Bioinformatic analysis predicted 18 potential M. tuberculosis targets that are expected to interact with 23 approved drugs. These drugs are expected to target several proteins involved in energy metabolism and membrane transport in M. tuberculosis. Most of the identified drugs are approved for a variety of indications, such as arrhythmia, epilepsy, chronic immune thrombocytopenia, and cancer and may serve as lead compounds for the development of new anti-TB drugs. The identified drugs were: bedaquiline (anti-TB drug - proof of concept), doxorubicin, fostamatinib, thiabendazole, valproic acid, ouabain, metformin, omeprazole, pantoprazole, acetyldigitoxin, bretylium, deslanoside, dexlansoprazole, enasidenib, esomeprazole, ethacrynic acid, fomepizole, halothane, isoflurane, ivosidenib, levoleucovorin, rabeprazole and tipiracil.
A group of selected drugs (deslanoside, doxorubicin, fostamatinib, thiabendazole and valproic acid) were sequentially evaluated using an algorithm consisting of different in vitro methodologies, in order to identify the most promising drugs with potential application against mycobacteria. Doxorubicin showed the most effective antimycobacterial activity with a minimum inhibitory concentration (MIC) < 20 µM. However, the confirmation of the predicted target of doxorubicin in M. tuberculosis through the selection of resistant mutants in the presence of the compound was inconclusive. The other four compounds showed a MIC ≥ 20 µM. The most promising was valproic acid that showed synergistic interactions with the antibiotic clarithromycin. However, even if a given drug proved itself to be promising after these studies, the issue of toxicity had to be addressed. Therefore, evaluation of drug cytotoxicity was carried out in human macrophages. Some compounds presented cytotoxicity at the MIC, in particular doxorubicin and deslanoside. The results obtained during this project generated one peer reviewed publication and were presented in several congresses and conferences. Moreover, this work will bring the opportunity to develop future projects and collaborations that will further explore these drugs as lead compounds for the development and optimization of new effective drugs.