A Brief Evaluation of Tumor Imaging in Mice with 99mTc-glucarate Including a Comparison with 18F-FDG

Objective: Recently 99mTc-glucarate, a radiolabeled glucose analogue, has been considered as a SPECT alternative to 18F-FDG and PET for non-invasive detection of certain tumors. Thus far there have been few studies on 99mTcglucarate for tumor imaging and fewer, if any, studies comparing 99mTc-glucarate with 18F-FDG. As a preliminary indication of the properties of 99mTc-glucarate as a possible substitute for 18F-FDG in animal studies, we have imaged mice bearing xenografts of four tumor types with 99mTc-glucarate and have compared in two mice with one of these tumor types the 99mTc and 18F biodistributions. Methods: Two mice bearing SUM190 breast cancer xenografts received 1 mCi of 99mTc-glucarate and were imaged on a NanoSPECT/CT small animal camera. One day later, the same animals received 1 mCi of 18F-FDG and were imaged on a MosaicHP PET small animal camera. In addition, 0.5-1 mCi of 99mTc-glucarate only was administered to mice bearing xenografts induced by BxPC3 pancreatic cancer cells, HEK-293 renal cell carcinomas cells or HCT-116 colorectal tumor cells. NanoSPECT/CT acquisitions were performed in these mice to evaluate tumor accumulations. Results: In the SUM190 xenografted mice, the average tumor accumulation was 1.4 % (ID%/cm3) for 99mTc-glucarate and 2.1 % (ID%/cm3) for 18F-FDG. While slightly higher than 99mTc-glucarate, the tumor accumulation of 18F-FDG was accompanied by higher bone marrow and muscle accumulations at levels that could interfere with the tumor image depending upon location. The whole body clearance of 99mTc-glucarate was faster than that of 18F-FDG. Tumor accumulation of 99mTc-glucarate varied among tumor types but the tumors were readily visible in all images. Conclusion: In a direct comparison in the same two SUM190 tumored animals, SPECT images obtained with 99mTcglucarate compared favorably with PET images obtained with 18F-FDG. Tumor images with 99mTc-glucarate were also positive in three additional tumor mouse models. While further comparison studies are necessary, we conclude that 99mTcglucarate may be a more convenient and less expensive alternative to 18F-FDG for tumored mouse studies.