In vivo evaluation of a microtubule PET ligand, [11C]MPC-6827, in mice following chronic alcohol consumption

Chronic MAP4343 reverses escalated alcohol drinking in a mouse model of alcohol use disorder

Alcohol use disorders can be driven by negative reinforcement. Alterations of the microtubule cytoskeleton have been associated with mood regulation in the context of depression. Notably, MAP4343, a pregnenolone derivative known to promote tubulin assembly, has antidepressant properties. In the present study, we tested the hypothesis that MAP4343 may reduce excessive alcohol drinking in a mouse model of alcohol dependence by normalizing affect during withdrawal. Adult male C57BL/6J mice were given limited access to voluntary alcohol drinking and ethanol intake escalation was induced by chronic intermittent ethanol (CIE) vapor inhalation. Chronic, but not acute, administration of MAP4343 reduced ethanol intake and this effect was more pronounced in CIE-exposed mice. There was a complex interaction between the effects of MAP4343 and alcohol on affective behaviors. In the elevated plus maze, chronic MAP4343 tended to increase open-arm exploration in alcohol-naive mice but reduced it in alcohol-withdrawn mice. In the tail suspension test, chronic MAP4343 reduced immobility selectively in Air-exposed alcohol-drinking mice. Finally, chronic MAP4343 countered the plasma corticosterone reduction induced by CIE. Parallel analysis of tubulin post-translational modifications revealed lower α-tubulin acetylation in the medial prefrontal cortex of CIE-withdrawn mice. Altogether, these data support the relevance of microtubules as a therapeutic target for the treatment of AUD.

Radiosynthesis and evaluation of [11C]AG-488, a dual anti-angiogenetic and anti-tubulin PET ligand

Combinations of antiangiogenic and cytotoxic agents show promising results in the treatment of cancer. However, there is a lack of single agent with both antiangiogenic and cytotoxic activities for clinical application. AG-488 aka FLAG-003 is a novel ligand with established antiangiogenetic properties via activation of receptor thymidine kinase (RTK) and anti-tubulin properties in tumor cells. AG-488 is also reported to reduce tumor volume and prolong survival in preclinical animal models of glioblastoma multiforme, breast cancer and is in clinical stage. Higher expression of RTKs and tubulins is reported in various cancers. This study reveals the development of [¹¹C]AG-488, a high affinity dual target inhibitor binding to RTK and anti-tubulin activities. We rationale that antiangiogenic RTK and anti-tubulin activity of [¹¹C]AG-488 may enhance the tumor to tissue ratio, assisting in cancer drug development. [¹¹C]AG-488 was synthesized in 35 ± 5 % radiochemical yield by radiomethylating the corresponding phenolate using [¹¹C]CH₃I. MicroPET studies in mice indicated blood-brain barrier penetration of [¹¹C]AG-488 and retention in the brain. However, blocking studies with antitubulin and RTK agent HD-800 and microtubule depolymerizing agent MPC-6827 show increased binding of [¹¹C]AG-488 in brain. The pattern of tracer binding in blocking conditions is similar to the baseline conditions. The higher binding may be due to the increased plasma uptake of radiotracer or the formation of more free tubulins due to microtubule dynamic instability during the blocking conditions.

Preliminary mechanistic insights of a brain-penetrant microtubule imaging PET ligand in a tau-knockout mouse model

BACKGROUND

Microtubules (MTs) are critical for cell structure, function, and survival. MT instability may contribute to Alzheimer's disease (AD) pathogenesis as evidenced by persistent negative regulation (phosphorylation) of the neuronal microtubule-associated protein tau. Hyperphosphorylated tau, not bound to MTs, forms intraneuronal pathology that correlates with dementia and can be tracked using positron emission tomography (PET) imaging. The contribution of MT instability in AD remains unknown, though it may be more proximal to neuronal dysfunction than tau accumulation. Our lab reported the first brain-penetrant MT-based PET ligand, [11C]MPC-6827, and its PET imaging with this ligand in normal rodents and non-human primates demonstrated high brain uptake and excellent pharmacokinetics. Target engagement and mechanism of action using in vitro, in vivo, and ex vivo methods were evaluated here.

