Cationic amphiphilic drugs cause a marked expansion of apparent lysosomal volume: implications for an intracellular distribution-based drug interaction

In vivo deposition of poorly soluble drugs

Administered drug molecules, whether dissolved or solubilized, have the potential to precipitate and accumulate as solid forms in tissues and cells within the body. This phase transition can significantly impact the pharmacokinetics of treatment. It is thus crucial to gain an understanding of how drug solubility/permeability, drug formulations and routes of administration affect in vivo behaviors of drug deposition. This review examines literature reports on the drug deposition in tissues and cells of poorly water-soluble drugs, as well as underlying physical mechanisms that lead to precipitation. Our work particularly highlights drug deposition in macrophages and the subcellular fate of precipitated drugs. We also propose a tissue permeability-based classification framework to evaluate precipitation potentials of poorly soluble drugs in major organs and tissues. The impact on pharmacokinetics is further discussed and needs to be considered in developing drug delivery systems. Finally, bioimaging techniques that are used to examine aggregated states and the intracellular trafficking of absorbed drugs are summarized.

Chemogenomics for NR1 nuclear hormone receptors

Nuclear receptors (NRs) regulate transcription in response to ligand binding and NR modulation allows pharmacological control of gene expression. Although some NRs are relevant as drug targets, the NR1 family, which comprises 19 NRs binding to hormones, vitamins, and lipid metabolites, has only been partially explored from a translational perspective. To enable systematic target identification and validation for this protein family in phenotypic settings, we present an NR1 chemogenomic (CG) compound set optimized for complementary activity/selectivity profiles and chemical diversity. Based on broad profiling of candidates for specificity, toxicity, and off-target liabilities, sixty-nine comprehensively annotated NR1 agonists, antagonists and inverse agonists covering all members of the NR1 family and meeting potency and selectivity standards are included in the final NR1 CG set. Proof-of-concept application of this set reveals effects of NR1 members in autophagy, neuroinflammation and cancer cell death, and confirms the suitability of the set for target identification and validation.

Exploring the potential of drug repurposing for liver diseases: A comprehensive study

Drug repurposing involves the investigation of existing drugs for new indications. It offers a great opportunity to quickly identify a new drug candidate at a lower cost than novel discovery and development. Despite the importance and potential role of drug repurposing, there is no specific definition that healthcare providers and the World Health Organization credit. Unfortunately, many similar and interchangeable concepts are being used in the literature, making it difficult to collect and analyze uniform data on repurposed drugs. This research was conducted based on understanding general criteria for drug repurposing, concentrating on liver diseases. Many drugs have been investigated for their effect on liver diseases even though they were originally approved (or on their way to being approved) for other diseases. Some of the hypotheses for drug repurposing were first captured from the literature and then processed further to test the hypothesis. Recently, with the revolution in bioinformatics techniques, scientists have started to use drug libraries and computer systems that can analyze hundreds of drugs to give a short list of candidates to be analyzed pharmacologically. However, this study revealed that drug repurposing is a potential aid that may help deal with liver diseases. It provides available or under-investigated drugs that could help treat hepatitis, liver cirrhosis, Wilson disease, liver cancer, and fatty liver. However, many further studies are needed to ensure the efficacy of these drugs on a large scale.

A 3D spheroid model of quadruple cell co-culture with improved liver functions for hepatotoxicity prediction

Drug-induced liver injury (DILI) is one of the major concerns during drug development. Wide acceptance of the 3 R principles and the innovation of in-vitro techniques have introduced various novel model options, among which the three-dimensional (3D) cell spheroid cultures have shown a promising prospect in DILI prediction. The present study developed a 3D quadruple cell co-culture liver spheroid model for DILI prediction via self-assembly. Induction by phorbol 12-myristate 13-acetate at the concentration of 15.42 ng/mL for 48 hours with a following 24-hour rest period was used for THP-1 cell differentiation, resulting in credible macrophagic phenotypes. HepG2 cells, PUMC-HUVEC-T1 cells, THP-1-originated macrophages, and human hepatic stellate cells were selected as the components, which exhibited adaptability in the designated spheroid culture conditions. Following establishment, the characterization demonstrated the competence of the model in long-term stability reflected by the maintenance of morphology, viability, cellular integration, and cell-cell junctions for at least six days, as well as the reliable liver-specific functions including superior albumin and urea secretion, improved drug metabolic enzyme expression and CYP3A4 activity, and the expression of MRP2, BSEP, and P-GP accompanied by the bile acid efflux transport function. In the comparative testing using 22 DILI-positive and 5 DILI-negative compounds among the novel 3D co-culture model, 3D HepG2 spheroids, and 2D HepG2 monolayers, the 3D culture method significantly enhanced the model sensitivity to compound cytotoxicity compared to the 2D form. The novel co-culture liver spheroid model exhibited higher overall predictive power with margin of safety as the classifying tool. In addition, the non-parenchymal cell components could amplify the toxicity of isoniazid in the 3D model, suggesting their potential mediating role in immune-mediated toxicity. The proof-of-concept experiments demonstrated the capability of the model in replicating drug-induced lipid dysregulation, bile acid efflux inhibition, and α-SMA upregulation, which are the key features of liver steatosis and phospholipidosis, cholestasis, and fibrosis, respectively. Overall, the novel 3D quadruple cell co-culture spheroid model is a reliable and readily available option for DILI prediction.

Uncovering the toxicity mechanisms of a series of carboxylic acids in liver cells through computational and experimental approaches

Hepatotoxicity poses a significant concern in drug design due to the potential liver damage that can be caused by new drugs. Among common manifestations of hepatotoxic damage is lipid accumulation in hepatic tissue, resulting in liver steatosis or phospholipidosis. Carboxylic derivatives are prone to interfere with fatty acid metabolism and cause lipid accumulation in hepatocytes. This study investigates the toxic behaviour of 24 structurally related carboxylic acids in hepatocytes, specifically their ability to cause accumulation of fatty acids and phospholipids. Using high-content screening (HCS) assays, we identified two distinct lipid accumulation patterns. Subsequently, we developed structure-activity relationship (SAR) and quantitative structure-activity relationship (QSAR) models to determine relevant molecular substructures and descriptors contributing to these adverse effects. Additionally, we calculated physicochemical properties associated with lipid accumulation in hepatocytes and examined their correlation with our chemical structure characteristics. To assess the applicability of our findings to a wide range of chemical compounds, we employed two external datasets to evaluate the distribution of our QSAR descriptors. Our study highlights the significance of subtle molecular structural variations in triggering hepatotoxicity, such as the presence of nitrogen or the specific arrangement of substitutions within the carbon chain. By employing our comprehensive approach, we pinpointed specific molecules and elucidated their mechanisms of toxicity, thus offering valuable insights to guide future toxicology investigations.

Evaluating β2-agonists as siRNA delivery adjuvants for pulmonary surfactant-coated nanogel inhalation therapy

The lung is an attractive target organ for inhalation of RNA therapeutics, such as small interfering RNA (siRNA). However, clinical translation of siRNA drugs for application in the lung is hampered by many extra- and intracellular barriers. We previously developed hybrid nanoparticles consisting of an siRNA-loaded nanosized hydrogel (nanogel) core coated with Curosurf®, a clinically used pulmonary surfactant. The surfactant shell was shown to markedly improve particle stability and promote intracellular siRNA delivery, both in vitro and in vivo. However, the full potential of siRNA nanocarriers is typically not reached as they are rapidly trafficked towards lysosomes for degradation and only a fraction of the internalized siRNA cargo is able to escape into the cytosol. We recently reported on the repurposing of widely applied cationic amphiphilic drugs (CADs) as siRNA delivery enhancers. Due to their physicochemical properties, CADs passively accumulate in the (endo)lysosomal compartment causing a transient permeabilization of the lysosomal membrane, which facilitates cytosolic drug delivery. In this work, we assessed a selection of cationic amphiphilic β2-agonists (i.e., salbutamol, formoterol, salmeterol and indacaterol) for their ability to enhance siRNA delivery in a lung epithelial and macrophage cell line. These drugs are widely used in the clinic for their bronchodilating effect in obstructive lung disease. As opposed to the least hydrophobic drugs salbutamol and formoterol, the more hydrophobic long-acting β2-agonist (LABA) salmeterol promoted siRNA delivery in both cell types for both uncoated and surfactant-coated nanogels, whereas indacaterol showed this effect solely in lung epithelial cells. Our results demonstrate the potential of both salmeterol and indacaterol to be repurposed as adjuvants for nanocarrier-mediated siRNA delivery to the lung, which could provide opportunities for drug combination therapy.

