Cell penetrating peptides can exert biological activity: a review

Cell penetrating peptides (CPPs) have been successful in delivering cargo into many different cell types and are an important alternative to other methods of permeation that might damage the integrity of the cell membrane. The traditional view of CPPs is that they are inert molecules that can be successfully used to deliver many cargos intracellularly. The goal of this review is to challenge this traditional understanding of CPPs. Recent literature has demonstrated that CPPs themselves can convey biological activity, including the alteration of gene expression and inhibition of protein kinases and proteolytic activity. Further characterization of CPPs is required to determine the extent of this activity. Research into the use of CPPs for intracellular delivery should continue with investigators being aware of these recent results.