A Pretargeted Imaging Strategy for Immune Checkpoint Ligand PD-L1 Expression in Tumor Based on Bioorthogonal Diels-Alder Click Chemistry

  • Lin Qiu
  • Hui Tan
  • Qingyu Lin
  • Zhan Si
  • Wujian Mao
  • Tingting Wang
  • Zhequan Fu
  • Dengfeng ChengEmail author
  • Hongcheng ShiEmail author
Research Article



The use of antibodies as tracers requires labeling with isotopes with long half-lives due to their slow pharmacokinetics, which creates prohibitively high radiation dose to non-target organs. Pretargeted methodology could avoid the high radiation exposure due to the slow pharmacokinetics of antibodies. In this investigation, we reported the development of a novel pretargeted single photon emission computed tomography (SPECT) imaging strategy (atezolizumab-TCO/[99mTc]HYNIC-PEG11-Tz) for evaluating immune checkpoint ligand PD-L1 expression in tumor based on bioorthogonal Diels-Alder click chemistry.


The radioligand [99mTc]HYNIC-PEG11-Tz was achieved by the synthesis of a 6-hydrazinonicotinc acid (HYNIC) modified 1,2,4,5-tetrazine (Tz) and subsequently radiolabeled with technetium-99m (Tc-99m). The stability of [99mTc]HYNIC-PEG11-Tz was evaluated in vitro, and its blood pharmacokinetic test was performed in vivo. Atezolizumab was modified with trans-cyclooctene (TCO). The [99mTc]HYNIC-PEG11-Tz and atezolizumab-TCO interaction was tested in vitro. Pretargeted H1975 cell immunoreactivity binding and saturation binding assays were evaluated. Pretargeted biodistribution and SPECT imaging experiments were performed in H1975 and A549 tumor-bearing modal mice to evaluate the PD-L1 expression level.


[99mTc]HYNIC-PEG11-Tz was successfully radiosynthesized with a specific activity of 9.25 MBq/μg and a radiochemical purity above 95 % as confirmed by reversed-phase HPLC (RP-HPLC). [99mTc]HYNIC-PEG11-Tz showed favorable stability in NS, PBS, and FBS and rapid blood clearance in mice. The atezolizumab was modified with TCO-NHS ester to produce a conjugate with an average 6.4 TCO moieties as confirmed by liquid chromatograph-mass spectrometer (LC-MS). Size exclusion HPLC revealed almost complete reaction between atezolizumab-TCO and [99mTc]HYNIC-PEG11-Tz in vitro, with the 1:1 Tz-to-mAb reaction providing a conversion yield of 88.65 ± 1.22 %. Pretargeted cell immunoreactivity binding and saturation binding assays showed high affinity to H1975 cells. After allowing 48 h for accumulation of atezolizumab-TCO in H1975 tumor, pretargeted in vivo biodistribution revealed high uptake of the radiotracer in the tumor with a tumor-to-muscle ratio of 27.51 and tumor-to-blood ratio of 1.91. Pretargeted SPECT imaging delineated the H1975 tumor clearly. Pretargeted biodistribution and SPECT imaging in control groups demonstrated a significantly reduced tracer accumulation in the A549 tumor.


We have developed a HYNIC-modified Tz derivative, and the HYNIC-PEG11-Tz was labeled with Tc-99m with a high specific activity and radiochemical purity. [99mTc]HYNIC-PEG11-Tz reacted rapidly and almost completely towards atezolizumab-TCO in vitro with the 1:1 Tz-to-mAb reaction. SPECT imaging using the pretargeted strategy (atezolizumab-TCO/[99mTc]HYNIC-PEG11-Tz) demonstrated high-contrast images for high PD-L1 expression H1975 tumor and a low background accumulation of the probe. The pretargeted imaging strategy is a powerful tool for evaluating PD-L1 expression in xenograft mice tumor models and a potential candidate for translational clinical application.

Key words

Pretargeted imaging Click chemistry PD-L1 Atezolizumab 



We want to thank for the technical supports from Prof. Yingjian Zhang and Dr. Jianping Zhang from Center for Biomedical Imaging, Fudan University, and Shanghai Engineering Research Center of Molecular Imaging Probes.

Funding Information

This study was funded by The National Nature Science Foundation of China (11875114, 81671735, and 81871407) and Open Large Infrastructure Research of Chinese Academy of Science.

Compliance with Ethical Standards

Ethical Approval

All applicable institutional and/or national guidelines for the care and use of animals were followed.

Conflict of Interest

The authors declare that they have no conflict of interest.

