Modifications of the Triaminoaryl Metabophore of Flupirtine and Retigabine Aimed at Avoiding Quinone Diimine Formation

Lead Optimization of Positive Allosteric KV7.2/3 Channel Modulators toward Improved Balance of Lipophilicity and Aqueous Solubility

The voltage-gated potassium channel KV7.2/3 is gaining attention for its association with several medical indications. While recently reported, potent compounds aimed to fill the therapeutic gap left by market-withdrawn activators, key physicochemical parameters did not meet the requirements of potential drug candidates. Targeting the membrane-located channel requires subtly balancing lipophilicity, activity, and aqueous solubility. This publication describes the lead optimization of a highly active compound toward optimized physicochemical parameters. Out of 42 newly synthesized compounds, 30 showed activity on KV7.2/3 channels, and 15 had also an increased solubility compared the to hit compound. The integration of a three-dimensional bulky structure and the probable onset of chameleonic behavior, led to a 20-fold solubility increase (S = 21.7 vs 1.1 μM) and only slightly reduced potency (pEC50 = 7.42 vs 7.96) for the lead. Additionally, the target engagement of the compound was theoretically enhanced by a reduction of membrane retention.

Advances in the design and development of chemical modulators of the voltage-gated potassium channels KV7.4 and KV7.5

INTRODUCTION

Hypertension remains a major public health concern, with significant morbidity and mortality worldwide. Despite the availability of various antihypertensive medications, blood pressure control remains suboptimal in many individuals. During the last decades, KV7.4 and KV7.5, which were already known from the view of neuronal regulation, emerged as possible important players in the regulation of vascular tone and blood pressure.

AREAS COVERED

This review covers physiological functions and current advancements in the development of KV7.4 and KV7.5 channel modulators. The authors highlight the structural elements likely to be important for the future design of KV7 subtype-selective modulators, underscoring their potential as an innovative hypertension treatment.

EXPERT OPINION

Extensive research has been focused on targeting neuronal KV7.2 and KV7.3 channels, while KV7.4 and KV7.5 attracted less attention. Many of the developed compounds represent derivatives of flupirtine or retigabine, whereby subtype channel selectivity has only been demonstrated for a handful of individual compounds. Novel substances address additional sites within the binding pocket by incorporating new functional groups. A comprehensive and systematic evaluation of a compound set with significant subtype selectivity should be performed. The discovery of new highly active, less toxic, and selective compounds, therefore, remains the goal of further research in the coming years.

Discovery of a novel KV7.2/7.3 channels agonist for the treatment of neuropathic pain

Here, we designed, synthesized and evaluated a series of compounds as KV7.2/7.3 channels (or KCNQ2/3) agonists. The new compounds were assayed in vitro for KCNQ2/3 and other receptors binding affinity. The desired compound 16 showed high activity for KCNQ2/3 (EC50 = 1.03 ± 0.07 μM) without acute liver injury compared to flupirtine. It demonstrated powerful dose-dependent effects in multiple analgesic models, such as chronic constriction injury (CCI, ED50 = 12.02 mg/kg) and streptozotocin-induced diabetic peripheral neuropathic pain (DPNP, ED50 = 9.63 mg/kg) models. Additionally, compound 16 showed low affinity for human ether-a-go-go-related gene (hERG), high thresholds for acute toxicity, good motor performance in the rotarod test and acceptable pharmacokinetic properties. These results suggest the potentiality of compound 16 for the treatment of neuropathic pain.

In Silico Methods for the Discovery of Kv7.2/7.3 Channels Modulators: A Comprehensive Review

The growing interest in Kv7.2/7.3 agonists originates from the involvement of these channels in several brain hyperexcitability disorders. In particular, Kv7.2/7.3 mutants have been clearly associated with epileptic encephalopathies (DEEs) as well as with a spectrum of focal epilepsy disorders, often associated with developmental plateauing or regression. Nevertheless, there is a lack of available therapeutic options, considering that retigabine, the only molecule used in clinic as a broad-spectrum Kv7 agonist, has been withdrawn from the market in late 2016. This is why several efforts have been made both by both academia and industry in the search for suitable chemotypes acting as Kv7.2/7.3 agonists. In this context, in silico methods have played a major role, since the precise structures of different Kv7 homotetramers have been only recently disclosed. In the present review, the computational methods used for the design of Kv.7.2/7.3 small molecule agonists and the underlying medicinal chemistry are discussed in the context of their biological and structure-function properties.

