Traditional toxicology practices focus on characterizing a single compound in regulatory GLP toxicology studies over a long period of time directly prior to clinical phase 1 trials. By this time, large amounts of time and resources have been invested into finding a single drug candidate. If a liability is found, researchers are left deciding if the benefits outweigh potential liabilities or if they need to start over, having spent time and resources on that single candidate. With late-stage failures due to toxicity continuing to be a primary cause for compound attrition, incorporating predictive in vitro testing into the discovery process is essential for those working in drug discovery.

Nuclear receptors act as transcription factors that mediate the effects of hormones, drugs, and other xenobiotics by regulating the expression of specific genes involved in many cellular functions including development, reproduction, and metabolism. The target gene and protein expression patterns of nuclear receptors and their physiological effects create a network that can be monitored by multimodal approaches, such as systems biology. Therefore, defining the biological niche of each nuclear receptor and understanding their overlapping pathways and functions can provide value to discovery researchers when evaluating a potential compound’s promise and liabilities.

When looking to perform in vitro cell-based target validation, pathway analysis, and compound screening there are several types of assays to choose from. One question you might ask when evaluating different cell-based reporter assay technologies is, what is better for my research: an assay system that uses fluorescence or an assay system that utilizes bioluminescence? Both technologies can provide researchers with valuable data so let us weigh their advantages and disadvantages.

The nuclear receptor superfamily is a group of intracellular transcription factors that directly regulate gene expression in response to lipophilic molecules. These receptors are found in metazoan organisms such as nematodes, insects, and vertebrates. Nuclear receptors affect a wide variety of physiologic functions including development, reproduction, and metabolism and are associated with diseases such as Alzheimer’s, cancer, and diabetes.

An animal model is a non-human species that has been widely studied and used during research to help understand biological processes in a laboratory setting. The use of animal models as human surrogates has provided a great deal of information about physiology and disease with over 150 Nobel Prizes awarded in physiology or medicine to professionals utilizing animal models for their research.

The primary reason for the use of animal models is the evolutionary principle that all organisms share some degree of relatedness and genetic similarity. Vertebrate models in particular are useful as human surrogates in drug discovery and medical research due to their more common ancestry. Though there are many vertebrates that could be used, a few are more common in research than others.

Growth factors are proteins that stimulate the growth of specific tissues. They bind to cells by growth factor receptors, activating cellular proliferation and differentiation. This activation of growth factor receptors creates a short, time-limited signal, which causes different parts of cellular proliferation and differentiation such as mitosis, clonal expansion, gene regulation, and cell apoptosis. While growth factor receptors operate on different cell types, their signal pathways often overlap, which makes them important targets for oncology research.

What are Growth Factors and How Do They Work?

First discovered by Rita Levi-Montalcini, growth factors are compact polypeptides, that bind to transmembrane receptors harboring kinase activity, to stimulate specific combinations of intracellular signaling pathways. The intracellular signaling pathways that are activated by growth factors are mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K), phospholipase C-γ, and transcription factors like the signal transducers and activators of transcription (STATs) or SMAD proteins. This activation of growth factor receptors creates a short, time-limited signal, which causes different parts of cellular proliferation and differentiation such as mitosis, clonal expansion, gene regulation, and cell apoptosis. Unlike hormones which have a wider systemic influence, growth factors usually transmit signals between cells to modulate their activity. They act as chemical messengers, communicating with different cells to stimulate growth. Depending on their function, growth factors can produce endocrine, paracrine, autocrine, or juxtracrine responses in cells.

The assessment of a drug candidate’s cross-activity with human xenobiotic-sensing receptors provides important early indications of that drug’s potential for downstream drug-drug interactions or other toxicology concerns. Prior to moving into human trials, preclinical studies utilize animals as human surrogates to assess a drug’s pharmacokinetic and toxicologic profiles. A wide range of animal models are used in preclinical studies for drug discovery including mice, rats, dogs, zebrafish, rabbits, and non-human primates. In research, these animals are used because they are orthologs. Orthologs are animals of different species that share genes that evolved from a common ancestor and have retained a similar function to those genes in humans.

The zebrafish (Danio rerio) is a small fish that has been making big waves as a popular vertebrate model for research. Zebrafish are a species of tropical fresh-water fish, that are native to southeast Asia specifically India, Nepal, Bhutan, Pakistan, Bangladesh, and Myanmar. Zebrafish live in schools and range from about 1 inch to 1.5 inches long. The name “zebrafish” comes from the blue stripes on both sides of their bodies and because of this, zebrafish were found in pet stores around the U.S long before they were used for research.

The discovery process is time consuming and expensive, and it is becoming increasingly more important that if you do fail that you fail fast before moving onto clinical trials. When planning your research, there are different options to test compounds for nuclear receptor activation or hepatotoxicity. The project might include performing cell-based reporter assays and if it does, you may consider designing your own assay rather than working with a company who specializes in this work. Before adding the process of designing an assay to a new project, consider these three important questions.