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Department of Microbiology, Immunology and Molecular Genetics and Jonsson Comprehensive Cancer Center, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA

Requests for Reprints: Benjamin Bonavida, Department of Microbiology, Immunology, and Molecular Genetics, School of Medicine, University of California at Los Angeles, 10833 Le Conte Avenue, A2-060 CHS, Los Angeles, CA 90095-1747. Phone: (310) 825-2233; Fax: (310) 206-3865. Email: bbonavida{at}mednet.ucla.edu

Resveratrol (trans-3,4,5-trihydroxystilbene) has received attention for its potential chemopreventive and antitumor effects in experimental systems. Recent evidence suggests that paclitaxel, alone or in combination with other drugs, can be effectively used in the treatment of non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). This study investigated whether resveratrol can sensitize NHL and MM cell lines to paclitaxel-mediated apoptosis and to delineate the underlying molecular mechanism of sensitization. Both resveratrol and paclitaxel negatively modulated tumor cell growth by arresting the cells at the G₂-M phase of the cell cycle. Low concentrations of resveratrol exerted a sensitizing effect on drug-refractory NHL and MM cells to apoptosis induced by paclitaxel. Resveratrol selectively down-regulated the expression of antiapoptotic proteins Bcl-x_L and myeloid cell differentiation factor-1 (Mcl-1) and up-regulated the expression of proapoptotic proteins Bax and apoptosis protease activating factor-1 (Apaf-1). Paclitaxel down-regulated the expression of Bcl-x_L, Mcl-1, and cellular inhibitor of apoptosis protein-1 antiapoptotic proteins and up-regulated Bid and Apaf-1. Combination treatment resulted in apoptosis through the formation of tBid, mitochondrial membrane depolarization, cytosolic release of cytochrome c and Smac/DIABLO, activation of the caspase cascade, and cleavage of poly(adenosine diphosphate-ribose) polymerase. Combination of resveratrol with paclitaxel had minimal cytotoxicity against quiescent and mitogenically stimulated human peripheral blood mononuclear cells. Inhibition of Bcl-x_L expression by resveratrol was critical for chemosensitization and its functional impairment mimics resveratrol-mediated sensitization to paclitaxel-induced apoptosis. Inhibition of Bcl-x_L expression by resveratrol was due to the inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway and diminished activator protein-1-dependent Bcl-x_L expression. The findings by resveratrol were corroborated with inhibitors of the ERK1/2 pathway. This study demonstrates that in resistant NHL and MM cell lines resveratrol and paclitaxel selectively modify the expression of regulatory proteins in the apoptotic signaling pathway and the combination, via functional complementation, results in synergistic apoptotic activity.

Grant support: Fellowship from the UCLA Jonsson Comprehensive Cancer Center (A. R. Jazirehi).

² M. I. Vega et al. Rituximab inhibits p38 MAPK activity in 2F7 B NHL and decreases IL-10 transcription: pivotal role of p38 MAPK in drug resistance, submitted for publication.

Received 6/ 2/03; revised 9/ 8/03; accepted 10/16/03.