Bioportides: bioactive cell-penetrating peptides that modulate cellular dynamics

The study and exploitation of cell-penetrating peptides (CPPs) now extends into a third exciting decade. Pharmacokinetic modulators, including the more common sequences Tat, penetratin and transportan-10, markedly enhance the intracellular delivery of small drugs, peptides, oligonucleotides and proteins. We introduced the term bioportide to distinguish cell penetrant peptides with intrinsic bioactivities from more typically inert CPP vectors. Our first examples included rhegnylogically organised bioportides, monomeric peptides presenting pharmacophores for both cellular internalization and bioactivity discontinuously distributed within the primary sequence. However, it is conceptually expedient to employ the same terminology to encompass sychnologic bioportides that comprise an inert CPP vector conjugated to an otherwise impermeable bioactive peptide. In such cases the CPP provides an obvious address function whilst the bioactive cargo, often a protein mimetic sequence, is the message. Additional targeting sequences, usually added as chimeric extensions, can also be accommodated within the design of CPPs and bioportides to enable cell- and tissue-selective targeting. Thus, the identification and exploitation of bioportides provides further scope to employ CPPs as research tools, diagnostics and therapeutics spanning a range of pathologies.