Prediction of metabolism-induced hepatotoxicity on three-dimensional hepatic cell culture and enzyme microarrays.

Human liver contains various oxidative and conjugative enzymes that can convert nontoxic parent compounds to toxic metabolites or, conversely, toxic parent compounds to nontoxic metabolites. Unlike primary hepatocytes, which contain myriad drug-metabolizing enzymes (DMEs), but are difficult to culture and maintain physiological levels of DMEs, immortalized hepatic cell lines used in predictive toxicity assays are easy to culture, but lack the ability to metabolize compounds. To address this limitation and predict metabolism-induced hepatotoxicity in high-throughput, we developed an advanced miniaturized three-dimensional (3D) cell culture array (DataChip 2.0) and an advanced metabolizing enzyme microarray (MetaChip 2.0). The DataChip is a functionalized micropillar chip that supports the Hep3B human hepatoma cell line in a 3D microarray format. The MetaChip is a microwell chip containing immobilized DMEs found in the human liver. As a proof of concept for generating compound metabolites in situ on the chip and rapidly assessing their toxicity, 22 model compounds were dispensed into the MetaChip and sandwiched with the DataChip. The IC50 values obtained from the chip platform were correlated with rat LD50 values, human C max values, and drug-induced liver injury categories to predict adverse drug reactions in vivo. As a result, the platform had 100% sensitivity, 86% specificity, and 93% overall predictivity at optimum cutoffs of IC50 and C max values. Therefore, the DataChip/MetaChip platform could be used as a high-throughput, early stage, microscale alternative to conventional in vitro multi-well plate platforms and provide a rapid and inexpensive assessment of metabolism-induced toxicity at early phases of drug development.

Dacomitinib versus gefitinib as first-line treatment for patients with EGFR-mutation-positive non-small-cell lung cancer (ARCHER 1050): a randomised, open-label, phase 3 trial.

BACKGROUND: Dacomitinib is a second-generation, irreversible EGFR tyrosine kinase inhibitor. We compared its efficacy and safety with that of the reversible EGFR tyrosine kinase inhibitor gefitinib in the first-line treatment of patients with advanced EGFR-mutation-positive non-small-cell lung cancer (NSCLC). METHODS: In this international, multicentre, randomised, open-label, phase 3 study (ARCHER 1050), we enrolled adults (aged ≥18 years or ≥20 years in Japan and South Korea) with newly diagnosed advanced NSCLC and one EGFR mutation (exon 19 deletion or Leu858Arg) at 71 academic medical centres and university hospitals in seven countries or special administrative regions. We randomly assigned participants (1:1) to receive oral dacomitinib 45 mg/day (in 28-day cycles) or oral gefitinib 250 mg/day (in 28-day cycles) until disease progression or another discontinuation criterion was met. Randomisation, stratified by race and EGFR mutation type, was done with a computer-generated random code assigned by a central interactive web response system. The primary endpoint was progression-free survival assessed by masked independent review in the intention-to-treat population. Safety was assessed in all patients who received at least one dose of study treatment. This study is registered with ClinicalTrials.gov, number NCT01774721, and is ongoing but no longer recruiting patients. FINDINGS: Between May 9, 2013, and March 20, 2015, 452 eligible patients were randomly assigned to receive dacomitinib (n=227) or gefitinib (n=225). Median duration of follow-up for progression-free survival was 22·1 months (95% CI 20·3-23·9). Median progression-free survival according to masked independent review was 14·7 months (95% CI 11·1-16·6) in the dacomitinib group and 9·2 months (9·1-11·0) in the gefitinib group (hazard ratio 0·59, 95% CI 0·47-0·74; p<0·0001). The most common grade 3-4 adverse events were dermatitis acneiform (31 [14%] of 227 patients given dacomitinib vs none of 224 patients given gefitinib), diarrhoea (19 [8%] vs two [1%]), and raised alanine aminotransferase levels (two [1%] vs 19 [8%]). Treatment-related serious adverse events were reported in 21 (9%) patients given dacomitinib and in ten (4%) patients given gefitinib. Two treatment-related deaths occurred in the dacomitinib group (one related to untreated diarrhoea and one to untreated cholelithases/liver disease) and one in the gefitinib group (related to sigmoid colon diverticulitis/rupture complicated by pneumonia). INTERPRETATION: Dacomitinib significantly improved progression-free survival over gefitinib in first-line treatment of patients with EGFR-mutation-positive NSCLC and should be considered as a new treatment option for this population. FUNDING: SFJ Pharmaceuticals Group and Pfizer.

