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Sep 15, 2013 (Vol. 33, No. 16)

Cell-Based Assays: Getting Back to Basics

  • Stem Cells and Toxicity Testing

    Click Image To Enlarge +
    Spontaneously contractile Cytiva™ Cardiomyocytes enable study of electrophysiological properties (left) and high-content analysis (right). Cells on the right are stained for nuclei (blue) and cardiac Troponin I (red), which localizes to sarcomeric structures along myofilaments. [GE Healthcare]

    Late-stage development failures and market withdrawal of drugs that were thought to be safe can result in losses of well over a billion dollars. Cardiotoxicity is frequently the chief culprit. “Although toxicity testing often involves traditional in vitro laboratory testing or animal studies, human cell models are likely to provide more accurate and reliable information for predicting human responses to new drugs,” notes Liz Roquemore, Ph.D., lead scientist and technology manager at GE Healthcare.

    One problem is that when human cell models are immortalized or genetically engineered, they may not entirely recapitulate normal cells. What’s needed is an unlimited supply of fully characterized human cell mimics. Enter stem cells.

    “Stem cell models provide a much improved and highly efficient way to test for toxicity, says Dr. Roquemore. “The challenge, once it has been determined how to differentiate stem cells into the required cell type, is in scaling up the process and reproducibly generating large batches of these cells. We collaborated with Geron to industrialize their method for creating heart muscle cells (cardiomyocytes) from stem cells, which resulted in development of our first stem cell derived model, Cytiva™ Cardiomyocytes.”

    While these cells provide insight into toxic effects on cardiac electrophysiology, more than 75% of toxicities result from adverse effects on other cellular functions such as mitochondrial (energy) metabolism, calcium homeostasis, or membrane integrity. “To assess impact on these aspects of the cell, we perform high-content analysis (HCA) using stem cell cardiomyocytes,” says Dr. Roquemore.

    “Most recently, in a collaboration with Genentech to identify and assess the cardiotoxic potential of selective kinase inhibitors, we identified all compounds in the set that had reported clinical cardiotoxicity using our IN Cell Analyzer 2200 system. Whole-well imaging and review scanning deliver methods for rapid assessment of cell density followed by detailed analyses of subcellular features and cell phenotypes. The ability to multiplex not only offers high-throughput toxicity assessments but also may help us develop more sensitive biomarkers and gain insight into mechanisms of action.”

  • Differentiating Stem Cells

    Reliable and scalable differentiation of stem cells in serum-free conditions is predicted to be one of the most significant barriers to their commercialization for drug discovery or clinical applications, according to Jey M. Jeyakumar, Ph.D., principal scientist at Plasticell Limited. “While advances in regenerative medicine are reported daily, clinical-grade stem cell differentiation media is still considered to be a major challenge in the field.

    “Differentiating stem cells requires their culture in a series of different cell culture media over time, each medium containing many different components,” says Dr. Jeyakumar. “This creates a combinatorial problem when trying to discover differentiation protocols using conventional methods. Searching for such protocols may take teams of scientists many months if not years and consumes a lot of resources. Even then, the resultant protocols may not optimal; that is, they may only be weakly effective.”

    Plasticell’s high-throughput platform for differentiating stem cells, called combinatorial cell culture (CombiCult®), tackles this problem using a bead-based screening method that allows sampling of up to 100,000 putative protocols in parallel in the time it takes for the stem cell to differentiate, that is, weeks.

    According to Dr. Jeyakumar, “CombiCult allows us to perform up to 100,000 trial-and-error equivalent experiments in parallel. This allows for the very rapid, low-risk, and cheap discovery of stem cell differentiation protocols. That is, it serves as a search engine for stem cell differentiation protocols.”

    The technology has been used successfully in the differentiation of embryonic stem cells, tissue stem cells, and induced pluripotent stem cells toward defined lineages, validating the technology and showing proof of its many applications.

    “We obtained a ranked list of protocols that are highly specific for osteocytes and chondrocytes using bone-marrow-derived mesenchymal stem cells (MSCs). In addition, for the first time in the industry, these protocols were serum-free, devoid of animal-derived components, and scalable. In the case of the osteocyte media, they turned out to be highly effective at differentiating MSCs into bone cells that secrete the mineral components for bone.”

    Dr. Jeyakumar projects that adoption of these techniques will rapidly accelerate efforts to industrialize stem cell differentiation by pharma and the field of regenerative medicine.

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