Terconazole, a synthetic triazole derivative structurally related to fluconazole, is an antifungal medication primarily used to treat vaginal fungal infections which also acts inhibiting de novo sterol biosynthesis through CYP51.

Effect of terconazole on epimastigotes

First, the effect of terconazole was evaluated on epimastigotes, the insect stage of T. cruzi, of the Y strain (DTU II). Epimastigotes were treated with the drug in concentrations between 0 and 100 μM and the trypanocidal effect was determined 48 h post treatment. The calculated IC50 (the concentration that kills 50% of the parasites) was 25.73 μM (±1.27). The reference drug, benznidazole, exhibited similar activity against this strain with an IC50 of 22.01 μM (±2.77). Considering that the DTU I is the most relevant DTU, in terms of geographical distribution, in South America, epimastigotes of the Dm28c strain were also tested. Similar results were obtained for terconazole with an IC50 value of 21.94 μM (±1.53), suggesting that terconazole is effective regardless of the DTU. On the contrary, the calculated IC50 for benznidazole was 1.8-fold higher for Dm28c epimastigotes, with a value of 38.55 μM (±1.76).

Effect of terconazole on trypomastigotes and amastigotes

Terconazole activity was also evaluated against the mammalian life-stages of T. cruzi and the IC50 (concentration that decrease the viability of parasites in a 50%) were calculated 24 h post treatment. The drug presented trypanocidal activity against both parasitic forms, trypomastigotes and amastigotes, with calculated IC50 values of 4.56 μM (±0.32) and 5.96 μM (±0.35), respectively. Interestingly, these results demonstrate that trypomastigotes and amastigotes are 5.6 and 4.3-fold more susceptible to terconazole treatment than the epimastigote stage, respectively. Moreover, terconazole was found to be more effective than the control drug benznidazole against trypomastigotes and amastigotes. The calculated IC50 values of benznidazole were 12.71 μM (±1.53) for trypomastigotes and 11.4 μM (±0.5) for amastigotes.

Predicted mechanism of action of terconazole

Figure 1. In silico predictions of the mechanism of action of terconazole.

In order to predict if terconazole has similar properties to those experimentally determined for fluconazole, the common chemical reactive groups and the binding parameters to the protein CYP51 were calculated. To identify the common chemical features (groups that can participate in chemical interactions with a macromolecule) between terconazole and fluconazole the LigandScout algorithm was used. Feature-based structure alignments were performed and the similarities were calculated as the number of matched feature pairs (MFP; i.e. aromatic ring, hydrophobic area, hydrogen bond donor or acceptor, negative or positive ionizable atom and metal binding location). For these comparisons the 14 features of fluconazole were set as references and results showed that terconazole share all of them including 5 hydrogen bond acceptors, 1 hydrogen bond donor, 3 aromatic rings, 4 hydrophobic interactions and 1 positive ionizable group. Alignment results are schematized in the figure above.

Reference

[1] Repurposing of terconazole as an anti Trypanosoma cruzi agent. doi: 10.1016/j.heliyon.2019.e01947