ELISA assay for prostaglandin E2 (PGE2) concentration

HCT116 caspase 3 KO or vector control cells were treated or untreated with X ray radiation at 10 Gy and plated in 6 well plates (1×10⁶ cells/well) in 2% fetal bovine serum culture medium. Supernatant from the cells was collected 96 hours after radiation and diluted 8 fold. Cells were counted by using the Bio Rad cell counter in order to normalize PGE₂ concentration to cell number. The concentration of PGE₂ in the supernatant was measured following a protocol from an ELISA kit purchased from Cayman Chemical Company (Ann Arbor, MI).