Multimodal imaging study of the 5-HT1A receptor biased agonist, NLX-112, in a model of L-DOPA-induced dyskinesia

INTRODUCTION

The leading treatment for motor signs of Parkinson's disease is L-DOPA, but, upon extended use, it can lead to levodopa-induced dyskinesia (LID). Serotonergic neurons are involved in LID etiology and previous pre-clinical studies have shown that NLX-112, a 5-HT1A biased agonist, has robust antidyskinetic effects. Here, we investigated its effects in hemiparkinsonian (HPK) rats with a unilateral nigrostriatal 6-OHDA lesion.

METHODS

We compared HPK rats with LID (i.e., sensitized to the dyskinetic effects of chronic L-DOPA) and without LID (HPK-non-LID), using [18F]FDG PET imaging and fMRI functional connectivity following systemic treatment with saline, L-DOPA, NLX-112 or L-DOPA + NLX-112.

RESULTS

In HPK-non-LID rats, [18F]FDG PET experiments showed that L-DOPA led to hypermetabolism in motor areas (cerebellum, brainstem, and mesencephalic locomotor region) and to hypometabolism in cortical regions. L-DOPA effects were also observed in HPK-LID rats, with the additional emergence of hypermetabolism in raphe nuclei and hypometabolism in hippocampus and striatum. NLX-112 attenuated L-DOPA-induced raphe hypermetabolism and cingulate cortex hypometabolism in HPK-LID rats. Moreover, in fMRI experiments NLX-112 partially corrected the altered neural circuit connectivity profile in HPK-LID rats, through activity in regions rich in 5-HT1A receptors.

CONCLUSION

This neuroimaging study sheds light for the first time on the brain activation patterns of HPK-LID rats. The 5-HT1A receptor agonist, NLX-112, prevents occurrence of LID, likely by activating pre-synaptic autoreceptors in the raphe nuclei, resulting in a partial restoration of brain metabolic and connectivity profiles. In addition, NLX-112 also rescues L-DOPA-induced deficits in cortical activation, suggesting potential benefit against non-motor symptoms of Parkinson's disease.

Single subanesthetic dose of ketamine produces delayed impact on brain [18F]FDG PET imaging and metabolic connectivity in rats

Introduction

Ketamine, a glutamate NMDA receptor antagonist, is suggested to act very rapidly and durably on the depressive symptoms including treatment-resistant patients but its mechanisms of action remain unclear. There is a requirement for non-invasive biomarkers, such as imaging techniques, which hold promise in monitoring and elucidating its therapeutic impact.

Methods

We explored the glucose metabolism with [¹⁸F]FDG positron emission tomography (PET) in ten male rats in a longitudinal study designed to compare imaging patterns immediately after acute subanaesthetic ketamine injection (i.p. 10 mg/kg) with its sustained effects, 5 days later. Changes in [¹⁸F]FDG uptake following ketamine administration were estimated using a voxel-based analysis with SPM12 software, and a region of interest (ROI) analysis. A metabolic connectivity analysis was also conducted to estimate the immediate and delayed effects of ketamine on the inter-individual metabolic covariance between the ROIs.

Results

No significant difference was observed in brain glucose metabolism immediately following acute subanaesthetic ketamine injection. However, a significant decrease of glucose uptake appeared 5 days later, reflecting a sustained and delayed effect of ketamine in the frontal and the cingulate cortex. An increase in the raphe, caudate and cerebellum was also measured. Moreover, metabolic connectivity analyses revealed a significant decrease between the hippocampus and the thalamus at day 5 compared to the baseline.

Discussion

This study showed that the differences in metabolic profiles appeared belatedly, 5 days after ketamine administration, particularly in the cortical regions. Finally, this methodology will help to characterize the effects of future molecules for the treatment of treatment resistant depression.

Safety and Therapeutic Optimization of Lutetium-177 Based Radiopharmaceuticals

Peptide receptor radionuclide therapy (PRRT) using Lutetium-177 (¹⁷⁷Lu) based radiopharmaceuticals has emerged as a therapeutic area in the field of nuclear medicine and oncology, allowing for personalized medicine. Since the first market authorization in 2018 of [¹⁷⁷Lu]Lu-DOTATATE (Lutathera®) targeting somatostatin receptor type 2 in the treatment of gastroenteropancreatic neuroendocrine tumors, intensive research has led to transfer innovative ¹⁷⁷Lu containing pharmaceuticals to the clinic. Recently, a second market authorization in the field was obtained for [¹⁷⁷Lu]Lu-PSMA-617 (Pluvicto®) in the treatment of prostate cancer. The efficacy of ¹⁷⁷Lu radiopharmaceuticals are now quite well-reported and data on the safety and management of patients are needed. This review will focus on several clinically tested and reported tailored approaches to enhance the risk-benefit trade-off of radioligand therapy. The aim is to help clinicians and nuclear medicine staff set up safe and optimized procedures using the approved ¹⁷⁷Lu based radiopharmaceuticals.

