Moving Toward Multicenter Therapeutic Trials In Amyotrophic Lateral Sclerosis: Feasibility Of Data Pooling Using Different Translocator Protein Pet Radioligands

Neuroinflammation has been implicated in amyotrophic lateral sclerosis (ALS) and can be visualized using translocator protein (TSPO) radioligands. To become a reliable pharmacodynamic biomarker for ALS multicenter trials, TSPO radioligands have some challenges to overcome. We aimed to investigate whether multicenter data pooling of different TSPO tracers (C-11-PBR28 and F-18-DPA714) is feasible, after validation of an established C-11-PBR28 PET pseudo reference analysis technique for F-18-DPA714. Methods: Seven ALS patients from Belgium (58.9 +/- 6.7 y old, 5 men and 2 women), 8 healthy volunteers from Belgium (52.1 +/- 15.2 y old, 3 men and 5 women), 7 ALS patients from the United States (53.4 +/- 9.8 y old, 5 men and 2 women), and 7 healthy volunteers from the United States (54.6 +/- 9.6 y old, 4 men and 3 women) from a previously published study underwent dynamic F-18-DPA714 (Leuven, Belgium) or C-11-PBR28 (Boston, Massachusetts) PET/MRI. For F-18-DPA714, maps of total volume of distribution (V-T) were compared with SUV ratio (SUVR) images from 40 to 60 min after injection (SUVR40-60) calculated using the pseudo reference regions cerebellum, occipital cortex, and whole brain (WB) without ventricles. For C-11-PBR28, SUVR images from 60 to 90 min after injection using the WB without ventricles were calculated. Results: In line with previous studies, increased F-18-DPA714 uptake (17.0% +/- 5.6%) in primary motor cortices was observed in ALS subjects, as measured by both V-T and SUVR40-60 approaches. The highest sensitivity was found for SUVR calculated using the WB without ventricles (average cluster, 21.6% +/- 0.1%). F-18-DPA714 VT ratio was highly correlated with the SUVR40-60 (r > 0.8, P < 0.001). A similar pattern of increased uptake (average cluster, 20.5% +/- 0.5%) in the primary motor cortices was observed in ALS subjects for C-11-PBR28 SUVR calculated using the WB without ventricles. Analysis of the F-18-DPA714 and C-11-PBR28 data together resulted in a more extensive pattern of significantly increased glial activation bilaterally in the primary motor cortices. Conclusion: The same pseudo reference region analysis technique for C-11-PBR28 PET can be extended toward F-18-DPA714 PET. Therefore, in ALS, standardized analysis across these 2 tracers enables pooling of TSPO PET data across multiple centers and increases the power of TSPO as a biomarker for future therapeutic trials.