Photodynamic therapy (PDT) - an initiation of apoptosis via the activation of stress-activated p38 MAPK and JNK signal pathway in human lung carcinoma

1375

Lung cancer remains at the top mortality for cancer worldwide. Photodynamic therapy (PDT) is an innovative cancer treatment, principally by generating singlet oxygen to induce cancer cell death in the presence of photosensitizers, specific light source and oxygen. 5-aminmolevulinic acid (ALA) and its hexyl ester (H-ALA) are widely used photosensitizers in this therapy. Here we compared the photocytotoxic effect of 5-aminmolevulinic acid (ALA) and hexyl ester (H-ALA) on a human non-small lung carcinoma cell (H460) and elucidated cell death signalling pathways being triggered including the p38 mitogen-activated protein kinase (MAPK), the c-jun N-terminal protein kinases (JNKs) and extracellular signal-regulated kinases (ERK). At 8 hours drug incubation, flow cytometric analysis revealed that H-ALA (5μM) reached an optimal fluoresecent intensity while ALA (0.5mM) was still far from saturation in H460 cells. Therefore H-ALA demonstrated a faster uptake ability with 100 fold lower drug concentration in this cell line. MTT results at LD₃₀ showed that Hexyl-ALA mediated PDT (30μM, 2J/cm²) exerted a more potent effect than ALA (3mM, 2J/cm²). Dark toxicity remained negligible for both photosensitizers. Western blot analysis indicated that the p38 MAPK and the stress-activated c-jun N-terminal kinases (JNK) were triggered with an up-regulated activity after H-ALA or ALA-PDT. However, there was no activation in the extracellular signal-regulated kinases (ERK) activity. By employing DAPI staining, apoptotic cell death changes including cytoplasmic and nuclear shrinkage, chromatin condensation and nuclear fragmentation were observed after PDT treatment for both drugs. In conclusion, ALA and Hexyl-ALA mediated PDT could initiate apoptotic cell death via the activation of p38 MAPK and JNK signal pathways in this human non-small cell lung carcinoma cells.