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Cancer Res. 2001 Jul 1;61(13):5137-44.

Rituximab inactivates signal transducer and activation of transcription 3 (STAT3) activity in B-non-Hodgkin's lymphoma through inhibition of the interleukin 10 autocrine/paracrine loop and results in down-regulation of Bcl-2 and sensitization to cytotoxic drugs.

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  • 1Department of Microbiology, Immunology and Molecular Genetics, Jonsson Comprehensive Cancer Center, University of California Los Angeles School of Medicine, University of California, Los Angeles, California 90095, USA.


Development of the chimeric mouse antihuman CD20 antibody, Rituximab, presented a notable advance in the treatment of patients with non-Hodgkin's lymphoma (NHL). Its use allowed the specific targeting of tumor B cells without the systemic toxicity of traditional therapies. The mechanisms by which Rituximab induces its antitumor activity are not fully understood. We have shown previously that Rituximab down-regulates Bcl-2 expression in some B-NHL cell lymphoma lines through an interleukin 10 (IL-10)-dependent autocrine loop, an effect that renders the resistant cells susceptible to chemotherapeutic drugs. The objective of this study was to delineate the signaling pathway by which Bcl-2 is controlled by Rituximab and IL-10. We hypothesized that the down-regulation of IL-10 by Rituximab decreases activation of the signal transducer and activator of transcription 3 (STAT3) protein, which in turn, is responsible for decreased levels of Bcl-2. We demonstrate by phosphoprotein immunoblotting and gel shift analyses that endogenous IL-10 induces activation of STAT3 in the 2F7 cell line. Furthermore, we show that Rituximab and anti-IL-10 antibody treatment decreases the ability of STAT3 to bind to its DNA binding site. The decrease in STAT3 activation by these treatments correlates with a decrease in Bcl-2 expression. Additionally, piceatannol, an inhibitor of STAT3 activation, down-regulates the expression of Bcl-2. Altogether, these results demonstrate that Bcl-2 expression is under the regulation of the STAT3 signaling pathway, which is regulated by endogenously secreted IL-10. Hence, Rituximab-induced down-regulation of IL-10 expression is responsible for the down-regulation of Bcl-2 and sensitization of NHL cells by therapeutic drugs. Furthermore, these findings support the notion that circulating IL-10 in vivo may control the resistance of NHL to drug-mediated cytotoxicity.

[PubMed - indexed for MEDLINE]
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