Efficacy and safety of palbociclib in combination with letrozole as first-line treatment of ER-positive, HER2-negative, advanced breast cancer: expanded analyses of subgroups from the randomized pivotal trial PALOMA-1/TRIO-18.

BACKGROUND: Palbociclib is an oral small-molecule inhibitor of cyclin-dependent kinases 4 and 6. In the randomized, open-label, phase II PALOMA-1/TRIO-18 trial, palbociclib in combination with letrozole improved progression-free survival (PFS) compared with letrozole alone as first-line treatment of estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, advanced breast cancer (20.2 months versus 10.2 months; hazard ratio (HR) = 0.488, 95 % confidence interval (CI) 0.319-0.748; one-sided p = 0.0004). Grade 3-4 neutropenia was the most common adverse event (AE) in the palbociclib + letrozole arm. We now present efficacy and safety analyses based on several specific patient and tumor characteristics, and present in detail the clinical patterns of neutropenia observed in the palbociclib + letrozole arm of the overall safety population. METHODS: Postmenopausal women (n = 165) with ER+, HER2-negative, advanced breast cancer who had not received any systemic treatment for their advanced disease were randomized 1:1 to receive either palbociclib in combination with letrozole or letrozole alone. Treatment continued until disease progression, unacceptable toxicity, consent withdrawal, or death. The primary endpoint was PFS. We now analyze the difference in PFS for the treatment populations by subgroups, including age, histological type, history of prior neoadjuvant/adjuvant systemic treatment, and sites of distant metastasis, using the Kaplan-Meier method. HR and 95 % CI are derived from a Cox proportional hazards regression model. RESULTS: A clinically meaningful improvement in median PFS and clinical benefit response (CBR) rate was seen with palbociclib + letrozole in every subgroup evaluated. Grade 3-4 neutropenia was the most common AE with palbociclib + letrozole in all subgroups. Analysis of the frequency of neutropenia by grade during the first six cycles of treatment showed that there was a downward trend in Grade 3-4 neutropenia over time. Among those who experienced Grade 3-4 neutropenia, 71.7 % had no overlapping infections of any grade and none had overlapping Grade 3-4 infections. CONCLUSION: The magnitude of clinical benefit seen with the addition of palbociclib to letrozole in improving both median PFS and CBR rate is consistent in nearly all subgroups analyzed, and consistent with that seen in the overall study population. The safety profile of the combination treatment in all subgroups was also comparable to that in the overall safety population of the study.

Development of a cell viability assay to assess drug metabolite structure-toxicity relationships.

Many adverse drug reactions are caused by the cytochrome P450 (CYP)-dependent activation of drugs into reactive metabolites. In order to reduce attrition due to metabolism-induced toxicity and to improve the safety of drug candidates, we developed a simple cell viability assay by combining a bioactivation system (human CYP3A4, CYP2D6 and CYP2C9) with Hep3B cells. We screened a series of drugs to explore structural motifs that may be responsible for CYP450-dependent activation caused by reactive metabolite formation, which highlighted specific liabilities regarding certain phenols and anilines.

Toxicity assessments of nonsteroidal anti-inflammatory drugs in isolated mitochondria, rat hepatocytes, and zebrafish show good concordance across chemical classes.

