Employing in vitro metabolism to guide design of F-labelled PET probes of novel α-synuclein binding bifunctional compounds

The Bifunctional Dimer Caffeine-Indan Attenuates α-Synuclein Misfolding, Neurodegeneration and Behavioral Deficits after Chronic Stimulation of Adenosine A1 Receptors

We previously found that chronic adenosine A1 receptor stimulation with N6-Cyclopentyladenosine increased α-synuclein misfolding and neurodegeneration in a novel α-synucleinopathy model, a hallmark of Parkinson's disease. Here, we aimed to synthesize a dimer caffeine-indan linked by a 6-carbon chain to cross the blood-brain barrier and tested its ability to bind α-synuclein, reducing misfolding, behavioral abnormalities, and neurodegeneration in our rodent model. Behavioral tests and histological stains assessed neuroprotective effects of the dimer compound. A rapid synthesis of the 18F-labeled analogue enabled Positron Emission Tomography and Computed Tomography imaging for biodistribution measurement. Molecular docking analysis showed that the dimer binds to α-synuclein N- and C-termini and the non-amyloid-β-component (NAC) domain, similar to 1-aminoindan, and this binding promotes a neuroprotective α-synuclein "loop" conformation. The dimer also binds to the orthosteric binding site for adenosine within the adenosine A1 receptor. Immunohistochemistry and confocal imaging showed the dimer abolished α-synuclein upregulation and aggregation in the substantia nigra and hippocampus, and the dimer mitigated cognitive deficits, anxiety, despair, and motor abnormalities. The 18F-labeled dimer remained stable post-injection and distributed in various organs, notably in the brain, suggesting its potential as a Positron Emission Tomography tracer for α-synuclein and adenosine A1 receptor in Parkinson's disease therapy.

The effect of diphenylethane side-chain substituents on dibenzocyclohexadiene formation and their inhibition of α-synuclein aggregation in vitro

The naturally-occurring di-catechol lignan nordihydroguaiaretic acid (NDGA) and an analog without methyl groups on the butyl linker both undergo intramolecular cyclization at pH 7.4 to form dibenzocyclooctadienes. Both NDGA and these dibenzocyclooctadienes have been shown to prevent in vitro aggregation of α-synuclein, an intrinsically disordered protein associated with Parkinson's disease. NDGA possesses two vicinal methyl groups on the butyl linker and the presence of these methyl groups attenuates the rate of intramolecular cyclization versus the unsubstituted analog, in opposition to the anticipated Thorpe-Ingold effect, likely due to steric repulsions during cyclization. Numerous 1,2-bis-ethane di-catechols are known to inhibit α-synuclein aggregation in vitro and we hypothesize that these compounds undergo a similar intramolecular cyclization and the cyclized products may be responsible for the activity. To test this hypothesis we prepared a series of 1,2-bis-ethane di-catechols with 0, 2 and 4 methyl substituents on the linker. We have confirmed that these compounds undergo intramolecular cyclization to form dibenzocyclohexadienes and that steric interactions between the methyl substituents leads to an increase in the rate of intramolecular cyclization, which is in contrast to what was observed for lignan di-catechols. The rate of cyclization to form six-membered rings is 10-30 times more rapid than formation of eight membered rings and the dibenzocyclohexadienes also prevent in vitro aggregation of α-synuclein.

Pharmacokinetic considerations to optimize clinical outcomes for COVID-19 drugs

The development of clinically effective drugs that could complement existing vaccines is urgently needed to reduce the morbidity and mortality associated with COVID-19. Drug-metabolizing enzymes, membrane-associated drug transporters, and inflammatory responses can partly determine the safety and efficacy of COVID-19 drugs by controlling their concentrations in both the systemic circulation and in peripheral tissues. It is still unknown how these factors affect how well COVID-19 drugs work in the clinic. We explore how drug metabolism and transport, as well as SARS-CoV-2-associated inflammatory response at disease target sites, may affect the clinical outcomes of COVID-19 drugs. In addition, we provide expert opinion on potential strategies for overcoming the clinical pharmacology and pathophysiological obstacles to improve COVID-19 drug effectiveness.

