DNA aptamers against the MUC1 tumour marker: design of aptamer-antibody sandwich ELISA for the early diagnosis of epithelial tumours

Aptamers are functional molecules able to bind tightly and selectively to disease markers, offering great potential for applications in disease diagnosis and therapy. MUC1 is a well-known tumour marker present in epithelial malignancies and is used in immunotherapeutic and diagnostic approaches. We report the selection of DNA aptamers that bind with high affinity and selectivity an MUC1 recombinant protein containing five repeats of the variable tandem repeat region. Aptamers were selected using the SELEX methodology from an initial library containing a 25-base-long variable region for their ability to bind to the unglycosylated form of the MUC1 protein. After ten rounds of in vitro selection and amplification, more than 90% of the pool of sequences consisted of target-binding molecules, which were cloned, sequenced and found to share no sequence consensus. The binding properties of these aptamers were quantified using ELISA and surface plasmon resonance. The lead aptamer sequence was subsequently used in the design of an aptamer-antibody hybrid sandwich ELISA for the identification and quantification of MUC1 in buffered solutions. Following optimisation of the operating conditions, the resulting enzyme immunoassay displayed an EC50 value of 25 mu g/ml, a detection limit of 1 mu g/ml and a linear range between 8 and 100 mu g/ml for the MUC1 five tandem repeat analyte. In addition, recovery studies performed in buffer conditions resulted in averaged recoveries between 98.2 and 101.7% for all spiked samples, demonstrating the usability of the aptamer as a receptor in microtitre-based assays. Our results aim towards the formation of new diagnostic assays against this tumour marker for the early diagnosis of primary or metastatic disease in breast, bladder and other epithelial tumours.