After demonstrating the on target effect of GMI-1359 via pharmacodynamic markers (CXCR4 and E-selectin), Sponsor terminated the trial due to COVID-related slow enrollment.

This trial is being conducted to investigate the safety, tolerability, pharmacokinetics (the effect the body has on the drug), and pharmacodynamics (the effect the drug has on the body) of GMI-1359 when given with standard-of-care treatment to subjects with HR+ metastatic breast cancer.

Inclusion Criteria:

• Pathologically confirmed HR+ metastatic breast cancer, currently stable or minimally progressive on current endocrine-based therapy.
• Continuing on current endocrine-based therapy with an aromatase inhibitor, selective estrogen receptor degrader, or selective estrogen receptor modulator; and must be medically eligible to remain on this therapy during the treatment period.

Exclusion Criteria:

• Uncontrolled acute life-threatening bacterial, viral, or fungal infection.
• Subjects who are pregnant or breastfeeding
• Concurrent treatment with any cytotoxic chemotherapy agent or other targeted therapies including HER2 targeting therapies
• Currently receiving, or less than 28 days since ending treatment on another investigational drug.
• Clinically significant cardiovascular disease.
• Abnormal liver function.
• Any medical, psychiatric, or other condition which, in the opinion of the investigator, is likely to interfere with trial completion, assessments, or interpretation of trial results, or otherwise would make the subject an inappropriate subject for this trial.