Weak base drug-induced endolysosome iron dyshomeostasis controls the generation of reactive oxygen species, mitochondrial depolarization, and cytotoxicity

Objectives

Approximately 75 % of marketed drugs have the physicochemical property of being weak bases. Weak-base drugs with relatively high pKa values enter acidic organelles including endosomes and lysosomes (endolysosomes), reside in and de-acidify endolysosomes, and induce cytotoxicity. Divalent cations within endolysosomes, including iron, are released upon endolysosome de-acidification. Endolysosomes are "master regulators of iron homeostasis", and neurodegeneration is linked to ferrous iron (Fe2+)-induced reactive oxygen species (ROS) generation via Fenton chemistry. Because endolysosome de-acidification-induced lysosome-stress responses release endolysosome Fe2+, it was crucial to determine the mechanisms by which a functionally and structurally diverse group of weak base drugs including atropine, azithromycin, fluoxetine, metoprolol, and tamoxifen influence endolysosomes and cause cell death.

Methods

Using U87MG astrocytoma and SH-SY5Y neuroblastoma cells, we conducted concentration-response relationships for 5 weak-base drugs to determine EC50 values. From these curves, we chose pharmacologically and therapeutically relevant concentrations to determine if weak-base drugs induced lysosome-stress responses by de-acidifying endolysosomes, releasing endolysosome Fe2+ in sufficient levels to increase cytosolic and mitochondria Fe2+ and ROS levels and cell death.

Results

Atropine (anticholinergic), azithromycin (antibiotic), fluoxetine (antidepressant), metoprolol (beta-adrenergic), and tamoxifen (anti-estrogen) at pharmacologically and therapeutically relevant concentrations (1) de-acidified endolysosomes, (2) decreased Fe2+ levels in endolysosomes, (3) increased Fe2+ and ROS levels in cytosol and mitochondria, (4) induced mitochondrial membrane potential depolarization, and (5) increased cell death; effects prevented by the endocytosed iron-chelator deferoxamine.

Conclusions

Weak-base pharmaceuticals induce lysosome-stress responses that may affect their safety profiles; a better understanding of weak-base drugs on Fe2+ interorganellar signaling may improve pharmacotherapeutics.

Macrolide and Ketolide Antibiotics Inhibit the Cytotoxic Effect of Trastuzumab Emtansine in HER2-Positive Breast Cancer Cells: Implication of a Potential Drug-ADC Interaction in Cancer Chemotherapy

Macrolides are widely used for the long-term treatment of infections and chronic inflammatory diseases. The pharmacokinetic features of macrolides include extensive tissue distribution because of favorable membrane permeability and accumulation within lysosomes. Trastuzumab emtansine (T-DM1), a HER2-targeting antibody-drug conjugate (ADC), is catabolized in the lysosomes, where Lys-SMCC-DM1, a potent cytotoxic agent, is processed by proteinase degradation and subsequently released from the lysosomes to the cytoplasm through the lysosomal membrane transporter SLC46A3, resulting in an antitumor effect. We recently demonstrated that erythromycin and clarithromycin inhibit SLC46A3 and attenuate the cytotoxicity of T-DM1; however, the effect of other macrolides and ketolides has not been determined. In this study, we evaluated the effect of macrolide and ketolide antibiotics on T-DM1 cytotoxicity in a human breast cancer cell line, KPL-4. Macrolides used in the clinic, such as roxithromycin, azithromycin, and josamycin, as well as solithromycin, a ketolide under clinical development, significantly attenuated T-DM1 cytotoxicity in addition to erythromycin and clarithromycin. Of these, azithromycin was the most potent inhibitor of T-DM1 efficacy. These antibiotics significantly inhibited the transport function of SLC46A3 in a concentration-dependent manner. Moreover, these compounds extensively accumulated in the lysosomes at the levels estimated to be 0.41-13.6 mM when cells were incubated with them at a 2 μM concentration. The immunofluorescence staining of trastuzumab revealed that azithromycin and solithromycin inhibit the degradation of T-DM1 in the lysosomes. These results suggest that the attenuation of T-DM1 cytotoxicity by macrolide and ketolide antibiotics involves their lysosomal accumulation and results in their greater lysosomal concentrations to inhibit the SLC46A3 function and T-DM1 degradation. This suggests a potential drug-ADC interaction during cancer chemotherapy.

Imipramine Treatment Alters Sphingomyelin, Cholesterol, and Glycerophospholipid Metabolism in Isolated Macrophage Lysosomes

Lysosomes are degradative organelles that facilitate the removal and recycling of potentially cytotoxic materials and mediate a variety of other cellular processes, such as nutrient sensing, intracellular signaling, and lipid metabolism. Due to these central roles, lysosome dysfunction can lead to deleterious outcomes, including the accumulation of cytotoxic material, inflammation, and cell death. We previously reported that cationic amphiphilic drugs, such as imipramine, alter pH and lipid metabolism within macrophage lysosomes. Therefore, the ability for imipramine to induce changes to the lipid content of isolated macrophage lysosomes was investigated, focusing on sphingomyelin, cholesterol, and glycerophospholipid metabolism as these lipid classes have important roles in inflammation and disease. The lysosomes were isolated from control and imipramine-treated macrophages using density gradient ultracentrifugation, and mass spectrometry was used to measure the changes in their lipid composition. An unsupervised hierarchical cluster analysis revealed a clear differentiation between the imipramine-treated and control lysosomes. There was a significant overall increase in the abundance of specific lipids mostly composed of cholesterol esters, sphingomyelins, and phosphatidylcholines, while lysophosphatidylcholines and ceramides were overall decreased. These results support the conclusion that imipramine's ability to change the lysosomal pH inhibits multiple pH-sensitive enzymes in macrophage lysosomes.

The alpha-adrenergic antagonist prazosin promotes cytosolic siRNA delivery from lysosomal compartments

The widespread use of small interfering RNA (siRNA) is limited by the multiple extra- and intracellular barriers upon in vivo administration. Hence, suitable delivery systems, based on siRNA encapsulation in nanoparticles or its conjugation to targeting ligands, have been developed. Nevertheless, at the intracellular level, these state-of-the-art delivery systems still suffer from a low endosomal escape efficiency. Consequently, the bulk of the endocytosed siRNA drug rapidly accumulates in the lysosomal compartment. We recently reported that a wide variety of cationic amphiphilic drugs (CADs) can promote small nucleic acid delivery from the endolysosomal compartment into the cytosol via transient induction of lysosomal membrane permeabilization. Here, we describe the identification of alternate siRNA delivery enhancers from the NIH Clinical Compound Collection that do not have the typical physicochemical properties of CADs. Additionally, we demonstrate improved endolysosomal escape of siRNA via a cholesterol conjugate and polymeric carriers with the α1-adrenergic antagonist prazosin, which was identified as the best performing delivery enhancer from the compound screen. A more detailed assessment of the mode-of-action of prazosin suggests that a different cellular phenotype compared to typical CAD adjuvants drives cytosolic siRNA delivery. As it has been described in the literature that prazosin also induces cancer cell apoptosis and promotes antigen cross-presentation in dendritic cells, the proof-of-concept data in this work provides opportunities for the repurposing of prazosin in an anti-cancer combination strategy with siRNA.

Cholesterol-dependent molecular mechanisms contribute to cationic amphiphilic drugs' prevention of silica-induced inflammation

Silicosis is considered an irreversible chronic inflammatory disease caused by the inhalation of crystalline silica (cSiO2). The cycle of inflammation that drives silicosis and other particle-caused respiratory diseases is mediated by NLRP3 inflammasome activity in macrophages resulting in the release of IL-1β. Lysosomal membrane permeability (LMP) initiated by inhaled particles is the key regulatory step in leading to NLRP3 activity. In addition to its role in LMP, the lysosome is crucial to cellular cholesterol trafficking. Lysosomal cholesterol has been demonstrated to regulate LMP while cationic amphiphilic drugs (CADs) reduce cholesterol trafficking from lysosomes and promote endolysosomal cholesterol accumulation as seen in Niemann Pick disease. Using a bone marrow derived macrophage (BMdM) model, four CADs were examined for their potential to reduce cSiO2-induced inflammation. Here we found that FDA-approved CAD drugs imipramine, hydroxychloroquine, fluvoxamine, and fluoxetine contributed to reduced LMP and IL-1β release in cSiO2 treated BMdM. These drugs inhibited lysosomal enzymatic activity of acid sphingomyelinase, decreased lysosomal proteolytic function, and increased lysosomal pH. CADs also demonstrated a significant increase in lysosomal-associated free cholesterol. Increased lysosomal cholesterol was associated with a significant reduction in cSiO2 induced LMP and IL-1β release. In contrast, reduced lysosomal cholesterol significantly exacerbated cSiO2-induced IL-1β release and reduced the protective effect of CADs on IL-1β release following cSiO2 exposure. Taken together, these results suggest that CAD modification of lysosomal cholesterol may be used to reduce LMP and cSiO2-induced inflammation and could prove an effective therapeutic for silicosis and other particle-caused respiratory diseases.

