The ancient Japanese art of flower arranging was the inspiration for a groundbreaking technique to create tiny “artificial brains” that could be used to develop personalized cancer treatments.
The organoids, clusters of thousands of human brain cells, cannot perform a brain’s basic functions, much less generate thought. But they provide a far more authentic model – the first of its kind – for studying how brain tumours grow, and how they can be stopped.
“This puts the tumour within the context of a brain, instead of a flat plastic dish,” said Christian Naus, a professor in the department of cellular and physiological sciences, who conceived the project with a Japanese company that specializes in bioprinting. He shared details about the technique at November’s annual Society for Neuroscience conference in San Diego. “When cells grow in three dimensions instead of two, adhering only to each other and not to plastic, an entirely different set of genes are activated.”
Naus studies glioblastoma, a particularly aggressive brain cancer that usually takes root deep inside the brain, and easily spreads. The standard care is surgery, followed by radiation and/or chemotherapy, but gliomas almost always return because a few malignant cells manage to leave the tumour and invade surrounding brain tissue. From the time of diagnosis, average survival is one year.
The idea for creating a more authentic model of glioblastoma originated when Naus partnered with a Japanese biotechnology company, Cyfuse, that has developed a particular technique for printing human tissues based on the Japanese art of flower arranging known as ikebana. In ikebana, artists use a heavy plate with brass needles sticking up, upon which the stems of flowers are affixed. Cyfuse’s bioprinting technique uses a much smaller plate covered with microneedles.
Working with Naus and research associate Wun Chey Sin, Kaori Harada of Cyfuse skewered small spheres of human neural stem cells on the microneedles. As the stem cells multiplied and differentiated into brain tissue, they merged and formed larger structures known as organoids, about two millimetres to three millimetres in diameter. Although the organoids lack blood vessels, they are small enough to allow oxygen and nutrients to permeate the tissue.
“The cells make their own environment,” said Naus, Canada Research Chair in Gap Junctions and Neurological Disorders. “We’re not doing anything except printing them, and then they self-assemble.”
The team then implanted cancerous glioma cells inside the organoids. Naus found that the gliomas spread into the surrounding normal cells.
Having shown that the tumour invades the surrounding tissue, Naus envisions that such a technique can be used with a patient’s own cells – both their normal brain cells and their cancerous cells – to grow a personalized organoid with a glioma at its core, and then test a variety of possible drugs or combinations of treatment to see if any of them stop the cancer from growing and invading.
“With this method, we can easily and authentically replicate a model of the patient’s brain, or at least some of the conditions under which a tumour grows in that brain,” said Naus. “Then we could feasibly test hundreds of different chemical combinations on that patient’s cells to identify a drug combination that shows the most promising result, offering a personalized therapy for brain cancer patients.”
Organoids are miniature organs that can be grown in the lab from a person’s stem cells. They can be used to model diseases, and in the future could be used to test drugs or even replace damaged tissue in patients.
But currently organoids are very difficult to grow in a standardized and controlled way, which is key to designing and using them. EPFL scientists have now solved the problem by developing a patent-pending “hydrogel” that provides a fully controllable and tunable way to grow organoids. The breakthrough is published in Nature.
Organoids need a 3D scaffold
Growing organoids begins with stem cells — immature cells that can grow into any cell type of the human body and that play key roles in tissue function and regeneration. To form an organoid, the stem cells are grown inside three-dimensional gels that contain a mix of biomolecules that promote stem cell renewal and differentiation.
The role of these gels is to mimic the natural environment of the stem cells, which provides them with a protein- and sugar-rich scaffold called the “extracellular matrix”, upon which the stem cells build specific body tissues. The stem cells stick to the extracellular matrix gel, and then “self-organize” into miniature organs like retinas, kidneys, or the gut. These tiny organs retain key aspects of their real-life biology, and can be used to study diseases or test drugs before moving on to human trials.
But the current gels used for organoid growth are derived from mice, and have problems. First, it is impossible to control their makeup from batch to batch, which can cause stem cells to behave inconsistently. Second, their biochemical complexity makes them very difficult to fine-tune for studying the effect of different parameters (e.g. biological molecules, mechanical properties, etc.) on the growth of organoids. Finally, the gels can carry pathogens or immunogens, which means that they are not suitable for growing organoids to be used in the clinic.
A hydrogel solution
The lab of Matthias Lütolf at EPFL’s Institute of Bioengineering has developed a synthetic “hydrogel” that eschews the limitations of conventional, naturally derived gels. The patent-pending gel is made of water and polyethylene glycol, a substance used widely today in various forms, from skin creams and toothpastes to industrial applications and, as in this case, bioengineering.
Nikolce Gjorevski, the first author of the study, and his colleagues used the hydrogel to grow stem cells of the gut into a miniature intestine. The functional hydrogel was not only a goal in and of itself, but also a means to identify the factors that influence the stem cells’ ability to expand and form organoids. By carefully tweaking the hydrogel’s properties, they discovered that separate stages of the organoid formation process require different mechanical environments and biological components.
One such factor is a protein called fibronectin, which helps the stem cells attach to the hydrogel. Lütolf’s lab found that this attachment itself is immensely important for growing organoids, as it triggers a whole host of signals to the stem cell that tell it to grow and build an intestine-like structure. The researchers also discovered an essential role for the mechanical properties, i.e. the physical stiffness, of the gel in regulating intestinal stem cell behavior, shedding light on how cells are able to sense, process and respond to physical stimuli. This insight is particularly valuable – while the influence of biochemical signals on stem cells is well-understood, the effect of physical factors has been more mysterious.
Because the hydrogel is man-made, it is easy to control its chemical composition and key properties, and ensure consistency from batch to batch. And because it is artificial, it does not carry any risk of infection or triggering immune responses. As such, it provides a means of moving organoids from basic research to actual pharmaceutical and clinical applications in the future.
Lütolf’s lab is now researching other types of stem cells in order to extend the capacities of their hydrogel into other tissues.
Learn more: Taking miniature organs from lab to clinic
Technique Produces ‘ ’ Useful in Cancer Research, Drug Screening
A UCSF-led team has developed a technique to build tiny models of human tissues, called organoids, more precisely than ever before using a process that turns human cells into a biological equivalent of LEGO bricks. These mini-tissues in a dish can be used to study how particular structural features of tissue affect normal growth or go awry in cancer. They could be used for therapeutic drug screening and to help teach researchers how to grow whole human organs.
The new technique — called DNA Programmed Assembly of Cells (DPAC) and reported in the journal Nature Methods on August 31, 2015 — allows researchers to create arrays of thousands of custom-designed organoids, such as models of human mammary glands containing several hundred cells each, which can be built in a matter of hours.