Organovo, a San Diego regenerative medicine company developing bio-printing technology, says it has used its proprietary NovaGen bioprinter to produce 3D samples of human liver cells that show some of the same characteristics as a functional liver in the body.
The results, which Organovo is reporting today at the 2013 Experimental Biology conference in Boston, could have important ramifications for pre-clinical drug discovery. The six-year-old company describes its findings as “highly reproducible,” and says its 3D liver tissue would make it much easier for scientists to test potential drug compounds for liver toxicity.
Organovo says it is the first time scientists have been able to fabricate liver tissue samples on a petri dish that are truly three-dimensional. Organovo says the liver cells, “printed” with droplets of a supportive gel, assembled themselves into a cellular matrix about 20 cell layers thick—roughly two-thirds the thickness of a credit card. More importantly—the fabricated liver tissue produced cholesterol (needed to build and maintain cellular membranes) and expressed enzymes that metabolize drugs and toxins.
Current pre-clinical testing of drug toxicity uses tissue samples that consist of a single layer of liver cells, which flatten out in a petri dish, according to Organovo CEO Keith Murphy. Flattening the shape appears to greatly diminish their cellular function.
Murphy says cultured liver tissue now used to test drug toxicity is supplied by such companies as BD Biosciences and Life Technologies. Organovo is working to begin marketing its 3D liver tissue by next year.
Organovo says its fabricated liver tissue consists of three distinct types of liver cells organized into the kind of cell architecture seen in normal human livers. Organovo says its 3D tissue also showed cellular density and spatial positioning comparable with healthy liver tissue in the body. The company says its fabricated liver tissue even shows the beginnings of microvascular networks—blood vessels.
“We’re showing characteristic liver function that you just don’t see in a 2D liver cell culture,” Murphy says. He acknowledges that the Organovo-produced tissue isn’t completely functional, but it nevertheless represents a significant innovation, “The current model is so inadequate, and just getting halfway to perfection is so useful that we can refine it over time.”
The company says its 3D liver cells also produced such proteins as albumin, fibrinogen, and transferrin—and expressed such key liver enzymes as CYP 1A2 and CYP 3A4.
In addition, Murphy says 2D liver cell cultures “don’t usually last more than 48 hours.” In contrast, he said Organovo’s tissue culture continued to function until the experiment ended at five and a half days. To hear Murphy tell the story, cell biologists who study whether new drug candidates might have toxic effects on the liver would be thrilled to get cell cultures that survive longer than two days.
Murphy explains that creating a 3D matrix of cells enables each cell to interact with adjoining cells, so they react to drug compounds much as they would in the body. The company also has been exploring other potential uses for bioprinting, such as working with the Oregon Health & Science University (OHSU) in Portland, OR, to create “constructs” of diseased or dysfunctional human cells that could be used to help scientists better understand cancer disease mechanisms and metastatic progression.
Organovo was founded in 2007 to commercialize technology developed by Gabor Forgacs, a professor of biological physics at the University of Missouri who showed in 2005 that it was possible to “print” a tube of living tissue, forming simple blood vessels.
The company’s latest advance followed scientific research published in 2010 by a team of scientists at the University of Missouri that showed cells have an innate regenerative capability to self-assemble and self-organize. While MIT’s Robert Langer and others pioneered methods for encouraging certain types of organ cells to grow on polymer scaffolding, the Missouri team suggested bioprinting might make it easier for cells to sort and fuse themselves.
In 2011, Murphy identified pre-clinical drug testing as a potential new market for Organovo’s bioprinting technology. As he explained at the time, producing a sample of human tissue that can live outside the body makes it possible for pharma scientists to test the toxicity of an experimental drug in ways that model the reactions of a living organism.