Anti-Payload antibodies assist in the pharmacokinetic analysis of ADC drugs

Antibody-drug conjugates(ADCs) are immunoconjugates comprised of a monoclonal antibody tethered to a cytotoxic drug(known as the payload) via a chemical linker. The components that make up an ADC are a tumour antigen-specific mAb, a stable cleavable or non-cleavable chemical linker, and a potent cytotoxic payload(figure 1).

Figure 1: Structure of an antibody-drug conjugate and properties of the antibody(and target antigen), linker, and cytotoxic payload components^[1] 

Payload Features

The payload is covalently bound to the antibody through the linker, and the ADC drug plays an important role in the cytotoxic activity within cells, as its mechanism of action will determine the potency of the resulting ADC as an anticancer compound and its potential indications.An ideal payload should have the following characteristics: high cytotoxicity; low immunogenicity; high stability; modifiable functional groups without significantly affecting its efficacy; bystander killing effect; appropriate solubility; and the target should be intracellular, as most ADCs need to enter tumor cells to release their payload.

Payload Classification

Payloads can be divided into cytotoxic and non-cytotoxic types, with the vast majority of ADCs using cytotoxic payloads. There are two main representatives of cytotoxic payloads: microtubule inhibitors and DNA inhibitors, with DNA inhibitors further divided into DNA damage agents and topoisomerase inhibitors. Microtubule inhibitors can disrupt mitosis, and tumor cells divide faster than most normal cells, making microtubule inhibitors more effective in killing cancer cells. Microtubule inhibitors can be divided into two types: one that promotes microtubule polymerization, causing uncontrolled microtubule growth, such as dolastatin derivative MMAE, MMAF; the other effectively inhibits microtubule assembly, inducing cell mitotic arrest, such as maytansine derivative DM1, DM4. Microtubule inhibitors are the most mature payloads currently used, with much stronger toxicity than traditional chemotherapy drugs, but they also have some problems, such as microtubule inhibitors can only kill tumor cells in the cell division phase, and are ineffective against non-dividing and static cancer cells, and are more prone to drug resistance. DNA inhibitors that act on the entire cell cycle not only have a killing effect on non-dividing cancer cells but also kill cancer cells resistant to classical microtubule inhibitors. As the third generation of payloads, DNA inhibitors can destroy DNA structure and function through double-strand breaks, alkylation, intercalation, cross-linking, and inhibition of topoisomerase I (TOPO1), promoting the death of cancer cells.

Among the 14 approved ADC drugs, there are 6 ADC drugs with payload MMAE or MMAF, accounting for nearly 50%. There are also more than 80 pipelines under research with MMAE as the payload, making dolastatin the most commonly used payload.

Table 1: Common Cytotoxic Payload Classification

ADC Drug Components and Corresponding Analysis Methods

ADCs have both macromolecules and small molecules, requiring a variety of bioanalytical methods and platforms to analyze the diversity of ADCs. Traditional LC-MS/MS small molecule analysis methods are commonly used to analyze the unconjugated payload and the distribution of DAR (Drug-to-antibody ratio, which represents the number of payload molecules bound to each antibody and is an important attribute of ADC) over time, while ligand binding analysis (LBA) and LC-MS/MS can both be used for the analysis of total antibody (TAb) and total ADC. Anti-payload antibodies play an important role in the immunogenicity analysis of ADCs.

Anti-Payload Antibody Applications

• Pharmacokinetic (PK) analysis of ADC drugs in plasma/serum
• Determination of drug binding affinity
• DAR value analysis
• Efficacy evaluation of ADC drugs

Anti-Payload Antibody Product Advantages

• High Purity: Purity verified by SDS-PAGE and HPLC, >95%
• High Affinity: Verified by ELISA and other activity detection methods, with high activity
• High Specificity: Specifically recognizes the target
• Professional Technical Support: Professional technical support to answer pre-sales and after-sales questions in a timely manner

References:

[1] Cindy H., Patricia S., William D.. Antibody-drug conjugates for cancer[J]. Lancet 2019, 394:793-804