V.P. Shah et al., Eur. J. Drug Metab. Pharmacokinet., 15 (1991) 249). The criteria of complete validation were specificity, linearity, precision, analytical recovery, dilution and stability. It involved extraction of the plasma with dichloromethane, followed by reversed-phase high-performance liquid chromatography using a Kromasil C8 column and UV detection at 360 nm. The retention times of the internal standard (tinidazol) and megazol were 6.10 and 9.60 min, respectively. The standard curve was linear from 2 ng ml-1 (limit of quantification) to 2000 ng ml-1. The coefficients of variation for all the criteria of validation were less than 6%; 85 to 92% extraction efficiencies were obtained. Megazol was stable during the storage period (one month at -20 degrees C) in plasma and for two months at 25 degrees C in standard solution. The method was tested by measuring the plasma concentration following oral administration to rat and was shown to be suitable for pharmacokinetic studies.