Name: synthesis and bioconjugation of thiol-reactive reagents for the creation of site-selectively modified immunoconjugates
Uploaded: 2019-03-06T14:30:00
Description: Watch this Scientific Journal Video about Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates at JoVE.com

The authors thank Dr. Sai Kiran Sharma for helpful conversations.

1. The synthesis of 4-[5-(methylthio)-1,3,4-oxadiazol-2-yl]-aniline (1)
NOTE: Due to the light-sensitivity of the compound, keep all reactions in foil-covered vessels.
<ol>
	<li>In a 10 mL round bottom flask, dissolve 100 mg (0.517 mmol, 1 equivalent) of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol in 3 mL of methanol.</li>
	<li>To this solution, add 360 &#956;L of diisopropylethylamine (DIPEA; 2.07 mmol; 4 equivalents; anhydrous) and a small magnetic stir bar. Cover the flask with a rubber st...

<ol>
	<li>Wu, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibodies+and+antimatter:+The+resurgence+of+immuno-PET.">Antibodies and antimatter: The resurgence of immuno-PET.</a> Journal of Nuclear Medicine. 50 (1), 2-5 (2009).</li><li>Zeglis, B. M., Lewis, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+practical+guide+to+the+construction+of+radiometallated+bioconjugates+for+positron+emission+tomography.">A practical guide to the construction of radiometallated bioconjugates for positron emission tomography.</a> Dalton Transactions. 40 (23), 6168-6195 (2011).</li><li>Agarwal, P., Bertozzi, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specific+antibody-drug+conjugates:+the+nexus+of+bioorthogonal+chemistry,+protein+engineering,+and+drug+development.">Site-specific antibody-drug conjugates: the nexus of bioorthogonal chemistry, protein engineering, and drug development.</a> Bioconjugate Chemistry. 26 (2), 176-192 (2015).</li><li>Adumeau, P., Sharma, S. K., Brent, C., Zeglis, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specifically+labeled+immunoconjugates+for+molecular+imaging-part+1:+Cysteine+residues+and+glycans.">Site-specifically labeled immunoconjugates for molecular imaging-part 1: Cysteine residues and glycans.</a> Molecular Imaging and Biology. 18 (1), 1-17 (2016).</li><li>Adumeau, P., Sharma, S. K., Brent, C., Zeglis, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specifically+labeled+immunoconjugates+for+molecular+imaging-part+2:+Peptide+tags+and+unnatural+amino+acids.">Site-specifically labeled immunoconjugates for molecular imaging-part 2: Peptide tags and unnatural amino acids.</a> Molecular Imaging and Biology. 18 (1), 153-165 (2016).</li><li>Alley, S. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contribution+of+linker+stability+to+the+activities+of+anticancer+immunoconjugates.">Contribution of linker stability to the activities of anticancer immunoconjugates.</a> Bioconjugate Chemistry. 19 (3), 759-765 (2008).</li><li>Baldwin, A. D., Kiick, K. 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Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conjugation+site+modulates+the+in+vivo+stability+and+therapeutic+activity+of+antibody-drug+conjugates.">Conjugation site modulates the in vivo stability and therapeutic activity of antibody-drug conjugates.</a> Nature Biotechnology. 30 (2), 184-189 (2012).</li><li>Jackson, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+and+in+vivo+evaluation+of+cysteine+and+site+specific+conjugated+herceptin+antibody-drug+conjugates.">In vitro and in vivo evaluation of cysteine and site specific conjugated herceptin antibody-drug conjugates.</a> Plos One. 9 (1), (2014).</li><li>Ponte, J. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+how+the+stability+of+the+thiol-maleimide+linkage+impacts+the+pharmacokinetics+of+lysine-linked+antibody-maytansinoid+conjugates.">Understanding how the stability of the thiol-maleimide linkage impacts the pharmacokinetics of lysine-linked antibody-maytansinoid conjugates.</a> Bioconjugate Chemistry. 27 (7), 1588-1598 (2016).</li><li>Stimmel, J. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specific+conjugation+on+serine+-&gt;+cysteine+variant+monoclonal+antibodies.">Site-specific conjugation on serine -&gt; cysteine variant monoclonal antibodies.</a> Journal of Biological Chemistry. 275 (39), 30445-30450 (2000).</li><li>Li, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduction+of+kidney+uptake+in+radiometal+labeled+peptide+linkers+conjugated+to+recombinant+antibody+fragments.+site-specific+conjugation+of+DOTA-peptides+to+a+cys-diabody.">Reduction of kidney uptake in radiometal labeled peptide linkers conjugated to recombinant antibody fragments. site-specific conjugation of DOTA-peptides to a cys-diabody.</a> Bioconjugate Chemistry. 13 (5), 985-995 (2002).</li><li>Li, J., Wang, X. H., Wang, X. M., Chen, Z. 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N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specifically+Zr-89-labeled+monoclonal+antibodies+for+ImmunoPET.">Site-specifically Zr-89-labeled monoclonal antibodies for ImmunoPET.</a> Nuclear Medicine and Biology. 37 (3), 289-297 (2010).</li><li>Li, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specific+conjugation+of+monodispersed+DOTA-PEGn+to+a+thiolated+diabody+reveals+the+effect+of+increasing+PEG+size+on+kidney+clearance+and+tumor+uptake+with+improved+64-copper+PET+imaging.">Site-specific conjugation of monodispersed DOTA-PEGn to a thiolated diabody reveals the effect of increasing PEG size on kidney clearance and tumor uptake with improved 64-copper PET imaging.</a> Bioconjugate Chemistry. 22 (4), 709-716 (2011).</li><li>Khalili, H., Godwin, A., Choi, J. -. w., Lever, R., Brocchini, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+binding+of+disulfide-bridged+PEG-Fabs.">Comparative binding of disulfide-bridged PEG-Fabs.</a> Bioconjugate Chemistry. 23 (11), 2262-2277 (2012).</li><li>Koniev, O., Wagner, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developments+and+recent+advancements+in+the+field+of+endogenous+amino+acid+selective+bond+forming+reactions+for+bioconjugation.">Developments and recent advancements in the field of endogenous amino acid selective bond forming reactions for bioconjugation.</a> Chemical Society Reviews. 44 (15), 5495-5551 (2015).</li><li>Patterson, J. T., Asano, S., Li, X., Rader, C., Barbas, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improving+the+serum+stability+of+site-specific+antibody+conjugates+with+sulfone+linkers.">Improving the serum stability of site-specific antibody conjugates with sulfone linkers.</a> Bioconjugate Chemistry. 25 (8), 1402-1407 (2014).</li><li>Toda, N., Asano, S., Barbas, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid,+stable,+chemoselective+labeling+of+thiols+with+Julia-Kocienski-like+reagents:+A+serum-stable+alternative+to+maleimide-based+protein+conjugation.">Rapid, stable, chemoselective labeling of thiols with Julia-Kocienski-like reagents: A serum-stable alternative to maleimide-based protein conjugation.</a> Angewandte Chemie-International Edition. 52 (48), 12592-12596 (2013).</li><li>Zhang, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Last-step+enzymatic+F-18-fluorination+of+cysteine-tethered+RGD+peptides+using+modified+Barbas+linkers.">Last-step enzymatic F-18-fluorination of cysteine-tethered RGD peptides using modified Barbas linkers.</a> Chemistry-a European Journal. 22 (31), 10998-11004 (2016).</li><li>Chiotellis, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+chemoselective+F-18-radiolabeling+of+thiol-containing+biomolecules+under+mild+aqueous+conditions.">Novel chemoselective F-18-radiolabeling of thiol-containing biomolecules under mild aqueous conditions.</a> Chemical Communications. 52 (36), 6083-6086 (2016).</li><li>Adumeau, P., Davydova, M., Zeglis, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thiol-reactive+bifunctional+chelators+for+the+creation+of+site-selectively+modified+radioimmunoconjugates+with+improved+stability.">Thiol-reactive bifunctional chelators for the creation of site-selectively modified radioimmunoconjugates with improved stability.</a> Bioconjugate Chemistry. 29, 1364-1372 (2018).