Bispecific Aptamer-Drug Conjugates Selectively Eliminate Malignant Hematologic Cells for Treating Acute Myeloid Leukemia

Surface antigen-directed immunotherapy is a curative treatment modality for acute myeloid leukemia (AML) that is characterized by the abundance and stability expression of surface antigens. However, current surface antigen-directed immunotherapies have shown poor outcomes and undesirable mortality rates in treating AML patients, primarily due to acquired resistance that arises from using single-target therapies to address the heterogeneous expression of surface antigens. Hence, in order to improve the efficacy of antigen-specific therapies for treating AML, we designed a bispecific aptamer-drug conjugate. In particular, cell-SELEX incorporating cell lysate-SELEX for aptamers with HEL cells yielded AptCD117, which specifically binds to CD117 (a highly expressed marker on both hematopoietic stem cells and primary AML cells) and has excellent performance in targeting human AML cells. Combined with CD71-binding aptamer LXD-11b (another broadly expressed surface antigen on leukemia cells), bispecific aptamers were designed to couple with monomethyl auristatin F (MMAF) for fabricating aptamer-drug conjugates. Results demonstrated that bispecific aptamer-MMAF conjugates efficiently kill different CD117 and CD71 expression levels of target AML cell lines in vitro. Importantly, the exposure of AML marrow specimens to bispecific aptamer-MMAF conjugates resulted in the selective elimination of primary AML cells in vitro and had no effect on healthy lymphocytes within the same specimens. Thus, these results provide a proof of concept for the generation of bispecific aptamer-drug conjugates directed against human AML cells, which hold the promise of advancing treatment strategies and improving AML patient outcomes.