An HPLC-UV validated bioanalytical method for measurement of in vitro phase 1 kinetics of α-synuclein binding bifunctional compounds

Aggregates of the protein α-synuclein are associated with pathophysiology of Parkinson's disease and are present in Lewy Bodies found in the brains of Parkinson's patients. We previously demonstrated that bifunctional compounds composed of caffeine linked via a six carbon chain to either 1-aminoindan (C₈-6-I) or nicotine (C₈-6-N) bind α-synuclein and protect yeast cells from α-synuclein mediated toxicity.A critical step in development of positron emission tomography (PET) probes for neurodegenerative diseases is evaluation of their metabolic stability. We determined that C₈-6-I, and C₈-6-N both undergo phase 1 P450 metabolism in mouse, rat, and human liver microsomes. We utilised this metabolic information to guide the design of fluorinated analogues for use as PET probes and determined that the fluorine in ¹⁹F-C₈-6-I and ¹⁹F-C₈-6-N is stable to P450 enzymes.We have developed and validated an analytical HPLC-UV method following FDA and EMA guidelines to measure in vitro phase 1 kinetics of these compounds and determine their V_max, K_M and CL_int,u in mouse liver microsomes. We found that C₈-6-I and ¹⁹F-C₈-6-I have a two- to fourfold lower CL_int,u than C₈-6-N, and ¹⁹F-C₈-6-N. Our approach shows a simple, specific, and effective system to design and develop compounds as PET probes.

Diagnostic and therapeutic agents that target alpha-synuclein in Parkinson's disease

The development of disease-modifying drugs and differential diagnostic agents is an urgent medical need in Parkinson’s disease. Despite the complex pathophysiological pathway, the misfolding of alpha-synuclein has been identified as a putative biomarker for detecting the onset and progression of the neurodegeneration associated with Parkinson’s disease. Identifying the most appropriate alpha-synuclein-based diagnostic modality with clinical translation will revolutionize the diagnosis of Parkinson’s. Likewise, molecules that target alpha-synuclein could alter the disease pathway that leads to Parkinson’s and may serve as first-in class therapeutics compared to existing treatment options such as levodopa and dopamine agonist that do not necessarily modify the disease pathway. Notwithstanding the promising benefits that alpha-synuclein presents to therapeutics and diagnostics development for Parkinson’s disease, finding ways to address potential challenges such as inadequate preclinical models, safety and efficacy will be paramount to achieving clinical translation. In this comprehensive review paper, we described the role of alpha-synuclein in the pathogenesis of Parkinson’s disease, as well as how its structure and function relationship delineate disease onset and progression. We further discussed different alpha-synuclein-based diagnostic modalities including biomolecular assays and molecular imaging. Finally, we presented current small molecules and biologics that are being developed as disease-modifying drugs or positron emission tomography imaging probes for Parkinson’s disease.

Relevance of ABC Transporters in Drug Development

ATP-binding cassette (ABC) transporters play a critical role in protecting vital organs such as the brain and placenta against xenobiotics, as well as in modulating the pharmacological and toxicological profile of several drug candidates by restricting their penetration through cellular and tissue barriers. This review paper provides a description of the structure and function of ABC transporters as well as the role of P-glycoprotein, multidrug resistance-associated protein 2 and breast cancer resistance protein in the disposition of drugs. Furthermore, a review of the in vitro and in vivo techniques for evaluating the interaction between drugs and ABC transporters are provided.

Bioanalytical strategies in drug discovery and development

A reliable, rapid, and effective bioanalytical method is essential for the determination of the pharmacokinetic, pharmacodynamic, and toxicokinetic parameters that inform the safety and efficacy profile of investigational drugs. The overall goal of bioanalytical method development is to elucidate the procedure and operating conditions under which a method can sufficiently extract, qualify, and/or quantify the analyte(s) of interest and/or their metabolites for the intended purpose. Given the difference in the physicochemical properties of small and large molecule drugs, different strategies need to be adopted for the development of an effective and efficient bioanalytical method. Herein, we provide an overview of different sample preparation strategies, analytical platforms, as well as procedures for achieving high throughput for bioanalysis of small and large molecule drugs.