Supramolecular Structures Generated via Self-Assembly of a Cell Penetrating Tetrapeptide Facilitate Intracellular Delivery of a Pro-apoptotic Chemotherapeutic Drug

Development of drug carriers, which can chaperone xenobiotics directly to their site of action, is an essential step for the advancement of precision medicine. Cationic nanoparticles can be used as a drug delivery platform for various agents including chemotherapeutics, oligonucleotides, and antibodies. Self-assembly of short peptides facilitates the formation of well-defined nanostructures suitable for drug delivery, and varying the polarity of the self-assembly medium changes the nature of noncovalent interactions in such a way as to generate numerous unique nanostructures. Here, we have synthesized an ultrashort cell-penetrating tetrapeptide (sequence Lys-Val-Ala-Val), with Lys as a cationic amino acid, and studied the self-assembly property of the BOC-protected (L1) and -deprotected (L2) analogues. Spherical assemblies obtained from L1/L2 in a 1:1 aqueous ethanol system have the ability to encapsulate small molecules and successfully enter into cells, thus representing them as potential candidates for intracellular drug delivery. To verify the efficacy of these peptides in the facilitation of drug efficacy, we generated encapsulated versions of the chemotherapeutic drug doxorubicin (Dox). L1- and L2-encapsulated Dox (Dox-L1 and Dox-L2), similar to the unencapsulated drug, induced upregulation of regulator of G protein signaling 6 (RGS6) and Gβ5, the critical mediators of ATM/p53-dependent apoptosis in Dox-treated cancer cells. Further, Dox-L1/L2 damaged DNA, triggered oxidative stress and mitochondrial dysfunction, compromised cell viability, and induced apoptosis. The ability of Dox-L1 to mediate cell death could be ameliorated via knockdown of either RGS6 or Gβ5, comparable to the results obtained with the unencapsulated drug. These data provide an important proof of principle, identifying L1/L2 as drug delivery matrices.

Self-assembly of an amphipathic ααβ-tripeptide into cationic spherical particles for intracellular delivery

The development of molecular carriers able to carry molecules directly into the cell is an area of intensive research. Cationic nanoparticles are effective delivery systems for several classes of molecules, such as anticancer agents, oligonucleotides and antibodies. Indeed, a cationic charge on the outer surface allows a rapid cellular uptake together with the possibility of carrying negatively charged molecules. In this work, we studied the self-assembly of an ultra-short ααβ-tripeptide containing an l-Arg-l-Ala sequence and an unnatural fluorine substituted β^2,3-diaryl-amino acid. The presence of the unnatural β^2,3-diaryl-amino acid allowed us to obtain a protease stable sequence. Furthermore, an arginine guanidinium group triggered the formation of spherical assemblies that were able to load small molecules and enter cells. These spherical architectures, thus, represent interesting candidates for the delivery of exogenous entities directly into cells.

Recent progress in gene therapy to deliver nucleic acids with multivalent cationic vectors

Due to the potential use as transfecting agents of nucleic acids (DNA or RNA), multivalent cationic non-viral vectors have received special attention in the last decade. Much effort has been addressed to synthesize more efficient and biocompatible gene vectors able to transport nucleic acids into the cells without provoking an immune response. Among them, the mostly explored to compact and transfect nucleic acids are: (a) gemini and multivalent cationic lipids, mixed with a helper lipid, by forming lipoplexes; and (b) cationic polymers, polycations, and polyrotaxanes, by forming polyplexes. This review is focused on the progress and recent advances experimented in this area, mainly during the present decade, devoting special attention to the lipoplexes and polyplexes, as follows: (a) to its biophysical characterization (mainly electrostatics, structure, size and morphology) using a wide variety of experimental methods; and (b) to its biological activity (transfection efficacy and cytotoxicity) addressed to confirm the optimum formulations and viability of these complexes as very promising gene vectors of nucleic acids in nanomedicine.

Biocompatible ELR-Based Polyplexes Coated with MUC1 Specific Aptamers and Targeted for Breast Cancer Gene Therapy

The search for new and biocompatible materials with high potential for improvement is a challenge in gene delivery applications. A cell type specific vector made of elastin-like recombinamer (ELR) and aptamers has been specifically designed for the intracellular delivery of therapeutic material for breast cancer therapy. A lysine-enriched ELR was constructed and complexed with plasmid DNA to give positively charged and stable polyplexes. Physical characterization of these polyplexes showed a particle size of around 140 nm and a zeta potential of approximately +40 mV. The incorporation of MUC1-specific aptamers into the polyplexes resulted in a slight decrease in zeta potential but increased cell transfection specificity for MCF-7 breast cancer cells with respect to a MUC1-negative tumor line. After showing the transfection ability of this aptamer-ELR vector which is facilitated mainly by macropinocytosis uptake, we demonstrated its application for suicide gene therapy using a plasmid containing the gene of the toxin PAP-S. The strategy developed in this work about using ELR as polymeric vector and aptamers as supplier of specificity to deliver therapeutic material into MUC1-positive breast cancer cells shows promising potential and continues paving the way for ELRs in the biomedical field.