</li><li>Sakamoto, J., Kojima, H., Kato, J., Hamashima, H., Suzuki, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organ-specific+expression+of+the+intestinal+epithelium-related+antigen+A33,+a+cell+surface+target+for+antibody-based+imaging+and+treatment+in+gastrointestinal+cancer.">Organ-specific expression of the intestinal epithelium-related antigen A33, a cell surface target for antibody-based imaging and treatment in gastrointestinal cancer.</a> Cancer Chemotherapy and Pharmacology. 46, S27-S32 (2000).</li><li>Sakamoto, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+phase+I+radioimmunolocalization+trial+of+humanized+monoclonal+antibody+huA33+in+patients+with+gastric+carcinoma.">A phase I radioimmunolocalization trial of humanized monoclonal antibody huA33 in patients with gastric carcinoma.</a> Cancer Science. 97 (11), 1248-1254 (2006).</li><li>Junutula, J. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specific+conjugation+of+a+cytotoxic+drug+to+an+antibody+improves+the+therapeutic+index.">Site-specific conjugation of a cytotoxic drug to an antibody improves the therapeutic index.</a> Nature Biotechnology. 26 (8), 925-932 (2008).</li><li>Pillow, T. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specific+trastuzumab+maytansinoid+antibody-drug+conjugates+with+improved+therapeutic+activity+through+linker+and+antibody+engineering.">Site-specific trastuzumab maytansinoid antibody-drug conjugates with improved therapeutic activity through linker and antibody engineering.</a> Journal of Medicinal Chemistry. 57 (19), 7890-7899 (2014).</li><li>Boswell, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+tumor+retention+of+a+radiohalogen+label+for+site-specific+modification+of+antibodies.">Enhanced tumor retention of a radiohalogen label for site-specific modification of antibodies.</a> Journal of Medicinal Chemistry. 56 (23), 9418-9426 (2013).</li><li>Boswell, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+drug+conjugation+on+pharmacokinetics+and+tissue+distribution+of+anti-STEAP1+antibody-drug+conjugates+in+rats.">Impact of drug conjugation on pharmacokinetics and tissue distribution of anti-STEAP1 antibody-drug conjugates in rats.</a> Bioconjugate Chemistry. 22 (10), 1994-2004 (2011).</li><li>Alvarez, V. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specifically+modified+111In+labelled+antibodies+give+low+liver+backgrounds+and+improved+radioimmunoscintigraphy.">Site-specifically modified 111In labelled antibodies give low liver backgrounds and improved radioimmunoscintigraphy.</a> Nuclear Medicine and Biology. 13 (4), 347-352 (1986).</li><li>Strop, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Location+matters:+SIte+of+conjugation+modulates+stability+and+pharmacokinetics+of+antibody+drug+conjugates.">Location matters: SIte of conjugation modulates stability and pharmacokinetics of antibody drug conjugates.</a> Chemistry, Biology. 20 (2), 161-167 (2013).</li><li>Hallam, T. J., Wold, E., Wahl, A., Smider, V. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibody+conjugates+with+unnatural+amino+acids.">Antibody conjugates with unnatural amino acids.</a> Molecular Pharmaceutics. 12 (6), 1848-1862 (2015).</li><li>Axup, J. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+site-specific+antibody-drug+conjugates+using+unnatural+amino+acids.">Synthesis of site-specific antibody-drug conjugates using unnatural amino acids.</a> Proceedings of the National Academy of Sciences. 109 (40), 16101-16106 (2012).</li><li>Lang, K., Chin, J. 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In this report, we have chosen not to include any protocols for radiolabeling or in vivo experimentation. Our reasons are straightforward. With respect to the former, the radiolabeling of a PODS-based immunoconjugate does not differ at all from that of an immunoconjugate synthesized using other bioconjugation strategies, and these procedures have been comprehensively reviewed elsewhere2. With regard to the latter, the specifics of preclinical in vivo experiments (i.e., mouse models, doses, etc.) c...

