Antidepressants enter cells, organelles, and membranes

We begin by summarizing several examples of antidepressants whose therapeutic actions begin when they encounter their targets in the cytoplasm or in the lumen of an organelle. These actions contrast with the prevailing view that most neuropharmacological actions begin when drugs engage their therapeutic targets at extracellular binding sites of plasma membrane targets-ion channels, receptors, and transporters. We review the chemical, pharmacokinetic, and pharmacodynamic principles underlying the movements of drugs into subcellular compartments. We note the relationship between protonation-deprotonation events and membrane permeation of antidepressant drugs. The key properties relate to charge and hydrophobicity/lipid solubility, summarized by the parameters LogP, pKa, and LogDpH7.4. The classical metric, volume of distribution (Vd), is unusually large for some antidepressants and has both supracellular and subcellular components. A table gathers structures, LogP, PKa, LogDpH7.4, and Vd data and/or calculations for most antidepressants and antidepressant candidates. The subcellular components, which can now be measured in some cases, are dominated by membrane binding and by trapping in the lumen of acidic organelles. For common antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) and serotonin/norepinephrine reuptake inhibitors (SNRIs), the target is assumed to be the eponymous reuptake transporter(s), although in fact the compartment of target engagement is unknown. We review special aspects of the pharmacokinetics of ketamine, ketamine metabolites, and other rapidly acting antidepressants (RAADs) including methoxetamine and scopolamine, psychedelics, and neurosteroids. Therefore, the reader can assess properties that markedly affect a drug's ability to enter or cross membranes-and therefore, to interact with target sites that face the cytoplasm, the lumen of organelles, or a membrane. In the current literature, mechanisms involving intracellular targets are termed "location-biased actions" or "inside-out pharmacology". Hopefully, these general terms will eventually acquire additional mechanistic details.

Fluorescence Screens for Identifying Central Nervous System-Acting Drug-Biosensor Pairs for Subcellular and Supracellular Pharmacokinetics

Subcellular pharmacokinetic measurements have informed the study of central nervous system (CNS)-acting drug mechanisms. Recent investigations have been enhanced by the use of genetically encoded fluorescent biosensors for drugs of interest at the plasma membrane and in organelles. We describe screening and validation protocols for identifying hit pairs comprising a drug and biosensor, with each screen including 13-18 candidate biosensors and 44-84 candidate drugs. After a favorable hit pair is identified and validated via these protocols, the biosensor is then optimized, as described in other papers, for sensitivity and selectivity to the drug. We also show sample hit pair data that may lead to future intensity-based drug-sensing fluorescent reporters (iDrugSnFRs). These protocols will assist scientists to use fluorescence responses as criteria in identifying favorable fluorescent biosensor variants for CNS-acting drugs that presently have no corresponding biosensor partner. This protocol was validated in: eLife (2022), DOI: 10.7554/eLife.74648 Graphical abstract.

Stable and Discriminatory Radiomic Features from the Tumor and Its Habitat Associated with Progression-Free Survival in Glioblastoma: A Multi-Institutional Study

BACKGROUND AND PURPOSE

Glioblastoma is an aggressive brain tumor, with no validated prognostic biomarkers for survival before surgical resection. Although recent approaches have demonstrated the prognostic ability of tumor habitat (constituting necrotic core, enhancing lesion, T2/FLAIR hyperintensity subcompartments) derived radiomic features for glioblastoma survival on treatment-naive MR imaging scans, radiomic features are known to be sensitive to MR imaging acquisitions across sites and scanners. In this study, we sought to identify the radiomic features that are both stable across sites and discriminatory of poor and improved progression-free survival in glioblastoma tumors.

MATERIALS AND METHODS

We used 150 treatment-naive glioblastoma MR imaging scans (Gadolinium-T1w, T2w, FLAIR) obtained from 5 sites. For every tumor subcompartment (enhancing tumor, peritumoral FLAIR-hyperintensities, necrosis), a total of 316 three-dimensional radiomic features were extracted. The training cohort constituted studies from 4 sites (n = 93) to select the most stable and discriminatory radiomic features for every tumor subcompartment. These features were used on a hold-out cohort (n = 57) to evaluate their ability to discriminate patients with poor survival from those with improved survival.

