G. Chauviere

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

Human African trypanosomiasis (HAT) or sleeping sickness is a major public health problem in 36 sub-Saharan African countries and is caused by Trypanosoma brucei gambiense and T. b. rhodesiense. About 25,000 new cases of the disease are reported annually, and around 50 million people are classed as at risk of contracting the disease. Until now; the only effective drug available for treatment of advanced HAT was the trypanocide melarsoprol. The mortality rate of melarsoprol treated patients is 1-5%. Megazol is a nitroimidazole derivative shown to be effective in vitro against T. b. brucei with an EC50 of 0.01 micrograms.ml-1. When this compound was tested for its in vivo activity in T. b. brucei infected Swiss mice, it was shown to cure the acute disease. However, megazol alone did not cause cure of mice carrying a subacute infection with involvement of the central nervous system (CNS). Combined suramin and megazol treatment did prove effective and the mice were shown to have remission without further relapse from the CNS. The study of three megazol derivatives is also described here. Substitution of a bromine, methyl or trifluoromethyl moiety at the 4 position of the imidazole ring abolished trypanocidal activity both in vivo and in vitro. Intermediates of megazol synthesis (imidazole sulfoxide and imidazole sulfone) were also tested, but were shown not to be active. It is thought that megazol trypanocidal effect may be due to the triggering of radical production by the compound, which have toxic effects on the trypanosomes metabolism. In depth study of megazol is needed to fully elucidate its pharmacokinetics and to precisely pin down its mode of action.

Cyclic voltammetric studies on nitro radical anion formation from megazol and some related nitroimidazole derivatives

Abstract Megazol (2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol, CAS 19622-55-0) and related nitroimidazole compounds are being tested as antichagasic drugs. Little is known on the mode of action of megazol. However, there is evidence that one-electron reduction of megazol to the corresponding nitro radical anion is a key step in the reaction mechanism. Consequently, this paper is focused on the cyclic voltammetric behaviour of megazol and related nitroimidazole derivatives with the aim of revealing the formation and stability of the corresponding nitro radical anions. All the compounds studied produce a well resolved nitro/nitro radical anion couple. The resolution of the couple was improved with the addition of tetrabutylammonium ions which hinders the protonation of the nitro radical anion at the electrode surface, thus enhancing the stability of the nitro radical anion. Only megazol produced a cyclic voltammogram distorted by the presence of a pre-peak due to strong adsorption of the corresponding nitro radical anion. The pre-peak occurs at potentials more positive than the diffusion controlled peak because the Gibbs energy of adsorption of the nitro radical anion makes the reduction of megazol to the adsorbed nitro radical anion easier than to the radical anion in solution. The sulphur atom in the thiadiazole ring plays a crucial role in the adsorption phenomena. Using the cyclic voltammetry theory for the disproportionation reaction, we have calculated the second-order decay rate constant, k2, and the half-life time, t1/2, for all the nitro radical anions of the studied nitroimidazole derivatives. The values obtained were compared with those of the corresponding nitro radical anions obtained from nifurtimox and benznidazole, the classic antichagasic drugs. Also, our results show that cyclic voltammetry is a good alternative to the classic pulse radiolysis method to obtain reliable values of the E17 parameter for nitro radical anions.

Megazol combined with suramin: a chemotherapy regimen which reversed the CNS pathology in a model of human African trypanosomiasis in mice

Chemotherapy for human African trypanosomiasis (HAT), or sleeping sickness, is unreliable because of resistance, refraction and toxic and adverse side‐effects. Using a long‐term experimental model of HAT with involvement of the central nervous system (CNS), we tested the ability of a megazol and suramin combination treatment to eliminate CNS trypanosomes. This consisted of 20 mg suramin per kg body weight administered intraperitoneally (IP), followed 24 h later by 4 daily doses (80 mg/kg) of megazol given either IP or per os. One week post‐treatment, neurological disorders had disappeared. One of 15 mice relapsed in each application group at 81 and 98 days after treatment, respectively. At six months, no signs of relapse were seen in remaining mice, indicating that this chemotherapy regimen was curative. Immunohistochemical (astrocytosis) and histological (inflammatory lesions) examinations of brain tissues showed that animals returned to normal from 2 months post‐treatment. These results suggest that the megazol‐suramin combination reversed the CNS pathology in this model.

