{'fraction_non_alphanumeric': 0.031180400890868598, 'fraction_numerical': 0.015590200445434299, 'mean_word_length': 5.5583941605839415, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Important Role of Caspase-8 for Chemosensitivity of ALL Cells

Purpose: Sensitivity of tumor cells toward chemotherapy mainly determines the prognosis of patients suffering from acute lymphoblastic leukemia (ALL); nevertheless, underlying mechanisms regulating chemosensitivity remain poorly understood. Here, we aimed at characterizing the role of caspase-8 for chemosensitivity of B- and T-ALL cells. Experimental Design: Primary tumor cells from children with ALL were evaluated for expression levels of the caspase-8 protein, were amplified in nonobese diabetic/severe combined immunodeficient mice, transfected with siRNA, and evaluated for their chemosensitivity in vitro. Results: Effective cell death in B- and T-ALL cells depended on the presence of caspase-8 for the majority of cytotoxic drugs routinely used in antileukemia treatment. Caspase-8 was activated independently from extrinsic apoptosis signaling. Accordingly in primary ALL cells, the expression level of caspase-8 protein correlated with cell death sensitivity toward defined cytotoxic drugs in vitro. In the subgroup of primary ALL cells, with low expression of caspase-8, methotrexate (MTX) upregulated the expression of caspase-8 mediated by the transcription factor p53, suggesting epigenetic silencing of caspase-8. RNA interference in patient-derived B- and T-ALL cells revealed that effective cell death induction by most routine drug combinations involving MTX depended on the presence of caspase-8. Conclusion: Our results indicate that caspase-8 is crucial for the high antileukemic efficiency of numerous routine cytotoxic drugs. Reexpression of epigenetically downregulated caspase-8 represents a promising approach to increase efficiency of antileukemic therapy. Clin Cancer Res; 17(24); 7605–13. ©2011 AACR.