Fmoc-PEG4-Val-Cit-PAB-OH是一種酶可裂解的ADC接頭，具有Boc保護(hù)的胺、親水性PEG間隔區(qū)和Val-Cit-PAB二肽。PAB上的芐醇可用于連接反應(yīng)性基團(tuán)，如PNP，以與藥物有效載荷結(jié)合。Fmoc保護(hù)基可以用哌啶除去以顯示伯胺，該伯胺可以用于偶聯(lián)反應(yīng)以形成酰胺。Val-Cit PAB被細(xì)胞蛋白酶切割，有效載荷有效釋放到細(xì)胞。

Fmoc-PEG4-Val-Cit-PAB-OH is an enzyme-cleavable ADC linker featuring a Boc-protected amine, a hydrophilic PEG spacer, and a Val-Cit-PAB dipeptide. The benzylic alcohol on the PAB can be used to attach with reactive groups such as PNP for conjugation with drug payloads. The Fmoc protecting group may be removed with piperidine to reveal a primary amine which may be used in coupling reactions to form amides. The Val-Cit-PAB is cleaved by cellular proteases for efficient release of payloads to the cell.

ADC linkers的介紹

ADC linkers are one of the three main components of the antibody drug conjugates (ADC) that connect an antibody with a potent drug (payload) through a chemical bond.

Role of ADC Linkers

ADC linkers play key roles in determining the overall success of the Antibody Drug Conjugates. One of the main challenges in developing a safe and effective ADC drug (Figure 1) is the assembly of a desirable chemical linker between cytotoxic payload and mAb. A well-designed ADC linker can help the antibody to selectively deliver and accurately release the cytotoxic drug at tumor sites. It also plays critical roles in an ADCs' stability during preparation, storage, and systemic circulation. A stable ADC drug ensures that less cytotoxic payloads fall off before reaching tumor cells, increasing safety, and limiting dose.

There are two main categories of ADC linkers in current ADC drugs, cleavable linkers and non-cleavable linkers.

Figure 1. There are three major components of an ADC drug; the antibody used, the linker, and the payload to be delivered.

Cleavable linkers are designed to be stable in the bloodstream and then release the payload once in the cell. Cleavable linker types include enzymatically-cleavable peptide linkers, acid sensitive hydrazone linkers, and glutathione-sensitive disulfide linkers.

Example of Cleavable Linkers in ADC

Figure 2. Adcetris with enzymatically cleavable val-cit linkage.

The non-cleavable linkers, such as SMCC, rely on lysosomal degradation within the cell to release the drug payload.

A summary of linker types is provided in Table 1.

Table 1. Linker type, mechanism and advantages of cleavable and non-cleavable linkers.

An interesting part of the ongoing discussion about linker stability is whether the payload can or should be released into the area outside of the tumor cell. This effect, referred to as the ‘bystander effect’, is seen by some as a beneficial attribute for an ADC to display. However, recent studies indicate that, depending on the linker and payload combination, this mechanism may not be essential, and ADCs can be cleaved extracellularly or via other mechanisms.

PEG Increases the Solubility of ADC Linkers

The solubility of the linker is another parameter that has been explored using Monodispered PEG chains. Two of the latest ADCs to be approved, Trodelvy and Zynlonta, were developed with PEG moiety as part of their linker technology to improve solubility and stability in vivo.

Example of ADC Linkers with PEG Chain

Figure 3. Zynlonta, shown above, has several unique features including a maleimide group for attachment to the mAbs, a PEG8 linker for solubility, and a cleavable Val-Ala section bound to the drug SG3199.

Journal Reference:

Halford, "A new generation of antibody-drug conjugates for cancer patients", Chemical and Engineering News, vol 98, 14, (2020) https://cen.acs.org/biological-chemistry/cancer/new-generation-antibody-drug-conjugates/98/i14

Staudacher, Brown, "Antibody drug conjugates and bystander killing: is antigen-dependent internalisation required?", Br J Cancer 117, (2017): 1736–1742, https://www.nature.com/articles/bjc2017367#citeas

Joubert, et al., "Antibody-Drug Conjugates: The Last Decade", Pharmaceuticals (Basel, Switzerland) vol 13,9, (2020): 245-276, https://pubmed.ncbi.nlm.nih.gov/32937862/