Study to Assess Safety and Tolerability of OPN-6602 in Subjects With Relapsed and/or Refractory Multiple Myeloma

• OPN-6602 (Drug): orally active, small molecule inhibitor of EP300 and CBP bromodomain; dosed daily
• Dexamethasone (Drug): Synthetic glucocorticoid; 40 mg Days 1, 8, 15 of each cycle

Primary outcomes

• Number and type of dose-limiting toxicities (DLTs) [Through up to approximately 30 days following last dose of OPN-6602]
• Number and type of treatment-emergent adverse events (TEAEs) [Through up to approximately 30 days following last dose of OPN-6602]
• Number of Participants With Clinical Laboratory Test Abnormalities [Through up to approximately 30 days following last dose of OPN-6602]: Number of participants who experienced a clinical laboratory test abnormality, including hematology and serum chemistry, and coagulation. Abnormalities considered are those Grade 3-4 events with a >= 1 grade increase from baseline using National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Confirmed diagnosis of multiple myeloma (MM)
* Relapsed or refractory to 3 or more different prior lines of therapy for MM that included immunomodulatory agents, proteosome inhibitors, and anti-CD38 antibody and not a candidate for or intolerant to established therapy known to provide clinical benefit
* Adequate hematologic, renal, liver, cardiac function

Exclusion Criteria:

* Monoclonal gammopathy of undetermined significance (MGUS), smoldering myeloma, Waldenström's macroglobulinemia, or IgM myeloma
* Active plasma cell leukemia
* Polyneuropathy, organomegaly, endocrinopathy, monoclonal protein and skin changes (POEMS syndrome)
* Prior Stevens Johnson syndrome
* Localized radiation therapy to disease site(s) within 2 weeks of the first dose
* Prior autologous peripheral stem cell transplant or prior autologous bone marrow transplantation within <90 days of the first dose of study drug
* Prior allogeneic stem cell transplantation or solid organ transplantation within 12 months of first dose of study drug; subjects receiving immunosuppressive medication for active graft vs host disease will be excluded.
* Prior chemotherapy, targeted anticancer or radiation therapy within 2 weeks prior to first dose of study drug
* Concomitant high-dose corticosteroids (except subjects on chronic steroids given for disorders other than myeloma)
* Known central nervous system involvement by multiple myeloma
* Active known second malignancy with exception of adequately treated basal cell carcinoma, squamous cell carcinoma of the skin, or in situ cervical cancer; adequately treated Stage 1 cancer from which the subject is currently in remission and has been in remission for ≥2 years; low-risk prostate cancer with a Gleason score <7 and a PSA level <10 ng/mL; any other cancer from which the subject has been disease-free for ≥3 years
* Ongoing systemic infection requiring parenteral treatment
* Poorly controlled Type 2 diabetes