Mouse Anti-DM1 Monoclonal Antibody, clone DM1

An antibody-drug conjugate (ADC) is a new type of targeted anti-tumour drug that uses antibodies to deliver the conjugated drug to the tumour cell site to enhance the therapeutic activity of antibodies, increase the targeting of cytotoxic drugs to kill tumour cells and reduce their toxic side effects on normal tissues. Despite their complex structure, two ADC drugs, Adcetris and Kadcyla, have been approved by the US FDA in recent years due to their advantages of high specificity, strong selectivity and non-cytotoxicity. In addition, dozens of ADC candidates have entered clinical research worldwide. ADCs have become a research hotspot and development direction for targeted tumour therapy. ADCs have three main structural components: 1. Selection of antibodies. The properties of antibodies play a crucial role in the key links of ADCs entering target cells, such as the binding of antibodies to target cell surface antigens and antibody internalisation. Surface antigens with high expression of tumour cell specificity should be selected as antibody targets, and the antibody should also have high affinity. There is some correlation between the number of tumour cell surface antigens expressed and the efficacy of ADCs, so it is necessary to have some understanding of antibodies that target specific tumour cells, or consider using marketed monoclonal antibodies as a starting point to ensure efficacy. 2. Warhead drug activity. The warhead drug is the core component of the ADC that ultimately exerts its activity, so it must have extremely high activity. In addition, since the warhead drug must be coupled to the antibody, it must also have a certain degree of chemical modifiability and water solubility to ensure that the warhead drug can be carried by the antibody into the cell and exert its effect. 3. Suitable linkers. Suitable linkers need to have two basic characteristics: first, the linker needs to have circulatory stability, and before the ADC reaches the target cell, it cannot be cleaved in the circulatory system to release cytotoxic molecules to avoid toxic effects; second, after entering the target cell, the linker needs to be quickly and effectively cleaved to effectively release the cytotoxic molecules to exert their due pharmacological activity. The effector cytotoxic molecules used in ADCs currently on the market and in clinical research can be divided into two categories: anti-mitotic cytotoxicity and DNA lytic cytotoxicity. Among them, the main function of anti-mitotic cytotoxicity is to interfere with microtubule self-assembly. The main types of cytotoxicity used in this type of cytotoxicity are maytansine analogs DM1, DM4 and auristatin analogs MMAE, MMAF; and the main mechanism of action of DNA lytic cytotoxicity is that the cytotoxic molecules bind to the minor groove of DNA to cause the break of the DNA double-stranded structure, such as calicheamicine derivatives and pyrrolobenzodiazopine (PBD) derivatives. Anti-mitotic cytotoxic agents MMAE, DM1, and DM4 are the most commonly used effector molecules. They preferentially destroy highly differentiated cells and enhance sensitivity to malignancy. In this sense, such cytotoxic agents also have a certain degree of selectivity. Both cytotoxic agents have very high activity, and their effects are 100 to 1,000 times that of traditional chemotherapy drugs (doxorubicin or paclitaxel).

Figure 1. Schematic diagram of the structure of ADC-DM1. (Sources: Chen K, et al. 2021)

Maytansine is a widely used cytotoxic molecule in ADC. It was first isolated from the alcohol extract of the bark of an African shrub (Maytenusovatus). Maytansine is the first ansa macrolide antibiotic with antitumor activity. It has strong killing activity against nasopharyngeal carcinoma tumor cells KB cells, murine lymphocytic leukemia P-388 cells and murine leukemia L1210 cells. In recent years of research, medicinal chemists have successively synthesized a series of maytansine derivatives containing disulfide bonds or thiol substitutions. These maytansine derivatives can be connected to monoclonal antibodies through covalent bonds to form antibody-drug conjugates. Among these derivatives, DM-1 and DM-4 are the two most commonly used maytansine ADC effector molecules in clinical practice. Through the structure-activity relationship study of maytansine, it is found that the N'-acetyl-N-methyl-L-alanine side chain at the C3 position of maytansine, the conjugated double bond structure formed by C4-C5 epoxy fragment, C9 carbonyl group and C11 and C13 are all the necessary structures for maytansine to show anti-tumor activity. In contrast, the influence of phenyl ring and N'-acetyl group on anti-tumor activity is not great, and appropriate chemical modification can be carried out to it, improving the physicochemical properties of maytansine derivatives. The N'-acetyl group originally present in maytansine is studied by the transformation of group, and it is found that the activity of such maytansine derivatives does not have significant reduction, therefore maytansine can be structurally modified, and under the premise of ensuring anti-tumor activity, appropriate coupling reaction site is provided. DM-1 and DM-4 are the maytansine derivatives found based on this structure-activity relationship, and DM1 and DM4 can react with monoclonal antibodies efficiently and in high yield in aqueous solution, and are combined with stable covalent bonds. Amino acids containing sulfhydryl or other forms of thiolation can easily undergo Michael addition with the double bonds of maleimide groups to form thioether bonds, and can also undergo disulfide exchange reactions with disulfide-containing groups to form new disulfide bonds. The main mechanism of action of maytansine is to block the polymerization of tubulin, arrest cells in the G2/M phase of the cell cycle, thereby inhibiting cell mitosis and leading to cell apoptosis. Maytansine triggers cell apoptosis by binding to the vinca alkaloid site on tubulin. In addition, studies have found that its effect of inhibiting the binding of guanine nucleotides to tubulin at the exchange site is stronger.

Drug Monomethyl Auristatin E
Maytansinoid DM1
Emtansine
S-methyl-DM1
Mertansine