Cancer-fighting compounds that look promising in the laboratory often fail in human clinical trials. One reason: standard tumor models consist of cancer cells growing in a flat plastic dish with nothing close to the complex architectural development and ongoing feedback from other tissues that take place in a living body.
Using 3-D printing, scientists at the OHSU Knight Cancer Institute are building incredibly realistic laboratory models of human cancers. The printer deposits living cells layer upon layer to form tissues composed of many cell types. Within these “bioprinted” tissues, cancer cells grow and exchange signals with other cell types. Together they mature, secrete extracellular matrix and self-organize to form features typical of real tumors, such as networks of blood vessels.
“When we print them, endothelial cells are just mixed in with other cell types. They find each other and organize into vessels,” says Ellen Langer, Ph.D., co-first author of a paper in Cell Reports describing the findings. Langer is a research assistant professor in the Department of Molecular and Medical Genetics at OHSU.
Cancer cells grown in three-dimensional, bioprinted tissues offer many advantages over standard tumor models, such as cancer cell lines and immune-deficient mice implanted with human tumors. Cell lines are too simplistic. Mouse xenografts are costly and time-consuming to develop. Their lack of functioning immune systems means they can’t model immune interactions. And mouse biology can differ in important ways from human biology.
“With bioprinting, we can use all human cells,” says senior author Rosalie Sears, Ph.D. “We can even use cells from the patient to recreate their tumors, and create a multitude of replicas to test.” Sears is a professor of molecular and medical genetics in the OHSU School of Medicine and co-director of the Brenden-Colson Center for Pancreatic Care.
The bioprinted tumor model neatly replicates aspects of cancer biology that are relevant to treatment response
The bioprinter technology was developed by Organovo Inc., a San Diego-based company. The OHSU researchers are pioneering its use in exploring cancer biology and testing experimental cancer treatments.
Co-first author Brittany Allen-Petersen, Ph.D., a postdoctoral fellow in the Sears lab, developed methods for taking pancreas cancer cells from patients, expanding their numbers, and growing them in 3-D printed tissue with a mixture of endothelial cells and normal human pancreatic stellate cells, which are thought to be responsible for the dense growth of fibrous tissue that occurs in pancreas cancers. (Langer, Allen-Petersen and Sears are inventors of technology that has been optioned to Organovo, Inc. by OHSU, a potential conflict of interest reviewed and managed by OHSU.)
The researchers are using bioprinted tissue to explore the role of the tumor microenvironment. They are able to add different cell types, such as fat cells that secrete hormones, and cells from the bone marrow known to also interact with tumors, and study the impact.
“If we include bone-marrow derived mesenchymal stem cells, we see increased collagen deposition,” Langer says. Collagen is not just a passive scaffold around cells, it is actively involved in promoting tumor progression by means of chemical and mechanical signals in the tumor microenvironment.
The researchers are also experimenting with the addition of immune cells in bioprinted tumor models. “We’re very interested in using this system to study crosstalk between cancer cells and resident immune cells, for example, how immune cells support cancer cell growth and how cancer cells suppress anti-tumor immune cells,” Sears says.
It may be possible, they say, to build tissue models that recapitulate the earliest stages of tumor development to advance early detection research. That would enable researchers to look for signals that allow pre-cancerous cells to avoid immune detection, survive and proliferate.
Already, the bioprinted tumor model neatly replicates aspects of cancer biology that are relevant to treatment response. In one experiment, the OHSU researchers compared cancer cells grown in traditional tissue culture with cancer cells grown in 3-D bioprinted tissue when both were treated with the chemotherapy drug doxorubicin. Cancer cells in 3-D culture were 20 times more resistant to the drug. The researchers say that may be due to the influence of the extracellular matrix and spatial organization of cells in the 3-D tissues.
In another experiment, the OHSU researchers treated bioprinted tissues with Sunitinib, a drug used to block the growth of new blood vessels in tumors. The drug dramatically reduced the blood-vessel-like networks in the bioprinted tumor models. Previous studies have shown that Sunitinib and related drugs can, in some patients, promote tumor aggressiveness at least in part through increasing collagen deposition and signaling. In bioprinted tumor models, Sunitinib treatment was followed by significant increases in collagen deposition, a result in line with results with tumors engrafted into animals.
“The flexibility of this system, including the ability to manipulate cells prior to printing, will facilitate mechanistic studies of the microenvironmental influence on tumor phenotypes and allow for patient-specific models of tumor biology,” their paper concludes.
Modeling Tumor Phenotypes In Vitro with Three-Dimensional Bioprinting by Ellen M. Langer, Brittany L. Allen-Petersen, Shelby M. King, Nicholas D. Kendsersky, Megan A. Turnidge, Genevra M. Kuziel, Rachelle Riggers, Ravi Samatham, Taylor S. Amery, Steven L. Jacques, Brett C. Sheppard, James E. Korkola, John L. Muschler, Guillaume Thibault, Young Hwan Chang, Joe W. Gray, Sharon C. Presnell, Deborah G. Nguyen and Rosalie C. Sears. Cell Reports (January 15, 2019)
The research was funded by NIH R01 CA196228 (RCS), NCI U54 grant CA209988 (RCS and JWG), SBIR Phase I Contract Grant HHSN261201400024C (Organovo, Inc.), Collins Medical Trust (EML), as well as philanthropic support from Brenden-Colson Center for Pancreatic Care Program Leader Discovery Science Funding and Prospect Creek SMMART Trials. Flow Cytometry work was performed in an OHSU Shared Resource supported by the Knight Cancer Institute Cancer Center Support Grant 5 P30 CA69533.