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

Abstract

Background and objective5-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 methodsHPV16 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. ResultsFluorescence 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 12J/cm2. Mitochondrial potential collapse occurred as early as 2h 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. ConclusionThis 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.