Pa-PDT circumvents MDR on resistant human hepatoma cells R-HepG2. (A) Intracellular accumulations of Pa and Dox in HepG2 and R-HepG2 cells. Cells (3 × 105/well) were incubated with Pa (2 μM) or Dox (2 μM) for 4 h, and then washed with PBS for 3 times. Fluorescence micrographs were acquired with an excitation wavelength at 400–440 nm and an emission wavelength at 590–650 nm under a Nikon TE2000 fluorescence microscope. Images are representative results of 3 independent experiments. Bar: 50 μm. (B) In vitro cytotoxicity of Pa-PDT in R-HepG2 cells. Cells (1 × 104/well) were incubated with increasing concentrations of Pa in a 96-well plate for 2 h and exposed to light illumination (84 J/cm2) for 20 min and subsequently incubated at 37°C, 5% CO2. For the control group, cells were treated with Pa only without light illumination. Cell survival was then assessed by MTT assay 24 h after treatment. Results are mean ± SD of three independent experiments. (C) In vivo study of Pa-PDT in R-HepG2 cells bearing mice. R-HepG2 cells (1 × 107) were injected into nude mice subcutaneously at day-7. At day 0, 8 nude mice in groups were treated with Pa (300 μg/kg) and photo-activation (30 min) was applied only once to the treatment group 24 h after the Pa pre-treatment. At day ten, the tumor size of each mouse was measured after the Pa-PDT treatment and the data was expressed as mean ± S.D. (n = 8, * p value < 0.05). (D) Tissue damages in Pa-PDT treated mice were assessed by an increase in the leakage of tissue specific enzymes (LDH for heart, and AST and ALT for liver) to the blood. The specific enzyme activities of the blood samples of the tested mice were measured and expressed as the mean ± S.D. (n = 8, * p value < 0.05).