ALDH activity assay

ALDH enzymatic activities were analyzed using ALDEFLUOR assay (STEMCELL technologies, Vancouver, BC, Canada) according to the manufacturer’s instructions. In brief, cells were harvested, washed, and then resuspended to a concentration of 1 × 10⁶ cells /ml with the ALDEFLUOR™ assay buffer. Then 5 μl ALDH substrate was added into 1 ml cell suspension and mixed. As a negative control, 0.5 ml cell mixture was immediately transferred to control tube containing 5 μl specific ALDH inhibitor DEBA. After incubation at 37 °C for 30 min, cells were analyzed using a flow cytometer (FACS Canto II, BD Biosciences, San Jose, CA).