Inclusion Criteria:

• Age ≥ 18 years.
• Must have RRMM after having received prior exposure to at least 3 prior lines of therapies in addition to being refractory to a Proteasome Inhibitor (PI), Immune-Modulatory agent (IMiD), and an anti-CD38 monoclonal antibody:
  • Refractory MM is defined as the development of disease progression during therapy with an anti-myeloma regimen or within 60 days of the last dose of an anti-myeloma regimen or the achievement of less than a partial response (< PR) within 60 days of stopping prior therapy.
  • For relapsing MM patients, the duration from the last dose of the last prior treatment regimen to relapse must be ≤ 12 months.
• Measurable disease MM defined by the following:
  • Serum M-protein ≥ 0.5 g/dL; OR
  • Urine M-protein ≥ 200 mg/24 hours; OR
  • Serum free light chain (FLC) assay; involved FLC level ≥ 10 mg/dL provided the serum FLC ratio is abnormal; OR
  • ≥ 30% clonal plasma cells in the bone marrow aspirate or biopsy sample.
• Pulse oximetry ≥ 92% on room air.
• ECOG performance status of 0, 1, or 2.
• Be willing and able to comply with the study schedule and all other protocol requirements.
• Females of childbearing potential (FCBP), defined as a sexually mature woman who has not undergone a hysterectomy or tubal ligation or who has not been naturally postmenopausal for at least 24 consecutive months, must have a negative pregnancy test during the Screening Period prior to treatment. All heterosexually active FCBP and all heterosexually active male patients must agree to use effective methods of birth control throughout the study.

Exclusion Criteria:

• Use of 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.
• Treatment with an allogeneic hematopoietic stem cell transplantation (HSCT) within 6 months prior to the planned infusion of STI-6129, or active graft-versus-host disease (GVHD) following the allogeneic transplant, or a requirement for currently receiving immunosuppressive therapy following the allogeneic transplant.
• Received the last dose of daratumumab (Darzalex) or other anti-CD38 treatment within 90 days.
• A diagnosis of other malignancies if the malignancy has required therapy within the last 3 years or is not in complete remission. Exceptions are non-metastatic basal cell or squamous cell carcinomas of the skin or prostate cancer or in situ cancer that does not require treatment or is well under control.
• A current history of CTCAE Grade 3 muscle paresis, eyelid conditions, glaucoma controlled with medication or watering eyes or any other ocular disorder that is CTCAE Grade 2.
• The following baseline hematological laboratory results at Screening (with no blood product or hematopoietic growth factor support during the prior 7 days):
  • Hemoglobin < 8.0 g/dL;
  • Platelet count < 50,000/μL;
  • Absolute neutrophil count (ANC) < 1000/ μL.
• The following baseline chemistry laboratory results at Screening:
  • Estimated creatinine clearance < 45 mL/min (using the Cockcroft-Gault equation);
  • Serum aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 3 x the upper limit of normal (ULN) or serum total bilirubin > 1.5x ULN (except for patients in whom hyperbilirubinemia is attributed to Gilbert’s Syndrome).
• INR or aPTT > 1.5 times ULN within one week prior to the infusion of STI-6129, unless on a stable dose of an anticoagulant
• Patients with ≥ Grade 3 neuropathy or Grade 2 neuropathy with associated pain.
• New York Heart Association (NYHA) Class > 2.
• QTcF > 470 msec on a 12-lead ECG.
• Left ventricular ejection fraction (LVEF) < 40%.
• Has an active COVID-19 infection or if recovered, must have a negative RT-PCR test and not have had symptoms within 4 weeks of D1.
• Active bacterial, viral, or fungal infection within 72 hours of the infusion of STI-6129; patients with ongoing use of prophylactic antibiotics, antifungal agents, or antiviral agents remain eligible as long as there is no evidence of active infection.
• Have human immunodeficiency virus (HIV) infection, human T-cell leukemia virus type 1 (HTLV1) infection, or hepatitis B virus (HBV) or hepatitis C virus (HCV) viremia or are at risk for HBV reactivation (at risk for HBV reactivation is defined as being HBs antigen [HbSAg] or HBV deoxyribonucleic acid (DNA) positive, or anti-HBc-antibody positive unless also HbSAg and HBV DNA negative). Note that HCV ribonucleic acid (RNA) must be undetectable by laboratory test.
• If a FCBP is pregnant or breast feeding or planning on either during the study
• Patient has any significant medical condition, laboratory abnormality, or psychiatric illness that would prevent the patient from participating in the study. Stable conditions or those controlled with medications may participate per investigator discretion if willing to maintain a stable dose of medications during the study.
• Any condition including the presence of laboratory abnormalities that places the patient at an unacceptable risk if the patient was to participate in the study.

Eligibility last updated 2/28/22. Questions regarding updates should be directed to the study team contact.