MALT1 DEGRADATION FOR THE TREATMENT OF ACTIVATED B‐CELL TYPE DIFFUSE LARGE B‐CELL LYMPHOMA (2021)

Introduction: The activated B-cell (ABC) type of diffuse large B-cell lymphoma (DLBCL) is associated with poor response to second line therapy and is characterized by constitutive activation of the NF-κB pathway. MALT1 is a central signaling molecule which promotes NF-κB via dual protease and scaffold functions. Clinical interest focuses on allosteric MALT1 inhibitors, one of which is being tested in a phase I trial, however this approach preserves NF-κB activation through MALT1 scaffold function. MALT1 protease is also critical for regulatory T-cells, raising concern that protease inhibition alone could cause immune toxicities. We hypothesize that MALT1 degradation will inhibit NF-κB more so than allosteric inhibitors while minimizing autoimmune effects. We developed several MALT1-directed proteolysis targeting chimera (PROTAC) compounds which consist of a MALT1-binding domain linked to a cereblon (CRBN)-binding moiety based on IMiD drugs such as pomalidomide. CRBN recruitment induces ubiquitination and proteasomal degradation of MALT1. Structure-activity analyses identified a lead compound, PS-II-115, for further study. Methods: To assess growth inhibition, human ABC-DLBCL cell lines (OCI-Ly3, OCI-Ly10, TMD8) and germinal center B-cell (GCB)-type DLBCL cell lines (OCI-Ly1, OCI-Ly7) were treated with PS-II-115 for 96 hours, and CellTiter Glo assay was performed. To assess protein degradation, cells were treated with PS-II-115 5-10 uM for 23.5 hours followed by vehicle or stimulation with PMA/IO for 30 minutes, and immunoblots of cell lysates were performed. Results: PS-II-115 induced MALT1 degradation in OCI-Ly3, an ABC-DLBCL cell line dependent on MALT1, and OCI-Ly1, a GCB-DLBCL cell line not dependent on MALT1 (MALT1 degradation mean ±SEM 73.94 ±9.8% and 53.63 ±4.4% respectively, N = 3). There was no significant degradation of IMiD-induced CRBN neosubstrates IKZF1, IKZF3, or GSPT1. PS-II-115 caused dose-dependent growth inhibition of ABC-DLBCL cell lines at 96 hours at lower concentrations than in GCB-DLBCL cell lines, suggesting the effect is due to MALT1 degradation rather than off-target effects (OCI-Ly3 IC50 2.54 uM, 95% CI 1.73-3.80, OCI-Ly1 IC50 not reached, N = 4). IκB, an inhibitor of NF-κB which is degraded following phosphorylation by MALT1-mediated IKK recruitment, was detected at a higher level in cells treated with PS-II-115 (IκB 206% compared to vehicle) compared to controls treated with vehicle or an allosteric MALT1 inhibitor, suggesting that MALT1 degradation inhibits NF-κB signaling. Conclusions: We report a PROTAC compound which induces potent degradation of MALT1 without degradation of IMiD-induced CRBN neosubstrates, associated with selective suppression of ABC-DLBCL cell lines and inhibition of the NF-κB pathway. Our findings suggest that MALT1 degradation is a promising strategy for treatment of ABC-DLBCL and warrants further development. Keywords: Molecular Targeted Therapies, Aggressive B-cell non-Hodgkin lymphoma Conflicts of interests pertinent to the abstract L. Fontán Employment or leadership position: Janssen Pharmaceuticals N. Gray Consultant or advisory role: Gatekeeper, Syros, Petra, C4, Allorion, Jengu, B2S, Inception, EoCys and Soltego Stock ownership: Gatekeeper, Syros, Petra, C4, Allorion, Jengu, B2S, Inception, EoCys and Soltego Research funding: Novartis, Takeda, Astellas, Taiho, Jansen, Kinogen, Her2llc, Deerfield and Sanofi A. Melnick Consultant or advisory role: Epizyme, Constellation, KDAC pharmaceuticals Research funding: Janssen Pharmaceuticals, Sanofi and Daiichi Sankyo