Study of the Safety and Efficacy of KRT-232 Combined with Ruxolitinib in Patients with Primary Myelofibrosis (PMF), Post–Polycythemia Vera MF (Post–PV-MF), Or Post–Essential Thrombocythemia MF (Post-ET-MF) Who Have a Suboptimal Response to Ruxolitinib

Prior treatment

• Active or chronic bleeding within 4 weeks prior to the first dose of navtemadlin.
• Other JAK inhibitors, except for ruxolitinib treatment; other recent/concurrent treatment such as a major surgery, chemotherapy, immunomodulating therapy, biologic therapy, radiation therapy, or investigational therapy within 4 weeks or approximately 5 half-lives before the first dose of navtemadlin, whichever is shorter. Hydroxyurea is permitted up until the day prior to study Day 1 of study treatment with navtemadlin.
• Prior splenectomy.
• Splenic irradiation within 3 months prior to the first dose of navtemadlin.
• Prior allogeneic stem-cell transplantation or eligible for allogeneic stem cell transplantation
• Prior MDM2 inhibitor therapy or p53-directed therapy

Other illness

• History of major organ transplant
• Subjects must be negative for HIV-1 antibody, negative for HbsAg, negative for Hepatitis B core antibody, and negative for viral RNA if HCV antibody is positive. Subjects must be negative for Hepatitis B DNA, if either HbsAg or Hepatitis B core antibody is positive.
• Active serious viral, mycobacterial, parasitic, fungal, and bacterial infections, including acute hepatitis A, herpes zoster, and progressive multifocal leukoencephalopathy (PML). Active serious infections must be resolved before screening/enrollment. Subjects with acute infections requiring systemic antibiotic use should delay screening/enrollment until the course of antibiotic therapy has been completed.
• Patients with uncontrolled intercurrent illness including, but not limited to; clinically significant cardiac disease (New York Heart Association Class III or IV); symptomatic congestive heart failure; unstable angina pectoris; ventricular arrhythmia; or patients with psychiatric illness/social situations that would limit compliance with study requirements; or patients who have been committed to an institution by judicial or administrative authority.
• Other malignancy within the last 3 years, other than curatively treated basal cell or squamous cell skin cancer, carcinoma in situ of the cervix, organ-confined or treated nonmetastatic prostate cancer with normal prostate-specific antigen, in situ breast carcinoma after complete surgical resection, or superficial transitional cell bladder carcinoma.
• Documented disease progression or clinical deterioration any time while on ruxolitinib treatment.

Lab values

• Grade 2 or higher QTc prolongation (>480 milliseconds per NCICTCAE criteria, version 5.0).

Other

• Patients who are positive for TP53 mutations.
• Women who are pregnant or breastfeeding
• For full list please refer to the Protocol.
• Patients who have had a documented spleen response to ruxolitinib.
• Participation in another interventional clinical trial within the past 4 weeks of the first dose of navtemadlin (participation in observational studies is permitted).

• Adults >18 years of age.
• For full list please refer to the Protocol
• Confirmed diagnosis of PMF, post–PV-MF, or post–ET-MF, as assessed by treating physician according to the World Health Organization (WHO) criteria.
• Treatment with ruxolitinib for ≥ 18 weeks prior to study entry, and on a stable dose of ruxolitinib in the 8 weeks prior to Sponsor approval of the enrollment form.
• Spleen ≥ 5 cm palpable below the LLCM or ≥450 cm3 by MRI or CT
• Patients must have at least 2 symptoms with a score of at least 1 on the MFSAF v4.0
• An MRI or CT scan for spleen volume must be performed no more than 14 days prior to the first dose of navtemadlin.
• ECOG performance status of 0 to 2.
• Adequate hematological, hepatic, and renal organ function (as per protocol definition and within 28 days prior to the first dose of navtemadlin).
• Female subjects of childbearing potential and their male partners, or male subjects who have female partners of childbearing potential must both use an effective contraception method during the study. In addition, after the last dose of study drug, female subjects must continue to use contraception for 1 month and 1 week and male subjects must continue to use contraception for 3 months and 1 week.