A Phase I Study of the Safety and Pharmacokinetics of Escalating Doses of MFGR1877S, a Fibroblast Growth Factor Receptor 3 (FGFR3) Antibody, in Patients with Relapsed or Refractory t(4;14)-Positive Multiple Myeloma

Abstract Abstract 4029 Introduction: Chromosomal translocation of the FGFR3 oncogene in t(4;14)-positive multiple myeloma (MM) causes FGFR3 overexpression in plasma cells, chemoresistance, and poor prognosis leading to shorter overall survival in MM patients (pts). MFGR1877S is a human monoclonal antibody that targets FGFR3 to prevent ligand binding, receptor-receptor association, and FGFR3 signaling. In preclinical studies, anti-FGFR3 antibody suppresses FGFR3-mediated cell proliferation, and exerts strong anti-tumor activity in mouse xenograft models of both t(4;14)-positive MM and bladder carcinoma. Methods: This Phase I study assessed the safety, tolerability, and biologic activity of MFGR1877S given intravenously, weekly for 3 weeks, followed by every 28-day dosing, to eligible patients with t(4;14)-positive MM. Dose escalation started with single-pt cohorts at 1 and 2 mg/kg, followed by a standard 3+3 dose-escalation scheme at doses ranging from 4–15 mg/kg. Dose escalation decisions were made based on monitoring pts for dose-limiting toxicities (DLT) during the first 22 days on study. FGFR3 expression, safety, pharmacokinetics (PK), and response (EBMT/IMWG criteria) were assessed. Main efficacy outcome measures include serum/urine M protein and free light chain (FLC) quantities. Results: A total of 14 pts (median age 66, range 45–78; 43% female) with a baseline ECOG status of 0–2, and a median number of 5 prior therapies (range 1–10), received a median of 3.5 doses (range 1–7) of MFGR1877S. Adverse events (AEs) deemed related to MFGR1877S were diarrhea, fatigue, and nausea (14% each), and anemia, increased creatinine, bone pain, confusion, decreased appetite, myalgia, and fever (7% each). The only Grade ≥ 3 related AE was fatigue (7%). Six pts experienced 9 serious AEs (SAE), one of which was Grade 2 pyrexia attributed to MFGR1877S that occurred within 24 hours of infusion and required hospitalization. This pt later discontinued due to a second SAE of Grade 2 pyrexia requiring hospitalization not attributed to MFGR1877S. One pt died of intracranial hemorrhage not attributed to MFGR1877S. No Grade 4 SAEs were reported. Other reported SAEs included Grade 3 hypercalcemia, neutropenia, pain in extremity, and musculoskeletal chest pain (1 pt each), Grade 2 ankle fracture, pneumonia, and pyrexia × 2 (1 pt each). No maximum tolerated dose was identified, as no DLTs were observed through the highest dose tested (15 mg/kg). Preliminary PK analysis for limited number of multiple myeloma patients (n=14) by non-linear mixed effect modeling demonstrated a trend of dose proportional increase of exposure (area under the concentration-time curve and maximal concentration) from 2 to 15 mg/kg. Population clearance of MFGR1877S was estimated to be ∼0.62 L/day, suggesting that MFGR1877S appeared to have a slightly faster clearance in MM patients, compared to the typical IgG1 monoclonal antibody clearance in human. The central volume of distribution of MFGR1877S was ∼3.4 L, which approximated human serum volume and appeared similar to the central volume of distribution of other typical IgG1 monoclonal antibodies. While some degree of FGFR3 expression was detected by immunohistochemistry in 10/14 patient bone marrow samples taken at screening, FACS analysis of FGFR3 surface expression on myeloma cells, although largely consistent with IHC measurements, also revealed heterogeneity in the levels of detectable surface FGFR3 expression. Six pts had stable disease as their best response: 2 pts up to 4 cycles, 1 pt up to 3 cycles, and 3 pts up to 1 cycle. Conclusions: MFGR1877S was well-tolerated overall in these patients with multiple relapsed or refractory MM. Although no objective responses were observed, stable disease was observed in 3 pts for 3–4 cycles. Disclosures: Off Label Use: MFGR1877S is a human monoclonal antibody that targets FGFR3 to prevent ligand binding, receptor-receptor association, and FGFR3 signaling. Singhal:Millennium and Celgene: Speakers Bureau. Niesvizky:Onyx, Millemium, Celgene. Speakers bureau: Millenium and Celgene: Consultancy, Research Funding. Comenzo:Millenium, Neotope; Onyx, Osiris, Millenium: Consultancy, Research Funding. Lebovic:Genentech: Speakers Bureau. Choi:Genentech: Employment. Lu:Genentech: Employment. French:Genentech: Employment. Penuel:Genentech: Employment. Ho:Genentech: Employment.

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