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Tetracyclines are among the most widely used antibiotics to treat respiratory tract infections, sexually transmitted diseases, and urinary tract infections. Tetracyclines are also used as growth promoters in livestock production. However, bacteria are becoming resistant to tetracycline antibiotics by producing an enzyme called Tet(X). This enzyme breaks down tetracycline antibiotics, rendering them ineffective against bacteria.
One effective strategy to restore the activity of the antibiotic is to use a combination therapy to counter bacterial resistance mechanisms. An antibiotic combination treatment includes an antibiotic and an inhibitor. The inhibitor prevents bacterial enzymes such as Tet(X) from breaking down the antibiotic before it has its desired effect to treat the infection.
Scientists at the IOI have developed a fluorescent tetracycline probe that can bind to Tet(X). When the probe binds to the enzyme, a change in the fluorescent light emitted by the probe can be measured. Molecules that act as an inhibitor for Tet(X) cause the probe to become displaced from the enzyme, which alters the fluorescent signal. By measuring changes in fluorescence, researchers can screen high volumes of compounds to quickly and reliably identify those that show promising inhibitory activity against Tet(X).
Using this new experiment, the team screened thousands of existing drugs and identified six promising Tet(X) inhibitors, including molecules already used as antipsychotics, antimalarials, and gut motility drugs. The antipsychotic trifluoperazine, its chemical cousin prochlorperazine, and the serotonin receptor agonist tegaserod were found to bind inside Tet(X)’s active site by X-ray crystallography. The crystallography allowed the researchers to look at the three-dimensional structure of Tet(X) with the inhibitors bound to understand how they block the enzyme from destroying tetracyclines. This can provide a basis from which to design new inhibitors.