Pep42 is a cyclic oligopeptide that, with its hydrophobic character, can selectively interact with cell surface glucose‐regulated protein 78 (GRP78), a member of 70 kDa heat shock proteins. GRP78, also known as BiP or HSPA5, under endoplasmic reticulum stress, can be translocated from the endoplasmic reticulum to the membrane and helps to maintain cellular integrity under physiologic and pathological stress. It critically contributes to various functions ranging from protein folding, transportation, and degradation to cell-signaling, proliferation, survival, apoptosis, inflammation, and immunity. The expression of GRP78 decreases with age.