BACKGROUND: A central challenge in toxicity testing is the large number of chemicals in commerce that lack toxicological assessment. In response, the Tox21 program is re-focusing toxicity testing from animal studies to less expensive and higher throughput in vitro methods using target/pathway-specific, mechanism-driven assays. OBJECTIVES: Our objective was to use an in-depth mechanistic study approach to prioritize and characterize the chemicals affecting mitochondrial function. METHODS: We used a tiered testing approach to prioritize for more extensive testing 622 compounds identified from a primary, quantitative high-throughput screen of 8,300 unique small molecules, including drugs and industrial chemicals, as potential mitochondrial toxicants by their ability to significantly decrease the mitochondrial membrane potential (MMP). Based on results from secondary MMP assays in HepG2 cells and rat hepatocytes, 34 compounds were selected for testing in tertiary assays that included formation of reactive oxygen species (ROS), upregulation of p53 and nuclear erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE), mitochondrial oxygen consumption, cellular Parkin translocation, and larval development and ATP status in the nematode Caenorhabditis elegans. RESULTS: A group of known mitochondrial complex inhibitors (e.g., rotenone) and uncouplers (e.g., chlorfenapyr), as well as potential novel complex inhibitors and uncouplers, were detected. From this study, we identified four not well-characterized potential mitochondrial toxicants (lasalocid, picoxystrobin, pinacyanol, and triclocarban) that merit additional in vivo characterization. CONCLUSIONS: The tier-based approach for identifying and mechanistically characterizing mitochondrial toxicants can potentially reduce animal use in toxicological testing. https://doi.org/10.1289/EHP2589.

Mucopolysaccharidosis type I (MPS I) is caused by deficiency of α-l-iduronidase (IDUA), a lysosomal enzyme involved in the breakdown and recycling of glycosaminoglycans (GAGs). Although enzyme replacement therapy is available, the efficacy of the treatment for neuropathic manifestations is limited. To facilitate drug discovery and model disease pathophysiology, we generated neural stem cells (NSCs) from MPS I patient-derived induced pluripotent stem cells (iPSCs). The NSCs exhibited characteristic disease phenotypes with deficiency of IDUA, accumulation of GAGs and enlargement of lysosomes, in agreement with the severity of clinical subgroups of MPS I. Transcriptome profiling of NSCs revealed 429 genes that demonstrated a more extensive change in expression in the most severe Hurler syndrome subgroup compared to the intermediate Hurler-Scheie or the least severe Scheie syndrome subgroups. Clustering and pathway analysis revealed high concordance of the severity of neurological defects with marked dysregulation of GAG biosynthesis, GAG degradation, lysosomal function and autophagy. Gene ontology (GO) analysis identified a dramatic upregulation of the autophagy pathway, especially in the Hurler syndrome subgroup. We conclude that GAG accumulation in the patient-derived cells disrupts lysosomal homeostasis, affecting multiple related cellular pathways in response to IDUA deficiency. These dysregulated processes likely lead to enhanced autophagy and progressively severe disease states. Our study provides potentially useful targets for clinical biomarker development, disease diagnosis and prognosis, and drug discovery.

A dose responsive quantitative high throughput screen (qHTS) of >350,000 compounds against a human relaxin/insulin-like family peptide receptor (RXFP1) transfected HEK293 cell line identified 2-acetamido-N-phenylbenzamides 1 and 3 with modest agonist activity. An extensive structure-activity study has been undertaken to optimize the potency, efficacy, and physical properties of the series, resulting in the identification of compound 65 (ML-290), which has excellent in vivo PK properties with high levels of systemic exposure. This series, exemplified by 65, has produced first-in-class small-molecule agonists of RXFP1 and is a potent activator of anti-fibrotic genes.

The re-emergence of Zika virus (ZIKV) and Ebola virus (EBOV) poses serious and continued threats to the global public health. Effective therapeutics for these maladies is an unmet need. Here, we show that emetine, an anti-protozoal agent, potently inhibits ZIKV and EBOV infection with a low nanomolar half maximal inhibitory concentration (IC50) in vitro and potent activity in vivo. Two mechanisms of action for emetine are identified: the inhibition of ZIKV NS5 polymerase activity and disruption of lysosomal function. Emetine also inhibits EBOV entry. Cephaeline, a desmethyl analog of emetine, which may be better tolerated in patients than emetine, exhibits a similar efficacy against both ZIKV and EBOV infections. Hence, emetine and cephaeline offer pharmaceutical therapies against both ZIKV and EBOV infection.

Metastasis remains a leading cause of cancer mortality due to the lack of specific inhibitors against this complex process. To identify compounds selectively targeting the metastatic state, we used the perinucleolar compartment (PNC), a complex nuclear structure associated with metastatic behaviors of cancer cells, as a phenotypic marker for a high-content screen of over 140,000 structurally diverse compounds. Metarrestin, obtained through optimization of a screening hit, disassembles PNCs in multiple cancer cell lines, inhibits invasion in vitro, suppresses metastatic development in three mouse models of human cancer, and extends survival of mice in a metastatic pancreatic cancer xenograft model with no organ toxicity or discernable adverse effects. Metarrestin disrupts the nucleolar structure and inhibits RNA polymerase (Pol) I transcription, at least in part by interacting with the translation elongation factor eEF1A2. Thus, metarrestin represents a potential therapeutic approach for the treatment of metastatic cancer.

