A Study of SDX-7320 in Combination With Eribulin for People With Breast Cancer

Inclusion Criteria: * Male or female with histologically and/or cytologically confirmed diagnosis of triple-negative metastatic breast cancer defined as estrogen and progesterone receptor staining ≤10%; and HER2-negative defined as IHC 0 to 1+ at enrolling institution (note: if IHC is equivocal, non-amplified status by FISH is acceptable) * Advanced (local regionally recurrent, not amenable to curative therapy or surgery) or metastatic stage with up to 2 prior lines of therapy in the advanced or metastatic setting * Received prior anthracycline and taxane chemotherapy in the neoadjuvant, adjuvant, or metastatic settings and considered appropriate for treatment with single agent eribulin OR was otherwise ineligible to receive anthracycline and/or taxane per treating physician OR patients with de novo metastatic disease. * Evidence of metabolic dysfunction defined as HbA1c \> 5.5 and/or BMI ≥ 30 kg/m\^2 * Measurable disease per the Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST 1.1), OR at least one evaluable, predominantly lytic bone lesion * Eastern Cooperative Oncology Group Performance Status (ECOG-PS) ≤1. * Adult ≥18 at the time of informed consent and has provided written informed consent before the performance of any study-related activities and according to local guidelines. * Adequate bone marrow and organ function as defined by the following laboratory values (as assessed by local laboratory for eligibility): * Absolute neutrophil count (ANC) ≥ 1,000 µL * Platelet count ≥ 140,000 µL * Hemoglobin ≥9.0 g/dL: * Calcium (corrected for serum albumin) and magnesium ≤ Grade 1 according to National Cancer Institute (NCI) Common Terminology * Calculate Corrected Calcium if the albumin and/or serum calcium are not within normal limits: Corrected Calcium= Serum Calcium + 0.8 x \[(Normal Albumin) - Patient Albumin\] Normal Albumin value = 4.4g/dL Criteria for Adverse Events (CTCAE), version 5.0, and not considered by the Investigator to be clinically significant * Potassium within normal limits, with or without correction with supplements. * In absence of liver metastases, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5×the upper limit of normal (ULN). If the patient has liver metastases, ALT and AST ≤5×ULN. * Total bilirubin ≤1.5×ULN except for patient with Gilbert's syndrome who may only be included if the total bilirubin is ≤3.0×ULN or direct bilirubin ≤1.5×ULN * Creatinine ≤1.5 mg/dL. * Patient is, in the treating Investigator's opinion, willing and able to comply with the study requirements, including the ability to fast prior to treatment days. * If sexually active female of childbearing potential, willing to use a contraception method listed below: * Oral, intravaginal, or transdermal combined (estrogen and progesterone containing) hormonal contraception * Oral, injectable, or implantable progesterone-only hormonal contraception * Intrauterine device (IUD) * Intrauterine hormone-releasing system (IUS) * Bilateral tubal occlusion * Vasectomized partner with documentation of successful vasectomy. * Complete abstinence from heterosexual intercourse * If a sexually active male, willing to use barrier contraception (condoms) Exclusion Criteria: * Three or greater prior lines of therapy for metastatic TNBC * Known primary brain malignancy, brain metastases or active CNS pathology, any of which as determined by the treating Investigator * Currently participating in a study of an investigational agent * Body mass index \< 18.5 kg/m2 * Known hypersensitivity to SDX-7320 or eribulin * Established diagnosis of diabetes mellitus type I or uncontrolled or insulin-dependent type II. Uncontrolled is defined as fasting blood glucose \>140 mg/dL and/or HbA1c ≥8% * Use of combination antihyperglycemic therapy (single agent metformin on stable dose for at least 3 months prior to enrollment is allowable) * Concurrent malignancy or malignancy within 3 years of randomization, with the exception of adequately treated, basal or squamous cell carcinoma, nonmelanomatous skin cancer or curatively resected cervical cancer. * Uncontrolled human immunodeficiency virus (HIV) infection. (Testing is not mandatory.) * Evidence of uncontrolled active Hepatitis B or C infection * History of Stevens-Johnson Syndrome (SJS), erythema multiforme (EM), toxic epidermal necrolysis (TEN), or other severe medication-related cutaneous reactions. * Any other concurrent severe and/or uncontrolled medical condition that would, in the Investigator's judgment, contraindicate patient participation in the clinical study (e.g., chronic active hepatitis, severe hepatic impairment). * Clinically significant, uncontrolled heart disease and/or recent cardiac events including any of the following: * History of angina pectoris, coronary artery bypass graft (CABG) symptomatic pericarditis, or myocardial infarction within 6 months prior to study entry. * History of documented congestive heart failure (New York Heart Association functional classification III-IV). * Documented cardiomyopathy. * Left ventricular ejection fraction (LVEF) \<45%, as determined by Multiple Gated acquisition (MUGA) scan or echocardiogram (ECHO). * History of any cardiac arrhythmias, (e.g., ventricular tachycardia), complete left bundle block, high grade atrioventricular (AV) block (e.g., bifascicular block, Mobitz type II and third-degree AV block) supraventricular, nodal arrhythmias, or conduction abnormality in the previous 12 months. * Uncontrolled hypertension, defined by a systolic blood pressure (SBP) ≥160 mmHg and/or diastolic blood pressure (DBP) ≥100 mmHg, with or without antihypertensive medication. Initiation or adjustment of antihypertensive medication(s) is allowed prior to screening * Long QT syndrome, family history of idiopathic sudden death or congenital long QT syndrome or any of the following: risk factors for torsades de pointe including uncorrected hypoka