Modulation of activation-induced cell death in lymphocytes by a pro-apoptotic benzodiazepine

The autoimmune disease systemic lupus erythematosus (SLE) poses formidable therapeutic challenges; neither the exact population of pathogenic lymphocytes nor specific targets for drug development are defined. As such, SLE is treated with immunosuppressive drugs that target all lymphocytes, and treatment with these agents is associated with serious, sometimes fatal complications. Previous studies have identified a pro-apoptotic 1,4-benzodiazepine (Bz-423) that reduces the severity of autoimmune nephritis in (NZB x NZW)F₁ mice, a murine model of SLE in which B cells are dominant. To further probe the properties of Bz-423, studies were conducted with MRL/MpJ-Faslpr mice. In this strain, the development of autoimmune disease is dependent on T cells. Administration of Bz-423 to these mice significantly attenuates the progression of autoimmune arthritis and nephritis and concomitantly decreases CD4+ T cells. Parallel experiments demonstrated that Bz-423 neither suppresses normal B and T cell immune responses nor alters normal lymphocyte populations in vivo. Thus, the effects of Bz-423 are specifically concentrated on autoimmune lymphocytes.; To define the cellular basis for selectivity, the effect of Bz-423 on receptor-stimulated lymphocytes was examined. In both B and T cells, moderate [Bz-423] that have minimal activity against non-stimulated cells, synergize with antigen receptor stimulation resulting in increased cell death. Moreover, Bz-423 rescues defective activation-induced cell death (AICD) in both autoimmune B and T lymphocytes. Since defective AICD is one mechanism by which autoreactive cells escape peripheral tolerance, the ability of Bz-423 to restore AICD is a plausible mechanism that explains its ability to attenuate autoimmune disease.; Studies in Ramos B cells to probe the molecular basis for the synergistic death response revealed that in non-stimulated cells, Bz-423 induces superoxide, which signals cellular changes ultimately leading to cell death. The generation of superoxide is not increased by ligation of the antigen receptor; rather stimulation sensitizes lymphocytes so that Bz-423-generated superoxide signals an apoptotic pathway that is not triggered in non-stimulated cells. Because receptor stimulation is a requirement for the development and maintenance of autoreactive lymphocytes, the pro-apoptotic properties of Bz-423 provide an opportunity to selectively target a central determinant of lupus pathogenesis.