Novel Bispecific Aptamer Enhances Immune Cytotoxicity Against MUC1-Positive Tumor Cells by MUC1-CD16 Dual Targeting

Abstract

A promising strategy in cancer immunotherapy is the employment of a bispecific agent that can bind with both tumor markers and immunocytes for recruitment of lymphocytes to tumor sites and enhancement of anticancer immune reactions. Mucin1 (MUC1) is a tumor marker overexpressed in almost all adenocarcinomas, making it a potentially important therapeutic target. CD16 is expressed in several types of immunocytes, including NK cells, γδ-T cells, monocytes, and macrophages. In this study, we constructed the first bispecific aptamer (BBiApt) targeting both MUC1 and CD16. This aptamer consisted of two MUC1 aptamers and two CD16 aptamers linked together by three 60 nt DNA spacers. Compared with monovalent MUC1 or CD16 aptamers, BBiApt showed more potent avidity to both MUC1-positive tumor cells and CD16-positive immunocytes. Competition experiments indicated that BBiApt and monovalent aptamers bound to the same sites on the target cells. Moreover, BBiApt recruited more CD16-positive immunocytes around MUC1-positive tumor cells and enhanced the immune cytotoxicity against the tumor cells in vitro. The results suggest that, apart from bispecific antibodies, bispecific aptamers may also potentially serve as a novel strategy for targeted enhancement of antitumor immune reactions against MUC1-expressing malignancies.

Cancer immunomodulation using bispecific aptamers

“… 80 2 + 2 MUC1 ( MA3 ) [DNA] CD16α/FcγRIII ( CLN0020 a ) [DNA] NK cell and γδ T cell activation Four aptamers (two MUC1, two CD16) linked by (3) 60 nt A/C rich ss spacers Li et al. 81 Other CD62L ( LD201t1 ) [DNA] Ramos cells ( TE02 ) [DNA] None Various dsDNA nanoscaffolds Liu et al. 82 ss, single stranded; ds, double stranded; deoxyA, deoxyadenosine.…”

“…A tetravalent, bispecific [ 2 + 2 ] aptamer was recently constructed that consisted of two anti-MUC1 DNA aptamers and two anti-CD16a DNA aptamers. 81 MUC1 is a transmembrane protein that is typically expressed in glandular and luminal epithelial cells of various tissues. This protein is overexpressed (and often aberrantly glycosylated) in almost all adenocarcinomas, and it is a marker of tumor initiation, progression, and prognosis.…”

“…This protein is overexpressed (and often aberrantly glycosylated) in almost all adenocarcinomas, and it is a marker of tumor initiation, progression, and prognosis. 81 , 126 Anti-MUC1 aptamer, previously selected by the same group, and anti-CD16a aptamer, selected by Boltz and colleagues, were linked together by three different single-stranded DNA (ssDNA) spacers, all of which were A/C rich and 60 nt in length. The group found that the anti-MUC1/anti-CD16a ([ 2 + 2 ]; Figure 3 C) bsApt but not the control could recruit CD16-positive immunocytes (PBMCs) to MUC1-containing A549 cells.…”

Recent advances in aptamer applications for analytical biochemistry

“…In a conceptually related study, Li et al [ 88 ] described a promising strategy for cancer immunotherapy that employed a bi-specific aptamer that can bind with both tumor cell markers and immunocytes for recruitment of lymphocytes to tumor sites and enhancement of anticancer immune reactions. MUC1 (section 4 .)…”

Discovery, Design, Synthesis, and Application of Nucleoside/Nucleotides

“…These highly unique bispecific aptamers can potentially serve as a novel strategy for the targeted enhancement of antitumor immune reactions against MUC1-expressing malignancies. [14] Several other papers in this Special Issue described new RNA structural studies, including one from the Xu et al, which is focused on an investigation of nucleoside stabilizers for Z-form RNA. [15] Another excellent paper from Prof. Maria Camarasa's group describes their efforts towards the design, synthesis and X-ray crystallographic studies of a series of compounds targeting the foot and mouth disease (FMDV) RNA-dependent RNA polymerase.…”