PI discretion

The purpose of this study is to evaluate the safety and tolerability of captopril and evaluate the effectiveness captopril as measured by changes in the grade of bone marrow scar tissue. The change in spleen size by ultrasound will also be measured.

Captopril is an investigational (experimental) drug that works by inhibiting the production of angiotensin II by blocking angiotensin converting enzyme. Reducing angiotensin II may reduce the bone marrow scar tissue in myelofibrosis. It is not approved by the Food and Drug Administration (FDA) for this indication. Participants in this study will be asked to have 2 bone marrow biopsies, a total of 3 blood samples, and fill out questionnaires asking about how you feel.

Inclusion Criteria:

• Participants must have histologically confirmed diagnosis of primary myelofibrosis (PMF), or post-polycythemia vera/essential thrombocythemia-MF (i.e. secondary MF) by 2016 WHO criteria
• Eastern Cooperative Oncology Group (ECOG) Performance Status 0 -2
• Creatinine clearance >30 ml/minute
• Women of childbearing potential should be advised to avoid becoming pregnant while receiving treatment. All men and women of childbearing potential must use acceptable methods of birth control throughout the study.
• Participants should be able to give voluntary informed written consent to participate in the study. Informed consent will be obtained prior to enrollment and before any study-related procedure is done that is not part of standard medical care, with the understanding that consent may be withdrawn by the participants any time without prejudice to future medical care.

Exclusion Criteria:

• Completed hematopoietic cell transplant (HCT)
• Presence of >10% blasts in peripheral blood or on bone marrow examination
• Screening blood pressure(BP)parameters of systolic BP < 100 and diastolic BP < 60
• Splenic irradiation within 3 months prior to the first dose of captopril
• Prior ACE inhibitor, angiotensin II receptor antagonist, or aliskiren use within 12 months prior to trial enrolment
• Known allergy/hypersensitivity to ACE inhibitors
• Participants receiving any other investigational agents
• Pregnant or nursing participants - captopril is a risk category D and is excreted in breast milk
• Participants with creatinine clearance <30 ml/minute or on dialysis
• Any serious medical condition, laboratory abnormality, or psychiatric illness that, in the view of the treating physician, would place the participant at an unacceptable risk if he or she were to participate in the study or would prevent that person from giving informed consent

There is a plan to make all individual participant data (IPD) and related data dictionaries available. We will also make the protocol available.