For an ever-changing industry, in the realm of targeted therapy, the production of cleavable peptide linkers has become an important method for making drug delivery more accurate and effective. Another new linker, DBCO-C4-Val-Cit-PABC-PNP, is becoming very popular because it can offer controlled, site-directed cleavage of drug-conjugates to biological triggers. DBCO-C4-Val-Cit-PABC-PNP's sequence contains a cleavable peptide that can be cleaved, by enzymes in the targeted tissue, to release a therapeutic drug at an optimal rate. This peptide linker is most useful in the ADC, because the ADCs release the drug directly on the target with less off-target effects and better therapeutic outcomes. As part of the linker structure, DBCO (dibenzocyclooctyne) is added to enable click chemistry conjugation to other elements like antibodies or nanoparticles. This novel technique has also been used in cancer treatment, and to direct the absorbed other bioactive drugs. The reason that DBCO-C4-Val-Cit-PABC-PNP is cleavable is because it has the Val-Cit (valine-citrulline) dipeptide motif, a commonly observed and known drug delivery system motif. Val-Cit is programmed to be cut by cathepsin B, a protease that's ubiquitous in many tumour cells and some of the inflamed disease sites. This cleavage-specific dissolution means that the drug payload can be selectively released at precisely the desired place and doesn't poison the healthy tissues. This peptide is further anchored to PABC (p-aminobenzylcarbamoyl) and PNP (p-nitrophenyl) components that serve not only to stabilize the linker but also to stimulate the drug release system. A PABC group makes the conjugate more solubilised in general and the PNP moiety, often used as a catalyst in the linker, lets the drug release under certain biological or chemical parameters, including pH or enzymes. This new combination of cleavable chains and functional groups make DBCO-C4-Val-Cit-PABC-PNP a powerful and versatile construct for targeted drug delivery systems. What makes DBCO-C4-Val-Cit-PABC-PNP different from other cleavable peptide linkers is the addition of the DBCO group, which acts as a functional moiety for bioorthogonal click chemistry. Click chemistry is a series of chemical reactions that are very efficient, highly localised and can be carried out in living systems without disrupting natural biochemical activity. DBCO add-in: By reacting with azides, you can pair DBCO-C4-Val-Cit-PABC-PNP with a range of biologically active molecules like antibodies, peptides or nanoparticles. This bioconjugation process is a lot better than the old one because you get high yield, minimal by-products and more selectivity. This bioorthogonal chemistry and the linker that can be cleaved provides a means of designing highly specific drug delivery, with a therapeutic agent only released if the linker is cleaved by a specific enzyme or under a specific environment within the diseased tissue. This control of the release of drugs means that the payload goes directly to the site of action – thus increasing the drug's therapeutic index and minimizing side effects.
Figure 1. Common cleavable linkers used in ADCs. (Ashman N, et al.; 2022)
What DBCO-C4-Val-Cit-PABC-PNP does as a cleavable peptide linker is a response to the enzymatic conditions of the disease-site. Val-Cit is very sensitive to cathepsin B, a lysosomal protease that's over-produced in the acidic environment of tumours, inflamed tissues or other pathologies. During use of a drug conjugate containing DBCO-C4-Val-Cit-PABC-PNP, the linker does not degrade in the bloodstream or under untargeted conditions, and so the drug does not release its active ingredient. When the conjugate arrives at the destination – usually a tumour or an inflammatory tissue – the acidic or enzymatic environment breaks down the Val-Cit peptide bond. That break releases the drug payload, which can then exert its anti-inflammatory effects only in the disease zone, and not in normal tissues. DBCO-C4-Val-Cit-PABC-PNP can significantly increase the specificity and performance of drug delivery, particularly for powerful or cytotoxic medications. For antibody-drug conjugates (ADCs) – the most common cancer drugs – cleavable linkers such as DBCO-C4-Val-Cit-PABC-PNP make sure that the drug only gets released when the conjugate reaches the cancer cell. This reduces the amount of drug absorbed into the body, reduces off-target toxicity, and increases the drug's window of effect. Further, bioorthogonal click chemistry (DBCO-azide reaction) is applied for controlled and effective conjugation of drugs to target agents, such as monoclonal antibodies, peptides or nanoparticles. Such a strategy allows for the development of highly targeted drug delivery systems, precisely tailored to individual diseases with the most therapeutic advantage with minimum side-effects. Another potential use for DBCO-C4-Val-Cit-PABC-PNP as a cleavable peptide linker is combination therapy. For instance, in cancer treatment, we can attach the linker to deliver cytotoxic drug as well as immune-modulatory drug, siRNA, or even gene therapy – all within the same carrier. This polyvalence means that they can target several pathways in cancer cells — something that can be extremely useful in countering resistance mechanisms that might arise from only using one treatment strategy. Moreover, having several different therapeutics in a conjugate creates synergies that may improve treatment effectiveness overall. DBCO-C4-Val-Cit-PABC-PNP lets doctors unleash a dose of drugs in a targeted and controlled way to bring better outcomes for patients with multi-factorial illnesses.
DBCO-C4-Val-Cit-PABC-PNP's versatility as a cleavable peptide linker also means that it will lend itself to many drug delivery platforms including oncology, immunotherapy and targeted gene delivery. In cancer therapy, the most common use cases is the creation of ADCs. ADCs are targeted treatments in which cytotoxic drugs are associated with monoclonal antibodies that recognise and interact with tumour antigens. DBCO-C4-Val-Cit-PABC-PNP cleavable linker ensures that the cytotoxic agent can be released directly at the tumour, yielding an increased therapeutic index and less threat of systemic toxicity. This is particularly relevant in the case of solid tumours, for which drug buildup in other tissue is dangerously side-effect-provoking. When you can use bioorthogonal click chemistry to connect the DBCO linker to a targeted agent, such as an antibody, conjugation is so efficient and targeted that tailored, highly targeted treatments can be developed. As well as oncology, DBCO-C4-Val-Cit-PABC-PNP is also being studied for immunotherapy to deliver immune-modulatory factors like cytokines or checkpoint inhibitors directly into the tumour microenvironment. The DBCO-C4-Val-Cit-PABC-PNP linker allows them to be injected precisely and sustainably at the site of the tumor, which will generate an immune response. This local administration optimizes the effectiveness of immunotherapies while limiting off-target effects, such as the immune system's firing in normal tissue that can cause an autoimmune response. DBCO-C4-Val-Cit-PABC-PNP is also used for gene therapy and RNA delivery systems. The linker can be used to link therapeutic genes or small RNA molecules (eg, siRNAs or microRNAs) to targeting agents, so that genetic material can be targeted specifically to cells or tissues. It's also potentially a useful strategy for genetic diseases, viral infections and even certain cancers, where the key to therapy is in getting the right payload of genes to the target cells. As the delivery system, the use of DBCO-C4-Val-Cit-PABC-PNP makes it more likely that the genes are released only in the right enzymatic environment, with no release during release and therefore increased stability and efficacy of the therapy.
Alternate Names:
DBCO-Linked Prodrug
DBCO-C4-Val-Cit-PABC-PNP Conjugate
C4-Val-Cit-PABC-PNP Prodrug
DBCO-Val-Cit Linker Conjugate
Val-Cit-PABC-PNP with DBCO Linker
Cytotoxic Prodrug with DBCO Linker
DBCO-Based Drug Release System
Val-Cit-PABC-PNP DBCO Conjugate
References:
1. Ashman N, et al.; Non-internalising antibody-drug conjugates. Chem Soc Rev. 2022, 51(22):9182-9202.
Datasheet