In the development of ADCs (Antibody-Drug Conjugates), internalization efficiency is one of the key factors determining drug efficacy.
Accurately assessing whether antibodies or ADC molecules can be effectively internalized by target cells is a crucial step in antibody screening and drug development.
Currently, the mainstream ADC internalization detection methods mainly fall into two categories:
● Detection methods based on pH-sensitive fluorescent probes
● Functional indirect detection methods based on toxin conjugation
These two methods each have their advantages:
● If the research focus is on the efficiency of antibody uptake by cells, pH-sensitive probe detection is recommended.
● If the research focus is on whether cytotoxicity occurs after internalization, toxin conjugation detection is considered the gold standard in the industry.
This article will systematically analyze ADC internalization detection methods, principles, differences, and application recommendations.
This method uses pH-sensitive fluorescent dyes to label antibodies or detection probes. When an ADC enters a cell and is internalized into endosomes or lysosomes, the fluorescent dye is activated due to the acidic environment (pH 4.5-6.0) of these organelles, resulting in a significant enhancement of the fluorescence signal. Researchers can assess the internalization efficiency of antibodies or ADCs by detecting the fluorescence signal.
● Flow Cytometry (FACS)
● High-Content Imaging System
● IncuCyte Real-Time Cell Imaging
● Confocal Microscopy
Fig 1: Schematic diagram of pH-sensitive probe detection of ADC internalization
Advantages:
● Real-time detection of endocytosis
● Strong quantitative capability (can obtain indicators such as MFI)
● Suitable for high-throughput screening
● Can observe subcellular localization
Applications:
● Early screening of ADCs
● Evaluation of antibody endocytosis ability
● Cell localization studies
This method indirectly reflects endocytosis efficiency by conjugating antibodies to toxin fragments and utilizing the cytotoxic effect of the toxin after entering the cell. Common toxins include:
● Saporin
● Diphtheria toxin fragment
● Tubulin inhibitor
● DNA Topoisomerase I inhibitor
● PBD toxins
When antibodies are endocytosed by cells, toxins are released and act on the cells, ultimately leading to decreased cell viability or cell death. Researchers can assess the endocytic capacity and functional killing effect of antibodies by detecting changes in cell viability. Common detection methods include:
● CTG (CellTiter-Glo)
● CCK-8 cell viability assay
Fig 2: Schematic diagram of indirect detection of toxin coupled with ADC endocytosis
Advantages:
● Directly reflects functional killing effect
● Closer to the mechanism of real ADC drugs
● Widely adopted in industry
Applications:
● ADC functional verification
● Toxin selection
● DAR optimization
Detection Methods | Core Principles | Main Technologies | Key Advantages | Main Limitations | Most Suitable Application |
1. Imaging | ADCs carry pH-sensitive dyes, which enhance or quench fluorescence upon entering acidic endosomes/lysosomes. | High-content/confocal imaging. | Intuitive, quantifiable, technologically mature, and with standardized procedures. | Requires optimization of dye labeling concentration; uneven labeling, etc. | Fast and intuitive comparison of the endocytosis efficiency of different candidate drugs. |
2. FACS | Flow cytometry | High throughput | Curious operation, not very intuitive. | Early screening of drug endocytosis activity. | |
3. Killing | ADCs are coupled with inactive "protoxins," which release active toxins in lysosomes after endocytosis, indirectly reflecting cell viability changes. | Cell viability detection (e.g.,CCK-8, CellTiter-Glo). | The final result of detecting functional endocytosis is directly related to downstream drug efficacy. | Indirect detection method; it is time-consuming; and it is subject to cytotoxic background interference. | Assessing the functional killing effect caused by endocytosis serves as a preliminary screening or validation of drug efficacy. |
Flow cytometry based on pH-sensitive probes is the most efficient and cost-effective option.
● Firstly, in terms of quantification and throughput: When used with flow cytometry, it can rapidly analyze tens of thousands of cells, providing accurate quantitative data such as mean fluorescence intensity (MFI), facilitating statistical comparison and screening.
● Secondly, in terms of visualization: When it is necessary to observe the subcellular localization of endocytosed drugs (e.g., co-localization with lysosomes), it can be combined with high-content imaging or confocal microscopy for direct, quantitative measurement and observation, which is the most intuitive and scientific choice. It is also suitable for 96- or 384-well plate modes, meeting the needs of large-scale screening.
Using improved toxin-coupled detection reagents, the functional killing effect caused by internalization can be evaluated simultaneously in one step, which is also the gold standard for detecting drug internalization in industry.
AlpVHHs utilizes second-generation Yeast Surface Display technology to develop high-affinity nanobodies, providing researchers with a variety of ADC internalization detection tools. These tools are widely used in:
● Immunoprecipitation (IP)
● Immunofluorescence (IF)
● Super-resolution imaging
● Cell sorting
● Antibody internalization detection
Compared to traditional antibody, nanobody/VHH antibody offers advantages such as low interference and high stability.
● Diverse Product Range: AlpVHHs has developed, produced, and sold multiple categories of reagents for endocytosis, including toxins with different mechanisms, such as microtubule inhibitors, DNA topoisomerase I inhibitors, and PBD inhibitors; as well as pH-sensitive fluorescent probe reagents such as pH630 and pH600.
● Wide Range of Applications: Endocytosis reagents are suitable for various detection methods, including FACS, imaging, and endpoint-based cell viability assays.
● Core Advantage (Ⅰ): Overcomes the problems of large molecular weight and heterogeneous polyclonal recognition sites in traditional secondary antibody reagents, minimizing the impact of detection reagents on antibody function evaluation.
● Core Advantage (Ⅱ): Employs a site-specific conjugation method to couple a fixed number (nanobody reagent ratio 1:2) of toxins/fluorescence onto nanobodies, ensuring scientifically reliable quantitative endocytosis detection results.
● Core Advantage (Ⅲ): Using nanobodies targeting different sites (H chain, L chain) of antibodies, by combining and conjugating toxins with different mechanisms, we can evaluate the functional killing effect caused by different DAR values and different toxins after endocytosis, and assist in screening the optimal DAR value and conjugation site of the toxin.
Fig 3. Mechanism diagram of a partial product for critical point ADC internalization detection
In ADC drug development, selecting the appropriate endocytosis detection method is crucial:
● Early antibody screening
● Evaluation of endocytosis efficiency
● High-throughput experiments
● Functional validation
● ADC killing effect assessment
● DAR optimization studies
Nanobody internalization detection reagents from AlpVHHs, with their advantages of accurate quantification, low interference, and flexible application, have become important research tools for many pharmaceutical companies.
In the future, we will combine experimental data to further demonstrate the performance advantages of ADC internalization detection products.
Code | Description | Application |
023-101-101 | Internalization Test | |
023-101-111 | Internalization Test | |
023-102-101 | Internalization Test | |
023-102-111 | Internalization Test | |
023-101-102 | Internalization Test | |
023-101-112 | Internalization Test | |
023-102-102 | Internalization Test | |
023-101-112 | Internalization Test | |
023-102-112 | Internalization Test | |
023-101-104 | Internalization Test |
Code | Description | Application |
023-102-012 | Internalization Test | |
023-102-014 | Internalization Test | |
023-101-014 | Internalization Test | |
001-101-014 | Internalization Test | |
001-101-013 | Internalization Test | |
023-101-013 | Internalization Test | |
023-101-012 | Internalization Test | |
001-101-012 | Internalization Test | |
APK021 | Internalization Test | |
APK022 | Internalization Test |
