Cell-penetrating peptides in drug development: enabling intracellular targets.

A large body of literature has shown that CPPs (cell-penetrating peptides) are capable of carrying macromolecules across the plasma membrane. CPPs can penetrate a wide variety of tissue types and enable modulation of intracellular targets with molecules that, by themselves, are incapable of penetrating cells. As a result, CPPs are recognized for their potential value in validating intracellular targets that could lead to drug discovery programmes [Dietz and Bahr (2004) Mol. Cell Neurosci. 27, 85-131]. The potential for CPP-drug conjugates to be used as human therapeutic agents has not been extensively explored and there is limited knowledge regarding the characteristics of CPPs which are necessary for drug development. A better understanding of the properties of CPPs relating to in vivo pharmacology, pharmacokinetics, pharmacodynamics and safety will continue to inform and encourage novel drug development efforts using CPPs as therapeutics. Here we will discuss areas of interest for drug development of CPP-conjugated compounds.