In vitro photoreaction with HPPH, 9 (HPPH-Gal), 10 (HPPH-Glu), 11 (HPPH-Lac), 12 (HPPH-Cel), 21 (HPPH-Monolac), 22 (HPPH-Dilac), and 23 (HPPH-Tetralac) in RIF (A) and Colon26 cells (B). Cells were incubated with the indicated PS in 10% serum-containing medium for 24 h and then exposed to light (665 nm at 3.2 mW/cm2) for a total fluence of 0.5 J/cm2 (lower panels). Cells exposed to the PS without light are shown in the upper panels. After treatment, the cells were incubated in growth medium for 48 h. Surviving cell population was measured by MTT assay. The data are expressed as mean of three experiments. Standard deviations are <6.1% and for most values are not indicated for clarity.