Synthetic Ionizable Colloidal Drug Aggregates Enable Endosomal Disruption

Colloidal drug aggregates enable the design of drug-rich nanoparticles; however, the efficacy of stabilized colloidal drug aggregates is limited by entrapment in the endo-lysosomal pathway. Although ionizable drugs are used to elicit lysosomal escape, this approach is hindered by toxicity associated with phospholipidosis. It is hypothesized that tuning the pKa of the drug would enable endosomal disruption while avoiding phospholipidosis and minimizing toxicity. To test this idea, 12 analogs of the nonionizable colloidal drug fulvestrant are synthesized with ionizable groups to enable pH-dependent endosomal disruption while maintaining bioactivity. Lipid-stabilized fulvestrant analog colloids are endocytosed by cancer cells, and the pKa of these ionizable colloids influenced the mechanism of endosomal and lysosomal disruption. Four fulvestrant analogs-those with pKa values between 5.1 and 5.7-disrupted endo-lysosomes without measurable phospholipidosis. Thus, by manipulating the pKa of colloid-forming drugs, a tunable and generalizable strategy for endosomal disruption is established.

Lysosomal nanotoxicity: Impact of nanomedicines on lysosomal function

Although several nanomedicines got clinical approval over the past two decades, the clinical translation rate is relatively small so far. There are many post-surveillance withdrawals of nanomedicines caused by various safety issues. For successful clinical advancement of nanotechnology, it is of unmet need to realize cellular and molecular foundation of nanotoxicity. Current data suggest that lysosomal dysfunction caused by nanoparticles is emerging as the most common intracellular trigger of nanotoxicity. This review analyzes prospect mechanisms of lysosomal dysfunction-mediated toxicity induced by nanoparticles. We summarized and critically assessed adverse drug reactions of current clinically approved nanomedicines. Importantly, we show that physicochemical properties have great impact on nanoparticles interaction with cells, excretion route and kinetics, and subsequently on toxicity. We analyzed literature on adverse reactions of current nanomedicines and hypothesized that adverse reactions might be linked with lysosomal dysfunction caused by nanomedicines. Finally, from our analysis it becomes clear that it is unjustifiable to generalize safety and toxicity of nanoparticles, since different particles possess distinct toxicological properties. We propose that the biological mechanism of the disease progression and treatment should be central in the optimization of nanoparticle design.

Desloratadine, an FDA-approved cationic amphiphilic drug, inhibits SARS-CoV-2 infection in cell culture and primary human nasal epithelial cells by blocking viral entry

The 2019 global coronavirus (COVID-19) pandemic has brought the world to a grinding halt, highlighting the urgent need for therapeutic and preventive solutions to slow the spread of emerging viruses. The objective of this study was to assess the anti-SARS-CoV-2 effectiveness of 8 FDA-approved cationic amphiphilic drugs (CADs). SARS-CoV-2-infected Vero cells, Calu-3 cells and primary Human Nasal Epithelial Cells (HNEC) were used to investigate the effects of CADs and revealed their antiviral mode of action. Among the CADs tested, desloratadine, a commonly used antiallergic, well-tolerated with no major side effects, potently reduced the production of SARS-CoV-2 RNA in Vero-E6 cells. Interestingly, desloratadine was also effective against HCoV-229E and HCoV-OC43 showing that it possessed broad-spectrum anti-coronavirus activity. Investigation of its mode of action revealed that it targeted an early step of virus lifecycle and blocked SARS-CoV-2 entry through the endosomal pathway. Finally, the ex vivo kinetic of the antiviral effect of desloratadine was evaluated on primary Human Nasal Epithelial Cells (HNEC), showing a significant delay of viral RNA production with a maximal reduction reached after 72 h of treatment. Thus, this treatment could provide a substantial contribution to prophylaxis and systemic therapy of COVID-19 or other coronaviruses infections and requires further studies.

Imatinib disturbs lysosomal function and morphology and impairs the activity of mTORC1 in human hepatocyte cell lines

The tyrosine kinase inhibitors (TKIs) imatinib and lapatinib are associated with severe hepatotoxicity, whose mechanisms are currently under investigation. As amphiphilic drugs, imatinib and lapatinib enrich in lysosomes. In the present study, we investigated their effects on lysosomal morphology and function in HepG2 and HuH-7 cells and explored possible links between lysosomal dysfunction and hepatotoxicity. Both TKIs increased the lysosomal volume time and concentration-dependently in HepG2 and HuH-7 cells. In HepG2 cells, lapatinib and imatinib raised the lysosomal pH and destabilized the lysosomal membrane, thereby impairing lysosomal proteolytic activity such as cathepsin B processing. Imatinib activated the transcription factor EB (TFEB), a regulator of lysosomal biogenesis and function, as demonstrated by nuclear TFEB accumulation and increased expression of TFEB-target genes. Because of lysosomal dysfunction, imatinib impaired mTORC1 activation, a protein complex activated on the lysosomal surface, which explained TFEB activation. HepG2 cells treated with imatinib showed increased levels of MAP1LC3A/B-II and of ATG13 (S318) phosphorylation, indicating induction of autophagy due to TFEB activation. Finally, imatinib induced apoptosis in HepG2 cells in a time and concentration-dependent manner, explained by lysosomal and mitochondrial toxicity. Our findings provide a new lysosome-centered mechanism for imatinib-induced hepatotoxicity that could be extended to other lysosomotropic drugs.

Raman and fluorescence imaging of phospholipidosis induced by cationic amphiphilic drugs in endothelial cells

Cationic amphiphilic drugs (CADs) are known from lysosomotropism, drug-induced phospholipidosis (DIPL), activation of autophagy, and decreased cell viability, but the relationship between these events is not clear and little is known about DIPL in the endothelium. In this work, the effects of fluoxetine, amiodarone, clozapine, and risperidone on human microvascular endothelial cells (HMEC-1) were studied using a combined methodology of label-free Raman imaging and fluorescence staining. Raman spectroscopy was applied to characterize biochemical changes in lipid profile and their distribution in the cellular compartments, while fluorescence staining (LysoTracker, LipidTOX, LC3B, and JC-1) was used to analyze lysosome volume expansion, activation of autophagy, lipid accumulation, and mitochondrial membrane depolarization. We demonstrated that fluoxetine, amiodarone, and clozapine, but not risperidone, at non-toxic concentrations induced lipid accumulations in the perinuclear and cytoplasmic regions of endothelial cells. Spectroscopic markers of DIPL included a robust increase in the ratio (lipid/(protein + lipid)), an increase in choline-containing lipid, fatty acids, and the presence of cholesterol esters, while starvation-induced activated autophagy revealed a spectroscopic signature associated with subtle changes in the lipid profile only. Interestingly, lysosomal volume expansion, occurrence of DIPL, and activation of autophagy induced by selected CADs all depended on drug-accumulation in acidic pH of lysosome cellular compartments whereas reduced endothelial viability did not, and was attributed to mitochondrial mechanisms as evidenced by a decreased mitochondrial transmembrane potential. In conclusion, drug-induced phospholipidosis in the endothelium did not reduce endothelial viability per se and can be efficiently assayed by Raman imaging.

Exploring four South African Croton species for potential anti-inflammatory properties: in vitro activity and toxicity risk assessment

ETHNOPHARMACOLOGICAL RELEVANCE

The African Continent harbours approximately 26 Croton species. Many Croton species are used in traditional medicine in southern Africa to treat a variety of ailments including malaria, tuberculosis, microbial infection and inflammation. Considering the high diversity of the genus Croton, the ethnopharmacological information available on southern African species is rather limited. Furthermore, the potential for novel anti-inflammatory drug scaffolds has not previously been investigated.

AIM OF THE STUDY

The aim of the study was to evaluate the potential of four South African Croton species extracts (Croton gratissimus, Croton pseudopulchellus, Croton sylvaticus, and Croton steenkampianus) for anti-inflammatory activity targeting the TLR4 signalling pathway and to assess the potential risk for hepatotoxicity and genotoxicity using an in vitro cellomics approach.

MATERIAL AND METHODS

Leaf extracts of C. gratissimus, C. pseudopulchellus, C. sylvaticus and C. steenkampianus were prepared using methanol and chloroform (1:1, v/v). The anti-inflammatory activity was determined using LPS induced nitric oxide production in RAW 264.7 macrophages, while the hepatotoxicity and genotoxicity was evaluated using multi-parameter end point analysis in C3A and Vero cells, respectively. Mitochondrial membrane potential, mitochondrial mass, oxidative stress, lysosomal content and lipid accumulation were used as markers to assess the risk for hepatotoxicity.

