Induction of apoptosis in HPV16 E7 transfected human keratinocyte by ALA-mediated photodynamic therapy

Abstract

Background and objective: 5-Aminolevulinic acid (ALA)-mediated photodynamic therapy (ALA-PDT) is effective for the treatment of condyloma and intraepithelial neoplasia associated with human papillomaviruses (HPV). However, the mechanism of PDT on HPV-infected host cells is not fully understood. The aim of this in vitro study was to examine ALA-PDT induced apoptosis in a high-risk HPV E7 gene transfected cell line.

Materials and methods: HPV16 E7 gene obtained from HPV16 positive human cervical carcinoma was transfected into a human keratinocyte cell line. PpIX generation and ALA-PDT-induced apoptosis and mitochondrial damage were investigated in vitro.

Results: Fluorescence examination showed that HPV16E7 transfected cells could produce PpIX fairly quickly in the presence of 1mM ALA. Apoptosis occurred after ALA-PDT at dose levels of 4, 8, and 12 J/cm(2). Mitochondrial potential collapse occurred as early as 2 h post PDT. ALA-PDT induced a relatively weak and shorter caspase-9 activation but a strong and long lasting caspase-3 activation. However, mRNA levels of caspase-9 and -3 genes in cells treated with ALA-PDT were unchanged.

Conclusion: This in vitro study demonstrated that HPV16 E7 transfected keratinocytes could generate PpIX in the presence of ALA. Under light irradiation, ALA-PDT could induce mitochondrial-dependent apoptosis in HPV16 E7 transfected cells.

Keywords: ALA; Apoptosis; HPV; Keratinocyte; PDT; PpIX.