Aptamer-mediated selective delivery of a cytotoxic cationic NHC-Au(i) complex to cancer cells

Abstract

A novel cationic NHC-Au(i) complex was synthesized and studied for its antitumor activity. For all the cell lines tested, cationic NHC-Au(i) complex 2 shows much higher cytotoxicity than its neutral analogue 1. To achieve selective cancer cell targeting, complex 2 was covalently conjugated to aptamer AS1411, a DNA aptamer with strong binding affinity for nucleolin. The successful conjugation was confirmed by HPLC, gel electrophoresis, fluorescence spectroscopy and UV-Vis absorption. Conjugate AS1411-2 was then examined for its specific targeting and binding ability towards cancer cells over human normal cells using flow cytometry analysis and confocal microscopy. The cytotoxicity of AS1411-2 was then estimated by MTS assay. It was found that AS1411-2 exhibits higher activity than complex 2 towards targeted cells. Importantly, AS1411-2 exhibits much lower cytotoxicity towards healthy normal cell lines. Concurrently, the control groups without the AS1411 aptamer or without the NHC-Au(i) complex do have significant impact on cancer cell viability.

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“…40 Moreover, enrichment and separation by magnetic particles and fluorescence detection by gold nanoclusters (AuNCs) are powerful tools for their evaluation because of their controllability and high sensitivity. 41,42 In one study, Cheng et al indicated a new method for the detection of S. aureus in which recognition molecules, such as an aptamer, and antibiotic were combined together. In this study, S. aureus was quantified via the use of aptamer-coated magnetic beads (Apt-MB) and Vancomycin (Van)-functionalized fluorescent nanoclusters (AuNCs@Van, with 2.0±0.6 nm) in a mixture of other non-targeted bacteria and was also detected in authentic samples including milk and human serum.…”

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“…All the cell lines showed resistance to neutral complex 284 (IC 50 value is >100 μM) except CCRF‐CEM cell line which showed IC 50 value 31.3±2.11 μM. The authors concluded that higher cytotoxicity is due to the presence of a delocalized lipophilic cation that can easily penetrate through the hydrophobic cell membrane [164] …”

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“…Additionally, AS1411 modified with FITC (fluorescein isothiocyanate) on its 3′ end, an amine group on its 5′ and six extra T bases to prevent fluorescent (5′-TTT TTT GGT GGT GGT GGT TGT GGT GGT GGT GG TTT TTT-FITC-3′) was used to react with N-heterocyclic carbene (NHC)-Au(I) [ 38 ]. The aptamer-NHC-Au(I) conjugate exhibited higher recognition and binding to the target cancer cells (MDA-MB-231, HeLa and DU145 cell lines) as demonstrated by flow cytometry and confocal microscopy [ 38 ].…”

“…Additionally, AS1411 modified with FITC (fluorescein isothiocyanate) on its 3′ end, an amine group on its 5′ and six extra T bases to prevent fluorescent (5′-TTT TTT GGT GGT GGT GGT TGT GGT GGT GGT GG TTT TTT-FITC-3′) was used to react with N-heterocyclic carbene (NHC)-Au(I) [ 38 ]. The aptamer-NHC-Au(I) conjugate exhibited higher recognition and binding to the target cancer cells (MDA-MB-231, HeLa and DU145 cell lines) as demonstrated by flow cytometry and confocal microscopy [ 38 ]. Moreover, by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay, enhanced cytotoxicity was observed when AS1411- NHC-Au(I) conjugate was applied to cancer cell lines and did not significantly reduce proliferation in two healthy normal cell lines (HEK293 and HU1545v) [ 38 ].…”

“…The aptamer-NHC-Au(I) conjugate exhibited higher recognition and binding to the target cancer cells (MDA-MB-231, HeLa and DU145 cell lines) as demonstrated by flow cytometry and confocal microscopy [ 38 ]. Moreover, by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay, enhanced cytotoxicity was observed when AS1411- NHC-Au(I) conjugate was applied to cancer cell lines and did not significantly reduce proliferation in two healthy normal cell lines (HEK293 and HU1545v) [ 38 ]. The authors suggested that this method can be expanded to other metal–ligand constructs, and particular attention should be given to cationic species [ 38 ].…”