ABSTRACT
Therapeutic monoclonal antibodies (MoAb) have become important tools in the treatment of numerous diseases. Many of these MoAb are present in the blood at very high levels due to high dosing and long half-lives. Quantification of biomarkers bound by these therapeutic MoAb can be an important factor in determining efficacy and dosing requirements. However, quantitation of these biomarkers with reasonable accuracy can be very difficult to accomplish due to concomitant binding of the therapeutic MoAb. We describe here a novel method for quantifying total (free plus bound) biomarker concentration in the presence of high levels of therapeutic MoAb using a single non-competing MoAb in a capture/elution format. This assay has the capability to accurately detect and quantitate circulating ng/ml biomarker levels in the presence of 200 microg/ml or more of therapeutic MoAb.
Subject(s)
Antibodies, Monoclonal/immunology , Biomarkers/analysis , Antibodies/immunology , Antibodies, Monoclonal/therapeutic use , Antibody Specificity/immunology , Biomarkers/metabolism , Biotinylation , Computer Simulation , Drug Tolerance , Enzyme-Linked Immunosorbent Assay , Epitopes/metabolism , Humans , Models, Biological , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
Proprotein convertase subtilisin/kexin type 9 (PCSK9) has gained attention as a key regulator of serum low density lipoprotein cholesterol (LDL-C) levels. This novel protease causes the degradation of hepatic low density lipoprotein receptors. In humans, gain-of-function mutations in PCSK9 cause a form of familial hypercholesterolemia, whereas loss-of-function mutations result in significantly decreased LDL-C levels and cardiovascular risk. Previous studies have demonstrated that statins upregulate PCSK9 mRNA expression in cultured cells and animal models. In light of these observations, we studied the effect of atorvastatin on circulating PCSK9 protein levels in humans using a sandwich ELISA to quantitate serum PCSK9 levels in patients treated with atorvastatin or placebo for 16 weeks. We observed that atorvastatin (40 mg/day) significantly increased circulating PCSK9 levels by 34% compared with baseline and placebo and decreased LDL-C levels by 42%. These results suggest that the addition of a PCSK9 inhibitor to statin therapy may result in even further LDL-C decreases.
