Pevonedistat potentiates the antitumor activity of rituximab in vitro and in vivo. (A) Preincubation of MCL cell lines for 48 hours with pevonedistat increased rituximab-associated ADCC in vitro. Both the Granta cell line (pevonedistat-sensitive) and the Jeko-1 cell line (pevonedistat-resistant) were evaluated. ADCC was assessed using standard ⁵¹Cr release assays. Each experiment was done in triplicate. (B-E) Pevonedistat exhibits synergistic activity in combination with rituximab in 2 SCID-mouse models: NK cell–deficient NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ (B-D) and NK cell–competent C.B-Igh-1 b/lcrTac-Prkdc^scid/Ros (E). (B) Gross and microscopic response to pevonedistat exposure in MCL preclinical in vivo models were also evaluated via necropsy and investigation of mouse spleens from each treatment group (control, rituximab, pevonedistat, or pevonedistat plus rituximab), as well as assessment of human (h)CD45 by immunohistochemistry. (C) In vivo treatment of NK cell–deficient SCID mice bearing the Granta cell lines with pevonedistat, rituximab, or the combination of both agents resulted in a decreased tumor burden when compared with control animals. The combination of pevonedistat and rituximab resulted in a larger decrease of lymphoma involvement in several organs as determined by pathological analysis. (D-E) In vivo treatment of MCL-bearing SCID mice with rituximab and pevonedistat resulted in synergistic activity when compared with single agent–treated or control-treated animals. Survival differences between groups were compared using log rank analysis. Experiments were repeated 3 separate times. MAb, monoclonal antibody; n/a, not applicable; NS, not significant; PBMC, peripheral blood mononuclear cell.