Radiopharmaceutical chemists have long exploited the selectivity and specificity of antibodies for biomarkers of disease for both nuclear imaging and targeted radiotherapy1. Far and away the most common approach to the radiolabeling of antibodies is predicated on the indiscriminate attachment of radiolabeled prosthetic groups or radiometal chelators to amino acids &#8212; most often lysines &#8212; within the structure of the immunoglobulin (Figure 1A)2. While this strategy is certainly effective, its random, non-site-specific nature can create problems. Specifically, traditional bioconjugation approaches produce poorly-defined and heterogeneous immunoconjugates composed of mixtures of thousands of different regioisomers, each with its own set of biological and pharmacological properties3. Furthermore, random bioconjugation can impede the immunoreactivity of antibodies if the cargo is appended to the immunoglobulin&#8217;s antigen-binding domains.
Over the years, a variety of site-specific and site-selective bioconjugation strategies have been developed in order to address these problems4,5. The most common of these approaches relies on the ligation of maleimide-bearing probes to the sulfhydryl groups of cysteines (Figure 1B). IgG1 antibodies naturally contain 4 inter-chain disulfide bridges, linkages that can be selectively reduced to yield free thiols capable of undergoing Michael addition reactions with maleimides to form succinimidyl thioether bonds. The use of thiols and maleimides is certainly an improvement over traditional methods, and a wide variety of maleimide-bearing synthons and bifunctional chelators are currently available. However, it is important to note that this methodology has serious limitations as well. Maleimide-based immunoconjugates exhibit limited stability in vivo because the thioether linkage can undergo a retro-Michael reaction (Figure 2)6,7,8,9,10. This, of course, can lead to the release of the radioactive payload or its exchange with thiol-bearing biomolecules in circulation (e.g., glutathione or serum albumin). Both of these processes can increase activity concentrations in healthy organs as well as decrease activity concentrations in target tissues, resulting in reduced imaging contrast and lower therapeutic ratios. Several alternative thiol-reactive reagents have been developed in an effort to circumvent these issues, including tosylates, bromo- and iodo-acetyls, and vinyl sulfones11,12,13,14,15,16,17. However, all of these approaches have limitations that have hampered their widespread application.
About five years ago, the laboratory of the late Carlos Barbas III at Scripps Research Institute pioneered the use of phenyloxadiazolyl methyl sulfones as reagents for the selective formation of highly stable linkages with thiols (Figure 1C and Figure 3)18,19. The authors employed a phenyloxadiazolyl methyl sulfone-bearing variant of fluorescein to modify several antibodies engineered to contain free cysteine residues, ultimately producing immunoconjugates with higher stability than analogous constructs created using maleimide-based probes. Upon seeing this promising work, we were somewhat surprised that this technology had only been used scarcely in radiochemistry and had not yet been used at all in the synthesis of bifunctional chelators or radioimmunoconjugates20,21. This dearth of applications, however, soon began to make more sense: several attempts at procuring the reagent from Sigma-Aldrich resulted in the receipt of complex mixtures of degradation products with &#60;15% of the desired compound. In addition, synthesizing the reported reagent ourselves was not a realistic option either, as the published synthetic route is somewhat cumbersome and requires sophisticated organic chemistry equipment that most radiochemistry and molecular imaging laboratories &#8212; including ours &#8212; simply do not possess.
In response to these obstacles, we set out to create an easily accessible and highly stable phenyloxadiazolyl methyl sulfone reagent that can be obtained via a robust and reasonably facile synthetic route. Earlier this year, we reported the creation of a modular, stable, and easily accessible phenyloxadiazolyl methyl sulfone reagent &#8212; dubbed &#8216;PODS&#8217; &#8212; as a platform for thiol-based bioconjugations (Figure 1C and Figure 3)22. The key difference between PODS and the reagent reported by Barbas, et al. is that the former employs an aniline ring attached to the phenyloxadiazolyl methyl sulfone moiety, while the latter features a phenol in the same position (Figure 4). This change facilitates a more straightforward and accessible synthetic route as well as &#8212; if our experience with the commercially available compound is emblematic &#8212; a more stable final reagent. In this work, we also synthesized a pair of PODS-bearing bifunctional chelators &#8212; PODS-DFO and PODS-CHX-A&#39;&#39;-DTPA &#8212; to facilitate the creation of 89Zr- and 177Lu-labeled radioimmunoconjugates, respectively. As we will discuss, we have demonstrated that PODS-based site-selective bioconjugations reproducibly and robustly create homogenous, well-defined, highly immunoreactive, and highly stable radioimmunoconjugates. Furthermore, preclinical experiments in murine models of colorectal cancer have shown that these site-selectively labeled radioimmunoconjugates exhibit superior in vivo performance compared to radiolabeled antibodies synthesized via maleimide-based conjugations.
The over-arching goal of this work is to facilitate the creation of well-defined, homogeneous, highly stable, and highly immunoreactive immunoconjugates for in vitro and in vivo applications. The synthetic approach is simple enough to be performed in almost any laboratory, and the parent PODS reagent can be modified with a plethora of different chelators, fluorophores, or cargoes. In this protocol and the accompanying video, we will describe the simple, four-step synthesis of PODS (Figure 5); the creation of a PODS-bearing variant of DOTA, a widely used chelator for the coordination of 64Cu, 68Ga, 111In, 177Lu, and 225Ac (Figure 6); and the bioconjugation of PODS-DOTA to a model antibody, the HER2-targeting IgG1 trastuzumab (Figure 7).

