A Phase 2 Multicenter Study of Siltuximab, An Anti-IL-6 Monoclonal Antibody, in Patients with Relapsed or Refractory Multiple Myeloma,
Authors: Voorhees Peter M. , Manges Robert F , Sonneveld Pieter , Jagannath Sundar , Somlo George , Krishnan Amrita , Lentzsch Suzanne , Frank Richard C , Zweegman Sonja , Wijermans P.W. , Rijnbeek Britte , Qin Xiang , Cornfeld Mark J. , Xie Hong , Thomas Sheeba K. 
Published: October 2019

Abstract
Abstract 3971

Background:
Although outcomes have improved for patients (pts) with multiple myeloma (MM), relapsed/refractory MM remains associated with short survival and constitutes an unmet medical need. Glucocorticoids (GCs) are an important component of MM therapy; however, resistance is common. In preclinical models, interleukin-6 (IL-6) promotes the proliferation and survival of MM cells in the context of the bone marrow microenvironment and protects these cells from GC-induced apoptosis. Therefore, blocking IL-6 may disrupt resistance and restore sensitivity to GCs. Here, we report the final results from a Phase 2 open-label, non-randomized study that evaluated the safety and efficacy of siltuximab (S), a monoclonal antibody targeting soluble human IL-6, in combination with high-dose dexamethasone (D) in pts with relapsed and relapsed/refractory MM.

Methods:
Pts with measurable, secretory disease who had received at least 2 prior lines of therapy, one of which contained bortezomib, and progressed during or after their last line of treatment were eligible. Other key eligibility criteria included a creatinine clearance ≥20 mL/min, platelets ≥50,000/mm3, and neutrophils ≥1,000/mm3. S was administered 6 mg/kg IV on days 1 and 15 of a 28-day cycle and oral D 40mg once daily, on days 1–4, 9–12, and 17–20 for a max of 4 cycles; days 1–4 for subsequent cycles. The first 14 pts received S alone for the initial 1 to 2 cycles; 10 pts had D added for progressive disease post-Cycle 1 or suboptimal response post-Cycle 2. 39 subsequent pts received S+D concurrently as none of the first 14 pts achieved ≥PR while on S monotherapy. The primary endpoint was overall response rate (ORR, CR+PR) using EBMT criteria. Secondary endpoints were time to progression (TTP), progression-free survival (PFS), overall survival (OS), and incidence of AEs and SAEs.

Results:
Forty-nine pts received S+D. The median age was 65 yrs (range 43–89) and 43% of pts were female. The median disease duration was 4 yrs (range 0.7–13.2). Pts were heavily pretreated, having received prior bortezomib (100%), steroids (100%), IMIDs (90%), alkylating agents (91%) and ASCT (65%). The median number of prior lines of therapy was 4 (range 2–9); 86% had disease that was refractory to the last prior line. Of the 44 pts with prior D exposure, 32 (73%) were refractory to the last D-containing regimen. The median duration of therapy was 4 cycles (99 days). Of the 47 pts evaluable for response, the ORR by EBMT criteria was 17% (0 CRs, 8 PRs); the ORR + minimal response (MR) rate was 23.4% (N=11). Using IMWG criteria, the ORR + MR rate was 27.7% (9 PRs, 4 MRs). Of the 11 pts with at least MR by EBMT criteria, 5 pts were refractory to the last D-containing regimen and 7 experienced less than MR on a prior D-containing regimen. The median duration of response was 5.9 months (181 days, 95% CI: 147, 365). Three pts had a long-lasting response of 9 months or more. For all 49 pts, the median PFS was 3.7 months (114 days, 95% CI: 84, 148) and median OS was 20.4 months (621 days, 95% CI: 347,984). AEs occurring in ≥25% of pts were thrombocytopenia, fatigue, anemia, abnormal hepatic function, neutropenia, diarrhea, peripheral edema, dyspnea and dizziness. 74% of pts experienced a grade ≥3 AE; the most frequent non-hematologic grade ≥3 AEs were fatigue (8%), abnormal hepatic function (8%), and pneumonia (6%). Grade 4 hematologic toxicities were thrombocytopenia (12%), neutropenia (4%) and anemia (2%). 25% of pts discontinued treatment due to an AE. Twenty (41%) of the 49 pts experienced ≥1 SAE. The most frequently occurring SAEs were pneumonia (8%), thrombocytopenia (6%), septic shock, anemia, and hemolytic anemia (4% each). Five pts died during the study; 3 due to progressive disease, 2 due to infection (nosocomial infection, septic shock).

Conclusions:
The combination of siltuximab with dexamethasone was well tolerated. Although the ORR was modest in this relapsed/refractory patient population, responses were seen in pts with MM refractory to prior dexamethasone-containing therapy, suggesting that siltuximab may be able to at least partially overcome dexamethasone resistance in some cases. Overall, these results provide a rationale for further studies of siltuximab in combination with dexamethasone-based MM therapy.

Disclosures:
Voorhees: MedImmune: Consultancy; Pfizer: Research Funding; Centocor Ortho Biotech: Research Funding; Celgene: Research Funding; Merck: Research Funding. Off Label Use: Siltuximab for the treatment of multiple myeloma. Manges:Centocor Ortho Biotech: Research Funding. Sonneveld:Millennium Pharmaceuticals: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Onyx: Consultancy, Research Funding. Jagannath:Merck: Honoraria; Millennium Pharmaceuticals: Honoraria; Johnson and Johnson Pharmaceuticals: Consultancy; Celgene: Consultancy, Honoraria; Centocor Ortho Biotech: Research Funding. Somlo:Onyx: Consultancy; Millennium: Consultancy; Celgene: Consultancy, Speakers Bureau; Centocor Ortho Biotech: Research Funding. Krishnan:Celgene: Speakers Bureau; Millennium Pharmaceuticals: Speakers Bureau; Centocor Ortho Biotech: Research Funding. Lentzsch:Celgene: Consultancy, Research Funding; Onyx: Consultancy; Genzyme: Consultancy; Centocor Ortho Biotech: Research Funding. Frank:Centocor Ortho Biotech: Research Funding. Zweegman:Centocor Ortho Biotech: Research Funding. Wijermans:Centocor Ortho Biotech Research & Development: Research Funding. Rijnbeek:Ortho Biotech Oncology Research and Development: Employment. Qin:Johnson & Johnson Pharmaceutical Research & Development, LLC: Employment. Cornfeld:Ortho Biotech Oncology Research and Development: Employment. Xie:Ortho Biotech Oncology Research & Development: Employment. Thomas:Centocor Ortho Biotech: Research Funding; Millennium Pharmaceuticals: Research Funding; Celgene: Research Funding; Novartis: Research Funding; Immunomedics: Research Funding.