Antibody-drug Conjugates: A Comprehensive Guide

Antibody-drug conjugates (ADCs) are a potent combination of chemotherapy and immunotherapy. The concept was first proposed more than 100 years ago by German scientist Paul Ehrlich. He likens ADCs to "magic bullets" because they can specifically identify their targets (cancer cells) without harming the organism, much like "snipers." In recent years, with the continuous approval and marketing of ADCs, this kind of drug has become one of the hottest technology fields in the current global biotechnology drug research and development. So, why are ADCs so amazing? How do they achieve "precision guidance"? This article collects several FAQs of ADCs, including:


1. What are Antibody-drug Conjugates?

Antibody-drug conjugates (ADCs) are new biological drugs, which combine the high specificity of monoclonal antibody drugs with the high activity of small molecule cytotoxic drugs to improve the targeting of tumor drugs and reduce the toxic and side effects.


2. Antibody-drug Conjugates Structure

ADCs consist of three main parts: antibodies responsible for selectively recognizing cancer cell surface antigens, payloads responsible for killing cancer cells, and linker used to connect antibodies with Payloads.

the structure of ADCs

Fig.1 the structure of ADCs [1]


3. How do Antibody-drug Conjugates work?

First, the ADCs injected into the body bind to the target cell antigen after many obstacles, and the ADCs-antigen complex formed by it enters the cell through reticulin-mediated endocytosis. After the complex enters the cell, lysosome fusion with endosome causes linker cleavage in the cell, releasing and activating small molecule cytotoxic drugs. After the drug is released into cytoplasm, it can be inserted into DNA or inhibit microtubule polymerization, killing tumor cells and causing apoptosis of target cells. When the target cell dies, the active payloads may also kill the surrounding tumor cells, also known as Bystander effect.

the working mechanism of ADCs

Fig.2 the working mechanism of ADCs [1]


4. Antibody-drug Conjugates Components

4.1 Selection of Targets

The successful development of ADCs depends on the specific binding of antibodies to targets. The ideal targets of ADCs are high expression on the surface of tumor cells, low expression or no expression in normal cells, and minimizing toxicity of on-target and off-tumor. In addition to specificity and sufficient expression, the best target should also cause an efficient internalization effect.

Target antigens regulated from
driver oncogenes

Target antigens in the tumor
vasculature and stroma

Fig.3 Target for ADCs in development and in the clinic and developed

4.2 Selection of Antibodies

Antibodies should have high antigen affinity and long circulating half-life, so that they can specifically enrich cytotoxins in tumor sites. Considering the half-life, structural stability, Fc fragment immune function and coupling convenience of different IgG types antibodies, ADCs mostly choose IgG1 but seldom use IgG4. According to the immunogenicity of antibodies, they can be divided into fully humanized antibodies, humanized antibodies and chimeric antibodies. In order to reduce immune response, completely humanized or humanized antibodies are more selected.

4.3 Selection of Payloads

Toxin molecule (Payload) is the key factor for the success of ADCs research and development. Because ADCs have to go through multiple steps from entering human body to finally releasing cytotoxic agents, considering the efficiency of each step, payloads should have high anti-tumor activity, so toxic molecules with nanomolar level (IC50 value is 0.01-0.1 nM) are the appropriate payloads. In addition, payloads must have suitable functional groups that can be coupled, strong cytotoxicity, proper hydrophilic-hydrophobic balance, and high stability.

4.4 Selection of Linker

Linker, as the bridge of ADCs, connects with antibodies through cleavable connectors or non-cleavable connectors. Linker needs exquisite design, which not only needs stability to prevent chain breaking in the physiological state but also has the characteristics of high release efficiency in specific parts.


5. Advantages of Antibody-drug Conjugates

Compared with traditional completely or partially humanized antibodies or antibody fragments, ADCs have a higher theoretical curative effect because they can release highly active cytotoxins in tumor tissues. On the other hand, ADCs have a higher tolerance and lower side effects than fusion protein. They can accurately identify targets and not affect normal cells, which greatly improves the efficacy and reduces the toxic and side effects, so they have attracted the attention of people in the field of pharmaceutical research and development.


