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

Summary 

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 (0.8μg/ml) in chamber slides for 20h and subjected to light irradiation at 2J/cm² (LD₈₀). Morphologic changes of treated cells were examined under light microscopy and confocal microscopy at 0–4h 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 1h 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.

Keywords: mTHPC, Phototoxicity, PDT, Apoptosis, Nasopharyngeal carcinoma