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

Abstract

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.

Key words:
genotoxicity; mutagenicity; megazol; nitroimidazoles


Chagas disease caused by the protozoan Trypanosoma cruzi remains a major social and public health problem in Latin America and is regarded as a neglected tropical disease by World Health Organization (WHO). WHO estimates 5-7 million people are infected with T. cruzi worldwide, mainly in Latin America highlighting Argentina, Brazil, Mexico and Bolivia.11. WHO - World Health Organization. Chagas disease (American trypanosomiasis). The disease: what is Chagas disease? 2018. Available from: http://www.who.int/chagas/disease/en/
http://www.who.int/chagas/disease/en/...
In the last two decades, cases have been found in European countries, Japan, Australia and the USA, resulting from the immigration of infected individuals.11. WHO - World Health Organization. Chagas disease (American trypanosomiasis). The disease: what is Chagas disease? 2018. Available from: http://www.who.int/chagas/disease/en/
http://www.who.int/chagas/disease/en/...

Only two drugs, the 2-nitroimidazole benznidazole (Bnz) (1) and the 5-nitrofuran nifurtimox (Nfx) (2) (Fig. 1), are licensed for the treatment of Chagas disease, although their safety and efficacy profile are far from ideal.22. Pérez-Molina JA, Molina I. Chagas disease. Lancet. 2018; 391(10115): P82-94. doi: 10.1016/S0140-6736(17)31612-4.
https://doi.org/10.1016/S0140-6736(17)31...
Treatment with these drugs is always recommended for all patients in acute phase, in case of accidental contamination with sharp-cutting and contact with mucous membranes, congenital Chagas disease, infected mothers of childbearing age, transfusion-related transmission, reactivated infections in immunosuppressed hosts and chronic disease in children younger than 12 years.33. Dias JC, Ramos Jr AN, Gontijo ED, Luquetti A, Shikanai-Yasuda MA, Coura JR, et al. 2nd Brazilian consensus on Chagas disease, 2015. Rev Soc Bras Med Trop. 2016; 49(Suppl. 1): 3-61. doi: 10.1590/0037-8682-0505-2016. Both drugs have shown successful results and the parasitological cure of treatment with Bnz, occurs in estimated 80% to 100% of patients during the acute phase, but the effectiveness decreases with advancement of the infection; and the data on adults with late chronic infection indicates serological cure only in 5-20% of cases.44. Pérez-Molina JA, Pérez-Ayala A, Moreno S, Fernández-González MC, Zamora J, López-Velez R. Use of benznidazole to treat chronic Chagas' disease: a systematic review with a meta-analysis. J Antimicrob Chemother. 2009; 64(6): 1139-47. doi: 10.1093/jac/dkp357.
https://doi.org/10.1093/jac/dkp357...
The frequency of adverse effects with Nfx is 43.0-97.5% in adults with chronic infection, leading to the discontinuation of the treatment in 14-75% of cases.55. Jackson Y, Alirol E, Getaz L, Wolff H, Combescure C, Chappuis F. Tolerance and safety of nifurtimox in patients with chronic Chagas disease. Clin Infect Dis. 2010; 51(10): e69-75. doi: 10.1086/656917.
https://doi.org/10.1086/656917...
Compound Bnz is generally preferred over Nfx because of its better tolerability profile, tissue penetration, and, possibly, efficacy. The most common adverse events associated with Bnz are skin rash (29-50%), digestive intolerance (5-15%), and general symptoms such as anorexia, asthenia, headache, and sleep disturbances (40%) leading to discontinuation of treatment in 9-29% of cases.66. Pinazo MJ, Mun~oz J, Posada E, López-Chejade P, Gállego M, Ayala E, et al. Tolerance of benznidazole in treatment of Chagas' disease in adults. Antimicrob Agents Chemother. 2010; 54(11): 4896-9. doi: 10.1128/AAC.00537-10.
https://doi.org/10.1128/AAC.00537-10...
The Laboratory of the State of Pernambuco (Lafepe) is the only public laboratory worldwide with authorisation by the Brazilian Health Regulatory Agency (ANVISA) for the production of Bnz since June 2016.77. Lafepe. Laboratório Farmacêutico do Estado de Pernambuco. 2018. Available from: http://www.lafepe.pe.gov.br/category/benznidazol.
http://www.lafepe.pe.gov.br/category/ben...

Fig. 1:
chemical structures of nitroheterocyclic compounds: Benznidazole (Bnz) (1), Nifurtimox (Nfx) (2) and Megazol (3).

