From ugly duckling to swan: unexpected identification from cell-SELEX of an anti-Annexin A2 aptamer targeting tumors.
BACKGROUND
Cell-SELEX is now widely used for the selection of aptamers against cell surface biomarkers. However, despite negative selection steps using mock cells, this method sometimes results in aptamers against undesirable targets that are expressed both on mock and targeted cells. Studying these junk aptamers might be useful for further applications than those originally envisaged.


RESULTS
Cell-SELEX was performed to identify aptamers against CHO-K1 cells expressing human Endothelin type B receptor (ETBR). CHO-K1 cells were used for negative selection of aptamers. Several aptamers were identified but no one could discriminate between both cell lines. We decided to study one of these aptamers, named ACE4, and we identified that it binds to the Annexin A2, a protein overexpressed in many cancers. Radioactive binding assays and flow cytometry demonstrated that the aptamer was able to bind several cancer cell lines from different origins, particularly the MCF-7 cells. Fluorescence microscopy revealed it could be completely internalized in cells in 2 hours. Finally, the tumor targeting of the aptamer was evaluated in vivo in nude mice xenograft with MCF-7 cells using fluorescence diffuse optical tomography (fDOT) imaging. Three hours after intravenous injection, the aptamer demonstrated a significantly higher uptake in the tumor compared to a scramble sequence.


CONCLUSIONS
Although aptamers could be selected during cell-SELEX against other targets than those initially intended, they represent a potential source of ligands for basic research, diagnoses and therapy. Here, studying such aptamers, we identify one with high affinity for Annexin A2 that could be a promising tool for biomedical application.
Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Direction des Sciences du Vivant (DSV), Intitut d'imagerie Biomédicale (I2 BM) ; Institut National de la Santé et de la Recherche Médicale (INSERM) U1023, Laboratoire d'Imagerie Moléculaire Expérimentale, Orsay, France ; Université Paris Sud, Orsay, France.
Agnes
A
Cibiel
Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Direction des Sciences du Vivant (DSV), Intitut d'imagerie Biomédicale (I2 BM) ; Institut National de la Santé et de la Recherche Médicale (INSERM) U1023, Laboratoire d'Imagerie Moléculaire Expérimentale, Orsay, France ; Université Paris Sud, Orsay, France.
Nam Nguyen
NN
Quang
Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Direction des Sciences du Vivant (DSV), Intitut d'imagerie Biomédicale (I2 BM) ; Institut National de la Santé et de la Recherche Médicale (INSERM) U1023, Laboratoire d'Imagerie Moléculaire Expérimentale, Orsay, France ; Université Paris Sud, Orsay, France.
Karine
K
Gombert
Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Direction des Sciences du Vivant (DSV), Intitut d'imagerie Biomédicale (I2 BM) ; Institut National de la Santé et de la Recherche Médicale (INSERM) U1023, Laboratoire d'Imagerie Moléculaire Expérimentale, Orsay, France ; Université Paris Sud, Orsay, France.
Benoit
B
Thézé
Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Direction des Sciences du Vivant (DSV), Intitut d'imagerie Biomédicale (I2 BM) ; Institut National de la Santé et de la Recherche Médicale (INSERM) U1023, Laboratoire d'Imagerie Moléculaire Expérimentale, Orsay, France ; Université Paris Sud, Orsay, France.
Anikitos
A
Garofalakis
Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Direction des Sciences du Vivant (DSV), Intitut d'imagerie Biomédicale (I2 BM) ; Institut National de la Santé et de la Recherche Médicale (INSERM) U1023, Laboratoire d'Imagerie Moléculaire Expérimentale, Orsay, France ; Université Paris Sud, Orsay, France.
Frédéric
F
Ducongé
D000230:Adenocarcinoma / Q000175:diagnosis* / Q000235:genetics; D000818:Animals; D017306:Annexin A2 / Q000235:genetics / Q000378:metabolism*; D052157:Aptamers, Nucleotide / Q000235:genetics / Q000302:isolation & purification; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000235:genetics; D016466:CHO Cells; D003412:Cricetulus; D004705:Endocytosis; D005260:Female; D005434:Flow Cytometry; D015870:Gene Expression; D006801:Humans; D033162:Incidental Findings; D008024:Ligands; D061986:MCF-7 Cells; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009368:Neoplasm Transplantation; D011485:Protein Binding; D044023:Receptor, Endothelin B / Q000235:genetics / Q000378:metabolism; D052156:SELEX Aptamer Technique
C472822:ANXA2 protein, human; D017306:Annexin A2; D052157:Aptamers, Nucleotide; D008024:Ligands; D009363:Neoplasm Proteins; D044023:Receptor, Endothelin B