Antitumor Activity of Bortezomib Alone and in Combination with TRAIL in Human Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) is a malignant disease characterized by abnormal proliferation of clonal precursor cells. Although different strategies have been adopted to obtain complete remission, the disease actually progresses in about 60–70% of patients. Bortezomib has documented antitumor activity in multiple myeloma and other lymphoid malignancies. TRAIL is a member of the TNF family that induces apoptosis in tumor cells while sparing normal cells. Here we examined the sensitivity to Bortezomib alone or in combination with TRAIL of bone marrow cells from AML patients (34 patients: 25 newly-diagnosed, 4 relapsed, 5 refractory). Immunofluorescence analysis showed that NF-κB was located in the nuclei of the AML blasts and it did not translocate after exposure to Bortezomib. Bortezomib induced cell death in blasts from each patient sample. The cytotoxic effect was dose- and time-dependent (concentration from 0.001 to 10 μM for 24 and 48 hours) and was associated with down-regulation of Bcl-xL and Mcl-1, up-regulation of TRAIL-R1, TRAIL-R2, p21 and activation of executioner caspases. Moreover, low doses of Bortezomib primed TRAIL-resistant AML cells for enhanced TRAIL-mediated killing. Thus, the combination of proteasome inhibitors and TRAIL is effective for treating AML patients, even patients who are refractory to conventional chemotherapy.