Spray dried tigecycline dry powder aerosols for the treatment of Nontuberculous mycobacterial pulmonary infections

Abstract

Nontuberculous mycobacterial (NTM) pulmonary infections are a global health concern and a significant contributor to lung disease. Systemic therapies of a cocktail of antibiotics administered over a long period often lead to adverse reactions and/or treatment failure. NTM pathogens, such as Mycobacterium abscessus (Mabs), are notoriously difficult to treat due to resistance to many traditional antibiotics. However, the antibiotic tigecycline has demonstrated efficacy in vitro and in vivo against Mabs strains varying in drug susceptibility. Tigecycline exhibits instability in aqueous medium, posing delivery challenges, and has caused severe adverse gastrointestinal effects following intravenous administration, requiring treatment discontinuation. To mitigate both of these concerns, inhalation therapies using dry powder aerosols are proposed as an alternative administration route and means of delivery. Tigecycline dry powder formulations were prepared, characterized, and optimized to develop a therapeutic aerosol with low moisture, high dispersibility, and a large fraction of particles in the respirable size range (1-5 μm). The addition of lactose, leucine, and phosphate buffer salts was investigated to achieve additional stability, dispersibility, and tolerability. Preliminary delivery of the dry powders to Mabs-infected mice for 30 min per day over 7 d demonstrated a 0.91-log (87.7%) decrease in lung bacterial burden.

Keywords: Aerosol; Dry powder inhaler; Inhalation therapy; Mycobacterium abscessus; Nontuberculous mycobacteria; Tigecycline.

Fig. 1.

Morphology of preliminary tigecycline formulations. Ratios displayed are TGC:LAC:PB content with respect to weight. All SEM images are displayed at 5,000x magnification.

Fig. 2.

XRPD patterns for, from top to bottom, lactose as received (red), spray dried lactose (orange), tigecycline as received (green), 90:0:10 TGC:LAC:PB formulation (purple), 80:10:10 TGC:LAC:PB formulation (teal), and 70:20:10 TGC:LAC:PB formulation (blue). SD = spray dried.

Fig. 3.

Thermogram curves of weight with respect to temperature for lactose as received (red), spray dried lactose (orange), tigecycline as received (green), 90:0:10 TGC:LAC:PB formulation (purple), 80:10:10 TGC:LAC:PB formulation (teal), and 70:20:10 TGC:LAC:PB formulation (blue). SD = spray dried.

Fig. 4.

Mass distribution following actuation of 10 mg spray dried tigecycline formulations, including 90:0:10 TGC:LAC:PB formulation (purple), 80:10:10 formulation TGC:LAC:PB (teal), and 70:20:10 TGC:LAC:PB formulation (blue), via RS-01 inhaler. The NGI was operated at an air flow of 60 L/min for 4 s. Error bars represent the standard deviation of three separate analyses.

Fig. 5.

M. abscessus in murine lung tissue (log₁₀ CFU per lung) after infection with M. abscessus strain 21 (Day 0–2), followed by 7 d of no treatment (Day 9 control) or 7 d of passive inhalation of 80:10:10 TGC:LAC:PB formulation (Day 9 treatment). Error bars represent the standard deviation of 3–5 mice.

Fig. 6.

Morphology of design of experiment tigecycline formulations. All SEM images are displayed at 5,000x zoom.

Fig. 7.

Prediction model for the effect of lactose content, leucine content, solution concentration, and feed rate on particle physicochemical properties and aerodynamic performance metrics. Of note, the red dashed line indicates the properties of the formulation utilized in the preliminary in vivo study, consisting of 10 wt% lactose and 0 wt% leucine and prepared using a solution concentration and feed rate of 15 mg/mL and 5 mL/min, respectively.

Fig. 8.

Morphology of optimized tigecycline formulations. SEM images are displayed at 5,000x magnification.

Fig. 9.

Mass distribution following actuation of 10 mg optimized spray dried tigecycline formulations, including OPT-A (coral) and OPT-B (red), via RS-01 inhaler. The NGI was operated at an air flow of 60 L/min for 4 s. Error bars represent the standard deviation of three separate analyses. Two spray drying batches are presented, with one shown as a solid bar and the other as a striped bar.

Fig. 10.

Aerodynamic properties of optimized tigecycline formulations OPT-A (A, C, E, G) and OPT-B (B, D, F, H) following 0–4 week storage at room temperature (blue circles), 4 °C (red squares), or −20 °C (teal triangles). Aerodynamic metrics include (A–B) mass median aerodynamic diameter (MMAD), (C–D) emitted dose, (E–F) fine particle fraction with respect to the nominal capsule dose, and (G–H) fine particle fraction with respect to the emitted dose. Error bars represent the standard deviation of duplicate analyses. *p < 0.05 with respect to the formulation analyzed at week 0 (initial).

Fig. 11.

(A) OPT-A and (B) OPT-B tigecycline drug stability over 4 weeks of storage at room temperature (blue circles), 4 °C (red squares), or −20 °C (teal triangles). Error bars represent the standard deviation of triplicate analyses.