Synthesis and in vivo preclinical evaluation of an (18)F labeled uPA inhibitor as a potential PET imaging agent.
BACKGROUND
The urokinase plasminogen activator (uPA) system is a proteolytic cascade involved in tumor invasion and metastasis. uPA and its inhibitor PAI-1 are described as biomarkers for breast cancer with the highest level of evidence. The present study describes the synthesis and first in vivo application of an activity based uPA PET probe.


METHODS
Based on the design of a small irreversible and selective uPA inhibitor we developed an (18)F-labeled activity based probe for uPA imaging. Human uPA expressing MDA-MB-231-luc2-GFP cells were inoculated in the mammary fat pads of nude mice and treated with the probe once tumors reached a volume of 150mm(3). Scans were performed at 0.25, 0.75, 1.5, 4 and 6h post injection. To evaluate tumor uptake in vivo and ex vivo data were gathered. Biodistribution data of the organs and tissues of interest were collected at all time points. Due to a relatively low tumor uptake, probe stability was further evaluated.


RESULTS
The uPA targeting PET tracer was produced in high purity and with good specific radioactivity. In vivo PET data showed a maximum tumor uptake of 2,51±0,32 %ID/g at 4h p.i. A significant correlation between in vivo and ex vivo tumor uptake calculation was found (R=0.75; p<0.01). Due to a high blood signal at all time points, probe stability was further examined revealing high plasma protein binding and low plasma stability.


CONCLUSIONS
In vivo and ex vivo results clearly demonstrate that uPA expressing tumors can be detected with non-invasive PET imaging. Stability tests suggest that further optimization is needed to provide a better tumor-to-background contrast.
Laboratory of Medicinal Chemistry, University of Antwerp (UAMC), Universiteitsplein 1, B-2610 Antwerp, Belgium; Laboratory of Cancer Research and Clinical Oncology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Johan
J
Ides
Molecular Imaging Center of Antwerp (MICA), University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium; Laboratory of Medicinal Chemistry, University of Antwerp (UAMC), Universiteitsplein 1, B-2610 Antwerp, Belgium.
David
D
Thomae
Molecular Imaging Center of Antwerp (MICA), University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Leonie
L
Wyffels
Molecular Imaging Center of Antwerp (MICA), University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Christel
C
Vangestel
Laboratory of Medicinal Chemistry, University of Antwerp (UAMC), Universiteitsplein 1, B-2610 Antwerp, Belgium.
Jonas
J
Messagie
Laboratory of Medicinal Chemistry, University of Antwerp (UAMC), Universiteitsplein 1, B-2610 Antwerp, Belgium.
Jurgen
J
Joossens
Laboratory of Cancer Research and Clinical Oncology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Filip
F
Lardon
Laboratory of Medicinal Chemistry, University of Antwerp (UAMC), Universiteitsplein 1, B-2610 Antwerp, Belgium.
Pieter
P
Van der Veken
Laboratory of Medicinal Chemistry, University of Antwerp (UAMC), Universiteitsplein 1, B-2610 Antwerp, Belgium.
Koen
K
Augustyns
Molecular Imaging Center of Antwerp (MICA), University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Sigrid
S
Stroobants
Molecular Imaging Center of Antwerp (MICA), University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium. Electronic address: Steven.Staelens@uantwerpen.be.
Steven
S
Staelens
D000818:Animals; D045744:Cell Line, Tumor; D060326:Chemistry Techniques, Synthetic; D004355:Drug Stability; D005462:Fluorine Radioisotopes; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007553:Isotope Labeling; D051379:Mice; D049268:Positron-Emission Tomography / Q000379:methods*; D011480:Protease Inhibitors / Q000138:chemical synthesis* / Q000493:pharmacokinetics / Q000494:pharmacology; D014018:Tissue Distribution; D014568:Urokinase-Type Plasminogen Activator / Q000037:antagonists & inhibitors* / Q000378:metabolism
D005462:Fluorine Radioisotopes; D011480:Protease Inhibitors; D014568:Urokinase-Type Plasminogen Activator
Breast cancer; Cancer biomarkers; Cancer xenograft; Fluorine-18; PET imaging; Urokinase