Screening the Human Proteome for Peptides Targeting the Acidic Environment of Tumor Tissues

Acidic-environment targeting peptides (AEPs), which insert into cell membranes under acidic conditions, have been gaining attention as potential targeting ligands for acidic tissues such as tumors. Conventional AEPs have been taken from archaea or designed rationally; therefore, they have a risk of antigenicity. Here, we propose screening for AEPs from the human proteome. AEP candidates were screened from more than 20000 human proteome transmembrane peptides based on 4 conditions AEPs should fulfill. Twenty-seven peptides were found to satisfy the four conditions. The same number of candidate peptides were identified in the mouse membrane proteome, most of which originated from the orthologous membrane proteins identified in the human proteome. Four of the 27 peptides selected from the human proteome were synthesized with a fluorescence label attached or expressed as fusion proteins with green fluorescent protein to examine their acid-responsive accumulation in vitro and in vivo. We found that 1 of the 4 peptides performed similarly to the pH-low insertion peptide, the first reported AEP.