Quantitative determination of STPP toxicity in human lung carcinoma cells. Percent cell viability in A, C: A549 cells and B, D: H69/AR cells, treated with STPP liposomes, STPP in DMSO and STPP in DMSO mixed with PC: Cholesterol liposomes for A, B: 5 h and C, D: 12 h at indicated concentrations of STPP. Values represent mean ± standard deviation from three independent experiments.