Frozen RPTECs vials were removed from liquid nitrogen storage and placed in a 37 °C water bath until the contents were completely thawed. The cells were gently resuspended and dispensed into a cell culture flask at a seeding density of ~7500 cells/cm 2 . The flask was placed in a 37°C, 5% CO2 incubator. Cell cultures were given fresh medium the following morning and then every other day until the cell culture was approximately 90% confluent. When the cell culture was 90% confluent, medium was removed and the cells were rinsed with warmed PBS. Cells were harvested and split into new flasks based on a cell density of 7500 cells/cm 2 . Cells were incubated at 37°C for 3 days, with fresh medium added each day. Cells were harvested and diluted with growth medium to a density of 200,000 cells/mL. 100 µL of cell suspension per well (20,000 cells/well) was added to a clear-bottom 96-well microplate for luminescence assays. The plated cells were incubated in the 37°C incubator for 3 days.