METHODS

In vitro cell uptake assay was performed in SH-SY5Y neuronal cells with [11C]MPC-6827, with various MT stabilizing and destabilizing agents. To validate the in vitro results, wild type (WT) mice (n = 4) treated with a brain-penetrant MT stabilizing drug (EpoD) underwent microPET/CT brain imaging with [11C]MPC-6827. To determine the influence of tau protein on radiotracer binding in the absence of protein accumulation, we utilized tau knockout (KO) mice. In vivo microPET imaging, ex vivo biodistribution, and autoradiography studies were performed in tau KO and WT mice (n = 6/group) with [11C]MPC-6827. Additionally, α, β, and acetylated tubulin levels in both brain samples were determined using commercially available cytoskeleton-based MT kit and capillary electrophoresis immunoblotting assays.

RESULTS

Cell uptake demonstrated higher radioactive uptake with MT destabilizing agents and lower uptake with stabilizing agents compared to untreated cells. Similarly, acute treatment with EpoD in WT mice decreased [11C]MPC-6827 brain uptake, assessed with microPET/CT imaging. Compared to WT mice, tau KO mice expressed significantly lower β tubulin, which contains the MPC-6827 binding domain, and modestly lower levels of acetylated α tubulin, indicative of unstable MTs. In vivo imaging revealed significantly higher [11C]MPC-6827 uptake in tau KOs than WT, particularly in AD-relevant brain regions known to express high levels of tau. Ex vivo post-PET biodistribution and autoradiography confirmed the in vivo results.

CONCLUSIONS

Collectively, our data indicate that [11C]MPC-6827 uptake inversely correlates with MT stability and may better reflect the absence of tau than total tubulin levels. Given the radiotracer binding does not require the presence of aggregated tau, we hypothesize that [11C]MPC-6827 may be particularly useful in preclinical stages of AD prior to tau deposition. Our study provides immediate clarity on high uptake of the MT-based radiotracer in AD brains, which directly informs clinical utility in MT/tau-based PET imaging studies.

Preclinical evaluation of a microtubule PET ligand [11C]MPC-6827 in tau and amyotrophic lateral sclerosis animal models

BACKGROUND

Microtubules are abundant in brain and their malfunctioning occurs in the early-to-advanced stages of neurodegenerative disorders. At present, there is no in vivo test available for a definitive diagnosis of most of the neurodegenerative disorders. Herein, we present the microPET imaging of microtubules using our recently reported Positron Emission Tomography (PET) tracer, [¹¹C]MPC-6827, in transgenic mice models of tau pathology (rTg4510) and amyotrophic lateral sclerosis pathology (SOD1*G93A) and compared to corresponding age-matched controls.

METHODS

Automated synthesis of [¹¹C]MPC-6827 was achieved in a GE-FX2MeI/FX2M radiochemistry module. In vivo PET imaging studies of [¹¹C]MPC-6827 (3.7 ± 0.8 MBq) were performed in rTg4510 and SOD1*G93A mice groups and their corresponding littermates (n = 5 per group). Dynamic PET images were acquired using a microPET Inveon system (Siemens, Germany) at 55 min for rTg4510 and 30 min for SOD1*G93A and corresponding controls. PET images were reconstructed using the 3D-OSEM algorithm and analyzed using VivoQuant version 4 (Invicro, MA). Tracer uptake in ROIs that included whole brain was measured as %ID/g over time to generate standardized uptake values (SUV) and time-activity curves (TACs).

RESULTS

[¹¹C]MPC-6827 exhibit a trend of lower tracer binding in mouse models of Alzheimer's disease (tau pathology, line rTg4510) and Amyotrophic Lateral Sclerosis (line SOD1*G93A) compared to wild-type littermates.

CONCLUSIONS

Our finding indicates a trend of loss of microtubule binding of [¹¹C]MPC-6827 in the whole brain of AD and ALS transgenic mice models compared to control mice. The pilot studies described herein show that [¹¹C]MPC-6827 could be used as a PET ligand for preclinical and human brain imaging of Alzheimer's disease, ALS, and other neurodegenerative diseases. Preclinical Evaluation of a Microtubule PET Ligand [¹¹C]MPC-6827 in Tau and Amyotrophic Lateral Sclerosis Animal Models. J. S. Dileep Kumar, Andrei Molotkov, Jongho Kim, Patrick Carberry, Sidney Idumonyi, John Castrillon, Karen Duff, Neil A. Shneider, Akiva Mintz.