Systemic optimization and structural evaluation of quinoline derivatives as transthyretin amyloidogenesis inhibitors

3-O-Methyltolcapone and Its Lipophilic Analogues Are Potent Inhibitors of Transthyretin Amyloidogenesis with High Permeability and Low Toxicity

Transthyretin (TTR) is an amyloidogenic homotetramer involved in the transport of thyroxine in blood and cerebrospinal fluid. To date, more than 130 TTR point mutations are known to destabilise the TTR tetramer, leading to its extracellular pathological aggregation accumulating in several organs, such as heart, peripheral and autonomic nerves, and leptomeninges. Tolcapone is an FDA-approved drug for Parkinson's disease that has been repurposed as a TTR stabiliser. We characterised 3-O-methyltolcapone and two newly synthesized lipophilic analogues, which are expected to be protected from the metabolic glucuronidation that is responsible for the lability of tolcapone in the organism. Immunoblotting assays indicated the high degree of TTR stabilisation, coupled with binding selectivity towards TTR in diluted plasma of 3-O-methyltolcapone and its lipophilic analogues. Furthermore, in vitro toxicity data showed their several-fold improved neuronal and hepatic safety compared to tolcapone. Calorimetric and structural data showed that both T4 binding sites of TTR are occupied by 3-O-methyltolcapone and its lipophilic analogs, consistent with an effective TTR tetramer stabilisation. Moreover, in vitro permeability studies showed that the three compounds can effectively cross the blood-brain barrier, which is a prerequisite for the inhibition of TTR amyloidogenesis in the cerebrospinal fluid. Our data demonstrate the relevance of 3-O-methyltolcapone and its lipophilic analogs as potent inhibitors of TTR amyloidogenesis.

Structure restoration and aggregate inhibition of V30M mutant transthyretin protein by potential quinoline molecules

Transthyretin (TTR) is a tetrameric protein found in human plasma and cerebrospinal fluid that functions as a transporter of thyroxine (T4) and retinol. A mutation resulting in the substitution of valine to methionine at position 30 (V30M) is the most common mutation that destabilizes the tetramer structure of TTR protein resulting in a fatal neuropathy known as TTR amyloidosis. The V30M TTR-induced neuropathy can be inhibited through stabilization of the TTR tetramer by the binding of small molecules. We accessed the potential of in-house synthesized quinoline molecules to stabilize the V30M TTR structure and analyzed the impact of protein-ligand interactions through molecular docking, molecular dynamics (MD) simulations, steered MD, and umbrella sampling simulations. This study revealed that the binding of quinoline molecules reverted back the structural changes including the residual flexibility, changes in secondary structural elements, and also restored the alterations in the electrostatic surface potential induced by the V30M mutation. Further, the top-most 4G and 4R molecules were compared with an FDA-approved drug (Tafamidis) and a reference quinoline molecule 14C. Here, we intend to suggest that the quinoline molecules could revert the structural changes, cease tetramer dissociation, prevent abnormal oligomerization and therefore could be developed as an effective therapeutics against TTR amyloidosis.

Novel Strategy To Inhibit Transthyretin Amyloidosis via the Synergetic Effect of Chemoselective Acylation and Noncovalent Inhibitor Release

Strategies for developing targeted covalent inhibitors (TCIs), which have the advantages of a prolonged duration of action and selectivity toward a drug target, have attracted great interest in drug discovery. Herein, we report chemoselective covalent inhibitors that specifically target lysine ε-amine groups that conjugate with an endogenous protein to prevent disease-causing protein misfolding and aggregation. These TCIs are unique because the benzoyl group is preferentially conjugated to Lys15 at the top of the T₄ binding site within transthyretin (TTR) while simultaneously releasing a potent noncovalent TTR kinetic stabilizer. The potency of these covalent inhibitors is superior to tafamidis, the only FDA-approved drug for the treatment of hereditary TTR amyloidosis. In addition to investigations into the covalent modification of TTR via reverse-phase high-performance liquid chromatography, direct methods are performed to confirm and visualize the presumed covalent interaction via mass spectrometry and X-ray crystallography.