<table>
	<tbody>
		<tr>
			<td>5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol</td>
			<td>Sigma-Aldrich</td>
			<td>675024</td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL LoBind Microcentrifugal Tube</td>
			<td>Eppendorf</td>
			<td>925000090</td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL Microcentrifugal Tube</td>
			<td>Fisherbrand</td>
			<td>05-408-129</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetonitrile</td>
			<td>Fisher Scientific</td>
			<td>A998-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Amicon Ultra-2 Centrifugal Filter Unit</td>
			<td>EMD Millipore</td>
			<td>EN300000141G</td>
			<td></td>
		</tr>
		<tr>
			<td>Cyclohexane</td>
			<td>Fisher Scientific</td>
			<td>C556-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Fisher Scientific</td>
			<td>AC383780010</td>
			<td></td>
		</tr>
		<tr>
			<td>Diisopropylethylamine</td>
			<td>MP Biomedicals, LLC</td>
			<td>150915</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethylsulfoxide</td>
			<td>Fisher Scientific</td>
			<td>31-727-5100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl Acetate</td>
			<td>Fisher Scientific</td>
			<td>E145 4</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric Acid</td>
			<td>Fisher Scientific</td>
			<td>A144-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Iodomethane</td>
			<td>Sigma-Aldrich</td>
			<td>289566-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Sulfate</td>
			<td>Acros Organics</td>
			<td>413485000</td>
			<td></td>
		</tr>
		<tr>
			<td>m-chloroperbenzoic acid</td>
			<td>Sigma-Aldrich</td>
			<td>273031</td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Fisher Scientific</td>
			<td>A412 1</td>
			<td></td>
		</tr>
		<tr>
			<td>NBoc-N&#8242;-succinyl-4,7,10-trioxa-1,13-tridecanediamine</td>
			<td>Sigma-Aldrich</td>
			<td>671401</td>
			<td>Store at -80 &#176;C</td>
		</tr>
		<tr>
			<td>N-ethyl-N&#8242;- [3- (dimethylamino)propyl] carbodiimide hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>3450</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline</td>
			<td>Sigma-Aldrich</td>
			<td>P5493</td>
			<td>10&#215; Concentration</td>
		</tr>
		<tr>
			<td>p-SCN-Bn-DOTA</td>
			<td>Macrocyclics</td>
			<td>B-205</td>
			<td>Store at -80 &#176;C</td>
		</tr>
		<tr>
			<td>Sephadex G-25 in PD-10 Desalting Columns</td>
			<td>GE Healthcare</td>
			<td>17085101</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Carbonate</td>
			<td>Sigma-Aldrich</td>
			<td>S7795</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Hydroxide</td>
			<td>Fisher Scientific</td>
			<td>S318-1</td>
			<td></td>
		</tr>
		<tr>
			<td>TCEP</td>
			<td>ThermoFischer Scientific</td>
			<td>20490</td>
			<td></td>
		</tr>
		<tr>
			<td>Triethylamine</td>
			<td>Fisher Scientific</td>
			<td>AC157911000</td>
			<td></td>
		</tr>
		<tr>
			<td>Trifluoroacetic Acid</td>
			<td>Fisher Scientific</td>
			<td>A116-50</td>
			<td></td>
		</tr>
	</tbody>
</table>

