Abstract
SummaryElucidating receptor occupancy (RO) of monoclonal antibodies (mAbs) is a crucial step in characterizing the therapeutic efficacy of mAbs. However, the in vivo assessment of RO, particularly within peripheral tissues, is greatly limited by current technologies. In the present study, we developed a bioluminescence resonance energy transfer (BRET)-based system that leverages the large signal:noise ratio and stringent energy donor-acceptor distance dependency to measure antibody RO in a highly selective and temporal fashion. This versatile and minimally invasive system enables longitudinal monitoring of the in vivo antibody-receptor engagement over several days. As a proof of principle, we quantified cetuximab-epidermal growth factor receptor binding kinetics using this system and assessed cetuximab RO in a tumor xenograft model. Incomplete ROs were observed, even at a supratherapeutic dose of 50 mg/kg, indicating that fractional target accessibility is achieved. The BRET-based imaging approach enables quantification of antibody in vivo RO and provides critical information required to optimize therapeutic mAb efficacy.
Highlights
Monoclonal antibodies are often regarded as ‘‘magic bullets’’ (Brodsky, 1988), which have been applied toward the treatment of an array of human diseases (Mould and Sweeney, 2007)
Elucidating the target engagement of a given Monoclonal antibodies (mAbs) is a crucial step toward characterizing its therapeutic potential and in determining its pharmacological dynamics, which helps define the optimal dosing regimens to achieve maximal therapeutic efficacy
We developed a bioluminescence resonance energy transfer (BRET)-based system to non-invasively quantify antibody receptor occupancy (RO) in live animals
Summary
Monoclonal antibodies (mAbs) are often regarded as ‘‘magic bullets’’ (Brodsky, 1988), which have been applied toward the treatment of an array of human diseases (Mould and Sweeney, 2007). These therapeutic mAbs are engineered to bind their cognate antigens with high affinities and have been deployed for neutralizing pathologic factors, blocking cellular signaling, and stimulating immune functions (Suzuki et al, 2015). Many other factors should be considered when interpreting RO, such as receptor epitope properties (Lipman et al, 2005; Rook et al, 2015), antibody-receptor binding is the first step required to elicit a pharmacological effect, and the binding kinetics of a given mAb to its targets within the tumor microenvironment dictates its general therapeutic potential
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