Durlobactam to boost the clinical utility of standard of care β-lactams against Mycobacterium abscessus lung disease

Abstract

β-Lactams present several desirable pharmacodynamic features leading to the rapid eradication of many bacterial pathogens. Imipenem (IPM) and cefoxitin (FOX) are injectable β-lactams recommended during the intensive treatment phase of pulmonary infections caused by Mycobacterium abscessus (Mab). However, their potency against Mab is many-fold lower than against Gram-positive and Gram-negative pathogens for which they were optimized, putting into question their clinical utility. Here, we show that adding the recently approved durlobactam-sulbactam (DUR-SUL) pair to either IPM or FOX achieves growth inhibition, bactericidal, and cytolytic activity at concentrations that are within those achieved in patients and below the clinical breakpoints established for each agent. Synergies between DUR-SUL and IPM or FOX were confirmed across a large panel of clinical isolates. Through in vitro resistant mutant selection, we also show that adding DUR-SUL abrogates acquired resistance to IPM and FOX. Since the use of β-lactam injectables is firmly grounded in clinical practice during the intensive treatment phase of Mab pulmonary disease, their potentiation by FDA-approved DUR-SUL to bring minimum inhibitory concentration distributions within achievable concentration ranges could offer significant short-term benefits to patients, while novel β-lactam combinations are optimized specifically against Mab pulmonary infections, for which no reliable cure exists.

Keywords: MmpL11; MspA; Mycobacterium abscessus; RshA; drug resistance; lung infection; β-lactams.

Fig 1

Impact of DUR on the growth inhibitory activity of IPM and FOX against Mab ATCC 19977. (A) Dose-response MIC of DUR, SUL, and DUR-SUL against Mab ATCC 19977 wild type and the isogenic Bla_Mab knockout (Δbla). (B) Dose-response growth inhibition of IPM and FOX with DUR fixed at 2 µg/mL and avibactam (AVI) at 4 µg/mL against Mab ATCC 19977. Percent growth inhibition was calculated relative to untreated control after subtracting partial growth inhibition due to DUR when relevant.

Fig 2

(A) Impact of SUL at 4 μg/mL on the MIC distribution of DUR against a panel of 72 clinical isolates representing the three subspecies of the Mab complex. (B) MIC distributions of IPM and FOX, in combination with DUR or DUR-SUL at the concentrations indicated (μg/mL) against 72 Mab clinical isolates: 38, 32, and 2 subsp. abscessus, massiliense, and bolletii, respectively, representing the frequency of clinical occurrence (46). MIC is defined as the minimum concentration inhibiting visible growth, or MIC_vis (44).

Fig 3

Impact of DUR-SUL and IPM or FOX on the bactericidal activity of each other, measured over 3 days. (A) Potentiation of IPM by DUR and DUR-SUL. (B) Potentiation of FOX by DUR or DUR-SUL. (C) Potentiation of DUR-SUL by IPM or FOX. All drug concentrations are at or below the published clinical breakpoints. The asterisk indicates that colony forming units (CFUs) were below the limit of detection (2 log, dotted line) in all replicates. Statistical analysis was performed using two-way analysis of variance with Tukey’s multiple comparison test. The statistical significance of relevant comparisons is shown. D₀: bacterial burden prior to drug treatment. The experiment was repeated three times independently and means/standard deviations of the three data sets are shown. For clarity, only ns (not statistically significant) effects are shown in (C). The effects of IPM or FOX at 2, 4, and 8 μg/mL were statistically significant in all other treatment groups.* P < 0.05; **P < 0.01; ****P < 0.0001.

Fig 4

Impact of DUR-SUL on mycobacterial cell lysis induced by IPM and FOX. Mab ATCC 19977 expressing mCherry was exposed to single agents and combinations as indicated, for 3 days. DUR and/or SUL were added at 2 and 4 μg/mL, respectively. Clarithromycin (CLR), a bacteriostatic macrolide, was used as negative cell lysis control at 16 μg/mL. Growth inhibition was monitored at OD_{600 nm}. The experiment was carried out twice independently in technical duplicates and all data points are shown. Data were analyzed by two-way analysis of variance and Tukey’s multiple comparison test. The addition of DUR-SUL had a positive statistically significant effect on cell lysis induced by IPM and FOX at all concentrations tested (****, P < 0.0001, not depicted on the graph for clarity).