Probody Therapeutic Design of 89Zr-CX-072 Promotes Accumulation in PD-L1-Expressing Tumors Compared to Normal Murine Lymphoid Tissue

Clin Cancer Res. 2020 Aug 1;26(15):3999-4009. doi: 10.1158/1078-0432.CCR-19-3137. Epub 2020 Jan 17.


Purpose: Probody therapeutic CX-072 is a protease-activatable antibody that is cross-reactive with murine and human programmed death-ligand 1 (PD-L1). CX-072 can be activated in vivo by proteases present in the tumor microenvironment, thereby potentially reducing peripheral, anti-PD-L1-mediated toxicities. To study its targeting of PD-L1-expressing tissues, we radiolabeled CX-072 with the PET isotope zirconium-89 (89Zr).

Experimental design: 89Zr-labeled CX-072, nonspecific Probody control molecule (PbCtrl) and CX-072 parental antibody (CX-075) were injected in BALB/c nude mice bearing human MDA-MB-231 tumors or C57BL/6J mice bearing syngeneic MC38 tumors. Mice underwent serial PET imaging 1, 3, and 6 days after intravenous injection (pi), followed by ex vivo biodistribution. Intratumoral 89Zr-CX-072 distribution was studied by autoradiography on tumor tissue sections, which were subsequently stained for PD-L1 by IHC. Activated CX-072 species in tissue lysates were detected by Western capillary electrophoresis.

Results: PET imaging revealed 89Zr-CX-072 accumulation in MDA-MB-231 tumors with 2.1-fold higher tumor-to-blood ratios at 6 days pi compared with 89Zr-PbCtrl. Tumor tissue autoradiography showed high 89Zr-CX-072 uptake in high PD-L1-expressing regions. Activated CX-072 species were detected in these tumors, with 5.3-fold lower levels found in the spleen. Furthermore, 89Zr-CX-072 uptake by lymphoid tissues of immune-competent mice bearing MC38 tumors was low compared with 89Zr-CX-075, which lacks the Probody design.

Conclusions: 89Zr-CX-072 accumulates specifically in PD-L1-expressing tumors with limited uptake in murine peripheral lymphoid tissues. Our data may enable clinical evaluation of 89Zr-CX-072 whole-body distribution as a tool to support CX-072 drug development (NCT03013491).

MeSH terms

  • Animals
  • Antibodies, Monoclonal / administration & dosage
  • Antibodies, Monoclonal / chemistry
  • Antibodies, Monoclonal / pharmacokinetics*
  • Autoradiography
  • B7-H1 Antigen / antagonists & inhibitors*
  • Cell Line, Tumor
  • Drug Design
  • Humans
  • Immune Checkpoint Inhibitors / administration & dosage
  • Immune Checkpoint Inhibitors / chemistry
  • Immune Checkpoint Inhibitors / pharmacokinetics*
  • Male
  • Mice
  • Neoplasms / diagnostic imaging
  • Neoplasms / drug therapy*
  • Neoplasms / immunology
  • Neoplasms / pathology
  • Positron-Emission Tomography
  • Radioisotopes / administration & dosage
  • Radioisotopes / chemistry
  • Radioisotopes / pharmacokinetics
  • Radiopharmaceuticals / administration & dosage
  • Radiopharmaceuticals / chemistry
  • Radiopharmaceuticals / pharmacokinetics*
  • Tissue Distribution
  • Tumor Microenvironment / drug effects
  • Tumor Microenvironment / immunology
  • Xenograft Model Antitumor Assays
  • Zirconium / administration & dosage
  • Zirconium / chemistry
  • Zirconium / pharmacokinetics


  • Antibodies, Monoclonal
  • B7-H1 Antigen
  • CD274 protein, human
  • Immune Checkpoint Inhibitors
  • Radioisotopes
  • Radiopharmaceuticals
  • Zirconium
  • Zirconium-89

Associated data