New Hope for the Treatment of Non-Tuberculous Mycobacterial Diseases—Research on Acetohydroxyacid Synthase Inhibitors

Academic Background

Non-tuberculous mycobacteria (NTM) infections have become an important cause of pulmonary diseases worldwide in recent years, especially among immunocompromised populations. The treatment of NTM infections faces numerous challenges, including antibiotic resistance, long treatment cycles, and drug side effects. Currently, clarithromycin (Clr) is the main drug for treating NTM infections, but the issue of drug resistance is becoming increasingly severe, necessitating the development of new therapeutic drugs.

Acetohydroxyacid synthase (AHAS) is an enzyme unique to microorganisms and plants, involved in the biosynthesis pathway of branched-chain amino acids. Due to its unique biological function, AHAS has become a potential target for the development of new antimicrobial drugs. Previous studies have shown that the AHAS inhibitor K13787 has a certain inhibitory effect on Mycobacterium tuberculosis (M. tuberculosis) and NTM, but its efficacy is insufficient to address the complexity of NTM infections. Therefore, this study aims to develop more potent AHAS inhibitors through structural modification of K13787 to address the challenges in treating NTM infections.

Source of the Paper

This paper was jointly completed by a research team from Chungnam National University and the Korea Research Institute of Chemical Technology. The main authors include Tam Doan Nguyen, Ji-Ae Choi, Hee-Jong Lim, and others. The paper was accepted for publication in The Journal of Antibiotics on December 2, 2024.

Research Process and Results

1. Research Process

a) Synthesis and Screening of AHAS Inhibitors

The research team first synthesized various structural derivatives of K13787 through molecular docking studies. These derivatives were modified based on the pyrazolopyrimidine sulfonamide backbone. The team used the crystal structure of Candida albicans AHAS as a model for molecular docking analysis to optimize compound design.

b) Determination of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC)

The research team conducted in vitro antibacterial activity tests on the synthesized compounds, determining their MIC and MBC against various NTM strains, including M. avium and M. abscessus. The experimental results showed that K13787 and its derivatives, KNT2077 and KNT2099, exhibited significant inhibitory effects on NTM strains, especially those resistant to clarithromycin.

c) Intracellular Survival Analysis

To evaluate the antibacterial effects of these compounds within cells, the research team conducted infection experiments using mouse bone marrow-derived macrophages (BMDMs). The results showed that K13787, KNT2077, and KNT2099 significantly inhibited the intracellular survival of M. avium and M. abscessus.

d) Synergistic Effect Study

The research team further evaluated the synergistic effects of these compounds with clarithromycin. Using the checkerboard method to determine the fractional inhibitory concentration (FIC), it was found that K13787, KNT2077, and KNT2099 exhibited significant synergistic effects (FIC ≤ 0.5) when combined with clarithromycin against M. avium and M. abscessus.

2. Main Results

a) Antibacterial Activity of AHAS Inhibitors

K13787 and its derivatives, KNT2077 and KNT2099, exhibited significant antibacterial activity against various NTM strains. Notably, KNT2099 showed strong antibacterial effects, with MIC values of 0.98 µg/mL and 7.81 µg/mL against M. avium and M. abscessus, respectively.

b) Intracellular Antibacterial Effects

In macrophage infection experiments, K13787, KNT2077, and KNT2099 significantly inhibited the intracellular survival of M. avium and M. abscessus without showing significant cytotoxicity.

c) Synergistic Effects

K13787, KNT2077, and KNT2099 exhibited significant synergistic effects when combined with clarithromycin against M. avium and M. abscessus. Particularly, the combination of K13787 and clarithromycin showed a strong synergistic effect against M. abscessus, with an FIC index of 0.18.

3. Conclusions and Significance

This study developed a series of novel AHAS inhibitors through structural modification of K13787. These compounds exhibited significant antibacterial activity against NTM strains, especially those resistant to clarithromycin. Additionally, these compounds showed significant synergistic effects when combined with clarithromycin, providing new insights for the treatment of NTM infections.

4. Research Highlights

• Development of Novel AHAS Inhibitors: Through structural modification of K13787, the research team successfully developed novel AHAS inhibitors with potent antibacterial activity.
• Discovery of Synergistic Effects: K13787 and its derivatives exhibited significant synergistic effects when combined with clarithromycin, offering a new strategy for treating NTM infections.
• Intracellular Antibacterial Effects: These compounds demonstrated significant antibacterial effects within macrophages, indicating their potential clinical application value.

Other Valuable Information

This study also found that K13787 and its derivatives exhibited significant antibacterial activity against clarithromycin-resistant NTM strains, providing new hope for addressing the issue of drug resistance in NTM infections. Additionally, the research team preliminarily explored the mechanism of action of these compounds, suggesting that they may inhibit NTM growth by limiting DNA synthesis.

Summary

This study provides new drug candidates for the treatment of NTM infections through the development of novel AHAS inhibitors. These compounds not only exhibit potent antibacterial activity but also produce synergistic effects with the existing drug clarithromycin, offering new approaches to addressing drug resistance in NTM infections. Future research will explore the clinical application potential of these compounds, potentially bringing new breakthroughs in the treatment of NTM infections.