Spectinamides are effective partner agents for the treatment of tuberculosis in multiple mouse infection models

Abstract

Objectives: New drug regimens employing combinations of existing and experimental antimicrobial agents are needed to shorten treatment of tuberculosis (TB) in humans. The spectinamides are narrow-spectrum semisynthetic analogues of spectinomycin, modified to avoid intrinsic efflux by Mycobacterium tuberculosis. Spectinamides, including lead 1599, have been previously shown to exhibit a promising therapeutic profile in mice as single agents. Here we explore the in vivo activity of lead spectinamides when combined with other agents. Methods: The efficacy of 1599 or 1810 was tested in combination in three increasingly advanced TB mouse models. Mice were infected by aerosol and allowed to establish acute or chronic infection, followed by treatment (≤4 weeks) with the spectinamides alone or in two- and three-drug combination regimens with existing and novel therapeutic agents. Bacteria were enumerated from lungs by plating for cfu. Results: Herein we show the following: (i) 1599 exhibits additive or synergistic activity with most of the first-line agents; (ii) 1599 in combination with rifampicin and pyrazinamide or with bedaquiline and pyrazinamide promotes significantly improved efficacy in the high-dose aerosol model; (iii) 1599 enhances efficacy of rifampicin or pyrazinamide in chronically infected BALB/c mice; and (iv) 1599 is synergistic when administered in combination with rifampicin and pyrazinamide in the C3HeB/FeJ mouse model showing caseous necrotic pulmonary lesions. Conclusions: Spectinamides were effective partner agents for multiple anti-TB agents including bedaquiline, rifampicin and pyrazinamide. None of these in vivo synergistic interactions was predicted from in vitro MIC chequerboard assays. These data support further development of the spectinamides as combination partners with existing and experimental anti-TB agents.

Primary Lung Dendritic Cell Cultures to Assess Efficacy of Spectinamide-1599 Against Intracellular Mycobacterium tuberculosis

“…This drug combination resulted in no observable CFUs on agar plates and we inferred that IFN-γ activation of the lung derived DCs is essential for synergy between spectinamide-1599 and PZA. These results concur with a previous in vivo study in mice showing synergy of spectinamide-1599 and PZA ( Robertson et al, 2017 ). In vivo , IFN-γ is present in the lungs during Mtb infection and may explain the observed synergy between PZA and spectinamide-1599.…”

“…Spectinamide-1599 and PZA demonstrated potent synergy in in vivo studies using murine models of TB infection ( Robertson et al, 2017 ). In this investigation, we expanded on these findings and assessed the efficacy of spectinamide-1599 against intracellular bacilli and its synergy in vitro with PZA.…”

“…Interferon gamma (IFN-γ) is a cytokine produced by the host in response to Mtb infection and is essential to control bacilli load in the lungs ( Flynn et al, 1993 ). In vivo studies using the murine model of TB have demonstrated synergy between spectinamide-1599 and PZA ( Robertson et al, 2017 ).…”

Transcriptomic signatures predict regulators of drug synergy and clinical regimen efficacy against Tuberculosis

“…For example, half of the inconsistencies arose in combinations featuring spectinomycin (SPC). Although SPC has been found to synergize with several anti-TB drugs with multiple modes of action (28, 29), the model tends to overpredict synergy for combinations that include SPC. This may be in part because SPC predictions were based on chemogenomic data from E. coli rather than MTB response transcriptomes.…”

Comparative pharmacokinetics of spectinamide 1599 after subcutaneous and intrapulmonary aerosol administration in mice

“…However, these analogs have poor permeability across the intestinal barrier, resulting in neligible oral bioavailability. Consequently, a parenteral route such as subcutaneous (SC) injection was selected for dosing in initial preclinical efficacy studies [2]. SC administration in a mouse model of Mtb infection at a dose of 200 mg/kg once daily for 5 days a week for a period of four weeks resulted for spectinamide 1599 in a 1.57 log CFU (colony forming unit) reduction in the lungs.…”