Anti-MMAE monoclonal antibody

Aplysiatoxin-10 is the first Aplysiatoxin to be isolated, with an IC50 of cytostatic activity of 0.5 nmol/L. In clinical trials, the toxicity was still within the acceptable range, but it was not carried out one-step single treatment trial due to lack of effectiveness. Aplysiatoxin 10, a mitotic spindle inhibitor, is a highly cytotoxic natural pentapeptide obtained from the intestinal tracts of Aplysia, cyanobacteria, and auricularia. Structurally, it is a linear pentamer containing 4 amino acids at the N-terminus and 1 amino acid at the C-terminus. The drug binds tightly to the beta subunit of tubulin and is more potent than other tubulin-binding drugs. Currently, Aplysiatoxin 10 analogues monomethyl auristatin E (MMAE) and monomethyl auristatin F (MMAF) are widely used as payload components of ADCs. ADC drugs are undoubtedly one of the hottest research fields in recent years. As we all know, antibody drug conjugates (ADCs) are composed of monoclonal antibodies targeting specific antigens and small molecule cytotoxic drugs linked through linkers. They combine the powerful killing effect of traditional small molecule chemotherapy and the tumor targeting of antibody drugs. An ADC consists of three main parts: an antibody responsible for selectively recognizing cancer cell surface antigens, a drug payload responsible for killing cancer cells, and a linker that connects the antibody and payload. ADC drugs can selectively reduce the off-target side effects of small molecule cytotoxic drugs while retaining the tumor-killing properties of small molecule cytotoxic drugs, effectively improving the benefit-risk ratio of anti-tumor treatment.

Figure 1. Structure of auristatine E (AE), monomethyl auristatin E (MMAE), and commercially approved auristatin-based ADCs. (Source: Kostova V, et al., 2021)

MMAE is a synthetic derivative of Aplysiatoxin 10. They induce tumor cell apoptosis by disrupting microtubule formation. Studies have shown that auristatin derivatives MMAE and MMAF are more effective than vinblastine. However, they are also susceptible to drug resistance because they are sensitive to drug efflux pumps and p-glycoprotein. The main function of MMAF is the same as that of MMAE, however, its activity is reduced compared to MMAE due to the presence of a charged C-terminal phenylalanine. There are currently five marketed drugs (Adcetris, Polivy, Padcev, Blenrep, Vidicitomab) with MMAE/MMAF as the payload, and there are more than 20 ADC drugs with auristatin as the payload in clinical practice, accounting for 10% of the More than 50% of the total ADC drugs are being developed.

MMAE/MMAF is 100-1000 times more potent than doxorubicin and cannot be used as a drug itself. However, as part of the ADC, MMAE/MMAF is linked to a monoclonal antibody (mAb) that recognizes specific marker expression in cancer cells and directs MMAE/MMAF to specific target cancer cells. The linker connecting MMAE/MMAF to the monoclonal antibody is stable in the extracellular fluid, but once the ADC binds to the target cancer cell antigen and enters the cancer cell, it is cleaved by cathepsin, and then the ADC releases toxic MMAE/MMAF and activates effective Antimitotic mechanisms. ADCs can enhance the antitumor effects of antibodies and reduce the adverse systemic effects of potent cytotoxic drugs. MMAF and MMAE each have their own advantages and disadvantages. Compared with MMAF, MMAE has stronger membrane permeability and lower IC50. However, compared to MMAE, MMAF is more hydrophilic and has a lower tendency to aggregate, showing lower systemic toxicity. Cytotoxic molecules are the key to determining the lethality of ADC. In addition to being extremely toxic, they also need to have sufficient water solubility and stability in serum. Among them, MMAE/MMAF are polypeptides composed of 5 units. The molecules are highly stable. They are found in plasma, liver lysosomal extracts or proteases such as cathepsin B. No signs of degradation. MMAE has also shown strong activity in some clinical trials of lymphoma, leukemia and solid tumors. Among the 14 approved ADC drugs, 6 have MMAE/MMAF payloads, accounting for nearly 50%. At the same time, there are more than 40 pipelines of drugs under development using MMAE as payload.

Monomethyl auristatin E