RESULTS

All four species attenuated nitric oxide production with negligible cytotoxicity. However, C. gratissimus yielded the most favorable profile. Cell density was significantly reduced in both C3A and Vero cells with the C. gratissimus extract providing a suitable toxicity profile amenable to further high content analysis. While there was no meaningful effect on mitochondrial dynamics, a strong dose dependent increase in lipid content, paralleled by an expansion of the lysosomal compartment, identifies a potential risk for steatosis. Risk for genotoxicity was investigated using the micronucleus assay which revealed a dose dependent increase in micronuclei formation. Changes in nuclear morphology and cell ploidy further strengthens the associated risk for genotoxicity and suggests the extract from C. gratissimus may function as an aneugen. Collectively, the data demonstrates that although the selected species possess anti-inflammatory components, the risk for possible hepatotoxic and genotoxic side effects may negate their prospect towards further drug development.

Analytical and Omics-Based Advances in the Study of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a significant clinical issue, affecting 1-1.5 million patients annually, and remains a major challenge during drug development-toxicity and safety concerns are the second-highest reason for drug candidate failure. The future prevalence of DILI can be minimized by developing a greater understanding of the biological mechanisms behind DILI. Both qualitative and quantitative analytical techniques are vital to characterizing and investigating DILI. In vitro assays are capable of characterizing specific aspects of a drug's hepatotoxic nature and multiplexed assays are capable of characterizing and scoring a drug's association with DILI. However, an even deeper insight into the perturbations to biological pathways involved in the mechanisms of DILI can be gained through the use of omics-based analytical techniques: genomics, transcriptomics, proteomics, and metabolomics. These omics analytical techniques can offer qualitative and quantitative insight into genetic susceptibilities to DILI, the impact of drug treatment on gene expression, and the effect on protein and metabolite abundance. This review will discuss the analytical techniques that can be applied to characterize and investigate the biological mechanisms of DILI and potential predictive biomarkers.

Late endosomal/lysosomal accumulation of a neurotransmitter receptor in a cellular model of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a congenital and developmental malformation syndrome associated with defective cholesterol biosynthesis. It is characterized by accumulation of 7-dehydrocholesterol (the immediate biosynthetic precursor of cholesterol in the Kandutsch-Russell pathway) and an altered cholesterol to total sterol ratio. Because SLOS is associated with neurological malfunction, exploring the function and trafficking of neuronal receptors and their interaction with membrane lipids under these conditions assume significance. In this work, we generated a cellular model of SLOS in HEK-293 cells stably expressing the human serotonin_1A receptor (an important neurotransmitter G-protein coupled receptor) using AY 9944, an inhibitor for the enzyme 3β-hydroxy-steroid-∆⁷ -reductase (7-DHCR). Using a quantitative flow cytometry based assay, we show that the plasma membrane population of serotonin_1A receptors was considerably reduced under these conditions without any change in total cellular expression of the receptor. Interestingly, the receptors were trafficked to sterol-enriched LysoTracker positive compartments, which accumulated under these conditions. To the best of our knowledge, our results constitute one of the first reports demonstrating intracellular accumulation and misregulated traffic of a neurotransmitter GPCR in SLOS-like conditions. We believe these results assume relevance in our overall understanding of the molecular basis underlying the functional relevance of neurotransmitter receptors in SLOS.

The role of lysosomal ion channels in lysosome dysfunction

Lysosomes offer a unique arrangement of degradative, exocytic, and signaling capabilities that make their continued function critical to cellular homeostasis. Lysosomes owe their function to the activity of lysosomal ion channels and transporters, which maintain concentration gradients of H⁺, K⁺, Ca²⁺, Na⁺, and Cl^- across the lysosomal membrane. This review examines the contributions of lysosomal ion channels to lysosome function, showing how ion channel function is integral to degradation and autophagy, maintaining lysosomal membrane potential, controlling Ca²⁺ signaling, and facilitating exocytosis. Evidence of lysosome dysfunction in a variety of disease pathologies creates a need to understand how lysosomal ion channels contribute to lysosome dysfunction. For example, the loss of function of the TRPML1 Ca²⁺ lysosome channel in multiple lysosome storage diseases leads to lysosome dysfunction and disease pathogenesis while neurodegenerative diseases are marked by lysosome dysfunction caused by changes in ion channel activity through the TRPML1, TPC, and TMEM175 ion channels. Autoimmune disease is marked by dysregulated autophagy, which is dependent on the function of multiple lysosomal ion channels. Understanding the role of lysosomal ion channel activity in lysosome membrane permeability and NLRP3 inflammasome activation could provide valuable mechanistic insight into NLRP3 inflammasome-mediated diseases. Finally, this review seeks to show that understanding the role of lysosomal ion channels in lysosome dysfunction could give mechanistic insight into the efficacy of certain drug classes, specifically those that target the lysosome, such as cationic amphiphilic drugs.

Propranolol Sensitizes Vascular Sarcoma Cells to Doxorubicin by Altering Lysosomal Drug Sequestration and Drug Efflux

Angiosarcoma is a rare cancer of blood vessel-forming cells with a high patient mortality and few treatment options. Although chemotherapy often produces initial clinical responses, outcomes remain poor, largely due to the development of drug resistance. We previously identified a subset of doxorubicin-resistant cells in human angiosarcoma and canine hemangiosarcoma cell lines that exhibit high lysosomal accumulation of doxorubicin. Hydrophobic, weak base chemotherapeutics, like doxorubicin, are known to sequester within lysosomes, promoting resistance by limiting drug accessibility to cellular targets. Drug synergy between the beta adrenergic receptor (β-AR) antagonist, propranolol, and multiple chemotherapeutics has been documented in vitro, and clinical data have corroborated the increased therapeutic potential of propranolol with chemotherapy in angiosarcoma patients. Because propranolol is also a weak base and accumulates in lysosomes, we sought to determine whether propranolol enhanced doxorubicin cytotoxicity via antagonism of β-ARs or by preventing the lysosomal accumulation of doxorubicin. β-AR-like immunoreactivities were confirmed in primary tumor tissues and cell lines; receptor function was verified by monitoring downstream signaling pathways of β-ARs in response to receptor agonists and antagonists. Mechanistically, propranolol increased cytoplasmic doxorubicin concentrations in sarcoma cells by decreasing the lysosomal accumulation and cellular efflux of this chemotherapeutic agent. Equivalent concentrations of the receptor-active S-(-) and -inactive R-(+) enantiomers of propranolol produced similar effects, supporting a β-AR-independent mechanism. Long-term exposure of hemangiosarcoma cells to propranolol expanded both lysosomal size and number, yet cells remained sensitive to doxorubicin in the presence of propranolol. In contrast, removal of propranolol increased cellular resistance to doxorubicin, underscoring lysosomal doxorubicin sequestration as a key mechanism of resistance. Our results support the repurposing of the R-(+) enantiomer of propranolol with weak base chemotherapeutics to increase cytotoxicity and reduce the development of drug-resistant cell populations without the cardiovascular and other side effects associated with antagonism of β-ARs.

Consideration of the Unbound Drug Concentration in Enzyme Kinetics

The study of enzyme kinetics in drug metabolism involves assessment of rates of metabolism and inhibitory potencies over a suitable concentration range. In all but the very simplest in vitro system, these drug concentrations can be influenced by a variety of nonspecific binding reservoirs that can reduce the available concentration to the enzyme system(s) under investigation. As a consequence, the apparent kinetic parameters, such as K_m or K_i, that are derived can deviate from the true values. There are a number of sources of these nonspecific binding depots or barriers, including membrane permeation and partitioning, plasma or serum protein binding, and incubational binding. In the latter case, this includes binding to the assay apparatus as well as biological depots, depending on the characteristics of the in vitro matrix being used. Given the wide array of subcellular, cellular, and recombinant enzyme systems utilized in drug metabolism, each of these has different components which can influence the free drug concentration. The physicochemical properties of the test compound are also paramount in determining the influential factors in any deviation between true and apparent kinetic behavior. This chapter describes the underlying mechanisms determining the free drug concentration in vitro and how these factors can be accounted for in drug metabolism studies, illustrated with case studies from the literature.

Can endolysosomal deacidification and inhibition of autophagy prevent severe COVID-19?

The possibility is examined that immunomodulatory pharmacotherapy may be clinically useful in managing the pandemic coronavirus disease 2019 (COVID-19), known to result from infection by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a positive-sense single-stranded RNA virus. The dominant route of cell entry of the coronavirus is via phagocytosis, with ensconcement in endosomes thereafter proceeding via the endosomal pathway, involving transfer from early (EEs) to late endosomes (LEs) and ultimately into lysosomes via endolysosomal fusion. EE to LE transportation is a rate-limiting step for coronaviruses. Hence inhibition or dysregulation of endosomal trafficking could potentially inhibit SARS-CoV-2 replication. Furthermore, the acidic luminal pH of the endolysosomal system is critical for the activity of numerous pH-sensitive hydrolytic enzymes. Golgi sub-compartments and Golgi-derived secretory vesicles also depend on being mildly acidic for optimal function and structure. Activation of endosomal toll-like receptors by viral RNA can upregulate inflammatory mediators and contribute to a systemic inflammatory cytokine storm, associated with a worsened clinical outcome in COVID-19. Such endosomal toll-like receptors could be inhibited by the use of pharmacological agents which increase endosomal pH, thereby reducing the activity of acid-dependent endosomal proteases required for their activity and/or assembly, leading to suppression of antigen-presenting cell activity, decreased autoantibody secretion, decreased nuclear factor-kappa B activity and decreased pro-inflammatory cytokine production. It is also noteworthy that SARS-CoV-2 inhibits autophagy, predisposing infected cells to apoptosis. It is therefore also suggested that further pharmacological inhibition of autophagy might encourage the apoptotic clearance of SARS-CoV-2-infected cells.

