Uptake of [N-methyl- ¹¹C]α-methylaminoisobutyric acid in untreated head and neck cancer studied by PET

Abstract.

Amino acid transport system A is expressed strongly in neoplastic cells. [N-methyl-¹¹C]α-Methylaminoisobutyric acid (¹¹C-MeAIB) is a recently developed tracer for PET studies on system A amino acid transport. ¹¹C-MeAIB is a metabolically stable amino acid analogue which is transported from plasma into the tissue by system A. This study evaluated the kinetics of ¹¹C-MeAIB uptake from plasma into tumour tissue and normal tissues in 13 patients with untreated head and neck cancer. ¹¹C-MeAIB uptake in tumour was compared with histological grade and proliferative activity. Tracer uptake was quantitated by calculating the standardised uptake values (SUVs) and the kinetic influx constants (K _i) using graphical analysis. All tumours accumulated ¹¹C-MeAIB and were visualised clearly. In the graphical analysis, linear plots were achieved; the mean K _i value of tumour was 0.056±0.026 min^–1, and the mean SUV was 6.1±2.7. A close correlation between graphically obtained K _i and semi-quantitative SUV in tumours was found (r=0.887, P=0.00005). We could not demonstrate a correlation between the uptake of ¹¹C-MeAIB and the grade of malignancy or the proliferative index, as assessed using Ki-67 immunohistochemical assay. Head and neck cancer can be effectively imaged with ¹¹C-MeAIB PET. ¹¹C-MeAIB showed active and rapid transport into tumour tissue and salivary glands. Further studies on the applicability of ¹¹C-MeAIB PET for radiation treatment planning in the head and neck region and the regulation of system A amino acid transport under different metabolic states are warranted.