Higher Binding Affinity and Potency of Reslizumab for Interleukin-5 Compared With Mepolizumab.

Reslizumab and mepolizumab are recently approved monoclonal antibodies for the treatment of severe (uncontrolled) eosinophilic asthma. Both are effective in neutralizing the function of interleukin-5 (IL-5). This study is the first to compare the binding affinity and potency of both antibodies in head-to-head assays. Two assays assessed binding affinity (using the equilibrium dissociation constant [K]) of each drug for human IL-5. In the Biacore surface plasmon resonance assay, the association constant (k) values for human IL-5 for reslizumab and mepolizumab were 3.93 × 10⁶ and 1.83 × 10⁵, respectively. The dissociation constant (k) values were 4.29 × 10⁻⁴ and 2.14 × 10⁻⁴, respectively. Calculated K values for human IL-5 for reslizumab and mepolizumab were 109 and 1,170 pM, respectively, representing an approximately 11-fold stronger binding affinity with reslizumab. In the Kinetic Exclusion Assay, the k values for human IL-5 for reslizumab and mepolizumab were 3.17 × 10⁶ and 1.32 × 10⁵, respectively. The k values were 1.36 × 10⁻⁵ and 1.48 × 10⁻⁵, respectively. Measured K values for human IL-5 for reslizumab and mepolizumab were 4.3 and 112 pM, respectively, representing an approximately 26-fold stronger binding affinity for reslizumab. A human-IL-5-dependent cell proliferation assay was developed to assess potency, based on a human cell line selected for enhanced surface expression of IL-5 receptor-alpha and consistent proliferation response to IL-5. The concentration at which 50% inhibition occurred (IC₅₀) was determined for both antibodies. Reslizumab and mepolizumab inhibited IL-5-dependent cell proliferation, with IC₅₀ values of approximately 91.1 and 286.5 pM, respectively, representing on average 3.1-fold higher potency with reslizumab. In conclusion, comparative assays show that reslizumab has higher affinity binding for and potency against human IL-5 compared with mepolizumab. However, these results do not take into consideration the different methods of administration of reslizumab and mepolizumab.