In vitro cell porphyrin accumulation during and after ALA exposure. LB45 (▪), LBN (▴), and LB45-LUDSN7 (□) cells were cultured in RPMI 1640 and 7% FCS in the presence of 1 mmol/L ALA, 2 mmol/L melatonin, and 50 μmol/L FeSO₄ for 12 hours as indicated at the top of the figure. The medium was then removed, and cells were washed with PBS and then resuspended with regular medium (RPMI 1640 and 7% FCS). At regular time intervals, the porphyrin level was measured in the cells.