Membrane acting Povarov-Doebner derived compounds potently disperse preformed multidrug resistant Gram-positive bacterial biofilms

The National Institute of Health (NIH) estimates that the majority of human microbial infections are either linked to or directly caused by bacterial biofilms and these infections are immune to most currently approved FDA drugs. Hence, there is a need for the development of potent antibiotics against biofilms. We have previously shown that pentafluorosulfanyl (SF₅)-containing quinoline compounds, which were synthesized via the Povarov reaction, kill persister bacteria (Onyedibe et al. RSC Med Chem, 2021, 12, 1879-1893). Inspired by this earlier discovery, we expanded upon the compounds in the library to identify additional members that could have similar or better potencies, with a goal of increasing the diversity of compounds that could be further developed into therapeutics. Compounds from the Povarov derived SF₅-containing compounds inhibited both clinical and laboratory strains of Gram-positive bacteria at minimum inhibitory concentration (MIC) of 0.5 μg/mL to 2 μg/mL. Interestingly, the lead compound, HSD 1919 exhibited rapid bactericidal mode of action against multidrug resistant (MDR) staphylococcal and enterococcal strains such as MRSA and VRE via bacterial membrane disruption. HSD 1919 eradicated persister MRSA in 2 h-8 h. Most remarkably, we found that HSD 1919 (newly identified compound) and HSD 1835 (previously disclosed, Onyedibe et al. RSC Med Chem, 2021, 12, 1879-1893), dispersed preformed MRSA and VRE biofilms at relatively low concentrations (8 μg/mL). Bithionol (at 1 μg/mL) or nitroxoline (at 4 μg/mL) did not appreciably disperse pre-existing biofilms but when combined with HSD 1919 or HSD 1835 (at 0.5-4 μg/mL), preformed MRSA biofilms could be dispersed, highlighting exciting synergy at reasonably low concentrations of the drugs. Biofilm dispersal was verified by scanning electron microscopy (SEM) whilst membrane disruption properties of HSD 1919 were confirmed by both transmission electron microscopy (TEM) and SEM. Further mechanistic studies showed inhibition of DNA, RNA, cell wall and protein synthesis in a macromolecular biosynthesis assay indicating that these compounds inhibit bacteria via multiple mechanisms, which is now being appreciated as an effective way to tackle resistant bacteria. Toxicity studies showed that HSD 1919 was nontoxic in-vitro to mammalian red blood cells at 10X MIC. Herein, we report HSD 1919 and analogs thereof as critical chemical scaffolds, which can be harnessed to develop highly potent antibiofilm therapeutics.