Development and preclinical comparison of two non- non-peptidomimetic MMP/ADAM inhibitors for PET
Methyl 1-((4-nitrophenyl)sulfonyl)piperazine-2-carboxylate hydrochloride (14) Thionyl chloride (7.00 mL, 96.5 mmol) was added dropwise to a solution of
4.10 Preclinical studies
Animals were injected with [18F]-1A or [18F]-2 when the tumors had reached an adequate size (0.3-0.6 mL), after 14 to 21 days of inoculation. The mice were randomly divided into two groups: tumor-bearing mice injected with [18F]-1A (or [18F]-2) and with or without coinjection of 2.5 mg/kg of 1A (or 2). [18F]-1A (1.55 ± 1.38 MBq, 0.031 ± 0.028 nmol) (or [18F]-2 (2.12 ± 3.28 MBq, 0.043 ± 0.080 nmol)), dissolved in saline (maximum volume 200 μL per injection), was intravenously injected into the penile vein of mice anesthetized with 5% isoflurane (Pharmacie BV, The Netherlands) that was mixed with medical air at a flow rate of 2 mL.min-1, after which anesthesia was maintained with 2% isoflurane. For each tracer, 12 mice were used. In each group (either baseline or block), one animal was scanned using PET. Following induction of anesthesia, the mice were then positioned in the bed of the microPET camera (Focus 220, Siemens Medical Solutions USA, Inc.) in transaxial position. The body temperature of mice was maintained by electronically regulated heating pads. Data acquisition of the microPET camera was initiated and continued for a period of 90 min. After the completion of the dynamic emission scan, a 515 sec transmission scan with a Co-57 point source was made for correc-tion of attenuacorrec-tion of 511 keV photons by tissue. After microPET scanning, the mice were terminated by administering a high dose of isoflurane (5%) for about 20 min.
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Ex vivo biodistribution
Ex vivo biodistribution studies were performed on the sacrificed mice 90 min p.i of [18F]-1A (± 1A) or [18F]-2 (± 2). The following organs were taken: bladder, bone, brain, heart, kidney, large intestine, liver, lungs, muscle, pancreas, small intestine, spleen, stomach, tumor and urine. A small drop of infusate was collected for cal-culation of SUVmean. The blood was centrifuged in order to collect plasma and red blood cells. All samples were weighed and levels of radioactivity were determined using a gamma counter. Tracer uptake was expressed as the standardized uptake value (SUVmean), defined as [tissue activity concentration (MBq/g)/(injected activity (MBq)/mouse body weight (g))].
MicroPET image analysis
Emission sinograms were iteratively reconstructed (OSEM2d) after being nor-malized, corrected for attenuation, and corrected for decay of radioactivity. The list-mode data of the emission scans were separated into 22 frame sinograms (15 frames of 2 minutes, 3 frames of 5 minutes, 2 frames of 7.5 minutes, 2 frames of 15 minutes; zoom factor, 4). PET image analysis was performed using Inveon Research Workplace (Siemens) software. Regions of interest were drawn around the tumor.
The uptake of the tracer in the region of interest was determined in Bq.cm-3, which was converted to PET-SUVmean using the following formula: [tissue activity concen-tration (MBq/cc)/(injected activity (MBq)/mouse body weight (g))].
Acknowledgements
The authors wish to thank the Dutch Technology Foundation (STW) for financial support (project 08008).
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