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Abstract 4568: Reversal of immune tolerance and increased anti tumoral immune response in a mouse model of CNS B cell lymphoma after combined XPO1 and BCR inhibition

Primary CNS lymphoma (PCNSL) is an aggressive non-Hodgkin lymphoma usually classified as ABC-DLBCL. Selinexor inactivates XPO-1 protein and induces anti-tumor effects mainly due to forced nuclear retention of tumor suppressors. It has shown excellent brain penetrance and promising results in glioblastoma and can inhibit both BCR and NF-kB signaling in malignant B-cells. Herein, we assessed the role of XPO-1 inhibition in intracerebral xenograft murine models. Proliferation and survival analysis in DLBCL cell lines showed that cell of origin does not influence sensitivity to selinexor and a strong synergy with ibrutinib mainly in ABC-DLBCL. We then established an orthotopic xenograft model of PCNSL by stereotactic injection of OCI-Ly10 cells transfected with luciferase into the brain parenchyma of nude athymic mice. Mice were treated with 5mg/kg oral selinexor or vehicle three times a week and bioluminiscence was assessed twice a week. Selinexor significantly blocked tumoral growth with differences starting as soon as 12 days after treatment. Also, selinexor improved mice survival (median: 48 days vs. 34 days). Next, we evaluated the potential synergy between ibrutinib and selinexor in vivo. For that mice were assigned into one of the following groups: selinexor (5mg/kg twice a week), ibrutinib (25mg/kg daily), combination or vehicle. The combination of both drugs significantly increased survival compared to both treatments as single agent, whereas there was no significant difference between ibrutinib and selinexor alone. Tumoral growth was equally blocked by all treatments. We next evaluated the innate immune response to the lymphoma by flow cytometry. Remarkably, CNS lymphomas were infiltrated by PD-1 positive M2 macrophages, as well as NK cells. Treatment with selinexor was able to decrease the proportion of M2-protumoral macrophages by half whereas the combination induced a 3-fold reduction (V: 22.72%+/-1.6, S: 12.29%+/-1.38, C: 7.1%+/-1.19). As a consequence, the proportion of M1 macrophages increased (V: 70.22%+/-1.8, S: 82.4%+/-1.7, C: 86.59%+/-1.5). In turn, ibrutinib was the main responsible for downregulation of PD-L1 in malignant cells (V: 3.7%+/-0.68, I: 0.6%+/-0.19, C: 0.19%+/- 0.08). Only when both treatments were combined there was significant downregulation of PD1 expression in M2 (V: 37.6%+/-5.5, C: 24.61%+/- 2.2) and a downregulation in PD1/SIRPα double positive M2 (V: 14.4%+-/1.44, C: 9.16%+/- 0.78). Selinexor and combination were able to significantly increase the proportion of NK cells (V:4.8%+/-0.21, S:9.7%+/-1.16, C:11.54%+/-2.02) and downregulate their PD1 expression (V:8.2%+/-2.7, S:3.7%+/-0.9, C: 2.8%+/-1.06). These results provide pre-clinical evidence for the development of selinexor and ibrutinib combination as new therapeutic option for PCNSL or DLBCL with CNS involvement. Citation Format: Marta Crespo, Isabel Jimenez, Julia Carabia, Sabela Bobillo, Pau Abrisqueta, Carles Palacio, Juan Camilo Nieto, Joan Boix, Cecilia del Carmen Carpio, Josep Castellvi, Joan Seoane, Francesc Bosch. Reversal of immune tolerance and increased anti tumoral immune response in a mouse model of CNS B cell lymphoma after combined XPO1 and BCR inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4568.