Determining the minimum inhibitory concentration of the novel drug candidates of Mycobacterium tuberculosis, GPK91 and GPK96, that target fatty acid enoyl-acyl carrier protein reductase and ß-ketoacyl-acyl carrier protein synthase

Abstract

Background: The cell wall of Mycobacterium tuberculosis (M. tuberculosis) consists of mycolic acids that protect the organism from macrophage phagocytosis. The study aimed to determine the minimum inhibitory concentration (MIC) of GPK91 and GPK96 using Mycobacterium smegmatis (M. smegmatis) as a surrogate for the M. tuberculosis H37Rv strain. Fatty acid enoyl-acyl carrier protein reductase (InhA) and ß-ketoacyl-acyl carrier protein synthase (KasA) are the primary targets of action for isoniazid (INH) and thiolactomycin (TLM) in M. tuberculosis. After designing seven drug compounds that target the InhA and KasA proteins responsible for synthesising M. tuberculosis mycolic acid cell walls, we selected the two compounds with the highest binding energy to the amino acid residue binding sites.
Method: Serial concentrations of GPK91 and GPK96 ranging from 25.0 µg/ml to 0.049 µg/ml were allowed to set on Mueller–Hinton agar (MHA) plates 1–5 inoculated with M. smegmatis on areas 1–4, 5–8, 9–12, 13–16, and 17–20. TLM (25.0 µg/ml), a known antimicrobial, was applied on area 21 of plate MHA_6. Escherichia coli (E. coli) was used as a positive control, while uninoculated areas on all MHA plates served as a negative control. The MIC is designated when a 99.9% reduction in colony-forming units (CFU) is observed at a specific compound concentration compared with the control.
Results: The MIC of GPK91 and GPK96 for M. smegmatis were determined at 0.781 µg/ml and 3.125 µg/ml, respectively.
Conclusion: Both compounds induced inhibition at low concentrations and are recommended good candidates for novel antimicrobial drugs for clinical pre-screening.