Megazol (3) (Fig. 1) is a 5-nitroimidazole with 1,3,4-thiadiazole which exhibits potent in vitro and in vivo activity against T. cruzi, including strains resistant to Bnz, and also Trypanosoma brucei, which causes sleeping sickness,88. Filardi LS, Brener Z. Nitroimidazole-thiadiazole derivative with curative action in experimental Trypanosoma cruzi infections. Ann Trop Med Parasitol. 1982; 76(3): 293-7. PMID: 6812514.,99. Bouteille B, Marie-Daragon A, Chauvière G, Albuquerque C, Enanga B, Dardé ML, et al. Effect of megazol on Trypanosoma brucei brucei acute and subacute infections in Swiss mice. Acta Tropica. 1995; 60(2): 73-80. doi: 10.1016/0001-706X(95)00109-R.
https://doi.org/10.1016/0001-706X(95)001...
,1010. Enanga B, Keila M, Chauvière G, Dumas M, Bouteille B. Megazol combined with suramin: a chemotherapy regimen which reversed the CNS pathology in a model of human African trypanosomiasis in mice. Trop Med Int Health. 1998; 3(9): 736-41. doi: 10.1046/j.1365-3156.1998.00291.x.
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,1111. Barrett MP, Fairlamb AH, Rousseau B, Chauviere G, Perie J. Uptake of nitroimidazole drug megazol by African trypanosomes. Biochem Pharmacol. 2000; 59(6): 615-20. doi: 10.1016/S0006-2952(99)00368-8.
https://doi.org/10.1016/S0006-2952(99)00...
,1212. Buschini A, Giordani F, de Albuquerque CN, Pellacani C, Pelosi G, Rossi C, et al. Trypanocidal nitroimidazole derivatives: relationships among chemical structure and genotoxic activity. Biochem Pharmacol. 2007; 73(10): 1537-47. doi: 10.1016/j.bcp.2007.01.024.
https://doi.org/10.1016/j.bcp.2007.01.02...
,1313. Salomão K, de Souza EM, Carvalho SA, Silva EF, Fraga CAM, Barbosa HS, et al. In vitro and in vivo activity of 1,3,4-thiadiazole-2-arylhydrazone derivatives of megazol on Trypanosoma cruzi. Antimicrob Agents Chemother. 2010; 54(5): 2023-31. doi: 10.1128/AAC.01241-09.
https://doi.org/10.1128/AAC.01241-09...
which may be due to the triggering of oxidative stress by the compound.99. Bouteille B, Marie-Daragon A, Chauvière G, Albuquerque C, Enanga B, Dardé ML, et al. Effect of megazol on Trypanosoma brucei brucei acute and subacute infections in Swiss mice. Acta Tropica. 1995; 60(2): 73-80. doi: 10.1016/0001-706X(95)00109-R.
https://doi.org/10.1016/0001-706X(95)001...
,1414. Chauvière G, Bouteille B, Enanga B, de Albuquerque C, Croft SL, Dumas M, et al. Synthesis and biological activity of nitro heterocycles analogous to megazol, a trypanocidal lead. J Med Chem. 2003; 46(3): 427-40. doi: 10.1021/jm021030a.
https://doi.org/10.1021/jm021030a...
Compound 3 shows a superior profile of action when compared to Nfx and by the employment of lower doses.1414. Chauvière G, Bouteille B, Enanga B, de Albuquerque C, Croft SL, Dumas M, et al. Synthesis and biological activity of nitro heterocycles analogous to megazol, a trypanocidal lead. J Med Chem. 2003; 46(3): 427-40. doi: 10.1021/jm021030a.
https://doi.org/10.1021/jm021030a...
However, it is not used clinically because it has mutagenic activity1111. Barrett MP, Fairlamb AH, Rousseau B, Chauviere G, Perie J. Uptake of nitroimidazole drug megazol by African trypanosomes. Biochem Pharmacol. 2000; 59(6): 615-20. doi: 10.1016/S0006-2952(99)00368-8.
https://doi.org/10.1016/S0006-2952(99)00...
,1515. Ferreira RC, Ferreira LC. Mutagenicity of CL 64855, a potent anti-Trypanosoma cruzi drug. Mutat Res. 1986; 171(1): 11-5. doi: 10.1016/0165-1218(86)90003-0.
https://doi.org/10.1016/0165-1218(86)900...
,1616. Poli P, Mello MA, Buschini A, Mortara RA, de Albuquerque CN, da Silva S, et al. Cytotoxic and genotoxic effects of megazol, an anti-Chagas' disease drug, assessed by different short-term tests. Biochem Pharmacol. 2002; 64(11): 1617-27. doi: 10.1016/S0006-2952(02)01390-4.
https://doi.org/10.1016/S0006-2952(02)01...
,1717. Mital A. Synthetic nitroimidazoles: biological activities and mutagenicity relationships. Sci Pharm. 2009; 77(3): 497-520. Available from: http://dx.doi.org/10.3797/scipharm.0907-14.
http://dx.doi.org/10.3797/scipharm.0907-...
associated with the reduction of the nitro group located at position 5 of the nitroimidazole ring.1818. Nesslany F, Brugier S, Mouries MA, Le Curieux F, Marzin D. In vitro and in vivo chromosomal aberrations induced by megazol. Mutat Res. 2004; 560(2): 147-58. doi: 10.1016/j.mrgentox.2004.02.013.
https://doi.org/10.1016/j.mrgentox.2004....
In view of this, several researchers have been using 3 as a prototype to search for new bioactive substances with high trypanocidal activity1919. Boechat N, Carvalho AS, Fernández-Ferreira E, Soares RO, Souza AS, Gibaldi D, et al. Novel nitroimidazoles with trypanocidal and cell growth inhibition activities. Cytobios. 2001; 105(409): 83-90. PMID: 11393774.,2020. Rosselli FP, Albuquerque CN, da Silva ABF. Quantum chemical and statistical study of megazol-derived compounds with trypanocidal activity. Int J Quantum Chem. 2005: 103(5): 738-48. doi: 10.1002/qua.20532.
https://doi.org/10.1002/qua.20532...
,2121. Carvalho AS, Gibaldi D, Pinto AC, Bozza M, Boechat N. Synthesis and trypanocidal evaluation of news 5-[N-(3-(5-substituted)-1,3,4-thiadiazolyl)]amino-1-methyl-4-nitroimidazoles. Lett Drug Des Discov. 2006; 3(2): 98-101. doi: 10.2174/157018006775789667.
https://doi.org/10.2174/1570180067757896...
,2222. Carvalho AS, Menna-Barreto RFS, Romeiro NC, de Castro SL, Boechat N. Design, synthesis and activity against Trypanosoma cruzi of azaheterocyclic analogs of megazol. Med Chem. 2007; 3(5): 460-5. doi: 10.2174/157340607781745519.
https://doi.org/10.2174/1573406077817455...
but without the toxic effect.2323. Carvalho SA, Silva EF, Santa-Rita RM, de Castro SL, Fraga CAM. Synthesis and antitrypanosomal profile of new functionalized 1,3,4-thiadiazole-2-arylhydrazone derivatives, designed as non-mutagenic megazol analogues. Bioorg Med Chem Lett. 2004; 14(24): 5967-70. doi: 10.1016/j.bmcl.2004.10.007.
https://doi.org/10.1016/j.bmcl.2004.10.0...

Nitroimidazoles, as well as nitro compounds in general, have been the subject of discussion about their mutagenicity since their biological activity seems to be related to the damage caused by the bioreduction products of the nitro group to DNA. Previous work of our group showed that the nitro group is not the sole responsible for the genotoxic activity.2424. Boechat N, Carvalho AS, Salomão K, de Castro SL, Araujo-Lima CF, Mello FVC, et al. Studies of genotoxicity and mutagenicity of nitroimidazoles: demystifying this critical relationship with the nitro group. Mem Inst Oswaldo Cruz. 2015; 110(4): 492-99. doi: 10.1590/0074-02760140248.
https://doi.org/10.1590/0074-02760140248...
The type and position of different substituents bonded to the imidazole ring have a significant influence on the toxicological activity. Continuing our work in the search for bioactive substances and knowing that mutagenicity is an undesirable property in clinically used drugs because raises the question of their potential carcinogenicity, more studies are needed for complete evaluation of nitroimidazole effect on DNA, contributing to the elucidation of mechanisms involved in these processes. A nitroimidazole possessing high trypanocidal activity with none mutagenicity is of great interest not only from a safety point of view, but also provides a basis for further investigations of the mode of action and mechanism of expression of mutagenicity of this class of compounds.1717. Mital A. Synthetic nitroimidazoles: biological activities and mutagenicity relationships. Sci Pharm. 2009; 77(3): 497-520. Available from: http://dx.doi.org/10.3797/scipharm.0907-14.
http://dx.doi.org/10.3797/scipharm.0907-...

In this article we investigate seven nitroimidazole compounds (4-10) analogs to 32222. Carvalho AS, Menna-Barreto RFS, Romeiro NC, de Castro SL, Boechat N. Design, synthesis and activity against Trypanosoma cruzi of azaheterocyclic analogs of megazol. Med Chem. 2007; 3(5): 460-5. doi: 10.2174/157340607781745519.
https://doi.org/10.2174/1573406077817455...
(Fig. 2) using biososterism among rings in order to elucidate the relationship between chemical structure, trypanomicidal and genotoxic activities.1919. Boechat N, Carvalho AS, Fernández-Ferreira E, Soares RO, Souza AS, Gibaldi D, et al. Novel nitroimidazoles with trypanocidal and cell growth inhibition activities. Cytobios. 2001; 105(409): 83-90. PMID: 11393774.,2121. Carvalho AS, Gibaldi D, Pinto AC, Bozza M, Boechat N. Synthesis and trypanocidal evaluation of news 5-[N-(3-(5-substituted)-1,3,4-thiadiazolyl)]amino-1-methyl-4-nitroimidazoles. Lett Drug Des Discov. 2006; 3(2): 98-101. doi: 10.2174/157018006775789667.
https://doi.org/10.2174/1570180067757896...
,2222. Carvalho AS, Menna-Barreto RFS, Romeiro NC, de Castro SL, Boechat N. Design, synthesis and activity against Trypanosoma cruzi of azaheterocyclic analogs of megazol. Med Chem. 2007; 3(5): 460-5. doi: 10.2174/157340607781745519.
https://doi.org/10.2174/1573406077817455...
In compound 4, the 1,3,4-thiadiazole nucleus presents in 3 was replaced by the 1,2,4-triazole nucleus2222. Carvalho AS, Menna-Barreto RFS, Romeiro NC, de Castro SL, Boechat N. Design, synthesis and activity against Trypanosoma cruzi of azaheterocyclic analogs of megazol. Med Chem. 2007; 3(5): 460-5. doi: 10.2174/157340607781745519.
https://doi.org/10.2174/1573406077817455...
(Fig. 2); in 5 in addition to replacing the 1,3,4-thiadiazole nucleus of 3 by the 1,2,4-triazole nucleus with a CF3 substituent, the position of this nucleus from the C-2 to the C-5 of the imidazole nucleus was changed with the nitro group at the 4-position, plus NH as a spacer group1919. Boechat N, Carvalho AS, Fernández-Ferreira E, Soares RO, Souza AS, Gibaldi D, et al. Novel nitroimidazoles with trypanocidal and cell growth inhibition activities. Cytobios. 2001; 105(409): 83-90. PMID: 11393774. (Fig. 2); in 6, the nitro group was transferred from the 5-position of the imidazole ring of 3 to the 4-position of 6 and the 1,3,4-thiadiazole ring of 3 replaced by the pyrazole ring in the α-position with the nitro group.1919. Boechat N, Carvalho AS, Fernández-Ferreira E, Soares RO, Souza AS, Gibaldi D, et al. Novel nitroimidazoles with trypanocidal and cell growth inhibition activities. Cytobios. 2001; 105(409): 83-90. PMID: 11393774. Ring bioisosterism was also performed to obtain 7, 8, 9 and 10 replacing the pyrazole ring by another azoles with addition of hydrophilic and lipophilic groups respectively, as described in Fig. 2.