To reduce costly late-stage compound attrition, there has been an increased focus on assessing compounds in in vitro assays that predict attributes of human safety liabilities, before preclinical in vivo studies are done. Relevant questions when choosing a panel of assays for predicting toxicity are (a) whether there is general concordance in the data among the assays, and (b) whether, in a retrospective analysis, the rank order of toxicity of compounds in the assays correlates with the known safety profile of the drugs in humans. The aim of our study was to answer these questions using nonsteroidal anti-inflammatory drugs (NSAIDs) as a test set since NSAIDs are generally associated with gastrointestinal injury, hepatotoxicity, and/or cardiovascular risk, with mitochondrial impairment and endoplasmic reticulum stress being possible contributing factors. Eleven NSAIDs, flufenamic acid, tolfenamic acid, mefenamic acid, diclofenac, meloxicam, sudoxicam, piroxicam, diflunisal, acetylsalicylic acid, nimesulide, and sulindac (and its two metabolites, sulindac sulfide and sulindac sulfone), were tested for their effects on (a) the respiration of rat liver mitochondria, (b) a panel of mechanistic endpoints in rat hepatocytes, and (c) the viability and organ morphology of zebrafish. We show good concordance for distinguishing among/between NSAID chemical classes in the observations among the three approaches. Furthermore, the assays were complementary and able to correctly identify "toxic" and "non-toxic" drugs in accordance with their human safety profile, with emphasis on hepatic and gastrointestinal safety. We recommend implementing our multi-assay approach in the drug discovery process to reduce compound attrition.

Assessment of drug-induced mitochondrial dysfunction via altered cellular respiration and acidification measured in a 96-well platform.

High-throughput applicable screens for identifying drug-induced mitochondrial impairment are necessary in the pharmaceutical industry. Hence, we evaluated the XF96 Extracellular Flux Analyzer, a 96-well platform that measures changes in the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) of cells. The sensitivity of the platform was bench-marked with known modulators of oxidative phosphorylation and glycolysis. Sixteen therapeutic agents were screened in HepG2 cells for mitochondrial effects. Four of these compounds, thiazolidinediones, were also tested in primary feline cardiomyocytes for cell-type specific effects. We show that the XF96 platform is a robust, sensitive system for analyzing drug-induced mitochondrial impairment in whole cells. We identified changes in cellular respiration and acidification upon addition of therapeutic agents reported to have a mitochondrial effect. Furthermore, we show that respiration and acidification changes upon addition of the thiazoldinediones were cell-type specific, with the rank order of mitochondrial impairment in whole cells being in accord with the known adverse effects of these drugs.

Mitochondrial bioenergetics and drug-induced toxicity in a panel of mouse embryonic fibroblasts with mitochondrial DNA single nucleotide polymorphisms.

Mitochondrial DNA (mtDNA) variations including single nucleotide polymorphisms (SNPs) have been proposed to be involved in idiosyncratic drug reactions. However, current in vitro and in vivo models lack the genetic diversity seen in the human population. Our hypothesis is that different cell strains with distinct mtDNA SNPs may have different mitochondrial bioenergetic profiles and may therefore vary in their response to drug-induced toxicity. Therefore, we used an in vitro system composed of four strains of mouse embryonic fibroblasts (MEFs) with mtDNA polymorphisms. We sequenced mtDNA from embryonic fibroblasts isolated from four mouse strains, C57BL/6J, MOLF/EiJ, CZECHII/EiJ and PERA/EiJ, with the latter two being sequenced for the first time. The bioenergetic profile of the four strains of MEFs was investigated at both passages 3 and 10. Our results showed that there were clear differences among the four strains of MEFs at both passages, with CZECHII/EiJ having a lower mitochondrial robustness when compared to C57BL/6J, followed by MOLF/EiJ and PERA/EiJ. Seven drugs known to impair mitochondrial function were tested for their effect on the ATP content of the four strains of MEFs in both glucose- and galactose-containing media. Our results showed that there were strain-dependent differences in the response to some of the drugs. We propose that this model is a useful starting point to study compounds that may cause mitochondrial off-target toxicity in early stages of drug development, thus decreasing the number of experimental animals used.

Quantitative systems toxicology (QST) reproduces species differences in PF-04895162 liver safety due to combined mitochondrial and bile acid toxicity.

