Rapid identification of Human Serum Albumin binding peptides from a phage display library：a back-of-the-envelope assessment of positive binders using titer-based criteria

Human serum albumin (HSA) is the most abundant protein in blood and has a 19-day in vivo half-life, the longest human blood protein. HSA has also been extensively studied as a drug carrier in a wide variety of clinical applications. HSA-binding, compared with HSA-fusion, is promising strategy for extending the plasma half-life of protein therapeutics. The construction of albumin-binding drugs requires assessment of a large enough quantity of HSA-binding peptide candidates for conjugation with therapeutic proteins. Here, we report a back-of-the-envelope assessment method to facilitate phage display selection of HSA-binding peptides. With an experimentally determined number of phage titers, we can calculate the specificity ratios and the recovery yields. The recovery yield is calculated using the titers of eluted phage divided by the titers of input phage. The specificity ratio is calculated using the titer of eluted phage from a target-coated plate divided by the titer of eluted phage from a blank-control plate. These parameters are defined as quantitative criteria for panning and characterization of binding phage clones. Consequently, this approach may enable more rapid and low-cost phage display screening of HSA-binding peptides, which could be used as candidates of HSA binders for conjugation with therapeutic proteins.