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Departments of Radiation Oncology [A. Y., C. M., J. B., E. R., L. Q., R. M., K. V., P. D.] and Hematology/Oncology [S. G.], Virginia Commonwealth University, Richmond, Virginia 23298; National Cancer Institute, Urologic Oncology Branch, Bethesda, Maryland 20852 [W. M. L.]; and Departments of Pathology [Z-s. S., D. S., I. V. L., R. V. G., P. B. F.], Neurosurgery [P. B. F.], and Urology [P. B. F.], Columbia University, New York, New York 10032

² To whom requests for reprints should be addressed, at Department of Radiation Oncology, Medical College of Virginia, Virginia Commonwealth University, 401 College Street, Richmond, VA 23298-0058. Phone: (804) 628-0861; Fax: (804) 828-6042; E-mail: pdent{at}hsc.vcu.edu

The median survival of metastatic renal cell carcinoma (RCC) is 12 months, and the majority of treatment options are palliative. MDA-7 (interleukin-24), when expressed via a recombinant replication defective adenovirus, Ad.mda-7, has profound antiproliferative and cytotoxic effects in a wide variety of tumor cells but not in nontransformed cells. The studies in this study examined the impact of MDA-7 on RCC proliferation and survival. RCC lines (A498 and UOK121N), but not primary renal epithelial cells, were resistant to adenoviral infection that correlated with a lack of coxsackievirus and adenovirus receptor expression. Additional studies were performed using purified preparations of bacterially synthesized glutathione S-transferase (GST)-MDA-7 protein. GST-MDA-7, but not GST, caused a dose-dependent inhibition of RCC proliferation but not of primary renal epithelial cells. Clinically achievable concentrations of the novel therapeutic agent arsenic trioxide (0.5–1 µM) were found to have little effect on RCC growth. However, the combination of GST-MDA-7 and arsenic trioxide resulted in a greater than additive reduction in cell growth that correlated with a large increase in tumor cell death. The free radical scavenger N-acetyl cysteine abolished the potentiating effect of arsenic trioxide. Although pro-caspase 3, poly(ADP-ribose) polymerase, and Bcl-_XL levels, as well as nucleosomal DNA integrity, were reduced by combined treatment, cell killing was predominantly nonapoptotic. Combined treatment of RCC lines with GST-MDA-7 and arsenic trioxide also resulted in a substantial reduction in clonogenic survival compared with either treatment individually. Collectively, these findings demonstrate that MDA-7 protein, in combination with agents that generate free radicals, may have potential in the treatment of RCC.