A fructose transporter (GLUT 5) as a target for breast cancer therapy and imaging

Abstract

Introduction: Positron Emission Tomography (PET) has revolutionized the diagnostic and imaging fields in cancer research. PET has opened new avenues in the pre-clinical study of radiotracers and radio-therapeutic compounds of which the full potentials are yet to be explored. To date 18F-Fluoro-Deoxy-Glucose1 (18F-FDG) is the most widely used radiotracer for PET imaging. The success of 18F-FDG is due to the existence of several trans-membrane proteins responsible for the facilitated transport of glucose. A related protein is a specific fructose selective trans-membrane transporter (GLUT 5) that has been observed to be over-expressed by some types of cancer cells suggesting that D-fructose is utilized by these cancer cells for energy production. Thus labeled D-fructose derivatives are potential candidates for selective PET imaging for cancer cells similar to 18F-FDG in active cells. Aim: The aim of this study was to investigate the effect of D-fructose on GLUT 5 positive and negative cell cultures and to evaluate the feasibility of GLUT 5 as a target for PET imaging of breast cancer. Objectives: The following were investigated: <ul> i. The extent of expression of GLUT 5 in three cancer cell lines: breast cancer cells (MCF-7), Baby Hamster Kidney cells (BHK) and cervical epithelial carcinoma cells (Hela). ii. The colony formation potential of D-fructose enriched medium (glucose-free) and its effect on proliferation of the investigated cell lines. iii. The effect of anti-GLUT 5 antibodies on the proliferation of breast cancer cells in vitro. iv. The synthesis and characterization of a non-radioactive fluorinated D-fructose derivative (1-deoxy-fluoro–D-fructose) </ul> Results: D-fructose was observed to mediate cell growth in MCF-7 cell lines but not in Hela and BHK cell lines. Glucose stimulated significantly greater cell proliferation than D-fructose for all 3 cell lines but more noticeably for the Hela (p<0.001) and BHK (p=0.0110) cell lines at all tested concentrations. Cell growth of MCF-7 cell lines where only D-fructose was present suggests a role for the highly expressed fructose specific transporter (GLUT 5) in the use of D-fructose for energy production and cell growth by these breast cancer cells. No significant differences were observed in the ability of D-fructose enriched medium to induce 3D colony formation among the three cell lines studied (p>0.05) suggesting that D-fructose is not linked directly with aggressive carcinogenesis in these cell lines despite the observed evidence of D-fructose involvement in cell proliferation and energy consumption. Anti-GLUT 5 antibodies did not show an inhibitory effect on MCF-7 cell proliferation at concentration up to 1 μg/ml (1:1000) despite these cells high expression of GLUT 5. GLUT 5 is highly expressed by MCF-7 but not by Hela and BHK cell lines making it an important selective target for imaging of this type of breast cancer and a possible therapeutic target for antibody targeted therapy of breast cancer. A chemical reaction sequence for the synthesis of 1-deoxy-fluoro–D-fructose (1-FDF) was carried out and an acceptable yield for an isotope labeling friendly reaction sequence was obtained and the product chemically characterized. Conclusion: The D-fructose transporter GLUT 5 shows potential for possible application with PET imaging of breast cancer. Isotope labeled 1-FDF can be synthesized in good yield and should be the object of further studies such as development of an automated synthesis module for its radio-labeled derivative as well as pre-clinical animal and human studies. Copyright