Open-Label Extension Study of Ubenimex in Patients With Pulmonary Arterial Hypertension (WHO Group 1)

Inclusion Criteria: * Patients must have completed Study EIG-UBX-001 through Week 24. * In the opinion of the Principal Investigator, has been generally compliant with study requirements during Study EIG-UBX-001. * Agrees to use a medically acceptable method of contraception throughout the entire study period. * Willing and able to comply with scheduled visits, treatment plans, and laboratory tests and other study procedures. Exclusion Criteria: * Is pregnant or lactating. * Concurrent regular use of another leukotriene pathway inhibitor. * Any reason that, in the opinion of the investigator, precludes the patient from participating in the study. 1. Any condition that is unstable or that could jeopardize the safety of the patient and his/her compliance in the study 2. A serious uncontrolled medical disorder/condition that in the opinion of the investigator would impair the ability of the patient to receive protocol therapy * An ongoing, drug-related, serious adverse event (SAE). * Significant/chronic renal insufficiency. * Transaminases (alanine transaminase, aspartate transaminase) levels \>3 × upper limit of normal (ULN) and/or bilirubin level \>2 × ULN. * Absolute neutrophil count \<1500 mm3. * Hemoglobin concentration \<9 g/dL at Screening.