Objective    To investigate the potential use of 5-aminolevulinic acid (5-ALA) for photodynamic therapy (PDT) of nasopharyngeal carcinoma (NPC) cell line CNE2 and CNE2/DDP cultured in vitro.     Methods    CNE2 and CNE2/DDP cells were incubated in a medium containing  5-ALA (0.01， 0.05， 0.10，

0.25， 0.5， 1.0， 2.0， 4.0 mmol/L) for 4 h and illuminated with different light doses (2

5

10

20 J/cm2) using a semiconductor laser at 630 nm. After 24-hour incubation with 5-ALA-PDT

the survival rate of CNE2 and CNE2/DDP cells were analyzed by MTT assay. The intracellular fluorescence of PpIX generated by 5-ALA of each cell was determined by flow cytometry after incubation with 2.0 mmol/L 5-ALA for 4 h.      Results    5-ALA-PDT could effectively kill CNE2 and CNE2/DDP cells cultured in vitro. The killing degree was positively correlated with the concentration of 5-ALA and the dosage of radiation.  Exposed to 20 J/cm

2

the IC

50

of CNE2 and CNE2/DDP was 0.07 mmol/L and 0.375 mmol/L respectively (P0.01). The survival rate of CNE2/DDP was higher than that of CNE2 under the same 5-ALA concentration and radiation dosage (P0.05). The intracellular fluorescence of PpⅨ in CNE2 and CNE2/DDP was (197.33±1.45) and (106.36±2.31) respectively (P0.01).       Conclusion    5-ALA-PDT can effectively kill CNE2 and CNE2/DDP cells cultured in vitro

though CNE2/DDP cells are less sensitive to 5-ALA-PDT than CNE2 cells. The cross-resistance of CNE2/DDP might be overcome through increasing 5-ALA concentration and radiation dosage.