Phase 1/2 Study of Elotuzumab in Combination with Bortezomib in Patients with Multiple Myeloma with One to Three Prior Therapies: Interim Results.

Elotuzumab is a humanized monoclonal IgG1 antibody directed against CS1, a cell surface glycoprotein, which is highly and uniformly expressed in multiple myeloma (MM). In mouse xenograft models of MM, elotuzumab demonstrated significantly enhanced anti-tumor activity when combined with bortezomib compared to bortezomib alone (Van Rhee et al., Mol. Cancer Ther., in press, 2009). This phase 1/2 trial will determine the maximum tolerated dose (MTD), overall safety, pharmacokinetics (PK) and clinical response of elotuzumab in combination with bortezomib in patients with relapsed MM following 1-3 prior therapies.

The study consists of 4 escalating cohorts of elotuzumab (2.5 mg/kg to 20 mg/kg) administered on Days 1 and 11 and bortezomib (1.3 mg/m²) administered on Days 1, 4, 8 and 11 of a 21-day cycle. Patients with progressive disease at the end of Cycle 2 or 3 also receive oral dexamethasone (20 mg) on Days 1, 2, 4, 5, 8, 9, 11 and 12 of each subsequent cycle. Patients with stable disease or better at the end of 4 cycles will continue treatment for 6 or more cycles unless withdrawn earlier due to unexpected toxicity or disease progression. Key entry criteria: age ≥ 18 years; confirmed diagnosis of MM and documentation of 1 to 3 prior therapies; measurable disease M-protein component in serum and/or in urine; and no prior bortezomib treatment within 2 weeks of first dose.

To date, a total of 16 MM patients with a median age of 64 years have been enrolled in the study. The median time from initial diagnosis of MM was 3.5 years and patients had received a median of 2 prior MM treatments. Patients have been treated in four cohorts; 3 each in 2.5, 5 and 10 mg/kg elotuzumab cohorts, and 7 in the 20 mg/kg elotuzumab cohort. No dose limiting toxicity (DLT) was observed during the first cycle of the study and the MTD was not established. Five SAEs have been reported in four patients in later treatment cycles; two events, chest pain and gastroenteritis, occurring in one patient, were considered elotuzumab-related. Other SAEs include grade 3 sepsis, vomiting, pneumonia and grade 2 dehydration. The most common AEs reported include Grade 1-3 diarrhea, constipation, nausea, fatigue, thrombocytopenia, neutropenia, anemia and peripheral neuropathy. The best clinical response (EBMT criteria) for the 16 patients who have received at least two cycles of treatment is shown in the table below.

Preliminary PK analysis suggests a serum half-life of 10-11 days at higher doses (10 and 20 mg/kg). Preliminary analysis of peripheral blood mononuclear cells and bone marrow of patients on study indicates that objective responses in the study correlate well with complete saturation of CS1 sites by elotuzumab on bone marrow plasma and NK cells.

The combination of elotuzumab with bortezomib has a manageable adverse event profile and shows promising preliminary efficacy with ≥PR in 44% and ≥MR in 75% of all enrolled patients. Accrual is ongoing in the expanded 20 mg/kg cohort. Updated safety, efficacy, and PK data will be presented at the meeting.

Jakubowiak:Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Centocor Ortho Biotech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Exelixis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Off Label Use: Bortezomib in combination with elotuzumab for the treatment of relapsed/refractory multiple myeloma. Bensinger:Millennium: Membership on an entity's Board of Directors or advisory committees. Siegel:Millennium: Speakers Bureau; Celgene: Speakers Bureau. Zimmerman:Millennium: Speakers Bureau; Centecor: Speakers Bureau. Van Tornout:BMS: Employment. Zhao:Facet Biotech: Employment. Singhal:Facet Biotech: Employment. Anderson:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.