FDG injected intravenously accumulates and is retained inside tumour cells rather than being washed out. What accounts for this metabolic trapping?
- A Hexokinase phosphorylates FDG to FDG-6-phosphate, which cannot undergo further glycolysis ✓
- B FDG binds irreversibly to glucose transporters at the cell membrane
- C FDG is actively pumped into lysosomes by P-glycoprotein
- D FDG is incorporated directly into DNA during replication
Correct answer: A. Hexokinase phosphorylates FDG to FDG-6-phosphate, which cannot undergo further glycolysis
Explanation
FDG enters cells through GLUT transporters and is phosphorylated by hexokinase to FDG-6-phosphate. Unlike glucose-6-phosphate, FDG-6-phosphate is not a substrate for subsequent glycolytic enzymes and is effectively trapped because most tumours have low glucose-6-phosphatase activity. The signal therefore reflects regional glucose utilisation, which is the basis of SUV measurement. Transporter binding, lysosomal sequestration and nucleic acid incorporation are all incorrect mechanisms.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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