Amino Acid Solutions for 177Lu-Oxodotreotide Premedication: A Tolerance Study

Background: The co-infusion of amino acid solutions during peptide receptor radionuclide therapy reduces the tubular reabsorption of 177Lu-oxodotreotide, thus minimizing nephrotoxicity. In our nuclear medicine department, the patients received two different types of amino acid perfusion over time: a commercial solution (CS) containing 10% amino acids, and a 2.5% lysine−arginine (LysArg) hospital preparation, produced by a referral laboratory. The aim of the present study was to analyze the tolerance of the two amino acid solutions. Methods: The patient files were analyzed and double-checked. The study parameters comprised the gender, age, primary tumor site, type of amino acid perfusion, adverse events (AE) and WHO AE grades, antiemetic premedication, creatinine, and serum potassium level. Results: From February 2016 to February 2019, 76 patients were treated, for a total 235 cycles. AEs occurred in 71% of the CS cycles (n = 82/116), versus 18% (n = 21/119) in the LysArg group (p < 0.0001). In the CS group, the AEs were mostly WHO grade 4 (n = 24/82), and mostly grade 1 in the LysArg group (n = 13/21). Poisson regression showed a higher risk of AE overall and of grades 3 and 4 in the females and with CS. The mean creatinine clearance was identical before and after the PRRT cycles, whichever amino acid perfusion was used. Conclusions: The lysine−arginine preparation showed better tolerance than the commercial solution. The change to LysArg reduced the antiemetic premedication from four molecules to one.

Different Alterations of Agonist and Antagonist Binding to 5-HT1A Receptor in a Rat Model of Parkinson’s Disease and Levodopa-Induced Dyskinesia: A MicroPET Study

Background: The gold-standard treatment for Parkinson’s disease is L-DOPA, which in the long term often leads to levodopa-induced dyskinesia. Serotonergic neurons are partially responsible for this, by converting L-DOPA into dopamine leading to its uncontrolled release as a “false neurotransmitter”. The stimulation of 5-HT1A receptors can reduce involuntary movements but this mechanism is poorly understood. Objective: This study aimed to investigate the functionality of 5-HT1A receptors using positron emission tomography in hemiparkinsonian rats with or without dyskinesia induced by 3-weeks daily treatment with L-DOPA. Imaging sessions were performed “off” L-DOPA. Methods: Each rat underwent a positron emission tomography scan with [18F]F13640, a 5-HT1AR agonist which labels receptors in a high affinity state for agonists, or with [18F]MPPF, a 5-HT1AR antagonist which labels all the receptors. Results: There were decreases of [18F]MPPF binding in hemiparkinsonian rats in cortical areas. In dyskinetic animals, changes were slighter but also found in other regions. In hemiparkinsonian rats, [18F]F13640 uptake was decreased bilaterally in the globus pallidus and thalamus. On the non-lesioned side, binding was increased in the insula, the hippocampus and the amygdala. In dyskinetic animals, [18F]F13640 binding was strongly increased in cortical and limbic areas, especially in the non-lesioned side. Conclusion: These data suggest that agonist and antagonist 5-HT1A receptor-binding sites are differently modified in Parkinson’s disease and levodopa-induced dyskinesia. In particular, these observations suggest a substantial involvement of the functional state of 5-HT1AR in levodopa-induced dyskinesia and emphasize the need to characterize this state using agonist radiotracers in physiological and pathological conditions.

Serotonin 5-HT1A Receptor Biased Agonists Induce Different Cerebral Metabolic Responses: A [18F]-Fluorodesoxyglucose Positron Emission Tomography Study in Conscious and Anesthetized Rats