Fig. 2:
rational planning of nitroimidazole compounds (4-10) analogs to megazol (3).

The aim of the present study was to evaluate whether the genotoxic effect was abolished in the seven synthesised nitroimidazoles (4-10) analogs to 3, as well as to correlate this effect to their in vitro activity in T. cruzi. The in vitro alkaline comet assay (CA) and the in vitro cytokinesis-block micronucleus assay (CBMN) in whole human blood cells (WHBC) were employed as genotoxicity assays. The in vitro CA is a useful, fast screening system in mammalian cells that can be used in a test battery during drug development.2525. Hartmann A, Elhajouji A, Kiskinis E, Poetter F, Martus H-J, Fjällman A, et al. Use of the alkaline comet assay for industrial genotoxicity screening: comparative investigation with the micronucleus test. Food Chem Toxicol. 2001; 39(8): 843-58. doi: 10.1016/S0278-6915(01)00031-X.
https://doi.org/10.1016/S0278-6915(01)00...
It is widely used in basic research in the pharmaceutical and chemical industry2626. Frötschl R. Experiences with the in vivo and the in vitro comet assay in regulatory testing. Mutagenesis. 2015; 30(1): 51-7. doi:10.1093/mutage/geu069.
https://doi.org/10.1093/mutage/geu069...
to investigate genotoxic mechanisms as screening assay but it is not preconised for regulatory purposes.2727. Collins AR. The comet assay: a heavenly method! Mutagenesis. 2015; 30(1): 1-4. doi:10.1093/mutage/geu079.
https://doi.org/10.1093/mutage/geu079...
The single cell gel electrophoresis (SCGE) or the CA measures the migration of DNA from agarose-embedded cells in an electric field; it detects initial DNA lesions as primary single-strand breaks (SSB) and double-strand breaks (DSB), DNA breaks resulting from spontaneous hydrolysis of adducts, and repair intermediates associated with abasic sites and DNA incisions.2828. Singh NP, McCoy MT, Tice RR, Schneider EL. A simple technique for quantitation of low levels of DNA damage in individual cells. Exp Cell Res. 1988; 175(1): 184-91. doi: 10.1016/0014-4827(88)90265-0.
https://doi.org/10.1016/0014-4827(88)902...
The CBMN is the standard genotoxicity test for the detection of clastogenic and aneugenic activities of chemicals and considered as a gold standard test in mutagenesis by the International Workshop on Genotoxicity Test Procedures.2929. Kirsch-Volders M, Sofuni T, Aardema M, Albertini S, Eastmond D, Fenech M, et al. Report from the in vitro micronucleus assay working group. Mutat Res. 2003; 540(2): 153-63. doi: 10.1016/j.mrgentox.2003.07.005.
https://doi.org/10.1016/j.mrgentox.2003....
An OECD guideline (No. 487) for the in vitro mammalian cell micronucleus test has been published.3030. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD Guideline for the testing of chemicals. 487: in vitro mammalian cell micronucleus test. doi: http://dx.doi.org/10.1787/9789264264861-en.
http://dx.doi.org/10.1787/9789264264861-...
Micronucleus (MN) can arise from acentric fragments via chromosome breakage (clastogenicity) or they may be whole chromosomes resulting from aneugenic events. Acentric fragments or whole chromosomes are not included in the main nucleus on cell division and manifest as small MN, almost one-third the size of the main nucleus. Therefore, the presence of MN indicates unrepaired chromosomal damage which is manifested after anaphase.3030. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD Guideline for the testing of chemicals. 487: in vitro mammalian cell micronucleus test. doi: http://dx.doi.org/10.1787/9789264264861-en.
http://dx.doi.org/10.1787/9789264264861-...
Increased MN frequency in lymphocytes is a recognised predictor of cancer risk.3131. Bonassi M, Znaor A, Ceppi M, Lando C, Chang WP, Holland N, et al. An increased micronucleus frequency in peripheral blood lymphocytes predicts the risk of cancer in humans. Carcinogenesis. 2007; 28(3): 625-31. doi: 10.1093/carcin/bgl177.
https://doi.org/10.1093/carcin/bgl177...

MATERIALS AND METHODS

The compounds 5-10 were prepared as previoulsly reported by our group.1919. Boechat N, Carvalho AS, Fernández-Ferreira E, Soares RO, Souza AS, Gibaldi D, et al. Novel nitroimidazoles with trypanocidal and cell growth inhibition activities. Cytobios. 2001; 105(409): 83-90. PMID: 11393774.,2222. Carvalho AS, Menna-Barreto RFS, Romeiro NC, de Castro SL, Boechat N. Design, synthesis and activity against Trypanosoma cruzi of azaheterocyclic analogs of megazol. Med Chem. 2007; 3(5): 460-5. doi: 10.2174/157340607781745519.
https://doi.org/10.2174/1573406077817455...
,3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
,3333. Quaresma BMCS. Síntese e avaliação tripanomicida e mutagênica de novos nitroimidazóis substituídos com diferentes anéis azólicos [Dissertação de mestrado em Ciências Biológicas]. Farmacologia e Química Medicinal. Rio de Janeiro: Universidade Federal do Rio de Janeiro; 2015.

In vitro trypanocidal assay - To accomplishment of the experiments were used bloodstream trypomastigotes form Y strain of T. cruzi, obtained at the peak of the parasitemia (7th day after infection) of infected Swiss albino mice.3434. Silva LHP, Nussenzweig V. Sobre uma cepa de Trypanosoma cruzi altamente virulenta para o camundongo branco. Folia Clín Biol. 1953; 20: 191-208. The trypomastigotes underwent a differential centrifugation process for the separation of erythrocytes, leukocytes and concentration of the parasites in the plasma, and the purified parasites were resuspended in RPMI medium and cell concentration was determined by counting in the Neubauer chamber. Stock solution of each compound was prepared in dimethyl sulfoxide (DMSO), and the assays were performed in Dulbecco’s modified Eagle medium in 96-well plates. In the first well was placed twice the highest desired concentration of each compound, in a final volume of 200 μL, in the following wells were added 100 μL of medium supplemented with 10% foetal bovine serum (FBS) and 2% L-glutamine. Subsequently, 100 μL of parasite suspension (106 trypomastigotes) were added, resulting in a final concentration of 5 x 106 parasites/mL, incubated for 24 h at 37ºC under a 5% CO2 atmosphere and quantified in Neubauer’s chamber by light microscopy. The activity of the derivatives was expressed by the parameter which corresponds to the concentration of the compound that produces 50% lysis of the parasites (IC50). At least four independent experiments were performed and the mean and standard deviation were calculated. Benznidazole (1) was used as a reference drug. The experiments were performed in accordance with the guidelines established by the Oswaldo Cruz Foundation Committee of Ethics for the Use of Animals (L 038/2018).

