P14.38 Clinical experience with tumor treating fields (TTFields) treatment for posterior fossa tumors

Introduction: TTFields brought a new concept in the treatment of brain tumors. It was tested and recommended for use in supra-tentorial lesions. There is a paucity of data available about TTFields safety and efficacy for infra-tentorial lesion.

Method: Patients with posterior fossa tumors were treated with the Optune® system. Initial transducer array positioning and all technical characteristic were performed with technical support from Novocure.

Results: Two patients with posterior fossa glial tumors were treated. The first is a 27 years old male with DIPG (without pathological confirmation of the tumor grade) who was treated with Stupp protocol. Treatment with TTFields commenced with TMZ adjuvant phase. The second patient is a 33 years old female with cerebello-pontine astrocytoma WHO grade III, IDH I mutated. This patient was treated with partial resection and Stupp protocol. TTFields treatment was started after completing 12 TMZ adjuvant cycles with measurable stable disease. Duration and compliance of TTFields treatment for first patient is 286 days and 86% and for second patient is 168 days and 93.6%. The skin toxicity is minimal and did not require treatment interruption. There is no other TTFields related toxicity. The MRI evaluation had showed improvement in the first patient and stable disease in the second.

Conclusion: According to our knowledge, this is the first report of clinical experience with TTFields treatment for posterior fossa tumors. In our experience, the treatment is feasible and with equal toxicity to previously reported supra-tentorial lesions. Small patient population and short follow up do not allow efficacy evaluation.

Pathological gamma oscillations, impaired dopamine release, synapse loss and reduced dynamic range of unitary glutamatergic synaptic transmission in the striatum of hypokinetic Q175 Huntington mice

Huntington's disease (HD) is a severe genetically inherited neurodegenerative disorder. Patients present with three principal phenotypes of motor symptoms: choreatic, hypokinetic-rigid and mixed. The Q175 mouse model of disease offers an opportunity to investigate the cellular basis of the hypokinetic-rigid form of HD. At the age of 1 year homozygote Q175 mice exhibited the following signs of hypokinesia: Reduced frequency of spontaneous movements on a precision balance at daytime (-55%), increased total time spent without movement in an open field (+42%), failures in the execution of unconditioned avoidance reactions (+32%), reduced ability for conditioned avoidance (-96%) and increased reaction times (+65%) in a shuttle box. Local field potential recordings revealed low-frequency gamma oscillations in the striatum as a characteristic feature of HD mice at rest. There was no significant loss of DARPP-32 immunolabeled striatal projection neurons (SPNs) although the level of DARPP-32 immunoreactivity was lower in HD. As a potential cause of hypokinesia, HD mice revealed a strong reduction in striatal KCl-induced dopamine release, accompanied by a decrease in the number of tyrosine hydroxylase-(TH)- and VMAT2-positive synaptic varicosities. The presynaptic TH fluorescence level was also reduced. Patch-clamp experiments were performed in slices from 1-year-old mice to record unitary EPSCs (uEPSCs) of presumed cortical origin in the absence of G-protein-mediated modulation. In HD mice, the maximal amplitudes of uEPSCs amounted to 69% of the WT level which matches the loss of VGluT1+/SYP+ synaptic terminals in immunostained sections. These results identify impairment of cortico-striatal synaptic transmission and dopamine release as a potential basis of hypokinesia in HD.