BACKGROUND: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been reported to induce apoptosis in various tumor cells but not in normal cells, which suggests its potential use as a tumor-specific antineoplastic agent. In the present study, we examined here that the treatment of TRAIL-resistant leukemia cells with a low dose doxorubicin in combination of TRAIL induces a synergistic apoptotic response.
METHODS : Cell growth inhibition was assessed by MTT assay, and the induction of apoptosis was examined using flow cytometry after stained with Annexin V. To find out the molecular change of the TRAIL receptors and caspase expression in acute leukemia cell lines and human umbilical cord blood (UCB) mononuclear cells, RT-PCR for TRAIL receptors and western blot analysis for DR4, DR5, and caspase 3, 7, 8, and 9 were performed.
RESULTS : The Jurkat cell line was TRAIL sensitive and TRAIL-resistant Molt-4 cell line became sensitive after treatment with TRAIL and a low dose of doxorubicin (0.1 μM), but UCB mononuclear cells remained resistant. DR4 expression was increased when TRAIL-sensitive Jurkat cells were treated with TRAIL. DR5 expression was increased after exposing TRAIL- resistant Molt-4 cell line to TRAIL plus a low dose of doxorubicin for 24 hours. The expression of DR4 and DR5 in UCB mononuclear cells was unchanged after treatment with TRAIL, a low dose doxorubicin, or TRAIL plus a low dose of doxorubicin. Activated caspase 3 expression was augmented by
TRAIL plus a low dose of doxorubicin than TRAIL or a low dose of doxorubicin alone in TRAIL-resistant Molt-4 cells.
CONCLUSION : A low dose doxorubicin in combination with TRAIL may effectively promote caspase activation in TRAIL-resistant leukemia cells. Apoptosis synergistically induced by the combination of a low dose doxorubicin and TRAIL might be considered as an effective and safe tool in treating TRAIL-resistant acute leukemia.

Keywords: TRAIL, Doxorubicin, Apoptosis, Acute leukemia,