The transcription factor nuclear factor-κB (NF-κB) is a central mediator of growth and homeostasis for both normal and neoplastic cells. IκBα is the natural intracellular inhibitor of NF-κB and can effectively complex with and thereby inhibit the biologic activity and translocation of NF-κB to the nucleus. We designed a fusion protein designated IκBα/scFvMEL composing of human IκBα and the single-chain antibody scFvMEL, targets melanoma gp240 antigen. Cells treated with IκBα/scFvMEL before irradiation showed specifically inhibition of both constitutive and radiation-induced NF-κB activity on gp240 antigen-positive A375M cells. Pretreatment of A375M cells with IκBα/scFvMEL significantly sensitized melanoma cells to ionizing radiation assessed using a clonogenic survival assay. Mechanistic studies showed that IκBα/scFvMEL, when exogenously added to A375M cells, could be coimmunoprecipitated with the p65 subunit of NF-κB. IκBα/scFvMEL inhibited in a time and/or dose-dependent manner oftumor necrosis factor α- or radiation-induced NF-κB activity in vitro. IκBα/scFvMEL was also shown to specifically inhibit the translocation of the NF-κB p65 subunit to the cell nucleus and NF-κB-mediated gene transcription. Further, initial studies showed that mice bearing well-established A375M xenografts were treated (intravenously) with IκBα/scFvMEL and showed a significant suppression of tumor growth. We also observed a decrease in levels of Bcl-2 and Bcl-XL signaling events downstream of NF-κB in the tumor model. These studies demonstrate for the first time that tumor cell-targeted delivery of IκBα may be beneficial for the treatment of melanoma when combined with standard anticancer therapies such as radiation.
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Abbreviations: NF-κB, nuclear factor-kappa B; scFv, recombinant single-chain Fv antibody Address all correspondence to: Michael G. Rosenblum, PhD, Department of Experimental Therapeutics, University of Texas MD Anderson Cancer Center, Unit 44, 1515 Holcombe Blvd, Houston, TX 77030. E-mail: email@example.com 1This research was supported, in part, by the Clayton Foundation for Research. 2This article refers to supplementary materials, which are designated by Figures W1 to W5 and are available online at www.neoplasia.com. Received 25 January 2010; Revised 17 June 2010; Accepted 22 June 2010 Copyright © 2010 Neoplasia Press, Inc. All rights reserved 1522-8002/10/$25.00 DOI 10.1593/neo.10214