Effects of differentiating agents on Epstein-Barr virus-associated B cell lymphomagenesis.

Abstract

Patients with acquired immunodeficiency syndrome (AIDS) or post-transplant patients are at risk for the development of Epstein-Barr Virus (EBV)-associated immunoblastic B cell lymphomas (IBL). Chemotherapy has had limited efficacy in the treatment of EBV-associated IBL. Differentiation therapy is an alternative to traditional chemotherapy that induces terminal differentiation of malignant cells into mature, non-replicating cells. Five agents (retinoic acid, sodium butyrate, trichostatin A, bryostatin and TGF-beta1) that have been shown to induce differentiation in other hematopoietic cell lines were screened for their ability to decrease proliferation and/or induce terminal differentiation in lymphoblastoid cell lines (LCL), an <italic> in vitro</italic> model for IBL. The drugs that decreased proliferation (retinoic acid, sodium butyrate and trichostatin A) were further examined to determine whether or not proliferation was reduced by the induction of terminal differentiation, cell cycle arrest, apoptosis or changes in viral gene expression. Sodium butyrate (SB) and trichostatin A (TSA) induced cell cycle arrest and apoptosis without the induction of terminal differentiation. In contrast all-trans retinoic acid (ATRA), a natural derivative of retinoic acid, arrested cells in the G₁ compartment of the cell cycle and induced differentiation in a subset of LCL. When used in combination, TSA potentiated the effects of ATRA, synergistically producing G₁ arrest, promoting apoptosis and inducing terminal differentiation. Our preliminary results suggest that combination treatment with ATRA and TSA may hold great promise in the future of differentiation therapy for EBV-associated IBL. To determine if ATRA and SB could inhibit growth of LCL <italic>in vivo </italic>, SCID mice were injected with the EW LCL and mice were given subcutaneous drug pellets or placebo pellets at the time of intraperitoneal inoculation. SB treatment was ineffective, due to its short half-life <italic>in vivo</italic>. However, morbid tumor burdens arose 4 days earlier for untreated (n = 21) and placebo-implanted (n = 13) mice compared with ATRA-treated (n = 15) mice. No differences in patterns of viral gene expression or the phenotype of the tumors were found thus suggesting that ATRA treatment affected only a subset of cells. This data provides evidence that retinoids may have potential as an <italic>in vivo</italic> therapeutic treatment for EBV-associated IBL.