Combination of bortezomib and venetoclax targets the pro-survival function of LMP-1 and EBNA-3C of Epstein-Barr virus in post-transplant lymphoproliferative disorder

Epstein-Barr virus (EBV) manipulates the ubiquitin-proteasome system and regulators of Bcl-2 family to enable the persistence of the virus and survival of the host cells through the expression of viral proteins in distinct latency patterns. We postulate that the combination of bortezomib (proteasome inhibitor) and venetoclax (Bcl-2 inhibitor) [bort/venetoclax] will cause synergistic killing of post-transplant lymphoproliferative disorder (PTLD) through targeting the pro-survival function of latent viral proteins such as latent membrane protein-1 (LMP-1) and EBV nuclear antigen-3C (EBNA-3C). Bort/venetoclax could synergistically kill spontaneous lymphoblastoid cell lines (sLCLs) derived from patients with PTLD and EBV-associated hemophagocytic lymphohistiocytosis by inducing DNA damage response, apoptosis and G1-S cell cycle arrest in a ROS-dependent manner. Bortezomib potently induced the expression of Noxa, a pro-apoptotic initiator and when combined with venetoclax, inhibited Mcl-1 and Bcl-2 simultaneously. Bortezomib prevented LMP-1 induced proteasomal degradation of IκBα leading to the suppression of the NF-κB signaling pathway. Bortezomib also rescued Bcl-6 from EBNA-3C mediated proteasomal degradation thus maintaining the repression of cyclin D1 and Bcl-2 causing G1-S arrest and apoptosis. Concurrently, venetoclax inhibited Bcl-2 upregulated by either LMP-1 or EBNA-3C. Bort/venetoclax decreased the expression of phosphorylated p65 and Bcl-2 at serine 70 thereby suppressing the NF-κB signaling pathway and promoting apoptosis, respectively. These data corroborated the marked suppression of the growth of xenograft of sLCL in SCID mice (p<0.001). Taken together, the combination of bortezomib and venetoclax targets the pro-survival function of LMP-1 and EBNA-3C of Epstein-Barr virus in post-transplant lymphoproliferative disorder. Author Summary Epstein-Barr virus (EBV) is an oncogenic virus associated with different cancers and can directly drive the development of a lymphoma type condition in organ transplant patients known as post-transplant lymphoproliferative disorder (PTLD) as a result of weakened immune surveillance of EBV. The malignant spectrum of PTLD will require multi-agent chemotherapy regimen which is not well tolerated by the immunocompromised patients. Here, we combined bortezomib (proteasome inhibitor) with venetoclax (Bcl-2 inhibitor) as a novel strategy to target the pro-survival function of key EBV onco-proteins, namely LMP-1 and EBNA-3C. We demonstrated that this chemotherapy-free regimen could be highly effective in killing patient-derived spontaneous lymphoblastoid cell lines which represent cell models of PTLD. The novel drug regimen can avoid the toxic effects of chemotherapy and may have high efficacy and specificity for the treatment of PTLD. ### Competing Interest Statement The authors have declared no competing interest.