Tagworks has pioneered the use of in vivo click chemistry for the on-target actuation of prodrugs, antibody drugs, radiotherapeutics and imaging agents.

Tagworks invented the pyridazine elimination reaction, the only bioorthogonal cleavage reaction that is selective and fast enough for clinical use. This reaction underlies Tagworks’ Click-to-Release approach that is now widely applied in the selective on-target release and activation of a range of therapeutics, including antibody-drug conjugates and small molecule prodrugs.

Tagworks has a broad IP estate on Click-to-Release and Click-Conjugation technology & assets.

Antibody Drug Conjugates

Current antibody-drug conjugates (ADCs) target internalizing receptors on cancer cells leading to intracellular drug release via biological cleavage. Typically, only a subset of patients with solid tumors has sufficient expression of such a receptor, while there are sufficient suitable non-internalizing receptors and stroma targets.

Tagworks makes those targets amenable to ADC therapy through the Click-to-Release approach: the use of a click reaction (the pyridazine elimination reaction) for selective antibody-drug cleavage in vivo instead of relying on intracellular biological activation mechanisms. In this two-step approach, tumor binding of the ADC and blood clearance of the unbound fraction is followed by systemic administration of an activator that reacts with the ADC linker in the extracellular space of the tumor, leading to drug release in the tumor microenvironment and subsequent uptake into surrounding cancer cells as well as tumor supporting stromal cells.

Click-cleavable ADCs expand the target scope and, in contrast to the inherent variability that can hamper endogenous mechanisms, enable universal and direct temporal control over drug release in the tumor microenvironment. This will allow a more homogenous drug delivery, thus potentially improving therapeutic efficacy in heterogeneous or poorly penetrated tumors.

Companion Diagnostics

Antibodies have long been recognized as selective and effective biopharmaceuticals and there is a widespread interest in imaging these drugs during drug development or as a companion diagnostic in the clinic. As antibodies circulate for a long time, there is a clear need to increase the target-nontarget ratio for better image quality and to reduce the radiation dose to the patient.

Tagworks’ technology improves the effectiveness of radioimmunoimaging by “pretargeting”, which centers on target binding of a tagged antibody and clearance from blood followed by binding of a small, fast-clearing, radiolabeled probe to the tag of the target-bound antibody in a second step. Optionally, remaining freely circulating antibody is cleared to the liver by injection of a clearing agent prior to probe injection. The resulting superior target-blood ratios enable effective imaging at markedly lower radiation doses to the animal or patient.


Clearing agents are designed to rapidly bind to the tag of the freely circulating antibody, after which the clearing agent-antibody combination is rapidly cleared from blood via the liver. In addition to increasing the target-blood ratios in the context of pretargeting this approach also enables increased ratios when imaging radiolabeled antibodies. In this approach, the radiolabeled and tagged antibody is allowed to circulate and bind its target, and subsequently unbound antibody is directed to the liver,  improving image quality.


A.H.A.M. van OnzenR.M. VersteegenF.J.M. HoebenI.A.W. FilotR. RossinT. ZhuJ. WuP.J. HudsonH. M. JanssenW. ten HoeveM.S. Robillard; Bioorthogonal Tetrazine Carbamate Cleavage by Highly Reactive Trans-Cyclooctene, J. Am. Chem. Soc. 2020, 142, 25, 10955–10963doi: 10.1021/jacs.0c00531

R.M. Versteegen, W. ten Hoeve, R. Rossin M.A.R. de Geus, H.M. Janssen, M.S. Robillard; Click‐to‐Release from trans‐Cyclooctenes: Mechanistic Insights and Expansion of Scope from Established Carbamate to Remarkable Ether Cleavage, Angew. Chem. Int. Ed. 2018, 57, 10494 –10499. doi: 10.1002/anie.201800402

R. Rossin, R.M. Versteegen, J. Wu, A. Khasanov, H.J. Wessels, E.J. Steenbergen, W. ten Hoeve, H.M. Janssen, A.H.A.M. van Onzen, P.J. Hudson, M.S. Robillard; Chemically triggered drug release from an antibody-drug conjugate leads to potent antitumour activity in mice, Nature Comm. 2018, 9, 1484. doi:10.1038/s41467-018-03880-y

