This study evaluates KRT-232, a novel oral small molecule inhibitor of MDM2, for the treatment of patients with phlebotomy-dependent polycythemia vera (PV). Inhibition of MDM2 in PV is a new mechanism of action in PV. In Part A, patients must be resistant or intolerant to hydroxyurea or have undergone treatment with interferon. In Part B, patients must be resistant or intolerant to hydroxyurea.

This study is a global, open-label Phase 2a/2b study to determine the efficacy and safety of KRT-232. In Part A of the study, patients will be randomly assigned to 5 arms with 2 different doses and 3 different dosing schedules of KRT 232. In Part B of the study, patients will be randomized either to treatment with KRT-232 administered at the recommended dose and schedule from Part A or to treatment with ruxolitinib.

Inclusion Criteria:

• Confirmed diagnosis of PV (WHO 2016)
• ECOG ≤ 2
• Part A: patients with and without splenomegaly are eligible
• Part A: patients must be resistant or intolerant to hydroxyurea or have undergone treatment with interferon
• Part B: only patients with splenomegaly are eligible
• Part B: patients must be resistant or intolerant to hydroxyurea

Exclusion Criteria:

• Diagnosis of post-PV myelofibrosis (IWG-MRT)
• Prior treatment with MDM2 inhibitors, p53-directed therapies, HDAC, BCL 2 inhibitors
• Splenic irradiation within 3 months prior to the first dose of study treatment
• Clinically significant thrombosis within 3 months of screening
• Grade 2 or higher QTc prolongation
• Part B: prior treatment with a JAK inhibitor