Preclinical activity of brincidofovir in Peripheral T-cell and NK/T-cell Lymphoma

Introduction: Brincidofovir (BCV) is a novel nucleoside phosphonate analogue with unique dual anti-viral and anti-tumor properties. Methods: Activity of BCV was evaluated in forty-four cell-line models, including T/NK-cell non-Hodgkin lymphoma (T/NK-NHL, n=25) and B-cell lymphoma (BCL, n=19), as well as their respective NOD/SCID mice xenograft models (NK/T-cell lymphoma, peripheral T-cell lymphoma, not otherwise specified, TP63 -rearranged anaplastic large cell lymphoma, and MYC / BCL2 -rearranged diffuse large B-cell lymphoma). Potential in vivo immunogenic effects were examined in a syngeneic EL4-C57BL/6 murine lymphoma model. Results: BCV demonstrated potent anti-tumor activity in vitro across the majority of cell-lines regardless of EBV positivity, with IC50 values within clinically-achievable human plasma concentrations (2 µg/ml) in 17/25 (68.0%) T/NK-NHL and in 13/19 (68.4%) BCL. In vivo treatment via intraperitoneal BCV (40mg/kg, 2X per week) significantly inhibited tumor growth in all xenograft models when compared to vehicle control. Notably, RNAseq analysis demonstrated BCV downregulated MYC and MYC-target pathways in T/NK-NHL models. Further mechanistic studies showed that BCV evoked S-phase cell cycle arrest, replication stress, DNA damage and apoptosis, while also triggering STING pathway-mediated interferon responses, PD-L1 expression and immunogenic cell death. In the syngeneic EL4-C57BL/6 model, BCV in combination with anti-PD1 significantly inhibited tumor growth and triggered an immune reaction characterized by highest scores for adaptive immune response, cytokines/chemokines & receptors, cytotoxic cells, dendritic cells, NK CD56dim cells and neutrophils (NanoString Immunology Panel). Conclusions: Taken together, these results demonstrate a novel role of BCV in the treatment of lymphoma, and suggest potential for combination with checkpoint immunotherapy.