Accelerated Dosing Frequency of a Pulmonary Formulation of Tissue Plasminogen Activator Is Well‐tolerated in Mice

Abstract

Summary 1.Tissue plasminogen activator (tPA) has both fibrinolytic and anti-inflammatory activity.These properties may be useful in treating inflammatory lung diseases, such as acute respiratory distress syndrome (ARDS). 2.We have previously demonstrated the feasibility of targeted pulmonary delivery of tPA. As part of our research to develop a clinically viable pulmonary formulation of tPA, we assessed the tolerability and incidence of haemorrhage associated with the administration of a pulmonary formulation of mouse tPA (pf-mtPA). 3.Intratracheal doses of nebulized pf-mtPA or sterile saline were administered with increasing frequency to male and female B6C3F1 mice. After dosing, the mice entered a recovery period, after which they were killed and their lungs were lavaged and harvested. Postmortem gross necropsy was performed and all major organs were assessed histologically for haemorrhage. The bronchoalveolar lavage fluid was assessed for markers of lung injury. 4.Mouse tPA that was formulated to mimic a previously characterized human pf-tPA was well tolerated when given intratracheally with increasing dosing frequency. The administration of pf-mtPA did not result in any detectable haemorrhagic-related events or signs of lung injury. 5.The results of the present longitudinal study demonstrate that a maximally feasible dose of pf-mtPA (3 mg/kg) can be given frequently over a short period of time (12 h) without haemorrhagic complications. Although these data were generated in a healthy mouse model, they provide support for the continued evaluation of pf-tPA for the treatment of pulmonary diseases, such as ARDS.

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

“…The stability and function of the mouse formulation (pf-mtPA) was assessed by measuring protein aggregation index (AI), an indicator of protein self-association, by ultraviolet (UV) spectroscopy and fibrinolytic activity as described in previous work [13, 14]. An AI of ≤ 10 was considered optimal.…”

“…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. We have also shown that a maximally feasible dose (3 mg/kg) of pf-tPA can be given repeatedly with increasing frequency over a short period of time without complications [14]. However, the anticipated clinical situation will require prolonged repeated administration of pf-tPA.…”