Photodynamic therapy (
PDT) is a promising treatment that is approved by the US FDA for the treatment of oesophageal and
lung cancer as well as for
age-related macular degeneration. In this study, using standard tissue culture techniques, the photo cytotoxicity and apoptotic mechanisms of
Calphostin C (Cal C), a
perylenequinone microbial compound in combination with visible light dose was examined in different tumor cell lines. Our results demonstrated both a time and
drug-light dose dependence in Cal-C-
PDT induced photo toxicity and apoptotic cell death. The induction of apoptosis by Cal C-
PDT was found to transit to necrotic cell death at higher
drug and light doses. The detection of apoptosis in irradiated
tumor cells was performed using various approaches including cell morphology analysis, flow cytometry [DNA fragmentation and
phosphatidylserine (PS) externalization] and biochemical assays (activation of
caspases). Time-course analysis of Cal C cellular uptake and distribution showed a rapid increase within the cellular compartments. The activation of
caspases and nuclear fragmentation was evidenced at a maximum time point of 3 h after irradiation. By the use of specific
caspase substrates, significant activation of
caspase-8 and -3 was found. Mitochondrial involvement during Cal C-
PDT-induced apoptosis was proven by a rapid reduction of the mitochondrial membrane potential. Furthermore, Cal C-
PDT also enhanced FasL expression, which then induced Fas signalling-dependent cell death in NPC and
colon cancer cell lines tested. Our results contribute to a deeper understanding of the processes involved in apoptotic cell death following photodynamic treatment with Cal C.