RESULTS

Incorporating the most stable and discriminatory features within a linear discriminant analysis classifier yielded areas under the curve of 0.71, 0.73, and 0.76 on the test set for distinguishing poor and improved survival compared with discriminatory features alone (areas under the curve of 0.65, 0.54, 0.62) from the necrotic core, enhancing tumor, and peritumoral T2/FLAIR hyperintensity, respectively.

CONCLUSIONS

Incorporating stable and discriminatory radiomic features extracted from tumors and associated habitats across multisite MR imaging sequences may yield robust prognostic classifiers of patient survival in glioblastoma tumors.

Role of defects and grain boundaries in the thermal response of wafer-scale hBN films

With more widespread applications of nanotechnology, heat dissipation in nanoscale devices is becoming a critical issue. We study the thermal response of wafer-scale hexagonal boron nitride (hBN) layers, which find potential applications as ideal substrates in two dimensional devices. Sapphire-supported thin hBN films, 2'' in size and of different thicknesses, were grown using metalorganic vapour phase epitaxy. These large-scale films exhibit wrinkles defects and grain boundaries over their entire area. The shift of [Formula: see text] phonon mode with temperature is analysed by considering the cumulative contribution of anharmonic phonon decay along with lattice thermal expansion, defect, and strain modulation. The study demonstrates that during heat treatment the strain evolution plays a dominating role in governing the characteristics of the wrinkled thinner films. Interestingly we find that both defects and strain determine the spectral line-width of these wafer-scale films. To the end, from Raman line-width, the changes in phonon lifetime in delaminated and as-grown films is estimated. The results suggest the possibility of a reduction in thermal transport in these wafer-scale films compared to their bulk counterpart.

Metal nanoparticle alters adenine induced charge transfer kinetics of vitamin K3 in magnetic field

In this article, we highlight the alterations in the photoinduced electron transfer (ET) and hydrogen atom transfer (HAT) pathways between an anti-tumor drug vitamin-K3 (MQ) and a nucleobase adenine (ADN) in the presence of gold (Au) and iron (Fe) nanoparticles (NPs). Inside the confined micellar media, with laser flash photolysis corroborated with an external magnetic field (MF), we have detected the transient geminate radicals of MQ and ADN, photo-generated through ET and HAT. We observe that the presence of AuNP on the MQ-ADN complex (^AuMQ-ADN) assists HAT by limiting the ET channel, on the other hand, FeNP on the MQ-ADN complex (^FeMQ-ADN) mostly favors a facile PET. We hypothesize that through selective interactions of the ADN molecules with AuNP and MQ molecules with FeNP, a preferential HAT and PET process is eased. The enhanced HAT and PET have been confirmed by the escape yields of radical intermediates by time-resolved transient absorption spectroscopy in the presence of MF.

Biosensors Show the Pharmacokinetics of S-Ketamine in the Endoplasmic Reticulum

The target for the “rapid” (<24 h) antidepressant effects of S-ketamine is unknown, vitiating programs to rationally develop more effective rapid antidepressants. To describe a drug’s target, one must first understand the compartments entered by the drug, at all levels—the organ, the cell, and the organelle. We have, therefore, developed molecular tools to measure the subcellular, organellar pharmacokinetics of S-ketamine. The tools are genetically encoded intensity-based S-ketamine-sensing fluorescent reporters, iSKetSnFR1 and iSKetSnFR2. In solution, these biosensors respond to S-ketamine with a sensitivity, S-slope = delta(F/F₀)/(delta[S-ketamine]) of 0.23 and 1.9/μM, respectively. The iSKetSnFR2 construct allows measurements at <0.3 μM S-ketamine. The iSKetSnFR1 and iSKetSnFR2 biosensors display >100-fold selectivity over other ligands tested, including R-ketamine. We targeted each of the sensors to either the plasma membrane (PM) or the endoplasmic reticulum (ER). Measurements on these biosensors expressed in Neuro2a cells and in human dopaminergic neurons differentiated from induced pluripotent stem cells (iPSCs) show that S-ketamine enters the ER within a few seconds after appearing in the external solution near the PM, then leaves as rapidly after S-ketamine is removed from the extracellular solution. In cells, S-slopes for the ER and PM-targeted sensors differ by <2-fold, indicating that the ER [S-ketamine] is less than 2-fold different from the extracellular [S-ketamine]. Organelles represent potential compartments for the engagement of S-ketamine with its antidepressant target, and potential S-ketamine targets include organellar ion channels, receptors, and transporters.

