Design and Synthesis of the Linezolid Bioisosteres to Resolve the Serotonergic Toxicity Associated with Linezolid.

Serotonergic toxicity due to MAO enzyme inhibition is a significant concern when using linezolid to treat MDR-TB. To address this issue, we designed linezolid bioisosteres with a modified acetamidomethyl side chain at the C-5 position of the oxazolidine ring to balance activity and reduce toxicity. Among these bioisosteres, R7 emerged as a promising candidate, demonstrating greater effectiveness against M. tuberculosis (Mtb) H37Rv cells with an MIC of 2.01 µM compared to linezolid (MIC = 2.31 µM). Bioisostere R7 also exhibited remarkable activity (MIC50) against drug-resistant Mtb clinical isolates, with values of 0.14 µM (INHR, inhA+), 0.53 µM (INHR, katG+), 0.24 µM (RIFR, rpoB+), and 0.92 µM (INHR INHR, MDR). Importantly, it was >6.52 times less toxic as compared to the linezolid toward the MAO-A and >64 times toward the MAO-B enzyme, signifying a substantial improvement in its drug safety profile.

Bioisosteric modification of Linezolid identified the potential M. tuberculosis protein synthesis inhibitors to overcome the myelosuppression and serotonergic toxicity associated with Linezolid in the treatment of the multi-drug resistance tuberculosis (MDR-TB).

Linezolid is the first and only oxazolidinone antibacterial drug was approved in the last 35 years. It exhibits bacteriostatic efficacy against M. tuberculosis and is a crucial constituent of the BPaL regimen (Bedaquiline, Pretomanid, and Linezolid), which was authorized by the FDA in 2019 for the treatment of XDR-TB or MDR-TB. Despite its unique mechanism of action, Linezolid carries a considerable risk of toxicity, including myelosuppression and serotonin syndrome (SS), which is caused by inhibition of mitochondrial protein synthesis (MPS) and monoamine oxidase (MAO), respectively. Based on the structure toxicity relationship (STR) of Linezolid, in this work, we used a bioisosteric replacement approach to optimize the structure of Linezolid at the C-ring and/or C-5 position for myelosuppression and serotogenic toxicity. Extensive hierarchical multistep docking, drug likeness prediction, molecular binding interactions analyses, and toxicity assessment identified three promising compounds (3071, 7549 and 9660) as less toxic potential modulators of Mtb EthR protein. Compounds 3071, 7549 and 9660 were having the significant docking score of -12.696 Kcal/mol, -12.681 Kcal/mol and -15.293 Kcal/mol towards the Mtb EthR protein with less MAO-A and B affinity [compound 3071: MAO A (-4.799 Kcal/mol) and MAO B (-6.552 Kcal/mol); compound 7549: MAO A (> -2.00 Kcal/mol) and MAO B (> -2.00 Kcal/mol) and compound 9660: MAO A (> -5.678 Kcal/mol) and MAO B (> -6.537Kcal/mol) and none of them shown the Leukopenia as a side effect due to the Myelosuppression. The MD simulation results and binding free energy estimations correspond well with docking analyses, indicating that the proposed compounds bind and inhibit the EthR protein more effectively than Linezolid. The quantum mechanical and electrical characteristics were evaluated using density functional theory (DFT), which also demonstrated that the proposed compounds are more reactive than Linezolid.Communicated by Ramaswamy H. Sarma.

Repurposing Azoles to Resolve Serotogenic Toxicity Associated with Linezolid to Combat Multidrug-Resistant Tuberculosis.

Serotogenic toxicity is a major hurdle associated with Linezolid in the treatment of drug-resistant tuberculosis (TB) due to the inhibition of monoamine oxidase (MAO) enzymes. Azole compounds demonstrate structural similarities to the recognized anti-TB drug Linezolid, making them intriguing candidates for repurposing. Therefore, we have repurposed azoles (Posaconazole, Itraconazole, Miconazole, and Clotrimazole) for the treatment of drug-resistant TB with the anticipation of their selectivity in sparing the MAO enzyme. The results of repurposing revealed that Clotrimazole showed equipotent activity against the Mycobacterium tuberculosis (Mtb) H37Rv strain compared to Linezolid, with a minimal inhibitory concentration (MIC) of 2.26 µM. Additionally, Clotrimazole exhibited reasonable MIC50 values of 0.17 µM, 1.72 µM, 1.53 µM, and 5.07 µM against the inhA promoter+, katG+, rpoB+, and MDR clinical Mtb isolates, respectively, compared to Linezolid. Clotrimazole also exhibited 3.90-fold less inhibition of MAO-A and 50.35-fold less inhibition of MAO-B compared to Linezolid, suggesting a reduced serotonergic toxicity burden.

Synthesis, Molecular Modeling Study, and Quantum-Chemical-Based Investigations of Isoindoline-1,3-diones as Antimycobacterial Agents.

The condensation of phthalic anhydride afforded structurally modified isoindoline-1,3-dione derivatives with selected amino-containing compounds. The title compounds (2-30) have been characterized by thin-layer chromatography (TLC), infrared spectroscopy, 1H and 13C NMR spectroscopy, and mass spectroscopy. All of the compounds were assessed for their antimycobacterial activity toward the H37Rv strain by a dual read-out assay method. Among the synthesized compounds, compound 27 possessed a significant IC50 of 18 µM, making it the most potent compound of the series. The InhA inhibitory (IC50) activity of compound 27 was 8.65 µM in comparison to Triclosan (1.32 µM). Computational studies like density functional theory (DFT) study, molecular docking, and dynamic simulation studies illustrated the reactivity and stability of the synthesized compounds as InhA inhibitors. A quantum-mechanics-based DFT study was carried out to investigate the molecular and electronic properties, reactivities, and nature of bonding present in the synthesized compounds and theoretical vibrational (IR) and isotropic value (1H and 13C NMR) calculations.

Optimizing Bedaquiline for cardiotoxicity by structure based virtual screening, DFT analysis and molecular dynamic simulation studies to identify selective MDR-TB inhibitors.

Since the last 4 decades, Bedaquiline has been the first drug discovered as a new kind of anti-tubercular agent and received FDA approval in December 2012 to treat pulmonary multi-drug resistance tuberculosis (MDR-TB). It demonstrates excellent efficacy against MDR-TB by effectively inhibiting mycobacterial ATP synthase. In addition to these apparent assets of Bedaquiline, potential disadvantages of Bedaquiline include inhibition of the hERG (human Ether-à-go-related gene; KCNH2), potassium channel (concurrent risk of cardiac toxicity), and risk of phospholipidosis due to its more lipophilic nature. To assist the effective treatment of MDR-TB, highly active Bedaquiline analogs that display a better safety profile are urgently needed. A structure-based virtual screening approach was used to address the toxicity problems associated with Bedaquiline. Among the virtually screened compound, CID 15947587 had significant docking affinity (- 5.636 kcal/mol) and highest binding free energy (ΔG bind - 85.2703 kcal/mol) towards the Mycobacterial ATP synthase enzyme with insignificant cardiotoxicity and lipophilicity. During MD simulation studies (50 ns), the molecule optimizes its conformation to fit better the active receptor site justifying the binding affinity. The obtained results showed that CID15947587 could be a useful template for further optimizing the MDR-TB inhibitor. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40203-021-00086-x.