Direct inhibitory effect on viral entry of influenza A and SARS-CoV-2 viruses by azithromycin

Objectives

Using strategy of drug repurposing, antiviral agents against influenza A virus (IAV) and newly emerging SARS‐coronavirus 2 (SARS‐CoV‐2, also as 2019‐nCoV) could be quickly screened out.

Materials and Methods

A previously reported engineered replication‐competent PR8 strain carrying luciferase reporter gene (IAV‐luc) and multiple pseudotyped IAV and SARS‐CoV‐2 virus was used. To specifically evaluate the pH change of vesicles containing IAV, we constructed an A549 cell line with endosomal and lysosomal expression of pHluorin2.

Results

Here, we identified azithromycin (AZ) as an effective inhibitor against multiple IAV and SARS‐CoV‐2 strains. We found that AZ treatment could potently inhibit IAV infection in vitro. Moreover, using pseudotyped virus model, AZ could also markedly block the entry of SARS‐CoV‐2 in HEK293T‐ACE2 and Caco2 cells. Mechanistic studies further revealed that such effect was independent of interferon signalling. AZ treatment neither impaired the binding and internalization of IAV virions, nor the viral replication, but rather inhibited the fusion between viral and vacuolar membranes. Using a NPC1‐pHluorin2 reporter cell line, we confirmed that AZ treatment could alkalize the vesicles containing IAV virions, thereby preventing pH‐dependent membrane fusion.

Conclusions

Overall, our findings demonstrate that AZ can exert broad‐spectrum antiviral effects against IAV and SARS‐CoV‐2, and could be served as a potential clinical anti‐SARS‐CoV‐2 drug in emergency as well as a promising lead compound for the development of next‐generation anti‐IAV drugs.

The Emerging and Diverse Roles of Bis(monoacylglycero) Phosphate Lipids in Cellular Physiology and Disease

Although understudied relative to many phospholipids, accumulating evidence suggests that bis(monoacylglycero)phosphate (BMP) is an important class of regulatory lipid that plays key roles in lysosomal integrity and function. BMPs are rare in most mammalian tissues, comprising only a few percent of total cellular lipid content, but are elevated in cell types such as macrophages that rely heavily on lysosomal function. BMPs are markedly enriched in endosomal and lysosomal vesicles compared to other organelles and membranous structures, and their unique sn-1:sn-1′ stereoconfiguration may confer stability within the hydrolytic lysosomal environment. BMP-enriched vesicles serve in endosomal-lysosomal trafficking and function as docking structures for the activation of lysosomal hydrolytic enzymes, notably those involved in the catabolic breakdown of sphingolipids. BMP levels are dysregulated in lysosomal storage disorders, phospholipidosis, metabolic diseases, liver and kidney diseases and neurodegenerative disorders. However, whether BMP alteration is a mediator or simply a marker of pathological states is unclear. Likewise, although BMP acyl chain composition may be altered with disease states, the functional significance of specific BMP species remains to be resolved. Newly developed tools for untargeted lipidomic analysis, together with a deeper understanding of enzymes mediating BMP synthesis and degradation, will help shed further light on the functional significance of BMPs in cellular physiology and pathology.

Regulating Interactions Between Targeted Nanocarriers and Mononuclear Phagocyte System via an Esomeprazole-Based Preconditioning Strategy

Purpose

The mononuclear phagocyte system (MPS) presents a formidable obstacle that hampers the delivery of various nanopreparations to tumors. Therefore, there is an urgent need to improve the off-MPS targeting ability of nanomedicines. In the present study, we present a novel preconditioning strategy to substantially increase the circulation times and tumor targeting of nanoparticles by regulating nanocarrier-MPS interactions.

Methods

In vitro, the effect of different vacuolar H⁺-ATPase inhibitors on macrophage uptake of targeted or nontargeted lipid vesicles was evaluated. Specifically, the clinically approved proton-pump inhibitor esomeprazole (ESO) was selected as a preconditioning agent. Then, we further investigated the blocking effect of ESO on the macrophage endocytosis of nanocarriers. In vivo, ESO was first intravenously administered into A549-tumor-bearing nude mice, and 24 h later, the c(RGDm7)-modified vesicles co-loaded with doxorubicin and gefitinib were intravenously injected.

Results

In vitro, ESO was found to reduce the interactions between macrophages and c(RGDm7)-modified vesicles by interfering with the latter’s lysosomal trafficking. Studies conducted in vivo confirmed that ESO pretreatment greatly decreased the liver and spleen distribution of the targeted vesicles, enhanced their tumor accumulation, and improved the therapeutic outcome of the drug-loaded nanomedicines.

Conclusion

Our findings indicate that ESO can regulate the nanoparticle-MPS interaction, which provides a feasible option for enhancing the off-MPS targeting of nanomedicines.

Existing highly accumulating lysosomotropic drugs with potential for repurposing to target COVID-19

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Lysosomotropic drugs show moderate antiviral effects even on coronaviruses.

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The antiviral activity is likely due to interference with endosomal pathway.

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530 existing drugs were analysed for lysosomotropism, pharmacokinetics and toxicity.

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36 drugs were identified that may possibly be suitable for repurposing for COVID-19.

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Further research is needed to confirm their antiviral effects and safety limits.

Given the speed of viral infection spread, repurposing of existing drugs has been given the highest priority in combating the ongoing COVID-19 pandemic. Only drugs that are already registered or close to registration, and therefore have passed lengthy safety assessments, have a chance to be tested in clinical trials and reach patients quickly enough to help in the current disease outbreak.

Here, we have reviewed available evidence and possible ways forward to identify already existing pharmaceuticals displaying modest broad-spectrum antiviral activity which is likely linked to their high accumulation in cells. Several well studied examples indicate that these drugs accumulate in lysosomes, endosomes and biological membranes in general, and thereby interfere with endosomal pathway and intracellular membrane trafficking crucial for viral infection. With the aim to identify other lysosomotropic drugs with possible inherent antiviral activity, we have applied a set of clear physicochemical, pharmacokinetic and molecular criteria on 530 existing drugs. In addition to publicly available data, we have also used our in silico model for the prediction of accumulation in lysosomes and endosomes. By this approach we have identified 36 compounds with possible antiviral effects, also against coronaviruses. For 14 of them evidence of broad-spectrum antiviral activity has already been reported, adding support to the value of this approach.

Presented pros and cons, knowledge gaps and methods to identify lysosomotropic antivirals, can help in the evaluation of many drugs currently in clinical trials considered for repurposing to target COVID-19, as well as open doors to finding more potent and safer alternatives.

Drug Sequestration in Lysosomes as One of the Mechanisms of Chemoresistance of Cancer Cells and the Possibilities of Its Inhibition

Resistance to chemotherapeutics and targeted drugs is one of the main problems in successful cancer therapy. Various mechanisms have been identified to contribute to drug resistance. One of those mechanisms is lysosome-mediated drug resistance. Lysosomes have been shown to trap certain hydrophobic weak base chemotherapeutics, as well as some tyrosine kinase inhibitors, thereby being sequestered away from their intracellular target site. Lysosomal sequestration is in most cases followed by the release of their content from the cell by exocytosis. Lysosomal accumulation of anticancer drugs is caused mainly by ion-trapping, but active transport of certain drugs into lysosomes was also described. Lysosomal low pH, which is necessary for ion-trapping is achieved by the activity of the V-ATPase. This sequestration can be successfully inhibited by lysosomotropic agents and V-ATPase inhibitors in experimental conditions. Clinical trials have been performed only with lysosomotropic drug chloroquine and their results were less successful. The aim of this review is to give an overview of lysosomal sequestration and expression of acidifying enzymes as yet not well known mechanism of cancer cell chemoresistance and about possibilities how to overcome this form of resistance.

