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Effects of Plasmid-Based Stat3-Specific Short Hairpin RNA and GRIM-19 on PC-3M Tumor Cell Growth

Authors' Affiliations: ¹ Prostate Diseases Prevention and Treatment Research Center and Department of Pathophysiology, School of Basic Medicine, Jilin University, Changchun, P.R. China; ² Greenebaum Cancer Center, Department of Microbiology and Immunology, Molecular Biology Program, University of Maryland School Medicine, Baltimore, Maryland; and ³ Laboratory of Enteric and Sexually Transmitted Diseases, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland

Requests for reprints: Zhao Xuejian, Prostate Diseases Prevention and Treatment Research Centre, and Department of Pathophysiology, School of Basic Medicine, Jilin University, Xinmin Street, Changchun, 130021, P. R. China. Phone: 011-86-431-563-2348; Fax: 011-86-431-563-2348; E-mail: pro_2{at}jlu.edu.cn or De-Qi Xu, Laboratory of Enteric and Sexually Transmitted Diseases, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892. Phone: 301-496-1894; Fax: 301-402-8701; E-mail: deqi.xu{at}fda.hhs.gov.

Purpose: Persistent activation of signal transducers and activators of transcription 3 (Stat3) and its overexpression contribute to the progression and metastasis of several different tumor types. For this reason, Stat3 is a reasonable target for RNA interference–mediated growth inhibition. Blockade of Stat3 using specific short hairpin RNAs (shRNA) can significantly reduce prostate tumor growth in mice. However, RNA interference does not fully ablate target gene expression in vivo, owing to the idiosyncrasies associated with shRNAs and their targets. To enhance the therapeutic efficacy of Stat3-specific shRNA, we applied a combination treatment involving gene associated with retinoid-IFN–induced mortality 19 (GRIM-19), another inhibitor of STAT3, along with shRNA.

Experimental Design: The coding sequences for GRIM-19, a cellular STAT3-specific inhibitor, and Stat3-specific shRNAs were used to create a dual expression plasmid vector and used for prostate cancer therapy in vitro and in mouse xenograft models in vivo.

Results: The coexpressed Stat3-specific shRNA and GRIM-19 synergistically and more effectively suppressed prostate tumor growth and metastases when compared with treatment with either single agent alone.

Conclusion: The simultaneous use of two specific, but mechanistically different, inhibitors of STAT3 activity exerts enhanced antitumor effects.