ИСТИНА

Translating aptatheranostics into biomedicine requires knowledge of the direct interactions of aptamers with cells. Most measurements aimed to establish specificity of aptamers, requiring blocking nucleic acids, which may not be applicable in treatment. This research focused on a studying two tumor markers: EGFR is WHO glioblastoma (GB) marker of proliferation, and CD133 is a tentative marker of stem-like cells. Known aptamers (anti-EGFR: ME07, CL4, U31, GR20, U2, Gol1; and anti-CD133: A15, B19, Cs5 and Ap1M) were used for flow cytometry assessments of direct interactions with both cell lines (A431, U87, MCF7 for EGFR; Caco-2 for CD133) and continuous cell cultures developed from GB patients (107, G01, Sus, ets.). It turned out that flow cytometry signal per se could not be an indicator of specific the aptamer-target interactions, the signal reflects both target-driven interactions, and membrane-mediated events; therefore, only titration experiment could reveal specific interactions. Even in this case the half-saturation concentrations are about 150 nM or so. Our bio-layer interferometry data shows that interactions of aptamers with recombinant EGFR have Kd in the nM range, matching published data. Thus, an intriguing discrepancy exists between aptamer-protein and aptamer-cell interactions.