A Study of an MMSET Inhibitor in Patients With Relapsed and Refractory Multiple Myeloma

Key Inclusion Criteria: ≥ 18 years of age ECOG score ≤ 2 Relapsed or refractory multiple myeloma (as per IMWG) ≥ 3 prior lines of therapy, including a PI, an IMiD, and an anti-CD38 antibody Patients must have exhausted available therapeutic options that are expected to provide a meaningful clinical benefit, either through disease relapse, treatment refractory disease, intolerance, or refusal of the therapy t(4;14) confirmed by standard of care FISH testing, or GOF mutation in MMSET confirmed by local sequencing test (Part B dose expansion cohorts only) Measurable disease, including at least 1 of the following criteria: Serum M protein ≥ 0.50 g/dL (by SPEP) Serum IgA ≥ 0.50 g/dL (IgA myeloma patients) Urine M protein ≥ 200 mg/24 h (by UPEP) sFLC involved light chain ≥ 10 mg/dL (100 mg/L) (patients with abnormal sFLC ratio) ≥ 1 extramedullary lesion ≥ 1 cm in size and able to be followed by imaging assessments (Part A dose escalation cohorts only) Bone marrow plasma cells ≥ 10% (Part A dose escalation cohorts only) Key Exclusion Criteria: Treatment with the following therapies in the specified time period prior to first dose: Radiation, chemotherapy, immunotherapy, or any other anticancer therapy ≤ 2 weeks Cellular therapies ≤ 8 weeks Autologous transplant < 100 days Allogenic transplant ≤ 6 months, or > 6 months with active GVHD Major surgery ≤ 4 weeks History of or current plasma cell leukemia, POEMS (polyneuropathy, organomegaly, endocrinopathy, and skin changes) syndrome, solitary bone lesion or bone lesions as the only evidence for plasma cell dyscrasia, myelodysplastic syndrome or a myeloproliferative neoplasm or light chain amyloidosis Active CNS disease Inadequate bone marrow function Inadequate renal, hepatic, pulmonary, and cardiac function Active, ongoing, or uncontrolled systemic viral, bacterial, or fungal infection. Permitted prophylactic medications, antimicrobials or antiretroviral therapies defined in protocol. Use of acid reducing agents and strong inhibitors or inducers of CYP3A4 within 14 days or 5 half-lives prior to first dose Active malignancy not related to myeloma requiring therapy within < 3 years prior to enrollment, or not in complete remission, with exceptions defined in protocol.