Multi-tracer and multiparametric PET imaging to detect the IDH mutation in glioma: a preclinical translational in vitro, in vivo, and ex vivo study.

Background: This translational study explores multi-tracer PET imaging for the non-invasive detection of the IDH1 mutation which is a positive prognostic factor in glioma.

Methods: U87 human high-grade glioma (HGG) isogenic cell lines with or without the IDH1 mutation (CRISP/Cas9 method) were stereotactically grafted into rat brains, and examined, in vitro, in vivo and ex vivo. PET imaging sessions, with radiotracers specific for glycolytic metabolism ([F]FDG), amino acid metabolism ([F]FDopa), and inflammation ([F]DPA-714), were performed sequentially during 3-4 days. The in vitro radiotracer uptake was expressed as percent per million cells. For each radiotracer examined in vivo, static analyses included the maximal and mean tumor-to-background ratio (TBR and TBR) and metabolic tumor volume (MTV). Dynamic analyses included the distribution volume ratio (DVR) and the relative residence time (RRT) extracted from a reference Logan model. Ex vivo analyses consisted of immunological analyses.

Results: In vitro, IDH1+ cells (i.e. cells expressing the IDH1 mutation) showed lower levels of [F]DPA-714 uptake compared to IDH1- cells (p < 0.01). These results were confirmed in vivo with lower [F]DPA-714 uptake in IDH+ tumors (3.90 versus 5.52 for TBR, p = 0.03). Different values of [F]DPA-714 and [F] FDopa RRT (respectively 11.07 versus 22.33 and 2.69 versus - 1.81 for IDH+ and IDH- tumors, p < 0.02) were also observed between the two types of tumors. RRT [F]DPA-714 provided the best diagnostic performance to discriminate between the two cell lines (AUC of 100%, p < 0.01). Immuno-histological analyses revealed lower expression of Iba-1 and TSPO antibodies in IDH1+ tumors.

Conclusions: [18F]DPA-714 and [18F] FDopa both correlate with the presence of the IDH1 mutation in HGG. These radiotracers are therefore good candidates for translational studies investigating their clinical applications in patients.