Nanodrug delivery systems (NDDs) capable of conveying chemotherapeutics directly into malignant cells without harming healthy ones are of significant interest in the field of cancer therapy. However, the development of nanostructures with the requisite biocompatibility, inherent optical properties, cellular penetration ability, encapsulation capability, and target selectivity has remained elusive. In an effort to develop cell-selective NDDs, we have synthesized a cationic tripeptide Boc-Arg-Trp-Phe-OMe (PA1), which self-assembles into well-ordered spheres in 100% aqueous medium. The inherent fluorescence properties of the peptide PA1 were shifted from the ultraviolet to the visible region by the self-assembly. These fluorescent nanostructures are proteolytically stable, photostable, and biocompatible, with characteristic blue fluorescence signals that permit us to monitor their intracellular entry in real time. We also demonstrate that these tripeptide spherical structures (TPSS) have the capacity to entrap the chemotherapeutic drug doxorubicin (Dox), shuttle the encapsulated drug within cancerous cells, and initiate the DNA damage signaling cascade, which culminates in apoptosis. Next, we functionalized the TPSS with an epithelial-cell-specific epithelial cell adhesion molecule aptamer. Aptamer-conjugated PA1 (PA1-Apt) facilitated efficient Dox delivery into the breast cancer epithelial cell line MCF7, resulting in cell death. However, cells of the human cardiomyocyte cell line AC16 were resistant to the cell killing actions of PA1-Apt. Together, these data demonstrate that not only can the self-assembly of cationic tripeptides like PA1 be exploited for efficient drug encapsulation and delivery but their unique chemistry also allows for functional modifications, which can improve the selectivity of these versatile NDDs.
Keywords: DNA damage; apoptosis; aptamer functionalization; drug delivery; self-assembly; tripeptide.