Engineered Aptamers to Probe Molecular Interactions on the Cell Surface.

Significant progress has been made in understanding the nature of molecular interactions on the cell membrane. To decipher such interactions, molecular scaffolds can be engineered as a tool to modulate these events as they occur on the cell membrane. To guarantee reliability, scaffolds that function as modulators of cell membrane events must be coupled to a targeting moiety with superior chemical versatility. In this regard, nucleic acid aptamers are a suitable class of targeting moieties. Aptamers are inherently chemical in nature, allowing extensive site-specific chemical modification to engineer sensing molecules. Aptamers can be easily selected using a simple laboratory-based in vitro evolution method enabling the design and development of aptamer-based functional molecular scaffolds against wide range of cell surface molecules. This article reviews the application of aptamers as monitors and modulators of molecular interactions on the mammalian cell surface with the aim of increasing our understanding of cell-surface receptor response to external stimuli. The information gained from these types of studies could eventually prove useful in engineering improved medical diagnostics and therapeutics.

Structural optimization of an aptamer generated from Ligand-Guided Selection (LIGS) resulted in high affinity variant toward mIgM expressed on Burkitt's lymphoma cell lines.

Aptamers are synthetic, short nucleic acid molecules capable of specific target recognition. Aptamers are selected using a screening method termed Systematic Evolution of Ligands by Exponential enrichment (SELEX). We recently have introduced a variant of SELEX called "Ligand-Guided-Selection" (LIGS) that allows the identification of specific aptamers against known cell-surface proteins. Utilizing LIGS, we introduced three specific aptamers against membrane-bound IgM (mIgM), which is the hallmark of B cells. Out of the three aptamers selected against mIgM, an aptamer termed R1, in particular, was found to be interesting due to its ability to recognize mIgM on target cells and then block anti-IgM antibodies binding their antigen. We systematically truncated parent aptamer R1 to design shorter variants with enhanced affinity. Importantly, herein we show that the specificity of the most optimized variant of R1 aptamer is similar to that of anti-IgM antibody, indicating that the specificity of the ligand utilized in selective elution of the aptamer determines the specificity of the LIGS-generated aptamer. Furthermore, we report that truncated variants of R1 are able to recognize mIgM-positive human B lymphoma BJAB cells at physiological temperature, demonstrating that LIGS-generated aptamers could be re-optimized into higher affinity variants. Collectively, these findings show the significance of LIGS in generating highly specific aptamers with potential applications in biomedicine.