Compound Libraries

When using a compound library during model or assay development, researchers aim to validate the utility of their model/assay using compounds with known action.

The blood-brain barrier (BBB) prevents conventional chemotherapeutic agents from reaching brain tumors such as gliomas, making them very hard to treat with drugs. Traditional methods for testing BBB permeability of compounds in high throughput screening is limited to assessing radio- or fluorescently-labeled compounds passing through a monolayer cell culture. However, in most cases, this does not accurately recapitulate the physical environment of a glioma. Sherman & Rossi (2019) developed a 3D ‘BBB plus tumor’ model to allow label-free investigation of brain permeability alongside tumor toxicity. To validate this model they screened compounds from the Tocriscreen Kinase Inhibitor Library for their cytotoxicity against LN-229 glioma spheroids alone and with the BBB model. They identified 27 compounds that showed tumor cytotoxicity in LN-229 glioma spheroids, however addition of the BBB in the 3D ‘BBB plus tumor’ model narrowed this number to 9, showing 18 compounds would not penetrate the BBB and so are unsuitable for treatment of gliomas.

Sherman & Rossi (2019) A novel three-dimensional glioma blood-brain barrier model for high-throughput testing of tumoricidal capability. Front Oncol 9 PMID: 31131260

Drug repurposing, also known as drug repositioning, involves investigating new therapeutic uses for drugs that already have clinical approval. By leveraging validated safety and efficacy data, this process aims to bring a drug to market faster, with reduced cost. Compound libraries consisting of FDA-approved drugs are an essential starting point for drug repurposing studies.

First identified in the early 2000s, Middle East Respiratory Syndrome is a viral respiratory disorder, caused by the MERS coronavirus (MERS-CoV), with the potential to progress into acute respiratory distress. Shin et al (2018) used the Tocriscreen FDA-approved Drugs Library to identify compounds that have antiviral action against MERS-CoV in a cell-based antiviral screening assay. Huh-7 cells were infected with MERS-CoV and treated with compounds, which identified Saracatinib, a potent and selective Src tyrosine kinase family inhibitor, as having antiviral activity against MERS-CoV.

Shin et al (2018) Saracatinib inhibits Middle East Respiratory Syndrome-coronavirus replication in vitro. Viruses 10 283 PMID: 29795047

Bioactive compound libraries can be used to identify compounds that enhance the efficiency of experimental techniques and processes, such as stem cell differentiation and reprogramming, and molecular biology techniques. 

CRISPR-Cas9 technology has emerged as a powerful tool for sequence-specific gene knockout through non-homologous end joining. However, the experimental process required is inefficient for the precise editing of genome sequences. Yu et al (2015) screened compounds from the Tocriscreen Plus Library, a precursor to Tocriscreen 2.0 Max, to identify small molecules that enhance the efficiency of CRISPR-Cas9 mediated homology-directed repair, and identified a range of compounds in diverse cell types. 

Induced pluripotent stem cells can be directed to differentiate into all cell types, and so provide an unlimited source of cells for in vitro disease modeling. Differentiation of pluripotent stem cells into myotubes produces myotubes with an embryonic identity, which does not accurately model skeletal disease phenotypes. Selvaraj et al (2019) used the Tocriscreen Stem Cell Library to identify compounds that would enhance the maturation of myotubes during differentiation, and found a combination of compounds that enable the generation of mature muscle constructs from pluripotent stem cells. 

Selvaraj et al (2019) Screening identifies small molecules that enhance the maturation of human pluripotent stem cell-derived myotubes. Elife 8 e47970 PMID: 31710288

Yu et al (2015) Small molecules enhance CRISPR genome editing in pluripotent stem cells. Cell Stem Cell 16 142 PMID: 25658371

When using a compound library for target validation, researchers aim to demonstrate that their hypothesis about a target and its involvement in a cellular or disease process is correct, by using compounds with a known target protein.

For example, Markussen et al (2018) used the Tocriscreen Kinase Inhibitor Library to identify glycogen synthase kinase 3 (GSK3) as a negative regulator of fibroblast growth factor 21 (FGF21) in brown adipose tissue (BAT). BAT activity has beneficial metabolic functions that may have therapeutic potential in disorders such diabetes and obesity, as it is able to improve systemic insulin sensitivity and glucose homeostasis, and increase tissue oxygen consumption. This paper investigated the signaling pathways that regulate expression of Fgf21 in BAT, and identified two GSK3 inhibitors that increased Fgf21 expression and oxygen consumption in brown adipocytes.

Sartori et al (2019) showed that expression of BIN1, a commonly identified risk factor gene for Alzheimer's disease, modulates its interaction with Tau, possibly through signaling pathways that regulate phosphorylation. To investigate these pathways further, they developed a high-throughput screening approach using primary hippocampal neurons. They tested compounds from the Tocriscreen Mini Library (a precursor of Tocriscreen 2.0 Mini), with subsequent cellular assays for validation, and identified two compounds that modulate the BIN1-Tau interaction in neurons. This interaction has previously been shown to be inhibited by Tau phosphorylation, and both compounds identified target regulators of phosphorylation, one via calcineurin and one via the MEK-dependent signaling pathways.

The Hippo signaling pathway exhibits regulatory cross-talk with multiple signaling networks via the transcriptional cofactor YAP. This pathway is dysregulated in many types of cancer, but how YAP is controlled in tumorigenesis is poorly understood. Yang et al (2019) screened compounds from the Tocriscreen Kinase Inhibitor Library to identify Hippo pathway regulators. They show that nerve growth factor receptor tyrosine kinase (NTRK1) regulates YAP oncogenic activity in vitro and in vivo.

Markussen et al (2018) GSK3 is a negative regulator of the thermogenic program in brown adipocytes. Sci Rep 22 3469 PMID: 29472592

Sartori et al (2019) BIN1 recovers tauopathy-induced long-term memory deficits in mice and interacts with Tau through Thr³⁴⁸ phosphorylation. Acta Neuropathol 138 631 PMID: 31065832

Yang et al (2019) NTRK1 is a positive regulator if YAP oncogenic function. Oncogene 38 2778 PMID:30542115