In vitro photodynamic therapy of human lung cancer

Photodynamic therapy (PDT) using a dihematoporphyrin ether (DHE) sensitizes malignant cells to damage by 630-nm light. This study investigated in vitro PDT sensitivity of human lung cancer cells (A549) and those factors which influence cell survival as determined by the colony formation assay. After incubation for 2, 4, or 6 hr with [DHE] of 2.5, 25, or 50 micrograms/ml, A549 received red light at dose rates of 0.27 or 0.09 mW/cm2 and energies of 0-250 mJ/cm2. Neither 630-nm light alone nor DHE alone affected cell survival. A dose rate of 0.27 mW/cm2 required less energy than 0.09 mW/cm2 for 90% cytotoxicity (180 mJ/cm2 vs 250 mJ/cm2, P less than 0.05). The energy required for 90% cytotoxicity with 25 micrograms/ml [DHE] was dependent on DHE incubation time (2 hr, 90% cytotoxicity not reached; 4 hr, 116 mJ/cm2; 6 hr, 69 mJ/cm2; P less than 0.05). In contrast, cellular [DHE] as measured by fluorescence, plateaued after 2 hr of incubation. Fluorescence microscopy revealed a time-dependent redistribution of fluorescence from the cell membrane to perinuclear and intracytoplasmic organelles. A 99% cytotoxicity required significantly less energy as [DHE] was increased (2.5 micrograms/ml, no cytotoxicity; 25 micrograms/ml, 243 mJ/cm2; 50 micrograms/ml, 111 mJ/cm2; P less than 0.05). Intracellular [DHE] was directly dependent on the incubating media [DHE] (2.5 micrograms/ml, 0.09 +/- 0.01 micrograms/10(6) cells; 25 micrograms/ml, 0.80 +/- 0.07 micrograms/10(6) cells; 50 micrograms/ml, 1.31 +/- 0.11 micrograms/10(6) cells; P less than 0.05). PDT cytotoxicity was inversely proportional to concentration of serum in the DHE media. These data illustrate that lung cancer in vitro is sensitive to PDT and is influenced by dose rate, energy input, and DHE environmental manipulations. These factors may be important in increasing the efficiency of PDT of thoracic malignancies in vivo.