Serotonin 5-HT_1A receptors constitute an attractive therapeutic target for various psychiatric or neurodegenerative disorders. These receptors are expressed in multiple brain regions on different neuronal populations and can be coupled with distinct G-protein subtypes; such functional diversity complicates the use of 5-HT_1A ligands in several pathologies where it would be desirable to stimulate the receptors in a precise region. Therefore, using "biased agonists" able to target specifically certain subpopulations of 5-HT_1A receptors would enable achievement of better therapeutic benefit. Several 5-HT_1A receptor biased agonists are currently in development, including NLX-101 (aka F15599) and NLX-112 (aka F13640, befiradol), with preclinical data suggesting that they preferentially target different populations of 5-HT_1A receptors. However, most previous studies used invasive and regionally limited approaches. In this context, [¹⁸F]-fluorodesoxyglucose (FDG)-positron emission tomography (PET) imaging constitutes an interesting technique as it enables noninvasive mapping of the regional brain activity changes following a pharmacological challenge in conscious animals. We report here the evaluation of cerebral glucose metabolism following intraperitoneal injection of different doses of NLX-112 or NLX-101 in conscious or isoflurane-anesthetized rats. The biased agonists produced different metabolic "fingerprints" with distinct regional preferences, consistent with previous studies. At equal doses, the effect of NLX-101 was less marked than NLX-112 in the piriform cortex, in the striatum (in terms of inhibition), and in the pontine nuclei and the cerebellum (in terms of activation); furthermore, only NLX-112 increased the glucose metabolism in the parietal cortex, whereas only NLX-101 induced a clear activation in the colliculi and the frontal cortex, which may be related to its distinctive procognitive profile. Both agonist effects were almost completely unapparent in anesthetized animals, underlining the importance of studying serotonergic neurotransmission in the conscious state. In this regard, [¹⁸F]FDG-PET imaging seems very complementary with other functional imaging techniques such as pharmacological MRI.

PET imaging of the influence of physiological and pathological α-synuclein on dopaminergic and serotonergic neurotransmission in mouse models

AIMS

Alpha-synuclein (α-syn) aggregation is a neuropathological hallmark of neurodegenerative synucleinopathies. This in vivo study explored glucose metabolism and dopaminergic and serotoninergic neurotransmission in KO α-syn, wild-type mice and an accelerated murine model of synucleinopathy (M83).

METHODS

MicroPET acquisitions were performed in all animals aged 5-6 months using five radiotracers exploring brain glucose metabolism ([¹⁸ F]FDG), dopamine neurotransmission ([¹¹ C]raclopride, [¹¹ C]PE2I) and serotonin neurotransmission ([¹⁸ F]MPPF, [¹¹ C]DASB). For all radiotracers, except [¹⁸ F]FDG, PET data were analyzed with a MRI-based VOI method and a voxel-based analysis.

RESULTS

MicroPET data showed a decrease in [¹¹ C]raclopride uptake in the caudate putamen of KO α-syn mice, in comparison with M83 and WT mice, reflecting a lower concentration of D₂ receptors. The increase in [¹⁸ F]MPPF uptake in M83 vs WT and KO mice indicates overexpression of 5-HT_1A receptors. The lack of change in dopamine and serotonin transporters in all groups suggests unchanged neuronal density.

CONCLUSIONS

This PET study highlights an effect of α-syn modulation on the expression of the D₂ receptor, whereas aggregated α-syn leads to overexpression of 5-HT_1A receptor, as a pathophysiological signature.

Quantitative longitudinal imaging of activated microglia as a marker of inflammation in the pilocarpine rat model of epilepsy using [11C]-( R)-PK11195 PET and MRI

Inflammation may play a role in the development of epilepsy after brain insults. [¹¹C]-( R)-PK11195 binds to TSPO, expressed by activated microglia. We quantified [¹¹C]-( R)-PK11195 binding during epileptogenesis after pilocarpine-induced status epilepticus (SE), a model of temporal lobe epilepsy. Nine male rats were studied thrice (D0-1, D0 + 6, D0 + 35, D0 = SE induction). In the same session, 7T T2-weighted images and DTI for mean diffusivity (MD) and fractional anisotropy (FA) maps were acquired, followed by dynamic PET/CT. On D0 + 35, femoral arterial blood was sampled for rat-specific metabolite-corrected arterial plasma input functions (AIFs). In multiple MR-derived ROIs, we assessed four kinetic models (two with AIFs; two using a reference region), standard uptake values (SUVs), and a model with a mean AIF. All models showed large (up to two-fold) and significant TSPO binding increases in regions expected to be affected, and comparatively little change in the brainstem, at D0 + 6. Some individuals showed increases at D0 + 35. AIF models yielded more consistent increases at D0 + 6. FA values were decreased at D0 + 6 and had recovered by D0 + 35. MD was increased at D0 + 6 and more so at D0 + 35. [¹¹C]-( R)-PK11195 PET binding and MR biomarker changes could be detected with only nine rats, highlighting the potential of longitudinal imaging studies.

[The PICC line, a new approach for venous access]

Peripheral Inserted Central Catheter (PICC) line is a peripherally inserted central catheter. This implantable medical device is placed into a peripheral vein of the arm in order to obtain an intravenous central access. This device can find its use in various applications like intravenous delivery of parenteral nutrition, anticancer agents and antibiotics, as well as for blood sampling. PICC line is not widely used in medical practice because it remains largely unknown. The aim of this review is thus to introduce PICC line to the medical and scientific community. First, we will approach its insertion and maintenance of the dressing. We will then detail the benefits and drawbacks associated with its use, and finally discuss its position with regards to the other central venous access available.