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J Nucl Med. 2008; 49 (Supplement 1):98P
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Radiopharmaceutical Chemistry: New Chemistry-Oncology

New Chemistry-Oncology II: Small Molecules

[13N]Gemcitabine: A new PET tracer to assess gemcitabine (GT) tumor uptake

Shankar Vallabhajosula1, Andrej Zatorski1, Paresh Kothari1, Lawrence Anderson2 and Stanley Goldsmith1

1 Radiology, Citigroup Biomedical Imaging Center (CBIC), Weill Cornell Medical College, Cornell University, New York, New York; 2 Lab. Clin. Pharmacology, CDER, FDA, Silver Spring, Maryland

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Objectives: GT was approved in 2005 as first-line treatment of advanced or recurrent breast cancer (Ca), and in combination with carboplatin for ovarian Ca. In order to assess tumor localization, we developed [13N]GT.

Methods: A tetrazole derivative of GT, 1-(β-D-2'-deoxy-2',2'-difluororibofuranosyl)-4-tetrazolo-2 (1H)-pyrimidinone (DeTet) was prepared as a precursor for nucleophilic displacement of tetrazole residue by ammonia. [13N]Ammonia was made by proton bombardment of water (containing 5 mM ethanol). The irradiated water (4.6 mL) was first passed through a QMA cartridge (to remove the anionic impurities) and then [13N]NH3 was trapped on a CM cartridge. [13N]NH3 was eluted with sodium acetate (0.6 mL) into a vial containing 2-10 mg of precursor. The mixture was incubated for 6 min at 110oC and then [13N]GT was purified by HPLC. MicroPET imaging studies were performed in prostate cancer LNCaP xenografts over a period of 30 min to assess tumor uptake and biodistribution.

Results: Radiochemically pure (>98%) [13N]GT (in 4 mL) with a specific activity of <2GBq/mmole was obtained after HPLC purification. The highest radiochemical yield (6%) was obtained with 10 mg of precursor. Synthesis of GT using cold ammonia, however, yielded very high (>90%) labeling yields. Preliminary imaging studies demonstrated that the tumor uptake of [13N]GT was much lower compared to that of FDG and FLT.

Conclusions: The strategy of using DeTet as a precursor does provide radiochemically pure [13N]GT. Lower tumor uptake compared to FLT may suggest that higher SA is essential for useful tumor uptake. Lower labeling yields and SA are the focus of further optimization studies.

Research Support: SAIC-Frederick, Inc.





This Article
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Right arrow Articles by Vallabhajosula, S.
Right arrow Articles by Goldsmith, S.
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Right arrow Articles by Vallabhajosula, S.
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