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The identification of the tumor necrosis factor (TNF) superfamily member TNF-related apoptosis-inducing ligand (TRAIL) a few years ago generated considerable enthusiasm for it as a potential cancer therapeutic agent. This is because TRAIL shows potent apoptosis inducing activity in a wide spectrum of transformed cell lines but not in cell lines derived from normal tissue origin. As the details in the signal transduction pathway of TRAIL-induced apoptosis are clarified, various defects of TRAIL pathway have been identified in TRAIL resistant cancer cells. Neuroblastoma is the most common extracranial solid tumor in children and those with a poor prognosis require more sensitive therapies. Unlike other cancer cells, most neuroblastoma cell lines are resistant to TRAIL induced apoptosis and the resistance correlates with caspase 8 deficiency, which is attributed to the methylation of the gene. Interferon (IFN)-gamma induces caspase 8 expression in most neuroblastoma cell lines regardless of the methylation status but fails to sensitize most NB to TRAIL. Further analysis indicates a TRAIL receptor deficiency contributes to TRAIL resistance in NB. Multiple lesions suggest that this path may play an important role in tumorigenesis and/ or evasion from therapies. Furthermore it indicates that the clinical application of TRAIL in NB will require a multi-modality approach. Important questions remain unanswered: How does IFN-gamma induce caspase 8 and why is the induction heterogeneous? How to stimulate the caspase 8 induction in cells that fail to respond to IFN-gamma? How to target other TRAIL pathway lesions with the clinically feasible approaches?

The resistance of neuroblastoma (NB) cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis has been attributed to a lack of caspase 8 expression. Here we demonstrate a clinically applicable molecular targeting strategy that not only increases caspase 8 expression ex vivo in NB cell lines but also in the tumor tissues of NB patients receiving IFN-gamma treatment. We identify the functional caspase 8 promoter, which is different from the methylated region reported previously, and show promoter activity is up-regulated by IFN-gamma through a IFN-gamma activation site-containing region. IFN-gamma also induces TRAIL expression in NB cell lines. However, the IFN-gamma restoration of caspase 8 in some NB cells revealed persistent TRAIL resistance in most NB cell lines examined. This additional lesion in the TRAIL path is because of a loss of cell membrane TRAIL receptors (TR1/TR2) not only in cell lines but in most of the NB tumor tissues evaluated. Restoration of TR2 expression by transfection enhances IFN-gamma-induced TRAIL sensitivity. Furthermore, we have found that we can improve TRAIL sensitivity in NB by reconstituting caspase 8 with IFN-gamma and TR2 with chemotherapeutic agents.