Assessing the Feasibility of Neutralizing Osteopontin with Various Therapeutic Antibody Modalities

Abstract

Osteopontin is a secreted glycophosphoprotein that is highly implicated in many physiological and pathological processes such as biomineralization, cell-mediated immunity, inflammation, fibrosis, cell survival, tumorigenesis and metastasis. Antibodies against osteopontin have been actively pursued as potential therapeutics for various diseases by pharmaceutical companies and academic laboratories. Many studies have demonstrated the efficacy of osteopontin inhibition in a variety of preclinical models of diseases such as rheumatoid arthritis, cancer, nonalcoholic steatohepatitis, but clinical utility has not yet been demonstrated. To evaluate the feasibility of osteopontin neutralization with antibodies in a clinical setting, we measured its physiological turnover rate in humans, a sensitive parameter required for mechanistic pharmacokinetic and pharmacodynamic (PK/PD) modeling of biotherapeutics. Results from a stable isotope-labelled amino acid pulse-chase study in healthy human subjects followed by mass spectrometry showed that osteopontin undergoes very rapid turnover. PK/PD modeling and simulation of different theoretical scenarios reveal that achieving sufficient target coverage using antibodies can be very challenging mostly due to osteopontin's fast turnover, as well as its relatively high plasma concentrations in human. Therapeutic antibodies against osteopontin would need to be engineered to have much extended PK than conventional antibodies, and be administered at high doses and with short dosing intervals.

Figure 1

(a) Workflow for measurement of physiological protein turnover rate in human. A stable isotope labeled (D₃-leucine) pulse-chase was combined with immunoaffinity enrichment and liquid chromatography-tandem mass spectrometry (IA-LC-MS/MS) analysis. (b) Chromatograms show the MRM signal of heavy (blue) and light (red) peptide (GDSVVYGLR) of osteopontin at selected time points.

Figure 2

(a) D₃-leucine enrichment profiles in serum of three human subjects. (b) Dynamic four compartmental PK model for osteopontin half-life estimation. (c) Time course of labeled leucine enrichment in osteopontin peptide (GDSVVYGLR) during the study.

Figure 3

Simulations illustrating effects of varying antibody doses and dosing intervals in an antibody-ligand PK/PD model.