Nitazoxanide Analogs: Synthesis, In Vitro Giardicidal Activity, and Effects on Giardia lamblia Metabolic Gene Expression

Giardiasis is a common intestinal infection caused by <i>Giardia lamblia</i>. The standard treatment for this parasitic infection involves the administration of nitroimidazoles, albendazoles, and nitrothiazoles. However, in recent years, <i>Giardia lamblia</i> strains resistant to these treatments have been reported. Additionally, the current therapies exhibit considerable side effects, highlighting the need for new compounds that specifically target this parasite. The aim of this study was to evaluate nitrothiazole analogs and assess their impact on the metabolic, redox, and structural gene expression of this parasite. First, the compounds CNZ-7, CNZ-8, FLP-2, FLP-6, and FLP-8 were tested at concentrations ranging from 0 to 50 µM to determine their IC₅₀ in <i>G. lamblia</i> cultures. Subsequently, gene expression changes and structural cell damage in trophozoites were analyzed following incubation with the IC₅₀ of each compound. The giardicidal activity of the compounds was also evaluated in a nitazoxanide-resistant strain. The results showed that FLP-2, FLP-6, and FLP-8 exhibited a stronger effect on trophozoite viability compared to nitazoxanide (NTZ) and metronidazole (MTZ). Both compounds induced an increase in the expression of phosphofructokinase (<i>PFK)</i>, glyceraldehyde-3-phosphate dehydrogenase <i>(GAPDH)</i>, pyruvate kinase <i>(PK)</i>, pyruvate phosphate dikinase <i>(PPDK)</i>, and pyruvate:ferredoxin oxidoreductase (<i>PFOR)</i>. Additionally, FLP-2 caused ultrastructural alterations in trophozoites. Furthermore, FLP-2, FLP-6, and FLP-8 demonstrated efficacy against drug-resistant strains. These findings suggest that FLP-2, FLP-6, and FLP-8 are promising candidates for the treatment of giardiasis, as they effectively reduce parasite viability, modify gene expression, and exhibit activity against drug-resistant <i>G. lamblia</i> strains.