Photo-oxidative killing of human colonic cancer cells using indocyanine green and infrared light

Abstract

Summary Despite of the approval of Photofrin® in various countries, chemically defined sensitizers for photodynamic therapy (PDT) are still needed for the absorption of light in the infrared spectrum, which provides a maximal penetration of light into tissue. Therefore, both the efficacy and the mechanism of action of the clinically approved dye indocyanine green (ICG) and laser irradiation were investigated in vitro. For the investigation of phototoxic effects, HT-29 cells were incubated 24 h prior to irradiation by using different concentrations of ICG (10-500 µM). In each experiment, cells were irradiated using a continuous wave (cw)-diode laser (λ ex = 805 nm, 30 J cm -2 , 40 mW cm -2 ). After laser irradiation, cell viability of dark control and of cells incubated with 500 µM ICG was 1.27 ± 0.11 or 0.28 ± 0.05 respectively. Using 100 µM ICG and D 2 O, cell viability was further decreased from 0.46 ± 0.03 (H 2 O) to 0.11 ± 0.01 (D 2 O). Using D 2 O and 100 µM ICG, the concentration of malondialdehyde, a marker of lipid peroxidation, increased from 0.89 ± 0.10 nmol 10 -6 cells to 11.14 ± 0.11 nmol 10 -6 cells. Using 100 µM ICG and laser irradiation sodium azide or histidine (50 mM), quenchers of singlet oxygen reduced the cell killing significantly. In contrast, when using mannitol, a quencher of superoxide anion and hydroxyl radical, cell killing was not inhibited. According to the present results, photoactivated ICG seems to kill colonic cancer cells due to the generation of singlet oxygen and the subsequent formation of lipid peroxides. Therefore, ICG might present a promising photosensitizer for PDT; first clinical results confirm these findings.

Targeting cancer cells by using an antireceptor antibody-photosensitizer fusion protein

“…A greatly increased phototoxicity in D 2 O is expected for photosensitizers, and it generates singlet oxygen because of its longer lifetime in this solvent photosensitizer (25,26). Surprisingly, phototoxicity of 4D5scFv-KillerRed in D 2 O was even lower compared with water.…”

“…To test 4D5scFv-KillerRed photochemistry further, we compared cytotoxicity of the immunophotosensitizer in water and D 2 O. Deuterium oxide is known to extend a lifetime of 1 O 2 and thus increases efficiency of singlet oxygen-generating photosensitizers (25,26). SKOV-3 cell survival was analyzed after incubation and illumination with 1.8 M 4D5scFv-KillerRed (as described above) in either water or D 2 O-based buffers.…”

The role of singlet oxygen and oxygen concentration in photodynamic inactivation of bacteria

“…In photodynamic action, singlet oxygen ( 1 O 2 ) is considered to play the major role (14,15). This highly reactive oxygen initiates further oxidative reactions in the proximate environment, such as the bacterial cell wall, lipid membranes, enzymes, or nucleic acids (16,17). Therefore, the photodynamic inactivation of bacteria is based on the concept that a photosensitizer can accumulate to a significant extent in or at the cytoplasmic membrane, which is the critical target for irreversible damage in bacteria after irradiation (8).…”

Morphological Study in B16F10 Murine Melanoma Cells after Photodynamic Hyperthermal Therapy with Indocyanine Green (ICG)

“…In studies of HT-29 human colon cancer cells, irradiation was performed at 805 nm with a light dose of 30 J/cm 2 , along with 500 µM ICG, and the temperature was measured to ensure that no hyperthermic conditions were imposed on the cells. The cell viability was significantly decreased after 24 hr post ICG-PDT in that study [5]. In our current study with PHT, a lower molar concentration was used, and a significant decrease in the cell viability was rapidly achieved with the imposition of hyperthermia at 43°C.…”