Determining the pharmacokinetics of nicotinic drugs in the endoplasmic reticulum using biosensors

Nicotine dependence is thought to arise in part because nicotine permeates into the endoplasmic reticulum (ER), where it binds to nicotinic receptors (nAChRs) and begins an "inside-out" pathway that leads to up-regulation of nAChRs on the plasma membrane. However, the dynamics of nicotine entry into the ER are unquantified. Here, we develop a family of genetically encoded fluorescent biosensors for nicotine, termed iNicSnFRs. The iNicSnFRs are fusions between two proteins: a circularly permutated GFP and a periplasmic choline-/betaine-binding protein engineered to bind nicotine. The biosensors iNicSnFR3a and iNicSnFR3b respond to nicotine by increasing fluorescence at [nicotine] <1 µM, the concentration in the plasma and cerebrospinal fluid of a smoker. We target iNicSnFR3 biosensors either to the plasma membrane or to the ER and measure nicotine kinetics in HeLa, SH-SY5Y, N2a, and HEK293 cell lines, as well as mouse hippocampal neurons and human stem cell-derived dopaminergic neurons. In all cell types, we find that nicotine equilibrates in the ER within 10 s (possibly within 1 s) of extracellular application and leaves as rapidly after removal from the extracellular solution. The [nicotine] in the ER is within twofold of the extracellular value. We use these data to run combined pharmacokinetic and pharmacodynamic simulations of human smoking. In the ER, the inside-out pathway begins when nicotine becomes a stabilizing pharmacological chaperone for some nAChR subtypes, even at concentrations as low as ∼10 nM. Such concentrations would persist during the 12 h of a typical smoker's day, continually activating the inside-out pathway by >75%. Reducing nicotine intake by 10-fold decreases activation to ∼20%. iNicSnFR3a and iNicSnFR3b also sense the smoking cessation drug varenicline, revealing that varenicline also permeates into the ER within seconds. Our iNicSnFRs enable optical subcellular pharmacokinetics for nicotine and varenicline during an early event in the inside-out pathway.

Shape Features of the Lesion Habitat to Differentiate Brain Tumor Progression from Pseudoprogression on Routine Multiparametric MRI: A Multisite Study

BACKGROUND AND PURPOSE

Differentiating pseudoprogression, a radiation-induced treatment effect, from tumor progression on imaging is a substantial challenge in glioblastoma management. Unfortunately, guidelines set by the Response Assessment in Neuro-Oncology criteria are based solely on bidirectional diametric measurements of enhancement observed on T1WI and T2WI/FLAIR scans. We hypothesized that quantitative 3D shape features of the enhancing lesion on T1WI, and T2WI/FLAIR hyperintensities (together called the lesion habitat) can more comprehensively capture pathophysiologic differences across pseudoprogression and tumor recurrence, not appreciable on diametric measurements alone.

MATERIALS AND METHODS

A total of 105 glioblastoma studies from 2 institutions were analyzed, consisting of a training (n = 59) and an independent test (n = 46) cohort. For every study, expert delineation of the lesion habitat (T1WI enhancing lesion and T2WI/FLAIR hyperintense perilesional region) was obtained, followed by extraction of 30 shape features capturing 14 "global" contour characteristics and 16 "local" curvature measures for every habitat region. Feature selection was used to identify most discriminative features on the training cohort, which were evaluated on the test cohort using a support vector machine classifier.

RESULTS

The top 2 most discriminative features were identified as local features capturing total curvature of the enhancing lesion and curvedness of the T2WI/FLAIR hyperintense perilesional region. Using top features from the training cohort (training accuracy = 91.5%), we obtained an accuracy of 90.2% on the test set in distinguishing pseudoprogression from tumor progression.

CONCLUSIONS

Our preliminary results suggest that 3D shape attributes from the lesion habitat can differentially express across pseudoprogression and tumor progression and could be used to distinguish these radiographically similar pathologies.

Fluorogenic Detection of Monoamine Neurotransmitters in Live Cells

Monoamine neurotransmission is key to neuromodulation, but imaging monoamines in live neurons has remained a challenge. Here we show that externally added ortho-phthalaldehyde (OPA) can permeate live cells and form bright fluorogenic adducts with intracellular monoamines (e.g., serotonin, dopamine, and norepinephrine) and with L-DOPA, which can be imaged sensitively using conventional single-photon excitation in a fluorescence microscope. The peak excitation and emission wavelengths (λ_ex = 401 nm and λ_em = 490 nm for serotonin; λ_ex = 446 nm and λ_em = 557 nm for dopamine; and λ_ex = 446 nm and λ_em = 544 nm for norepinephrine, respectively) are accessible to most modern confocal imaging instruments. The identity of monoamine containing structures (possibly neurotransmitter vesicles) in serotonergic RN46A cells is established by quasi-simultaneous imaging of serotonin using three-photon excitation microscopy. Mass spectrometry of cell extracts and of in vitro solutions helps us identify the chemical nature of the adducts and establishes the reaction mechanisms. Our method has low toxicity, high selectivity, and the ability to directly report the location and concentration of monoamines in live cells.

