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

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