Background: This study assesses the chemotherapeutic drug gemcitabine in the human non-small cell lung cancer (NSCLC) cell line KNS62 in relation to the CD95-induced apoptotic pathway, and the role of the anti-apoptotic protein Bcl-xL in vitro and in vivo.
Materials and methods: Apoptosis was determined by JAM assay and DAPI staining analysis. Activation of key apoptotic proteins, including caspases 3, 8 and 9 and BID, as well as cytochrome c release and mitochondrial transmembrane potential (MTP), were measured. The impact of the caspase inhibitor zVAD on gemcitabine-induced apoptosis was quantified. The in vitro results were verified in vivo in an orthotopic murine xenotransplantation model.
Results: Gemcitabine treatment, as well as stimulation of CD95, resulted in cleavage of effector caspase 3 as well as its substrate PARP and caspase 9, followed by DNA fragmentation. Cleavage of caspase 8 was demonstrated after CD95 activation but not after the application of gemcitabine. In KNS62-Bcl-xL clones, release of cytochrome c and loss of mitochondrial transmembrane potential were suppressed. Consequently, apoptosis after gemcitabine therapy, as well as CD95-induced apoptosis, were significantly inhibited. Caspase inhibitor zVAD only partly reversed gemcitabine-induced DNA fragmentation. In vivo, there was a significant reduction in tumour volume under gemcitabine therapy. Bcl-xL over-expressing tumours were completely resistant to gemcitabine therapy.
Conclusions: In NSCLC cell line KNS62 gemcitabine activated the mitochondrial apoptotic pathway downstream of mitochondria without activation of initiator caspases. Bcl-xL over-expression induced significant resistance to gemcitabine. In vivo, the anti-apoptotic effect of Bcl-xL was more pronounced than in vitro. Gemcitabine also induced caspase-independent DNA fragmentation in KNS62 cells.