Induction of early apoptosis in human nasopharyngeal carcinoma cells by mTHPC-mediated photocytotoxicity

Objectives: In this study, the early apoptotic events elicited by mTHPC-mediated photo-cytotoxicity were explored in a human nasopharyngeal carcinoma cell line (NPC/HK1). Methods and materials: NPC/HK1 cells (5 × 10³) were incubated with photosensitizer mTHPC (0.8 μg/ml) in chamber slides for 20 h and subjected to light irradiation at 2 J/cm² (LD₈₀). Morphologic changes of treated cells were examined under light microscopy and confocal microscopy at 0-4 h after the light irradiation. The early stage of apoptosis was detected by fluorescein-conjugated Annexin V (Annexin V-FITC) assay. Mitochondrial membrane damage and cytochrome c release were determined by flowcytometric analysis. Bcl-2 expression was measured by Western blot analysis. Results: One hour after mTHPC-mediated photodynamic therapy (PDT), microscopic examination showed membrane blebbing and cell shrinkage. Annexin V-FITC assay showed that a considerable number of NPC/HK1 cells became apoptotic. Flowcytometric analysis showed that the cytochrome c was released at 1 h after PDT. Bcl-2 expression also declined significantly compared to control groups. Conclusions: mTHPC-mediated photo-cytotoxicity can effectively induce early apoptotic responses in NPC/HK1 cells which might be modulated by mitochondrial damages and Bcl-2 inhibition.