Intracellular ABCB1 as a Possible Mechanism to Explain the Synergistic Effect of Hydroxychloroquine-Azithromycin Combination in COVID-19 Therapy

The co-administration of hydroxychloroquine with azithromycin is proposed in COVID-19 therapy. We hypothesize a new mechanism supporting the synergistic interaction between these drugs. Azithromycin is a substrate of ABCB1 (P-glycoprotein) which is localized in endosomes and lysosomes with a polarized substrate transport from the cell cytosol into the vesicle interior. SARS-CoV-2 and drugs meet in these acidic organelles and both basic drugs, which are potent lysosomotropic compounds, will become protonated and trapped within these vesicles. Consequently, their intra-vesicular concentrations can attain low micromolar effective cytotoxic concentrations on SARS-CoV-2 while concomitantly increase the intra-vesicular pH up to around neutrality. This last effect inhibits lysosomal enzyme activities responsible in virus entry and replication cycle. Based on these considerations, we hypothesize that ABCB1 could be a possible enhancer by confining azithromycin more extensively than expected when the trapping is solely dependent on the passive diffusion. This additional mechanism may therefore explain the synergistic effect when azithromycin is added to hydroxychloroquine, leading to apparently more rapid virus clearance and better clinical benefit, when compared to monotherapy with hydroxychloroquine alone.

Investigating the role of endogenous opioid system in chloroquine-induced phospholipidosis in rat liver by morphological, biochemical and molecular modelling studies

Drug-induced phospholipidosis (DIPL) is characterized by phospholipid storage in the lysosomes of affected tissues. Many severe effects and toxicities have been linked to DIPL. The aim of this study was to determine whether the endogenous opioid system is involved in chloroquine-induced phospholipidosis. The effect of naltrexone as an antagonist of opioid receptors in chloroquine-induced phospholipidosis in rat liver was investigated by morphological, biochemical, and molecular modelling studies. Transmission electron microscopy (TEM) showed that morphological characteristic changes of rat liver, including the number of lamellar bodies, grade of vacuolization and cell steatosis, were markedly attenuated in rats treated with naltrexone alone or in combination with chloroquine, in comparison with chloroquine-treated rats. The results of liquid chromatography mass spectrometry (LC/MS) showed that the concentrations of phenylacetylglycine (PAG) and hippuric acid (HA) were significantly decreased and increased, respectively, in target groups. Besides, the concentration ratio of PAG/HA was significantly decreased. Spectrophotometry resulted in a notable decrease in alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities in target groups. The results from the molecular docking and molecular dynamic simulation studies demonstrated clear chloroquine interaction with the active site cavity of the µ opioid receptor. These data suggest that administration of naltrexone alone, or in combination with chloroquine, notably attenuates the side effects of chloroquine-induced phospholipidosis, as well as demonstrating an increased probability of the endogenous opioid system involvement in chloroquine-induced phospholipidosis in rat liver.

Identification of a clinical compound losmapimod that blocks Lassa virus entry

Lassa virus (LASV) causes Lassa hemorrhagic fever in humans and poses a significant threat to public health in West Africa. Current therapeutic treatments for Lassa fever are limited, making the development of novel countermeasures an urgent priority. In this study, we identified losmapimod, a p38 mitogen-activated protein kinase (MAPK) inhibitor, from 102 screened compounds as an inhibitor of LASV infection. Losmapimod exerted its inhibitory effect against LASV after p38 MAPK down-regulation, and, interestingly, had no effect on other arenaviruses capable of causing viral hemorrhagic fever. Mechanistic studies showed that losmapimod inhibited LASV entry by affecting the stable signal peptide (SSP)-GP2 subunit interface of the LASV glycoprotein, thereby blocking pH-dependent viral fusion. As an aryl heteroaryl bis-carboxyamide derivative, losmapimod represents a novel chemical scaffold with anti-LASV activity, and it provides a new lead structure for the future development of LASV fusion inhibitors.

SORLA regulates endosomal trafficking and oncogenic fitness of HER2

The human epidermal growth factor receptor 2 (HER2) is an oncogene targeted by several kinase inhibitors and therapeutic antibodies. While the endosomal trafficking of many other receptor tyrosine kinases is known to regulate their oncogenic signalling, the prevailing view on HER2 is that this receptor is predominantly retained on the cell surface. Here, we find that sortilin-related receptor 1 (SORLA; SORL1) co-precipitates with HER2 in cancer cells and regulates HER2 subcellular distribution by promoting recycling of the endosomal receptor back to the plasma membrane. SORLA protein levels in cancer cell lines and bladder cancers correlates with HER2 levels. Depletion of SORLA triggers HER2 targeting to late endosomal/lysosomal compartments and impairs HER2-driven signalling and in vivo tumour growth. SORLA silencing also disrupts normal lysosome function and sensitizes anti-HER2 therapy sensitive and resistant cancer cells to lysosome-targeting cationic amphiphilic drugs. These findings reveal potentially important SORLA-dependent endosomal trafficking-linked vulnerabilities in HER2-driven cancers.

The EGF receptor HER2 is an oncogene protein thought to reside at the plasma membrane, but its endosomal trafficking is currently unclear. Here, the authors report that HER2 is endocytosed and that sortillin-related receptor 1 (SORLA) promotes endosomal HER2 recycling and HER2 oncogenic signalling.

Examining P-gp efflux kinetics guided by the BDDCS - Rational selection of in vitro assay designs and mathematical models

The generation of reliable kinetic parameters to describe P-glycoprotein (P-gp) activity is essential for predicting the impact of efflux transport on gastrointestinal drug absorption. The compound-specific selection of in vitro assay designs and ensuing data analysis methods is explored in this manuscript. We measured transcellular permeability and cellular uptake of five P-gp substrates in Caco-2 and LLC-PK1 MDR1 cells. Kinetic parameters of P-gp-mediated efflux transport (K_m, V_max) were derived from conventional and mechanistic compartmental models. The estimated apparent K_m values based on medium concentrations in the conventional permeability model indicated significant differences between the cell lines. The respective intrinsic K_m values based on unbound intracellular concentrations in the mechanistic compartmental models were significantly lower and comparable between cell lines and assay formats. Non-specific binding or lysosomal trapping were shown to cause discrepancies in the kinetic parameters obtained from different assay formats. A guidance for the selection of in vitro assays and kinetic assessment methods is proposed in line with the Biopharmaceutics Drug Disposition Classification System (BDDCS). The recommendations are expected to aid the acquisition of robust and reproducible kinetic parameters of P-gp-mediated efflux transport.

Antimicrobial treatment with the fixed-dose antibiotic combination RHB-104 for Mycobacterium avium subspecies paratuberculosis in Crohn's disease: pharmacological and clinical implications

INTRODUCTION

Crohn's disease (CD) is an inflammatory bowel disease of unknown etiology. However, increasing evidence suggests Mycobacterium avium subspecies paratuberculosis (MAP) as a putative causative agent: 1) MAP is the etiological agent of Johne's disease, a granulomatous enteritis affecting ruminants, which shares clinical and pathological features with CD; 2) MAP has been detected in tissues and blood samples from CD patients; 3) case reports have documented a favorable therapeutic response to anti-MAP antibiotics. Area covered: This review provides an appraisal of current information on MAP characteristics, diagnostic methodologies and emerging drug treatments. The authors focus on RHB-104, a novel oral formulation containing a fixed-dose combination of clarithromycin, clofazimine and rifabutin, endowed with synergistic inhibitory activity on MAP strains isolated from CD patients. Expert opinion: Based on encouraging in vitro data, RHB-104 has entered recently the clinical phase of its development, and is being investigated in a randomized, placebo-controlled phase III trial aimed at evaluating its efficacy and safety in CD. Provided that the overall clinical development will support the suitability of RHB-104 for inducing disease remission in CD patients with documented MAP infection, this novel antibiotic combination will likely take a relevant position in the therapeutic armamentarium for CD management.

An Expandable Mechanopharmaceutical Device (1): Measuring the Cargo Capacity of Macrophages in a Living Organism

PURPOSE

Clofazimine (CFZ) is an FDA-approved, poorly soluble small molecule drug that precipitates as crystal-like drug inclusions (CLDIs) which accumulate in acidic cytoplasmic organelles of macrophages. In this study, we considered CLDIs as an expandable mechanopharmaceutical device, to study how macrophages respond to an increasingly massive load of endophagolysosomal cargo.

METHODS

First, we experimentally tested how the accumulation of CFZ in CLDIs impacted different immune cell subpopulations of different organs. Second, to further investigate the mechanism of CLDI formation, we asked whether specific accumulation of CFZ hydrochloride crystals in lysosomes could be explained as a passive, thermodynamic equilibrium phenomenon. A cellular pharmacokinetic model was constructed, simulating CFZ accumulation driven by pH-dependent ion trapping of the protonated drug in the acidic lysosomes, followed by the precipitation of CFZ hydrochloride salt via a common ion effect caused by high chloride concentrations.

RESULTS

While lower loads of CFZ were mostly accommodated in lung macrophages, increased CFZ loading was accompanied by organ-specific changes in macrophage numbers, size and intracellular membrane architecture, maximizing the cargo storage capabilities. With increasing loads, the total cargo mass and concentrations of CFZ in different organs diverged, while that of individual macrophages converged. The simulation results support the notion that the proton and chloride ion concentrations of macrophage lysosomes are sufficient to drive the massive, cell type-selective accumulation and growth of CFZ hydrochloride biocrystals.

