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Sep 15, 2011 (Vol. 31, No. 16)

Injecting New Life into Cell-Based Assays

Late-Stage Drug Failures Prompt Push for More Effective Approaches to Designing Therapies

  • Cell-based assays continue to provide powerful tools to fuel drug discovery. However, costly late-stage failures are driving the industry’s search for improved approaches and novel tools for interrogating cells. Throughput, reliability, cost, and physiologic relevance of cellular models for predictive toxicology remain central issues in the field.

    Visiongain’s “Cell-Based Assays” conference next month will feature topics ranging from technological advances in cellular models to challenges to traditional drug discovery paradigms. Additionally, presentations will provide the latest developments in stem cell biology and demonstrate how applying engineering/computing principles to living systems could revolutionize the design of new therapies.

    “In many ways, progress in the drug discovery industry has been quite disappointing in the last 10 years,” reports Mark Slack, Ph.D., group leader of cellular assays, Evotec.

    “The inertia and lack of productivity relate to failures in efficacy, poor clinical translation, and stagnant methodologies. The old one-gene, one-drug paradigm is no longer relevant, giving way to phenotypic approaches, capturing targets in their functional background. The landscape is beginning to change with an emerging paradigm that considers the physiology of diseases and the whole organism.

    “We are seeing that high-throughput screening formats are employing more physiologically relevant cellular models including use of primary cells and label-free, nonintrusive methods to interrogate new compounds. One rapidly emerging area is the use of stem cell technologies.

    “Because of difficult ethical issues in the generation of such cell lines, landmark work has studied and now demonstrated that it is possible to induce the reversal of somatic tissues into stem cell populations (i.e., induced pluripotent stem cells, or iPSCs).

    “We can perform assays from affected patients via iPSC technologies and generate cells expressing the disease phenotype. These will be very useful for drug discovery for specific diseases such as Parkinson and Huntington diseases.”

    Another area that has benefitted from technological advances is automated electrophysiology. Tiny patch clamp electrodes are now applied to individual cells in a 384-well format, allowing the screening of tens of thousands of compounds.

    “This has been an underexploited target class,” Dr. Slack says. “With the emergence of automated patch-clamp assays, a major bottleneck was overcome. However, we now need to deal with the high cost per data point and the relatively low throughput and efficiency of the devices.”

    According to Dr. Slack, one of the more exciting recent developments slowly establishing itself in mainstream drug development is atomic force microscopy (AFM). Developed as an add-on to enhance the scanning tunneling microscope, AFM adds an atomically sharp tip.

    “By monitoring the surface of biological specimens with the sensitive tip, one can actually see the cellular membranes and even their subcellular components at high resolution. Ultimately, these and other emerging technologies are providing more physiologically relevant models.”

  • Hepatotoxicity Testing

    Unanticipated toxicity and adverse drug reactions after licensing a drug are the leading causes of late-stage attrition and withdrawal of drugs from the market. “Up to 30% of compound failures happen due to toxicity and issues of clinical safety,” notes Neil A. Hanley, M.D., Ph.D., professor of medicine at the University of Manchester.

    Liver toxicity tops the list of drug-induced injury. “The underlying mechanisms of damage are quite complex and not completely understood. A major issue is that such toxicity is not reliably testable in a cell culture system, nor completely accurate in animal models.” Dr. Hanley suggests that, not only are better cellular models for hepatotoxicity needed, but that generating hepatocyte-like cells from human embryonic stem cells (hESCs) or induced pluripotent stem cells (hIPSCs) may hold the answer as an assay of choice.

    “In theory, these stem cells could be utilized to generate all the different cell types of the adult liver. This is a key advantage that may allow better mirroring of the complexity of an intact organ. There have been a number of advances aimed at differentiating hESC into liver cell types. Three components needing to be addressed are soluble growth factors, support cells, and an extracellular matrix medium.”

    Dr. Hanley indicates that there are many challenges that remain before this system is ready for more widespread use. “Many academic laboratories can reliably generate progenitor-like cells. That is about three-fourths of the journey. The last one-fourth, getting to the mature liver cell, is most likely contingent on the precision of preceding steps plus optimizing conditions for the final differentiation.

    “An example of the last step is optimizing extracellular matrix composition to provide a scaffold for growth and differentiation.”

    Before big pharma can utilize hESCs for hepatotoxicity, testing the industry must also tackle issues of scale-up and consistency of production, suggests Dr. Hanley. “Scale-up, the bioprocessing step, is a huge science in itself.”

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