Status update in the use of cell-penetrating peptides for the delivery of macromolecular therapeutics.

INTRODUCTION: In this review, recent developments and applications with cell-penetrating peptides (CPP) are discussed. CPPs are widely used tools for the delivery of various macromolecular therapeutics, such as proteins and nucleic acids. AREAS COVERED: The current review focuses on recent important advances and reports that demonstrate high clinical and translational potential. Most important clinical developments have occurred with the CPP-drug conjugate approaches that target various protein-protein interactions, and these have been highlighted subsequently. Most of the applications are targeting cancer, but recently, noteworthy advances have taken place in the field of antisense oligonucleotides and muscular dystrophies, lung targeting, and trans-BBB targeting. EXPERT OPINION: Successful applications and clinical development with the drug conjugate approaches are discussed. On the other hand, the reasons of why the nanoparticle approaches are not as far in development are analyzed.