Increasing evidence indicates that the release of exosomes by tumor cells play a key role in tumor progression, drug resistance, immune surveillance escape, angiogenesis, tumor invasion, and metastasis. For this reason, cancer-derived exosomes are emerging as very interesting targets for early diagnosis and therapy in cancer, including breast cancer. Indeed, progresses in developing nucleic acids-based therapeutic compounds, including antisense DNAs, aptamers, short interfering/microRNAs, and short activator RNAs, have attracted great interest as emerging platforms for precise cancer treatment.
We have recently developed a novel differential SELEX (Systematic Evolution of Ligands by Exponential enrichment) strategy by using exosomes purified from epithelial BC primary cells in the positive selection step and exosome-derived from primary normal epithelial breast cell lines in the negative selection step.
Three aptamers have been shown to be enriched in different families, and their ability to selectively bind BC cells-derived exosomes has been proven. Interestingly, two of them can selectively bind triple negative-derived exosomes, compared to more differentiated BC cells. To optimize the best aptamers, shortened version of aptamers (about 35mer) have been generated and their binding ability has been tested. Moreover, the aptamers showed no binding affinity for lung cancer and glioblastoma-derived exosomes. We also tested by binding assay the ability of one of the identified aptamers, named ex-50sh, to selective recognize exosomes isolated from serum of breast cancer patients. Proteomic analysis of the putative target is in progress. Immunofluorescent experiments showed that the short aptamers can also block the uptake of MDA-231-derived exosomes on MDA-231 cell lines. Moreover, ex-50sh is able to block the EMT transformation induced by MDA-231 exosomes in low malignant MCF7.
Altogether, the selected aptamers will provide new insights in the molecular characterization of breast cancer exosomes and, most importantly, innovative tools for early breast cancer diagnosis.
Gerolama Condorelli.
University of Naples Federico II.
All authors have declared no conflicts of interest.