Development of a high-throughput screen targeting caspase-8-mediated cleavage of the amyloid precursor protein

Caspase inhibitors: a review on recently patented compounds (2016-2023)

INTRODUCTION

Caspases are a family of protease enzymes that play a crucial role in apoptosis. Dysregulation of caspase activity has been implicated in various pathological conditions, making caspases an important focus of research in understanding cell death mechanisms and developing therapeutic strategies for diseases associated with abnormal apoptosis.

AREAS COVERED

It is a comprehensive review of caspase inhibitors that have been comprising recently granted patents from 2016 to 2023. It includes peptide and non-peptide caspase inhibitors with their application for different diseases.

EXPERT OPINION

This review categorizes and analyses recently patented caspase inhibitors on various diseases. Diseases linked to caspase dysregulation, including neurodegenerative disorders, and autoimmune conditions, are highlighted to accentuate the therapeutic relevance of the patented caspase inhibitors. This paper serves as a valuable resource for researchers, clinicians, and pharmaceutical developers seeking an up-to-date understanding of recently patented caspase inhibitors. The integration of recent patented compounds, structural insights, and mechanistic details provides a holistic view of the progress in caspase inhibitor research and its potential impact on addressing various diseases.

Enantioselective Synthesis of Octahydrofuranoindole Core of Aspidosperma Alkaloids via a Diels-Alder/Reduction/Fluoroetherification Reaction Sequence

Herein, we disclose the enantioselective synthesis of novel tricyclic fluorooctahydrofuranoindole spirooxindoles bearing five contiguous stereocenters via an organocatalytic sequential Diels-Alder/Reduction/Fluoroetherifiction reaction strategy. The potential of the developed approach was witnessed by generating vast examples (up to 20 examples) of library molecules embedding natural product core with good yields and phenomenal diastereo- and enantioselectivities (up to 77 % overall yield, up to 99 % ee and 10 : 1 dr). The synthetic utility of our protocol was further demonstrated by synthesizing tricyclic iodooctahydroindole spirooxindole framework through sequential Diels-Alder/reduction/iodoetherification reaction in 65 % overall yield and excellent stereoselectivity (99 % ee and 4 : 1 dr).

Asymmetric synthesis of the perhydroepoxyethanoindole core via sequential [4 + 2]-addition/reduction/fluoroannulation reactions

Herein, we present the sequential aminocatalytic [4 + 2]-addition/reduction and fluoroannulation reactions to afford a novel class of bridged fluoro-perhydroepoxyethanoindole spiropyrazolone and fluoro-perhydroepoxyethanoindole spirooxindole moieties with six contiguous stereocenters. An array of perhydroepoxyethanoindole core derivatives (up to 31 examples) mimicking aspidosperma alkaloids were obtained with moderate to good yields and excellent enantio- and diastereo-selectivities (up to 69% overall yield, up to 99.9% ee and up to >20 : 1 dr). Furthermore, we have also disclosed the synthesis of the unexpected tribromo derivative of hexahydroepoxyethanoindole spiropyrazolone in a moderate yield with excellent selectivity by employing the developed protocol in sequential bromoannulation reactions.

The application of C–H bond functionalization in the total syntheses of indole natural products

The recent advances in total synthesis of indole natural products focusing on the application of C–H bond functionalization are summarized.

A review on α-mangostin as a potential multi-target-directed ligand for Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive memory loss, declining language skills and other cognitive disorders. AD has brought great mental and economic burden to patients, families and society. However due to the complexity of AD's pathology, drugs developed for the treatment of AD often fail in clinical or experimental trials. The main problems of current anti-AD drugs are low efficacy due to mono-target method or side effects, especially high hepatotoxicity. To tackle these two main problems, multi-target-directed ligand (MTDL) based on "one molecule, multiple targets" has been studied. MTDLs can regulate multiple biological targets at the same time, so it has shown higher efficacy, better safety. As a natural active small molecule, α-mangostin (α-M) has shown potential multi-factor anti-AD activities in a series of studies, furthermore it also has a certain hepatoprotective effect. The good availability of α-M also provides support for its application in clinical research. In this work, multiple activities of α-M related to AD therapy were reviewed, which included anti-cholinesterase, anti-amyloid-cascade, anti-inflammation, anti-oxidative stress, low toxicity, hepatoprotective effects and drug formulation. It shows that α-M is a promising candidate for the treatment of AD.

Enantioselective Total Syntheses of (+)-Fendleridine and (+)-Acetylaspidoalbidine

Enantioselective syntheses of hexacyclic aspidoalbidine alkaloids (+)-fendleridine (2) and (+)-acetylaspidoalbidine (3) are described. These syntheses feature an asymmetric decarboxylative allylation and photocyclization of a highly substituted enaminone. Also, the synthesis highlights the formation of a C19-hemiaminal ether via a reduction/condensation/intramolecular cyclization cascade with the C21-alcohol. The present synthesis provides convenient access to the aspidoalbidine hexacyclic alkaloid family in an efficient manner.

Neuroprotective effect of α-mangostin on mitochondrial dysfunction and α-synuclein aggregation in rotenone-induced model of Parkinson's disease in differentiated SH-SY5Y cells

The study was designed to evaluate the protective effect of α-mangostin and explore its mechanism in an in vitro model of Parkinson's disease (PD) induced by rotenone. SH-SY5Y cells were treated with rotenone and α-mangostin for 24 h. α-Mangostin significantly and concentration-dependently inhibited rotenone-induced cytotoxicity. The rotenone-induced aggregation of α-synuclein and loss of TH were alleviated by α-mangostin. α-Mangostin treatment also reversed the rotenone-induced overproduction of reactive oxygen species, activation of caspases (-8 and -3) and mitochondrial dysfunction, reflected by decrease in mitochondrial membrane potential and cellular ATP levels. These findings suggest that α-mangostin has neuroprotective effects against PD-related neuronal injury.