Many compounds that appear promising in preclinical species, fail in human clinical trials due to safety concerns. The FDA has strongly encouraged the application of modeling in drug development to improve product safety. This study illustrates how DILIsym, a computational representation of liver injury, was able to reproduce species differences in liver toxicity due to PF-04895162 (ICA-105665). PF-04895162, a drug in development for the treatment of epilepsy, was terminated after transaminase elevations were observed in healthy volunteers (NCT01691274). Liver safety concerns had not been raised in preclinical safety studies. DILIsym, which integrates in vitro data on mechanisms of hepatotoxicity with predicted in vivo liver exposure, reproduced clinical hepatotoxicity and the absence of hepatotoxicity observed in the rat. Simulated differences were multifactorial. Simulated liver exposure was greater in humans than rats. The simulated human hepatotoxicity was demonstrated to be due to the interaction between mitochondrial toxicity and bile acid transporter inhibition; elimination of either mechanism from the simulations abrogated injury. The bile acid contribution occurred despite the fact that the IC50 for bile salt export pump (BSEP) inhibition by PF-04895162 was higher (311 µmol/L) than that has been generally thought to contribute to hepatotoxicity. Modeling even higher PF-04895162 liver exposures than were measured in the rat safety studies aggravated mitochondrial toxicity but did not result in rat hepatotoxicity due to insufficient accumulation of cytotoxic bile acid species. This investigative study highlights the potential for combined in vitro and computational screening methods to identify latent hepatotoxic risks and paves the way for similar and prospective studies.

Biguanide-induced mitochondrial dysfunction yields increased lactate production and cytotoxicity of aerobically-poised HepG2 cells and human hepatocytes in vitro.

As a class, the biguanides induce lactic acidosis, a hallmark of mitochondrial impairment. To assess potential mitochondrial impairment, we evaluated the effects of metformin, buformin and phenformin on: 1) viability of HepG2 cells grown in galactose, 2) respiration by isolated mitochondria, 3) metabolic poise of HepG2 and primary human hepatocytes, 4) activities of immunocaptured respiratory complexes, and 5) mitochondrial membrane potential and redox status in primary human hepatocytes. Phenformin was the most cytotoxic of the three with buformin showing moderate toxicity, and metformin toxicity only at mM concentrations. Importantly, HepG2 cells grown in galactose are markedly more susceptible to biguanide toxicity compared to cells grown in glucose, indicating mitochondrial toxicity as a primary mode of action. The same rank order of potency was observed for isolated mitochondrial respiration where preincubation (40 min) exacerbated respiratory impairment, and was required to reveal inhibition by metformin, suggesting intramitochondrial bio-accumulation. Metabolic profiling of intact cells corroborated respiratory inhibition, but also revealed compensatory increases in lactate production from accelerated glycolysis. High (mM) concentrations of the drugs were needed to inhibit immunocaptured respiratory complexes, supporting the contention that bioaccumulation is involved. The same rank order was found when monitoring mitochondrial membrane potential, ROS production, and glutathione levels in primary human hepatocytes. In toto, these data indicate that biguanide-induced lactic acidosis can be attributed to acceleration of glycolysis in response to mitochondrial impairment. Indeed, the desired clinical outcome, viz., decreased blood glucose, could be due to increased glucose uptake and glycolytic flux in response to drug-induced mitochondrial dysfunction.

Distribution of Abeta peptide in whole blood.

The measurement of amyloid beta peptides (Abeta) in blood and plasma is expected to be a useful biomarker as potential therapeutics designed to lower Abeta peptide enter clinical trials. Many reports have suggested that Abeta could bind to substances in blood that may influence the recovery of Abeta peptide in plasma, its detection by conventional ELISAs or the actual turnover and half-life of the peptide in blood. In this study we describe a process for analyzing total Abeta in whole blood and plasma using denaturing solid-phase extraction followed by reverse-phase HPLC linked to ELISA. Comparison of total Abeta peptide levels in whole blood and plasma from the same bleed showed that most of the Abeta peptide is captured in the plasma if the samples are first denatured. In contrast, plasma that was assayed without denaturation could show greater than 70% reduction in apparent total Abeta peptide. This suggested that there was a pool of Abeta peptide in non-denatured plasma that is occluded from detection by ELISA, perhaps by binding to plasma proteins.

Target identification of drug induced mitochondrial toxicity using immunocapture based OXPHOS activity assays.

