Bortezomib, Selinexor, and Dexamethasone in Patients With Multiple Myeloma

Inclusion Criteria:

1. Histologically confirmed MM with measurable disease per IMWG guidelines as defined by at least 1 of the following:

   1. Serum M-protein ≥ 0.5 g/dL (\> 5 g/L) by serum protein electrophoresis (SPEP) or for immunoglobulin (Ig) A myeloma, by quantitative serum IgA levels; or
   2. Urinary M-protein excretion at least 200 mg/24 hours; or
   3. Serum free light chain (FLC) ≥ 100 mg/L, provided that the serum FLC ratio is abnormal (normal FLC ratio: 0.26 to 1.65).
2. Had at least 1 prior anti-MM regimen and no more than 3 prior anti-MM regimens. Induction therapy followed by stem cell transplant and consolidation/maintenance therapy will be considered as 1 anti-MM regimen.
3. Documented evidence of progressive MM (based on the Investigator's determination according to the modified IMWG response criteria) on or after their most recent regimen.
4. Prior treatment with bortezomib or other Proteasome Inhibitor (PI) is allowed, provided all of the following criteria are met:

   1. Best response achieved with prior bortezomib at any time was ≥ PR and with the last PI (PI therapy (alone or in combination) was ≥ PR, AND
   2. Participant did not discontinue bortezomib due to ≥ Grade 3 related toxicity, AND
   3. Must have had at least a 6-month PI-treatment-free interval prior to Cycle 1 Day 1 (C1D1) of study treatment.
5. Must have an ECOG Status score of 0, 1, or 2.
6. Written informed consent in accordance with federal, local, and institutional guidelines.
7. Age ≥18 years.
8. Resolution of any clinically significant non-hematological toxicities (if any) from previous treatments to ≤ Grade 1 by C1D1. Patients with chronic, stable Grade 2 non-hematological toxicities may be included following approval from the Medical Monitor.
9. Adequate hepatic function within 28 days prior to C1D1.

   1. Total bilirubin \<1.5 × upper limit of normal (ULN) (except patients with Gilbert's syndrome who must have a total bilirubin of \<3 × ULN), and
   2. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) normal to \<2 × ULN.
10. Adequate renal function within 28 days prior to C1D1 (estimated creatinine clearance \[CrCl\] of ≥20 mL/min, calculated using the formula of Cockroft and Gault):

(140-Age) × Mass (kg)/(72 × creatinine mg/dL) Multiply by 0.85 if the patient is female, or if CrCl is ≥20 mL/min as measured by 24-hour urine collection.

11\. Adequate hematopoietic function within 7 days prior to C1D1: total white blood cell (WBC) count ≥1500/mm3, absolute neutrophil count ≥1000/mm3, hemoglobin ≥8.5 g/dL and platelet count ≥75,000/mm3 (patients for whom \< 50% of bone marrow nucleated cells are plasma cells) or ≥50,000/mm3 (patients for whom ≥50% of bone marrow nucleated cells are plasma cells).

1. Patients receiving hematopoietic growth factor support, including erythropoietin, darbepoetin, granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage-colony stimulating factor (GM-CSF), and platelet stimulators (eg, eltrombopag, romiplostim, or interleukin-11) must have a 2-week interval between growth factor support and the Screening assessments, but they may receive growth factor support during the study.
2. Patients must have:

   * At least a 2-week interval from the last red blood cell (RBC) transfusion prior to the Screening hemoglobin assessment, and
   * At least a 1-week interval from the last platelet transfusion prior to the Screening platelet assessment.

However, patients may receive RBC and/or platelet transfusions as clinically indicated per institutional guidelines during the study.

12\. Female patients of childbearing potential must have a negative serum pregnancy test at Screening. Female patients of childbearing potential and fertile male patients who are sexually active with a female of childbearing potential must use highly effective methods of contraception throughout the study and for 3 months following the last dose of study treatment.

Exclusion Criteria:

1. Prior exposure to a SINE compound (i.e. an XPO-1 inhibitor), including selinexor.
2. Prior malignancy that required treatment or has shown evidence of recurrence (except for non-melanoma skin cancer or adequately treated cervical carcinoma in situ) during the 5 years prior to randomization. Cancer treated with curative intent for \>5 years previously and without evidence of recurrence will be allowed.
3. Has any concurrent medical condition or disease (e.g., uncontrolled active hypertension, uncontrolled active diabetes, active systemic infection, etc.) that is likely to interfere with study procedures.
4. Uncontrolled active infection requiring parenteral antibiotics, antivirals, or antifungals within 1 week prior to C1D1. Patients on prophylactic antibiotics or with a controlled infection within 1 week prior to C1D1 are acceptable.
5. Active plasma cell leukemia.
6. Documented systemic light chain amyloidosis.
7. MM involving the central nervous system.
8. Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome.
9. Spinal cord compression.
10. Greater than Grade 2 neuropathy or ≥ Grade 2 neuropathy with pain at baseline, regardless of whether or not the patient is currently receiving medication
11. Known intolerance, hypersensitivity, or contraindication to glucocorticoids.
12. Radiation, chemotherapy, or immunotherapy or any other anticancer therapy (including investigational therapies) ≤ 2 weeks prior to C1D1. Localized radiation to a single site at least 1 week before C1D1 is permitted. Glucocorticoids within 2 weeks of C1D1 are permitted. Patients on long-term glucocorticoids during Screening do not require a washout period but must be able to tolerate the specified dexamethasone dose in this study.
13. Prior autologous stem cell transplantation \< 1 month or allogeneic stem cell transplantation \< 4 months prior to C1D1.
14. Active graft versus host disease (after allogeneic stem cell transplantation) at C1D1.
15. Pregnant or breastfeeding females.
16. Body Surface Area \< 1.4 m² at baseline, calculated by the Dubois or Mosteller method.
17. Life expectancy of \< 4 months.
18. Major surgery within 4 weeks prior to C1D1.
19. Active, unstable cardiovascular function:

    1. Symptomatic ischemia, or
    2. Uncontrolled clinically significant conduction abnormalities (e.g., patients with ventricular tachycardia on anti-arrhythmics are excluded; patients with first-degree atrioventricular block or asymptomatic left anterior fascicular block/right bundle branch block will not be excluded), or
    3. Congestive heart failure of New York Heart Association Class ≥ 3 or known left ventricular ejection fraction \< 40%, or
    4. Myocardial infarction within 3 months prior to C1D1.
20. Known active human immunodeficiency virus (HIV) infection or HIV seropositivity
21. Known active hepatitis A, B, or C infection; or known to be positive for hepatitis C virus ribonucleic acid (RNA) or hepatitis B virus surface antigen.
22. Any active gastrointestinal dysfunction interfering with the patient's ability to swallow tablets, or any active gastrointestinal dysfunction that could interfere with absorption of study treatment.
23. Any active, serious psychiatric, medical, or other conditions/situations that, in the opinion of the Investigator, could interfere with treatment, compliance, or the ability to give informed consent.
24. Contraindication to any of the required concomitant drugs or supportive treatments.
25. Patients unwilling or unable to comply with the protocol, including providing 24-hour urine samples for urine protein electrophoresis at the required time points.