In vitro treatment and cytotoxicity assay in whole human blood cells (WHBC) - Heparinised WHBC was obtained by venipuncture from healthy young non-smoking volunteers with no known recent exposures to genotoxic chemicals or radiation immediately before the assays. WHBC was treated for 2 h at 37ºC with different concentrations of compounds 3, 5, 8, 10 (149-10,000 µM) or 4, 6, 7, 9 (149-6,400 µM) in 5% (v/v) DMSO (solvent-control) and then used in the assays. The cytotoxicity assay aims to establish the degree of cell viability after treatment with nitroimidazoles to define the ranges concentrations to be tested in the in vitro CA. Cell viability was determined at the end of the treatment using the fluorescein diacetate (FDA)/ethidium bromide (EtBr)-assay, in which viable cells are labelled in green, while dead ones display orange-stained nuclei. WHBC (50 μL) was mixed with an equal volume of the freshly prepared staining solution consisting of 30 μg/mL FDA plus 8 μg/mL EtBr in phosphate-buffered saline (PBS). Samples (50 μL) were spread on a microscope slide and covered with a coverslip and observed using a fluorescence microscope. Two hundred cells were analysed for each treatment.3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
The research project involving the use of human blood samples was approved by the Committee on Ethics in Research with Human Beings - CEP Fiocruz/IOC (CAAE: 41684815.3.0000.5248) under the consolidated opinion of CEP No. 1066061.

In vitro alkaline comet assay (CA) in whole human blood cells (WHBC) - DNA damage in WHBC was evaluated at the end of 2 h-treatment in duplicate with compounds 3 to 10, at the same concentrations indicated above using the in vitro CA. Methyl methane-sulfonate (MMS) (160 μM) (Sigma-Aldrich) was used as a positive control. Aliquots of 5 μL WHBC were mixed with 120 μL of 0.5% low melting-point agarose (LMPA) (Sigma-Aldrich) in PBS at 37ºC and were applied to microscope slides (with frosted ends), previously covered with 1.5% normal melting-point agarose (Sigma-Aldrich). Slides were prepared, lysed (pH 10; 4-5ºC) and processed as described earlier,3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
using a time of alkali denaturation of 20 min and electrophoresis (0.86 V/cm and 300 mA) of 20 min at a pH > 13. After the neutralisation, fixation and staining steps3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
the slides were analysed using a fluorescence microscope at 400 X magnification. Fifty randomly selected cells per slide (200 cells per treatment) stained with EtBr (20 µg/mL) were analysed visually according to tail size into one of four classes of DNA damage: 0 (undamaged, i.e., no visible tail), 1 (slightly damaged), 2 (moderately damaged) and 3 (maximally damaged, i.e, head of comet was very small and most of the DNA in the tail).2424. Boechat N, Carvalho AS, Salomão K, de Castro SL, Araujo-Lima CF, Mello FVC, et al. Studies of genotoxicity and mutagenicity of nitroimidazoles: demystifying this critical relationship with the nitro group. Mem Inst Oswaldo Cruz. 2015; 110(4): 492-99. doi: 10.1590/0074-02760140248.
https://doi.org/10.1590/0074-02760140248...
,3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
The DNA damage was expressed as percentage of cells into four classes and as arbitrary units (AU) according to the formula: AU = (0 x n 0) + (1 x n 1) + (2 x n 2) + (3 x n 3), where n = the number of cells analysed in each class. The total DNA damage score in AU (TAU) for 200 cells can range from 0 TAU (200 undamaged cells) to 600 TAU (all cells maximally damaged). Differences between the mean values of TAU from two and three independent experiments under the same conditions, respectively, for each concentration of compounds 4-8,10 and 3, 9 were tested for significance (p < 0.05) in relation to the solvent-control group using Student’s one-tailed t-test. In addition, the effects of compounds 3-10 on the intercellular distribution of DNA damage were tested for statistical significance using one-way ANOVA followed by a Dunnett’s multiple comparison test to compare each concentration of the compounds.3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
The computer program GraphPad Prism® sixth version was employed in the statistical analysis of the data.

In vitro cytokinesis-block micronucleus assay (CBMN) with whole human blood cells (WHBC) - Heparinised WHBC samples were obtained by venipuncture from volunteers as described above. The CBMN was performed with WHBC cultures following the OECD guideline 487.3030. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD Guideline for the testing of chemicals. 487: in vitro mammalian cell micronucleus test. doi: http://dx.doi.org/10.1787/9789264264861-en.
http://dx.doi.org/10.1787/9789264264861-...
WHBC cultures were set up in 10 mL plastic culture tubes (Nunc, Denmark) by adding 0.5 mL freshly collected blood to 4.5 mL of pre-warmed (37ºC) 1640 RPMI medium (Gibco, USA) supplemented with 20% FBS (Gibco, USA), 102 UI/mL penicillin G potassium, 102 µg/mL streptomycin sulfate, 3% phytohaemagglutinin M (PHA-M: Gibco, USA) and incubated at 37ºC. WHBC cultures were treated for 4 h at 37ºC with different concentrations of compounds 3 to 10 (150-10,000 µM) in 5% (v/v) DMSO (solvent-control) 44 h after the start of the cultures. WHBC cultures exposed to mitomycin C (MMC) (1.0 µg/mL in water) (Bristol, USA) for 2 h or to N-deacetyl-N-methylcolchicine in water (Demecolcine: Sigma-Aldrich) 0.02 µg/mL for 28 h were used as positive control cultures. After the treatment, the WHBC cultures were centrifuged (900 rpm, 10 min) and washed with 5 mL PBS. After another centrifugation, the cell pellets were resuspended in 5 mL fresh complete RPMI medium as described above, but without PHA-M and with 4.5 µg/mL cytochalasin B (CytB) (Sigma-Aldrich) and incubated at 37ºC. CytB has cytokinesis-block activity leading to the formation of binucleate cells. Then, the cultures were harvested at the end of a total culture time of 72 h by centrifugation and treated with 5 mL hypotonic solution (0.56% KCl, 4-6ºC) for 10 min and fixed once for 10 min at room temperature with 5 mL methanol/glacial acetic acid (5:1, -20ºC) mixed with an equal amount of 0.9% NaCl and then fixed three times with methanol/glacial acetic acid (5:1, -20ºC) for 15 min at room temperature. The fixed cell suspension was dropped on a clean glass slide and the slide was air-dried on a heating plate (60ºC). Air-dried slides were stained with 60 µg/mL acridine orange in Sörensen buffer (0.03 M KH2PO4, 0.03 M Na2HPO4) for 3s, then they were embedded in distilled water and covered with a coverslip. MN showing bright green fluorescence were analysed using a fluorescence microscope at 400 X magnification. MN were scored in 2,000 binucleated cells (BNC) for culture and the number of the micronucleate cells (MNC) in 2,000 BNC was determined. Cytotoxicity was measured using the cytokinesis-block proliferation index (CBPI) and the replication index (RI) which were calculated from 500 cells. The CBPI indicates the average number of nuclei per cell, and may be used to calculate cell proliferation. The RI indicates the relative number of cell cycles per cell during the period of exposure to cytoB in treated cultures compared to control cultures and can be used to calculate the % cytostasis. CBPI was calculated according to the formula: CBPI = [(No. mononucleate cells) + (2 x No. binucleate cells) + (3 x No. multinucleate cells)] / N, where N indicates the total number of cells scored. RI (%) was calculated according to the formula:

