Aptamers that bind to the hemagglutinin of the recent pandemic influenza virus H1N1 and efficiently inhibit agglutination

A homogenous fluorescence quenching based assay for specific and sensitive detection of influenza virus A hemagglutinin antigen

Influenza pandemics cause millions of deaths worldwide. Effective surveillance is required to prevent their spread and facilitate the development of appropriate vaccines. In this study, we report the fabrication of a homogenous fluorescence-quenching-based assay for specific and sensitive detection of influenza virus surface antigen hemagglutinins (HAs). The core of the assay is composed of two nanoprobes namely the glycan-conjugated highly luminescent quantum dots (Gly-QDs), and the HA-specific antibody-modified gold nanoparticle (Ab-Au NPs). When exposed to strain-specific HA, a binding event between the HA and the two nanoprobes takes place, resulting in the formation of a sandwich complex which subsequently brings the two nanoprobes closer together. This causes a decrease in QDs fluorescence intensity due to a non-radiative energy transfer from QDs to Au NPs. A resulting correlation between the targets HA concentrations and fluorescence changes can be observed. Furthermore, by utilizing the specific interaction between HA and glycan with sialic acid residues, the assay is able to distinguish HAs originated from viral subtypes H1 (human) and H5 (avian). The detection limits in solution are found to be low nanomolar and picomolar level for sensing H1-HA and H5-HA, respectively. Slight increase in assay sensitivity was found in terms of detection limit while exposing the assay in the HA spiked in human sera solution. We believe that the developed assay could serve as a feasible and sensitive diagnostic tool for influenza virus detection and discrimination, with further improvement on the architectures.

Specific aptamer-conjugated mesoporous silica-carbon nanoparticles for HER2-targeted chemo-photothermal combined therapy

Tumor-specific therapeutic platforms designed for combined tumor therapy has recently received wide attention. In this work, a new HB5 aptamer-functionalized mesoporous silica-carbon based doxorubicin (DOX)-loaded system (MSCN-PEG-HB5/DOX) was successfully constructed and characterized for chemo-photothermal combined therapy of human epithelial growth factor receptor 2 (HER2)-positive breast cancer cells. The in vitro release result showed that MSCN-PEG-HB5/DOX exhibited pH-sensitive and NIR-triggered release manner. HB5-modified nanoparticles showed significant higher cellular uptake in HER2-positive breast cancer cells (SK-BR-3) but not in normal breast epithelial cells (MCF-10A), compared to unmodified counterparts. The intracellular uptake of functional nanoparticles was mainly based on the receptor-mediated mechanism which was energy-dependent. Cytotoxicity experiments demonstrated that combined therapy induced highest cell killing effect compared to chemotherapy and photothermal therapy alone. The combination index (CI) was 0.253 indicating the synergistic effect of chemotherapy and photothermal therapy. These findings suggested that MSCN-PEG-HB5/DOX was a potential chemo-photothermal therapeutic platform targeting to HER2-positive breast cancers.

Characterization of an RNA aptamer against HPV-16 L1 virus-like particles

The human papillomavirus (HPV) capsid is mainly composed of the L1 protein that can self-assemble into virus-like particles (VLPs) that are structurally and immunologically similar to the infectious virions. We report here the characterization of RNA aptamers that recognize baculovirus-produced HPV-16 L1 VLPs. Interaction and slot-blot binding assays showed that all isolated aptamers efficiently bound HPV-16 VLPs, although the Sc5-c3 aptamer showed the highest specificity and affinity (Kd=0.05 pM). Sc5-c3 secondary structure consisted of a hairpin with a symmetric bubble and an unstructured 3'end. Biochemical and genetic analyses showed that the Sc5-c3 main loop is directly involved on VLPs binding. In particular, binding specificity appeared mediated by five non-consecutive nucleotide positions. Experiments using bacterial-produced HPV-16 L1 resulted in low Sc5-c3 binding, suggesting that recognition of HPV-16 L1 VLPs relies on quaternary structure features not present in bacteria-produced L1 protein. Sc5-c3 produced specific and stable binding to HPV-16 L1 VLPs even in biofluid protein mixes and thus it may provide a potential diagnostic tool for active HPV infection.

Aptamers as a replacement for antibodies in enzyme-linked immunosorbent assay

The application of antibodies in enzyme-linked immunosorbent assay (ELISA) is the basis of this diagnostic technique which is designed to detect a potpourri of complex target molecules such as cell surface antigens, allergens, and food contaminants. However, development of the systematic evolution of Ligands by Exponential Enrichment (SELEX) method, which can generate a nucleic acid-based probe (aptamer) that possess numerous advantages compared to antibodies, offers the possibility of using aptamers as an alternative molecular recognition element in ELISA. Compared to antibodies, aptamers are smaller in size, can be easily modified, are cheaper to produce, and can be generated against a wide array of target molecules. The application of aptamers in ELISA gives rise to an ELISA-derived assay called enzyme-linked apta-sorbent assay (ELASA). As with the ELISA method, ELASA can be used in several different configurations, including direct, indirect, and sandwich assays. This review provides an overview of the strategies involved in aptamer-based ELASA.

Selection of aptamers targeting the sialic acid receptor of hemagglutinin by epitope-specific SELEX

A new SELEX scheme is proposed for the selection of aptamers targeting a specific epitope of a native protein. Anti-sialic acid receptor (SAR) aptamers that inhibit H1 hemagglutination at a low picomole dose are selected accordingly.

An aptamer that binds efficiently to the hemagglutinins of highly pathogenic avian influenza viruses (H5N1 and H7N7) and inhibits hemagglutinin-glycan interactions

Highly pathogenic avian influenza (HPAI) H5 and H7 viruses have ravaged the poultry industry in numerous countries in Asia, Europe, Africa and the Middle East, and have resulted in the deaths of millions of birds. Although HPAI H5N1 viruses currently remain avian viruses, they are continuously evolving and have the potential to become pandemic-type viruses capable of human-human transmission. To develop specific reagents to allow better preparedness against this threat, we selected an aptamer (8-3) from a completely random RNA pool that binds with high affinity (∼ KD 170pM) to the hemagglutinins (HAs) derived from HPAI H5N1 (A/H5N1/Vietnam/1194/2004 and A/H5N1/Indonesia/05/2005) and H7N7 (A/H7N7/Netherlands/219/2003) influenza A viruses. Aptamer 8-3 was able to efficiently distinguish HAs derived from subtypes of influenza A virus other than H5 and H7. Aptamer 8-3 was analyzed further to assess its ability to interfere with HA-glycan interactions using our previously established SPR-based competitive assay, and we found that aptamer 8-3 efficiently interferes with HA-glycan binding (EC50 ∼ 25 nM). To derive shorter variants for other applications, aptamer 8-3 was shortened to a 44-mer by deletion analyses. The shortened aptamer, 8-3S, retains the full-length aptamer's affinity and specificity for its cognate Has, and also interferes with HA-glycan interactions. These studies suggest that aptamer 8-3S should be studied further to explore its potential applications not only in surveillance and diagnosis, but also in the development of H5N1- and H7N7-specific virucidal products that interfere with virus-host interactions to contain future H5N1 and H7N7 pandemics.