Multitarget Drug Discovery for Tuberculosis and Other Infectious Diseases

Abstract

We report the discovery of a series of new drug leads that have potent activity against Mycobacterium tuberculosis as well as against other bacteria, fungi, and a malaria parasite. The compounds are analogues of the new tuberculosis (TB) drug SQ109 (1), which has been reported to act by inhibiting a transporter called MmpL3, involved in cell wall biosynthesis. We show that 1 and the new compounds also target enzymes involved in menaquinone biosynthesis and electron transport, inhibiting respiration and ATP biosynthesis, and are uncouplers, collapsing the pH gradient and membrane potential used to power transporters. The result of such multitarget inhibition is potent inhibition of TB cell growth, as well as very low rates of spontaneous drug resistance. Several targets are absent in humans but are present in other bacteria, as well as in malaria parasites, whose growth is also inhibited.

Antiinfectives targeting enzymes and the proton motive force

“…smegmatis, S. cerevisiae, S. aureus, and M. tuberculosis growth inhibition assays; the porcine liver mitochondria Δψ assay; ΔpH and Δψ assays with IMV; MD simulation of Rv3378c; Rv3378c inhibition; DSC; and EPR were performed as described previously (13,70,77,91,92), with full details given in SI Methods.…”

“…Interestingly, SQ109 (2) has similar activity against both organisms (29), and with H. pylori, SQ109 (2) once again has a very low (≈10 −12 ) frequency of resistance (29). In addition, nitazoxanide (13) has been found to kill both replicating and nonreplicating M. tuberculosis (30)(31)(32)(33), and Nathan and coworkers (30,31) were unable to develop resistant colonies using up to 10 12 cfu, proposing a dual "PMF + unknown target" mechanism of action. Niclosamide (12) has been proposed as a lead for the treatment of type II diabetes (34), and it is also an inhibitor of breast cancer stem-like cells (35) and an inhibitor of Pseudomonas aeruginosa quorum sensing (36).…”

“…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 than was SQ109 (2) against M. tuberculosis H37Rv [0.063 vs. 0.25 μg/mL minimal inhibitory concentration (MIC)], and that at least one protonatable nitrogen in the linker was essential for activity. The latter observation suggested to us that SQ109 (2) and ethanolamine (3) might have activity as uncouplers, collapsing the proton motive force (PMF; ΔP) used to drive ATP synthesis, because we had observed similar uncoupling effects for lipophilic bases, US Food and Drug Administration (FDA)-approved drugs, in trypanosomatid parasites (14,15).…”

“…Several of these compounds also have enzyme targets. For example, SQ109 (2), ethanolamine (3), and Ro 48-8071 (8) have been found (13,20) to inhibit enzymes involved in menaquinone biosynthesis, particularly the prenyl transferase 1,4-dihydroxy-2-naphthoate octaprenyltransferase (MenA) and human oxidosqualene cyclase (OSC) (21), and bedaquiline (1) is a potent ATP synthase inhibitor, indicating the possibility of multitarget activity for such compounds. These results are of interest because they show that several recently discovered M. tuberculosis drug leads can act as uncouplers in addition to targeting one or more enzymes that are essential for bacterial cell growth, with membrane targeting being of particular interest because it might be expected to be less susceptible to the development of resistance than is purely enzyme targeting, and SQ109 (2) does indeed have a low frequency of resistance in M. tuberculosis (∼2.55 × 10 −11 ) (22).…”

“…DNP functions as a protonophore, a proton-translocating molecule, and analogs such as niclosamide (12) and nitazoxanide (13) [active form, tizoxanide (14)] are used clinically: niclosamide (12) to treat tapeworm infections (27) and nitazoxanide (13) to treat infections due to Giardia lamblia (28) and Cryptosporidium parvum. Nitazoxanide (13) has also been in clinical trials for the treatment of Helicobacter pylori and Clostridium difficile infections.…”