6. Do Antibody-drug Conjugates have any weaknesses?

The structure of ADCs is complex and the design is diversified, which brings difficulties to the production and quality control related to CMC research. At the same time, the superposition of ADCs and complex biological process in vivo also makes non-clinical research and clinical research face multiple challenges. Because the production of ADCs mostly involves highly active cytotoxic drugs, it requires high hardware equipment, process design and personnel training, and requires a large amount of capital investment and technical reserves, so the production threshold is high.

At present, there are three main challenges and opportunities in the development of ADCs:

6.1 Instability of Linker

This instability can lead to premature release of payload into blood, and lead to nonspecific uptake and miss-target toxicity of ADCs.

6.2 Nonspecific Endocytosis

Hydrophobicity will promote the aggregation and nonspecific endocytosis of ADCs, especially ADCs with high DAR (drug-antibody ratio), resulting in miss-target effect. ADCs with high DAR will also be cleared by other cells with nonspecific and strong endocytosis ability. So optimizing DAR is also an important strategy to improve TI (therapeutic index).

6.3 Receptor-mediated Uptake Mechanism

The off-target toxicity of ADC mediated by Fc γ Rs is mainly manifested in blood toxicity. Blood toxicity is the most common off-target dose-limiting toxicity (DLTs) of ADCs containing Auristatin (MAME, MMAF), Calicheamicin and Maytansinoid (DM-1).


7. FDA-approved Antibody-drug Conjugates

Among the ten ADCs approved for marketing, six of them are for the treatment of hematological tumors, and the others are for solid tumors (Table 1). At present, more than eighty ADCs are undergoing active clinical trials, most of which are in Phase I and Phase I/II. More than 80% of clinical trials are studying the safety and effectiveness of ADCs in various solid tumors, while the rest involve hematological malignant tumors. This indicates that following the success of T-DM1 early and the recent approval of sacituzumab govitecan and Loncastuximab tesirine, research on ADCs have gradually turned into the solid tumor in recent years.

Table1 FDA-approved ADCs

Drug Name Trade Name Company Target Payload Indications Approval year
Gemtuzumab ozogamicin Mylotarg Pfizer/Wyeth CD33 Calicheamicin AML 2000
2017
Brentuximab vedotin Adcetris Seattle Genetics, Millennium/Takeda CD30 MMAE cHL、sALCL、PTCL 2011
Trastuzumab emtansine Kadcyla Genentech/Roche HER2 DM1 mBC 2013
Inotuzumab ozogamicin Besponsa Pfizer/Wyeth CD22 Calicheamicin ALL 2017
Polatuzumab vedotin Polivy Genentech/Roche CD79b MMAE r/r DLBCL 2019
Enfortumab vedotin Padcev Astellas/Seattle Genetics Nectin-4 MMAE mUC 2019
Trastuzumab deruxtecan Enhertu AstraZeneca/ Daiichi Sankyo HER2 Dxd mBC、mGC 2019
Sacituzumab govitecan Trodelvy Immunomedics TROP2 SN-38 mTNBC 2020
Belantamab mafodotin Blenrep GlaxoSmithKline BCMA MMAF MM 2020
Loncastuximab tesirine Zynlonta ADC Therapeutics CD19 SG3199 r/r DLBCL 2021

ADCs have been continuously innovated and optimized since the concept of "biological missile" was put forward and have been greatly improved, making it one of the important means in the field of cancer treatment. As more and more ADCs enter the clinical stages, the industry is gradually shifting from traditional technologies to more innovative technologies to develop this complex product, which includes exploring new tumor antigens, new antibody structures, new payloads, new linkers and advanced coupling methods. With the in-depth study of ADCs, the molecular structure design of ADCs will be more reasonable, the uniformity will be greatly improved, and the stability in vivo will be continuously improved, thus reducing the toxic and side effects, improving the efficacy and activity, expanding the treatment window, and bringing new hope to tumor patients.


8. Hot Products

CUSABIO has developed a series of products with different species and tags for a variety of hot targets, which are suitable for immune, antibody screening, SPR, cell activity detection and other experiments. CUSABIO is committed to assisting you in drug development, and all activity test protocols are available for free. In addition, CUSABIO also provides related research antibodies and ELISA kits. If you don't find the targets you desired, you can leave message or chat to us by livechat.

