Therapeutic Effects of MLN4924 on Sclerodermatous Chronic Graft Versus Host Disease

![Graphic][1] Allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curative option for the treatment of a variety of hematological diseases. However, high incidences of graft versus host disease (GVHD) and tumor relapse remain as major hurdles to this approach. While recent advances in transplant preparation and prophylactic regimens have lowered the incidence of acute GVHD, chronic GVHD (cGVHD) still remains a major cause of long-term morbidity and mortality. Recent studies have suggested that post-translation modifications (PTMs) may serve as therapeutic targets during GVHD. PTMs of proteins are important pathways that confer biochemical alterations, such as acetylation, phosphorylation, and ubiquitination. Targeting PTMs by using small molecular inhibitors has demonstrated potent anti-tumor effects, as well as immune modulatory properties. We have previously shown that bortezomib, an inhibitor of PTMs pathways, can successfully ameliorate sclerodermatous cGVHD responses in both preclinical and clinical studies. Here we reported a new small molecular targeting agent, MLN4924, a selective inhibitor of NEDD8-activating enzyme, on the treatment of cGVHD. MLN4924 is a selective inhibitor of NEDD8-activating enzyme and has been shown to be well tolerated at higher doses and exhibit potent anti-tumor activity in murine models and in early clinical trials. Furthermore, MLN4924 can suppress dendritic cell functions, as well as their production of proinflammatory cytokines during allogeneic responses. Due to these findings, we sought to test the treatment effects of MLN4924 on cGVHD responses. To investigate this, we utilized a minor MHC mismatch murine model by transferring donor B10.D2 (H-2d) cells into BALB/c (H-2d) recipients. MLN4924 or vehicle control (10% 2-hydroxy-propyl-beta cyclodextrin) was injected intraperitoneally on day 20, the point at which skin sclerodermatous cGVHD is initiated. Compared with the vehicle groups, animals that received either bortezomib (0.1 mg/kg) or MLN4924 (20 mg/kg) developed significantly less cGVHD, as determined by clinical scores (2.34±0.34 versus 1.03±0.37 versus 0.8±0.14, respectively; P <0.01 ). Surprisingly, a preventive approach started from either day 0 or day 10 post-HSCT resulted in higher cGVHD scores compared to early therapeutic interventions, started from Day 20, (3.3 and 2.37± 0.18 versus 0.8±0.14, respectively). The temporally dependent efficacy of MLN4924 suggests that PTMs may play a suppressive role in the early development of cGVHD pathogenesis while worsening cGVHD response as a prevention treatment. Flow cytometric analysis revealed a significant reduction in the total number of macrophages and dendritic cells with MLN4924 treatment starting on day 20, while no significant changes were noticed in T cell subpopulations. Similarly, MLN4924 can successfully inhibit mixed lymphocyte reactions (MLR) in vitro. Importantly, a reduction in the total number of plasma cells, a major source of autoantibody production, was also observed. Together these data suggest that inhibition of neddylation with small molecules, such as MLN4924, can be used as a new approach for the treatment of patients with sclerodermatous cGVHD, while potentially maintaining graft versus tumor effects through preserving T cell populations. Disclosures No relevant conflicts of interest to declare. [1]: /embed/inline-graphic-2.gif