| The factors that cause the autoimmune disease systemic lupus erythematosus (SLE) remain poorly understood. As such, treatment of this debilitating and potentially fatal disease is based on global immunosuppression. However, these drugs non-specifically target all lymphocytes, and are accompanied by serious complications that limit treatment. In effort to develop a new therapeutic for SLE without these limitations, a benzodiazepine (Bz-423) possessing novel cytotoxic properties was identified. Administration of Bz-423 to lupus-prone (NZB x NZW)F1 mice reduces the severity of autoimmune kidney disease with similar efficacy to that previously observed for corticosteroids, azathioprine, and cyclophosphamide, the standard treatments for lupus nephritis. However, unlike these therapies, Bz-423 is not associated with systemic toxicities and is not adversely immunosuppressive. In vivo, Bz-423 induces B-cell apoptosis, with some apparent specificity for pathogenic B-lymphocytes. Because of the well-established link between B-cell autoantibody production and kidney disease, the ability of Bz-423 to reduce B-cell numbers is a plausible mechanism explaining its ability to reduce the signs of autoimmune disease.; To define its cellular mechanism of action, the effects of Bz-423 were examined using transformed cell lines. Morphological and biochemical evidence demonstrates that Bz-423 triggers apoptosis. Bz-423-induced apoptosis involves collapse of the mitochondrial transmembrane gradient prior the acquisition of other apoptotic features. Mechanistically, these findings suggest that Bz-423 acts through an apoptotic second messenger. Caspase inhibition prevents apoptosis but does not prevent mitochondrial alterations, suggesting that Bz-423 does not act along the signal transduction pathway activated by ligation of apoptotic death receptors.; Comparison of Bz-423 to central and peripheral benzodiazepine receptor ligands indicates that only Bz-423 induces apoptosis. By screening a library of structurally related analogs, it is clear that the naphthylalanine side chain of Bz-423 is a critical structural element. These findings demonstrate a unique structure-activity relationship for benzodiazepines. Because of its ability to treat autoimmune kidney disease and to induce apoptosis in a wide spectrum of cancer-cell-derived cell lines, Bz-423 represents a promising new lead compound for the treatment of many human diseases including SLE, rheumatoid arthritis, and cancer. |
