An increase in the expression of
estrogen receptors (ER) and the expanded population of ER-positive cells are two common phenotypes of
breast cancer. Detection of the aberrantly expressed ERα in
breast cancer is carried out using ERα-
antibodies and radiolabelled
ligands to make decisions about
cancer treatment and targeted
therapy. Capitalizing on the beneficial advantages of aptamer over the conventional antibody or radiolabelled
ligand, we have identified
a DNA aptamer that selectively binds and facilitates the detection of ERα in human
breast cancer tissue sections. The aptamer is identified using the high throughput sequencing assisted SELEX screening. Biophysical characterization confirms the binding and formation of a thermodynamically stable complex between the identified
DNA aptamer (ERaptD4) and ERα (Ka = 1.55±0.298×108 M(-1); ΔH = 4.32×104±801.1 cal/mol; ΔS = -108 cal/mol/deg). Interestingly, the specificity measurements suggest that the ERaptD4 internalizes into ERα-positive
breast cancer cells in a target-selective manner and localizes specifically in the nuclear region. To harness these characteristics of ERaptD4 for detection of ERα expression in
breast cancer samples, we performed the aptamer-assisted histochemical analysis of ERα in tissue samples from
breast cancer patients. The results were validated by performing the immunohistochemistry on same samples with an ERα-antibody. We found that the two methods agree strongly in assay output (kappa value = 0.930, p-value <0.05 for strong ERα positive and the ERα negative samples; kappa value = 0.823, p-value <0.05 for the weak/moderate ER+ve samples, n = 20). Further, the aptamer
stain the ERα-positive cells in breast tissues without cross-reacting to ERα-deficient fibroblasts, adipocytes, or the inflammatory cells. Our results demonstrate a significant consistency in the aptamer-assisted detection of ERα in strong ERα positive, moderate ERα positive and ERα negative
breast cancer tissues. We anticipate that the ERaptD4 aptamer targeting ERα may potentially be used for an efficient grading of ERα expression in
cancer tissues.