The Case Back on the TRAIL: Death Receptors as Markers for rhTRAIL Sensitivity
BACKGROUND: Personalized cancer treatments can be applied to the clinical use of recombinant human tumor necrosis factor-related apoptosis-inducing ligand (rhTRAIL). rhTRAIL holds great promise because of its selectivity for cancer cells. However, rhTRAIL clinical trials were conducted without the screening of patients' tumors for rhTRAIL-binding death receptor (DR)4 and DR5, and the unselected treatment resulted in a lack of clinical benefit. Here we propose an in vitro test to analyze tumor cells isolated from patients for the membrane expression of DRs to determine patient suitability for rhTRAIL treatment. METHODS: Using a panel of malignant melanoma cell lines, the correlation between DR membrane expression and rhTRAIL sensitivity was evaluated. The membrane expression of DR4 and DR5 was examined through staining with anti-DR4 and -DR5 antibodies followed by fluorescence-activated cell sorting. rhTRAIL sensitivity was determined through Annexin-V and propidium iodide staining and Western blotting after rhTRAIL treatment. RESULTS: Here we show a direct correlation between the membrane expression of DRs and rhTRAIL sensitivity. rhTRAIL-sensitive melanoma lines, on average, had nearly 4-fold more DR4 and >2-fold more DR5 than rhTRAIL-resistant lines. For a cancer cell to display rhTRAIL sensitivity, the optimum expression of DRs is essential. To overcome the apoptotic threshold, cancer cells must express DRs >2-fold higher compared with their benign counterpart. CONCLUSION: These data show the potential of this flow cytometry-based assay for the analysis of isolated tumor cells for DR membrane expression. By first determining a patient's susceptibility to rhTRAIL-based treatments, they can be more appropriately placed in rhTRAIL clinical trials and improve rhTRAIL as an anticancer therapeutic.