In vitro selection of a peptide inhibitor of human IL-6 using mRNA display.

Interleukin-6 (IL-6) plays a crucial role in malignant diseases, such as rheumatoid arthritis, Castleman disease, and multiple myeloma, and as such, is an attractive therapeutic target. Here, the authors isolated a novel IL-6 inhibitor peptide by in vitro selection using mRNA display. The authors first used a random-primed human cDNA library to isolate IL-6-binding peptides. After four rounds of selection, a 19-amino acid peptide named CA11 was selected and confirmed to specifically interact with IL-6. The authors then performed an alanine scan analysis of CA11 and determined the amino acid residues necessary to interact with IL-6. Next, the authors constructed a CA11-based partially randomized library and after ten more rounds of selection, isolated several groups of peptides. The most frequently occurring sequence, RA07, bound to IL-6 with 3 to 4-fold higher affinity than CA11. Furthermore, RA07 inhibited IL-6-dependent KT-3 cell proliferation in a dose-dependent manner. ELISAs revealed that RA07 could not inhibit IL-6 from binding to the IL-6 receptor (IL-6R), but could inhibit the IL-6/IL-6 complex binding to gp130.