Inclusion Criteria

To be eligible to participate in this study, patients must meet all the following criteria:

1. Male or female, greater than or equal to18 years of age;
2. Patients with diagnosis of MM per the International Myeloma Working Group criteria ;
3. Eligible for ASCT at the Investigator's discretion;
4. \>4 weeks since completion of last cycle of chemotherapy prior to Day 1;
5. Patient must be on first or second complete response or partial response;
6. Eastern Cooperative Oncology Group performance status of 0 or 1 (see Appendix C);
7. Systolic blood pressure (SBP) 100 - 160 mmHg inclusive, and diastolic blood pressure (DBP) 60 - 100 mmHg inclusive;
8. ANC greater than or equal to1.0 x 109/L on Screening laboratory assessments;
9. Platelet count greater than or equal to100 x 109/L on Screening laboratory assessments;
10. Creatinine clearance greater than or equal to 30 ml/min, as calculated according to the Cockcroft-Gault formula;
11. Aspartate aminotransferase and alanine aminotransferase less than or equal to 2 x upper limit of normal (ULN) and total bilirubin less than or equal to1.5 x ULN on Screening laboratory assessments;
12. Adequate cardiac (left ventricular ejection fraction \[LVEF\] greater than or equal to 50%) and pulmonary function (room air O2 saturation value greater than or equal to 92%);
13. For females, 1 of the following criteria must be fulfilled:

1. At least 1 year postmenopausal; or
2. Surgically sterile, or willing to use a double-barrier method of contraception (e.g., intrauterine device plus condom, spermicidal gel plus condom) from Day 1 until 28 days after the last dose of GPC-100.
14. Males must be willing to use a reliable form of contraception (e.g., use of a condom or a partner fulfilling the above criteria) from Day 1 until 28 days after the last dose of GPC-100; and
15. Patients must be willing and able to provide signed informed consent. 4.2 Exclusion Criteria

Patients must be excluded if they meet any of the following criteria:

1. greater than or equal to 25% of BM irradiated within 5 years prior to Day 1 (see Appendix D);
2. No more than one year of therapy administered prior to stem cell mobilization, per institution standards;
3. Patients who have undergone previous stem cell transplant;
4. Receipt of G-CSF within 2 weeks prior to Day 1;
5. History of another malignancy except for the following:

1. Adequately treated local basal cell or squamous cell carcinoma of the skin;
2. Adequately treated carcinoma in situ of the cervix without evidence of disease;
3. Adequately treated papillary, noninvasive bladder cancer; or
4. Low-grade prostate cancer that is on active surveillance and not expected to clinically progress over 2 years.
6. Patients who are on BBs and unable to switch therapy; Note: Patients on BBs who are able to switch therapy will undergo a gradual tapering of their current BB under the guidance of the Investigator. At the Investigator's discretion, the initial days of propranolol administration may be permitted to overlap with the final days of tapering of the previous BB. Patients may not be treated with cardiovascular drugs that would interact with propranolol including angiotensin-converting enzyme (ACE) inhibitors, calcium channel blockers, and alpha blockers at study enrollment and while on propranolol during the study.
7. Patients with severe asthma who require beta agonist therapy;
8. History of poor and uncontrolled cardiovascular or pulmonary disease such as myocardial infarction, cardiac arrhythmias, transient ischemic attack, congestive heart failure (New York Heart Association heart failure class \>2), stroke, unexplained syncope, or chronic obstructive pulmonary disease;
9. History of long QT syndrome or torsade de pointes;
10. Patients with a QTcF \>470 msec or PR interval \>280 msec on Screening 12-lead electrocardiogram (ECG);
11. Active infection requiring treatment in the 7 days before Day 1;
12. Positive polymerase chain reaction test from nasal specimen for SARS-CoV-2 within 7 days prior to Day 1;
13. Pregnant or breastfeeding;
14. Known psychiatric or substance abuse disorder that would interfere with Protocol compliance;
15. Receipt of any other investigational drug or device within 1 month before Day 1; or
16. Receipt of prior treatment with CXCR4 inhibitor for stem cell collection.