Supplementary material

11307_2019_1441_MOESM1_ESM.docx (794 kb)
ESM 1 (DOCX 793 kb)


  1. 1.
    Herbst RS, Soria JC, Kowanetz M, Fine GD, Hamid O, Gordon MS, Sosman JA, McDermott DF, Powderly JD, Gettinger SN, Kohrt HEK, Horn L, Lawrence DP, Rost S, Leabman M, Xiao Y, Mokatrin A, Koeppen H, Hegde PS, Mellman I, Chen DS, Hodi FS (2014) Predictive correlates of response to the anti-PD-L1 antibody MPDL3280A in cancer patients. Nature 515:563–567CrossRefGoogle Scholar
  2. 2.
    Ehlerding EB, England CG, McNeel DG, Cai W (2016) Molecular imaging of immunotherapy targets in cancer. J Nucl Med 57:1487–1492CrossRefGoogle Scholar
  3. 3.
    Nedrow JR, Josefsson A, Park S, Ranka S, Roy S, Sgouros G (2017) Imaging of programmed cell death ligand 1: impact of protein concentration on distribution of anti-PD-L1 SPECT agents in an immunocompetent murine model of melanoma. J Nucl Med 58:1560–1566CrossRefGoogle Scholar
  4. 4.
    Josefsson A, Nedrow JR, Park S et al (2016) Imaging, biodistribution, and dosimetry of radionuclide-labeled PD-L1 antibody in an immunocompetent mouse model of breast cancer. Cancer Res 76:472–479CrossRefGoogle Scholar
  5. 5.
    Lesniak WG, Chatterjee S, Gabrielson M et al (2016) PD-L1 detection in tumors using [(64)Cu] Atezolizumab with PET. Bioconjug Chem 27:2103–2110CrossRefGoogle Scholar
  6. 6.
    Chatterjee S, Lesniak WG, Gabrielson M et al (2016) A humanized antibody for imaging immune checkpoint ligand PD-L1 expression in tumors. Oncotarget 7:10215–10227CrossRefGoogle Scholar
  7. 7.
    Hettich M, Braun F, Bartholoma MD et al (2016) High-resolution PET imaging with therapeutic antibody-based PD-1/PD-L1 checkpoint tracers. Theranostics 6:1629–1640CrossRefGoogle Scholar
  8. 8.
    Moroz A, Lee CY, Wang YH et al (2018) A preclinical assessment of (89)Zr-atezolizumab identifies a requirement for carrier added formulations not observed with (89)Zr-C4. Bioconjug Chem 29:3476–3482CrossRefGoogle Scholar
  9. 9.
    Truillet C, Oh H, Yeo SP et al (2018) Imaging PD-L1 expression with ImmunoPET. Bioconjug Chem 29:96–103CrossRefGoogle Scholar
  10. 10.
    Bensch F, van der Veen EL, Lub-de HM et al (2018) 89Zr-atezolizumab imaging as a non-invasive approach to assess clinical response to PD-L1 blockade in cancer. Nat Med 24:1852–1858CrossRefGoogle Scholar
  11. 11.
    Gonzalez TD, Meng X, McQuade P et al (2017) In vivo imaging of the programmed death ligand 1 by 18F PET. J Nucl Med 58:1852–1857CrossRefGoogle Scholar
  12. 12.
    Donnelly DJ, Smith RA, Morin P et al (2018) Synthesis and biologic evaluation of a novel (18)F-labeled adnectin as a PET radioligand for imaging PD-L1 expression. J Nucl Med 59:529–535CrossRefGoogle Scholar
  13. 13.
    Chatterjee S, Lesniak WG, Miller MS et al (2017) Rapid PD-L1 detection in tumors with PET using a highly specific peptide. Biochem Biophys Res Commun 483:258–263CrossRefGoogle Scholar
  14. 14.
    Boerman OC, van Schaijk FG, Oyen WJ, Corstens FH (2003) Pretargeted radioimmunotherapy of cancer: progress step by step. J Nucl Med 44:400–411PubMedGoogle Scholar
  15. 15.
    Rossin R, Verkerk PR, van den Bosch SM et al (2010) In vivo chemistry for pretargeted tumor imaging in live mice. Angew Chem Int Ed Engl 49:3375–3378CrossRefGoogle Scholar
  16. 16.
    Rossin R, van den Bosch SM, Ten HW et al (2013) Highly reactive trans-cyclooctene tags with improved stability for Diels-Alder chemistry in living systems. Bioconjug Chem 24:1210–1217CrossRefGoogle Scholar
  17. 17.
    Rossin R, Lappchen T, van den Bosch SM et al (2013) Diels-Alder reaction for tumor pretargeting: in vivo chemistry can boost tumor radiation dose compared with directly labeled antibody. J Nucl Med 54:1989–1995CrossRefGoogle Scholar
  18. 18.
    Altai M, Perols A, Tsourma M et al (2016) Feasibility of affibody-based bioorthogonal chemistry-mediated radionuclide pretargeting. J Nucl Med 57:431–436CrossRefGoogle Scholar
  19. 19.
    van Duijnhoven SM, Rossin R, van den Bosch SM et al (2015) Diabody pretargeting with click chemistry in vivo. J Nucl Med 56:1422–1428CrossRefGoogle Scholar
  20. 20.
    Garcia MF, Zhang X, Shah M et al (2016) 99mTc-bioorthogonal click chemistry reagent for in vivo pretargeted imaging. Bioorg Med Chem 24:1209–1215CrossRefGoogle Scholar
