Background
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.
Alternative Names
Monomethyl auristatin E
References
- 1. Kostova V, et al., The Chemistry Behind ADCs. Pharmaceuticals (Basel) . 2021, 14(5):442.
References
Payload-Binding Fab Fragments Increase the Therapeutic Index of MMAE Antibody-Drug Conjugates
Mol Cancer Ther
Authors: Bordeau BM, Nguyen TD, Polli JR, Chen P, Balthasar JP.
Abstract
Monomethyl auristatin E (MMAE) is a potent tubulin inhibitor that is used as the payload for four FDA-approved antibody-drug conjugates (ADC). Deconjugated MMAE readily diffuses into untargeted cells, resulting in off-target toxicity. Here, we report the development and evaluation of a humanized Fab fragment (ABC3315) that enhances the therapeutic selectivity of MMAE ADCs. ABC3315 increased the IC50 of MMAE against human cancer cell lines by > 500-fold with no impact on the cytotoxicity of MMAE ADCs, including polatuzumab vedotin (PV) and trastuzumab-vc-MMAE (TvcMMAE). Coadministration of ABC3315 did not reduce the efficacy of PV or TvcMMAE in xenograft tumor models. Coadministration of ABC3315 with 80 mg/kg TvcMMAE significantly (P < 0.0001) increased the cumulative amount of MMAE that was excreted in urine 0 to 4 days after administration from 789.4±19.0 nanograms (TvcMMAE alone) to 2625±206.8 nanograms (for mice receiving TvcMMAE with coadministration of ABC3315). Mice receiving 80 mg/kg TvcMMAE and PBS exhibited a significant drop in white blood cell counts (P = 0.025) and red blood cell counts (P = 0.0083) in comparison with control mice. No significant differences, relative to control mice, were found for white blood cell counts (P = 0.15) or for red blood cell counts (P = 0.23) for mice treated with 80 mg/kg TvcMMAE and ABC3315. Coadministration of ABC3315 with 120 mg/kg PV significantly (P = 0.045) decreased the percentage body weight loss at nadir for treated mice from 11.9%±7.0% to 4.1%±2.1%. Our results demonstrate that ABC3315, an anti-MMAE Fab fragment, decreases off-target toxicity while not decreasing antitumor efficacy, increasing the therapeutic window of MMAE ADCs.
Conjugating MMAE to a novel anti-HER2 antibody for selective targeted delivery
Eur Rev Med Pharmacol Sci
Authors: Li L, Xu MZ, Wang L, Jiang J, Dong LH, Chen F, Dong K, Song HF
Abstract
Objective: To investigate the target delivery properties of RC48-ADC, a novel antibody drug conjugate (ADC) comprising cytotoxic monomethyl auristatin E (MMAE) and an anti-human epidermal growth factor receptor 2 (HER2) antibody tethered via valine-citrulline linker, in vitro and in vivo.
Materials and methods: Dissociation rate of MMAE from RC48-ADC was used as an estimate of its stability in serum. Cytotoxicity of the antibody and RC48-ADC towards multiple cell lines was measured. Subcellular distribution of the drug was determined by fluorescence imaging. The mechanism of lysosome targeting was verified. Endocytic pathways of RC48-ADC were assessed by the cellular fluorescence intensity of fluorescently-labelled drugs. Intracellular and extracellular distribution of MMAE was analysed after RC48-ADC or MMAE administration to characterize MMAE release. The serum and tumour concentration of MMAE was compared after tail-vein injection of RC48-ADC into tumour-bearing mice.
Results: RC48-ADC was highly stable in human serum. HER2-overexpressed cell line SK-BR-3 proliferation was stronger when suppressed by RC48-ADC than by the naked antibody. Both RC48-ADC and naked antibody were internalized via caveolae-mediated and clathrin-mediated endocytosis and concentrated in lysosomes. Higher HER2 expression was associated with enhanced uptake and intracellular release of conjugated MMAE; free MMAE could kill tumour cells via the bystander effect. Although serum RC48-ADC concentration was higher than that in tumours, exposure of MMAE in tumours was ~200 times higher than in serum, which rationalized the reduced toxicity of RC48-ADC.
Conclusions: In vitro and in vivo experiments confirmed the targeted transport and release of RC48-ADC; it could selectively deliver MMAE to the targeted HER2-positive cell or tumour tissue, which could reduce off-target toxicity and enhance anti-tumour potency in humans.
COA
Publication 
Loading ......
