iPS cells: Bioactive small molecules make exogenous reprogamming genes dispensable!
Cell reprogramming of Mouse and Human somatic cells to induced Pluripotent Stem Cells (iPSC) have opened outstanding new opportunities for biomedical research. iPSC are now becoming unique cellular models for personalized therapies and regenerative medicine.
In parallel, these pluripotent cells are potientially “unlimited” cellular sources from healthy and disease tissues for in vitro drug dicovery and toxicology studies.
Safety and kinetics issues of initial viral cell reprogramming approaches
iPSC were initially generated by using viral transduction methods with insertion of transcription factor. Among these reprogramming genes, two (c-Myc and Oct4) are known to be related to cancer pathways.
In addition to risks linked to genome integrity and cancers, reprogramming viral procedures were long (several weeks) and relatively unefficient (<0.001%). (1, 2)
To overcome these hurdles, obtain clinically relevant iPSC and optimally support iPSC reprogramming, researchers have progressively designed experimental protocols combining both chemical and genetic approaches (3). In 2009, Lin et al. described a chemical approach for transforming efficiently adult human cells iPSC (200 times more efficient and twice as fast as conventional methods (4)).
Small molecules make exogenous reprogamming genes dispensable
Small molecules are attractive alternatives for iPSC generation. In 2013, Hou et al. have introduced the notion of “Chemically induced Pluripotent Stem Cells” (CiPSC). In their work, the authors showed that CiPSC share characteritics with ESCs. They finally concluded that a well-defined chemical reprogramming strategy has potential use in generating functional desirable cell types for clinical applications (5). This has been confirmed by Wang et al. who used a cocktail of 4 small molecules for cardiac reprogramming with one single reprogramming factor (Oct4). Such Induced cardiomyocytes showed cardiac-specific features and were spontaneously beating. (6)
Recently, various combinations of small molecules have been used to reprogram mouse fibroblasts to pancreatic lineages with Functional ß-like cells (7) and to generate human fibroblast-derived hepatocytes able to repopulate mouse livers. (8)
(1) Takahashi et al. “Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by De?ned Factors” (2007) Cell no. 131, 861–872.
(2) Yu et al. “Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells” (2007) Science, Vol. 318 no. 5858, 1917-1920. DOI: 10.1126/science.1151526
(3) Shi et al. “A Combined Chemical and Genetic Approach for the Generation of Induced Pluripotent Stem Cells” (2008) Cell Stem Cell, Vol. 2, 525-528. DOI 10.1016/j.stem.2008.05.011
(4) Lin et al. “ A chemical platform for improved induction of human iPSCs” (2009) Nat Methods, Vol. 6 no. 11, :805-808. DOI: 10.1038/nmeth.1393. Epub 2009 Oct 18.
(5) Hou et al. (2013) “Pluripotent Stem Cells Induced from Mouse Somatic Cells by Small-Molecule Compounds” (2013) Science, Vol. 341 no. 6146, 651-654. DOI: 10.1126/science.1239278
(6) Wang et al. “Small Molecules Enable Cardiac Reprogramming of Mouse Fibroblasts with a Single Factor, Oct4” (2014) Cell Reports, Vol. 6 no.5, 951-960. doi:10.1016/j.celrep.2014.01.038
(7) Li et al. “Small Molecules Facilitate the Reprogramming of Mouse Fibroblasts into Pancreatic Lineages” (2014) Cell Stem Cell, Vol. 14 no. 2, 228-236. DOI 10.1016/j.stem.2014.01.006
(8) Saiyong et al. “Mouse liver repopulation with hepatocytes generated from human fibroblasts” (2014) Nature. DOI:10.1038/nature13020
Bioactive small molecules as unique reprogramming factors
No doubt, small molecules will remain at the center of numerous experimental reprogramming approaches. Will they replace completely or partially classical reprogramming transcription factors?
Because of their cell permeability and lack of immunogenicity, small molecules overcome the main safety and technical issues seen with viral reprogramming methods. Researchers can define their cocktail of small molecules to specifically modulate targeted signal transduction pathways and activate (or/and inhibit) proteins involved in cellular fate.
Where to find a collection of high quality small molecules?
Whatever the reprogramming strategy used (transdifferentiation, dedifferentiation, transdetermintation, direct cell convertion…), the access to a large collection of pure and affordable small molecules is crucial.
Below is a selection of small molecules from high quality sources available at tebu-bio.com:
- BIX-01294 (HMT inhibitor)
- CHIR-99021 (GSK3 inhibitor)
- Cyclopamine (Inhibits hedgehog signaling)
- DAPT – (initially described as a potent Gamma-secretase inhibitor, DAPT is regularly used in cell reprogramming strategies)
- PD 0325901 (MEK inhibitor)
- DLPC (Dilauroyl PhosphatidylCholine (liver receptor homologue-1 agonist)
- Forskolin (Adenylate cyclase activator)
- Icg-001 (Wnt/b-catenin inhibitor)1
- KY-02111 (Wnt pathway inhibitor)
- NA Valproate (HDAC inhibitor)
- SAHA (Suberoylanilide Hydroxamic Acid, Vorinostat, Zolinza™) (HDAC inhibitor)
- SB 431542
- VAP – Valproic Acid (HDAC inhibitor)
- Y-27632 (ROCK kinase inhibitor)