Pharmacokinetics and toxicology of therapeutic proteins: Advances and challenges

Table 3 Bioanalytical methods applied to absorption, distribution, metabolism and excretion studies of therapeutic proteins

Methods	Capability to assay for	Current throughput	Currently use	Current sensitivity
Immunoassay	Total, free, intact	High for serum, low for tissues, requires homogenization	Mostly serum/plasma, physiological fluids (e.g., synovial and bronchoalveolar lavage )	Usually high for serum/plasma
Bioassay	Activity of targets, biomarker, ex vivo efficacy	Medium to low, may require fresh samples for certain assays	Serum/plasma and tissues	Varies depending on individual assay
Radioactivity counting	Total, intact and degradants	High, requires probe preparation and characterization	Serum/plasma, tissues, biological fluids, and excreta	Usually high, depending on specific activity of labeled materials
MS	Total, free, intact and degradants	High for peptides in serum/plasma, requires homogenization for tissues	Serum/plasma, tissues, biological fluids, and excreta	Usually high for peptides
		Medium to low for proteins in plasma/serum, requires purification (e.g., immunocapture) and digestion for large MW biologics		Low for large proteins
Imaging	Total, intact and degradants	Medium to low, requires probe preparation and characterization	Live animals, clinical studies in humans, cells and tissues	Varies, depending on probes used and study settings
Auto-radiography	Total, intact and degradants	Low, requires tissue slicing and film developing	Tissues	Varies, depending on specific activity of labeled materials

“Low” and “High” sensitivity is an assessment of likelihood of obtaining a sufficient data-set for quantitative assessment of absorption, distribution, metabolism and excretion properties. MW: Molecular weight; MS: Mass spectrometry.