Mutations in bone morphogenetic protein receptor 2 (BMPR2) are present in >80% of familial and ~20% of sporadic pulmonary arterial hypertension (PAH) patients. Furthermore dysfunctional BMP signaling is a general feature of pulmonary hypertension even in non-familial PAH.

We therefore hypothesized that increasing BMP signaling might prevent and reverse the disease. We screened > 3500 FDA approved drugs for their propensity to increase BMP signaling and found FK506 (Tacrolimus) to be a strong activator of BMP signaling. Tacrolimus restored normal function of pulmonary artery endothelial cells, prevented and reversed experimental PAH in mice and rats.

Given that Tacrolimus is already FDA approved with a known side-effect profile, it is an ideal candidate drug to use in patients with pulmonary arterial hypertension.

The aims of our trial are:

1. Establish the Safety of FK506 in patients with PAH.
2. Evaluate the Efficacy of FK506 in PAH
3. Identify ideal candidates for future FK506 phase III clinical trial.

Study Design:

Randomized, placebo-controlled, four arm clinical trial.

Sample Size: 10 subjects in each arm, Total enrollment = 40 patients.

1. 10 patients: FK-506 blood level: 3 - 5 ng/ml
2. 10 patients: FK-506 blood level: 2 - 3 ng/ml
3. 10 patients: FK-506 level: < 2.0 ng/ml
4. 10 patients: Placebo

Study Duration:

16 weeks

Primary Endpoints:

1) Safety of low-dose FK506 in PAH

Secondary Objectives/Endpoints:

1. Combined Clinical Events/Time to Clinical Worsening @ 16 weeks:

   • All cause mortality
   • Transplantation
   • Atrial septostomy
   • Need for escalation of therapies as deemed by site investigator
   • Worsening of NYHA/WHO classification by at least 1 point.
   • Hospitalization for right heart failure.

2. Change in 6MWD at 16 weeks

3. Change in NT-Pro-BNP at 16 weeks

4. Change in Uric Acid at 16 weeks

5. Change in DLCO at 16 weeks

6. Change in novel RV parameters by transthoracic echocardiography: Change in RV size, RA size, RV function, TAPSE, RVSP

Inclusion Criteria:

1. Age ≥ 18 and < 70 years

2. Diagnosis of WHO Group I Pulmonary Arterial Hypertension (PAH) (Idiopathic (I)PAH, Heritable PAH (including Hereditary Hemorrhagic Telangiectasia), Associated (A)PAH (including collagen vascular disorders, drugs+toxins exposure, congenital heart disease, and portopulmonary disease).

3. Stable on active PAH treatment including any prostacycline or phosphodiesterase inhibitors and the endothelin antagonist Ambrisentan alone or in combination (stability defined as: <10% change in 6MWD, no change in NYHA class, no hospitalization or addition of PAH therapy for at least 3 months).

4. Previous Right Heart Catheterization that documented:

   1. Mean PAP ≥ 25 mmHg.
   2. Pulmonary capillary wedge pressure < 15 mmHg.
   3. Pulmonary Vascular Resistance ≥ 3.0 Wood units or 240 dynes/sec/cm5

5. WHO functional class I to IV as judged by the investigator.

Exclusion Criteria:

1. WHO Group II - V Pulmonary Hypertension.

2. Current or prior experimental PAH treatments within the last 6 months (including but not limited to tyrosine kinase inhibitors, rho-kinase inhibitors, or cGMP modulators).

3. Current active treatment with the dual endothelin receptor antagonist bosentan.

4. TLC < 60% predicted; if TLC b/w 60 and 70% predicted, high resolution computed tomography must be available to exclude significant interstitial lung disease.

5. FEV1 / FVC < 70% predicted and FEV1 < 60% predicted

6. Significant left-sided heart disease (based on screening Echocardiogram):

   1. Significant aortic or mitral valve disease
   2. Diastolic dysfunction ≥ Grade II
   3. LV systolic function < 45%
   4. Pericardial constriction
   5. Restrictive cardiomyopathy
   6. Significant coronary disease with demonstrable ischemia.

7. Chronic renal insufficiency defined as an estimated creatinine clearance < 30 ml/min (by MDRD equation).

8. Current atrial arrhythmias not under optimal control.

9. Uncontrolled systemic hypertension: SBP > 160 mm or DBP > 100mm

10. Severe hypotension: SBP < 80 mmHg.

11. Pregnant or breast-feeding.

12. Psychiatric, addictive, or other disorder that compromises patient's ability to provide informed consent, follow study protocol, and adhere to treatment instructions.

13. Active cyclosporine use.

14. Known allergy or hypersensitivity to FK-506.

15. Planned initiation of cardiac or pulmonary rehabilitation during period of study.

16. Human Immunodeficiency Virus infection.

17. Moderate to severe hepatic dysfunction with a Pugh score >10.

18. Hyperkalemia defined as Potassium > 5.1 mEq/L at screening .

19. Known active infection requiring antibiotic, antifungal, or antiviral therapies.

20. Co-morbid conditions that would impair a patient's exercise performance and ability to assess WHO functional class, including but not limited to chronic low-back pain or peripheral musculoskeletal problems.

Adverse events were collected from every study subject who started the study regardless whether the subject finished the study. Events were collected during the time frame between baseline and 18 weeks.

Of note the study drug was stopped at 16 weeks, an additional observation period of 2 weeks was used to capture possible adverse events of study drug.

Due to slow patient recruitment in single academic center we recruited fewer patients than originally expected.

Follow-up multicenter phase IIb efficacy trial is planned