The lengthy treatment time for tuberculosis (TB) is a primary cause for the emergence of multidrug resistant tuberculosis (MDR-TB). One approach to improve TB therapy is to develop an inhalational TB therapy that when administered in combination with oral TB drugs eases and shortens treatment. Spectinamides are new semisynthetic analogues of spectinomycin with excellent activity against Mycobacterium tuberculosis (Mtb), including MDR and XDR Mtb strains. Spectinamide-1599 was chosen as a promising candidate for development of inhalational therapy. Using the murine TB model and intrapulmonary aerosol delivery of spectinamide-1599, we characterized the pharmacokinetics and efficacy of this therapy in BALB/c and C3HeB/FeJ mice infected with the Mtb Erdman strain. As expected, spectinamide-1599 exhibited dose-dependent exposure in plasma, lungs, and ELF, but exposure ratios between lung and plasma were 12-40 times higher for intrapulmonary compared to intravenous or subcutaneous administration. In chronically infected BALB/c mice, low doses (10 mg/kg) of spectinamide-1599 when administered thrice weekly for two months provide efficacy similar to that of higher doses (50-100 mg/kg) after one month of therapy. In the C3HeB/FeJ TB model, intrapulmonary aerosol delivery of spectinamide-1599 (50 mg/kg) or oral pyrazinamide (150 mg/kg) had limited or no efficacy in monotherapy, but when both drugs were given in combination, a synergistic effect with superior bacterial reduction of >1.8 log10 CFU was observed. Throughout the up to eight-week treatment period, intrapulmonary therapy was well-tolerated without any overt toxicity. Overall, these results strongly support the further development of intrapulmonary spectinamide-1599 as a combination partner for anti-TB therapy.

Pulmonary Mycobacterium abscesssus (pAMB) infection is particularly challenging to treat because this bacillus displays intrinsic antibiotic resistance to most front-line drugs. Tigecycline, a glycyclcycline tetracycline, shows potent bactericidal effects against pMAB, while successfully evading bacterial resistance mechanisms. Tigecycline is FDA approved as a twice daily IV administration but provokes intolerable side effects in patients. More than its potent antimicrobial effects, tigecycline has demonstrated immunomodulatory properties observed in preclinical animal models of bacterial infection. We hypothesized that inhaled therapy of tigecycline reduces side effects and improve efficacy against pMAB. GM-CSF knockout mice with pMAB were treated daily for 28 days with aerosols of tigecycline at 0.25, 1.25 and 2.50 mg/dose. Thereafter, bacterial burden was assessed, and samples were prepared for immunophenotyping of lymphocyte and myeloid cell populations through H&E staining and IHC techniques. The results demonstrated that treatment with aerosols of tigecycline to mice with pAMB was tolerated and highly effective at reducing bacterial burden. Furthermore, this therapy was associated with the influx of macrophages and lymphocytes in both perivascular zones and granulomatous-like formations. There was also an increase in alveoli lined by hypertrophied cells with vesicular nuclei, suggesting induced Type II cell hyperplasia. To summarize, inhaled tigecycline not only demonstrated bactericidal effects against pMAB, but it invokes unique immunomodulatory effects that appear to aid the significant reduction in pulmonary bacteria.