EXTH-73. PROTEASOME INHIBITION EXPOSES SELECTIVE VULNERABILITY IN CENTRAL NERVOUS SYSTEM LYMPHOMA

• Published in: Neuro-oncology (Charlottesville, Va.) Vol. 23; no. Supplement_6; p. vi180
• Main Authors: Miyake, Yohei, Kawazu, Masahito, Wakimoto, Hiroaki, Tateishi, kensuke, Yamamoto, Tetsuya
• Format: Journal Article
• Language: English; Japanese
• Published: 12.11.2021
• ISSN: 1522-8517; 1523-5866
• DOI: 10.1093/neuonc/noab196.712

Central nervous system lymphoma (CNSL), including primary and secondary CNSL, has a poor prognosis despite standard intensive chemotherapy. Since the majority of CNSL tumors are highly dependent on NF-κB signaling pathway for survival, Bruton’s kinase inhibitors, which target upstream in the NF-κB pathway, have demonstrated favorable clinical response in PCNSL patients. However, early recurrence is frequently observed. Therefore, novel therapeutic strategies are required in this progressive CNS disease. To understand the underlying tumor biology and explore a novel therapeutic strategy of CNSL, we previously established a panel of patient-derived xenograft (PDX) models, from both immunocompetent and Epstein-Barr virus (EBV)-positive CNSL patients. We confirmed that these PDX models highly recapitulated the phenotypic and genetic features of patient tumors. Using 19 PDX models, including 17 originally established PDXs, we found that NF-κB pathway related genomic alterations and AKT/mTOR signaling did not correlate with sensitivity to BTK inhibitors. We also found that RelA/p65 dephosphorylation as a biomarker of CNSL cells, which are responding to ibrutinib. Through high-throughput and NF-κB pathway-targeted drug screenings, we discovered that proteasome inhibitors suppressed cell viability across all CNSL models. The therapeutic effect, observed at a lower nanomolar range, was mediated by inhibition of the canonical NF-κB and AKT/mTOR pathways and was reversed by silencing of MYD88/CD79B in immunocompetent CNSL or LMP1 in EBV-positive CNSL. The second-generation proteasome inhibitor marizomib prolonged overall survival in CNSL orthotopic xenograft models through simultaneous suppression of RelA/p65 and AKT/mTOR signaling. Proteasome inhibition deregulated Mcl-1 and mediated caspase-dependent apoptosis, which was further enhanced by Bcl-2 family inhibition. Our results demonstrate the potential of proteasome inhibition as a novel therapeutic strategy in patients with immunocompetent and EBV-positive CNSL.