Phase 1/2 Study of Elotuzumab in Combination with Lenalidomide and Low Dose Dexamethasone in Relapsed or Refractory Multiple Myeloma: Interim Results.
Authors: Lonial Sagar , Vij Ravi , Harousseau Jean-Luc , Facon Thierry , Kaufman Jonathan , Mazumder Amitabha , Moreau Philippe , Leleu Xavier , Fry John , Singhal Anil , Jagannath Sundar 
Published: October 2019

Abstract
Abstract 432

Elotuzumab is a humanized monoclonal IgG1 antibody directed against CS1, a cell surface glycoprotein, which is highly and uniformly expressed in multiple myeloma (MM). Elotuzumab induces significant antibody-dependant cytotoxicity (ADCC) against primary myeloma cells in the presence of either autologous or allogeneic peripheral lymphocytes (PBMC), which is significantly enhanced when PBMC effector cells were pretreated with lenalidomide (Tai et al., Blood 112:1329, 2008). The primary objective of the phase 1 portion of the study is to evaluate the maximum tolerated dose (MTD) of elotuzumab in combination with lenalidomide and low dose dexamethasone in patients with relapsed MM. The study is also evaluating safety, pharmacokinetics (PK) and clinical response. Lenalidomide (25 mg PO) is given on Days 1-21 of a 28-day cycle. Elotuzumab in three escalating dose cohorts (5, 10 and 20 mg/kg) is administered by IV infusion on Days 1, 8, 15 and 22 of the 28-day cycle in the first two cycles and then on Days 1 and 15 of each subsequent cycle. Dexamethasone is given weekly at 40 mg PO. Initially, patients received 6 cycles of treatment unless withdrawn earlier due to disease progression or unacceptable. toxicity. The protocol was amended to allow for patients in the 10 and 20 mg/kg cohorts to receive treatment for up to 12 months following enrollment of the last patient. Key entry criteria: age ≥ 18 years; MM with at least one relapse; measurable disease M-protein component in serum and/or in urine; and prior lenalidomide treatment, if any, more than 6 weeks of first dose. To date, 24 patients with a median age of 60 years have been enrolled in the study and 23 patients have received study drug. The median time from initial diagnosis of MM was 5 years and patients had received a median of 3 prior MM treatments. Patients had been previously treated with thalidomide (58%), bortezomib (67%) or lenalidomide (21%) and 42% were refractory to their most recent MM therapy. Patients have been treated in the 3 cohorts; 3 patients each in the first two cohorts (5 and 10 mg/kg elotuzumab) and 17 patients (7 in dose-escalation phase and 10 in the expansion phase) in the third cohort (20 mg/kg). No dose limiting toxicities were identified during the dose-escalation phase of the study and no MTD was established. One patient discontinued in the first cycle due to grade 4 allergic reaction resulting from elotuzumab infusion in the expansion phase of the study. Additional SAEs (1 of each) included grade 2 atrial fibrillation (related to lenalidomide/dexamethasone) and unrelated grade 4 ruptured diverticulum, grade 3 neutropenic fever and grade 3 diarrhea.. Other common grade 3 or 4 AEs included neutropenia (25%) and thrombocytopenia (25%), which were managed by dose withholding or dose reduction of lenalidomide. Approximately 25% of patients experienced grade 1 or 2 chills and/or pyrexia associated with elotuzumab infusion. The best clinical response (IMWG criteria) in the 13 patients who have received at least two cycles of treatment is shown in the table below.
Preliminary PK analysis of elotuzumab suggests a serum half-life of 10-11 days at 10 and 20 mg/kg. Elotuzumab at all three doses resulted in near complete saturation of CS1 sites on plasma cells and NK cells in bone marrow and NK cells in the peripheral compartment. In conclusion, the combination of elotuzumab with lenalidomide and low-dose dexamethasone has a manageable adverse event profile and compared to historical data for lenalidomide and high-dose dexamethasone, the preliminary efficacy data (≥ PR of 92%) are very encouraging. Additional safety, efficacy and PK/PD data will be presented at the meeting.

Disclosures:
Lonial: Celgene: Consultancy; Millennium: Consultancy, Research Funding; BMS: Consultancy; Novartis: Consultancy; Gloucester: Research Funding. Off Label Use: Lenalidomide/dexamethasone in combination with elotuzumab in patients with relapsed/refractory multiple myeloma. Vij:Celgene: Research Funding, Speakers Bureau. Harousseau:Celgene France: Advisory Board; Janssen Cilag France: Advisory Board; Celgene: Honoraria; Janssen Cilag: Honoraria; Novartis: Honoraria; Amgen: Honoraria. Facon:Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen Cilag: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Kaufman:Celgene: Consultancy, Research Funding; Millennium: Consultancy; Genzyme: Consultancy; Merck: Research Funding. Mazumder:Celgene: Speakers Bureau; Millennium: Speakers Bureau. Leleu:Celgene: Research Funding, Speakers Bureau. Fry:Facet Biotech: Employment. Singhal:Facet Biotech: Employment. Jagannath:Millennium: Advisory Board; Merck: Advisory Board.