Mitochondrial dysfunction has been shown to be a pharmacotoxicological response to a variety of currently-marketed drugs. In order to reduce attrition due to mitochondrial toxicity, high throughput-applicable screens are needed for early stage drug discovery. We describe, here, a set of immunocapture based assays to identify compounds that directly inhibit four of the oxidative phosphorylation (OXPHOS) complexes: I, II, IV, and V. Intra- and inter-assay variation were determined and specificity tested by using classical mitochondrial inhibitors. Twenty drugs, some with known mitochondrial toxicity and others with no known mitochondrial liability, were studied. Direct inhibition of one or more of the OXPHOS complexes was identified for many of the drugs. Novel information was obtained for several drugs including ones with previously unknown effects on oxidative phosphorylation. A major advantage of the immunocapture approach is that it can be used throughout drug screening from early compound evaluation to clinical trials.

Interstitial Lung Disease Associated With Crizotinib in Patients With Advanced Non-Small Cell Lung Cancer: Independent Review of Four PROFILE Trials.

INTRODUCTION: Interstitial lung disease (ILD) is a rare, but potentially serious, side effect associated with crizotinib, a tyrosine kinase inhibitor for anaplastic lymphoma kinase-positive (ALK+) advanced non-small cell lung cancer. Our objective was to determine the incidence and nature of ILD associated with crizotinib in 4 PROFILE trials (ClinicalTrials.gov identifiers, NCT00585195, NCT00932451, NCT00932893, and NCT01154140). MATERIALS AND METHODS: Grade ≥ 3 respiratory adverse events (AEs) and serious AEs (SAEs) and any grade AEs/SAEs reported as pneumonitis, ILD, or radiation pneumonitis in trials PROFILE 1001, PROFILE 1005, PROFILE 1007, and PROFILE 1014 were evaluated by an expert independent review committee that included a pulmonologist, medical oncologist, and radiologist. Events were designated as disease progression, de novo ILD possibly or probably related to crizotinib, exacerbation or recurrence of pre-existing ILD, concurrent illness, other toxicity not thought to be related to ILD, or inconclusive. RESULTS: The independent review committee evaluated 446 events (in 368 of 1669 patients who had received crizotinib therapy). They classified these events as follows: progressive disease, 77; de novo ILD, 20; pre-existing ILD, 3; concurrent illness, 9; other toxicities, 310; and inconclusive, 27. The incidence of de novo ILD was 1.2% overall, 1.3% in whites, and 1.2% overall in Asians, but greater at 3.7% in Japanese patients. The median onset of ILD from the initiation of crizotinib therapy was 23 days (range, 3-763 days). The mortality rate due to ILD was 50%. Survival was improved if crizotinib was discontinued on presentation of ILD (9 of 14 patients) compared with discontinued later or continued (1 of 6 patients). CONCLUSION: ILD associated with crizotinib, although rare, can occur at any time and requires close monitoring.

Impact of a planned dose interruption of dacomitinib in the treatment of advanced non-small-cell lung cancer (ARCHER 1042).

OBJECTIVES: Dacomitinib is a pan-HER inhibitor for advanced non-small-cell lung cancer (NSCLC). We explored the impact of a planned 4-day dacomitinib dose interruption on plasma exposure of dacomitinib and adverse events (AEs) of interest in Cohort III of the ARCHER 1042 study. MATERIALS AND METHODS: Patients, treatment-naïve for advanced NSCLC with EGFR activating mutations, received oral dacomitinib 45mg QD (once daily). A planned dose interruption occurred in Cycle 1 from Days 11 through 14. The primary endpoint was the pharmacokinetic (PK) characteristics of dacomitinib in Cycle 1Day 10 and during dose interruption. Secondary endpoints included safety and concomitant medications used to treat AEs of interest. RESULTS: Cohort III enrolled 25 patients. Median plasma Cmax of dacomitinib in Cycle 1 Day 10 was 83.40ng/mL. Average median plasma dacomitinib concentration during the 4-day dose interruption was 42.63ng/mL. In the first 8 weeks of treatment 1) 80% of patients used concomitant medications for dermatologic AEs, 76% for diarrhea, and 44% for stomatitis, and 2) all patients experienced treatment-emergent AEs and 28% had all-causality Grade 3 AEs. CONCLUSION: At 45mg QD dosing, PK parameters of plasma dacomitinib in Cycle 1 Day 10 were comparable to that obtained in Cycle 1 Day 14 from other dacomitinib studies. Average median plasma dacomitinib concentration during the 4-day dose interruption was approximately half of the median plasma Cmax of dacomitinib observed prior to dose interruption. The toxicity profile was consistent with that from other studies of dacomitinib.

