Similar problems were observed during the treatment of non-small-cell lung cancers [42]. In addition, many tumors are inherently resistant to or become resistant to anti-EGFR antibodies [43]. number of cells counted. (B) Binding was measured were using 0.1 nM aptamer and 50 ug of hEGFR or hEGFRvIII. Binding assays were carried out in triplicate and the average values and standard deviations are shown.(TIF) pone.0020299.s003.tif (501K) GUID:?0A8BF5BA-C0D1-42F5-88C8-D70E3497F4CD Table S1: Sequences of anti-EGFR aptamers isolated from the N62 pool. Only the random sequence portions of the aptamers are shown. The known Fc-binding motif CD 437 GGUGCU was highlighted in red. N represents an undetermined nucleotide. The number of times the aptamer was isolated is shown on the right.(XLS) pone.0020299.s004.xls (21K) GUID:?95DA7700-274E-42E9-A36F-270EE85E7652 Table S2: Sequences of anti-EGFR aptamers isolated from a doped Aptamer E01 pool. Only the random sequence portions of the aptamers are shown. Aptamer E30 and E39 (red) appeared twice. N represents an undetermined nucleotide.(XLS) pone.0020299.s005.xls (26K) GUID:?7A3BDF09-3E56-4005-ABC7-6B9D6D2AB6EE Abstract Aptamers continue to receive interest as potential therapeutic agents for the treatment of diseases, including cancer. In order to determine whether aptamers might eventually prove to be as useful as other clinical biopolymers, such as antibodies, we selected aptamers against an important clinical target, human epidermal growth factor receptor (hEGFR). The initial selection yielded only a single clone that could bind to hEGFR, but further mutation and optimization yielded a family of tight-binding aptamers. One of the selected aptamers, E07, bound tightly to the wild-type receptor (Kd?=?2.4 nM). This aptamer can compete with EGF for binding, binds to a novel epitope on EGFR, and also binds a deletion mutant, EGFRvIII, that is commonly found in breast and lung cancers, and especially in grade IV glioblastoma multiforme, a cancer which has for the most part proved unresponsive to current therapies. The aptamer binds to cells expressing EGFR, blocks receptor autophosphorylation, and prevents proliferation of tumor cells in three-dimensional matrices. In short, the aptamer is a promising candidate for further development as an anti-tumor therapeutic. In addition, Aptamer E07 is readily internalized into EGFR-expressing cells, raising the possibility that it might be used to escort other anti-tumor or contrast agents. Introduction Aptamers have been selected against a surprising range of targets, ranging from ions to small organics to proteins to supramolecular structures such as viruses and tissues [1], [2]. Aptamers targeting proteins in the bloodstream or on cell surfaces have proven to be useful for CD 437 therapy. For instance, aptamers have been selected against a number of growth factors such as basic fibroblast growth factor (bFGF) [3], vascular endothelial growth factor (VEGF) [4], platelet-derived growth factor (PDGF) [5], and keratinocyte growth factor (KGF) [6]. These aptamers could block the interactions between growth factors and their receptors, and have proven to be excellent drug candidates. An anti-VEGF aptamer has been approved by FDA in 2004 for the treatment of neovascular age-related macular degeneration. Aptamers are not only useful in their own right, but as escorts for therapeutic or diagnostic reagents. Modified RNA anti-PSMA (prostate-specific membrane antigen) aptamers [7] have been used by many research groups as targeting agents and conjugated to a variety of molecules including gold nanoparticles, siRNA, and drug encapsulated polymer particles for specific delivery [8], [9], [10], [11], [12]. Modified RNA aptamers against the virion surface glycoprotein, gp120 [13] were conjugated to an anti-human CD 437 immunodeficiency virus siRNA, and both the aptamer and the siRNA portions of the chimera had potent anti-HIV activity [14]. Aptamers targeting cell surface receptors may be amongst the most useful for biomedical applications (reviewed in [15], [16]). HER3 (human epidermal growth factor receptor-3) is membrane-bound protein and is related to the development of some malignant tumors. RNA aptamers against CD 437 HER3 have shown strong inhibitory effects on hrg (heregulin)-induced growth stimulation of MCF7 cells [17]. Both DNA and RNA anti-mouse transferrin receptor aptamers have been selected and used to mediate the endocytosis of lysosomal enzymes [18]. Anti-RET receptor tyrosine kinase aptamers have been selected against cells expressing human RET, and Rabbit Polyclonal to POLE1 one of them was found to block RET-dependent intracellular signaling pathways. [19]. We have previously isolated a RNA aptamer.