R I % = ( ( N o . b i n u c l e a t e c e l l s ) + ( 2 x N o . m u l t i n u c l e a t e c e l l s ) ) ÷ ( T o t a l n u m b e r o f c e l l s ) T ( ( N o . b i n u c l e a t e c e l l s ) + ( 2 x N o . m u l t i n u c l e a t e c e l l s ) ) ÷ ( T o t a l n u m b e r o f c e l l s ) C x 100

where T indicates treated cultures and C control cultures

% cytostasis = 100 - RI

Cytotoxicity was evidenced in the occurrence of reduction in CBPI or RI of cultures treated by test substances when compared to control cultures. The measurement of cytotoxicity was used to select the concentrations of the test substance to be analysed for the presence of MN. The maximum concentration used in MN analysis recommended by OECD 487 in the presence of CytB is the one that induces 45 ± 5% reduction of CBPI or RI when compared to the solvent - control.3030. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD Guideline for the testing of chemicals. 487: in vitro mammalian cell micronucleus test. doi: http://dx.doi.org/10.1787/9789264264861-en.
http://dx.doi.org/10.1787/9789264264861-...
However, it was adopted in this work as the maximum concentration in CBMN one that induced a proliferation inhibition not exceeding about 50% established by ICH S2 (R1) for lymphocyte cultures.3535. ICH - International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. Guideline, guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use S2(R1). Approval by the Steering Committee of S2(R1) under Step 4 and recommendation for adoption to the three ICH regulatory bodies (9 November 2011). Available from: http://www.fda.gov/downloads/Drugs/Guidances/ucm074931.pdf.
http://www.fda.gov/downloads/Drugs/Guida...

The chi-square test was performed from a contingency table tabulating the number of BNC with and without MN to test the significance (p < 0,05) of the results of each concentration of compounds 3-10 in relation to the solvent-control culture or of each concentration of positive controls in relation to untreated cultures (control culture). The chi-square test for trend was performed to analyse if the increase of MNC was concentration-related.3030. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD Guideline for the testing of chemicals. 487: in vitro mammalian cell micronucleus test. doi: http://dx.doi.org/10.1787/9789264264861-en.
http://dx.doi.org/10.1787/9789264264861-...

RESULTS

In addition to 3, the trypanocidal activity was tested against trypomastigote forms of T. cruzi (Table I). After 24 h of treatment, the compound 10 showed the highest activity with an IC50 = 5.4 ± 0.6 μM, about eight times higher than 9 (IC50 = 45.3 ± 4.0 μM), 48 times higher than 4 (IC50 256.8 ± 53.0 μM), 65 times higher than 8 (IC50 = 353.7 ± 27.0 μM), at least 93 times higher than 5 (IC50 > 500 μM) and 6 (IC50 > 500 μM) and 370 times higher than 7 (IC50 > 2000 μM) (Table I). Compound 10 showed the highest activity, about two times higher than 3 (IC50 = 9.9 ± 0.8 µM) and compound 1 (IC50 = 8.8 ± 1.1 µM) that is used clinically. Compounds 4-9 were considered inactive molecules based on their IC50 values.2020. Rosselli FP, Albuquerque CN, da Silva ABF. Quantum chemical and statistical study of megazol-derived compounds with trypanocidal activity. Int J Quantum Chem. 2005: 103(5): 738-48. doi: 10.1002/qua.20532.
https://doi.org/10.1002/qua.20532...
Using the FDA/EtBr assay and in vitro CA, it was investigated the cytotoxicity of compounds 3-10 (Table II) and their capacity to induce DNA damage in WHBC (Fig. 3). Compound 8 (149-10,000 µM) was the only nitroimidazole that did not reduce cell viability. The treatment of WHBC with 3, 5 and 10 (range: 149-10,000 µM) and with 4, 6, 7 and 9 (149-6,400 µM) for 2h at 37ºC slightly reduced cell viability (lethality variation range: 1-4%) compared to solvent-control and this effect was not concentration dependent (Table II). All concentrations of the eight compounds studied showed acceptable levels of cytotoxicity, ie, they did not induce values greater than 30% decrease in cell viability when compared to the solvent-control and consequently used in the CA.3636. Henderson L, Wolfreys A, Fedy J, Bouner C, Windebank S. The ability of the comet assay to discriminate between genotoxins and cytotoxins. Mutagenesis. 1998; 13(1): 89-94. PMID: 9491401. The compounds 43232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
and 7 did not cause DNA strand breaks in the range of 149-6,400 µM compared to the solvent-control group (p > 0.1). However, a significant (p < 0.05) genotoxic effect was observed at concentrations higher than to 610 µM for 5, higher than to 977 µM for 3 and 9, higher than to 1,562 µM for 10, and highly significant (p < 0.01) at concentration higher than 4,000 µM (6,400 µM) and significant (p < 0.05) at 10,000 µM for 8. The genotoxic effect was concentration-dependent for these compounds (Fig. 3) and was not associated with cytotoxicity as shown in Table II. And for compound 6 it was showed a significant (p < 0.05) DNA damage only in the highest concentration tested (6,400 µM). The positive control, 160 μM MMS, induced an extremely significant (p < 0.001) genotoxic effect compared to the control group with a TAU mean value of 554.2 ± 9.9.

TABLE I
Effect of the nitroimidazoles (3-10) on trypomastigote forms of Trypanosoma cruzi
TABLE II
Effect of nitroimidazoles on cytotoxicity assay in the human whole blood cells viability

Fig. 3:
DNA damage induction by nitroimidazoles (3-10) in human whole blood cells using the in vitro alkaline comet assay. A: megazol (3) (n = 3); B: compound 4 (n = 2); C: compound 5 (n = 2); D: compound 6 (n = 2); E: compound 7 (n = 2); F: compound 8 (n = 2); G: compound 9 (n =3); H: compound 10 (n = 2). Results are expressed as mean ± standard error mean of total arbitrary units (AU) from two and three independent experiments, respectively for each concentration of compounds 4-8, 10 and 3,9. Only the result of compound 4 has already published (ref. 32). Control corresponds to untreated culture; solvent-control corresponds to 5% dimethyl sulfoxide and positive control to 160 µM methyl methane-sulfonate. For Student’s one-tailed t- test, the asterisks indicate significance at 5% (*) and 1% (**) levels in relation to the solvent-control and 0.1% (***) in relation to the control.

In cells treated with 6,400 or 10,000 µM concentrations of compound 3, significant (p < 0.05) class 1 (22.5 % and 27.5%, respectively) of DNA damage was observed compared to the percentage of 4.2% showed by the solvent-control group. Compound 9 (6,400 µM) induced significant (p < 0.05) class 1 (40.7%) and highly significant (p < 0.01) class 2 (3.7%) damage compared to 9.0% and 0.7%, respectively for solvent-control. Compound 10 (10,000 µM) caused significant (p < 0.05) class 2 (2.5%) and class 3 (10.2%) damage compared to 0.2% and 2.2%, respectively for solvent-control. Compound 6 (6,400 µM) induced a significant increase of percentage of class 1 (10.5%) DNA damage in relation to 4.8% (solvent-control). In contrast, highly significant (p < 0.01) class 3 (87.7%) damage was observed after treatment with MMS (160 µM) compared to 0% for control culture.

