Comparison of Cellular Death Pathways after mTHPC-mediated Photodynamic Therapy (PDT) in Five Human Cancer Cell Lines

Abstract

One of the most promising photosensitizers (PS) used in photodynamic therapy (PDT) is the porphyrin derivative 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC, temoporfin), marketed in Europe under the trade name Foscan®. A set of five human cancer cell lines from head and neck and other PDT-relevant tissues was used to investigate oxidative stress and underlying cell death mechanisms of mTHPC-mediated PDT in vitro. Cells were treated with mTHPC in equitoxic concentrations and illuminated with light doses of 1.8–7.0 J/cm2 and harvested immediately, 6, 24, or 48 h post illumination for analyses. Our results confirm the induction of oxidative stress after mTHPC-based PDT by detecting a total loss of mitochondrial membrane potential (Δψm) and increased formation of ROS. However, lipid peroxidation (LPO) and loss of cell membrane integrity play only a minor role in cell death in most cell lines. Based on our results, apoptosis is the predominant death mechanism following mTHPC-mediated PDT. Autophagy can occur in parallel to apoptosis or the former can be dominant first, yet ultimately leading to autophagy-associated apoptosis. The death of the cells is in some cases accompanied by DNA fragmentation and a G2/M phase arrest. In general, the overall phototoxic effects and the concentrations as well as the time to establish these effects varies between cell lines, suggesting that the cancer cells are not all dying by one defined mechanism, but rather succumb to an individual interplay of different cell death mechanisms. Besides the evaluation of the underlying cell death mechanisms, we focused on the comparison of results in a set of five identically treated cell lines in this study. Although cells were treated under equitoxic conditions and PDT acts via a rather unspecific ROS formation, very heterogeneous results were obtained with different cell lines. This study shows that general conclusions after PDT in vitro require testing on several cell lines to be reliable, which has too often been ignored in the past.

Photodynamic therapy regulates fate of cancer stem cells through reactive oxygen species

“…Essentially, the exogenous ROS induced by this cold photochemical reaction are the most important and first effector molecules of PDT, although they also depend on the intracellular oxygen levels most of the time. In addition to exogenous ROS, PDT-induced ROS can also cause intracellular metabolic changes, induce endoplasmic reticulum stress[ 12 ], and/or destroy mitochondrial potential[ 13 ] to increase endogenous ROS production. On the one hand, the photochemical reaction directly caused by PDT produces a short ROS duration (< 0.05 μs), with high reactivity and a limited diffusion distance (< 0.02 μm)[ 14 ].…”

Optical properties of photodynamic therapy drugs in different environments: the paradigmatic case of temoporfin

“…The reasonable agreement between the calculated spectroscopic properties also constitutes a further validation of the novel force field, with an obvious improvement over the parametrization used in our previous work. 61 Note that experimental results have been conducted in ethanol instead of water, 104,105 because of the global low solubility of the sensitizers. In the simulations, we decided to use water as a solvent to mimic the most biologically relevant solvent.…”

Photodynamic therapy induces autophagy-mediated cell death in human colorectal cancer cells via activation of the ROS/JNK signaling pathway

“…Zhu et al 31 indicated that inhibition of autophagy enhanced sinoporphyrin sodium mediated-PDT (DVDMS-PDT) induced apoptosis in CRC cells, indicating that autophagy was protective in DVDMS-PDT-treated CRC cells. In addition, Lange et al indicated that m-THPC-PDT could induce cell death and autophagy in human cancer cells, and found that autophagy might occur in parallel to apoptosis or that autophagy might be dominant, eventually resulting in autophagy-associated apoptosis 47 . Huang et al 43 revealed that inhibition of autophagy decreased the apoptosis induced by pyropheophorbide-α methyl ester-mediated PDT in osteosarcoma cells.…”