We selected DNA aptamers to the epithelial cell adhesion molecule (EpCAM) expressed on primary lung cancer cells isolated from the tumors of patients with non-small cell lung cancer using competitive displacement of aptamers from EpCAM by a corresponding antibody. The resulting aptamers clones showed good nanomolar affinity to EpCAM-positive lung cancer cells.
Confocal microscopy imaging and spectral profiling of lung cancer tissues confirmed the same protein target for the aptamers and anti-EpCAM antibodies. Furthermore, the resulted aptamers were successfully applied for isolation and detection of circulating tumor cells in clinical samples of peripheral blood of lung cancer patients.
The scheme of DNA aptamer selection using aptamer displacement via antibody. The first several rounds include only positive selection and start with the incubation of the ssDNA library or aptamer pools with receptor positive cells, followed by partitioning unbound DNA, and amplifying bound DNA with symmetric and asymmetric polymerase chain reaction (PCR). In the next rounds, positive rounds alternate with antibody displacement steps and include the incubation of aptamers with the receptor positive cells, washing, the displacement of the bound aptamers by antibodies (Ab), and the following amplification of free aptamers.