Treatment of Gamma-Herpes Virus Associated Lymphomas with Lytic-Inducing Agents.

Abstract 4786

Gamma-herpes viruses are the etiologic cause of a significant portion of human lymphomas. Epstein Barr virus (EBV) is virtually found in nearly all cases of endemic Burkitt lymphoma (BL), AIDS-related Hodgkin's lymphoma, and primary CNS lymphoma (PCNSL). EBV also affects 30-60% of AIDS related BL cases, and the great majority of immunoblastic lymphomas (IBLs) and primary effusion lymphomas (PELs). PELs are usually also co-infected with human herpes virus 8 (HHV-8), which is thought to drive the proliferation of this tumor. A hallmark of viral-related lymphomas is the high constitutive expression of NF-κB, a key molecule which activates anti-apoptotic pathways. Investigators have demonstrated that pharmacologic blocking of NF-κB disrupts viral latency inducing apoptosis in EBV and HHV-8 lymphomas. In a recent study, the combination of arginine butyrate and gancyclovir (GCV) was found to be efficacious in patients with EBV-related lymphoproliferative diseases. The investigators postulated that butyrate induces EBV lytic replication and expression of the viral thymidine kinase, which in turn phosphorylates the nucleoside analog GCV which gets incorporated into DNA. We recently reported that azidothymidine (AZT) alone inhibited NF-κB and disrupted EBV latency inducing apoptosis in primary low-passage EBV+ Burkitt lines, while GCV did not exert this effect. BL displays a restricted EBV latency pattern (Type I) and lack the expression of latent membrane proteins (LMPs), while primary EBV+ IBL lines express LMP-1. This EBV-encoded oncoprotein activates NF-κB and enforces latency. While IBLs are generally resistant to the effects of AZT alone, we recently found that adding hydroxyurea sensitized them to AZT. Hydroxyurea is a ribonucleotide reductase inhibitor, which increases the intracellular levels of AZT monophosphate. The use of AZT in targeting gamma-herpes virus tumors is an attractive concept given that this drug is preferentially phosphorylated intracellularly thus exploiting viral kinases potentiating its own cytostatic and anti-tumor effects. We have recently opened to accrual a phase II study evaluating the combination of EBV lytic-inducing chemotherapy drugs (methotrexate, doxorubicin, and AZT/hydroxyurea) for relapsed EBV-related NHL. So far, an HIV+ patient suffering from EBV+ and HHV-8+ solid PEL variant has been treated, and undergone a complete remission with this therapy. We are actively investigating new combinations of lytic inducing agents in our established primary EBV+ BL and IBL cell lines, including the proteasome inhibitor bortezomib, DNA methyltransferase (DNMT) inhibitors such as 5-azacytidine (5-AZA), and histone-deacteylase (HDAC) inhibitors. Here we report, that sub lethal doses of 5-AZA and HDAC-inhibitors (sodium butyrate, and suberoylanilide hydroxamic or SAHA) potently synergize to induce EBV lytic proteins Zebra and EAD in both primary BL and IBL lines. Sodium butyrate by itself appeared to be more potent than 5-AZA or SAHA at inducing EBV lytic replication in all cell lines tested, and also synergized with the nucleoside analog AZT. Experiments are currently ongoing testing the ability of these biological agents to sensitize EBV+ lymphoma lines to nucleoside analogs. Our goal is to continue the development of promising therapeutic approaches for gamma-herpes virus lymphomas. These data will be presented at the meeting.