In Vitro Characterization of the Anti-Bacterial Activity of SQ109 against Helicobacter pylori

Abstract

The most evident challenge to treatment of Helicobacter pylori, a bacterium responsible for gastritis, peptic ulcers and gastric cancer, is the increasing rate of resistance to all currently used therapeutic antibiotics. Thus, the development of novel therapies is urgently required. N-geranyl-N'-(2-adamantyl) ethane-1, 2-diamine (SQ109) is an ethylene diamine-based antitubercular drug that is currently in clinical trials for the treatment of tuberculosis (TB). Previous pharmacokinetic studies of SQ109 revealed that persistently high concentrations of SQ109 remain in the stomach 4 hours post oral administration in rats. This finding, combined with the need for new anti- Helicobacter therapies, prompted us to define the in vitro efficacy of SQ109 against H. pylori. Liquid broth micro-dilution was used for susceptibility studies to determine the antimicrobial activity of SQ109 against a total of 6 laboratory strains and 20 clinical isolates of H. pylori; the clinical isolates included a multi-drug resistant strain. All strains tested were susceptible to SQ109 with MIC and MBC ranges of 6-10 µM and 50-60 µM, respectively. SQ109 killing kinetics were concentration- and time-dependent. SQ109 killed H. pylori in 8-10 h at 140 µM (2MBCs) or 4-6 h at 200 µM (~3MBCs). Importantly, though the kinetics of killing were altered, SQ109 retained potent bactericidal activity against H. pylori at low pH. Additionally, SQ109 demonstrated robust thermal stability and was effective at killing slow growing or static bacteria. In fact, pretreatment of cultures with a bacteriostatic concentration of chloramphenicol (Cm) synergized the effects of typically bacteriostatic concentrations of SQ109 to the level of five-logs of bacterial killing. A molar-to-molar comparison of the efficacy of SQ109 as compared to metronidazole (MTZ), amoxicillin (AMX), rifampicin (RIF) and clarithromycin (CLR), revealed that SQ109 was superior to MTZ, AMX and RIF but not to CLR. Finally, the frequency of resistance to SQ109 was low and electron microscopy studies revealed that SQ109 interacted with bacterial inner membrane and cytoplasmic content(s). Collectively, our in vitro data demonstrate that SQ109 is an effective monotherapy against susceptible and multi-drug resistant strains of H. pylori and may be useful alone or in combination with other antibiotics for development as a new class of anti- Helicobacter drugs.

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“…In an in vitro study, SQ109 had anti-H. pylori activity and a low H. pylori resistance rate [156] . Pyridodiazepines are potent and selective molecules that target the H. pylori MurI inhibitor not effective against other bacteria [157] .…”

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“…However, while they were able to isolate spontaneous mutants with resistance to related diamines, they were unable to isolate compounds that mutated in response to 228 . This, in addition to its biological activity against non‐mycolic acid producing microbes and reported capacity to bind to Staphylococcus aureus SQS (PDB IDs: https://www.rcsb.org/structure/4EA2 and https://www.rcsb.org/structure/3NPR), suggested that 228 may inhibit multiple targets . Li et al.…”

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“…Nitazoxanide (13) has also been in clinical trials for the treatment of Helicobacter pylori and Clostridium difficile infections. 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.…”