Exploring the Mechanisms Underlying Cellular Uptake and Activation of Dendritic Cells by the GK-1 Peptide

The use of peptides for cancer immunotherapy is a promising and emerging approach that is being intensively explored worldwide. One such peptide, GK-1, has been shown to delay the growth of triple-negative breast tumors in mice, reduce their metastatic capacity, and reverse the intratumor immunosuppression that characterizes this model. Herein, it is demonstrated that GK-1 is taken up by bone marrow dendritic cells in a dose-dependent manner 15 min after exposure, more efficiently at 37 °C than at 4 °C, implying an entrance into the cells by energy-independent and -dependent processes through clathrin-mediated endocytosis. Theoretical predictions support the binding of GK-1 to the hydrophobic pocket of MD2, preventing it from bridging TLR4, thereby promoting receptor dimerization and cell activation. GK-1 can effectively activate cells via a TLR4-dependent pathway based on <i>in vitro</i> studies using HEK293 and HEK293-TLR4-MD2 cells and <i>in vivo</i> using C3H/HeJ mice (hyporesponsive to LPS). In conclusion, GK-1 enters the cells by passive diffusion and by activation of the transmembrane Toll-like receptor 4 triggering cell activation, which could be involved in the GK-1 antitumor properties.