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"Click Chemistry" Holds Promise For Non-internalized ADC Applications

Release time:2022/8/16 18:05:07

"Click Chemistry" is a class of reactions involving the formation of carbon-heteroatom bonds, which are charact…

What is "Click Chemistry"?

The term "click chemistry" was first coined by Professor K. B. Sharpless of the Scripps Research Institute (2001 Nobel Laureate in Chemistry). It is a class of reactions involving the formation of carbon-heteroatom bonds, which are characterized by high yield and selectivity.

Bioorthogonal click chemistry can be performed in living systems without interfering with normal life activities. Over the past two decades, bioinorganic and medicinal chemists have increasingly used this chemical approach, especially in the development of targeted drugs, such as antibody-drug conjugates (ADCs).

What are the characteristics of "click chemistry"?

1. The chemical yield of the target product is very high.

2. It is a combination of simple and easily available structural fragments.

3. Almost no by-products are generated.

4. Product separation process is simple, no need to use chromatography for separation.

5. The reaction can be carried out in water and organic solvents.

Examples of early applications of "click chemistry"

Click chemistry was first used for tracing, because some in vitro methods of labelling reinjection are not fully effective and may also cause rejection.

In the figure below, if we want to study the distribution and changes of SiaNAz (a sugar on the surface of cells) in vivo, we need to trace it. The operation of click chemistry is as follows: Ac4ManNAz can be converted into SiaNAz in vivo. The researchers added an N3 group (azide group) to the former, and then injected AC4MannaZ-N3 into mice. A few days later, the mice were injected with a FLAG-labeled molecule, which carried a group that could react with N3 group (alkynyl group). When the molecule met SiaNAz in the process of metabolism in vivo, it will "click" like the buckle of a safety belt, and the FLAG will be carried to our sugar molecules by chemical reactions, thus achieving the effect of tracing (and because N3 is so small, it won't affect the bioconversion process of sugar molecules).

 Copper-free click chemistry in living animals.png

Copper-free click chemistry in living animals, PNAS, 2010, 5, 1821-1826.
Source: Carolyn R. Bertozzi et al.

Application of click chemistry in ADC field

The application of click chemistry in the field of ADC is still in the clinical stage, and there are not many research and development companies. It belongs to an emerging field, but according to the current efficacy, it is very worth exploring.

bioorthogonal chemistry for ADC preparation.png

Biotech companies that use bioorthogonal click chemistry to prepare ADCs

Source: Nat Biotechnol. 2019 Aug;37(8):835-837.

1. Cleavage of non-internalized ADCs by click chemistry

Tagworks Pharmaceuticals is developing a bioorthogonal click chemistry strategy to overcome some of the shortcomings of ADCs in targeting solid tumors. Traditional antibody-drug conjugates (ADCs) target internalized receptors on cancer cells, resulting in drug release by intracellular cleavage of linkers. However, only a subset of patients with solid tumors have adequate expression of specific internalizing receptors.

Based on this, Tagworks Pharmaceuticals has developed a Click-to-Release approach to make non-internalized targets applicable to ADC therapeutics: ADC targets non-internalized receptors, which contain a connector that can only be destroyed by bioorthogonal chemical click reaction. When the ADC is enriched around tumor cells, systemic administration of an activator reacts with the ADC linker outside the tumor cell, resulting in drug release in the tumor microenvironment and subsequent uptake into surrounding cancer cells and tumor-supporting stromal cells for action.

ADCs cleaved by click chemistry have expanded their use, enabling pervasive and direct temporal control of drug release in the tumor microenvironment. This would allow for more uniform drug delivery, potentially improving the therapeutic effect of heterogeneous or poorly penetrating tumors.

 cleave non-internalized-ADCs.png

Tagworks Pharmaceuticals uses click chemistry to cleave non-internalized ADCs

2. Tagworks: A Chemically-cleavable ADC for TAG72 Targets

Tumor-associated glycoprotein 72 (TAG72) is a non-internalized target that is widely expressed in a range of human adenocarcinomas of epithelial origin, such as breast, colorectal, gastric, lung, pancreatic, prostate, and ovarian cancers. Tagworks is developing click-cleavable anti-TAG72 ADCs based on antibody fragment types, conjugated to the anti-mitotic agent MMAE.

The activator is administered 1-3 days later, thereby rapidly releasing MMAE in the tumor microenvironment and spreading into surrounding tumor cells, maximizing the bystander effect.

A dual-antibody-based anti-TAG72 ADC showed potent antitumor efficacy in mice with colorectal and ovarian cancer xenografts without detectable toxicity. In contrast, similar ADC controls with valine-citrulline linker were less effective in these models.

Chemically-cleavable ADC.png

"Chemically-cleavable ADC + activator" has significant efficacy and long survival

3. Shasqi Bio: CAPAC™ Platform--SQ3370  (Click Activated Protodrugs Against Cancer)

Shasqi, from San Francisco, California, is also working on bioorthogonal chemical click reactions in patients with the Click Activated Protodrugs Against Cancer (CAPAC™) platform, a way to activate cancer drugs at the tumor site and reduce systemic toxicity. Shasqi is clinically validating the efficacy of its platform by using SQ3370, which also marks the first time that click chemistry has been performed in a patient.

The researchers locally injected an alginate hydrogel modified with a chemical click handle (tetrazine) at the tumor site, followed by intravenous injection of a prodrug with a complementary handle (for example, trans-cyclooctene-modified doxorubicin). The prodrug is stable in vivo and has little activity until it is metabolically contacted with the hydrogel, at which point a chemical click reaction occurs, thereby releasing the drug. This reduces off-target exposure and enables very high local doses of the drug.

 CAPAC platform.png

Click Activated Protodrugs Against Cancer (CAPAC™) platform

Source: ACS Cent Sci. 2016 Jul 27;2(7):476-82.

After treatment monitoring in the xenograft model over 100 days, the median tumor size of the doxorubicin prodrug cohort remained unchanged and both were undetectable (P = 0.021), while the control group rebounded rapidly at day 50. At the same time, the body weight of the doxorubicin prodrug group has been at a stable level, while the body weight of the control group mice has been declining with the treatment time.


doxorubicin pro-drug.png

Therapeutic effect of doxorubicin prodrug in soft tissue sarcoma xenograft model


“Click Chemistry" has many different forms of application in the field of ADCs, all of which are highly effective and are at an early stage of research, and it relies on reactions that can operate in the organism without disrupting biochemical processes, and has a wide application potential.

Huateng Pharma is a leading CDMO for PEG derivatives and pharmaceutical intermediates which can meet customers’ needs from lab research to pilot plant to large sacle commercial production. We supply a variety of PEG reagents for click chemistry reaction.



[1] Click chemistry targets antibody-drug conjugates for the clinic

[2] Copper-free click chemistry in living animals

[3].In Vivo Bioorthogonal Chemistry Enables Local Hydrogel and Systemic Pro-Drug To Treat Soft Tissue Sarcoma

[4]  In vivo bioorthogonal chemistry enables local hydrogel and systemic pro-drug to treat soft tissue sarcoma

Related articles:

[1] Antibody-Drug Conjugates for Cancer Therapy - Prospects and Challenges

[2] ADC Linker - Development and Challenges