The molecular mechanism of ATP synthesis by F1F0-ATP synthase.

ATP synthesis by oxidative phosphorylation and photophosphorylation, catalyzed by F1F0-ATP synthase, is the fundamental means of cell energy production. Earlier mutagenesis studies had gone some way to describing the mechanism. More recently, several X-ray structures at atomic resolution have pictured the catalytic sites, and real-time video recordings of subunit rotation have left no doubt of the nature of energy coupling between the transmembrane proton gradient and the catalytic sites in this extraordinary molecular motor. Nonetheless, the molecular events that are required to accomplish the chemical synthesis of ATP remain undefined. In this review we summarize current state of knowledge and present a hypothesis for the molecular mechanism of ATP synthesis.

Analysis of protein fragmentation inhibition by an MMP-inhibitor in an in vivo model of heart failure using automated chromatography.

Proteomic strategies have continued to demonstrate value in studying disease by exploiting new technologies that can develop significant numbers of measurements from single samples. However, using complex samples such as tissues or blood has continued to be problematic due to the presence of major interfering substances. In this study, a process is described that uses denaturing peptide extraction from whole tissue and automated chromatography in order to allow subsequent analysis of more than 1000 tissue-derived peptides per sample. The process was employed to identify cardiac proteins that were spared degradation by administration of a heart-protecting matrix metalloproteinase (MMP) inhibitor (compound SC-621) following experimental myocardial infarction (MI). HPLC peptide fingerprints were developed from rat heart left ventricles and the resultant integrated peak data was compared across experimental animals. Surprisingly, although protein fragmentation was generally increased in MI hearts, the effect of the MMP inhibitor was only observed on a few species. The results from this study demonstrated that whole-tissue sample enrichment and peptide analysis using HPLC could be linked in order to study the effects of new compounds on a disease state. The system is flexible and amenable to improvements such as incorporating detection by mass spectrometry.

High-Content Imaging Assays for Identifying Compounds that Generate Superoxide and Impair Mitochondrial Membrane Potential in Adherent Eukaryotic Cells.

Reactive oxygen species (ROS) are constantly produced in cells as a result of aerobic metabolism. When there is an excessive production of ROS and the cell's antioxidant defenses are overwhelmed, oxidative stress occurs. The superoxide anion is a type of ROS that is produced primarily in mitochondria but is also generated in other regions of the cell including peroxisomes, endoplasmic reticulum, plasma membrane, and cytosol. Here, a high-content imaging assay using the dye dihydroethidium is described for identifying compounds that generate superoxide in eukaryotic cells. A high-content imaging assay using the fluorescent dye tetramethylrhodamine methyl ester is also described to identify compounds that impair mitochondrial membrane potential in eukaryotic cells. The purpose of performing both assays is to identify compounds that (1) generate superoxide at lower concentrations than they impair mitochondrial membrane potential, (2) impair mitochondrial membrane potential at lower concentrations than they generate superoxide, (3) generate superoxide and impair mitochondrial function at similar concentrations, and (4) do not generate superoxide or impair mitochondrial membrane potential during the duration of the assays.

Assessment of fatty acid beta oxidation in cells and isolated mitochondria.

Fatty acid beta oxidation is a major pathway of energy metabolism and occurs primarily in mitochondria. Drug-induced modulation of this pathway can cause adverse effects such as liver injury, or be beneficial for treating heart failure, type 2 diabetes, and obesity. Hence, in vitro assays that are able to identify compounds that affect fatty acid oxidation are of value for toxicity assessments, as well as for efficacy assessments. Here, we describe two high-throughput assays, one for assessing fatty acid oxidation in cells and the other for assessing fatty acid oxidation in isolated rat liver mitochondria. Both assays measure fatty acid-driven oxygen consumption and can be used for rapid and robust screening of compounds that modulate fatty acid oxidation.

