NR4A1 and cancer: Another classification is based on the mechanism of action: molecularly targeted peptides, which directly act on cancer cells via cytotoxic, antiproliferative, and apoptotic activities, ‘guiding missile’ peptides, or binding peptides, which are drug-binding peptides used for transporting drugs into cancer cell targets, and cell-stimulating peptides that indirectly influence other stimulating cells to kill cancer cells, e.g., via immunomodulatory activities and hormone receptors [22,23].