Antiinfectives targeting enzymes and the proton motive force

Abstract

There is a growing need for new antibiotics. Compounds that target the proton motive force (PMF), uncouplers, represent one possible class of compounds that might be developed because they are already used to treat parasitic infections, and there is interest in their use for the treatment of other diseases, such as diabetes. Here, we tested a series of compounds, most with known antiinfective activity, for uncoupler activity. Many cationic amphiphiles tested positive, and some targeted isoprenoid biosynthesis or affected lipid bilayer structure. As an example, we found that clomiphene, a recently discovered undecaprenyl diphosphate synthase inhibitor active against Staphylococcus aureus, is an uncoupler. Using in silico screening, we then found that the anti-glioblastoma multiforme drug lead vacquinol is an inhibitor of Mycobacterium tuberculosis tuberculosinyl adenosine synthase, as well as being an uncoupler. Because vacquinol is also an inhibitor of M. tuberculosis cell growth, we used similarity searches based on the vacquinol structure, finding analogs with potent (∼0.5-2 μg/mL) activity against M. tuberculosis and S. aureus. Our results give a logical explanation of the observation that most new tuberculosis drug leads discovered by phenotypic screens and genome sequencing are highly lipophilic (logP ∼5.7) bases with membrane targets because such species are expected to partition into hydrophobic membranes, inhibiting membrane proteins, in addition to collapsing the PMF. This multiple targeting is expected to be of importance in overcoming the development of drug resistance because targeting membrane physical properties is expected to be less susceptible to the development of resistance.T here is a need for new antibiotics, due to the increase in drug resistance (1, 2). For example, some studies report that by 2050, absent major improvements in drug discovery and use, more individuals will die from drug-resistant bacterial infections than from cancer, resulting in a cumulative effect on global gross domestic product of as much as 100 trillion dollars (3, 4). To discover new drugs, new targets, leads, concepts, and implementations are needed (5, 6).Currently, one major cause of death from bacterial infections is tuberculosis (TB) (7), where very highly drug-resistant strains have been found (8). Therapy is lengthy, even with drug-sensitive strains, and requires combination therapies with four drugs. Two recent TB drugs/drug leads (9-11) are TMC207 [bedaquiline (1); Sirturo] and SQ109 (2) (Fig. 1). Bedaquiline (1) targets the Mycobacterium tuberculosis ATP synthase (9) whereas SQ109 (2) has been proposed to target MmpL3 (mycobacterial membrane protein large 3), a trehalose monomycolate transporter essential for cell wall biosynthesis (12). SQ109 (2) is a lipophilic base containing an adamantyl "headgroup" connected via an ethylene diamine "linker" to a geranyl (C 10 ) "side chain," and in recent work (13), we synthesized a series of 11 analogs of SQ109 (2) finding that the ethanolamine (3) was more potent th...

Bioluminescent Reporters for Rapid Mechanism of Action Assessment in Tuberculosis Drug Discovery

“…During this period, sustained induction occurred only at the MIC 99 of SQ109, with a slight reduction in luminescence signal observed at higher drug concentrations (Ͼ2-fold above the MIC 99 ). Recent evidence suggests that SQ109 has multiple sites of action in the cell wall, inhibiting menaquinone biosynthesis and functioning as a protonophore in collapsing membrane potential (40,41), and this might account for the decreased luminescence signal observed at higher concentrations.…”

Inhibition of Leishmania mexicana Growth by the Tuberculosis Drug SQ109

“…As noted above, in earlier work on M. smegmatis, we and others (10)(11)(12) showed that a major mechanism of action of SQ109 (as well as amiodarone) was on the proton motive force (PMF), with SQ109 collapsing pH gradients, as determined by nuclear magnetic resonance spectroscopy, and electrochemical potentials (in both M. smegmatis and Escherichia coli membrane vesicles), as determined by fluorescence spectroscopy. Similar results were obtained with amiodarone and dronedarone in T. cruzi and L. mexicana (1)(2)(3)(4)(5).…”

“…Rather, Ca 2ϩ is released from internal stores, mitochondria and acidocalcisomes, again, just as found for T. cruzi and L. mexicana with amiodarone and dronedarone (1)(2)(3)(4)(5). This disruption of Ca 2ϩ homeostasis in addition to the effects on the proton motive force (as seen also in mycobacteria [10][11][12]) are likely to make major contributions to L. mexicana cell killing.…”

The Mycobacterium tuberculosis MmpL11 Cell Wall Lipid Transporter Is Important for Biofilm Formation, Intracellular Growth, and Nonreplicating Persistence

“…In recent years MmpL3 has been identified as the target of several compounds by use of genetic approaches (19,(48)(49)(50). Ultimately, these compounds appear to indirectly inhibit MmpL3 by perturbing the proton motive force (PMF) (51,52). The point-substituted residues identified in MmpL3 that confer resistance likely allow the protein to compensate for a disruption of PMF strength.…”