Redirecting Approved Drugs
Identifying new applications for FDA-approved drugs using HCS and image-based systems biology is the focus of work being done by Stephen Wong, Ph.D., founding director of the bioinformatics and biomedical engineering program and the cellular and tissue microscopy core at the Methodist Hospital Research Institute and professor of radiology and neurosciences at Weill Cornell Medical College.
Dr. Wong gave examples of screening campaigns to decipher targets in the pathways responsible for the metastasis of breast cancer to the brain in his talk. He specifically described the computational tools his group is developing for high-content and network analysis, and the animal-imaging techniques being used to evaluate combinations of small molecule chemotherapeutic agents for their ability to cross the blood-brain barrier and to have an effect against central nervous system metastases in breast cancer.
Dr. Wong’s group has also developed a series of quantitative image-analysis tools, including zebrafish image quantifier (ZFIQ), as well as software for studying neuronal spines (NeuronIQ), neurites (Neurite IQ), and time-lapse mitotic events in cells (DCellIQ). Dr. Wong’s HCS/systems biology research is funded by the NCI, NIA, and NLM.
Because the compounds being studied are already approved drugs, Phase I trials are not needed. The quantitative data generated from HCS provides the evidence necessary for moving into Phase II studies, shortening the drug-development cycle to a year or less.
The types of studies essential to Dr. Wong’s efforts, such as assays to monitor cell-cycle regulation or dendritic spine dynamics, require time-lapse, live-cell imaging. Looking at fixed cells provides only an artificial snapshot of where cells are at a particular point in time, explained Dr. Wong. “We want to look at a 384-well plate of continuously growing cells over five to six days,” he said, and in his view none of the instrument manufacturers competing in the HCS market has yet to provide a robust, incubator-based, environmentally controlled system that can achieve this.
Vendors have tended to view HCS as just another type of high-throughput screening, but live-cell imaging done in as natural an environment as possible has quite different requirements, contended Dr. Wong.
“Vendors are going in the wrong direction. The power of HCS is in the ability to visualize things in action and to extract lots more quantitative information from the images. If you, instead, retrofit HCS to HTS, you are losing its advantages,” such as the ability to see cells or spines change over time, to visualize cell-cell interactions, and to sync cell populations and study cell-cycle events in time-lapse, said Dr. Wong.
In any experiment, “if you generate enough data you will get hits, but how many will be real hits versus false positives?” asked Dr. Wong. “We need to push the quality upfront on the biology side” and screen out, earlier in the discovery process, compounds that are destined to fail.
Researchers at Pfizer are using HCS to study the genetic variation and physiologic interactions that underlie hepatic insulin resistance in type 2 diabetes and the prediabetic state. Diabetes is a complex, multigenic disease, and while advances in genomic and SNP-based technologies have led to the identification of at least 30 genes that contribute to the diabetic phenotype, much work remains to understand their role in cell biology and disease and how they interact.
“If you are careful about the cell models you choose, you can use HCS to characterize these genes and monitor their effects on biochemical pathways,” said Steven Haney, Ph.D., associate fellow in biological profiling at Pfizer’s biotherapeutics and bioinnovation center. The company has invested heavily in developing cell models that are representative of human physiology, including hepatocytes that faithfully mimic liver function when grown in culture.
The other main aspect of this research effort involves identifying changes that affect the diabetic phenotype, specifically glucose storage and utilization pathways, and distinguishing between effects that involve the insulin-signaling pathway from more general phenomena related to activation of toxicologic or stress pathways.
“HCS can alert us to things we don’t necessarily know to look for, in a mechanism-independent way,” said Dr. Haney. “The increasing throughput of HCS allows us to look at a lot of cells and determine whether subtle phenotypic changes are significant or spurious.”