Hey there! As a supplier of peptide linkers for ADC (Antibody - Drug Conjugates), I've been getting a lot of questions lately about how to design peptide linkers to control the release rate of the payload in ADC. So, I thought I'd share some insights on this topic.
First off, let's quickly understand what ADCs are. ADCs are basically a type of targeted therapy that combines the specificity of monoclonal antibodies with the cytotoxicity of small - molecule drugs. The peptide linker plays a crucial role here. It connects the antibody and the payload (the cytotoxic drug), and its design can greatly affect when and how the payload is released inside the target cell.
Factors Affecting Payload Release Rate
Cleavability
One of the most important factors is the cleavability of the peptide linker. We want the linker to stay intact during circulation in the bloodstream but break down once it reaches the target cell. There are two main types of cleavable linkers: enzyme - cleavable and pH - cleavable.
Enzyme - cleavable linkers are designed to be recognized and cut by specific enzymes that are highly expressed in tumor cells. For example, cathepsin B is an enzyme that's often over - expressed in many cancer cells. Peptide sequences like Val - Cit are commonly used in linkers because they can be cleaved by cathepsin B. When the ADC enters the target cell and is taken up into the lysosome, cathepsin B cuts the Val - Cit bond, releasing the payload. Our Fmoc - Val - Cit - PAB - OH is a great example of an enzyme - cleavable linker. It contains the Val - Cit sequence and can be easily incorporated into ADC designs.
pH - cleavable linkers, on the other hand, break down in the acidic environment of the endosome or lysosome. This is because the chemical bonds in these linkers are sensitive to low pH. For instance, some hydrazone - based linkers are stable at physiological pH (around 7.4) but hydrolyze at the lower pH (around 5 - 6) found inside the cell's compartments.
Hydrophobicity
The hydrophobicity of the peptide linker also impacts the release rate. A more hydrophobic linker can affect the solubility of the ADC in the bloodstream. If the linker is too hydrophobic, the ADC might aggregate, which can lead to clearance from the body before it reaches the target. On the other hand, a very hydrophilic linker might cause the payload to be released too early in the circulation. We need to find a balance.
We can modify the hydrophobicity of the linker by choosing different amino acids. Amino acids like leucine and isoleucine are more hydrophobic, while serine and threonine are more hydrophilic. By carefully selecting and arranging these amino acids, we can fine - tune the hydrophobicity of the linker.
Linker Length
The length of the peptide linker matters too. A shorter linker might restrict the movement of the payload and the antibody, which could affect the binding of the ADC to the target antigen. A longer linker, however, gives more flexibility but might also increase the chance of non - specific cleavage or premature release of the payload.
In general, linkers with 3 - 10 amino acids are commonly used. But the optimal length depends on the specific antibody, payload, and target antigen. We've found that for some ADCs targeting certain types of cancer cells, a linker with 5 - 7 amino acids works best in terms of both stability in circulation and efficient payload release at the target.
Design Strategies
Rational Design
Rational design involves using our knowledge of the target cell's biology, the properties of the antibody and payload, and the characteristics of different peptide sequences. We start by identifying the enzymes or pH conditions that are unique to the target cell. Then, we choose the appropriate cleavable motif for the linker.
For example, if we know that a particular tumor over - expresses a certain protease, we can design a linker with a sequence that's recognized by that protease. We also consider the hydrophobicity and length of the linker based on the solubility and binding requirements of the ADC.
High - Throughput Screening
Another approach is high - throughput screening. We can synthesize a large library of different peptide linkers and test them in vitro and in vivo. This allows us to quickly identify the linkers that give the best performance in terms of payload release rate, stability, and efficacy.
We can use techniques like phage display or peptide microarrays to screen thousands of linkers at once. By analyzing the results, we can find the optimal linker design for a specific ADC application.
Examples of Our Linkers
Let's take a look at some of our popular peptide linkers for ADCs. Our Acetylene - linker - Val - Cit - PABC - MMAE is a powerful linker - payload conjugate. The Val - Cit sequence makes it enzyme - cleavable, and the acetylene group can be used for conjugation to the antibody. This linker - payload combination has shown great potential in pre - clinical studies for targeting various types of cancer.
Another one is MC - Val - Cit - PAB - PNP. It contains the Val - Cit motif and is designed for efficient payload release. The MC group provides a stable connection to the antibody, and the PAB spacer helps in the proper release of the payload.
Conclusion
Designing peptide linkers to control the release rate of the payload in ADCs is a complex but rewarding process. By considering factors like cleavability, hydrophobicity, and linker length, and using strategies like rational design and high - throughput screening, we can create linkers that optimize the performance of ADCs.
If you're working on ADC development and are interested in our peptide linkers, we'd love to have a chat. Whether you need help with linker design, want to learn more about our products, or are ready to place an order, don't hesitate to reach out. We're here to support you in your journey to develop effective ADC therapies.
References
- Ducry, L., & Stump, B. (2010). Antibody - drug conjugates: linking cytotoxic payloads to monoclonal antibodies. Bioconjugate Chemistry, 21(1), 5 - 13.
- Alley, S. C., Okeley, N. M., & Senter, P. D. (2010). Antibody - drug conjugates: targeted drug delivery for cancer. Current Opinion in Chemical Biology, 14(3), 529 - 537.
- Shen, B. Q., et al. (2012). Controlling the location of drug attachment in antibody - drug conjugates. Nature Biotechnology, 30(2), 184 - 189.