Detection of Sotatercept (ACE-011) in human serum by SAR-PAGE and western single blotting

A method for the detection of Sotatercept (ACE-011, ACVR2A-Fc) in human serum is presented. The method is a modification of a recently published protocol for Luspatercept (ACE-536, ACVR2B-Fc), another erythropoiesis stimulating fusion protein. Out of 27 tested antibodies against either the extracellular domain of ACVR2A or the full-length protein, only 4 antibodies bound strongly enough to Sotatercept for usage with immunoprecipitation followed by SAR-PAGE and Western single blotting. The adapted protocol allows the detection of 0.1 ng/mL Sotatercept in just 50 μL human serum. None of the 3 commercial ACVR2-ELISAs was able to detect Sotatercept and the 2 tested surrogate proteins, even in the μg/mL range. As for Luspatercept, only IPG-IEF/2D-PAGE generated discrete isoforms. Due to the long serum half-life, the SAR-PAGE method will be able to detect Sotatercept for several weeks and will be very useful in doping testing.