Deep Learning Algorithm Based on Molecular Fingerprint for Prediction of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is one the rare adverse drug reaction (ADR) and multifactorial endpoints. Current preclinical animal models struggle to anticipate it, and in silico methods have emerged as a way with significant potential for doing so. In this study, a high-quality dataset of 1573 compounds was assembled. The 48 classification models, which depended on six different molecular fingerprints, were built via deep neural network (DNN) and seven machine learning algorithms. Comparing the results of the DNN and machine learning models, the optional performing model was found as the one developed based on the DNN with ECFP_6 as input, which achieved the area under the receiver operating characteristic curve (AUC) of 0.713, balanced accuracy (BA) of 0.680, and F1 of 0.753. In addition, we used the SHapley Additive exPlanations (SHAP) algorithm to interpret the models, identified the crucial structural fragments related to DILI risk, and selected the top ten substructures with the highest contribution rankings to serve as warning indicators for subsequent drug hepatotoxicity screening studies. The study demonstrates that the DNN models developed based on molecular fingerprints can be a trustworthy and efficient tool for determining the risk of DILI during the pre-development of novel medications.

Metabophore-mediated retro-metabolic ('MeMeReMe') approach in drug design

Preclinical toxicity assessments of new drugs require the use of in silico prediction techniques as ethics, cost, time, and complexity limit in vitro and in vivo methods. This review discusses the fundamental concepts of biophores especially toxicophores and their detection methodologies, tools and techniques, as well as ongoing challenges, and methods for overcoming them. This will guide the design community in manipulating lead compounds via a pre-determined pathway based on the MeMeReMe approach. The ideas discussed will be useful both for predicting toxicity and for de-risking leads through optimization.

Three-Step Synthesis of the Antiepileptic Drug Candidate Pynegabine

Pynegabine, an antiepileptic drug candidate in phase I clinical trials, is a structural analog of the marketed drug retigabine with improved chemical stability, strong efficacy, and a better safety margin. The reported shortest synthetic route for pynegabine contains six steps and involves the manipulation of highly toxic methyl chloroformate and dangerous hydrogen gas. To improve the feasibility of drug production, we developed a concise, three-step process using unconventional methoxycarbonylation and highly efficient Buchwald-Hartwig cross coupling. The new synthetic route generated pynegabine at the decagram scale without column chromatographic purification and avoided the dangerous manipulation of hazardous reagents.

A graphite furnace-atomic absorption spectrometry-based rubidium efflux assay for screening activators of the Kv 7.2/3 channel

For the characterization of K_v 7.2/3 channel activators, several analytical methods are available that vary in effort and cost. In addition to the technically elaborate patch-clamp method, which serves as a reference method, there exist several medium to high-throughput screening methods including a rubidium efflux flame-atomic absorption spectrometry (F-AAS) assay and a commercial thallium uptake fluorescence-based assay. In this study, the general suitability of a graphite furnace atomic absorption spectrometry (GF-AAS)-based rubidium efflux assay as a screening method for K_v 7.2/3 channel activators was demonstrated. With flupirtine serving as a reference compound, 16 newly synthesizedcompounds and the known K_v 7.2/3 activator retigabine were first classified as either active or inactive by using the GF-AAS-based rubidium (Rb) efflux assay. Then, the results were compared with a thallium (Tl) uptake fluorescence-based fluorometric imaging plate reader (FLIPR) potassium assay. Overall, 16 of 17 compounds were classified by the GF-AAS-based assay in agreement with their channel-activating properties determined by the more expensive Tl uptake, fluorescence-based assay. Thus, the performance of the GF-AAS-based Rb assay for primary drug screening of K_v 7.2/3-activating compounds was clearly demonstrated, as documented by the calculated Z'-factor of the GF-AAS-based method. Moreover, method development included optimization of the coating of the microtiter plates and the washing procedure, which extended the range of this assay to poorly adherent cells such as the HEK293 cells used in this study.

