Proteasome Inhibitor Bortezomib Disrupts Tumor Necrosis Factor-Related Apoptosis-Inducing ligand (TRAIL) Expression and Natural Killer (NK) Cell Killing of TRAIL Receptor-Positive Multiple Myeloma Cells

Abstract 5021

Bortezomib, a potent 26S proteasome inhibitor, is approved for the treatment of multiple myeloma (MM) and clinical trials are under way to evaluate its efficacy in other malignant diseases. However, cytotoxic effects of bortezomib on immune-competent cells have also been observed. The aim of this study was to investigate the putative effects of Bortezomib on activated human natural killer (NK) cell function. In this project, primary lymphocytes or NK cells were isolated or purified from peripheral blood mononuclear cells of healthy donors. Expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by interleukin (IL)-2-activated NK cells was quantified by flow cytometry and real time-PCR method. NK cell degranulation activity and cytotoxicity against MM cell lines were evaluated by CD107a surface translocation and ⁵¹Cr release assays, respectively. Our results demonstrate that bortezomib markedly downregulated cell surface expression of TRAIL on primary human IL-2-activated NK cells in a dose-dependent manner. Moreover, bortezomib reduced TRAIL mRNA expression in these cells, suggesting that bortezomib regulates TRAIL expression of activated NK cells at the transcriptional level. Interestingly, pharmacological inhibition of the transcription factor NF-κB also profoundly decreased TRAIL expression both at protein and mRNA levels, indicating a novel role of NF-κB in the regulation of TRAIL expression in activated human NK cells. Furthermore, perforin-independent killing of the human MM cell lines was significantly suppressed following bortezomib treatment. In addition, blocking cell surface-bound TRAIL with a TRAIL antibody impaired lymphokine-activated killer (LAK) cell-mediated lysis of the TRAIL-sensitive MM cell line, RPMI8226. Our study demonstrated that bortezomib decreases TRAIL expression by IL-2 activated NK cells in a dose-dependent manner and disrupts TRAIL-mediated killing of TRAIL-sensitive myeloma cells, suggesting that Bortezomib may potentially hamper NK-dependent immunosurveillance against tumors in patients treated with this drug.