Absolute quantification of monoclonal antibodies in biofluids by liquid chromatography--tandem mass spectrometry

The development of a quantification method for monoclonal antibodies in serum has been accomplished by high-performance liquid chromatography multiple reactions monitoring mass spectrometry. A human monoclonal antibody (HmAb) was used as the model protein for method development and validation. A peptide from the CDR3-region of its heavy chain was selected and used for quantifying the entire mAb. This signature peptide served as a template for the internal standard. Prior to mass spectrometric analysis approximately 50% of the total serum protein content was removed by albumin depletion. The accuracy of the method ranged between 99 and 112% in cynomolgus monkey serum. The intra-assay coefficient of variation (CV) was lower than 4% at 4 [micro]g/mL and 200 [micro]g/mL HmAb (n = 3). The CV at 400 [micro]g/mL corresponded to 9% (n = 3). In addition, the interassay variation was investigated in a male cynomolgus serum pool and in a female cynomolgus serum pool. The CV for the male cynomolgus pool at 4 [micro]g/mL HmAb was 7% (n = 3). The CV obtained from the female pool was 8% (n = 3), at 4 [micro]g/mL. The dynamic range of the method was 3 orders of magnitude. After albumin depletion of 25 [micro]L of serum, a lowest limit of quantification of 2 [micro]g/mL HmAb was reached in both human and cynomolgus monkey samples.