Foreword
Antibody-Drug Conjugates (ADCs): Advancing Precision Cancer Therapy
Antibody-drug conjugates (ADCs) are one of the most promising modalities in the global oncology market. By combining the high specificity of monoclonal antibodies with the potent cytotoxicity of small-molecule drugs, ADCs aim to selectively eliminate tumor cells while minimizing systemic toxicity.
Despite their reputation as “magic bullets,” the clinical success of ADC drugs remains constrained by multiple biological and delivery challenges. Among these, antibody internalization via endocytosis has emerged as the central determinant of ADC efficacy—making quantitative internalization detection a critical requirement in ADC drug development.
ADC mechanisms: different toxicity loading mechanisms
Antibody-drug conjugates (ADCs) are innovative therapies that combine the advantages of antibody drugs and chemotherapy drugs. After intravenous administration, ADCs reach tumor tissue via the bloodstream. The antibody portion recognizes and binds to specific antigens highly expressed on the surface of tumor cells. Subsequently, the entire ADC-antigen complex is internalized into the cell. In an acidic environment such as lysosomes, the linker is cleaved, releasing the cytotoxic payload, which exerts its toxic effect, leading to cancer cell death. Some ADCs can also produce a "bystander effect," killing cells. The antibody portion may also retain the biological functions of the original antibody, such as inhibiting key signaling pathways or inducing immune responses to kill tumors.
Fig 1. Key structures and mechanisms of action of antibody-drug conjugates (ADCs)
Major ADC Payload Mechanisms Include:
(A) General mechanisms of action of ADCs;
(B) Mechanism of action of DNA inhibitors as ADC payloads;
(C) Mechanism of action of splicing inhibitors as ADC payloads;
(D) Mechanism of action of microtubule inhibitors as ADC payloads;
(E) Mechanism of action of PROTAC molecules as ADC payloads;
(F) Mechanism of action of Bcl-xL inhibitors and proteasome inhibitors as ADC payloads;
(G) Mechanism of action of NAMPT inhibitors as ADC payloads;
(H) Mechanism of action of near-infrared photoimmunotherapy (NIR-PIT) ADCs.
Delivery Challenges and opportunities in ADC Drug Development
Despite being hailed as "magic bullets" in cancer treatment, ADCs face significant delivery challenges in clinical application—approximately 99% of systemic administrations fail to reach the tumor site. This inefficient delivery stems from several obstacles: the limited time drugs spend in the bloodstream and their rapid clearance or breakdown by the liver and kidneys.
Most ADC targets are also expressed at low levels in normal tissues, potentially leading to off-target effects and impacting drug delivery.
The tumor microenvironment is the most significant factor limiting ADC delivery efficiency. First, the disordered vascular network causes uneven blood flow, increasing the difficulty of effective drug delivery.
Second, the abundance of extracellular matrix forming "binding site barriers" in tumor tissue causes ADC drugs to remain around blood vessels, making it difficult to reach cancer cells far from blood vessels.
However, the tumor microenvironment presents both challenges and opportunities. Some ADC designs leverage the acidic conditions and abundant proteases of the tumor microenvironment, using pH-sensitive or protease-sensitive linkers to release cytotoxic payloads within the tumor tissue, improving therapeutic specificity.
For example, Yilian Bio has developed the TMALIN™ (Tumor Microenvironment Activable LINKer-payload) platform. The B7-H3-targeting ADC drug YL201 developed by the TMALIN technology platform utilizes the dual extracellular and intracellular cleavage mechanism of "tumor microenvironment" and "traditional lysosomes" to effectively kill esophageal cancer tumor cells, and this has been validated in preclinical and clinical data.
Fig 2. Structure of YL201
However, the journey of ADC drugs is not without its challenges. Even with highly advanced delivery vehicles (such as microenvironment activation), endocytosis remains the key factor in the efficacy of ADCs in current drug delivery development and clinical applications. In ADC drug development, endocytosis only indicates potential drug activity but cannot support clinical decision-making. Therefore, quantitative detection of endocytosis is crucial. It transforms a complex biological phenomenon into measurable data. In the early stages of drug development, quantitative endocytosis detection can rapidly and objectively assess the endocytic capacity of each molecule. As preclinical research progresses, it can also provide visualized data models for dosage.
AlpVHHs Antibody Internalization Detection
AlpVHHs offers a new generation of nano-secondary antibody-drug conjugates linked to MMAE, MMAF, DM1, or Duocarmycin, etc for antibody internalization detection. Using Nano-secondary antibody-drug conjugates (nano-2°ADC) in a cell-based cytotoxic assay is a quick and economical alternative to pre-screening monoclonal antibodies as ADC candidates against tumor cells. Nano-2°ADCs are highly specific with minimally toxicity to cells in the absence of primary antibodies. No obvious change of the primary antibody activity in the presence of the unconjugated secondary antibody.
Code | Description | Application |
023-101-102 | Internalization Test | |
023-101-103 | Internalization Test | |
001-101-012 | Internalization Test | |
023-101-014 | Internalization Test | |
001-101-020 | Internalization Test | |
023-101-020 | Internalization Test |
Accelerate Your ADC Research with AlpVHHs
Quantitative endocytosis detection is no longer optional—it is essential for successful ADC development.
Learn more about AlpVHHs nanobody-based solutions for ADC internalization assays
