Cell-penetrating peptides (CPPs) are attractive tools for delivering macromolecules that have poor membrane permeability, such as antibodies, into cells. However, the major drawback of conventional CPPs is their instability in bodily fluids. We previously reported a novel CPP employing a collagen-like triple-helical structure that exhibited remarkable resistance against serum proteases. Herein, we report the delivery of full-length immunoglobulin G (IgG) antibody into cells using a triple-helical CPP. The CPP was conjugated to IgG via a one-pot reaction using 2-iminothiolane as a crosslinking reagent. The triple-helical CPP was less prone to being aggregated and neutralized by serum than was octaarginine, a conventional CPP. However, most of the conjugates were found to be entrapped in endosomes.
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