Protein kinases are central to cellular signaling and modulate many functions in life including cell growth, differentiation, metabolism and apoptosis. As kinase function is uncontrolled by disease, including cancer, protein kinases are ideal targets for drug discovery. Imaging techniques are now key to research and development of kinase inhibitors, as they allow us to know how they act, how effective they are, and how they could go 'off-target'. This post is about the development and uses of protein kinase imaging in drug development.

Figure 1. Recent advances in kinase drug discovery span the drug discovery pipeline from target identification through to pharmacovigilance. (Tucker JA, et al.; 2021)

The Function of Protein Kinases in the Body

Protein kinases transport phosphate groups from donor molecules (ATP, for example) to substrates. It's this process of phosphorylation that makes it necessary for the activation or inhibition of target proteins, thus modulating many cell functions. Mutations and dysfunctional kinases can also allow cancer cells to grow and spread out of control. Kinase inhibitors have thus become a very important group of drugs.

Imagery is Important for Kinase Drug Discovery

Imaging is a safe way to see and measure biology as it happens. For kinase drug discovery, imaging is used to:

1. Verify Drug Target Accrual: Imaging can monitor if the drug binds to its target kinase in cells or tissues.
2. Assess Pharmacokinetics and Biodistribution: It helps you know the Absorption, Distribution, Metabolism and excretion (ADME) of kinase inhibitors.
3. Compare Effectiveness and Mechanisms of Action: Kinase inhibition's biochemical and cellular effects can be seen with imaging.
4. Anticipate Off-Target Interactions: Helps in identifying unintended interactions with other proteins or pathways, which are very important for drug safety.

Kinase Drug Development: Imaging Methods for Drug Design

There are different imaging techniques used to monitor protein kinases, and each of them is better for a specific task:

1. Fluorescence Imaging

Protein kinases detected with fluorescence images, using fluorescent probes. Those probes might be fluorescent antibodies or small molecules that attach to kinases. Enhancements to fluorescence microscopy, such as confocal and super-resolution microscopy, have increased kinase imaging's spatial and temporal resolution.

• Fluorescent Resonance Energy Transfer (FRET): FRET sensors measure kinase function via measuring energy flow between two fluorophores. PK phosphorylation or conformational modifications in FRET efficiency.
• Genetically Encoded Biosensors: The biosensors are made of fluorescent proteins paired with substrates of kinases, so that we can measure kinase activity in real-time in living cells.

2. Positron Emission Tomography (PET) and Single-Photon Emission Computed Tomography (SPECT)

PET and SPECT are nuclear imaging tests, which offer quantitative information on the movement of radioactively labeled kinase inhibitors throughout the body. They are sensitive and are good for whole-body imaging.

• Radiolabelled Inhibitors: Kinase inhibitors are radiolabeled using positron-emitting isotopes (for PET) or gamma-emitting isotopes (for SPECT). These radiolabelled molecules enable us to imagine the in vivo process of drugs, from uptake to distribution to clearance.

3. Magnetic Resonance Imaging (MRI)

Anatomically and functionally, tissues can be MRI-described. Kinase inhibitors are measured by MRI with contrast agents.

• Chemical Exchange Saturation Transfer (CEST): In CEST-MRI, exchangeable protons in contrast agents are reacted to create MRI signals. CEST agents can be made to track kinase function, giving you indirect information about kinase activity.

4. Bioluminescence Imaging

Imaging with bioluminescence is dependent on the light from luciferase-expressing cells or organisms. It is highly sensitive and applicable to longitudinal studies with wild animals.

• Bioluminescent Reporters: Kinase activity can be monitored using bioluminescent reporters that light up when events occur. It is a way of monitoring the activity of kinases in real time in animals.

Our Services

Protein Kinases Imaging Analysis

Applications in Drug Development

1. Target Validation

It is a matter of imaging that proves the protein kinases to be therapeutic targets. Map the location and function of kinases in disease models so that researchers can establish the role of particular kinases in disease.

2. Drug Screening and Lead Optimization

Imaging tests with high resolution make it easy to screen for potential kinase inhibitors on large compound libraries. These assays can measure in real-time drug-target interactions and cellular activity to help design optimized lead compounds.

3. Preclinical and Clinical Studies

Imaging is a necessity in preclinical studies to determine pharmacodynamics and pharmacokinetics of kinase inhibitors. Imaging biomarkers can be scanned in clinical trials to observe how patients respond to treatment, and these allow for individualised medicine.

4. Mechanistic Studies

Drug development is dependent on the kinase inhibitor's kinetics. Images are used to cut up signalling circuits and pinpoint downstream consequences of kinase inhibition.

Challenges and Future Directions

Despite the dramatic improvements, there are still some problems in protein kinase imaging:

• Specificity and Sensitivity: There is a barrier to the creation of highly specific and sensitive imaging probes for kinases because of the ATP-binding site which is common among kinases.
• Measurement and Standardization: Imaging protocols and measurement are needed to be standardised for reproducible and comparable data.
• In Vivo Imaging: In vivo imaging is lacking the resolution and resolution required to detect kinase activity in thick tissue.

Future directions for protein kinase imaging are multiplex imaging to look at multiple kinases at the same time and combining imaging information with other omics technology to give us a full picture of kinase biology.

Conclusion

Protein kinase imaging has changed the way we can develop drugs, by allowing us to better understand how kinases operate and what kinase inhibitors do. The more imaging technology develops, the more it will be important in discovering and creating new therapeutics and helping patients experience better outcomes for various diseases.

1. Tucker JA, Martin MP. Recent Advances in Kinase Drug Discovery Part I: The Editors' Take. Int J Mol Sci. 2021, 22(14):7560.

*If your organization requires the signing of a confidentiality agreement, please contact us by email.

Please note: Our services can only be used for research purposes. Do not use in diagnostic or therapeutic procedures!