Population Pharmacokinetic and Pharmacodynamic Modeling of an Anti–Interleukin-6 Chimeric Monoclonal Antibody, Siltuximab (CNTO 328), in Patients with B-Cell Non-Hodgkin's Lymphoma, Multiple Myeloma, or Castleman's Disease
Authors: Xie Lanyi , Li Lilian Y , Kurzrock Razelle , van Rhee Frits , Qin Xiang , Reddy Manjula , Qi Ming , Davis Hugh M , Zhou Honghui , Puchalski Thomas A 
Published: October 2019

Abstract
Abstract 1365

Introduction
Siltuximab (CNTO 328) is a chimeric, murine-human, monoclonal antibody that specifically binds human interleukin (IL)-6 with high affinity. C-reactive protein (CRP) can be a pharmacodynamic (PD) marker of IL-6 bioactivity, i.e., reductions in CRP suggest inhibition of systemic IL-6. A population mechanistic pharmacokinetic (PK)/PD model was developed to describe the relationship between siltuximab serum concentrations and CRP suppression in patients with B-cell non-Hodgkin's lymphoma (NHL), multiple myeloma (MM), or Castleman's disease (CD). Simulation was used to support the dose selection in the CD registration study and future clinical studies.

Methods
PK/PD data were obtained from a phase 1 clinical study examining multiple dosing regimens of siltuximab administered intravenously in patients with NHL, MM, or CD. Dosing regimens included siltuximab 2.8, 5.5, or 11 mg/kg every 2 weeks; 11 mg/kg every 3 weeks; or 5.5 mg/kg every week. Serial samples to determine serum concentration of siltuximab and serial CRP samples were collected following the first dose. NONMEM 7 was used to simultaneously fit a two-compartment PK model and an inhibitory indirect-response PD model to the observed data. Simulation of 1000 replications was then used to identify siltuximab dosage regimens that would maintain CRP suppression below the lower limit of quantification (LLOQ) of 1 mg/L.

Results
The mechanistic PK/PD model was able to describe the serum siltuximab and CRP concentration-time profiles. Volume of distribution and systemic clearance rate constant of siltuximab were estimated at 68.42 mL/kg and 0.0584/day, respectively. The PD parameter estimates (Kin and Kout of CRP) were 5.03 mg/L/day and 0.457/day, respectively, and were similar between the three disease types in this study. IC50was estimated at 9.73 μg/mL and was also similar between disease types. For all disease types, simulations showed that siltuximab 11 mg/kg every 3 weeks or 15 mg/kg every 4 weeks after the second dose would reduce serum CRP to below the LLOQ throughout the entire treatment period. However, lower dose intensive schedules, including a dose of 5.5 mg/kg every 2 weeks, would not reduce CRP to below the LLOQ at any time point during the treatment period.

Conclusion
The population PK/PD modeling and simulation support using a siltuximab dose of 11 mg/kg every 3 weeks or 15 mg/kg every 4 weeks in future clinical development studies. This dosing recommendation is supported by the observed efficacy dose-response relationship in patients with CD (J Clin Oncol 2010;28:3701–8).

Disclosures:
Xie: Johnson & Johnson: Employment, Equity Ownership. Li:Johnson & Johnson: Employment, Equity Ownership. Kurzrock:Johnson & Johnson: Honoraria, Research Funding. van Rhee:Johnson & Johnson: Research Funding. Qin:Johnson & Johnson: Employment, Equity Ownership. Reddy:Johnson & Johnson: Employment, Equity Ownership. Qi:Johnson & Johnson: Employment, Equity Ownership. Davis:Johnson & Johnson: Employment, Equity Ownership. Zhou:Johnson & Johnson: Employment, Equity Ownership. Puchalski:Johnson & Johnson: Employment, Equity Ownership.