Antibody–drug conjugates (ADC) are one of the fastest growing anticancer drugs. This approach comprises a mAb conjugated to the cytotoxic payload via a chemical linker that directed toward a target antigen expressed on the cancer cell surface, reducing systemic exposure and therefore toxicity. ADCs are complex molecules that require careful attention to various components. Selection of an appropriate target, an mAb, cytotoxic payload, and the manner in which the antibody is linked to the payload are key determinants of the safety and efficacy of ADCs. This review provides an overview of the systemic evaluation of each component of an ADC design, improved understanding of the mechanism of action of ADC, and mechanistic pathways involved in ADC resistance and various strategies to optimize ADC design. Moreover, this review also shed light on the current status of ADCs that have gained regulatory approval from the FDA including a description of biology and chemistry, metabolic profiles, adverse events, drug interactions, and the future perspective on combination strategies with other agents, including immunotherapy.

Nitric oxide (NO) has a wide range of potential applications in tumor therapy. However, a targeted delivery system for NO donors has remained elusive, creating a bottleneck that limits its druggability. The antibody–drug conjugate (ADC) is a targeted drug delivery system composed of an antibody linked to an active cytotoxic drug. This design may compensate for the weak targeting ability and various biological functions of the NO donor. In this study, we designed the NO donor HL-2, which had a targeted, cleaved disulfide bond and an attachable maleimide terminal. We conjugated HL-2 with an antibody that targeted CD24 through a thioether bond to generate an ADC-like immunoconjugate, antibody-nitric oxide conjugate (ANC), which we named HN-01. HN-01 showed efficient internalization and significantly increased the release of NO in hepatic carcinoma cells in vitro. HN-01 induced apoptosis of tumor cells and suppressed tumor growth in hepatic carcinoma-bearing nude mice through antibody-dependent co-toxicity; HN-01 also increased NO levels in tumor cells. Collectively, this study expands the concept of ADC and provides an innovative NO donor and ANC to address current challenges in targeted delivery of NO. This new inspiration for an ANC design can also be used in future studies for other molecules with intracellular targets.Significance: This study is the first to expand the concept of ADC with an antibody-nitric oxide conjugate that suppresses hepatic carcinoma in vitro and in vivo.

B-cell maturation antigen (BCMA) is a highly plasma cell-selective protein expressed on malignant plasma cells of patients with multiple myeloma (MM), and it is a defined therapeutic target. Major histocompatibility complex class I-related chain A (MICA) is frequently expressed in lymphoproliferative malignancies including MM. MICA activates natural killer (NK) cells and costimulates T cells by interaction with its immunoreceptor NK cell receptor G2D (NKG2D). Nonetheless, during full-blown MM, tumor cells promote efficient MICA shedding, which evokes NKG2D internalization and immune suppression. To enhance the directional killing efficacy of immune cells against myeloma cells, we constructed a novel bispecific antibody 2A9-MICA and explored its potential antimyeloma activity against MM. 2A9-MICA consists of human MICA extracellular region and a single–chain antibody fragment (scFv) that targets BCMA generated by phage display technology. In vitro, 2A9-MICA activated NK cell-mediated cytotoxicity and induced NK cells to kill BCMA–positive human myeloma cells. Moreover, in BCMA-positive, MM-bearing nude mice, 2A9-MICA specifically targeted tumor tissue, where it effectively recruited immune cells and inhibited tumor tissue growth showed superior antitumor activity. Taken together, bispecific antibody 2A9-MICA provides a new approach for MM-targeting immunotherapy and has attractive potential for clinical applications.