Inhaled Tissue Plasminogen Activator for Acute Plastic Bronchitis

Plastic bronchitis (PB) is a rare, most often pediatric disease characterized by the formation of obstructive airway casts primarily composed of fibrin. There is presently no FDA-approved pharmacotherapy for PB, but acute exacerbations of the illness are often treated with inhaled tissue plasminogen activator (tPA). To date, this is done somewhat anecdotally because there has been no safety or efficacy testing of this treatment. In addition, there is presently no reliable surrogate marker of adverse drug events. Nevertheless, in the absence of inhaled tPA treatment, PB-induced respiratory distress can be severe, often warranting urgent or emergent bronchoscopy for cast removal, or can sometimes result in respiratory failure. As such there is a significant unmet need for safety and efficacy testing of inhaled tPA and for biomarkers of drug response.

Objectives and Endpoints: The objectives of this protocol are to: 1) test the safety and efficacy of an inhaled tPA regimen in children with PB; and 2) identify potential candidate biomarkers of inhaled tPA drug response. Safety endpoints will consist of the development of new, active bleeding that is systemic and/or pulmonary and/or new hematuria (defined as gross hematuria). Secondary endpoints of efficacy will also be measured (e.g., frequency of cast production). Urine and blood will also be collected for the development of potential biomarkers of inhaled tPA drug response.

Funding source- FDA OOPD

Background and Rationale: Plastic bronchitis (PB) is a rare, disease characterized by the formation of obstructive fibrin airway casts. Presently, acute exacerbations of the illness are often treated with inhaled tissue plasminogen activator (tPA), in part, because there are no FDA approved treatments. To date, there has been no safety or efficacy testing of inhaled tPA. In addition, there is presently no reliable marker that could be used to assess adverse drug events. However, in the absence of inhaled tPA treatment, PB-induced respiratory distress can be severe, often warranting urgent or emergent bronchoscopy for cast removal, or can sometimes result in respiratory failure. This clinical trial will address the unmet need for safety and efficacy testing of inhaled tPA and for assessing biomarkers of drug response.

Objectives and Endpoints: This is an open-label, multi-center clinical trial of inhaled tPA for the treatment of acute PB. The objectives of this protocol are to: 1) test the safety and efficacy of an inhaled tPA regimen in children with PB; and 2) identify potential candidate biomarkers of inhaled tPA drug response. Safety endpoints will consist of the development of new, active bleeding that is systemic and/or pulmonary and/or new hematuria (defined as gross hematuria). Secondary endpoints of efficacy will also be measured (e.g., frequency of cast production). Urine and blood will also be collected for the development of potential biomarkers of inhaled tPA drug response.

Assessments: Enrolled subjects will be routinely clinically monitored and blood work will be assessed for the development of new, active bleeding that is systemic and/or pulmonary or new gross hematuria. Levels of oxygenation and pulmonary function will be assessed during the study period. We will also include the incidence of expectorated casts as a measurement of efficacy.

Statistical Methods: This is an open-label study of up to 13 subjects with PB that will serve as their own controls. A group of healthy subjects (n=12), Fontan subjects without PB (n=12), and Fontan subjects with protein losing enteropathy (PLE) (n=12) will serve as controls for biomarker assay development. The incidence of new, active bleeding events and the frequency of airway cast expectoration will be assessed in subjects with PB. PLE is another illness that is associated with congenital heart disease in children that has been surgically remedied by the Fontan procedure.

The active treatment arm (inhaled tPA) will be conducted across six clinical centers. In addition, these centers will enroll PLE control patients. All other control subjects will only be enrolled at the University of Michigan.

The outcome measures only pertain to tPA treated patients. Since the control subjects are not included in the outcome analysis, recruitment/enrollment status pertains to the PB patients. The University of Michigan has initiated enrollment of healthy control subjects and there have been consented subjects.

Eligibility Criteria:
Inclusion Criteria (patients with plastic bronchitis):

1. ≥ 5 years of age but ≤24 years of age and weigh at least 18.6 kg (41 lbs).
2. Patients with CHD that have a history of PB with previous airway cast production and/or present with symptoms of an acute exacerbation (e.g., difficulty breathing, dyspnea) of PB that requires hospitalization. An acute exacerbation of PB is defined as either respiratory symptoms suspicious for airway cast formation and/or the expectoration of, or a bronchoscopy retrieved, fibrin PB cast.
3. Patients without CHD that present with an acute exacerbation of PB, defined as the expectoration of, or a bronchoscopy retrieved, fibrin PB cast that causes acute respiratory distress (e.g., severe coughing, difficulty breathing, dyspnea) or a history of PB with pathologic evidence of fibrin airway cast production. Either a cast sample (at least ½ inch (\~4cm)) or a pathology report that documents PB cast fibrin content must be submitted to the UM pathology core.
4. Must be able to use a mouthpiece nebulizer.
5. Informed consent (with parental if age ≥14 years) or assent for age ≥10 and \< 14 years old with parental informed consent.

