Transcription factor decoy.

Numerous studies have demonstrated the importance of altered gene expression in disease pathophysiology. Thus, modification of gene expression has emerged as an important therapeutic strategy.1 Agents that inhibit the transcription of disease-mediating genes or transactivate the expression of genes whose products disrupt pathophysiological processes are being developed. Regulation of gene expression is a complex biological process involving transcription factor–DNA interaction that initiates gene transcription. Transcription factors are proteins residing in the cell nucleus or cytoplasm that upon activation bind with specific DNA motifs in the promoter region of the target gene. The activation process may involve phosphorylation, dimerization, proteolytic cleavage, ubiquitination, and/or translocation. Accordingly, molecules that block one or more steps of the transcription machinery can potentially modify the expression of a specific gene or group of genes, yielding a functional response(s). It has been shown that short sequences of DNA containing the consensus binding site, even in the absence of surrounding DNA, can bind transcription protein in a highly specific manner. Indeed, such oligonucleotides have been used as radiolabeled probes for the detection and characterization of transcription factors (TFs) in electrophoretic mobility shift assays. Specific DNA sequences have been used successfully as “decoys” to bind specific TFs in cultured cells or in vivo, rendering the TFs incapable of subsequent binding to the promoter region of target genes.1 This approach has been shown to be effective in modulating gene expression in vitro and in vivo. Indeed, the use of transcription factor decoy (TFD) as a tool to study gene expression in vivo was first demonstrated for tissue-specific regulation of renin gene expression. The data showed that decoy mimicking a specific negative regulatory element (CNRE) in the promoter region of the renin gene resulted in the derepression of renin expression in extra renal tissues such as liver and submandibular gland, thereby documenting the functional role of CNRE in suppressing renin expression in these tissues.2,3 Similar approaches have been used by others in studying the regulation of gene expression.4–8 The in vivo effectiveness of TFD in modulating gene expression prompted the consideration of its use in therapy.9,10 We reported the development of a decoy that targeted the E2F family of transcription factors that regulate cell cycle at the G1/S checkpoint with the aims of blocking vascular smooth muscle cell (VSMC) proliferation in vitro and inhibiting neointimal formation in vivo. Since this initial report, numerous TFDs have been successfully used to modulate the expression of a variety of target genes yielding therapeutic actions. These include TFDs to E2F, NFB, CREB, AP-1, AGE, etc, that have been shown experimentally to be effective in treating vascular proliferation, myocardial infarction, tumor growth and invasiveness, and hypertension, etc.11–22 In this issue of Circulation Research, Ahn et al23 reported the inhibitory effects of AP-1 decoy oligonucleotide on VSMC proliferation in vitro and neointimal formation in vivo. The rationale for targeting AP-1 is based on the data that vascular injury activates JNK and ERK that translocate to the nucleus to activate c-Jun and c-Fos, which subsequently dimerize to form the AP-1 complex. AP-1 binds to specific DNA motif in a number of genes involved in VSMC proliferation. The AP-1 decoy strategy used by these authors is an extension of our earlier work as well as those of others demonstrating the effectiveness of AP-1 decoy in inhibiting target gene expression and VSMC growth in vitro17 and neointimal formation in vivo.18,19 Thus, AP-1 decoy joins E2F and NFB as TFDs that show much promise as molecular therapy for vascular proliferative disorders including restenosis, atherosclerosis, bypass graft failure, and transplant vasculopathy. What is the evidence that TFD can exert biological effect and produce therapeutic benefit? Will TFD be effective as human therapy? Among the TFDs reported to date, E2F decoy has undergone the most extensive evaluation with successful completion of preclinical and toxicology studies, as well as phase I/II human trials.10,11 E2F was targeted because it is hypothesized that blocking cell cycle, the common denominator of the pathophysiological process of vascular proliferation, is the most effective strategy to prevent neointimal hyperplasia. Indeed the first clinical trial (PREVENT-I) on human bypass vein grafts demonstrated that E2F decoy inhibited PCNA and c-myc expression and blocked vascular cell proliferation of the graft.10 PREVENT-I studied a cohort of patients at high risk for lower-extremity graft failure in a prospective, randomized, and controlled fashion. The study results met the primary end points, which were safety and feasibility. A second larger phase IIB clinical trial was performed to study the effect of E2F decoy on coronary artery bypass grafts (CABGs). The result demonstrated a 30% to 40% decrease in CABG failure as documented by angiography and intravascular ultrasound.24 Two The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association. From the Department of Medicine, Brigham & Women’s Hospital, Boston, Mass. Correspondence to Victor J. Dzau, MD, Chairman, Department of Medicine, Brigham & Women’s Hospital, Hersey Professor of Theory and Practice of Physic (Medicine), Harvard Medical School, 75 Francis St, Boston, MA 02115. E-mail [email protected] (Circ Res. 2002;90:1234-1236.) © 2002 American Heart Association, Inc.