Potentiation of phototherapy cytotoxicity with light scattering media

Lung cancer cells are susceptible to photodynamic therapy (PDT) using 630 nm light and dihematoporphyrin ether (DHE). A light scattering media, intralipid (IL), was compared to balanced salt solution (PBS) for PDT of A549 human lung cancer cells. Differences in cellular DHE content after IL or PBS exposure were determined. Cells were incubated in 25 micrograms/ml DHE for 2 hr and then incubated in various concentrations of IL or PBS at room temperature for 2.5 to 10.0 min. Significant amounts of DHE were lost from IL-incubated cells compared to cells incubated in PBS. After 5 min in 1% IL, cellular DHE content was 0.32 +/- 0.04 microgram DHE/10(6) cells compared to 0.56 +/- 0.11 microgram DHE/10(6) cells in PBS-incubated cells (P less than 0.05). Despite this, superior PDT cytotoxicity was noted when cells were treated in IL with energy densities greater than or equal to 105 mJ/cm2. At an energy density of 210 mJ/cm2, the survival fraction (SF) of cells treated in 1% IL was 0.004 +/- 0.001 compared to 0.071 +/- 0.022 in PBS-treated cells (P less than 0.05). SF was dependent upon the IL concentration with the greatest cell killing noted with 1% IL. An apparent loss of cellular DHE ("DHE washout") was confirmed by demonstration of a higher SF of cells incubated in IL, rinsed, and subsequently PDT-treated in PBS with 157.5 mJ/cm2 (SF = 0.85 +/- 0.11) compared to cells incubated and treated in PBS (SF = 0.50 +/- 0.03, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)