Agents that can deliver cell-impermeable biologics inside live cells have the potential to greatly improve the treatment of human diseases and benefit medical research in general. The delivery of peptides, proteins, or siRNAs into cells can for instance be used to reintroduce tumor-suppressors into cancer cells or to knock down disease-causing genes by RNA interference. Yet, methodologies that deliver macromolecules into cells are inefficient and this bottleneck has greatly limited the development of protein or RNA-based therapies. Over the past decade, cell-penetrating peptides (CPPs) have generated a lot of enthusiasm because of their ability to carry macromolecular cargos into cells. A major obstacle to the use of CPPs is that, while they are able to enter cells by endocytosis, CPPs and cargo are retained in endosomes, greatly limiting their usefulness. We have recently uncovered the ability of a specific CPP derivative, a disulfide-bonded dimer of fluorescently labeled TAT (dfTAT), to escape endosomes with astonishingly high efficiency. Consequently, we have further established that dfTAT can deliver proteins into live cells with great ease. Remarkably, the endosomal escape mediated by this agent is not cytotoxic. dfTAT is therefore an extremely promising delivery agents that holds the secret to effective and safe cellular penetration. The objectives of this proposal are to establish the mechanisms of dfTAT-mediated endosomal escape and to identify molecular and cellular features required for this activity. We will identify the structural and molecular determinants of dfTAT endosomal escape by establishing critically needed structure- activity relationships. In addition, we will identify the triggers of endosomal leakage and establish the cellular factors that contribute to this process. The rationale for the proposed research is that the mechanistic knowledge gained will permit the design of improved endosomolytic reagents that can be optimally incorporated into therapeutically relevant drug delivery systems. This should in turn greatly facilitate the development of protein and RNA-based therapeutics and benefit researchers as well as patients.
Reagents that can deliver proteins or nucleic acids inside live cells have the potential of revolutionizing the development of therapeutics for the treatment of human diseases. Currently, a major bottleneck in the field is that protein or nucleic acid therapeutics cannot penetrate cells efficiently. Recently, we have identified several cell-penetrating peptides that can potentially solve this problem. While extremely promising, optimization and mechanistic studies are required to make these delivery peptides more effective. We will determine how the structure and chemical properties of these compounds affects their ability to penetrate cells. We will also establish how they cross biological membranes. This knowledge will provide a strong foundation for the rational design of delivery tools with properties optimized for future in vivo therapeutic applications.
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