Inhibition of RANKL is critical for accurate assessment of anti-drug antibody incidence to denosumab in clinical studies

Abstract

Denosumab is an approved monoclonal antibody therapeutic for the treatment of bone loss in the postmenopausal osteoporosis and oncology settings and acts by binding and neutralizing the activity of receptor activator of nuclear factor-kappa-B ligand (RANKL). Anti-drug antibodies (ADAs) to denosumab are measured via a standard electrochemiluminescence- (ECL) based bridging assay. In this format, the presence of soluble RANKL (sRANKL) in clinical samples can lead to false positive results. In a denosumab bioequivalence study, approximately 50 % of the serum samples showed reactivity to denosumab in the absence of a specific reagent to sequester the sRANKL. However, upon addition of osteoprotegerin (OPG) as a reagent to neutralize the sRANKL, the overall ADA incidence was lowered to <1 %. To address this RANKL reactivity over the long-term use of this assay, the performance of 3 RANKL inhibitors was evaluated using healthy donor sera samples spiked with different concentrations of positive control ADA, sRANKL, or both, in an ECL based immunoassay utilizing the Meso Scale Discovery (MSD) platform. Based on these data, the denosumab antibody assay was modified to include a neutralizing anti-RANKL monoclonal antibody to eliminate the assay reactivity or false positivity due to sRANKL. Use of an anti-RANKL antibody did not impact the ADA-specific signal but inhibited the false positive assay signal due to sRANKL, resulting in an accurate detection of ADA incidence. Therefore, inhibition of interference posed by sRANKL in study samples is critical for the accurate assessment of ADA incidence towards denosumab and any biosimilars for this product that are undergoing clinical development.