Circumventing Antibiotic Resistance

Development of Aminoquinoline Inhibitors: Membrane Disruptors of Gram + Organisms

Drug-resistant Gram+ bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), pose an emerging threat to public health. Our lab is particularly interested in developing new therapeutics with novel mechanisms of action to target these resistant organisms.  In pursuit of this aim, phenotypic screening identified several lead molecules containing a conserved 4-aminoquinoline core (A). This scaffold imparts undesirable PK properties, including high sp2 character and low predicted aqueous solubility (cLogP = 7.75).  We have introduced polar substituents at the C3 and C4 positions of the quinoline ring in an attempt to reduce the lipophilicity of these lead molecules (B).

Our current lead compounds 15 and 17 (C) have been shown to act as membrane disruptors in MRSA USA300 strains in vitro via fluorescence microscopy.  After 5 min incubation with 2x MIC of each compound, large membrane disruption can be seen compared to DMSO control. Treatment does not seem to affect the bacterial cell wall, suggesting this membrane disruption specifically as a potential mechanism of action.

• Schultz JR, Costa SK, Jachak GR, Hegde P, Zimmerman M, Pan Y, Josten M, Ejeh C, Hammerstad T, Sahl HG, Pereira PM, Pinho MG, Dartois V, Cheung A, Aldrich CC. Identification of 5-(Aryl/Heteroaryl)amino-4-quinolones as Potent Membrane- Disrupting Agents to Combat Antibiotic-Resistant Gram-Positive Bacteria. Journal of Medicinal Chemistry. 2022 [PDF]

Several projects in the lab seek to repurpose or redesign existing antibiotics for use against resistant organisms. Rifamycin antibiotics inhibit RNA synthesis through binding to prokaryotic RNA polymerase, and are employed as first-line agents against Mtb. However, these antibiotics lack efficacy against pathogenic nontuberculous mycobacteria (NTM) infections, in part due to expression of an ADP-ribosyltransferase Arr, which inactivates these antibiotics via ribosylation of an essential hydroxyl group. Our group is currently developing novel rifabutin analogues with modifications that prevent modification by Arr and circumvent this resistance mechanism.

• Lan T, Ganapathy US, Sharma S, Ahn YM, Zimmerman M, Molodtsov V, Hegde P, Gengenbacher M, Ebright RH, Dartois V, Freundlich JS, Dick T, Aldrich CC. Redesign of Rifamycin Antibiotics to Overcome ADP-Ribosylation-Mediated Resistance. Angewandte Chemie International Edition. 2022. [PDF]

A second class of molecules we have explored are the β-lactam antibiotics. These molecules inhibit cell wall synthesis via covalent modification of penicillin-binding proteins (PBPs) but lack activity against Mtb due to an inherent expression of β-lactamase enzymes which cleave the electrophilic C-N bond required for activity (A). We have developed β-lactam conjugates containing antitubercular payloads, which are released following β-lactamase cleavage (B,C). β-lactamases are not expressed by commensal organisms, allowing for selective delivery to the infection site.

• Cole MS, Hegde PV, Aldrich CC. β-Lactamase-Mediated Fragmentation: Historical Perspectives and Recent Advances in Diagnostics, Imaging, and Antibacterial Design. ACS Infectious Diseases. 2022 [PDF]