Cells were plated in quadruplicate (2000 cells/well) in a 96-well plate for the CyQuant assay with the CyQuant reagent (Thermo Fisher Scientific) as previously described [25 (link)]. Cell viability was assessed by trypan blue staining [25 (link)]. Population doubling times were calculated using a population doubling time online calculator (http://www.doubling-time.com/compute.php) based on the reading from CyQuant and viability assays.