  21. 21.
    Yazdani A, Bilton H, Vito A et al (2016) A bone-seeking trans-cyclooctene for pretargeting and bioorthogonal chemistry: a proof of concept study using 99mTc- and 177Lu-labeled tetrazines. J Md Chem 59:9381–9389CrossRefGoogle Scholar
  22. 22.
    Zeglis BM, Sevak KK, Reiner T et al (2013) A pretargeted PET imaging strategy based on bioorthogonal Diels-Alder click chemistry. J Nucl Med 54:1389–1396CrossRefGoogle Scholar
  23. 23.
    Zeglis BM, Brand C, Abdel-Atti D et al (2015) Optimization of a pretargeted strategy for the PET imaging of colorectal carcinoma via the modulation of radioligand pharmacokinetics. Mol Pharm 12:3575–3587CrossRefGoogle Scholar
  24. 24.
    Reiner T, Zeglis BM (2014) The inverse electron demand Diels-Alder click reaction in radiochemistry. J Labelled Comp Radiopharm 57:285–290CrossRefGoogle Scholar
  25. 25.
    Topalian SL, Drake CG, Pardoll DM (2012) Targeting the PD-1/B7-H1(PD-L1) pathway to activate anti-tumor immunity. Curr Opin Immunol 24:207–212CrossRefGoogle Scholar
  26. 26.
    Meszaros LK, Dose A, Biagini SCG, Blower PJ (2010) Hydrazinonicotinic acid (HYNIC)—coordination chemistry and applications in radiopharmaceutical chemistry. Inorg Chim Acta 363:1059–1069CrossRefGoogle Scholar
  27. 27.
    Hamoudeh M, Kamleh MA, Diab R, Fessi H (2008) Radionuclides delivery systems for nuclear imaging and radiotherapy of cancer. Adv Drug Deliv Rev 60:1329–1346CrossRefGoogle Scholar
  28. 28.
    Goldenberg DM (2002) Targeted therapy of cancer with radiolabeled antibodies. J Nucl Med 43:693–713PubMedGoogle Scholar
  29. 29.
    Milenic DE, Brady ED, Brechbiel MW (2004) Antibody-targeted radiation cancer therapy. Nat Rev Drug Discov 3:488–499CrossRefGoogle Scholar
  30. 30.
    Powles T, Eder JP, Fine GD et al (2014) MPDL3280A (anti-PD-L1) treatment leads to clinical activity in metastatic bladder cancer. Nature 515:558–562CrossRefGoogle Scholar
  31. 31.
    Hamid O, Sosman JA, Lawrence DP et al (2013) Clinical activity, safety, and biomarkers of MPDL3280A, an engineered PD-L1 antibody in patients with locally advanced or metastatic melanoma (mM). J Clin Oncol 31:9010Google Scholar
  32. 32.
    Spigel DR, Gettinger SN, Horn L et al (2013) Clinical activity, safety, and biomarkers of MPDL3280A, an engineered PD-L1 antibody in patients with locally advanced or metastatic non-small cell lung cancer (NSCLC). J Clin Oncol 31:8008CrossRefGoogle Scholar
  33. 33.
    Cho DC, Sosman JA, Sznol M et al (2013) Clinical activity, safety, and biomarkers of MPDL3280A, an engineered PD-L1 antibody in patients with metastatic renal cell carcinoma (mRCC). J Clin Oncol 31:4505Google Scholar
  34. 34.
    Liu S (2008) Bifunctional coupling agents for radiolabeling of biomolecules and target-specific delivery of metallic radionuclides. Adv Drug Deliv Rev 60:1347–1370CrossRefGoogle Scholar
  35. 35.
    Surfraz MB, King R, Mather SJ et al (2007) Trifluoroacetyl-HYNIC peptides: synthesis and 99mTc radiolabeling. J Med Chem 50:1418–1422CrossRefGoogle Scholar
  36. 36.
    Surfraz MB, Biagini SC, Blower PJ (2008) A technetium intermediate specifically promotes deprotection of trifluoroacetyl HYNIC during radiolabelling under mild conditions. Dalton Trans:2920–2922Google Scholar
  37. 37.
    Shi J, Jin Z, Liu X et al (2014) PET imaging of neovascularization with (68)Ga-3PRGD2 for assessing tumor early response to Endostar antiangiogenic therapy. Mol Pharm 11:3915–3922CrossRefGoogle Scholar
  38. 38.
    Fournier P, Dumulon-Perreault V, Ait-Mohand S et al (2012) Novel radiolabeled peptides for breast and prostate tumor PET imaging: 64Cu/and 68Ga/NOTA-PEG-[D-Tyr(6),betaAla(11),Thi(13),Nle(14)]BBN(6–14). Bioconjug Chem 23:1687–1693CrossRefGoogle Scholar
  39. 39.
    Lappchen T, Rossin R, van Mourik TR et al (2017) DOTA-tetrazine probes with modified linkers for tumor pretargeting. Nucl Med Biol 55:19–26CrossRefGoogle Scholar

Copyright information

© World Molecular Imaging Society 2019

Authors and Affiliations

  1. 1.Department of Nuclear Medicine, Zhongshan HospitalFudan UniversityShanghaiChina

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