ES/iPS cell drug screening technology
Human ES/iPS cells are
the only cell source which can be developed into various types of human
functional cells including cardiomyocyte, neuron, hepatocyte and
insulin secreting beta cells.
Chikafumi Yokoyama, CEO,
Embryonic stem cell (ES cell) and induced pluripotent stem
cell (iPS cell) have been attracting a lot of attention. ES/iPS cells
have two key advantages as a cell source: pluripotency to develop into
various types of cells and the capacity for indefinite in-vitro
expansion in a normal state. The combination of these two basic
characteristics unleashes enormous potential for many new
The ES/iPS cell business can be divided into four fields:
research reagents, drug discovery tools, personalized medicine, and
regenerative medicine. The growth of the research reagent market has
accelerated since the invention of human iPS cell in 2007 by Prof.
Shinya Yamanaka in Kyoto University. Some countries,
including Japan, have set strict guidelines to use human ES cell
because of the ethical issues related to the destruction of embryos.
However, since iPS cells are derived from adult cells, the ethical
issues are less contentious. Moreover, iPS holds the promise of
autologous cell therapy for patients. These compelling advantages mean
the number of researchers involved in iPS cell is growing quickly.
The application of stem cells to drug discovery is emerging rapidly.
ReproCELL offers cardiotoxicity assay services using cardiomyocytes
derived from ES cells (from 2008) and iPS cells (from 2009). This is
the first commercially available stem cell drug discovery services, and
is the subject of this article.
Human ES/iPS cell technology will bring a paradigm shift in drug
discovery technology in future, because various types of functional
cells derived from human ES/iPS cells can be supplied infinitely.
Currently, immortalized cell lines and animal derived-primary cells are
usually used in drug discovery process. However, the former
lose the characteristics of normal cells, and therefore, their ability
to be usefully screened for specific functions, while the latter are
difficult to supply to mass production scale and suffer large
lot-to-lot variation. Human ES/iPS cells are the only cell source which
can be developed into various types of human functional cells including
cardiomyocyte, neuron, hepatocyte, and insulin secreting beta cells.
Cell-based assays using these human differentiated cells will change
the drug discovery process significantly.
Personalized medicine is a future target of drug discovery technology.
iPS technology has enormous potential in this area. Individual iPS
cells, obtained from individual somatic cells, have the potential to be
differentiated to any type of functional cells. In general,
metabolizing enzyme levels vary widely in individuals, and the rates of
drug metabolism also vary. If an individual’s hepatocyte can
be derived from iPS cells, it could be used to test the metabolism of
various commercially available drugs to define an appropriate
Regenerative medicine is the most promising application in ES/iPS cell
field. The clinical trial by Geron Corporation is set to be a
significant breakthrough in 2009.
Drug discovery technology
using ES/iPS cells
R&D costs in pharma companies are currently growing, consuming
15-20 percent of total revenues. The reasons for this increased cost
per drug are mainly due to a higher rate of attrition of candidates
drugs. As regulatory agencies raise safety standards, poor toxicity
profiles are increasingly seen as a liability that has to be better
managed. If the efficacy and toxicity of the drug candidate could be
predicted more accurately at earlier stages of drug development,
overall R&D cost and drug development period can be reduced
significantly. Human ES/iPS cells have enormous potential to
impact on this issue.
Drug-induced QT interval prolongation (DIQTIP) leading to serious
ventricular arrhythmias poses a major safety concern for the
development and use of new drug candidates. Candidate compounds in
clinical development have been dropped as a result of DIQTIP and many
marketed drugs have been withdrawn. This significant safety issue has
caused regulatory agencies such as the International Conference on
Harmonization of Technical Requirements for Registration of
Pharmaceuticals for Human Use (ICH) to require pharmaceutical companies
to implement safety studies to minimize the risk of QT interval
Several preclinical models are available to evaluate
compound’s potential to cause DIQTIP: the most widely used
are an in vitro hERG (human ether a-go-go-related gene) assay and
animal-based QT prolongation assays. However, these assays are usually
performed in late stages of preclinical development, due to cost and
resource limitation. To predict potential QT prolongation in early drug
development, we set out to establish a new assay system using
cardiomyocytes derived from human ES/iPS cells. The patch-clamp based
hERG assay is most widely used for this purpose and its use is
However, the hERG assay can be inaccurate (false positives and false
negatives) because it does not take account of non-hERG cardiac ion
channels and does not measure the overall effect of a compound on
cardiomyocyte function. ReproCELL has developed QTempo (QT prolongation
Examination with Myocardia derived from Pluripotent cell), a
significantly improved assay that incorporates spontaneously beating
cardiomyocytes derived from monkey, human ES cells and human iPS cells.
To validate QTempo, beating cardiomyocytes were placed on
micro-electrode arrays and challenged with reference compounds known to
cause clinical DIQTIP. Compounds tested included E-4031, astemizole,
rofecoxib, dofetilide, flecainide, lidocaine, quinidine and terfenadine
All compounds could be assayed using QTempo at drug concentrations
equal to, or lower than, those reported for the hERG assay. For
example, verapamil, which does not prolong QT interval in-vivo but
generates a false positive in the hERG assay, was correctly scored
negative for DIQTIP in the QTempo assay.
The QTempo assay is more predictive of clinical outcome
because it more closely reproduces clinical mechanisms involved in
potential regulation of cardiac action: it is not limited to a single
ion channel, and is built around beating cardiomyocytes. Data output
for QTempo resembles the familiar ECG and is readily understood by
clinicians as well as specialist scientists. Large numbers of beating
cardiomyocytes derived from hiPSC can be generated for this system
allowing parallel HTS screening of drugs. QTempo is a valuable tool for
the more accurate prediction of clinical cardiotoxicity.Cardiotoxicty
assay is the first commercialized technology for ES/iPS cell drug