This is a two-stage phase 1b/2a, open-label, multicenter, dose-escalation study of STI-6129 administered intravenously once in a 4-week cycle in subjects with relapsed or refractory multiple myeloma.

This is a two-stage phase 1b/2a, open-label, multicenter, dose-escalation study of STI-6129 administered intravenously once in a 4-week cycle in subjects with relapsed or refractory multiple myeloma.

The study is designed to identify the recommended phase 2 dose (RP2D) of STI-6129 by assessing the safety, preliminary efficacy and pharmacokinetics using a conventional 3+3 study design for dose escalation in stage one and then the second stage will be an expansion study to assess preliminary efficacy.

Patients will be enrolled sequentially within each cohort and between cohorts during the dose escalation portion of the study with a 28-day cycle of treatment.

Inclusion Criteria:

• Must have relapsed or refractory multiple myeloma (RRMM) after having received prior lines of anti-myeloma treatments, including being refractory to a proteasome inhibitor, immunomodulatory agent and an anti-CD38 monoclonal antibody
• Measurable disease as defined by one of the following: abnormal serum or M-protein levels; abnormal serum free light chain (FLC) assay; ≥ 30% clonal plasma cells in the bone marrow aspirate or biopsy sample
• Pulse oximetry ≥ 92% on room air
• Eastern Cooperative Oncology Group (ECOG) performance of 0 - 2
• Be willing and able to comply with the study schedule and all study requirements
• Willing to follow contraception guidelines

Exclusion Criteria:

• Prior systemic anti-tumor therapy or an investigational drug within 5 half-lives or 4 weeks of D1, whichever is shorter, preceding the first dose of study drug
• Prior treatment with allogeneic hematopoietic stem cell transplantation within 6 months, has active graft versus host disease following transplant or currently receiving immunosuppressive therapy following transplant
• Diagnosis of other malignancies if the malignancy required therapy in the last 3 years or is not in complete remission
• Current history of CTCAE Grade 3 muscle paresis or ocular disorders that are Grade 3 or 2
• Has any clinically significant low baseline lab results for hemoglobin, platelet counts, and neutrophil counts at screening
• Abnormal INR or aPTT, unless on a stable dose of an anticoagulant
• Has ≥ Grade 3 neuropathy or Grade 2 neuropathy with associated pain
• Has any clinically significant baseline lab results for creatinine clearance, serum aspartate aminotransferase, alanine aminotransferase, total bilirubin
• New York Heart Association Class > 2
• Left ventricular ejection fraction < 40%
• Prolonged QTcF interval on a 12-lead electrocardiogram
• Has active COVID-19 infection, and not present with symptoms within 4 weeks of study drug
• Has an active bacterial, viral, or fungal infection
• Has known HIV or acquired immunodeficiency syndrome-related illness, acute or history of chronic hepatitis B or C
• Is currently pregnant or breast feeding or planning on either during the study
• Has any significant medical condition, abnormality, or psychiatric illness that would prevent study participation
• Has any additional clinical history that would place the patient at an unacceptable risk if the patient participates in the study