Exploring the Mechanisms\nUnderlying Cellular Uptake\nand Activation of Dendritic Cells by the GK‑1 Peptide

The use of peptides\nfor cancer immunotherapy is a promising\nand\nemerging approach that is being intensively explored worldwide. One\nsuch peptide, GK-1, has been shown to delay the growth of triple-negative\nbreast tumors in mice, reduce their metastatic capacity, and reverse\nthe intratumor immunosuppression that characterizes this model. Herein,\nit is demonstrated that GK-1 is taken up by bone marrow dendritic\ncells in a dose-dependent manner 15 min after exposure, more efficiently\nat 37 °C than at 4 °C, implying an entrance into the cells\nby energy-independent and -dependent processes through clathrin-mediated\nendocytosis. Theoretical predictions support the binding of GK-1 to\nthe hydrophobic pocket of MD2, preventing it from bridging TLR4, thereby\npromoting receptor dimerization and cell activation. GK-1 can effectively\nactivate 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\nenters the cells by passive diffusion and by activation of the transmembrane\nToll-like receptor 4 triggering cell activation, which could be involved\nin the GK-1 antitumor properties.