Structure-Based Optimization of Coumestan Derivatives as Polyketide Synthase 13-Thioesterase(Pks13-TE) Inhibitors with Improved hERG Profiles for Mycobacterium tuberculosis Treatment

Abstract

Pks13 was identified as a key enzyme involved in the final step of mycolic acid biosynthesis. We previously identified antitubercular coumestans that targeted Pks13-TE, and these compounds exhibited high potency both in vitro and in vivo. However, lead compound 8 presented potential safety concerns because it inhibits the hERG potassium channel in electrophysiology patch-clamp assays (IC50 = 0.52 μM). By comparing the Pks13-TE-compound 8 complex and the ligand-binding pocket of the hERG ion channel, fluoro-substituted and oxazine-containing coumestans were designed and synthesized. Fluoro-substituted compound 23 and oxazine-containing coumestan 32 showed excellent antitubercular activity against both drug-susceptible and drug-resistant Mtb strains (MIC = 0.0039–0.0078 μg/mL) and exhibited limited hERG inhibition (IC50 ≥ 25 μM). Moreover, 32 exhibited improved metabolic stability relative to parent compound 8 while showing favorable bioavailability in mouse models via serum inhibition titration assays.

2B Determined: The Future of the Serotonin Receptor 2B in Drug Discovery

“…In addition to 5-HT 2A and other GPCRs, the current list of biological targets deemed “anti” is broad and includes kinases, ion channels, cytochrome P450s, and efflux pumps . Perhaps the most well-known and frequently encountered antitarget in the drug discovery literature is the human Ether-à-go-go-Related Gene, or the hERG channel. − hERG is a potassium ion channel expressed in cardiac tissue, and it plays a critical role in the regulation of the heart’s electrical activity . Specifically, disruption of hERG is associated with the development of potentially fatal Long QT Syndrome (LQTS), an unnatural lengthening of the QT cardiac repolarization interval …”

Identification and Optimization of Novel Inhibitors of the Polyketide Synthase 13 Thioesterase Domain with Antitubercular Activity

“…Optimization of the oxadiazole hit focused on improving potency and metabolic stability. As seen for other Pks13 TE inhibitors, ,, small changes in the chemical structure that had or would be expected to have minimal impact on enzyme inhibition, reduced or lost MIC potency. The reason for this disparity was not clear.…”

Inhibitors of the Thioesterase Activity of Mycobacterium tuberculosis Pks13 Discovered Using DNA-Encoded Chemical Library Screening

“…Unfortunately, the TAM16 series showed hERG cardiotoxicity stemming from its apolar nature and a primary amine required for potent activity. There has been much effort on finding new inhibitors to this very impactful target. − ,,, However, a challenging activity assay for Pks13-TE has hindered the discovery of new inhibitors using HTS. For example, a recent traditional HTS of Pks13-TE of 150,000 compounds produced only two confirmed hits and only one of them with a novel scaffold, thus underscoring the need to turn to larger more highly diverse compound libraries and alternative screening approaches, both provided by DEL screening.…”

“…Data points were plotted as an average of duplicates and analyzed using Prism software (GraphPad) to determine the kinetic parameters K m , V max , and k cat . The experiment was repeated in 20 Separate tubes were prepared to interrogate different DEL screening conditions, including a no-target control (NTC) lacking protein, His-Pks13-TE at three concentrations (10, 2, and 0.5 μM), and two concentrations of His-Pks13-TE (10 and 2 μM) preincubated with 50 μM of a known ligand (TAM16) for 45 min prior to library addition (conditions summarized in Table 1). 50 pmol of each library was added to each condition, and the library mixture was allowed to incubate for 1 h with each mixture.…”