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.

An effective axenic culture system for Trypanosoma brucei rhodesiense blood stream forms in vitro.

An effective axenic culture system for Trypanosoma brucei rhodesiense (ILRAD 1501) bloodstream forms is demonstrated. Bloodstream forms were continuously grown in 25 mM HEPES-buffered D-MEM supplemented with 10 microM bathocuproine sulfonate (BCS), 100 microM cysteine, and 20% heat-inactivated fetal bovine serum at 37 degrees C in vitro. At the initiation of the culture, T. b. rhodesiense bloodstream forms required the presence of 0.2 IU/ml insulin and 1 mM pyruvate, while bloodstream forms were grown in the culture medium without these supplements 4 days after initiation of the culture. Under this culture condition, T. b. rhodesiense bloodstream forms increased in number to 7 to 8 x 10(6) trypanosomes/ml, by day 4 after initiation of the culture. The trypanosomes cultured in this axenic system for 150 days were typically long and slender and retained their virulence for mice. This axenic culture system is extremely useful for in vitro cloning of T. b. rhodesiense bloodstream forms in vitro.