Validation of a HTS-amenable assay to detect drug-induced mitochondrial toxicity in the absence and presence of cell death.

Drug-induced mitochondrial dysfunction is known to contribute to late stage compound attrition. Recently, assays that identify mitochondrial dysfunction have been developed but many require expensive reagents, specialized equipment, or specialized expertise such as isolation of mitochondria. Here, we validate a new 384-well format cell-based dual parameter assay that uses commonly available detection methods to measure both mitochondrial toxicity and cytotoxicity. In our initial evaluation, antimycin A, CCCP, nefazodone, flutamide, and digitonin were tested in K562 cells in both glucose- and galactose-supplemented media with a 2h incubation. The assay was able to correctly differentiate these compounds into mitochondrial toxicants and non-mitochondrial toxicants, and had excellent reproducibility. We next tested 74 compounds in K562 cells in both types of media and show that the assay was able to correctly identify some of the compounds as mitochondrial toxicants. Moreover, the assay could be simplified, without loss of information, by using K562 cells in galactose-containing medium alone. This simple, robust assay can be positioned as a rapid, early readout of mitochondrial and cellular toxicity. However, since the assay fails to identify some mitochondrial toxicants, further assays may be required to detect mitochondrial toxicity once lead compounds have been selected.

A high-throughput dual parameter assay for assessing drug-induced mitochondrial dysfunction provides additional predictivity over two established mitochondrial toxicity assays.

Mitochondrial toxicity is a major reason for safety-related compound attrition and post-market drug withdrawals, highlighting the necessity for higher-throughput screens that can identify this mechanism of toxicity during the early stages of drug discovery. Here, we present the validation of a 384-well dual parameter plate-based assay capable of measuring oxygen consumption and extracellular acidification in intact cells simultaneously. The assay showed good reproducibility and robustness and is suitable for use with both suspension cells and adherent cells. To determine if the assay provides additional value in detecting mitochondrial toxicity over existing platforms, 200 commercially available drugs were tested in the assay using HL60 suspension cells as well as in two conventional mitochondrial toxicity assays: an oxygen consumption assay that uses isolated mitochondria and a cell-based assay that uses HepG2 cells grown in glucose and galactose media. The combination of the dual parameter assay and the isolated mitochondrial oxygen consumption assay identified more compounds that caused mitochondrial impairment than any other combination of the three assays or each of the three assays on its own. Furthermore, novel information was obtained from the dual parameter assay on drugs not previously reported to cause mitochondrial impairment.

Human A53T α-synuclein causes reversible deficits in mitochondrial function and dynamics in primary mouse cortical neurons.

Parkinson's disease (PD) is the second most common neurodegenerative disease. A key pathological feature of PD is Lewy bodies, of which the major protein component is α-synuclein (α-syn). Human genetic studies have shown that mutations (A53T, A30P, E46K) and multiplication of the α-syn gene are linked to familial PD. Mice overexpressing the human A53T mutant α-syn gene develop severe movement disorders. However, the molecular mechanisms of α-syn toxicity are not well understood. Recently, mitochondrial dysfunction has been linked with multiple neurodegenerative diseases including Parkinson's disease. Here we investigated whether mitochondrial motility, dynamics and respiratory function are affected in primary neurons from a mouse model expressing the human A53T mutation. We found that mitochondrial motility was selectively inhibited in A53T neurons while transport of other organelles was not affected. In addition, A53T expressing neurons showed impairment in mitochondrial membrane potential and mitochondrial respiratory function. Furthermore, we found that rapamycin, an autophagy inducer, rescued the decreased mitochondrial mobility. Taken together, these data demonstrate that A53T α-syn impairs mitochondrial function and dynamics and the deficit of mitochondrial transport is reversible, providing further understanding of the disease pathogenesis and a potential therapeutic strategy for PD.