Aptamer–biotin–streptavidin–C1q complexes can trigger the classical complement pathway to kill cancer cells

Nucleic acid aptamers are regarded as rivals for antibodies and as such are being investigated for their therapeutic potential. In the present work, it is shown that two different high-affinity DNA aptamers developed previously by Ferreira et al. against MUC1 antigen (designated MUC1-5TR-1 and MUC1-S1.3/S2.2) on MCF7 breast cancer cells can be linked to the first component of complement (C1q) via a biotin–streptavidin system and induce significant killing of MCF7 cells in vitro. Cell viability was assessed by Trypan blue uptake and absorbance at 590 nm of stained cells following buffer washes and lysis in 1% SDS. While the killing effect is demonstrable versus various controls, dependent on aptamer dose, and reproducible, it appears to kill maximally about half of treated MCF7 cells. Possible reasons for the marginal killing effect include antigenic shedding in vitro and membrane-bound complement regulatory proteins (mCRPs) on the cell surface such as CD46, CD55, and CD59 which act to inhibit complement-mediated lysis of cells. Future in vitro research could benefit from application of mCRP-specific aptamers in combination with anti-MUC1 aptamers to overcome surface protective mechanisms while attacking the plasma membrane of MCF7 cells or other MUC1-expressing cancer cells. However, in vivo such a combination could have deleterious effects on normal MUC1-expressing cells as well.