Targeting EGR1-Medited Metabolic Reprogramming to Overcome Ibrutinib Resistance in Aggressive B Cell Lymphomas

Targeting specific signaling pathways in malignant cells through the use of small-molecule kinase inhibitors has revolutionized the treatment of malignancies. Bruton tyrosine kinase (BTK), a key component of the B cell receptor (BCR) signaling pathway, is a promising molecular target in several types of lymphoma, including diffuse large B cell lymphoma (DLBCL) and mantle cell lymphoma (MCL). Ibrutinib, a selective BTK inhibitor, has achieved initial response rates as high as 70% in these lymphomas when used as a single agent. Acquired drug resistance, however, is significant and together with primary resistance makes ibrutinib by itself unsuitable if the goal of treatment is long-term survival. Therefore, understanding and targeting ibrutinib resistance mechanisms is an unmet clinical need. DLBCL, which represents 30% to 40% of newly diagnosed lymphomas, comprises two main molecular subtypes: activated B cell-like (ABC) and germinal center B cell-like (GCB). The BCR/BTK signaling pathway is essential for the growth of ABC DLBCL, which is more aggressive and less curable than GCB DLBCL with current regimens. We established two representative ABC DLBCL cell lines (TMD8 and OCI-Ly10) with ibrutinib resistance by gradually increasing the concentration of ibrutinib during passage in culture. RNA-seq analysis demonstrated that the BCR pathway gene signature is enriched in resistant cell lines when compared to parental cells. The most upregulated gene is EGR1, a transcription factor that activates multiple oncogenic pathways including MYC and E2F. Elevated EGR1 expression is also observed in ibrutinib-resistant primary mantle cell lymphoma cells when treated with ibrutinib. Using multiple metabolic and genetic approaches, we discovered that overexpression of EGR1 causes metabolic reprogramming to oxidative phosphorylation (OXPHOS) and ibrutinib resistance. Mechanistically, EGR1 mediates metabolic reprogramming through transcriptional activation of PDP1, a phosphatase that dephosphorylates and activates the E1 component of the large pyruvate dehydrogenase complex. Therefore, EGR1-mediated PDP1 activation accelerates intracellular ATP production via the mitochondrial tricarboxylic acid (TCA) cycle, leading to sufficient energy to enhance the proliferation and survival of ibrutinib-resistant lymphoma cells. Finally, we demonstrate that targeting OXPHOS with IM156, a newly developed OXPHOS inhibitor, inhibits the growth of ibrutinib-resistant lymphoma cells both in vitro and in patient-derived xenograft mouse models. These findings suggest that targeting EGR1-medited metabolic reprogramming to OXPHOS with IM156 provides a potential therapeutic strategy to overcome ibrutinib resistance in relapsed/refractory DLBCL or MCL.