While therapeutic use of induced pluripotent stem cells (iPS cells) may remain years away, such cells offer great promise for modeling a variety of human diseases.
James Thomson, director of regenerative biology at the Morgridge Institute for Research, and a founder of Cellular Dynamics International (CDI), commenting on the adoption of iPS cells as drug development tools, said, “I think there are tremendous parallels to the early days of recombinant DNA in this field. I don’t think people appreciated what a broad-ranging tool recombinant DNA was in the middle ‘70s.”
He further noted that stem cell use currently faces similar questions, and although therapeutic use may eventually occur, people may “underappreciate” how widely useful these cells may be in other applications.
Multiple partnerships attest to pharma companies’ interest in using the cells for drug discovery and testing. In 2010, Roche made a $20 million deal with Harvard University and Massachusetts General Hospital to use cell lines and protocols developed by academic researchers to screen for drugs to treat cardiovascular disease and other conditions.
John Walker, then CEO of iPierian, a San Francisco-based stem cell company, said at the time, “What needs to be demonstrated is the actual application of the technology.” Walker foresaw that this work could lead to what he called an “in vitro clinical trial” in which iPS cells derived from a wide variety of individuals could be used to predict patients’ response to a drug.
Critical for drug developers, and similarly to the history of other attempts to create in vitro models to test drug reactions, is whether regulatory agencies will accept data based on their use.
And scientists say, apart from more exactly modeling human diseases, iPS cells can introduce population diversity into early drug testing programs, as they can be generated from any individual. The autologous nature of iPS cells offers research tissue from virtually any genotype, ranging from normal individuals to clinical and disease cohorts, and individuals who experience specific side effects or idiosyncratic toxicities.
CDI, based on technology developed by founder Dr. Thomson and colleague Junying Yu, commercially produces iPS cell lines and tissue cells. The company makes its cells using its iPS 2.0 method, in which two or three plasmids containing multiple reprogramming genes are introduced into the cells. These plasmids, unlike viral vectors, do not integrate into the genome itself.
The company was awarded a contract from The National Institutes of Health Center for Regenerative Medicine (NIH-CRM) to provide human iPS cell lines and terminally differentiated tissue cells from normal or specified patient populations. The contract, worth up to $7.0 million for the three-year life of the agreement, follows on two NIH-CRM contracts awarded in September 2011, whereby CDI will generate and genetically engineer iPS cell lines; the company said it has delivered on several of these cell lines already.
Last December, CDI announced the commercial launch of its human iCell® Neurons for use in neuroscience drug discovery, neurotoxicity screens, and other health research. Several companies, including Galenea and Actelion Pharmaceuticals, have been using iCell Neurons to provide models of highly differentiated human neurons.
“We have been working with CDI for some time now and are very impressed with their iCell Neurons, which provide us with a unique model of pure and highly differentiated human neurons showing real potential for measuring functional neurotransmission,” said Pascal Laeng, head of molecular and cellular pharmacology at Galenea.
“The preliminary data is very promising, and we look forward to continued collaboration with CDI to implement iCell Neurons in our high-throughput assay of synaptic function.”
iPS Cell Production
GEN asked CDI vp and chief commercial officer Chris Parker about CDI’s approach to iPS cell production, as well as pharma’s acceptance of iPSC-derived human cell models of disease states.
“The relatively easy question for us to answer is whether you can make cells that represent a portion of the brain from a patient with neurodegenerative diseases,” he explained. But, he noted, the key question was whether you can generate them in sufficient quantity to be useful in a drug development environment. “We can create inventory of neurons sufficient to allow large-scale screening endeavors.” He further commented that “the therapy won’t come from a thimbleful of cells from a diseased patient, but from a vat.”
“We consistently produce these cells in large enough quantities such that pharma companies can build infrastructure around them. For CNS discovery, we produce forebrain neurons and will shortly provide dopaminergic neurons as well.”
Parker noted that some companies that were getting out of CNS research because of the lack of valid models for neurodegenerative disease are reinvigorating their studies. This is because, “for the first time, iPSC-derived neurons are available from patients in the quality, quantity, and purity required by pharma to represent those diseases,” he said.
He noted that the company has made a tremendous investment in the technology and infrastructure to industrially produce these iPS-based cell models in quantities sufficient to support drug development enterprises. For example, he says, a particular challenge is maintaining supplies for making the cells that “some manufacturers have never produced before, and a consistent supply is critical.”
Parker further notes that the company has developed numerous collaborations that will allow it to obtain cell samples for generation of iPS cells from different patients with the same disease and make panels of those neurons in quantity.
“The difference is going to be in the donor—can the disease be manifested in the dish based on its etiology, latency, and underlying cause? Our experience has shown that either through creation of a diseased patient’s iPS-derived cells or through manipulation of a healthy iPSC-derived human cell to mimic a disease state, the ability is there to study the disease in a dish,” he said.
Significant government support focuses on studying iPS cell-based models to support drug development and other basic research for these diseases. In 2009, the National Institute of Neurological Disorders and Stroke (NINDS) funded three consortia to develop iPS cell lines from individuals with Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD). By generating these cells to become specialized types of neurons, researchers hope to determine and examine how these neurons die in each disease as well as test drugs that may slow or prevent neuronal death.
And many teams of scientists are racing to create disease models in a dish for neurodegenerative disorders. Last June in the journal Cell Stem Cell, an international team of researchers from several institutions, including UCSF’s Gladstone Institute, working as part of the HD iPSC consortium, reported that they had generated and characterized 14 iPSC lines from HD patients and from individuals without the disease.
Microarray profiling of the iPS cells, the investigators said, showed the CAG-repeat expansion association gene expression patterns that distinguish HD patient-derived cell lines from controls, and early-onset vs. late-onset HD. Further, the differentiated HD neural cells showed disease-associated changes in electrophysiology, metabolism, cell adhesion, and, ultimately, cell death for lines with both medium and longer CAG-repeat expansions.
The longer repeat lines were, however, the most vulnerable to cellular stressors and BDNF withdrawal, as assessed using a range of assays across consortium laboratories.
This HD iPSC collection, the authors concluded, represents a resource to elucidate disease mechanisms in HD and provides a human stem cell platform for screening new candidate therapeutics.
“The track record of animal models for predicting therapies that will work in people has been poor, making drug discovery for neurodegenerative diseases very costly—and therefore less attractive to drug companies. We hope to change that,” said Gladstone senior investigator Steve Finkbeiner, M.D., Ph.D.
But other investigators note that plenty of challenges remain before enshrining iPS cells as a true reflection of human disease states. Although, they said, seeing expected disease phenotypes in differentiated cells from patient-derived iPSCs is “encouraging”, the next challenge will be discovering phenotypes in complex or idiopathic diseases including amyotrophic lateral sclerosis or AD or type 2 diabetes.
Nonetheless, as noted by Dimos et al., in their review of iPS cell technology, patient-derived iPS cells may prove highly complementary to current drug discovery methodologies, particularly high-throughput human pharmacology applications.