Additionally, (−)-agelamide D elevates the expression of protein kinase RNA-like endoplasmic reticulum kinase/eukaryotic translation initiation factor 2α/activating transcription factor 4 (PERK/eIF2α/ATF4) in multiple HCC cell lines, which is a key pathway of the unfolded protein response (UPR), and augments radiation-induced UPR signaling. This evidence concerns the gene EIF2A and hepatocellular carcinoma.