Inhibition of interleukin 10 by Rituximab results in down-regulation of Bcl-2 and sensitization of B-cell non-Hodgkin's lymphoma to apoptosis

Treatment of patients with non-Hodgkin's lymphoma (NHL) is frequently hampe red by development of chemoresistance, Rituximab is a chimeric mouse antihu man CD20 antibody that offers an alternative; however, its mechanism of act ion is not clearly understood. Treatment of lymphoma cell lines with Rituxi mab sensitizes the cells to the cytotoxic and apoptotic effects of therapeu tic drugs, e,g,, cisplatin, fludarabine, vinblastine, and Adriamycin, This study investigated the mechanism(s) involved in the reversal of drug resist ance by Rituximab therapy. NHL cells synthesize and secrete antiapoptotic c ytokines implicated in drug resistance, including interleukin (IL)-6, IL-10 , and tumor necrosis factor or. We hypothesized, therefore, that sensitizat ion by Rituximab may be due in part to modification of cytokine production. In this study, examination of cytokine secretion by NHL 2F7 tumor cells re vealed down-regulation of IL-10 by Rituximab treatment. Moreover, cytotoxic ity assays using exogenous IL-10 and IL-10-neutralizing antibodies demonstr ated that IL-10 serves as an antiapoptotic/protective factor in these tumor cells against cytotoxic drugs. Furthermore, expression in 2F7 cells of the protective factor, Bcl-2, was shown to be dependent on IL-10 levels and do wnregulated by Rituximab, Other gene products such as Bar, Bcl-x, Bad, p53, c-myc, and latent membrane protein-1 (LMP) were not affected by Rituximab treatment, Drug sensitization, as well as down-regulation of both IL-10 and Bcl-2, was corroborated in experiments using the NHL cell line 10C9, The R amos and Daudi NHL cell lines were not sensitizable, nor did their Bcl-2 or IL-10 levels change. These studies demonstrate that one mechanism by which Rituximab sensitizes NHL to chemotherapeutic drugs is mediated through dow n-regulation of antiapoptotic IL-10 autocrine/paracrine loops and Bcl-2, Th e clinical relevance of these findings is discussed.