Bringing new dimensions to drug discovery screening: impact of cellular stimulation technologies

A silicon diode-based optoelectronic interface for bidirectional neural modulation

The development of advanced neural modulation techniques is crucial to neuroscience research and neuroengineering applications. Recently, optical-based, nongenetic modulation approaches have been actively investigated to remotely interrogate the nervous system with high precision. Here, we show that a thin-film, silicon (Si)-based diode device is capable to bidirectionally regulate in vitro and in vivo neural activities upon adjusted illumination. When exposed to high-power and short-pulsed light, the Si diode generates photothermal effects, evoking neuron depolarization and enhancing intracellular calcium dynamics. Conversely, low-power and long-pulsed light on the Si diode hyperpolarizes neurons and reduces calcium activities. Furthermore, the Si diode film mounted on the brain of living mice can activate or suppress cortical activities under varied irradiation conditions. The presented material and device strategies reveal an innovated optoelectronic interface for precise neural modulations.

Bioresorbable thin-film silicon diodes for the optoelectronic excitation and inhibition of neural activities

Neural activities can be modulated by leveraging light-responsive nanomaterials as interfaces for exerting photothermal, photoelectrochemical or photocapacitive effects on neurons or neural tissues. Here we show that bioresorbable thin-film monocrystalline silicon pn diodes can be used to optoelectronically excite or inhibit neural activities by establishing polarity-dependent positive or negative photovoltages at the semiconductor/solution interface. Under laser illumination, the silicon-diode optoelectronic interfaces allowed for the deterministic depolarization or hyperpolarization of cultured neurons as well as the upregulated or downregulated intracellular calcium dynamics. The optoelectronic interfaces can also be mounted on nerve tissue to activate or silence neural activities in peripheral and central nervous tissues, as we show in mice with exposed sciatic nerves and somatosensory cortices. Bioresorbable silicon-based optoelectronic thin films that selectively excite or inhibit neural tissue may find advantageous biomedical applicability.

All-Optical and Label-Free Stimulation of Action Potentials in Neurons and Cardiomyocytes by Plasmonic Porous Metamaterials

Optical stimulation technologies are gaining great consideration in cardiology, neuroscience studies, and drug discovery pathways by providing control over cell activity with high spatio-temporal resolution. However, this high precision requires manipulation of biological processes at genetic level concealing its development from broad scale application. Therefore, translating these technologies into tools for medical or pharmacological applications remains a challenge. Here, an all-optical nongenetic method for the modulation of electrogenic cells is introduced. It is demonstrated that plasmonic metamaterials can be used to elicit action potentials by converting near infrared laser pulses into stimulatory currents. The suggested approach allows for the stimulation of cardiomyocytes and neurons directly on commercial complementary metal-oxide semiconductor microelectrode arrays coupled with ultrafast pulsed laser, providing both stimulation and network-level recordings on the same device.

Comparison of 10 Control hPSC Lines for Drug Screening in an Engineered Heart Tissue Format

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are commercially available, and cardiac differentiation established routine. Systematic evaluation of several control hiPSC-CM is lacking. We investigated 10 different control hiPSC-CM lines and analyzed function and suitability for drug screening. Five commercial and 5 academic hPSC-CM lines were casted in engineered heart tissue (EHT) format. Spontaneous and stimulated EHT contractions were analyzed, and 7 inotropic indicator compounds investigated on 8 cell lines. Baseline contractile force, kinetics, and rate varied widely among the different lines (e.g., relaxation time range: 118-471 ms). In contrast, the qualitative correctness of responses to BayK-8644, nifedipine, EMD-57033, isoprenaline, and digoxin in terms of force and kinetics varied only between 80% and 93%. Large baseline differences between control cell lines support the request for isogenic controls in disease modeling. Variability appears less relevant for drug screening but needs to be considered, arguing for studies with more than one line.

Automated Functional Screening for Modulators of Optogenetically Activated Neural Responses in Living Organisms

All-optical methods of probing in vivo brain function are advantageous for their compatibility with automated microscopy and fast spatial targeting of neural circuit excitation and response. Recent advances in optogenetic technologies allow simultaneous light activation of specific neurons and optical readout of neural activity via fluorescent calcium reporters, providing an attractive opportunity for high-throughput screening assays that directly assess dynamic neural function in vivo. Here we describe a method to automatically record optogenetically activated neural responses in living, hydrogel-embedded organisms over many hours in a multiwell plate format. This method is suitable for screening the neural effects of hundreds of chemical compounds and assessing the time course of bioactivity over 12 h or more. As examples, we show the suppression of neural responses over time with various concentrations of two voltage-gated calcium channel blockers and a full-plate screen of 320 chemicals with positive and negative controls in a single experiment.

Parallel All-Optical Assay to Study Use-Dependent Functioning of Voltage-Gated Ion Channels in a Miniaturized Format

Voltage-gated ion channels produce rapid transmembrane currents responsible for action potential generation and propagation at the neuronal, muscular, and cardiac levels. They represent attractive clinical targets because their altered firing frequency is often the hallmark of pathological signaling leading to several neuromuscular disorders. Therefore, a method to study their functioning upon repeated triggers at different frequencies is desired to develop new drug molecules selectively targeting pathological phenotype. Optogenetics provides powerful tools for millisecond switch of cellular excitability in contactless, physiological, and low-cost settings. Nevertheless, its application to large-scale drug-screening operations is still limited by long processing time (due to sequential well read), rigid flashing pattern, lack of online compound addition, or high consumable costs of existing methods. Here, we developed a method that enables simultaneous analysis of 384-well plates with optical pacing, fluorescence recording, and liquid injection. We used our method to deliver programmable millisecond-switched depolarization through light-activated opsin in concomitance with continuous optical recording by a fluorescent indicator. We obtained 384-well pacing of recombinant voltage-activated sodium or calcium channels, as well as induced pluripotent stem cell (iPSC)-derived cardiomyocytes, in all-optical parallel settings. Furthermore, we demonstrated the use-dependent behavior of known ion channel blockers by optogenetic pacing at normal or pathological firing frequencies, obtaining very good signal reproducibility and accordance with electrophysiology data. Our method provides a novel physiological approach to study frequency-dependent drug behavior using reversible programmable triggers. The all-optical parallel settings combined with contained operational costs make our method particularly suited for large-scale drug-screening campaigns as well as cardiac liability studies.

