Patients must meet all of the following inclusion criteria to be eligible:

          -  Confirmed pathological diagnosis of primary myelofibrosis (PMF) or post-PV-MF/post-ET-
             MF as per WHO diagnostic criteria and intermediate-2 or high-risk primary or secondary
             MF based on the Dynamic International Prognostic Scoring System (DIPSS)

          -  Previously treated with a JAKi and failed on a JAK inhibitor or are ineligible to be
             treated with Ruxolitinib or Fedratinib at the discretion of the investigator

          -  Grade ≥ 2 bone marrow fibrosis, as confirmed by bone marrow biopsy within 12 weeks
             prior to Screening

        Fulfill the following laboratory parameters:

          -  Platelet count ≥ 50 X 10^9 /L, without the assistance of growth factors or platelet
             transfusions

          -  Absolute Neutrophil Count (ANC) ≥ 1 x 10^9/L without the assistance of granulocyte
             growth factors

          -  Peripheral blood blast count < 10%

          -  Eastern Cooperative Oncology Group (ECOG) performance status ≤2

          -  Life expectancy ≥ 3 months

          -  Adequate renal function, as determined by clinical laboratory tests (serum creatinine
             ≤ 1.5 x upper limit of normal (ULN), and calculated creatinine clearance ≥ 30 mL/min)
             (Cockcroft-Gault)

          -  Adequate hepatic function (ALT/AST ≤ 3 x ULN, total bilirubin ≤ 1.5 x ULN; or ALT/AST
             ≤ 5 x ULN, direct bilirubin ≤ 2 x ULN if due to myelofibrosis), and coagulation ([PT
             and PTT] ≤ 1.5 x ULN)

          -  Agree to provide bone marrow biopsies during the study: at baseline or within 12 weeks
             prior to enrollment, and every 6 months during treatment.

          -  Splenomegaly during the screening period as demonstrated by splenic length ≥ 5 cm
             below the costal margin by palpation or spleen volume of ≥ 450 cm3 by Magnetic
             Resonance Imaging (MRI) or Computerized Tomography (CT) scan

          -  Show at least 2 symptoms measurable (score ≥ 1) using the MFSAF, v4.0.

        Patients meeting any one of these exclusion criteria will be prohibited from participating
        in this study:

          -  Received previous systemic antineoplastic therapy (including unconjugated therapeutic
             antibodies, toxin immunoconjugates, ESA, and alpha-interferon) or any experimental
             therapy within 14 days or 5 half-lives, whichever is longer, before the first dose of
             study treatment.

          -  Major surgery within 2 weeks before the first dose of either study drug.

          -  Splenic irradiation within 6 months prior to Screening or prior splenectomy.

          -  AML, MDS, or peripheral blasts ≥ 10%.

          -  Prior autologous or allogeneic stem cell transplant at any time.

          -  Eligible for allogeneic bone marrow or stem cell transplantation within 3 months
             following enrollment.

          -  Experiencing electrolyte abnormalities of NCI CTCAE Grade ≥ 2 unless they can be
             corrected during screening and are deemed not clinically significant by the
             Investigator.

          -  History of congestive heart failure, myocardial infarction within the past 6 months
             prior to Cycle 1/Day 1; left ventricular ejection fraction < 45% by echocardiogram or
             MUGA, unstable arrhythmia, or evidence of ischemia on electrocardiogram (ECG) within
             14 days prior to Cycle 1/Day 1.

          -  Corrected QT interval (using Fridericia's correction formula) of > 450 msec in men and
             > 470 msec in women.

          -  Central nervous system (CNS) cancer or metastases, meningeal carcinomatosis, malignant
             seizures, or a disease that either causes or threatens neurologic compromise (eg,
             unstable vertebral metastases).

          -  Other invasive malignancies within the last 3 years, except non-melanoma skin cancer,
             and localized cured prostate and cervical cancer

          -  Experienced portal hypertension or any of its complications.

          -  Active, uncontrolled bacterial, viral, or fungal infections, requiring systemic
             antimicrobial within 14 days.

          -  Known bleeding diathesis or signs of uncontrolled active bleeding (hematuria, GI
             bleeding) other than self-limited causes of benign etiology that have been adequately
             investigated at the discretion of the Investigator.

          -  Requiring anticoagulation with aspirin > 81mg daily, unfractionated heparin, low
             molecular weight heparin (LMWH), direct anti-thrombin inhibitors, or vitamin K
             antagonists (eg, warfarin).

          -  Severe chronic obstructive pulmonary disease with hypoxemia (defined as resting O2
             saturation of < 90% breathing room air).

          -  Medical condition or have undergone significant surgery to the gastrointestinal tract
             that could impair absorption or that could result in short bowel syndrome with
             diarrhea due to malabsorption.

          -  Used hydroxyurea or anagrelide within 24 hours prior to the first dose.

          -  Systemic steroid therapy (>10 mg daily prednisone or equivalent) within 7 days prior
             to the first dose of study treatment (note: topical, inhaled, nasal, and ophthalmic
             steroids are not prohibited).