We describe the use of four complementary biosensors (Biacore 3000, Octet QK, 
ProteOn XPR36, and KinExA 3000) in characterizing the kinetics of human nerve 
growth factor (NGF) binding to a humanized NGF-neutralizing monoclonal antibody 
(tanezumab, formerly known as RN624). Tanezumab is a clinical candidate as a 
therapy for chronic pain. Our measurements were consistent with the 
NGF/tanezumab binding affinity being tighter than 10 pM due to the formation of 
an extremely stable complex that had an estimated half-life exceeding 100 h, 
which was beyond the resolution of any of our methods. The system was 
particularly challenging to study because NGF is an obligate homodimer, and we 
describe various assay orientations and immobilization methods that were used to 
minimize avidity in our experiments while keeping NGF in as native a state as 
possible. We also explored the interactions of NGF with its natural receptors, 
TrkA and P75, and how tanezumab blocks them. The Biacore blocking assay that we 
designed was used to quantify the potency of tanezumab and is more precise and 
reproducible than the currently available cell-based functional assays.