Binding of αvβ3 Integrin-Specific Radiotracers Is Modulated by Both Integrin Expression Level and Activation Status

Alexandra Andriu, Julie Crockett, Sergio Dall'Angelo, Monica Piras, Matteo Zanda, Ian N Fleming

Research output: Contribution to journalArticle

9 Citations (Scopus)
9 Downloads (Pure)

Abstract

Purpose
Molecular imaging of αvβ3 integrin has exhibited real potential to guide the appropriate use of anti-angiogenic therapies. However, an incomplete understanding of the factors that influence binding of αvβ3 integrin-specific radiotracers currently limits their use for assessing response to therapy in cancer patients. This study identifies two fundamental factors that modulate uptake of these radiotracers.
Procedures
Experiments were performed in prostate cancer (PC3) and glioblastoma (U87MG) cells, which differentially express αvβ3 integrin. αvβ3 integrin-specific radiotracers were used to investigate the effect of manipulating αvβ3 integrin expression or activation in cellular binding assays. β3 integrin and αvβ3 integrin expression were measured by western blotting and flow cytometry, respectively. The effect of select pharmacological inhibitors on αvβ3 integrin activation and expression was also determined.

Results
Radiotracer binding was proportional to αvβ3 integrin expression when it was decreased (β3 knock-down cells) or increased, either using pharmacological inhibitors of cell signalling or by culturing cells for different times. Studies with both small molecule and arginine–glycine–aspartic acid (RGD)-based radiotracers revealed increased radiotracer binding after activation of αvβ3 integrin with Mn2+ or talin head domain. Moreover, inhibition of fundamental signalling pathways (mitogen-activated protein kinase kinase (MEK), Src and VEGFR2) decreased radiotracer binding, reflecting reduced αvβ3 integrin activity.
Conclusion:
Binding of small molecule ligands and radiolabelled RGD peptides is modulated by expression and activation status of αvβ3 integrin. αvβ3 integrin-specific radiotracers can provide otherwise inaccessible information of the effect of signalling pathways on αvβ3 integrin. This has significant implications for assessing response to anti-angiogenic therapies in clinical studies.
Original languageEnglish
Pages (from-to)27-36
Number of pages10
JournalMolecular imaging and biology : MIB : the official publication of the Academy of Molecular Imaging
Volume20
Issue number1
Early online date10 Jul 2017
DOIs
Publication statusPublished - Feb 2018

Keywords

  • Tumour angiogenesis
  • αvβ3 integrin
  • Integrin signalling
  • Response assessment
  • PET imaging
  • Radiolabelled RGD peptides

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