Targeting the Synthetic Lethality Interaction of MTAP and PRMT5 to Overcome Drug Resistance and Enhance Anti-Cancer Immunity in Mantle Cell Lymphoma

Background: Complex genetic, epigenetic alterations and metabolic reprogramming are among the hallmarks of mantle cell lymphoma, an aggressive B-cell type of non-Hodgkin's lymphoma. CDKN2A and MTAP are frequently co-deleted in human cancers including MCL. Deletion of MTAP gene results in the accumulation of methylthioadenosine (MTA), a selective inhibitor of protein arginine methyltransferase 5 (PRMT5), signifying a dependence of MTAP deleted tumors on PRMT5. PRMT5 plays an important role in normal cellular processes via epigenetic and post-translational modification of RNA splicing, DNA repair and cell cycle regulators. These pathways may be activated in response to targeted therapies to maintain tumor growth and survive chemotherapy. Sustained PRMT5 expression and activity could be therapeutically targeted in MTAP-deficient MCL. Mutations in RNA splicing factors are common in lymphoma and increase the susceptibility to perturbations in splicing events. Deregulated PRMT5 might induce alternative splicing, leading to loss of expression of proteins or epitopes, and subsequent immune evasion and failure of tumor specific immune therapy. Multiple mechanisms may co-exist. Results: CDKN2A and MTAP were commonly co-deleted in ibrutinib-resistant MCL tumors (71%, p = 0.01). To corroborate with this finding, we found that PRMT5 was overexpressed in both primary ibrutinib-resistant MCL and cell lines, with its expression levels inversely correlated with the patient responses to ibrutinib treatment (p = 0.004). Metabolomics analysis revealed elevated S-Adenosyl-methionine (SAM) and S-Adenosyl-homocysteine (SAH) (t-test p Conclusion: We presented evidence that MCL with MTAP deletion confers synthetic lethal dependence on PRMT5, making it an attractive therapeutic target. As an important metabolic and epigenetic regulator, loss of PRMT5 leads to malfunction of the constitutive splicing machinery that induces alternative splicing events, genetic instability and cell cycle arrest. Sustained PRMT5 expression and activity confers tumor aggressiveness and therapeutic resistance in MTAP-deficient MCL. Pharmacological blockade of PRMT5 may dramatically enhance T-cell immunity, while suppressing MCL cell proliferation and tumor growth in vivo. Further successful mechanistic studies would facilitate the identification of novel therapeutics and strategies to overcome resistance to targeted therapies and significantly improve the efficacy of immunotherapy for much better clinical outcomes of MCL. Disclosures Wang: Oncternal: Consultancy, Research Funding; Lu Daopei Medical Group: Honoraria; Juno: Consultancy, Research Funding; Guidepoint Global: Consultancy; Dava Oncology: Honoraria; MoreHealth: Consultancy; Targeted Oncology: Honoraria; Beijing Medical Award Foundation: Honoraria; Verastem: Research Funding; OncLive: Honoraria; Acerta Pharma: Research Funding; VelosBio: Research Funding; Molecular Templates: Research Funding; Nobel Insights: Consultancy; AstraZeneca: Consultancy, Honoraria, Other: Travel, accommodation, expenses, Research Funding; Janssen: Consultancy, Honoraria, Other: Travel, accommodation, expenses, Research Funding; Pharmacyclics: Consultancy, Honoraria, Other: Travel, accommodation, expenses, Research Funding; Pulse Biosciences: Consultancy; Loxo Oncology: Consultancy, Research Funding; Kite Pharma: Consultancy, Other: Travel, accommodation, expenses, Research Funding; BioInvent: Research Funding; Celgene: Consultancy, Other: Travel, accommodation, expenses, Research Funding; OMI: Honoraria, Other: Travel, accommodation, expenses; InnoCare: Consultancy.