A strategy for new regimens to treat pulmonary Mycobacteroides abscessus infection

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In the setting of structural lung conditions such as cystic fibrosis, bronchiectasis and COPD, non-tuberculous bacterium Mycobacteroides abscessus can cause chronic pulmonary disease that is often incurable and associated with rapid lung function decline. Additionally, existing treatment requires more than a year of daily intake of antibiotics with poor efficacies and significant toxicities. M. abscessus has been designated as an “antibiotic nightmare” and “an environmental bacterium turned clinical nightmare” due to extensive natural and acquired antibiotic resistance, which severely limits treatment options. Therefore, there is an urgent unmet need for new treatment options that are effective against these drug-resistant strains. β-lactams are the most widely used class of antibiotics globally to treat bacterial infections in humans and have a demonstrated record of safety and tolerability. However, today, only a single β-lactam is used at a time to treat M. abscessus infections. This recommendation is based on a now debunked historical concept that all β-lactams have the same single target (DD-transpeptidases), thus the inclusion of more than one β- lactam in a regimen would be redundant. We have completed proof-of-concept studies demonstrating that paired combinations of certain β-lactams, each at less than half the dose required for single β-lactams, exhibit synergy in bactericidal activity against M. abscessus in vitro and hypothesized that one agent optimally inhibits LD-transpeptidases while the other targets DD-transpeptidases to achieve synergy. Lastly, we have developed a mouse model of pulmonary M. abscessus disease based on the natural route of infection in humans and observed that synergy between β-lactams against M. abscessus observed in vitro is also preserved in this pre-clinical model. Three of the combinations identified in our in vitro synergy assessment are comprised of orally administered β-lactams. This finding has raised the possibility that a combination of select two oral β-lactams may be effective in treating M. abscessus disease. Here, we will test this hypothesis by assessing whether novel oral regimens consisting of select two β-lactams (which may include an additional oral traditional antibiotic) will produce a stable cure in mice infected with M. abscessus. The experimental regimens will be tested in a C3HeB/FeJ mouse model of pulmonary M. abscessus disease model against a range of recent clinical isolates of the M. abscessus complex. In addition to potency of the regimens, we will also assess their ability to minimize selection of drug-resistance.