Target Product Name Code Source Tag Info
ALCAM Recombinant Human CD166 antigen(ALCAM),partial CSB-EP614444HU E.coli N-terminal 6xHis-SUMO-tagged
ASGR1 Recombinant Human Asialoglycoprotein receptor 1(ASGR1),partial CSB-RP174694h E.coli N-terminal 6xHis-tagged
AXL Recombinant Human Tyrosine-protein kinase receptor UFO(AXL)(D266N),partial CSB-MP326981HU(M)d9 Mammalian cell C-terminal hFC-tagged
CA9 Recombinant Human Carbonic anhydrase 9(CA9), partial CSB-EP614990HUc0 E.coli N-terminal 6xHis-GST-tagged
CASP3 Recombinant Human Caspase-3(CASP3),partial,Escherichia Coli CSB-EP004548HU E.coli N-terminal 6xHis-tagged
CD19 Recombinant Human B-lymphocyte antigen CD19(CD19),partial CSB-CF004888HUc7 in vitro E.coli expression system C-terminal 6xHis-tagged
CD22In Stock Recombinant Human B-cell receptor CD22(CD22),partial (Active) CSB-MP004900HU Mammalian cell C-terminal 6xHis-tagged
CD276In Stock Recombinant Human CD276 antigen(CD276),partial (Active) CSB-MP733578HU Mammalian cell C-terminal hFc-Myc-tagged
CD33In Stock Recombinant Human Myeloid cell surface antigen CD33(CD33),partial (Active) CSB-MP004925HU Mammalian cell C-terminal hFc-Myc-tagged
CD46In Stock Recombinant Human Membrane cofactor protein(CD46) (Active) CSB-MP004939HU Mammalian cell C-terminal hFc-tagged
CD48 Recombinant Human CD48 antigen(CD48) (Active) CSB-MP004941HU Mammalian cell C-terminal hFc-tagged
CD70 Recombinant Human CD70 antigen(CD70),partial CSB-YP004954HU Yeast N-terminal 6xHis-tagged
CLDN18In Stock Recombinant Human Claudin-18.2(CLDN18.2)-VLPs (Active) CSB-MP005498HU(A5) Mammalian cell C-terminal 10xHis-tagged
DLK1 Recombinant Human Protein delta homolog 1(DLK1) ,partial CSB-MP006945HU Mammalian cell C-terminal Flag-Myc-tagged
DLL3In Stock Recombinant Human Delta-like protein 3(DLL3),partial (Active) CSB-MP882142HU Mammalian cell C-terminal 6xHis-tagged
DLL3In Stock Recombinant Macaca fascicularis Delta-like protein 3(DLL3),partial (Active) CSB-MP3536MOV Mammalian cell C-terminal 6xHis-tagged
EGFRIn Stock Recombinant Human Epidermal growth factor receptor(EGFR),partial (Active) CSB-MP007479HU Mammalian cell N-terminal 10xHis-tagged and C-terminal Myc-tagged
ERBB2In Stock Recombinant Human Receptor tyrosine-protein kinase erbB-2(ERBB2),partial (Active) CSB-MP007763HU Mammalian cell C-terminal 6xHis-tagged
ERBB3In Stock Recombinant Human Receptor tyrosine-protein kinase erbB-3(ERBB3),partial (Active) CSB-MP007765HU Mammalian cell C-terminal hFc-tagged
FOLH1 Recombinant Human Glutamate carboxypeptidase 2(FOLH1),partial CSB-EP008782HU E.coli N-terminal 6xHis-tagged
HAVCR1 Recombinant Human Hepatitis A virus cellular receptor 1(HAVCR1),partial CSB-MP010144HU Mammalian cell N-terminal 10xHis-tagged and C-terminal Myc-tagged
IGF1R Recombinant Human Insulin-like growth factor 1 receptor(IGF1R),partial CSB-MP011087HU Mammalian cell N-terminal 10xHis-tagged
KIT Recombinant Human Mast/stem cell growth factor receptor Kit(KIT),partial CSB-MP012375HU Mammalian cell C-terminal hFc-tagged
LY6E Recombinant Human Lymphocyte antigen 6E(LY6E) CSB-EP619076HU E.coli N-terminal 6xHis-SUMO-tagged
