TRAIL-induced apoptosis of HL60 leukemia cells: Two distinct phenotypes of acquired TRAIL resistance that are accompanied with resistance to TNFα but not to idarubicin and cytarabine

TNF-related apoptosis-inducing ligand (TRAIL) is a proapoptotic cytokine implicated in cancer cell surveillance. A potential of TRAIL as a cancer-specific therapeutic agent has been proposed, either as a single agent or in combination with chemotherapy. Prolonged exposure of TRAIL-sensitive leukemia cell line, wild-type (WT) HL60 cells to recombinant soluble TRAIL or to cytostatic agents, cytarabine and idarubicin, resulted in the establishment of resistant subclones with distinct phenotypic features. The TRAIL resistant HL60 subclones were characterized by decreased expression of TRAIL and TNFα death receptors. These resistant subclones had impaired activation of caspases 8 and 10 in response to TRAIL and TNFα, decreased TRAIL-induced nuclear translocation of NFκB RelA/p65, and dysregulation of the expression of several apoptosis regulators. Among the TRAIL resistant HL60 subclones we identified two separate phenotypes that differed in the expression of CD14, osteoprotegerin, and several apoptosis regulators. Both these TRAIL resistant HL60 subclones were resistant to TNFα, suggesting disruption of the extrinsic apoptotic pathway, but not to cytostatic agents, cytarabine and idarubicin. The concurrently derived HL60 subclones were cytarabine and idarubicin-resistant but remained sensitive to TRAIL-induced apoptosis. We identified distinct pathways for the development of HL60 leukemia cell resistance to apoptosis induction. These findings are relevant for the design of more effective strategies for leukemia therapy.