Table III summarises the results of the CBMN with WHBC cultures exposed to different concentrations of compounds 3-10 (150-10,000 µM) for 4 h. With the exception of compound 5, the maximum concentrations used in MN analysis for compounds 3, 4, 6-10, that induced in the maximum 50% reduction of CBPI or RI in relation to solvent-control are indicated in the Table III. All concentrations of compound 5 were considered for MN analysis, because at the highest tested concentration (10,000 μM) there was only a 36% reduction of CBPI and 22% of RI below the maximum acceptable value of 50% reduction.3535. ICH - International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. Guideline, guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use S2(R1). Approval by the Steering Committee of S2(R1) under Step 4 and recommendation for adoption to the three ICH regulatory bodies (9 November 2011). Available from: http://www.fda.gov/downloads/Drugs/Guidances/ucm074931.pdf.
http://www.fda.gov/downloads/Drugs/Guida...
The maximum concentration of 4,000 μM was established for compounds 3, 6 and 7; 1,600 μM determined for compounds 4 and 10 and 640 μM for compounds 8 and 9. Compounds 5, 6, 8-10 did not induce a significant increase in MN formation when compared to the solvent-control (p > 0.05 for 8 and 10; p > 0.1 for 5, 6 and 9) in the concentration range analysed. It was concluded that these five compounds did not induce chromosomal breaks and/or gain or loss of chromosomes in WHBC. In contrast, a highly significant mutagenic effect (p < 0.01) was observed at concentrations of 1,600 and 4,000 μM for compound 3, significant (p < 0.05) at 1,600 μM for compound 4 and at 4,000 μM for compound 7. When analysed by the chi-square test for trend, the increase in MN formation was concentration-dependent for compounds 3 (p < 0.001), 4 (p < 0.05) and 7 (p < 0.01). The positive control, MMC (1.0 μg/mL) caused an extremely significant clastogenic effect (p < 0.001) inducing in 2,000 BNC, 38 MNC compared to 13 MNC in the control culture and a significant effect (p < 0.05) with 56 and 40 MNC, respectively, compared at 32 and 20 MNC in the control culture. Demecolcine (0.02 μg/mL) showed a highly significant aneugenic effect (p < 0.01) inducing in 2,000 BNC, 37 and 42 MNC, respectively, compared at 13 and 20 MNC (control) and a significant effect (p < 0.05) with 30 MNC compared to 13 MNC in the control culture.

TABLE III
DNA damage induction by nitroimidazoles (3-10) in human whole blood cells using the in vitro cytokinesis-block micronucleus assay

DISCUSSION

In the present study it was evidenced for compound 3, a DNA strand break effect through the in vitro CA after 2 h treatment at the concentrations of 1,562, 6,400 and 10,000 μM in the WHBC. In the in vitro CA, the highest concentration (10,000 μM) employed corresponds to the maximum concentration to be tested in vitro for relatively non-cytotoxic substances.3737. Tice RR, Agurell E, Anderson D, Burlinson B, Hartmann A, Kobayashi H, et al. Single cell gel comet assay: guidelines for in vitro and in vivo genetic toxicology testing. Environ Mol Mutagen. 2000; 35(3): 206-21. PMID: 10737956. Similar results were obtained by Boechat et al.2424. Boechat N, Carvalho AS, Salomão K, de Castro SL, Araujo-Lima CF, Mello FVC, et al. Studies of genotoxicity and mutagenicity of nitroimidazoles: demystifying this critical relationship with the nitro group. Mem Inst Oswaldo Cruz. 2015; 110(4): 492-99. doi: 10.1590/0074-02760140248.
https://doi.org/10.1590/0074-02760140248...
and Carvalho et al.3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...
who reported a highly significant genotoxic effect for the compound 3 (p < 0.01) on the same test system and experimental conditions for concentrations of 1,562 μM, 2,500 μM and 4,000 μM without reduction of cell viability in the tested range (380-4,000 μM). The in vitro CA performed on Vero cells, lymphocytes and whole blood1616. Poli P, Mello MA, Buschini A, Mortara RA, de Albuquerque CN, da Silva S, et al. Cytotoxic and genotoxic effects of megazol, an anti-Chagas' disease drug, assessed by different short-term tests. Biochem Pharmacol. 2002; 64(11): 1617-27. doi: 10.1016/S0006-2952(02)01390-4.
https://doi.org/10.1016/S0006-2952(02)01...
was highly sensitive in detecting genotoxicity of 3 at concentrations in the range of 8.8 to 35 μM, well below those employed by Nesslany et al.1818. Nesslany F, Brugier S, Mouries MA, Le Curieux F, Marzin D. In vitro and in vivo chromosomal aberrations induced by megazol. Mutat Res. 2004; 560(2): 147-58. doi: 10.1016/j.mrgentox.2004.02.013.
https://doi.org/10.1016/j.mrgentox.2004....
with the same treatment period of 4 h. Poli et al.1616. Poli P, Mello MA, Buschini A, Mortara RA, de Albuquerque CN, da Silva S, et al. Cytotoxic and genotoxic effects of megazol, an anti-Chagas' disease drug, assessed by different short-term tests. Biochem Pharmacol. 2002; 64(11): 1617-27. doi: 10.1016/S0006-2952(02)01390-4.
https://doi.org/10.1016/S0006-2952(02)01...
showed in fresh leucocytes from rats and mice a dose-response relationship of DNA damage induced by 3. Our results showed that 3 induced chromosomal breaks and/or gain or loss of chromosomes in human lymphocytes evidenced by the highly significant increase of MNC at concentrations of 1,600 and 4,000 μM in a concentration dependent manner after treatment period of 4h. The highest concentration of 3 (10,000 μM) was not evaluated for induction of MNs because it caused 63% of CBPI reduction and 62% of RI reduction, higher than the limit of 50% of cytotoxicity recommended for analysis by the ICH S2(R1).3535. ICH - International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. Guideline, guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use S2(R1). Approval by the Steering Committee of S2(R1) under Step 4 and recommendation for adoption to the three ICH regulatory bodies (9 November 2011). Available from: http://www.fda.gov/downloads/Drugs/Guidances/ucm074931.pdf.
http://www.fda.gov/downloads/Drugs/Guida...
Nesslany et al.1818. Nesslany F, Brugier S, Mouries MA, Le Curieux F, Marzin D. In vitro and in vivo chromosomal aberrations induced by megazol. Mutat Res. 2004; 560(2): 147-58. doi: 10.1016/j.mrgentox.2004.02.013.
https://doi.org/10.1016/j.mrgentox.2004....
also reported for 3 provided by Farmanguinhos a high mutagenic activity in the in vitro micronucleus assay in L5178Y mouse lymphoma cells and treatment for 24 h at concentrations of 625 µM and 1,250 µM not associated to cytotoxicity. The compound 3 had its genotoxicity confirmed in other in vitro and in vivo mammalian cell assays. It was a potent inducer of structural chromosome aberrations in vitro in human lymphocytes after 4 h of treatment at the highest concentration possible to be analysed due to cytotoxicity (625 µM); significant increase at the three concentrations (156, 312 and 625 µM) for the treatment of 20 h and at 357 and 625 µM for the 44 h treatment. In the in vivo micronucleus assay in rat bone marrow cells, the two daily doses (two days) given orally (500 and 1,000 mg/kg), with 24 h sampling after the second dose induced a significant increase in frequency of micronucleated polychromatic erythrocytes in male and female Sprague-Dawley rats. Although 3 is a potent trypanomicidal and bioavailable agent when administered orally, its toxicity has led to the discontinuation of its development process for the treatment of Chagas’ disease and sleeping disease.1818. Nesslany F, Brugier S, Mouries MA, Le Curieux F, Marzin D. In vitro and in vivo chromosomal aberrations induced by megazol. Mutat Res. 2004; 560(2): 147-58. doi: 10.1016/j.mrgentox.2004.02.013.
https://doi.org/10.1016/j.mrgentox.2004....
This compound showed high trypanocidal activity in vitro, ie an IC50 = 9.9 ± 0.8 μM for T. cruzi and 0.14 ± 0.01 μM for T. brucei.3232. Carvalho AS, Salomão K, de Castro SL, Conde TR, Zamith HPS, Caffarena ER, et al. 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. Mem Inst Oswaldo Cruz. 2014; 109(3): 315-23. doi: 10.1590/0074-0276140497.
https://doi.org/10.1590/0074-0276140497...