Steroid-Quinoline Hybrids for Disruption and Reversion of Protein Aggregation Processes

Reversing protein aggregation within cells may be an important tool to fight protein-misfolding disorders such as Alzheimer's, Parkinson's, and cardiovascular diseases. Here we report the design and synthesis of a family of steroid-quinoline hybrid compounds based on the framework combination approach. This set of hybrid compounds effectively inhibited Aβ1-42 self-aggregation in vitro by delaying the exponential growth phase and/or reducing the quantity of fibrils in the steady state. Their disaggregation efficacy was further demonstrated against preaggregated Aβ1-42 peptides in cellular assays upon their endocytosis by neuroblastoma cells, as they reverted both the number and the average area of fibrils back to basal levels. The antiaggregation effect of these hybrids was further tested and demonstrated in a cellular model of general protein aggregation expressing a protein aggregation fluorescent sensor. Together, our results show that the new cholesterol-quinoline hybrids possess wide and marked disaggregation capacities and are therefore promising templates for the development of new drugs to deal with conformational disorders.

The discovery and development of transthyretin amyloidogenesis inhibitors: what are the lessons?

Transthyretin (TTR) is associated with several human amyloid diseases. Various kinetic stabilizers have been developed to inhibit the dissociation of TTR tetramer and the formation of amyloid fibrils. Most of them are bisaryl derivatives, natural flavonoids, crown ethers and carborans. In this review article, we focus on TTR tetramer stabilizers, genetic therapeutic approaches and fibril remodelers. The binding modes of typical bisaryl derivatives, natural flavonoids, crown ethers and carborans are discussed. Based on knowledge of the binding of thyroxine to TTR tetramer, many stabilizers have been screened to dock into the thyroxine binding sites, leading to TTR tetramer stabilization. Particularly, those stabilizers with unique binding profiles have shown great potential in developing the therapeutic management of TTR amyloidogenesis.

A quinoline–benzothiazole hybrid as the first near-infrared fluorescent probe for transthyretin

A quinoline-benzothiazole hybrid was rationally developed as the first NIR fluorescent probe for detecting transthyretin.

Rational Design, Synthesis, Characterization and Evaluation of Iodinated 4,4'-Bipyridines as New Transthyretin Fibrillogenesis Inhibitors

The 3,3',5,5'-tetrachloro-2-iodo-4,4'-bipyridine structure is proposed as a novel chemical scaffold for the design of new transthyretin (TTR) fibrillogenesis inhibitors. In the frame of a proof-of-principle exploration, four chiral 3,3',5,5'-tetrachloro-2-iodo-2'-substituted-4,4'- bipyridines were rationally designed and prepared from a simple trihalopyridine in three steps, including a Cu-catalysed Finkelstein reaction to introduce iodine atoms on the heteroaromatic scaffold, and a Pd-catalysed coupling reaction to install the 2'-substituent. The corresponding racemates, along with other five chiral 4,4'-bipyridines containing halogens as substituents, were enantioseparated by high-performance liquid chromatography in order to obtain pure enantiomer pairs. All stereoisomers were tested against the amyloid fibril formation (FF) of wild type (WT)-TTR and two mutant variants, V30M and Y78F, in acid mediated aggregation experiments. Among the 4,4'-bipyridine derivatives, interesting inhibition activity was obtained for both enantiomers of the 3,3',5,5'-tetrachloro-2'-(4-hydroxyphenyl)-2-iodo-4,4'-bipyridine. In silico docking studies were carried out in order to explore possible binding modes of the 4,4'-bipyridine derivatives into the TTR. The gained results point out the importance of the right combination of H-bond sites and the presence of iodine as halogen-bond donor. Both experimental and theoretical evidences pave the way for the utilization of the iodinated 4,4'-bipyridine core as template to design new promising inhibitors of TTR amyloidogenesis.

Review on the Structures and Activities of Transthyretin Amyloidogenesis Inhibitors

Transthyretin (TTR) is a tetrameric protein, and its dissociation, aggregation, deposition, and misfolding are linked to several human amyloid diseases. As the main transporter for thyroxine (T4) in plasma and cerebrospinal fluid, TTR contains two T4-binding sites, which are docked with T4 and subsequently maintain the structural stability of TTR homotetramer. Affected by genetic disorders and detrimental environmental factors, TTR degrades to monomer and/or form amyloid fibrils. Reasonably, stabilization of TTR might be an efficient strategy for the treatment of TTR-related amyloidosis. However, only 10-25% of T4 in the plasma is bound to TTR under physiological conditions. Expectedly, T4 analogs with different structures aiming to bind to T4 pockets may displace the functions of T4. So far, a number of compounds including both natural and synthetic origin have been reported. In this paper, we summarized the potent inhibitors, including bisaryl structure-based compounds, flavonoids, crown ethers, and carboranes, for treating TTR-related amyloid diseases and the combination modes of some compounds binding to TTR protein.