Bortezomib Induces Caspase-9-Mediated Apoptosis through Activation of the BH3-Only Proteins Noxa, Bik and Puma In Both ALK-Positive and ALK-Negative Anaplastic Large Cell Lymphoma Cells

Abstract 2847

Anaplastic large cell lymphoma (ALCL) is a CD30 positive T-cell lymphoma that can be divided into a systemic and a primary cutaneous type. Systemic ALCL can be further divided into an anaplastic lymphoma kinase (ALK) expressing type and an ALK-negative type. Despite intensive treatment regimens, the disease will be fatal in 20–30% of the systemic ALK-positive and 50–70% of the systemic ALK-negative ALCL patients. A recent study in primary ALCL samples has demonstrated an increased expression of a fraction of NF-κB target genes, suggesting upregulation of NF-κB activity in ALCL tumor cells. NF-κB activity can be inhibited by the proteasome inhibitor bortezomib resulting in induction of apoptosis. In this study, we therefore investigated if bortezomib can induce apoptosis of cultured lymphoma cells of three systemic ALK-positive and three ALK-negative ALCL patients and seven ALCL cell lines and we examined the mechanisms by which bortezomib induced cytotoxicity in these ALCL cells.

Treatment with bortezomib resulted in induction of apoptosis in all ALK-positive and ALK-negative ALCL patient samples and ALCL cell lines tested, when we compared the percentage cell death with the non-neoplastic CD4- and CD8-positive PBMC and tonsil T-cells from healthy donors. The lethal dose (LD₅₀) varied between 54nM and more than 100nM after 24 hours and varied between 21nM and 52nM after 48 hours of exposure. ALK-negative ALCL cases were more sensitive to bortezomib and showed significant lower LD₅₀ values than ALK-positive ALCL cells. We show that bortezomib-induced cell death in ALK-positive and ALK-negative ALCL is dependent on caspase-9 and/or caspase-8 mediated apoptosis and that bortezomib induces depolarization of the mitochondrial membrane. mRNA-expression and protein analysis revealed clearly upregulation of the BH3-only proteins Noxa, Bik and Puma, resulting in Bak and Bax release from the anti-apoptotic proteins Mcl-1 and Bcl-2. We also demonstrated that ALCL cells relatively resistant to bortezomib were characterized by high expression of Bcl-2A1, suggesting the possibility of pre-defining patients most likely to benefit from bortezomib therapy.

Our preclinical data support the therapeutic application of bortezomib as potential drug in the treatment of ALCL, especially ALK-negative ALCL patients to improve their prognosis.