Feasibility of Tissue Plasminogen Activator Formulated for Pulmonary Delivery

Abstract

Purpose-This study was conducted to assess the feasibility of a pulmonary formulation of tissue plasminogen activator (tPA) for nebulization into the airway by measuring protein stability, biologic activity, particle size, and estimating human lung distribution.Methods-Formulations were derived by varying the surfactant and protein concentrations. Protein stability and recovery of each nebulized tPA formulation were assessed by ultraviolet spectroscopy. Formulations that met protein stability feasibility criteria were assessed for biologic and fibrinolytic activities. Biologic activity was determined by their ability to inhibit superoxide anion production by human neutrophils. Fibrinolytic activity was assessed by the cleavage of plasminogen to plasmin. Aerodynamic properties were assessed using a cascade impactor, and an estimation of human airway deposition was made via a human lung replica.Results-Twenty-seven tPA formulations were initially assessed, 15 of which met protein stability criteria. Subsequently, three of these formulations maintained biologic and fibrinolytic activities. These formulations exhibited particle sizes of 2.4-3.1 μm, and had respirable doses ≥65%. A formulation of 1 mg mL −1 tPA and 0.1% Tween 80 exhibited a 45% deposition in the lower airways of a human lung replica.Conclusions-A suitable pulmonary tPA formulation was identified that, following nebulization, maintained protein stability as well as biologic and fibrinolytic activities, and resulted in an optimal respirable dose and human airway deposition. This formulation may be applicable in the treatment of lung diseases, such as acute respiratory distress syndrome by permitting targeted pulmonary delivery of a therapeutic protein to the lungs.

Prospective, Longitudinal Study of Plastic Bronchitis Cast Pathology and Responsiveness to Tissue Plasminogen Activator

“…In this study we showed that tPA, in amounts derived from experimental models, was effective in reducing cast mass ex vivo [10, 15, 25]. This is a reasonable approach for these initial experiments and while this is an encouraging result, much has yet to be done to optimize the pulmonary delivery of this therapeutic protein which appears to have a prolonged elimination in the lungs compared with that of the systemic circulation [15].…”

“…We report that our PB patients typically produce fibrin, cellular (lymphocytes) casts that are responsive to amounts of tPA that are consistent with those that may be safely delivered to the lungs [10, 15, 25]. …”

“…At the University of Michigan, inhaled tPA (Activase ® , Genentech, S. San Francisco, CA USA) is commonly used in repeated doses for the treatment of acute PB. Based on our clinical dosing schemes and data from experimental models, we have a reasonable estimate of the amount of tPA that can be safely delivered to the airways in the absence of PB casts [10, 15, 25]. However, there is presently little evidence of the effectiveness of tPA for PB cast reduction [7, 9, 28].…”

Safety of prolonged, repeated administration of a pulmonary formulation of tissue plasminogen activator in mice

“…We have previously demonstrated the feasibility of pf-tPA as evidenced by the retention of protein stability and activity following nebulization [13]. In addition, we have proved the concept of the delivery of active protein in a human lung replica by showing that the nebulized particle size distribution would permit diffuse airway distribution.…”

Comparison of Deposition in the USP and Physical Mouth–Throat Models with Solid and Liquid Particles

“…Lin et al (19) studied how the size of the mouth pieces affected particle deposition. Ali et al (20) and Dunn et al (21) tested metered dose inhalers, dry powder inhalers, and nebulizers for specific medicines with mouth-throat replicas.…”