A gene therapy for Parkinson’s disease, focusing on the subthalamic nucleus, appears to lead to the formation of unique brain circuitry that correlates with clinical improvement.
copyright graphicsdunia4you/Thinkstock
In a paper published online Nov. 28 in Science Translational Medicine, researchers describe the findings of a metabolic imaging study to explore the mechanism underlying benefits seen in a phase 2, blinded, sham-controlled clinical trial of the gene therapy.
The therapy in question used an adeno-associated viral vector to deliver the gene for glutamic acid decarboxylase into the subthalamic nucleus – a region of the brain known to be overactivated in Parkinson’s disease – which was intended to have an inhibitory effect on the neurons in that region.
Martin Niethammer, MD, PhD, of the Center for Neurosciences at The Feinstein Institute for Medical Research in New York, and his coauthors used 18F-fluorodeoxyglucose positron emission tomography at baseline, 6, and 12 months in 15 gene-therapy patients and 21 sham-treated patients, which revealed the development of new brain circuits in patients treated with the gene therapy.
The circuits, which researchers called the glutamic acid decarboxylase-related pattern, or GADRP, presented with increased metabolism in the premotor region – which also extended into the adjacent motor cortex – and in the supramarginal gyrus. There was also decreased metabolic activity in the caudate, anterior putamen, and adjacent globus pallidus; the ventral anterior and medial dorsal thalamic nuclei; and in the inferior frontal gyrus.
All 15 patients who received the gene therapy showed significant trends in GADRP expression after the treatment, compared with patients who underwent the sham procedure. Furthermore, these correlated significantly with improved clinical outcomes.
The imaging also revealed increased connectivity between regions in the GADRP space among patients who received the gene therapy, with researchers noting five new intrahemispheric node-to-node connections in these patients that were not seen in the sham procedure group.
These included connection linking the left caudate nucleus to the left superior frontal node, the right superior frontal node to the right supramarginal gyrus, and linking the left anterior putamen and globus pallidus with the ipsilateral thalamic node.
The authors also found that overall connectivity in the network rose to “abnormal” levels in the 12 months after gene therapy, while no similar increases were seen in the sham group.
Given that deep brain stimulation for Parkinson’s disease also targets the subthalamic nucleus, researchers looked at changes to the GADRP network in these patients, compared with those who received sham therapy and those who received gene therapy.
They saw that changes in GADRP expression were significantly different between the gene therapy-treated patients and those treated with deep brain stimulation and sham surgery. However, the differences between deep brain stimulation and sham surgery were not significant.
“The current study indicates that customized networks can be characterized using functional imaging data acquired in randomized, controlled phase 2 clinical trials and, if validated, could be used as quantitative outcome measures in more definitive, later-stage clinical trials,” the authors wrote.
The study was supported by Neurologix. Two authors were consultants and stockholders of MeiraGTx.
SOURCE: Niethammer N et al. Sci Transl Med. 2018 Nov 28. doi: 10.1126/scitranslmed.aau0713.