With the exception of compound 3, which showed in the concentrations 1,562, 6,400 and 10,000 μM, DNA strand break inducer effect and in 1,600 and 4,000 μM clastogenic and/or aneugenic effect in WHBC, all compounds analogs to 3 that were positive in the in vitro CA (5,6,8-10) did not induce chromosomal breaks and/or gain or loss of chromosomes.The DNA strand breaks induced by the five analogs (5, 6, 8-10) of 3 in the CA may be repaired, resulting in no persistent effect, and may be lethal to the cell.3838. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD guideline for the testing of chemicals 489: in vivo mammalian alkaline comet assay. doi: http://dx.doi.org/10.1787/9789264264885-en.
http://dx.doi.org/10.1787/9789264264885-...
On the other hand, compounds 43333. Quaresma BMCS. Síntese e avaliação tripanomicida e mutagênica de novos nitroimidazóis substituídos com diferentes anéis azólicos [Dissertação de mestrado em Ciências Biológicas]. Farmacologia e Química Medicinal. Rio de Janeiro: Universidade Federal do Rio de Janeiro; 2015. and 7 that did not induce DNA strand breaks were clastogenic and/or aneugenic in human blood cells, respectively at concentrations of 1,600 and 4,000 μM. Therefore, the clastogenic DNA damage of 4 and 7 was not detected by the in vitro CA.

In relation to compound 6, mutagenicity was reported in the Ames test in TA100 strain of Salmonella typhimurium at the highest tested concentration (50 μg/mL) in the absence and presence of S9 mixture.3939. Mello FVC, Carvalho AS, Bastos MM, Boechat N, Aiub CAF, Felzenszwalb I. Evaluation of genotoxic effects of new molecules with possible trypanocidal activity for Chagas disease treatment. ScientificWorld Journal. 2013; 8 pp. doi: 10.1155/2013/287319. It showed cytotoxic activity in the concentration of 50 μg/mL in TA98 and in the range of 1.0-50 μg/mL in TA100 and TA1535 strains.3939. Mello FVC, Carvalho AS, Bastos MM, Boechat N, Aiub CAF, Felzenszwalb I. Evaluation of genotoxic effects of new molecules with possible trypanocidal activity for Chagas disease treatment. ScientificWorld Journal. 2013; 8 pp. doi: 10.1155/2013/287319. Our results of the CBMN of 6 in WHBC, recommended by OECD (2016)3030. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD Guideline for the testing of chemicals. 487: in vitro mammalian cell micronucleus test. doi: http://dx.doi.org/10.1787/9789264264861-en.
http://dx.doi.org/10.1787/9789264264861-...
differed from those obtained by Mello et al.3939. Mello FVC, Carvalho AS, Bastos MM, Boechat N, Aiub CAF, Felzenszwalb I. Evaluation of genotoxic effects of new molecules with possible trypanocidal activity for Chagas disease treatment. ScientificWorld Journal. 2013; 8 pp. doi: 10.1155/2013/287319. who showed a significant increase of MNC in RAW 264.7 cells at concentrations of 10 and 100 μg/mL when treated for a period six times higher than that used in our study.

In the preclinical evaluation of drug candidates, genotoxicity tests are required by regulatory agencies to evaluate the potential risk of cancer induction. Among these tests the CA especially in vivo, the CBMN and the in vivo micronucleus assay are the most used in the evaluation of the potential risk of cancer induction.4040. Araldi RP, Melo TC, Mendes TB, de Sá Junior PL, Nozima BH, Ito ET, et al. Using the comet and micronucleus assays for genotoxicity studies: a review. Biomed Pharmacother. 2015; 72(May): 74-82. doi: 10.1016/j.biopha.2015.04.004.
https://doi.org/10.1016/j.biopha.2015.04...
According to ANVISA, in agreement with the other internationally recognised regulatory agencies, it is recommended that genotoxicity tests should be completed prior to conducting phase 2 clinical trials.4141. ANVISA - Agência Nacional de Vigilância Sanitária. Guia para condução de estudos não clínicos de toxicologia e segurança farmacológica necessários ao desenvolvimento de medicamentos. Gerência de Avaliação de Segurança e Eficácia. GESEF. Brasília; 2013. Available from: http://portal.anvisa.gov.br.
http://portal.anvisa.gov.br...

The CA allows the investigation of DNA damage in any cell culture or tissue that can be subjected to single cell isolation. Through this technique it is possible to evaluate DNA damage and repair in proliferating and non-proliferating cells at the individual level using extremely small cell samples (5-10 µL). The CA under highly alkaline conditions (pH > 13) during electrophoresis allowed the detection of a broader range of DNA damage.2828. Singh NP, McCoy MT, Tice RR, Schneider EL. A simple technique for quantitation of low levels of DNA damage in individual cells. Exp Cell Res. 1988; 175(1): 184-91. doi: 10.1016/0014-4827(88)90265-0.
https://doi.org/10.1016/0014-4827(88)902...
This includes SSB which may result from direct interaction of the test chemical with DNA or which are related to incomplete excision repair as well as alkali labile sites. As a result, not only clastogenic DNA damage can be detected but also lesions which may give rise to gene mutation.3838. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD guideline for the testing of chemicals 489: in vivo mammalian alkaline comet assay. doi: http://dx.doi.org/10.1787/9789264264885-en.
http://dx.doi.org/10.1787/9789264264885-...

The presence of MN in lymphocytes indicates unrepaired damage, from consequences of chromosome mis-segregation or clastogenic events which is manifested after anaphase.3030. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD Guideline for the testing of chemicals. 487: in vitro mammalian cell micronucleus test. doi: http://dx.doi.org/10.1787/9789264264861-en.
http://dx.doi.org/10.1787/9789264264861-...
Increased MN frequency in lymphocytes is a recognised predictor of cancer risk in humans and indicates pre-cancerous lesions.3131. Bonassi M, Znaor A, Ceppi M, Lando C, Chang WP, Holland N, et al. An increased micronucleus frequency in peripheral blood lymphocytes predicts the risk of cancer in humans. Carcinogenesis. 2007; 28(3): 625-31. doi: 10.1093/carcin/bgl177.
https://doi.org/10.1093/carcin/bgl177...

