Bortezomib Restores Defective Apoptosis by Upregulation of Noxa in Enteropathy-Associated T-Cell Lymphoma

Abstract 2722

Enteropathy-associated T-cell lymphoma (EATL) is a rare intestinal lymphoma that arises from intraepithelial lymphocytes. Clinical outcome of patients with EATL is very poor, due to chemotherapy-resistance and high relapse rates. Therefore, new therapeutic options for EATL are urgently needed. Studies in other types of lymphoma have shown that inhibition of apoptosis may cause chemotherapy-resistance and that restoration of defective apoptosis can induce cell death in these lymphomas. Preliminary data in EATL samples have demonstrated an increased expression of a fraction of NF-κB target genes, suggesting upregulation of NF-κB activity in EATL tumor cells. NF-κB activity can be inhibited by the proteasome inhibitor bortezomib resulting in induction of apoptosis. In the present study, we evaluated if apoptosis is inhibited in EATL cells and if Bortezomib can restore apoptosis in EATL cells.

Laser-capture microdissection was applied to 16 fresh frozen EATL samples to obtain purified tumor cells for RNA isolation. Intraepithelial lymphocytes (IEL) of healthy controls were obtained from fresh duodenal biopsies and isolated by cell sorting. RT-MLPA analysis revealed that the pro-apoptotic BH3-only gene Noxa was significantly downregulated in most EATL samples compared to healthy donor IEL. Induction with etoposide resulted in caspase-9 mediated apoptosis in EATL cells with relatively high Noxa expression, whereas in EATL cells with low Noxa expression no apoptosis was induced, suggesting an inhibition in the intrinsic apoptosis pathway. Treatment with Bortezomib resulted in induction of apoptosis in EATL cells. The lethal dose (LD₅₀) varied between 7.5 nM and 15 nM. Bortezomib induced cell death in EATL cells was caspase-9 mediated. mRNA and protein expression analysis showed upregulation of Noxa after incubation with bortezomib.

In conclusion, our study showed that bortezomib induces apoptosis by upregulation of Noxa in EATL cells. Bortezomib therefore may be a potential drug in the treatment of patients with EATL.