Interpretation of the Role of Transport Proteins in Scintigraphy

Method: Patients with oral malignant tumors were examined with scintigraphic agents of 201-TlCl (201-thallium-chloride), 18-F-FDG (18-F-fluoro-deoxy-glucose) or 99m-Tc-MIBI (99m-technetium-hexakis-methoxy-isobutyl-isonitrile). From scintigraphic examination, accumulation degrees (a tumor retention index; R-index in 201-TlCl and 99m-Tc-MIBI and a standardized uptake value; SUV in 18-F-FDG) were obtained. Concerning transport proteins, they were evaluated molecular-biologically and immuno-histochemically. The expression of transport proteins was estimated in relation with accumulation degrees and histopathological tissue differentiations of malignant tumors.  

Result: A marked expression of transport proteins was found in malignant tumor cells more than in benign tumor cells molecular-biologically and immuno-histochemically. Accumulation of 201-TlCl, 18-F-FDG or 99m-Tc-MIBI depended on transport proteins of Na/K-ATPase, Glut or P-gp respectively. 201-TlCl and 18-F-FDG showed a distinct accumulation in malignant tumors with a large R-index and a large SUV. On the contrary, the accumulation of 99m-Tc-MIBI showed that the accumulation in malignant tumor cells decreased with the passage of time resulting in a small R-index. These results showed that Na/K-ATPase and Glut transported scintigraphic agents to the inside of tumor cells, but P-gp pumped once-accumulated 99m-Tc-MIBI out from tumor cells.

Conclusion: Each transport protein of Na/K-ATPase, Glut and P-gp has an important role in the accumulation of scintigraphic agents in malignant tumors. Na/K-ATPase and Glut played as a positive transporter and P-gp worked as a negative transporter.