baseclick – Nucleic Acid Labeling and Bioconjugation

Click Chemistry is a powerful method to rapidly and selectively react ("click") a pair of functional groups with each other in mild, aqueous conditions. Click reactions are popular due to their high yields and straightforward reaction conditions.

One of the best-known click reactions is copper-catalyzed cycloaddition, which produces an effective, stereo-specific combination of two molecules under mild conditions. In this transformation, an azide and alkyne undergo a cycloaddition reaction with the help of a copper catalyst to form a triazole ring. This heterocycle formation chemistry has high tolerance to reaction conditions and substrate structures. Click Chemistry is therefore an excellent alternative to classic, more expensive methods for making nucleic acids and other biomolecules. It is also used for highly selective, low background labeling of biomolecules.

Click Chemistry has found applications in a wide variety of research areas, including materials science, polymer chemistry, bioscience, and drug discovery.

To be considered part of click chemistry, a reaction needs a few characteristics:

• Modular
• High yielding (minimal and inoffensive byproducts)
• Requires no or minimal purification
• Straightforward reaction conditions
• Readily available starting materials
• Using either no solvent, or something benign like water that is easily removed
• Highly selective
• Short reaction times

Experimental studies measuring cell proliferation have had implications in cancer biology, immunology, cell biology, and developmental biology. Monitoring active DNA-synthesis in cells is the best indicator of proliferation. Specific detection of DNA replication over a period of time can be measured by incorporating modified nucleosides, such as 3H-Thymidine, in which the radioactivity is detected. To avoid radioactivity, the anti-bromodeoxyuridine (BrdU) assay was developed in which the modified nucleoside BrdU is incorporated into DNA and subsequently detected using an antibody.

baseclick’s EdU cell proliferation assays provide a superior alternative to BrdU assays. These kits measure cell proliferation by detecting the incorporation of the alkyne-modified nucleoside EdU (5-Ethynyl-2′-deoxyuridine) into DNA using copper-catalyzed azide-alkyne click chemistry to attach fluorescent probes. The assays can be used for monitoring of cell vitality, determining genotoxicity, or evaluating anticancer drugs.

EdU incorporation and detection does not require DNA denaturation leading to fewer steps and reduced degradation of tissues. baseclick’s kits are convenient and can save researchers valuable time with assay times of about 1 ½ hours.

baseclick has developed different EdU kits for microscopy imaging, flow cytometry, and high throughput screening. Each kit comes with an optimized experimental protocol and the required components for each application. Also, special in vivo kits have been developed.

Following the outbreak of the corona epidemic, baseclick’s scientists were able to quickly begin development of a new vaccine against SARS-CoV-2 thanks to their specialized knowledge of mRNA and bioconjugation methods. baseclick’s proprietary technologies allow targeting agents to be directly linked to mRNA sequences, thus avoiding the need for lipid nanoparticle formulation. In this video they explain their vaccine strategy and its benefits.

In 2022, the Nobel Prize in Chemistry was jointly awarded to Carolyn R. Bertozzi, Morten P. Meldal, and K. Barry Sharpless, "for the development of click chemistry and bioorthogonal chemistry". Click chemical reactions are fast, efficient, modular, clean, selective, and compatible with aqueous conditions. Meldal and Sharpless independently and concomitantly developed what is known today as the canonical click reaction. In this transformation, an azide and alkyne undergo a cycloaddition reaction with the help of a copper catalyst to form a triazole ring (copper-catalyzed azide–alkyne cycloaddition), thereby linking together any cargoes attached to the members of this molecular duo.

In complex biologic systems, such as living organisms, it is just too difficult to get the azide, alkyne, and catalyst together in one place. A simpler, two-component version of the reaction was needed. This is where Bertozzi’s work comes in. Her variation on the cycloaddition still uses an azide but pairs it with a cyclic alkyne that is spring-loaded with what chemists call ring strain. The release of this ring strain when the alkyne reacts with the azide gives the cycloaddition the push it needs to proceed without a copper catalyst. This transformation was dubbed the strain-promoted azide–alkyne cycloaddition (SPAAC). As a bioorthogonal click reaction - a transformation that can occur in biologic systems without perturbing them - the SPAAC reaction has enabled the use of click chemistry in previously inaccessible biologic environments.