Preclinical evaluation of [ 111 In]MICA-401, an activity-based probe for SPECT imaging of in vivo uPA activity

Contrast Media Mol Imaging. 2016 Nov;11(6):448-458. doi: 10.1002/cmmi.1706. Epub 2016 Aug 24.

Abstract

Urokinase-type plasminogen activator (uPA) and its inhibitor PAI-1 are key players in cancer invasion and metastasis. Both uPA and PAI-1 have been described as prognostic biomarkers; however, non-invasive methods measuring uPA activity are lacking. We developed an indium-111 (111 In)-labelled activity-based probe to image uPA activity in vivo by single photon emission computed tomography (SPECT). A DOTA-conjugated uPA inhibitor was synthesized and radiolabelled with 111 In ([111 In]MICA-401), together with its inactive, hydrolysed form ([111 In]MICA-402). A biodistribution study was performed in mice (healthy and tumour-bearing), and tumour-targeting properties were evaluated in two different cancer xenografts (MDA-MB-231 and HT29) with respectively high and low levels of uPA expression in vitro, with either the active or hydrolysed radiotracer. MicroSPECT was performed 95 h post injection followed by ex vivo biodistribution. Tumour uptake was correlated with human and murine uPA expression determined by ELISA and immunohistochemistry (IHC). Biodistribution data with the hydrolysed probe [111 In]MICA-402 showed almost complete clearance 95 h post injection. The ex vivo biodistribution and SPECT data with [111 In]MICA-401 demonstrated similar tumour uptakes in the two models: ex vivo 5.68 ± 1.41%ID/g versus 5.43 ± 1.29%ID/g and in vivo 4.33 ± 0.80 versus 4.86 ± 1.18 for MDA-MB-231 and HT-29 respectively. Human uPA ELISA and IHC showed significantly higher uPA expression in the MDA-MB-231 tumours, while mouse uPA staining revealed similar staining intensities of the two tumours. Our data demonstrate non-invasive imaging of uPA activity in vivo, although the moderate tumour uptake and hence potential clinical translation of the radiotracer warrants further investigation. Copyright © 2016 John Wiley & Sons, Ltd.

Keywords: cancer xenografts; single photon emission computed; tomography; uPA activity; urokinase-type plasminogen activator.

Publication types

  • Evaluation Study

MeSH terms

  • Animals
  • Cell Line, Tumor
  • HT29 Cells
  • Heterografts
  • Humans
  • Indium Radioisotopes*
  • Mice
  • Molecular Imaging / methods*
  • Neoplasms / diagnostic imaging*
  • Radionuclide Imaging / methods
  • Radiopharmaceuticals / chemical synthesis
  • Radiopharmaceuticals / pharmacokinetics
  • Tissue Distribution
  • Tomography, Emission-Computed, Single-Photon / methods*
  • Urokinase-Type Plasminogen Activator / analysis*

Substances

  • Indium Radioisotopes
  • Radiopharmaceuticals
  • Urokinase-Type Plasminogen Activator