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 megazols 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.

Polarographic Reduction of Megazol and Derivatives, and Its Polarographic, UV Spectrophotometric, and HPLC Determination

Megazol (2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol, CAS 19622-55-0), a highly active compound used against several strains of Trypanosoma cruzi, the causative agent of Chagas disease, is electrochemically studied to propose a new electroanalytical alternative for its quantitative determination. Megazol is shown to be polarographically reducible in protic and mixed media. The polarogram of megazol shows two signals, the main signal is due to the reduction of the nitroimidazole moiety, and the second one is due to the reduction of the thiadiazole moiety in the molecule. We have synthesized several related molecules to megazol in order to study the␣influence of structural changes in the reducibility of the nitro group. Also we have compared the polarographic behavior of megazol with the currently used antichagasic drug, benznidazole. Based on the linear relation between the peak current and the megazol concentrations a differential pulse polarographic method was developed. The linearity was maintained between 6×10−6 and 1×10−4 M with a quantitation and detection limits of 6.7×10−6 and 3.2×10−6 M, respectively. Precision and accuracy of the developed method was checked by recovery study. For comparative purposes spectrophotometric and HPLCuv methodologies were developed. From the pH dependence of the absorbance band at 276 nm an apparent pKa of 8.5 was determined for megazol.

Nitro radical anions from megazol and related nitroimidazoles in aprotic media. A father–son type reaction triggered by an acidic proton

Abstract We have studied the electrochemical reduction of some nitroimidazoles such as megazol(2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol, CAS 19622-55-0) and two related derivatives in aprotic media (100% DMF, 0.1 M TBAP). All the studied compounds were easily reducible in aprotic media generating the corresponding nitro radical anions as products of the one electron reduction of the parent compound. The nitro radical anions decay by a dimerization reaction and the dimerization rate constants were obtained according to the Olmsteads approach by obtaining values of 150±24, 1690±42 and 640±32 M −1 s −1 for megazol, GC-361 and GC-284, respectively. The existence of an acidic proton on the acetamide group in the GC-361 molecule triggered the appearance of father–son type reactions between the nitro radical anion from GC-361 (son compound) and GC-361 (father compound) generating the neutral radical and the conjugate base of GC-361. Thus the nitro radical anion from GC-361 acts as a Bronsted base abstracting the proton of the acetamide group in the GC-361 derivative of megazol.

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.

Molecular structure of 2-Amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol (Megazol) and related compounds: A concerted study using X-ray crystallography, molecular mechanics, and semiempirical methods

A structural study of three nitroimidazoles was carried out using molecular mechanics, semiempirical methods, and X-ray crystallography. Structural features which might account for the high efficiency of1 (Megazol) as an antiparasitic drug and its opposite, the inactivity of its regiomers2 and3 were examined, i.e., coplanarity of the two rings, preferred conformations, and rotational barriers around the pivot bond between the two rings. For the three compounds an antiperiplanar conformation is preferred for the N(CH3) and C-S bonds. For compounds1 and3, the rings are coplanar, with2 being somewhat twisted. The geometry obtained by molecular mechanics for compound1 is in excellent agreement with the X-ray structure, and greater confidence can be placed in this method than in semiempirical ones. Similarities observed on the LUMO positions, as well as rotational barriers lead to the conclusion that the differences in biological activity of these compounds do not rely on their ground state properties but rather on their subsequent reactions with oxygen. In addition, the calculations revealed significant structural information of a family of biological importance (nitroimidazoles) and constitute a comparative test for the MM2, AM1, and PM3 methods.

Synthesis of 2‐amino‐5‐(1‐methyl‐5‐nitro‐[4‐3H]‐2‐imidazolyl)‐1,3,4‐thiadiazole

2-Amino-5-(1-methyl-5-nitro-4-iodo-2-imidazoyl)-1,3,4-thiadiazole (5) was prepared from imidazole via a 4-steps sequence. Reductive desiodination of 5 using a tetrahydrofuran solution of NaBH4 in the presence of tritiated water provided the title compound (specific radioactivity 12.6 Ci/mmol) in one step.