X-Ray, MRI, and Ultrasound Agents Basic Principles
George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos in Handbook of Small Animal Imaging, 2018
However, the only biological receptors that the microbubble can access are on the endothelium of the blood vessels or blood cells, and this severely limits the range of targets available to those expressed on endothelial cells, mainly. A few dozen 2 µm diameter bubbles could fit on one side of an endothelial cell, so receptor targeted imaging is nevertheless a recognized and vibrant field of research in USCA. For attachment of the targeting ligands (e.g., antibodies, peptides) to the microbubble surface, well-known techniques, such as carbodiimide, maleimide, and biotin–streptavidin coupling are used (see Figure 15.5). Biotin–streptavidin is a popular coupling strategy because biotin’s binding affinity for streptavidin is very high (>1015 M−1). Several commercial research companies supply these microbubbles ready to label with biotinylated targeting vectors (see Table 15.6).
Surface Chemistry for Cell Capture in Microfluidic Systems
Iniewski Krzysztof in Integrated Microsystems, 2017
Streptavidin, which is known to have high binding affinity for biotin, has also been widely used to improve antibody-based cell capture efficiency. Generally, up to four biotin molecules can be tightly bound to a streptavidin molecule simultaneously with an affinity constant of 2.5 × 1013 L/mol, which is one of the strongest noncovalent interactions [35]. The biotin–streptavidin affinity is generally used to control the orientation of coating antibodies on the surface, thus increasing the cell capture efficiency. In the adsorption method, antibodies can be immobilized onto the surface with its active antigen-binding site concealed. In addition, noncovalent linking between the antibody and the solid surface is reversible, which may lead to instability of the adsorbed antibody and loss of capture capability. The biotin–streptavidin interaction can be used to maximize the antibody orientation with exposed active binding sites. This interaction has been successfully implemented in various microfluidic devices, including for the capture of CD4+ T lymphocytes [6,36].
Immunocytochemical Detection Systems
Lars-Inge Larsson in Immunocytochemistry: Theory and Practice, 2020
Another important aspect of the avidin-biotin techniques is the properties of the avidin preparation. Natural avidin has a very high isoelectric point (above 10) and will bind nonspecifically to many tissue constituents, notably nucleic acids. The isoelectric point of avidin can be reduced by derivatizing some of its primary amino groups, and several such derivatized preparations showing less unspecific background labeling are available now. In addition, Streptomyces avidinii produce a protein, referred to as streptavidin. It possesses the strong binding avidity of egg-white avidin for biotin, yet has an isoelectric point near the neutral range and is not glycosylated.36 Streptavidin does not stick unspecifically to tissues and is the reagent of choice in the author’s laboratory. It is available from several commercial sources. A good illustration of the early problems with the stickiness of egg white avidin is that antibodies were raised to biotin and used in place of avidin. Although the use of streptavidin largely circumvents these problems, such antibodies are also commercially available, as are derivatized and less sticky avidin preparations.
Novel Methods to Improve the Efficiency of Radioimmunotherapy for Non-Hodgkin Lymphoma
Published in International Reviews of Immunology, 2019
Mahsa Eskian, MirHojjat Khorasanizadeh, Pier Luigi Zinzani, Tim M. Illidge, Nima Rezaei
In this method, Ab and radioactive agent are used separately. First, Ab-streptavidin (SA) conjugate is administered. After maximal accumulation of Ab-SA conjugate in targeted tissues (e.g. after 1–3 days), a clearing agent (CA) is administered to remove the circulating Ab-SA conjugate from the circulation, therefore minimizing toxicity. Clearance of the Ab-SA-CA complex occurs via high affinity binding of the CA (galactosamine) to the asialoglycoprotein receptors of liver; and therefore CA is rapidly endocytosed into the liver cells and cleared from circulation. Then radioactive biotin (90Y-DOTA-biotin) is administered (Figure 1B). Biotin has a high affinity to streptavidin. The affinity of streptavidin-biotin is 1,000,000-fold higher than the average affinity of antigen-antibody; moreover, four radioactive biotin molecules can bind to a tetravalent streptavidin molecule. Both these features result into the amplified delivery of radiation to the Ab-SA-targeted tissue. Interestingly, Press et al. showed that the biotin-binding capacity of the Ab-SA conjugate could be as high as 5 moles of biotin per mole of Ab-SA conjugate, reflecting the presence of conjugates containing two or more SA molecules per mAb moiety [70–73]. Therefore it can be concluded that this approach minimizes the toxicity of RIT through omitting the unbound antibodies from circulation and then adding the radioactive agent, and also enhances efficiency of RIT via radiation amplification.
Update on Proteomic approaches to uncovering virus-induced protein alterations and virus –host protein interactions during the progression of viral infection
Published in Expert Review of Proteomics, 2020
Kevin M. Coombs
In one example, Coyaud and colleagues analyzed which human host proteins interact with each of the Zika virus proteins [101]. Zika virus proteins were individually expressed with FLAG tags in 293 T-Rex cells. They were affinity purified with Flag-M2 agarose beads. Other cell preparations were affinity purified with biotin-streptavidin. Washed samples were trypsin digested and analyzed in a Q-Exactive HF quadrupole-Orbitrap mass spectrometer to identify host proteins that co-precipitated with each of their viral bait proteins. Coyaud et al. identified 1224 human proteins with high confidence that participated in 3033 interactions with the various expressed Zika proteins. Duplicate biological replicates were each examined by two technical replicates. Many Zika proteins commonly interacted with cellular proteins involved in nuclear, endoplasmic reticulum, Golgi and other membrane functions. Individual Zika proteins also tended to interact with specific types of cellular proteins. The Zika virus capsid protein interacted with multiple nucleolar proteins, the non-structural protein NS5 interacted with STAT2 signaling, and NS3 interacted with centrosomes, vesicular transport and the ubiquitin system [101]. Many of these interactions explain known, and previously unknown, aspects of the Zika virus life cycle and how this virus interacts with host cells.
Lung cancer: active therapeutic targeting and inhalational nanoproduct design
Published in Expert Opinion on Drug Delivery, 2018
Nasser Alhajj, Chin Fei Chee, Tin Wui Wong, Noorsaadah Abd Rahman, Noor Hayaty Abu Kasim, Paolo Colombo
Electrostatic and hydrophobic interactions are widespread approaches in non-covalent conjugation [137]. These interactions allow rapid binding and do not require additional chemical processing steps. However, the binding orientation of biomolecule with nanocarrier may not be subjectable to control. The electrostatic and hydrophobic interactions are therefore not appropriate for linking the targeting ligand to the nanocarrier in view of they may reduce the propensity of targeting ligand-receptor binding and site-specific drug action. In contrast, affinity interactions are relatively effective and appropriate for linking the targeting ligands to the nanocarrier. Streptavidin-biotin interaction is one representative example of affinity interactions (Figure 5). This protein-ligand interaction is non-covalent in nature and is the strongest known interaction of these components (Kd = 10−15 M) [138]. The streptavidin-biotin interaction is irreversible and unaffected by extreme pH, temperature, and chemical environments.
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