Introduction Platelet-derived growth factor receptor beta (PDGFRβ) is a widely used and important marker for mesenchymal cells, including fibroblasts, vascular smooth muscle cells, and pericytes. Dysfunction of the mesenchymal compartment is fundamentally linked to fibrotic disease and cancer. ATH001 is an Affibody molecule being developed for Positron Emission Tomography (PET) imaging for improved diagnosis and therapy follow-up in disease involving aberrant mesenchymal regulation. Here we present a novel NOTA-conjugated variant of ATH001 for PET imaging of PDGFRβ. Methods Transcription of PDGFRβ in human cells and tissues was investigated in the reference scRNAseq database Tabula Sapiens. ATH001 was generated by custom chemical solid phase peptide synthesis, followed by conjugation with NOTA via maleimide chemistry at a C-terminal cysteine. The resulting precursor NOTA-ATH001 was radiolabeled with Gallium-68. Affinity towards recombinant PDGFRβ was determined using a Surface Plasma Resonance assay. 68 GaGa-NOTA-ATH001 binding and biodistribution was evaluated by in vitro autoradiography and in vivo PET scanning of U87 xenografted immunodeficient mice. Results PDGFRβ transcription was restricted to mesenchymal components and was particularly high in pericytes and stellate cells. NOTA-ATH001 demonstrated picomolar affinity to human PDGFRβ. 68 GaGa-NOTA-ATH001 bound to PDGFRβ + U87 cells and fibrotic tissues, with low background binding in PDGFRβ − cells and tissues. 68 GaGa-NOTA-ATH001 exhibited high in vivo plasma stability, rapid tissue clearance and strong, blockable binding to U87 xenografts. However, 68 GaGa-NOTA-ATH001 was not superior to the previously reported analogue 68 GaGa-DOTA-ATH001. Conclusions 68 GaGa-NOTA-ATH001 is a novel, high affinity PDGFRβ-targeting PET tracer that enables in vivo PET imaging of mesenchymal cells in health and disease. Although it does not outperform its DOTA-conjugated analogue, the NOTA chelator offers practical advantages, such as convenient Al 18 F or 64 Cu radiolabeling.
Mitran et al. (Fri,) studied this question.