Epstein-Barr virus (EBV) infects >90% of the global population and is associated with various lymphoid malignancies, including Burkitt lymphoma, Hodgkin lymphoma, and diffuse large B-cell lymphoma. Many of these lymphomas exhibit overexpression of EBV latent proteins, including EBNA2, which directly upregulates MYC, a well-characterized oncogene. Currently, there are no approved therapies that specifically target EBV-associated oncogenesis. Given the role of PARP1 in maintaining EBV latency and its role in gene expression, this study aimed to investigate the potential of PARP1 inhibition as a therapeutic strategy.
A xenograft mouse model was utilized using 5 × 10⁶ EBV-positive lymphoblastoid cell line (LCL) expressing eLuciferase, which were implanted into 16 NSG mice. Once tumors were formed, mice were randomly divided into two groups (n = 8 for both treatment arms) and treated daily with either vehicle or BMN 673 (0.33 mg/kg) by oral administration. Tumor progression was monitored using bioluminescent imaging, and tissue samples were analyzed by a combination of immunohistochemistry, ELISA, RNA sequencing, or a series of molecular assays for DNA damage, gene expression, or protein interaction.
Tumor growth and metastasis were significantly reduced following PARP1 inhibition. Total bioluminescent flux was significantly decreased by Day 28 in the BMN 673-treated group compared to controls (p = 0.0012). Tumor Growth Inhibition (TGI%) was found to be 80.85% ± 4.15 SEM. The amount of liver metastases was extensive in control mice, while liver metastasis in treated mice showed minimal infiltration based on histological analysis. NUMA1 staining further confirmed a significant reduction in human LCL in treated mice (p = 0.004).
Even though PARP1 is known to play a major role in DNA repair, the treatment with BMN 673 did not increase the markers of DNA damage (e.g., γH2A.X), and single-cell gel electrophoresis showed no significant increase in DNA strand breaks. These results suggest that the antitumor effect of BMN 673 is not due to the induction of DNA damage.
RNA-seq analysis identified a total of 3,112 differentially expressed genes, of which 1,807 were upregulated and 1,305 were downregulated. The most notable examples of downregulation were the MYC oncogene and the family member MYCL, both confirmed as downregulated by qPCR and Western blot testing. Remarkably, IPA analysis revealed MYC was one of the most inhibited transcriptional regulators impacted. In addition, p53 significantly increased in BMN 673-treated tumors.
The ability of MYC to bind chromatin is impaired after PARP1 inhibition. MYC protein levels were markedly lower, and chromatin immunoprecipitation demonstrated lower MYC binding at the promoters of downstream targets, including PA2G4, FAM120A, and DDX21. Notably, PARP1 inhibition caused no trapping of PARP1, indicating a chromatin-regulatory mechanism versus a DNA-repair mechanism.
BMN 673 treatment downregulated latent genes, such as EBNA2, while upregulating lytic genes, which included BRLF1, BMRF1, and Zta. Thus, while there is apparent early lytic gene activation, viral genome copy numbers remained unchanged. This suggests that there was an abortive lytic reactivation rather than full viral replication.
This study provides strong evidence that BMN 673, a potent PARP1 inhibitor, inhibits EBV-induced lymphomagenesis by displacing the EBNA2/MYC oncogenic program. Unlike conventional chemotherapeutics, BMN 673 was shown to directly target the EBNA2 oncogene through epigenetic and transcriptional modulation, rather than causing DNA damage. These results emphasize the therapeutic potential of using PARP1 inhibitors to treat EBV-associated malignancies. This study highlights that MYC and EBNA2 as actionable oncogenic targets. Further clinical trials are needed to determine the safety and efficacy of PARP1 inhibitors in patients with EBV-positive lymphomas.
References: Caruso LB, Napoletani G, Soldan SS, et al. PARP1 inhibition halts EBV⁺ lymphoma progression by disrupting the EBNA2/MYC axis. J Med Virol. 2025;97(7):e70485. doi:10.1002/jmv.70485