Recent Strategic Developments in the Use of Superdisintegrants for Drug Delivery

Improving drug bioavailability in the pharmaceutical field is a challenge that has attracted substantial interest worldwide. The controlled release of a drug can be achieved with a variety of strategies and novel materials in the field. In addition to the vast development of innovative materials for improving therapeutic effects and reducing side effects, the exploration of remarkable existing materials could encourage the discovery of diverse approaches for adapted drug delivery systems. Recently, superdisintegrants have been proposed for drug delivery systems as alternative approaches to maximize the efficiency of therapy. Although superdisintegrants are well known and used in solid dosage forms, studies on strategies for the development of drug delivery systems using superdisintegrants are lacking. Therefore, this study reviews the use of superdisintegrants in controlled drug release dosage formulations. This overview of superdisintegrants covers developed strategies, types (including synthetic and natural materials), dosage forms and techniques and will help to improve drug delivery systems.

Graphene biointerfaces for optical stimulation of cells

Noninvasive stimulation of cells is crucial for the accurate examination and control of their function both at the cellular and the system levels. To address this need, we present a pioneering optical stimulation platform that does not require genetic modification of cells but instead capitalizes on unique optoelectronic properties of graphene, including its ability to efficiently convert light into electricity. We report the first studies of optical stimulation of cardiomyocytes via graphene-based biointerfaces (G-biointerfaces) in substrate-based and dispersible configurations. The efficiency of stimulation via G-biointerfaces is independent of light wavelength but can be tuned by changing the light intensity. We demonstrate that an all-optical evaluation of use-dependent drug effects in vitro can be enabled using substrate-based G-biointerfaces. Furthermore, using dispersible G-biointerfaces in vivo, we perform optical modulation of the heart activity in zebrafish embryos. Our discovery is expected to empower numerous fundamental and translational biomedical studies.

In Silico Assessment of Efficacy and Safety of IKur Inhibitors in Chronic Atrial Fibrillation: Role of Kinetics and State-Dependence of Drug Binding

Current pharmacological therapy against atrial fibrillation (AF), the most common cardiac arrhythmia, is limited by moderate efficacy and adverse side effects including ventricular proarrhythmia and organ toxicity. One way to circumvent the former is to target ion channels that are predominantly expressed in atria vs. ventricles, such as K_V1.5, carrying the ultra-rapid delayed-rectifier K⁺ current (I_Kur). Recently, we used an in silico strategy to define optimal K_V1.5-targeting drug characteristics, including kinetics and state-dependent binding, that maximize AF-selectivity in human atrial cardiomyocytes in normal sinus rhythm (nSR). However, because of evidence for I_Kur being strongly diminished in long-standing persistent (chronic) AF (cAF), the therapeutic potential of drugs targeting I_Kur may be limited in cAF patients. Here, we sought to simulate the efficacy (and safety) of I_Kur inhibitors in cAF conditions. To this end, we utilized sensitivity analysis of our human atrial cardiomyocyte model to assess the importance of I_Kur for atrial cardiomyocyte electrophysiological properties, simulated hundreds of theoretical drugs to reveal those exhibiting anti-AF selectivity, and compared the results obtained in cAF with those in nSR. We found that despite being downregulated, I_Kur contributes more prominently to action potential (AP) and effective refractory period (ERP) duration in cAF vs. nSR, with ideal drugs improving atrial electrophysiology (e.g., ERP prolongation) more in cAF than in nSR. Notably, the trajectory of the AP during cAF is such that more I_Kur is available during the more depolarized plateau potential. Furthermore, I_Kur block in cAF has less cardiotoxic effects (e.g., AP duration not exceeding nSR values) and can increase Ca²⁺ transient amplitude thereby enhancing atrial contractility. We propose that in silico strategies such as that presented here should be combined with in vitro and in vivo assays to validate model predictions and facilitate the ongoing search for novel agents against AF.

A high-throughput model for investigating neuronal function and synaptic transmission in cultured neuronal networks

Loss of synapses or alteration of synaptic activity is associated with cognitive impairment observed in a number of psychiatric and neurological disorders, such as schizophrenia and Alzheimer’s disease. Therefore successful development of in vitro methods that can investigate synaptic function in a high-throughput format could be highly impactful for neuroscience drug discovery. We present here the development, characterisation and validation of a novel high-throughput in vitro model for assessing neuronal function and synaptic transmission in primary rodent neurons. The novelty of our approach resides in the combination of the electrical field stimulation (EFS) with data acquisition in spatially separated areas of an interconnected neuronal network. We integrated our methodology with state of the art drug discovery instrumentation (FLIPR Tetra) and used selective tool compounds to perform a systematic pharmacological validation of the model. We investigated pharmacological modulators targeting pre- and post-synaptic receptors (AMPA, NMDA, GABA-A, mGluR2/3 receptors and Nav, Cav voltage-gated ion channels) and demonstrated the ability of our model to discriminate and measure synaptic transmission in cultured neuronal networks. Application of the model described here as an unbiased phenotypic screening approach will help with our long term goals of discovering novel therapeutic strategies for treating neurological disorders.