DNA Damage and Apoptosis Induction in Cancer Cells by Chemically Engineered Thiolated Riboflavin Gold Nanoassembly

Herein we have engineered a smart nuclear targeting thiol-modified riboflavin-gold nano assembly, RfS@AuNPs, which accumulates selectively in the nucleus without any nuclear-targeting peptides (NLS/RGD) and shows photophysically in vitro DNA intercalation. A theoretical model using Molecular Dynamics has been developed to probe the mechanism of formation and stability as well as dynamics of the RfS@AuNPs in aqueous solution and within the DNA microenvironment. The RfS@AuNPs facilitate the binucleated cell formation that is reflected in the significant increase of DNA damage marker, γ-H2AX as well as the arrest of most of the HeLa cells at the pre-G1 phase indicating cell death. Moreover, a significant upregulation of apoptotic markers confirms that the cell death occurs through the apoptotic pathway. Analyses of the microarray gene expression of RfS@AuNPs treated HeLa cells show significant alterations in vital biological processes necessary for cell survival. Taken together, our study reports a unique nuclear targeting mechanism through targeting the riboflavin receptors, which are upregulated in cancer cells and induce apoptosis in the targeted cells.

Structural Elements and Cough Suppressing Activity of Polysaccharides from Zingiber officinale Rhizome

Zingiber officinale is used for the management of fever, bronchial asthma and cough for thousands of years. While the link to a particular indication has been established in human, the active principle of the formulation remains unknown. Herein, we have investigated a water extracted polysaccharides (WEP) containing fraction from its rhizome. Utilizing a traditional aqueous extraction protocol and using chemical, chromatographic and spectroscopic methods a fraction containing a branched glucan and polygalaturonan in a ratio of 59:1 was characterized. This glucan, which has a molecular mass of 36 kDa, is made up of terminal-, (1,4)- and (1,4,6)-linked α-Glcp residues. Oral administration of WEP in doses of 25 and 50 mg/kg body weight significantly inhibited the number of citric acid-induced cough efforts in guinea pigs. It does not alter the specific airway smooth muscle reactivity significantly. Thus, traditional aqueous extraction method provides molecular entities, which induces antitussive activity without addiction.

Intermolecular disulfide bond formation promotes immunoglobulin aggregation: investigation by fluorescence correlation spectroscopy

Protein aggregation generally results from association between hydrophobic regions of individual monomers. However, additional mechanisms arising from specific interactions, such as intermolecular disulfide bond formation, may also contribute to the process. The latter is proposed to be the initiating pathway for aggregation of immunoglobulin (IgG), which is essential for triggering its immune response. To test the veracity of this hypothesis, we have employed fluorescence correlation spectroscopy to measure the kinetics of aggregation of IgG in separate experiments either allowing or inhibiting disulfide formation. Fluorescence correlation spectroscopy measurements yielded a diffusion time (τ(D)) of ∼200 µsec for Rhodamine-labeled IgG, corresponding to a hydrodynamic radius (R(H)) of 56 Å for the IgG monomer. The aggregation kinetics of the protein was followed by monitoring the time evolution of τ(D) under conditions in which its cysteine residues were either free or blocked. In both cases, the progress curves confirmed that aggregation proceeded via the nucleation-dependent polymerization pathway. However, for aggregation in the presence of free cysteines, the lag times were shorter, and the aggregate sizes bigger, than their respective counterparts for aggregation in the presence of blocked cysteines. This result clearly demonstrates that formation of intermolecular disulfide bonds represents a preferred pathway in the aggregation process of IgG. Fluorescence spectroscopy showed that aggregates formed in experiments where disulfide formation was prevented denatured at lower concentration of guanidine hydrochloride than those obtained in experiments where the disulfides were free to form, indicating that intermolecular disulfide bridging is a valid pathway for IgG aggregation.