CONCLUSION

CLDIs effectively function as an expandable mechanopharmaceutical device, revealing the coordinated response of the macrophage population to an increasingly massive, whole-organism endophagolysosomal cargo load.

Quantification of Intracellular Accumulation and Retention of Lysosomotropic Macrocyclic Compounds by High-Throughput Imaging of Lysosomal Changes

Many marketed pharmaceuticals reach extremely high tissue concentrations due to accumulation in lysosomes (lysosomotropism). Quantitative prediction of intracellular concentrations of accumulating drugs is challenging, especially for macrocyclic compounds that mainly do not fit in current in silico models. We tested a unique library of 47 compounds (containing 39 macrocycles) specifically designed to cover the entire range of accumulation intensities observed with pharmaceuticals so far. For the first time, we show that intracellular concentration of compounds measured by liquid chromatography with tandem mass spectrometry correlates with the induction of phospholipidosis and inhibition of autophagy, but the highest correlation was observed with the increase of lysosomal volume (R = 0.95), all measured by high-throughput imaging assays. Based only on imaging data, we developed a 5-class in vitro model for the prediction of compound accumulation with the accuracy of 81%. The measured change of total lysosomal volume can thus be used in high-throughput screening for determination of the actual intensity of intracellular accumulation of new macrocyclic compounds. The models are largely based on macrocycles, greatly improving the screening and prediction of intracellular accumulation of this challenging class. However, all tested nonmacrocyclic compounds fitted well in the models, indicating potential use of the models in broader chemical space.

Quantitation of Lysosomal Trapping of Basic Lipophilic Compounds Using In Vitro Assays and In Silico Predictions Based on the Determination of the Full pH Profile of the Endo-/Lysosomal System in Rat Hepatocytes

Lysosomal sequestration may affect the pharmacokinetics, efficacy, and safety of new basic lipophilic drug candidates potentially impacting their intracellular concentrations and tissue distribution. It may also be involved in drug-drug interactions, drug resistance, and phospholipidosis. However, currently there are no assays to evaluate the lysosomotropic behavior of compounds in a setting fully meeting the needs of drug discovery. We have, therefore, integrated a set of methods to reliably rank order, quantify, and calculate the extent of lysosomal sequestration in rat hepatocytes. An indirect fluorescence-based assay monitors the displacement of the fluorescence probe LysoTracker Red by test compounds. Using a lysosomal-specific evaluation algorithm allows one to generate IC₅₀ values at lower than previously reported concentrations. The concentration range directly agrees with the concentration dependency of the lysosomal drug content itself directly quantified by liquid chromatography-tandem mass spectrometry and thus permits a quantitative link between the indirect and the direct trapping assay. Furthermore, we have determined the full pH profile and corresponding volume fractions of the endo-/lysosomal system in plated rat hepatocytes, enabling a more accurate in silico prediction of the extent of lysosomal trapping based only on pK _a values as input, allowing early predictions even prior to chemical synthesis. The concentration dependency-i.e., the saturability of the trapping-can then be determined by the IC₅₀ values generated in vitro. Thereby, a more quantitative assessment of the susceptibility of basic lipophilic compounds for lysosomal trapping is possible.

Second generation of diazachrysenes: Protection of Ebola virus infected mice and mechanism of action

Ebola virus (EBOV) causes a deadly hemorrhagic fever in humans and non-human primates. There is currently no FDA-approved vaccine or medication to counter this disease. Here, we report on the design, synthesis and anti-viral activities of two classes of compounds which show high potency against EBOV in both in vitro cell culture assays and in vivo mouse models Ebola viral disease. These compounds incorporate the structural features of cationic amphiphilic drugs (CAD), i.e they possess both a hydrophobic domain and a hydrophilic domain consisting of an ionizable amine functional group. These structural features enable easily diffusion into cells but once inside an acidic compartment their amine groups became protonated, ionized and remain trapped inside the acidic compartments such as late endosomes and lysosomes. These compounds, by virtue of their lysomotrophic functions, blocked EBOV entry. However, unlike other drugs containing a CAD moiety including chloroquine and amodiaquine, compounds reported in this study display faster kinetics of accumulation in the lysosomes, robust expansion of late endosome/lysosomes, relatively more potent suppression of lysosome fusion with other vesicular compartments and inhibition of cathepsins activities, all of which play a vital role in anti-EBOV activity. Furthermore, the diazachrysene 2 (ZSML08) that showed most potent activity against EBOV in in vitro cell culture assays also showed significant survival benefit with 100% protection in mouse models of Ebola virus disease, at a low dose of 10 mg/kg/day. Lastly, toxicity studies in vivo using zebrafish models suggest no developmental defects or toxicity associated with these compounds. Overall, these studies describe two new pharmacophores that by virtue of being potent lysosomotrophs, display potent anti-EBOV activities both in vitro and in vivo animal models of EBOV disease.

Subcellular drug distribution: mechanisms and roles in drug efficacy, toxicity, resistance, and targeted delivery

After administration, drug molecules usually enter target cells to access their intracellular targets. In eukaryotic cells, these targets are often located in organelles, including the nucleus, endoplasmic reticulum, mitochondria, lysosomes, Golgi apparatus, and peroxisomes. Each organelle type possesses unique biological features. For example, mitochondria possess a negative transmembrane potential, while lysosomes have an intraluminal delta pH. Other properties are common to several organelle types, such as the presence of ATP-binding cassette (ABC) or solute carrier-type (SLC) transporters that sequester or pump out xenobiotic drugs. Studies on subcellular drug distribution are critical to understand the efficacy and toxicity of drugs along with the body's resistance to them and to potentially offer hints for targeted subcellular drug delivery. This review summarizes the results of studies from 1990 to 2017 that examined the subcellular distribution of small molecular drugs. We hope this review will aid in the understanding of drug distribution within cells.

Detection of nanocarrier potentiation on drug induced phospholipidosis in cultured cells and primary hepatocyte spheroids by high content imaging and analysis

Considerable effort has been made to develop nanocarriers for controlled drug delivery over the last decade, while it remains unclear how the strength of adverse drug effect will be altered when a drug is loaded on the nanocarrier. Drug-induced phospholipidosis (DIP) is characterized with excessive accumulation of phospholipids in cells and is common for cationic amphiphilic drugs (CAD). Previously, we have reported that PEGylated graphene oxide (PEG-GO) loaded with several CAD can potentiate DIP. In current study, we extended our study on newly identified phospholipidosis (PLD) inducers that had been identified from the Library of Pharmacologically Active Compounds (LOPAC), to investigate if PEO-GO loaded with these CAD can alter DIP. Twenty-two CAD were respectively loaded on PEG-GO and incubated with RAW264.7, a macrophage cell line. The results showed that when a CAD was loaded on PEG-GO, its strength of PLD induction can be enhanced, unchanged or attenuated. PEG-GO loaded with Ifenprodil exhibited the highest PEG-GO potentiation effect compared to Ifenprodil treatment alone in RAW264.7 cells, and this effect was confirmed in human hepatocellular carcinoma HepG2, another cell line model for PLD induction. Primary hepatocyte culture and spheroids mimicking in vivo conditions were used to further validate nanocarrier potentiation on DIP by Ifenprodil. Stronger phospholipid accumulation was found in PEG-GO/Ifenprodil treated hepatocytes or spheroids than Ifenprodil treatment alone. Therefore, evidences were provided by us that nanocarriers may increase the adverse drug effects and guidance by regulatory agencies need to be drafted for the safe use of nanotechnology in drug delivery.

Lysosomotropic cationic amphiphilic drugs inhibit adipocyte differentiation in 3T3-L1K cells via accumulation in cells and phospholipid membranes, and inhibition of autophagy

Some cationic amphiphilic drugs (CADs) have been individually reported to interfere with the differentiation of immune system cells, such as macrophages and dendritic cells. To investigate the possible generic nature of this process, in this study we aimed to see whether these drugs are capable of interfering with the differentiation of adipocytes. Further, we investigated whether this feature might be connected to the lysosomotropic character of these drugs, and their disturbance of intracellular membrane trafficking rather than to the individual pharmacologic properties of each drug. Thus, for the selected set of compounds consisting of seven structurally and pharmacologically diverse CADs and three non-CAD controls we have measured the impact on differentiation of 3T3-L1K murine preadipocytes to adipocytes. We conclude that CADs indeed inhibit adipocyte differentiation, as shown morphologically, at the level of lipid droplet formation and on the expression of genetic markers of adipocytes. Furthermore, the intensity of this inhibitory effect was found to strongly positively correlate with the extent of drug accumulation in adipocytes, with their affinity for phospholipid membranes, as well as with their ability to induce phospholipidosis and inhibit autophagy.

