Delivering FLT to the Central Nervous System by Means of a Promising Targeting System: Synthesis, [11C]Radiosynthesis, and in Vivo Evaluation

Straightforward Access to a New Class of Dual DYRK1A/CLK1 Inhibitors Possessing a Simple Dihydroquinoline Core

The DYRK (Dual-specificity tyrosine phosphorylation-regulated kinase) family of protein kinases is involved in the pathogenesis of several neurodegenerative diseases. Among them, the DYRK1A protein kinase is thought to be implicated in Alzheimer's disease (AD) and Down syndrome, and as such, has emerged as an appealing therapeutic target. DYRKs are a subset of the CMGC (CDK, MAPKK, GSK3 and CLK) group of kinases. Within this group of kinases, the CDC2-like kinases (CLKs), such as CLK1, are closely related to DYRKs and have also sparked great interest as potential therapeutic targets for AD. Based on inhibitors previously described in the literature (namely TG003 and INDY), we report in this work a new class of dihydroquinolines exhibiting inhibitory activities in the nanomolar range on hDYRK1A and hCLK1. Moreover, there is overwhelming evidence that oxidative stress plays an important role in AD. Pleasingly, the most potent dual kinase inhibitor 1p exhibited antioxidant and radical scavenging properties. Finally, drug-likeness and molecular docking studies of this new class of DYRK1A/CLK1 inhibitors are also discussed in this article.

Prodrug strategy for enhanced therapy of central nervous system disease

Central nervous system (CNS) disease is one of the most notorious arch-criminals of human health across the world. Although considerable efforts have been devoted to promote the development of CNS drugs, ideal therapeutical effects are yet far from enough. The blood-brain barrier remains a major player that impedes the full potential of CNS therapeutical agents as it blocks the entry of CNS drugs into the brain. The past few decades have witnessed the upspring of prodrug strategies as a promising method to accelerate CNS drug development. The prodrug strategy with the ability to overcome the formidable blood-brain barrier enhances the delivery to the brain and hence improves the effects of the CNS therapeutics. In this Feature Article, we summarize the reported barriers and strategies for CNS therapeutics and spotlight prodrug design strategies to improve the efficiency of crossing the blood-brain barrier.

Chemical Delivery System of MIBG to the Central Nervous System: Synthesis, 11C-Radiosynthesis, and in Vivo Evaluation

The norepinephrine transporter (NET) plays an important role in neurotransmission and is involved in a multitude of psychiatric and neurodegenerative diseases. [¹²³I/¹³¹I]meta-iodobenzylguanidine (MIBG) is a widely used radiotracer in the diagnosis and follow-up of peripheral neuroendocrine tumors overexpressing the norepinephrine transporter. MIBG does not cross the blood-brain barrier (BBB), and we have demonstrated the "proof-of-concept" that 1,4-dihydroquinoline/quinolinium salt as chemical delivery system (CDS) is a promising tool to deliver MIBG to the brain. To improve BBB passage, various substituents on the 1,4-dihydroquinoline moiety and a linker between CDS and MIBG were added. A series of CDS-MIBG 1a-d was synthesized, labeled with carbon-11, and evaluated in vivo into rats. The in vivo results demonstrated that, although adding substituents on CDS in 1a-c is of no benefit for brain delivery of MIBG, the presence of a linker in CDS-MIBG 1d greatly improved both brain penetration and the release rate of MIBG in the central nervous system.

Preclinical Evaluation of the First Adenosine A1 Receptor Partial Agonist Radioligand for Positron Emission Tomography Imaging

Central adenosine A₁ receptor (A₁R) is implicated in pain, sleep, substance use disorders, and neurodegenerative diseases, and is an important target for pharmaceutical development. Radiotracers for A₁R positron emission tomography (PET) would enable measurement of the dynamic interaction of endogenous adenosine and A₁R during the sleep-awake cycle. Although several human A₁R PET tracers have been developed, most are xanthine-based antagonists that failed to demonstrate competitive binding against endogenous adenosine. Herein, we explored non-nucleoside (3,5-dicyanopyridine and 5-cyanopyrimidine) templates for developing an agonist A₁R PET radiotracer. We synthesized novel analogues, including 2-amino-4-(3-methoxyphenyl)-6-(2-(6-methylpyridin-2-yl)ethyl)pyridine-3,5-dicarbonitrile (MMPD, 22b), a partial A₁R agonist of sub-nanomolar affinity. [¹¹C]22b showed suitable blood-brain barrier (BBB) permeability and test-retest reproducibility. Regional brain uptake of [¹¹C]22b was consistent with known brain A₁R distribution and was blocked significantly by A₁R but not A_2AR ligands. [¹¹C]22b is the first BBB-permeable A₁R partial agonist PET radiotracer with the promise of detecting endogenous adenosine fluctuations.

Access to Highly Enantioenriched Donepezil-like 1,4-Dihydropyridines as Promising Anti-Alzheimer Prodrug Candidates via Enantioselective Tsuji Allylation and Organocatalytic Aza-Ene-Type Domino Reactions

This work aims at exploiting both the enantioselective Tsuji allylation of allyl carbonate 6 and an organocatalytic aza-ene-type domino reaction between enal 3a and β-enaminone 4a to develop a straightforward access to all of the four possible stereoisomers of a donepezil-like 1,4-dihydropyridine 1a (er up to 99.5:0.5; overall yield up 64%), an anti-Alzheimer's prodrug candidate. This strategy was extended to the preparation of other enantioenriched 1,4-dihydropyridines 1b-i (eight examples), highlighting its potential in the development of these chiral AChE inhibitors.

Imaging of Tumor Characteristics and Molecular Pathways With PET: Developments Over the Last Decade Toward Personalized Cancer Therapy

PURPOSE

Improvements in personalized therapy are made possible by the advances in molecular biology that led to developments in molecular imaging, allowing highly specific in vivo imaging of biological processes. Positron emission tomography (PET) is the most specific and sensitive imaging technique for in vivo molecular targets and pathways, offering quantification and evaluation of functional properties of the targeted anatomy.

MATERIALS AND METHODS

This work is an integrative research review that summarizes and evaluates the accumulated current status of knowledge of recent advances in PET imaging for cancer diagnosis and treatment, concentrating on novel radiotracers and evaluating their advantages and disadvantages in cancer characterization. Medline search was conducted, limited to English publications from 2007 onward. Identified manuscripts were evaluated for most recent developments in PET imaging of cancer hypoxia, angiogenesis, proliferation, and clonogenic cancer stem cells (CSC).

RESULTS

There is an expansion observed from purely metabolic-based PET imaging toward antibody-based PET to achieve more information on cancer characteristics to identify hypoxia, proangiogenic factors, CSC, and others. ⁶⁴Cu-ATSM, for example, can be used both as a hypoxia and a CSC marker.

CONCLUSIONS

Progress in the field of functional imaging will possibly lead to more specific tumor targeting and personalized treatment, increasing tumor control and improving quality of life.