Development of [18F]FPy-WL12 as a PD-L1 Specific PET Imaging Peptide

Wojciech G. Lesniak, Ronnie C. Mease, Samit Chatterjee, Dhiraj Kumar, Ala Lisok, Bryan Wharram, Venkateswara Rao Kalagadda, Leisha Emens, Martin G. Pomper, Sridhar Nimmagadda

Research output: Contribution to journalArticlepeer-review


Expression of programmed cell death ligand 1 (PD-L1) within tumors is an important biomarker for guiding immune checkpoint therapies; however, immunohistochemistry-based methods of detection fail to provide a comprehensive picture of PD-L1 levels in an entire patient. To facilitate quantification of PD-L1 in the whole body, we developed a peptide-based, high-affinity PD-L1 imaging agent labeled with [18F]fluoride for positron emission tomography (PET) imaging. The parent peptide, WL12, and the nonradioactive analog of the radiotracer, 19FPy-WL12, inhibit PD-1/PD-L1 interaction at low nanomolar concentrations (half maximal inhibitory concentration [IC50], 26-32 nM). The radiotracer, [18F]FPy-WL12, was prepared by conjugating 2,3,5,6-tetrafluorophenyl 6-[18F]fluoronicotinate ([18F]FPy-TFP) to WL12 and assessed for specificity in vitro in 6 cancer cell lines with varying PD-L1 expression. The uptake of the radiotracer reflected the PD-L1 expression assessed by flow cytometry. Next, we performed the in vivo evaluation of [18F]FPy-WL12 in mice bearing cancer xenografts by PET imaging, ex vivo biodistribution, and blocking studies. In vivo data demonstrated a PD-L1-specific uptake of [18F]FPy-WL12 in tumors that is reduced in mice receiving a blocking dose. The majority of [18F]FPy-WL12 radioactivity was localized in the tumors, liver, and kidneys indicating the need for optimization of the labeling strategy to improve the in vivo pharmacokinetics of the radiotracer.

Original languageEnglish (US)
JournalMolecular imaging
StatePublished - Jun 11 2019


  • PD-L1
  • immunotherapy
  • molecular imaging
  • positron emission tomography

ASJC Scopus subject areas

  • Biotechnology
  • Molecular Medicine
  • Biomedical Engineering
  • Radiology Nuclear Medicine and imaging
  • Condensed Matter Physics


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