Inhibition of glutaminase-1 in DLBCL potentiates venetoclax-induced antitumor activity by promoting oxidative stress.

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma in adults, but first-line immunochemotherapy fails to produce a durable response in about one-third of the patients. Because tumor cells often reprogram their metabolism, we investigated the importance of glutaminolysis, a pathway converting glutamine to generate energy and various metabolites, for the growth of DLBCL cells. Glutaminase-1 (GLS1) expression was robustly detected in DLBCL biopsy samples and cell lines. Both pharmacological inhibition and genetic knockdown of GLS1 induced cell death in DLBCL cells regardless of their subtype classification, whereas primary B cells remained unaffected. Interestingly, GLS1 inhibition resulted not only in reduced levels of intermediates of the tricarboxylic acid cycle but also in a strong mitochondrial accumulation of reactive oxygen species. Supplementation of DLBCL cells with α-ketoglutarate or with the antioxidant α-tocopherol mitigated oxidative stress and abrogated cell death upon GLS1 inhibition, indicating an essential role of glutaminolysis in the protection from oxidative stress. Furthermore, the combination of the GLS1 inhibitor CB-839 with the therapeutic BCL2 inhibitor ABT-199 not only induced massive reactive oxygen species (ROS) production but also exhibited highly synergistic cytotoxicity, suggesting that simultaneous targeting of GLS1 and BCL2 could represent a novel therapeutic strategy for patients with DLBCL.

The Paracaspase MALT1 in Cancer.

Almost twenty years ago, the importance of the paracaspase MALT1 in antigen receptor-induced NF-κB activation was first described. Since then, several other immune receptors, G-protein-coupled receptors, and receptor tyrosine kinases were identified as relying on MALT1 to induce NF-κB activation. In various hematological malignancies and solid tumors, MALT1 is constitutively activated and drives chronic NF-κB target gene expression. Deregulated MALT1 activity in cancer thus promotes tumor cell survival, proliferation, and metastasis. Since the molecular function of MALT1 partially requires its protease activity, pharmacological targeting of MALT1 may represent a promising anti-cancer strategy. Here, we review the molecular features of MALT1 activation and function as well as the therapeutic potential of MALT1 inhibition in hematological malignancies and solid tumors.