In the drug evaluation strategy performed, greater relevance should be given to the results obtained in the CBMN than in the in vitro CA because the former is considered the standard genotoxicity test in the guidelines for drug evaluation.3535. ICH - International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. Guideline, guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use S2(R1). Approval by the Steering Committee of S2(R1) under Step 4 and recommendation for adoption to the three ICH regulatory bodies (9 November 2011). Available from: http://www.fda.gov/downloads/Drugs/Guidances/ucm074931.pdf.
http://www.fda.gov/downloads/Drugs/Guida...
,4141. ANVISA - Agência Nacional de Vigilância Sanitária. Guia para condução de estudos não clínicos de toxicologia e segurança farmacológica necessários ao desenvolvimento de medicamentos. Gerência de Avaliação de Segurança e Eficácia. GESEF. Brasília; 2013. Available from: http://portal.anvisa.gov.br.
http://portal.anvisa.gov.br...

It must also be considered that mutagenicity, clastogenicity and aneugenicity are the types of genotoxicity endpoints associated with human disease that should be given the most weight when conducting a human risk assessment. Assays evaluating DNA damage, such as DNA strand breaks in the CA and the measurement of DNA adducts can be useful to determine the presence of DNA damage and can be used to demonstrate an absence of strand breakage and therefore reduced potential to induce heritable alterations. However, their utility for quantitative evaluations is limited because the extent to which DNA damage may be repaired before conversion to a permanent genetic alteration is difficult to ascertain. DNA strand breaks occur during DNA repair and during apoptosis and before necrosis, and so strand breakage may not always be related directly to the formation of mutations or chromosomal aberrations.4242. Mac Gregor JT, Frötschl R, White PA, Crump KS, Eastmond DA, Fukushima S, et al. IWGT report on quantitative approaches to genotoxicity risk assessment II. Use of point-of-departure (PoD) metrics in de?ning acceptable exposure limits and assessing human risk. Mutat Res Genet Toxicol Environ Mutagen. 2015; 783(May): 66-78. doi: 10.1016/j.mrgentox.2014.10.008.
https://doi.org/10.1016/j.mrgentox.2014....

Among the negative substances in the CBMN (5, 6, 8-10), substance 10 was the most promising to proceed with the development as a drug candidate in the treatment of Chagas disease. In addition to the absence of a cytogenetic damage effect inducing chromosomal breaks and / or gain or loss of chromosomes in human blood cells, substance 10 showed high trypanomicidal activity for T. cruzi (IC50 = 5.4 ± 0.6 μM), about two times higher than 3 (IC50 = 9.9 ± 0.8 μM)2323. Carvalho SA, Silva EF, Santa-Rita RM, de Castro SL, Fraga CAM. Synthesis and antitrypanosomal profile of new functionalized 1,3,4-thiadiazole-2-arylhydrazone derivatives, designed as non-mutagenic megazol analogues. Bioorg Med Chem Lett. 2004; 14(24): 5967-70. doi: 10.1016/j.bmcl.2004.10.007.
https://doi.org/10.1016/j.bmcl.2004.10.0...
and 1 (IC50 = 8.8 ± 1.1 μM) used clinically. Substitution bioisosteric of 1,3,4-thiadiazole ring of 3 by lipophilic group linked to azole C-4 and the change from the 5-position nitro group to the 4-position of the imidazole ring in 10 abolished the undesirable mutagenic effect of prototype 399. Bouteille B, Marie-Daragon A, Chauvière G, Albuquerque C, Enanga B, Dardé ML, et al. Effect of megazol on Trypanosoma brucei brucei acute and subacute infections in Swiss mice. Acta Tropica. 1995; 60(2): 73-80. doi: 10.1016/0001-706X(95)00109-R.
https://doi.org/10.1016/0001-706X(95)001...
and as a consequence decreasing its effects on the carcinogenicity.1818. Nesslany F, Brugier S, Mouries MA, Le Curieux F, Marzin D. In vitro and in vivo chromosomal aberrations induced by megazol. Mutat Res. 2004; 560(2): 147-58. doi: 10.1016/j.mrgentox.2004.02.013.
https://doi.org/10.1016/j.mrgentox.2004....

As a follow-up test to evaluate metabolism, pharmacokinetics, and DNA repair of compound 10, the in vivo micronucleus assay for the detection of chromosome damage is recommended and performed in immature (polychromatic) bone marrow erythrocytes of mice or rats.3535. ICH - International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. Guideline, guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use S2(R1). Approval by the Steering Committee of S2(R1) under Step 4 and recommendation for adoption to the three ICH regulatory bodies (9 November 2011). Available from: http://www.fda.gov/downloads/Drugs/Guidances/ucm074931.pdf.
http://www.fda.gov/downloads/Drugs/Guida...
,4141. ANVISA - Agência Nacional de Vigilância Sanitária. Guia para condução de estudos não clínicos de toxicologia e segurança farmacológica necessários ao desenvolvimento de medicamentos. Gerência de Avaliação de Segurança e Eficácia. GESEF. Brasília; 2013. Available from: http://portal.anvisa.gov.br.
http://portal.anvisa.gov.br...
And as a second in vivo genotoxicity assay to evaluate DNA strand breaks is recommended the in vivo CA especially in liver or stomach cells of rodents after oral exposure to compound 10.3535. ICH - International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. Guideline, guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use S2(R1). Approval by the Steering Committee of S2(R1) under Step 4 and recommendation for adoption to the three ICH regulatory bodies (9 November 2011). Available from: http://www.fda.gov/downloads/Drugs/Guidances/ucm074931.pdf.
http://www.fda.gov/downloads/Drugs/Guida...
,3838. OECD - Organisation for Economic Cooperation and Development (Adopted: 29 July 2016). OECD guideline for the testing of chemicals 489: in vivo mammalian alkaline comet assay. doi: http://dx.doi.org/10.1787/9789264264885-en.
http://dx.doi.org/10.1787/9789264264885-...
The use of both assays allows also evaluating the systemic or in situ genotoxicity.4040. Araldi RP, Melo TC, Mendes TB, de Sá Junior PL, Nozima BH, Ito ET, et al. Using the comet and micronucleus assays for genotoxicity studies: a review. Biomed Pharmacother. 2015; 72(May): 74-82. doi: 10.1016/j.biopha.2015.04.004.
https://doi.org/10.1016/j.biopha.2015.04...

ACKNOWLEDGEMENTS

To Dr Daniel Zamith-Miranda for the help with the graphics.

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    » https://doi.org/10.1016/j.biopha.2015.04.004
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    ANVISA - Agência Nacional de Vigilância Sanitária. Guia para condução de estudos não clínicos de toxicologia e segurança farmacológica necessários ao desenvolvimento de medicamentos. Gerência de Avaliação de Segurança e Eficácia. GESEF. Brasília; 2013. Available from: http://portal.anvisa.gov.br
    » http://portal.anvisa.gov.br
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    Mac Gregor JT, Frötschl R, White PA, Crump KS, Eastmond DA, Fukushima S, et al. IWGT report on quantitative approaches to genotoxicity risk assessment II. Use of point-of-departure (PoD) metrics in de?ning acceptable exposure limits and assessing human risk. Mutat Res Genet Toxicol Environ Mutagen. 2015; 783(May): 66-78. doi: 10.1016/j.mrgentox.2014.10.008.
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  • Financial support: This study was financed in part by CAPES (Finance Code 001), CNPq, FAPERJ and FIOCRUZ.

Publication Dates

  • Publication in this collection
    27 June 2019
  • Date of issue
    2019

History

  • Received
    16 Jan 2019
  • Accepted
    28 May 2019
Instituto Oswaldo Cruz, Ministério da Saúde Av. Brasil, 4365 - Pavilhão Mourisco, Manguinhos, 21040-900 Rio de Janeiro RJ Brazil, Tel.: (55 21) 2562-1222, Fax: (55 21) 2562 1220 - Rio de Janeiro - RJ - Brazil
E-mail: memorias@fiocruz.br