Bi-specific Aptamers Mediating Tumor Cell Lysis

Antibody-dependent cellular cytotoxicity plays a pivotal role in antibody-based tumor therapies and is based on the recruitment of natural killer cells to antibody-bound tumor cells via binding of the Fc gamma receptor III (CD16). Here we describe the generation of chimeric DNA aptamers that simultaneously bind to CD16 alpha and c-Met, a receptor that is overexpressed in many tumors. By application of the systematic evolution of ligands by exponential enrichment (SELEX) method, CD16 alpha specific DNA aptamers were isolated that bound with high specificity and affinity (91 pM-195 nM) to their respective recombinant and cellularly expressed target proteins. Two optimized CD16 alpha specific aptamers were coupled to each of two c-Met specific aptamers using different linkers. Bi-specific aptamers retained suitable binding properties and displayed simultaneous binding to both antigens. Moreover, they mediated cellular cytotoxicity dependent on aptamer and effector cell concentration. Displacement of a bi-specific aptamer from CD16 alpha by competing antibody 3G8 reduced cytotoxicity and confirmed the proposed mode of action. These results represent the first gain of a tumor-effective function of two distinct oligonucleotides by linkage into a bi-specific aptamer mediating cellular cytotoxicity.