Use of selected kinase inhibitors leads to a 4- to 14-fold improvement in the yield of induced pluripotent stem cells derived from adult cells, according to a new study in Nature Communications (1). The cells have potential as therapeutics and assays.
The find could improve production of induced pluripotent stem cells (iPSCs) as well as reveal new details about the mechanism by which they are formed.
That’s a nice reward, but for scientists interested in testing hundreds or thousands of drugs against stem cell lines, it isn’t nearly enough.
Kinases regulate a number of other targets that play roles in cellular homeostasis, the cell cycle, and metabolic switching. Rana’s team speculated that kinases may play an important role in iPSC formation, potentially both enhancing and hindering it.
One of Rana’s graduate students, Zhonghan Li, surveyed more than 240 kinase inhibitors, adding them one at a time to iPSC batches to determine the effect. Several stood out as potentially useful, but Li did not stop there.
Kinase inhibitors are an inexact tool. Most aren’t terribly selective – they often have activity against a range of kinases. That makes them intriguing therapeutically. Companies have spent enormous amounts of money testing kinase inhibitors against a wide variety of cancers in the hope that a particular drug’s suite of kinase activity might prove useful in a specific tumor type.
But that broad activity made it impossible to pinpoint the specific kinases involved in iPSC development. To get around that problem, Li identified all of the potential kinases that could be affected by the inhibitors the team had identified. Li then used short-interfering RNA to knock down each kinase individually and measure its effect on iPSC transformation.
That process narrowed the responsible kinases down to p38, inositol trisphosphate 3-kinase, and Aurora A kinase, enzymes also known to have roles in tumor formation.
“We’re discovering what these kinases do. We think we will be able to understand, when we make iPSCs, what pathways are being changed. I think that’s a broader application that we are excited about,” said Rana.
The team is now using a combination of kinase inhibitors and small interfering RNA to effect transformation. Eventually the team hopes to eliminate the need for the retroviruses that are currently used to deliver the factors necessary for transformation. “That’s a fine method to do experiments in vitro, but if you want this to go into patients, you want to create iPSC cells that are virus-free. Here, the beauty is you could add a kinase inhibitor at one point (in the transformation), and when it attains the iPSC state, you take the drug away,” said Rana.
- Zhonghan, L. and T.M. Rana. 2012. A kinase inhibitor screen identifies small-molecule enhancers of reprogramming and iPS cell generation Nat Commun. 2012 Sep 25; 3:1085. doi:10.1038/ncomms2059