R. Rossin, S.M.J. van Duijnhoven, W. ten Hoeve, H.M. Janssen, L.H.J. Kleijn, F.J.M. Hoeben, R.M. Versteegen, M.S. Robillard; Triggered drug release from an antibody-drug conjugate  using fast “Click-to-release” chemistry in mice. Bioconj.Chem., 2016 27(7):1697-1706.  doi:10.1021/acs.bioconjchem.6b00231

S. van Duijnhoven, R. Rossin, S. van den Bosch, M. Wheatcroft, P. Hudson, M. Robillard; CC49 diabody pretargeting using click chemistry in vivo. J.Nucl.Med. 2015, 54, 1989–1995. doi:10.2967/jnumed.115.159145

R. Rossin and M.S. Robillard; Pretargeted imaging using bioorthogonal chemistry in mice. Current Opinion in Chemical Biology 2014, 21:161-169. doi/10.1016/j.cbpa.2014.07.023

R. Rossin, S.M.J. van Duijnhoven, T. Läppchen, S.M. van den Bosch, M.S. Robillard; Trans-cyclooctene tag with improved properties for tumor pretargeting with the Diels-Alder reaction. Mol. Pharmaceutics 2014, 11(9), 3090-3096. doi:10.1021/mp500275a

R.M. Versteegen, R. Rossin, W. ten Hoeve, H.M. Janssen, M.S. Robillard; Click to release: Instantaneous doxorubicin elimination upon tetrazine ligation. Angew. Chem. Int. Ed. 2013, 52, 14112–14116. doi:10.1002/anie.201305969

R. Rossin, T. Läppchen, S.M. van den Bosch, R. Laforest, M.S. Robillard; Diels-Alder reaction for tumor pretargeting: In vivo chemistry can boost tumor radiation dose compared with directly labeled antibody. J. Nucl. Med. 2013, 54, 11, 1989-1995. doi:10.2967/jnumed.113.12.3745

R. Rossin, S.M. van den Bosch, W. ten Hoeve, M. Carvelli, R.M. Versteegen, J. Lub, M.S. Robillard; Highly reactive trans-cyclooctene tags with improved stability for Diels-Alder chemistry in living systems. Bioconjug. Chem. 2013, 24, 7, 1210–1217. doi:10.1021/bc400153y

S.M. van den Bosch, R. Rossin, P. Renart Verkerk, W. ten Hoeve, H.M. Janssen, J. Lub, M.S. Robillard; Evaluation of strained alkynes for Cu-free click reaction in live mice. Nucl. Med. Biol. 2013, 40, 415-423. doi: 10.1016/j.nucmedbio.2012.12.006  

D.J. Vugts, A. Vervoort, M. Stigter-van Walsum, G.W.M. Visser, M.S. Robillard, R.M. Versteegen, R.C.M. Vulders, J.D.M. Herscheid, G.A.M.S. van Dongen; Synthesis of Phosphine and Antibody–Azide Probes for in Vivo Staudinger Ligation in a Pretargeted Imaging and Therapy Approach. Bioconjug. Chem. 2011, 22, 10, 2072–2081. doi: 10.1021/bc200298v

R. Rossin, P. Renart Verkerk, S.M. van den Bosch, R.C.M. Vulders, I. Verel, J. Lub, M.S. Robillard; In Vivo Chemistry for Pretargeted Tumor Imaging in Live Mice. Angew. Chem. Int. Ed. 2010, 49, 3375-3378. doi: 10.1002/anie.200906294; featured in Nature Nanotechnology 2010, 5, 384. doi:10.1038/nnano.2010.122

R. van Brakel, R.C.M. Vulders, R.J. Bokdam, H. Grüll, M.S. Robillard; A Doxorubicin Prodrug Activated by the Staudinger Reaction. Bioconjugate Chem. 2008, 19, 3, 714-718. doi: 10.1021/bc700394s