Characterization of Influenza Virus Pseudotyped with Ebolavirus Glycoprotein

We have produced a new Ebola virus pseudotype, E-S-FLU, that can be handled in biosafety level 1/2 containment for laboratory analysis. The E-S-FLU virus is a single-cycle influenza virus coated with Ebolavirus glycoprotein, and it encodes enhanced green fluorescence protein as a reporter that replaces the influenza virus hemagglutinin. MDCK-SIAT1 cells were transduced to express Ebolavirus glycoprotein as a stable transmembrane protein for E-S-FLU virus production. Infection of cells with the E-S-FLU virus was dependent on the Niemann-Pick C1 protein, which is the well-characterized receptor for Ebola virus entry at the late endosome/lysosome membrane. The E-S-FLU virus was neutralized specifically by an anti-Ebolavirus glycoprotein antibody and a variety of small drug molecules that are known to inhibit the entry of wild-type Ebola virus. To demonstrate the application of this new Ebola virus pseudotype, we show that a single laboratory batch was sufficient to screen a library (LOPAC¹²⁸⁰; Sigma) of 1,280 pharmacologically active compounds for inhibition of virus entry. A total of 215 compounds inhibited E-S-FLU virus infection, while only 22 inhibited the control H5-S-FLU virus coated in H5 hemagglutinin. These inhibitory compounds have very dispersed targets and mechanisms of action, e.g., calcium channel blockers, estrogen receptor antagonists, antihistamines, serotonin uptake inhibitors, etc., and this correlates with inhibitor screening results obtained with other pseudotypes or wild-type Ebola virus in the literature. The E-S-FLU virus is a new tool for Ebola virus cell entry studies and is easily applied to high-throughput screening assays for small-molecule inhibitors or antibodies.

IMPORTANCE Ebola virus is in the Filoviridae family and is a biosafety level 4 pathogen. There are no FDA-approved therapeutics for Ebola virus. These characteristics warrant the development of surrogates for Ebola virus that can be handled in more convenient laboratory containment to study the biology of the virus and screen for inhibitors. Here we characterized a new surrogate, named E-S-FLU virus, that is based on a disabled influenza virus core coated with the Ebola virus surface protein but does not contain any genetic information from the Ebola virus itself. We show that E-S-FLU virus uses the same cell entry pathway as wild-type Ebola virus. As an example of the ease of use of E-S-FLU virus in biosafety level 1/2 containment, we showed that a single production batch could provide enough surrogate virus to screen a standard small-molecule library of 1,280 candidates for inhibitors of viral entry.

Repurposing cationic amphiphilic drugs as adjuvants to induce lysosomal siRNA escape in nanogel transfected cells

Cytosolic delivery remains a major bottleneck for siRNA therapeutics. To facilitate delivery, siRNAs are often enclosed in nanoparticles (NPs). However, upon endocytosis such NPs are mainly trafficked towards lysosomes. To avoid degradation, cytosolic release of siRNA should occur prior to fusion of endosomes with lysosomes, but current endosomal escape strategies remain inefficient. In contrast to this paradigm, we aim to exploit lysosomal accumulation by treating NP-transfected cells with low molecular weight drugs that release the siRNA from the lysosomes into the cytosol. We show that FDA-approved cationic amphiphilic drugs (CADs) significantly improved gene silencing by siRNA-loaded nanogels in cancer cells through simple sequential incubation. CADs induced lysosomal phospholipidosis, leading to transient lysosomal membrane permeabilization and improved siRNA release without cytotoxicity. Of note, the lysosomes could be applied as an intracellular depot for triggered siRNA release by multiple CAD treatments.

Metformin-Induced Mitochondrial Complex I Inhibition: Facts, Uncertainties, and Consequences

Metformin is the most widely prescribed drug to treat patients with type II diabetes, for whom retrospective studies suggest that metformin may have anticancer properties. However, in experiments performed with isolated cells, authors have reported both pro- and anti-apoptotic effects of metformin. The exact molecular mechanism of action of metformin remains partly unknown despite its use for over 60 years and more than 17,000 articles in PubMed. Among the various widely recognized or recently proposed targets, it has been reported consistently that metformin is capable of inhibiting mitochondrial respiratory chain Complex I. Since most of the effects of metformin have been replicated by other inhibitors of Complex I, it has been suggested that the mechanism of action of metformin involved the inhibition of Complex I. However, compared to conventional Complex I inhibitors, the metformin-induced inhibition of Complex I has unique characteristics. Among these, the most original one is that the concentrations of metformin required to inhibit Complex I are lower in intact cells than in isolated mitochondria. Experiments with isolated mitochondria or Complex I were generally performed using millimolar concentrations of metformin, while plasma levels remain in the micromolar range in both human and animal studies, highlighting that metformin concentration is an important issue. In order to explain the effects in animals based on observations in cells and mitochondria, some authors proposed a direct effect of the drug on Complex I involving an accumulation of metformin inside the mitochondria while others proposed an indirect effect (the drug no longer having to diffuse into the mitochondria). This brief review attempts to: gather arguments for and against each hypothesis concerning the mechanism by which metformin inhibits Complex I and to highlight remaining questions about the toxicity mechanism of metformin for certain cancer cells.

Cellular accumulation and lipid binding of perfluorinated alkylated substances (PFASs) - A comparison with lysosomotropic drugs

Many chemicals accumulate in organisms through a variety of different mechanisms. Cationic amphiphilic drugs (CADs) accumulate in lysosomes and bind to membranes causing phospholipidosis, whereas many lipophilic chemicals target adipose tissue. Perfluoroalkyl substances (PFASs) are widely used as surfactants, but many of them are highly bioaccumulating and persistent in the environment, making them notorious environmental toxicants. Understanding the mechanisms of their bioaccumulation is, therefore, important for their regulation and substitution with new, less harmful chemicals. We compared the highly bioaccumulative perfluorooctanesulfonic acid PFOS to its three less bioaccumulative alternatives perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and perfluorobutane sulfonic acid (PFBS), in their ability to accumulate and remain in lung epithelial cells (NCI-H292) and adipocytes (3T3-L1K) in vitro. As a reference point we tested a set of cationic amphiphilic drugs (CADs), known to highly accumulate in cells and strongly bind to phospholipids, together with their respective non-CAD controls. Finally, all compounds were examined for their ability to bind to neutral lipids and phospholipids in cell-free systems. Cellular accumulation and retention of the test compounds were highly correlated between the lung epithelial cells and adipocytes. Interestingly, although an anion itself, intensities of PFOS accumulation and retention in cells were comparable to those of CAD compounds, but PFOS failed to induce phospholipidosis or alter lysosomal volume. Compared to other lipophilicity measures, phospholipophilicity shows the highest correlation (Rˆ2 = 0.75) to cellular accumulation data in both cell types and best distinguishes between high and low accumulating compounds. This indicates that binding to phospholipids may be the most important component in driving high cellular accumulation in lung epithelial cells, as well as in adipocytes, and for both CADs and bioaccumulating PFASs. Obtained continuous PLS models based on compound's affinity for phospholipids and neutral lipids can be used as good prediction models of cellular accumulation and retention of PFASs and CADs.

Imipramine blocks acute silicosis in a mouse model

BACKGROUND

Inhalation of crystalline silica is associated with pulmonary inflammation and silicosis. Although silicosis remains a prevalent health problem throughout the world, effective treatment choices are limited. Imipramine (IMP) is a FDA approved tricyclic antidepressant drug with lysosomotropic characteristics. The aim of this study was to evaluate the potential for IMP to reduce silicosis and block phagolysosome membrane permeabilization.

METHODS

C57BL/6 alveolar macrophages (AM) exposed to crystalline silica ± IMP in vitro were assessed for IL-1β release, cytotoxicity, particle uptake, lysosomal stability, and acid sphingomyelinase activity. Short term (24 h) in vivo studies in mice instilled with silica (± IMP) evaluated inflammation and cytokine release, in addition to cytokine release from ex vivo cultured AM. Long term (six to ten weeks) in vivo studies in mice instilled with silica (± IMP) evaluated histopathology, lung damage, and hydroxyproline content as an indicator of collagen accumulation.

RESULTS

IMP significantly attenuated silica-induced cytotoxicity and release of mature IL-1β from AM in vitro. IMP treatment in vivo reduced silica-induced inflammation in a short-term model. Furthermore, IMP was effective in blocking silica-induced lung damage and collagen deposition in a long-term model. The mechanism by which IMP reduces inflammation was explored by assessing cellular processes such as particle uptake and acid sphingomyelinase activity.

CONCLUSIONS

Taken together, IMP was anti-inflammatory against silica exposure in vitro and in vivo. The results were consistent with IMP blocking silica-induced phagolysosomal lysis, thereby preventing cell death and IL-1β release. Thus, IMP could be therapeutic for silica-induced inflammation and subsequent disease progression as well as other diseases involving phagolysosomal lysis.