synthesis and bioconjugation of thiol-reactive reagents for the creation of site-selectively modified immunoconjugates

Maleimide-bearing bifunctional probes have been employed for decades for the site-selective modification of thiols in biomolecules, especially antibodies. Yet maleimide-based conjugates display limited stability in vivo because the succinimidyl thioether linkage can undergo a retro-Michael reaction. This, of course, can lead to the release of the radioactive payload or its exchange with thiol-bearing biomolecules in circulation. Both of these processes can produce elevated activity concentrations in healthy organs as well as decreased activity concentrations in target tissues, resulting in reduced imaging contrast and lower therapeutic ratios. In 2018, we reported the creation of a modular, stable, and easily accessible phenyloxadiazolyl methyl sulfone reagent &#8212; dubbed &#8216;PODS&#8217; &#8212; as a platform for thiol-based bioconjugations. We have clearly demonstrated that PODS-based site-selective bioconjugations reproducibly and robustly create homogenous, well-defined, highly immunoreactive, and highly stable radioimmunoconjugates. Furthermore, preclinical experiments in murine models of colorectal cancer have shown that these site-selectively labeled radioimmunoconjugates exhibit far superior in vivo performance compared to radiolabeled antibodies synthesized via maleimide-based conjugations. In this protocol, we will describe the four-step synthesis of PODS, the creation of a bifunctional PODS-bearing variant of the ubiquitous chelator DOTA (PODS-DOTA), and the conjugation of PODS-DOTA to the HER2-targeting antibody trastuzumab.

The first four steps of this protocol&#160;&#8212; the synthesis&#160;of PODS&#160;&#8212; have been designed to be robust and reliable. The deprotonation and substitution of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol to form the desired thioether product affords the thioether in &#62;99% yield after just 45 minutes. Next, the ligation between 1 and N-Boc-N&#39;-succinyl-4,7,10-trioxa-1,13-tridecanediamine was achieved via a standard peptide coupling procedure, resulting ...

Watch this Scientific Journal Video about Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates at JoVE.com

Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates (Video) | JoVE

In this protocol, we will describe the synthesis of PODS, a phenyoxadiazolyl methyl sulfone-based reagent for the site-selective attachment of cargos to the thiols of biomolecules, particularly antibodies. In addition, we will describe the synthesis and characterization of a PODS-bearing bifunctional chelator and its conjugation to a model antibody.

Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates

Maleimide-bearing bifunctional probes have been employed for decades for the site-selective modification of thiols in biomolecules, especially antibodies. ...

Research

JoVE Journal

Chemistry

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We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

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