Preliminary Biological Evaluation of Leucine Labeled with Gallium-68—A Potential Agent for Tumor Imaging

Abstract

Amino acids are important nutrients for proliferating tumor cells, so their transport is generally increased in many malignant tumor cells. Radiolabeled amino acids are of great interest as they can be alternative or complement tracers to the already wellestablished radiopharmaceuticals such as 18F-FDG. The purpose of this study was to synthesize and characterize a novel 68Ga labeled leucine analog, 68Ga-leucine, as a potential imaging agent for tumors which may not be amenable to imaging by 18F-FDG PET. Biodistribution studies of 68Ga-leucine were performed in Wistar rats with transplanted cholangioma RS-1 xenografts after intravenous injection. 68Ga-leucine demonstrated high in vivo stability. Accumulation of 68Ga-leucine at xenograft tumors was about 2-4 higher as compared with 68GaCl3 and reached 0.79% ID/g. Among the soft tissue organs, only kidney had a relatively high uptake. The amount of radioactivity in other organs didn’t exceed 1% ID/g. The results suggest that 68Ga-leucine has the potential to be a new additional diagnostic tool for PET imaging of tumors.


Keywords: gallium-68, leucine, radiolabeled amino acids, positron emission tomography, tumor imaging.

References
[1] Rice S.L., Roney C.A., Daumar P., Lewis J.S. The next generation of positron emission tomography radiopharmaceuticals in oncology. Semin. Nucl. Med., 2011, V. 41, P. 265– 282.


[2] Wahl R.L., Herman J.M., Ford E. The Promise and Pitfalls of Positron Emission Tomography and Single-Photon Emission Computed Tomography Molecular Imaging- Guided Radiation Therapy. Semin. Radiat. Oncol., 2011, V. 21, P. 88–100.


[3] Hayashi K., Anzai N. Novel therapeutic approaches targeting L-type amino acid transporters for cancer treatment. World J. Gastrointest. Oncol., 2017, V. 9, No. 1, P. 21–29.


[4] Huang C., McConathy J. Radiolabeled amino acids for oncologic imaging. J. Nucl. Med., 2013, V. 54, No. 7, P. 1007–1010.


[5] Rösch F. Past, present and future of 68Ge/68Ga generators. Appl. Radiat. Isot., 2013, V. 76, P. 24–30.


[6] Chin B.B., McDougald D., Weitzel D.H., Hawk T., Reiman R.E., Zalutsky M.R., Vaidynathan G. Synthesis and Preliminary Evaluation of 5-[18F]fluoroleucine. Curr. Radiopharm., 2017, V. 10, No. 1, P. 41–50.


[7] Chin B.B., McDougald D., Weitzel D.H., Hawk T., Reiman R.E., Zalutsky M.R., Vaidynathan G. Synthesis and preliminary evaluation of 5-[18F]fluoroleucine: a novel LAT1 substrate. J. Nucl. Med., 2016, V. 57, P. 1390.


[8] Toegel S., Wadsak W., Mien L.K., Viernstein H., Kluger R., Eidherr H., Haeusler D., Kletter K., Dudczak R., Mitterhauser M. Preparation and pre-vivo evaluation of nocarrier- added, carrier-added and cross-complexed [68Ga]-EDTMP formulations. Eur. J. Pharm. Biopharm., 2008, V. 68, P. 406–412.This work was financially supported by Russian Foundation for Basic Research and The Government of Kaluga Region (project № 17-16-40007a(r)).