The acquisition of resistance is a major obstacle to the clinical use of platinum drugs for ovarian cancer treatment. Increase of DNA damage response is one of major mechanisms contributing to platinum-resistance. However, how DNA damage response is regulated in platinum-resistant ovarian cancer cells remains unclear. Using quantitative high throughput combinational screen (qHTCS) and RNA-sequencing (RNA-seq), we show that dual oxidase maturation factor 1 (DUOXA1) is overexpressed in platinum-resistant ovarian cancer cells, resulting in over production of reactive oxygen species (ROS). Elevated ROS level sustains the activation of ATR-Chk1 pathway, leading to resistance to cisplatin in ovarian cancer cells. Moreover, using qHTCS we identified two Chk1 inhibitors (PF-477736 and AZD7762) that re-sensitize resistant cells to cisplatin. Blocking this novel pathway by inhibiting ROS, DUOXA1, ATR or Chk1 effectively overcomes cisplatin resistance in vitro and in vivo. Significantly, the clinical studies also confirm the activation of ATR and DOUXA1 in ovarian cancer patients, and elevated DOUXA1 or ATR-Chk1 pathway correlates with poor prognosis. Taken together, our findings not only reveal a novel mechanism regulating cisplatin resistance, but also provide multiple combinational strategies to overcome platinum-resistance in ovarian cancer.

Antineoplastic platinum agents are used in first-line treatment of ovarian cancer, but treatment failure frequently results from platinum drug resistance. Emerging observations suggest a role of reactive oxygen species (ROS) in the resistance of cancer drugs including platinum drugs. However, the molecular link between ROS and cellular survival pathway is poorly understood. Using quantitative high-throughput combinational screen (qHTCS) and genomic sequencing, we show that in platinum-resistant ovarian cancer elevated ROS levels sustain high level of IL-11 by stimulating FRA1-mediated IL-11 expression and increased IL-11 causes resistance to platinum drugs by constitutively activating JAK2-STAT5 via an autocrine mechanism. Inhibition of JAK2 by LY2784544 or IL-11 by anti-IL-11 antibody overcomes the platinum resistance in vitro or in vivo. Significantly, clinic studies also confirm the activated IL-11-JAK2 pathway in platinum-resistant ovarian cancer patients, which highly correlates with poor prognosis. These findings not only identify a novel ROS-IL-11-JAK2-mediated platinum resistance mechanism but also provide a new strategy for using LY2784544- or IL-11-mediated immunotherapy to treat platinum-resistant ovarian cancer.

BACKGROUND: Infantile and late infantile neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage diseases affecting the central nervous system (CNS). The infantile NCL (INCL) is caused by mutations in the PPT1 gene and late-infantile NCL (LINCL) is due to mutations in the TPP1 gene. Deficiency in PPT1 or TPP1 enzyme function results in lysosomal accumulation of pathological lipofuscin-like material in the patient cells. There is currently no small-molecular drug treatment for NCLs. RESULTS: We have generated induced pluripotent stem cells (iPSC) from three patient dermal fibroblast lines and further differentiated them into neural stem cells (NSCs). Using these new disease models, we evaluated the effect of δ-tocopherol (DT) and hydroxypropyl-β-cyclodextrin (HPBCD) with the enzyme replacement therapy as the control. Treatment with the relevant recombinant enzyme or DT significantly ameliorated the lipid accumulation and lysosomal enlargement in the disease cells. A combination therapy of δ-tocopherol and HPBCD further improved the effect compared to that of either drug used as a single therapy. CONCLUSION: The results demonstrate that these patient iPSC derived NCL NSCs are valid cell- based disease models with characteristic disease phenotypes that can be used for study of disease pathophysiology and drug development.

The Ebola virus (EBOV) causes severe human infection that lacks effective treatment. A recent screen identified a series of compounds that block EBOV-like particle entry into human cells. Using data from this screen, quantitative structure-activity relationship models were built and employed for virtual screening of a ∼17 million compound library. Experimental testing of 102 hits yielded 14 compounds with IC50 values under 10 μM, including several sub-micromolar inhibitors, and more than 10-fold selectivity against host cytotoxicity. These confirmed hits include FDA-approved drugs and clinical candidates with non-antiviral indications, as well as compounds with novel scaffolds and no previously known bioactivity. Five selected hits inhibited BSL-4 live-EBOV infection in a dose-dependent manner, including vindesine (0.34 μM). Additional studies of these novel anti-EBOV compounds revealed their mechanisms of action, including the inhibition of NPC1 protein, cathepsin B/L, and lysosomal function. Compounds identified in this study are among the most potent and well-characterized anti-EBOV inhibitors reported to date.

Recent studies have illuminated the crucial role of astrocytes in maintaining proper neuronal health and function. Abnormalities in astrocytic functions have now been implicated in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Historically, drug development programs for neurodegenerative diseases generally target only neurons, overlooking the contributions of astrocytes. Therefore, targeting both disease neurons and astrocytes offers a new approach for drug development for the treatment of neurological diseases. Looking forward, the co-culturing of human neurons with astrocytes could be the next evolutionary step in drug discovery for neurodegenerative diseases.