LY75 Recombinant Mouse Lymphocyte antigen 75(Ly75) ,partial CSB-EP013251MO E.coli N-terminal 6xHis-tagged
LYPD3 Recombinant Human Ly6/PLAUR domain-containing protein 3(LYPD3) CSB-EP013263HU E.coli N-terminal 10xHis-tagged
MET Recombinant Human Hepatocyte growth factor receptor(MET),partial (Active) CSB-MP013714HU Mammalian cell C-terminal hFc-tagged
MS4A1In Stock Recombinant Human B-lymphocyte antigen CD20(MS4A1)-VLPs (Active) CSB-MP015007HU Mammalian cell C-terminal 10xHis-tagged
MSLNIn Stock Recombinant Human Mesothelin(MSLN),partial (Active) CSB-MP015044HUc9 Mammalian cell N-terminal hFc-tagged
NCAM1 Recombinant Human Neural cell adhesion molecule 1(NCAM1),partial CSB-EP015511HU1 E.coli N-terminal 6xHis-tagged
NECTIN4In Stock Recombinant Human Nectin-4(NECTIN4),partial (Active) CSB-MP822274HU Mammalian cell C-terminal 10xHis-tagged
PRLR Recombinant Human Prolactin receptor(PRLR),partial CSB-MP018727HU1 Mammalian cell C-terminal FC-tagged
PROM1 Recombinant Human Prominin-1(PROM1),partial CSB-YP018751HU Yeast N-terminal 6xHis-tagged
PTK7 Recombinant Human Inactive tyrosine-protein kinase 7 (PTK7),partial CSB-YP622651HU Yeast N-terminal 6xHis-tagged
ROR1In Stock Recombinant Human Inactive tyrosine-protein kinase transmembrane receptor ROR1(ROR1),partial (Active) CSB-MP020067HU1d7 Mammalian cell C-terminal 10xHis-tagged
SDC1 Recombinant Human Syndecan-1(SDC1),partial CSB-EP020888HU E.coli N-terminal 6xHis-SUMO-tagged
SLC34A2 Recombinant Human Sodium-dependent phosphate transport protein 2B(SLC34A2),partial CSB-YP021581HU Yeast N-terminal 6xHis-tagged
TACSTD2In Stock Recombinant Human Tumor-associated calcium signal transducer 2(TACSTD2),partial (Active) CSB-MP023072HU1 Mammalian cell C-terminal hFc-tagged
TDGF1 Recombinant Human TeRatocarcinoma-derived growth factor 1(TDGF1),partial CSB-EP023343HU1e0 E.coli N-terminal GST-tagged
TNFIn Stock Recombinant Human Tumor necrosis factor(TNF),partial (Active) CSB-EP023955HUc7 E.coli C-terminal 6xHis-tagged
TNFRSF10BIn Stock Recombinant Human Tumor necrosis factor receptor superfamily member 10B(TNFRSF10B),Partial (Active) CSB-AP002291HU E.coli Tag-Free
TNFRSF17In Stock Recombinant Human Tumor necrosis factor receptor superfamily member 17(TNFRSF17),partial (Active) CSB-MP023974HU1 Mammalian cell C-terminal hFc-tagged
TNFSF8In Stock Recombinant Human Tumor necrosis factor ligand superfamily member 8(TNFSF8),partial (Active) CSB-MP023996HU1 Mammalian cell N-terminal 6xHis-tagged
TNFSF8In Stock Recombinant Human Tumor necrosis factor ligand superfamily member 8(TNFSF8),partial (Active) CSB-MP023996HU1c9 Mammalian cell N-terminal hFc-tagged
VTCN1 Recombinant Human V-set domain-containing T-cell activation inhibitor 1(B7H4),partial CSB-EP801822HUe0 E.coli N-terminal GST-tagged

References

[1] Abuhelwa Z, Alloghbi A, Nagasaka M. A comprehensive review on antibody-drug conjugates (ADCs) in the treatment landscape of non-small cell lung cancer (NSCLC)[J]. Cancer treatment reviews, 2022, 106.

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