Duocarmycin-Based ADCs

Duocarmycins, derived from Streptomyces bacteria, are a group of potent toxins with antitumor properties. They are a class of DNA minor groove-binding alkylating molecules. In recent years, researchers have utilized duocarmycin analogues as payloads in the creation of antibody-drug conjugates (ADCs). These ADCs combine the tumor-targeting ability of antibodies with the cytotoxic effects of duocarmycins. Promisingly, over 15 duocarmycin-based ADCs have undergone preclinical studies, and some, like SYD985, have received Fast-Track Designation status, highlighting their potential as effective cancer therapies.

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Antibody-drug conjugates (ADCs)

ADCs are a type of targeted cancer therapy that combines specific antibodies with potent cytotoxic drugs. Over 80 ADCs are currently in clinical trials. Nine ADCs have been approved, targeting various cancers, such as lymphoma, myeloma, breast cancer, and urothelial tumors.

The success of ADCs relies on factors like target validation, antibody manipulation, linker chemistry, and cytotoxic drug potency. ADC payloads should have balanced properties, be chemically tractable, and display appropriate cytotoxicity. They should effectively kill cancer cells while minimizing harm to healthy tissues. Currently, the cytotoxic agents that have been used in ADCs are characterized as microtubule inhibitors and DNA-damaging agents. Other payload types under development include DNA synthesis disruptors and inhibitors of protein synthesis or metabolic processes. The utilization of potent compounds in ADCs enhances the diversity of pharmaceutical options, enabling different mechanisms of action. This broadens the effectiveness of ADCs in treating various cancer types with distinct characteristics like proliferation, invasiveness, metastasis, chemoresistance, and tumorigenic stemness. Among them, duocarmycin-based ADCs have shown promise in preclinical studies, with some advancing to later stages of clinical trials.

Duocarmycin-based ADCs: Mechanism of Action

Duocarmycin-based ADCs function by utilizing the unique characteristics of both the antibody and the cytotoxic payload. The antibody component specifically recognizes and binds to cancer cell surface antigens, facilitating internalization of the ADC. Once inside the cell, the ADC undergoes intracellular processing, leading to the release of the Duocarmycin payload.

Once released, the Duocarmycin payload exerts its cytotoxic effects by binding to DNA in the nucleus of the cancer cell. Duocarmycins are capable of binding to the minor groove of DNA, which is the narrow space between the DNA helix strands. This binding is highly specific and occurs in a sequence-dependent manner, with a preference for AT-rich sequences. Upon binding to DNA, the Duocarmycin induces irreversible alkylation of adenine at the N3 position. This alkylation disrupts the normal structure and integrity of the DNA molecule, leading to various downstream effects. The altered DNA structure hinders important cellular processes, such as DNA replication, transcription, and repair, ultimately causing DNA damage and cell death.

Figure 1. Chemical and biological processes for a duocarmycin-based ADC after internalization by cancer cells.
(Source: Yao, H. P. et al., 2021)