Exclusion Criteria (patients with plastic bronchitis):

1. Known contraindication(s) to the use of tPA, including:

   * active internal bleeding;
   * history of cerebrovascular accident;
   * recent intracranial or intraspinal surgery or trauma;
   * intracranial neoplasm, intracranial arteriovenous malformation or intracranial aneurysm;
   * known bleeding diathesis;
   * and/or severe uncontrolled hypertension
2. Body weight \>/= 100th percentile or BMI \> 30
3. Known cystic fibrosis
4. Currently receiving dornase-alfa and/or inhaled unfractionated or low molecular weight heparin and/or a direct acting oral anticoagulant (e.g., dabigatran, rivaroxaban)

   * Inhaled unfractionated or low molecular weight heparin must be discontinued at least 72h. Inhaled dornase alfa should be discontinued no later than the time of the start of enrollment in the treatment phase. If the patient is receiving inhaled tPA, this regimen must be discontinued and transitioned to the inpatient dosing regimen (5mg Q6h) of study drug.
   * Direct acting oral anticoagulants must be discontinued one week prior to the start of enrollment in the treatment phase.
5. Protein losing enteropathy
6. Liver dysfunction (defined as ≥ 3X the normal levels of one or both liver transaminases, AST and AST)

   • Transaminase levels acquired within the last 9 months can be used to assess liver function. If previously normal and there is no clinical indication that liver function has worsened, the patient can be enrolled. If there are no transaminase values within the last 9 months, they need to be acquired as part of screening
7. Need for concomitant intravenous or sub-cutaneous anti-coagulation with resulting anti- Xa levels \> 0.5 (low molecular weight heparins) or \> 0.3 (unfractionated heparin)
8. International normalized ratio (INR) \> 2.0 if not receiving warfarin
9. Patients being actively treated for thrombosis
10. Concomitant use of a thienopyridine class antiplatelet agent (e.g., clopidogrel)
11. A platelet count of \< 100,000 platelets/µL
12. A hematocrit \<30%
13. Gross hematuria on screening urinalysis
14. Pregnant or lactating women (negative pregnancy test required for girls/women of childbearing potential at the time of inhaled tPA administration). All women of child- bearing potential must be willing to practice appropriate contraception throughout the study.
15. Subjects who are known positive for, or are hospitalized with COVID-19 caused by the new coronavirus, SARS CoV-2, at the start of the treatment phase.
16. Suspected or active concurrent infectious illness.

Inclusion Criteria for Healthy Controls

1. Healthy children ≥ 5 years of age but ≤18 years of age with no other underlying concomitant illness or chronic medication use (with the exception of vitamin supplements)
2. Weigh at least 18.6 kg (41 lbs)

Inclusion Criteria for Healthy non-PB Fontan Controls

1. Children ≥ 5 years of age but ≤18 years of age with uncomplicated Fontan physiology with no history of PB, other Fontan-associated complications (e.g., hepatopathy, PLE), or other concomitant illnesses (e.g., asthma).
2. Weigh at least 18.6 kg (41 lbs)

Inclusion Criteria for PLE Fontan Controls

1. Children ≥ 5 years of age but ≤18 years of age with Fontan physiology, no history of PB and a diagnosis of PLE defined as clinically symptomatic hypoproteinemia and/or enteral protein loss.
2. Weigh at least 18.6 kg (41 lbs)

Exclusion Criteria for Healthy, non-PB Fontan Controls and PLE Fontan Controls

1. Exceed the 100th percentile for body weight or have a BMI greater than 30.
2. History of post-operative chylothorax following any palliation surgery (except for PLE controls).
3. Known liver dysfunction per medical record review (e.g., defined as ≥ 3X the normal levels of one or both liver transaminases \[ALT \& AST\])
4. COVID-19 positive within the last 14 days prior to the scheduled visit and/or the presence of symptoms consistent with COVID-19 at the time of the visit
5. Suspected or active concurrent infectious illness