Replacing the oxidation-sensitive triaminoaryl chemotype of problematic KV 7 channel openers: Exploration of a nicotinamide scaffold

K_V 7 channel openers have proven their therapeutic value in the treatment of pain as well as epilepsy and, moreover, they hold the potential to expand into additional indications with unmet medical needs. However, the clinically validated but meanwhile discontinued K_V 7 channel openers flupirtine and retigabine bear an oxidation-sensitive triaminoraryl scaffold, which is suspected of causing adverse drug reactions via the formation of quinoid oxidation products. Here, we report the design and synthesis of nicotinamide analogs and related compounds that remediate the liability in the chemical structure of flupirtine and retigabine. Optimization of a nicotinamide lead structure yielded analogs with excellent K_V 7.2/3 opening activity, as evidenced by EC₅₀ values approaching the single-digit nanomolar range. On the other hand, weighted K_V 7.2/3 opening activity data including inactive compounds allowed for the establishment of structure-activity relationships and a plausible binding mode hypothesis verified by docking and molecular dynamics simulations.

Attenuation of Epileptogenesis and Cognitive Deficits by a Selective and Potent Kv7 Channel Opener in Rodent Models of Seizures

Targeting neuronal Kv7 channels by pharmacological activation has been proven to be an attractive therapeutic strategy for epilepsy. Here, we show that activation of Kv7 channels by an opener SCR2682 dose-dependently reduces seizure activity and severity in rodent models of epilepsy induced by a GABAa receptor antagonist pentylenetetrazole (PTZ), maximal electroshock, and a glutamate receptor agonist kainic acid (KA). Electroencephalographic recordings of rat cerebral cortex confirm that SCR2682 also decreases epileptiform discharges in KA-induced seizures. Nissl and neuronal nuclei staining further demonstrates that SCR2682 also protects neurons from injury induced by KA. In Morris water maze navigation and Y-maze tests, SCR2682 improves PTZ- and KA-induced cognitive impairment. Taken together, our findings demonstrate that pharmacological activation of Kv7 by novel opener SCR2682 may hold promise for therapy of epilepsy with cognitive impairment. SIGNIFICANCE STATEMENT: A neuronal Kv7 channel opener SCR2682 attenuates epileptogenesis and seizure-induced cognitive impairment in rodent models of seizures, thus possessing a developmental potential for effective therapy of epilepsy with cognitive impairment.

Development of an automated screen for Kv7.2 potassium channels and discovery of a new agonist chemotype

To identify pore domain ligands on Kv7.2 potassium ion channels, we compared wild-type (WT) and W236L mutant Kv7.2 channels in a series of assays with previously validated and novel agonist chemotypes. Positive controls were retigabine, flupirtine, and RL-81; i.e. Kv7.2 channel activators that significantly shift voltage-dependent activation to more negative potentials (ΔV50) at 5 µM. We identified 6 new compounds that exhibited differential enhancing activity between WT and W236L mutant channels. Whole cell patch-clamp electrophysiology studies were conducted to identify Kv7.2. Kv7.2/3, Kv7.4, and Kv7.5 selectivity. Our results validate the SyncroPatch platform and establish new structure activity relationships (SAR). Specifically, in addition to selective Kv7.2, Kv7.2/3, Kv7.4. and Kv7.5 agonists, we identified a novel chemotype, ZK-21, a 4-aminotetrahydroquinoline that is distinct from any of the previously described Kv7 channel modifiers. Using flexible receptor docking, ZK-21 was predicted to be stabilized by W236 and bind perpendicular to retigabine, burying the benzyl carbamate group into a tunnel reaching the core of the pore domain.

Carba Analogues of Flupirtine and Retigabine with Improved Oxidation Resistance and Reduced Risk of Quinoid Metabolite Formation

The K_V7 potassium channel openers flupirtine and retigabine have been valuable options in the therapy of pain and epilepsy. However, as a result of adverse reactions, both drugs are currently no longer in therapeutic use. The flupirtine‐induced liver injury and the retigabine linked tissue discolouration do not appear related at first glance; nevertheless, both events can be attributed to the triaminoaryl scaffold, which is affected by oxidation leading to elusive reactive quinone diimine or azaquinone diimine metabolites. Since the mechanism of action, i. e. K_V7 channel opening, seems not to be involved in toxicity, this study aimed to further develop safer replacements for flupirtine and retigabine. In a ligand‐based design strategy, replacing amino substituents of the triaminoaryl core with alkyl substituents led to carba analogues with improved oxidation resistance and negligible risk of quinoid metabolite formation. In addition to these improved safety features, some of the novel analogues exhibited significantly improved K_V7.2/3 channel opening activity, indicated by an up to 13‐fold increase in potency and an efficacy of up to 176 % compared to flupirtine, thus being attractive candidates for further development.