Introduction to Kinase

A kinase is an enzyme that catalyzes the transfer of a phosphate group from a high-energy phosphate donor molecule (such as ATP) to a specific substrate (a compound containing a nucleophilic group). This process is called phosphorylation, and its reverse process is called dephosphorylation. From the perspective of chemical reactions, this process belongs to an ester exchange reaction, which produces a phosphorylated substrate (such as a phosphate) and ADP (adenosine diphosphate, if the donor molecule is ATP) (Figure 1).

Figure 1. Phospho-signaling networks. (Ardito, Fatima, et al. 2017)

From the perspective of substrates, kinases can be divided into four major categories: protein kinases, lipid kinases, carbohydrate kinases, and other kinases (such as riboflavin kinase and thymidine kinase, etc.), which catalyze the phosphorylation of proteins, lipids, sugars, and other receptors. The phosphorylation state of these molecules will significantly affect their biological activity, reactivity, and ability to bind to other molecules.

For example, the most important protein kinases in the kinase family act on proteins by phosphorylating serine, threonine, tyrosine, or histidine residues of proteins. They can increase or decrease the activity of a protein, stabilize it or mark it for destruction, localize it in specific cellular compartments, and initiate or disrupt its interaction with other proteins. Kinases are therefore crucial in metabolism, cell signaling, protein regulation, cellular transport, secretory processes and many other cellular pathways, which makes them very important for human physiology.

Relationship Between Kinases And Human Diseases

The human genome encodes 518 kinases, which phosphorylate up to one-third of the proteome. Virtually every signal transduction process occurs through a phosphotransfer cascade. As key regulators of most cellular pathways, protein kinases are often associated with disease, and kinases provide multiple nodes for therapeutic intervention of many abnormally regulated biological processes. In addition, kinases can also directly cause human diseases as pathogenic factors. Kinase-mediated diseases are most prominent in the field of cancer. In addition to cancer, dysregulation of kinase function has been shown to play a key role in immunity, inflammation, degeneration, metabolism, cardiovascular and infectious diseases. In general, cancer, immune diseases, and degenerative diseases are the three major types of diseases mediated by kinases.

Kinase Inhibitors

Protein kinases can act directly as pathogenic factors or as key nodes in the process of disease. Mutations, dysregulation, and overexpression of protein kinases are associated with a variety of disease processes. About 1 in 40 human genes encodes a protein kinase, and nearly half of these genes can be mapped to disease sites or cancer amplicons.

Therefore, the development of corresponding kinase inhibitors to target protein kinases that play a key role in the formation of diseases has become an important means of treating these kinase-related diseases, especially in the field of cancer treatment. Given that phosphorylation regulates many biological processes, protein kinase inhibitors can be used to treat diseases caused by overactive protein kinases or to regulate cell function to overcome other disease drivers.

In 2001, the FDA approved the tyrosine kinase inhibitor imatinib. Imatinib is an oral chemotherapy drug that belongs to the small molecule tyrosine kinase inhibitor. It targets multiple tyrosine kinase receptors, such as CSF1R, ABL, c-KIT, FLT3, and PDGFR-β. It is used for Philadelphia chromosome-positive (Ph+) chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL), certain types of gastrointestinal stromal tumors (GIST), hypereosinophilic syndrome (HES), chronic eosinophilic leukemia (CEL), systemic mastocytosis, and myelodysplastic syndrome. Since the introduction of imatinib, the use of tyrosine kinase inhibitors has continued to expand, particularly in cancer therapy due to the key role of tyrosine kinases in cell signaling.

Figure 2. (A) Chemical structure of imatinib and its depicted binding mode with BCR-Abl. (B) Imatinib co-crystal structure. (Wu, Peng, et al. 2015)

The launch of imatinib is a milestone in the development of kinase inhibitor drugs. Since its commercialization in 2001, kinase inhibitor drugs have been continuously approved by various regulatory agencies. After imatinib, at least 75 small molecule kinase inhibitor drugs have been approved by the FDA. Most of them are oral preparations that target more than 20 kinase families, representing nearly a quarter of the human kinome. Oncology remains the main battlefield for small molecule kinase inhibitor drugs, which has created blockbuster drugs such as Ibrutinib and Palbociclib.

From the perspective of chemical structure, many kinase inhibitors contain aromatic heterocyclic skeleton structures, such as pyrimidine, pyridine, purine, quinoline, etc. These aromatic heterocyclic rings can fully and effectively bind to the hinge binding region of receptor kinases.

Efficacy of Kinase Inhibitors in The Antiviral Field

Given the wide range of effects of kinases in organisms, kinase inhibitors can also play an important role in the antiviral field, especially in broad-spectrum antiviral drugs.

We know that most of the antiviral drugs currently on the market act directly on pathogenic viruses. This type of antiviral drug is called direct-acting antivirals (DAA), which target proteins encoded by the viral genome. The main disadvantages of this strategy are the development of drug resistance and a narrow treatment window for the virus. Therefore, broad-spectrum antiviral drugs represented by kinase inhibitors have begun to attract attention. Especially after the outbreak of Covid-19, people have become more deeply aware of the efficacy of broad-spectrum antiviral drugs in quickly and effectively inhibiting new viruses in the early stages of a viral outbreak. Viruses rely on a variety of host cell proteins, and phosphorylation is crucial in the viral life cycle.

A large body of evidence supports the relationship between kinase inhibition and antiviral properties, including Numb-associated kinases (NAKs), receptor tyrosine kinases (RTKs), mitogen-activated protein kinases (MAPKs), Src kinases, cyclin-dependent kinases (CDKs), and phosphatidylinositol 3-phosphate 5-kinase (PIKfyve).

Therefore, kinase inhibitors have made significant progress in drug repurposing, which can transform kinase inhibitors with antiviral activity into new strategies for treating viral infections. Notably, the antiviral research of the multi-kinase inhibitor Dasatinib has achieved important results, and it has shown great potential as an antiviral agent (anti-HIV) both alone and in combination with other compounds.

In the field of developing anti-SARS-CoV-2 viruses, kinases may be involved in the viral replication process. Kinase inhibitors may have antiviral, anti-inflammatory, anti-cytokine, and anti-fibrotic effects, making them useful against SARS-CoV-2. Infection can be prevented by directly targeting the virus and reducing clinical symptoms using kinase inhibitors. Kinase inhibitors can also be used to improve the efficacy of other antiviral drugs or tailor treatments for SARS-CoV-2. Many kinase inhibitors are now being tested in clinical studies to see if they can serve as a viable treatment.

In summary, the widespread use of FDA-approved kinase inhibitors is very useful for deciphering the role of host kinases in viral infections. Although the scientific community still needs to gain a deeper understanding of the specific mechanism of action of kinase inhibitors in the antiviral field, from a practical perspective, people need to focus on optimizing kinase inhibitors with antiviral properties to achieve the effective application of kinase inhibitors in the antiviral field.

Kinase Cell Lines at Creative Biogene

With decades of experience in cell line engineering and drug discovery, Creative Biogene has developed a large collection of kinase stable cell lines that can be used for in vitro cell-based kinase assays. The use of these cell lines allows for broad set of assays and reduced assay development time.