Concise Total Syntheses of (+)-Haplocidine and (+)-Haplocine via Late-Stage Oxidation of (+)-Fendleridine Derivatives

We report the first total syntheses of (+)-haplocidine and its N1-amide congener (+)-haplocine. Our concise synthesis of these alkaloids required the development of a late-stage and highly selective C-H oxidation of complex aspidosperma alkaloid derivatives. A versatile, amide-directed ortho-acetoxylation of indoline amides enabled our implementation of a unified strategy for late-stage diversification of hexacyclic C19-hemiaminal ether structures via oxidation of the corresponding pentacyclic C19-iminium ions. An electrophilic amide activation of a readily available C21-oxygenated lactam, followed by transannular cyclization and in situ trapping of a transiently formed C19-iminium ion, expediently provided access to hexacyclic C19-hemiaminal ether alkaloids (+)-fendleridine, (+)-acetylaspidoalbidine, and (+)-propionylaspidoalbidine. A highly effective enzymatic resolution of a non-β-branched primary alcohol (E = 22) allowed rapid preparation of both enantiomeric forms of a C21-oxygenated precursor for synthesis of these aspidosperma alkaloids. Our synthetic strategy provides succinct access to hexacyclic aspidosperma derivatives, including the antiproliferative alkaloid (+)-haplocidine.

Dysregulation of a potassium channel, THIK-1, targeted by caspase-8 accelerates cell shrinkage

Activation of caspases is crucial for the execution of apoptosis. Although the caspase cascade associated with activation of the initiator caspase-8 (CASP8) has been investigated in molecular and biochemical detail, the physiological role of CASP8 is not fully understood. Here, we identified a two-pore domain potassium channel, tandem-pore domain halothane-inhibited K⁺ channel 1 (THIK-1), as a novel CASP8 substrate. The intracellular region of THIK-1 was cleaved by CASP8 in apoptotic cells. Overexpression of THIK-1, but not its mutant lacking the CASP8-target sequence in the intracellular portion, accelerated cell shrinkage in response to apoptotic stimuli. In contrast, knockdown of endogenous THIK-1 by RNA interference resulted in delayed shrinkage and potassium efflux. Furthermore, a truncated THIK-1 mutant lacking the intracellular region, which mimics the form cleaved by CASP8, led to a decrease of cell volume of cultured cells without apoptotic stimulation and excessively promoted irregular development of Xenopus embryos. Taken together, these results indicate that THIK-1 is involved in the acceleration of cell shrinkage. Thus, we have demonstrated a novel physiological role of CASP8: creating a cascade that advances the cell to the next stage in the apoptotic process.

Protein truncation as a common denominator of human neurodegenerative foldopathies

Neurodegenerative foldopathies are characterized by aberrant folding of diseased modified proteins, which are major constituents of the intracellular and extracellular lesions. These lesions correlate with the cognitive and/or motor impairment seen in these diseases. The majority of the disease modified proteins in neurodegenerative foldopathies belongs to the group of proteins termed as intrinsically disordered proteins (IDPs). Several independent studies have showed that abnormal protein processing constitutes the key pathological feature of these disorders. The current review focuses on protein truncation as a common denominator of neurodegenerative foldopathies, which is considered to be the major driving force behind the pathological metamorphosis of brain IDPs. The aim of the review is to emphasize the key role of the protein truncation in the pathogenic pathways of neurodegenerative diseases. A deeper understanding of the complex downstream processing of the IDPs, resulting in the generation of pathologically modified proteins might be a prerequisite for the successful therapeutic strategies of several fatal neurodegenerative diseases.

Altered processing of amyloid precursor protein in cells undergoing apoptosis

Altered proteolysis of amyloid precursor protein is an important determinant of pathology development in Alzheimer's disease. Here, we describe the detection of two novel fragments of amyloid precursor protein in H4 neuroglioma cells undergoing apoptosis. Immunoreactivity of these 25-35 kDa fragments to two different amyloid precursor protein antibodies suggests that they contain the amyloid-β region and an epitope near the C-terminus of amyloid precursor protein. Generation of these fragments is associated with cleavage of caspase-3 and caspase-7, suggesting activation of these caspases. Studies in neurons undergoing DNA damage-induced apoptosis also showed similar results. Inclusion of caspase inhibitors prevented the generation of these novel fragments, suggesting that they are generated by a caspase-dependent mechanism. Molecular weight prediction and immunoreactivity of the fragments generated suggested that such fragments could not be generated by cleavage at any previously identified caspase, secretase, or calpain site on amyloid precursor protein. Bioinformatic analysis of the amino acid sequence of amyloid precursor protein revealed that fragments fitting the observed size and immunoreactivity could be generated by either cleavage at a novel, hitherto unidentified, caspase site or at a previously identified matrix metalloproteinase site in the extracellular domain. Proteolytic cleavage at any of these sites leads to a decrease in the generation of α-secretase cleaved secreted APP, which has both anti-apoptotic and neuroprotective properties, and thus may contribute to neurodegeneration in Alzheimer's disease.