Cancer stem cells (CSCs) are a subset of
tumor cells that has the ability to self-renew and to generate the diverse cells that comprise the
tumor mass. The
cell-surface glycoprotein CD44 is one of the most common surface markers used to identify CSCs. Aptamers are synthetic
oligonucleotides selected from pools of random sequences that can bind to a wide range of targets with high affinity and specificity. In this study, the systematic evolution of ligands by exponential enrichment (SELEX) technology was used to isolate
RNA aptamers using human recombinant full-length CD44
protein and 2'-F-pyrimidine modified
RNA library with a complexity of around 10(14) different molecules. Following 11 iterative rounds of SELEX, the selected aptamers were cloned and sequenced. Three different sequences were identified. The binding specificities for one of these
RNA aptamers was assessed using representative
breast cancer cell lines expressing CD44; namely, MDA-MB-231, MCF7, and T47D. The selected
RNA aptamer (Apt1) was found to interact specifically with such
cancer cells when analyzed by flow cytometry and fluorescent microscopy, with different intensities of fluorescence reflecting the level of CD44 expression on the surface of these cells. It can be concluded that the selected aptamers can be used to target CD44 positive cells, including cancer stem cells, for detection, sorting, and enrichment and for
drug delivery purposes.