New Imaging Technique Helps to Understand Bioprinted Glioblastoma Tumors

With cancer as the second leading cause of death globally, hundreds of researchers continue their efforts to fight the disease. Years of oncology investigations have suggested that each person’s cancer has a unique combination of genetic changes – such as mutations in DNA – yet some types are considered to be more combative, uncontrollable, and fatal than others. In the case of glioblastomas, a very aggressive brain tumor, the median survival time is between 15 to 16 months in people who get surgery, chemotherapy, and radiation treatment. However, a median means that only around half of all patients with this tumor survive to this length of time. Experts suggest that since glioblastoma is the deadliest form of brain tumor, less than 10 percent of people who are diagnosed with it will survive more than five years.

Glioblastomas grow very fast inside the brain. The National Cancer Institute indicates that its cells copy themselves quickly, and a lot of blood vessels feed these tumors. We have reported quite a few researchers in the last months that are developing bioprinting techniques to work on different ways to tackle the disease. Now a team of scientists has created a new imaging technique that enables the study of 3D printed brain tumors.

In a recently published paper in Science Advances, Xavier Intes, a professor of biomedical engineering at Rensselaer Polytechnic Institute, New York, joined a multidisciplinary team from Northeastern University, in Boston, and the Icahn School of Medicine at Mount Sinai, New York, to demonstrate a methodology that combines the bioprinting and imaging of glioblastoma cells cost-effectively that more closely models what happens inside the human body.

“There is a need to understand the biology and the complexity of the glioblastoma,” said Intes, who is also the co-director of the Center for Modeling, Simulation and Imaging for Medicine (CeMSIM) at Rensselaer. “What’s known is that glioblastomas are very complex in terms of their makeup, and this can differ from patient to patient.”

To create their 3D tumor cell model, a team, led by Guohao Dai, an associate professor of bioengineering at Northeastern University and corresponding author on the study, made bioinks out of patient-derived tumor cells and printed them along with blood vessels. That vasculature allowed the printed tissue to live and mature, enabling researchers to study it over a matter of months.

As detailed in the paper, an integrated platform enabled generating an in vitro 3D bioprinted glioblastoma multiforme (GBM) tumor model with perfused vascular channels that allow long-term culture and drug delivery, as well as a 3D imaging modality – a second-generation mesoscopic fluorescence molecular tomography (2GMFMT) imaging system – that enables researchers to noninvasively assess longitudinal fluorescent signals over the whole in vitro model. And according to Northeastern University, this work could help medical professionals better understand how the tumor grows and to speed up the potential discovery of new drugs to fight it.

The study indicated that each imaging session exposes laser light on samples, and cells undergo stressful conditions during these long imaging processes, which reduces the cell viability. Thereby they selected an imaging modality not only for the shortest possible image acquisition time but also without potential photodamage. The 2GMFMT offers the least stress on cell culture allowing frequent imaging sessions without compromising tissue integrity.

“This is a very difficult brain tumor to treat,” said Dai. “And it’s also difficult to do research on the brain tumor, because you cannot really see what’s happening.”

Associate professor Guohao Dai (Image: Matthew Modoono/Northeastern University)

Dai also described that animal studies (typically done in mice or rats) to understand a tumor’s development, are expensive, time-consuming, and don’t allow for day-to-day observations of the same tumor in living tissue. Dai’s lab, specializing in 3D printing live tissue, grew a three-dimensional model to act as brain tissue for tumor cells to infiltrate so that they would be able to study glioblastomas more directly.

“We use human brain blood vessel cells, and connect them with all the neurons, pericytes, astrocytes, the major cell types in the human brain,” Dai said. “A water-based substance known as a hydrogel serves as a matrix to hold these cells in place. Then we use 3D printing to stack them in three-dimensional fashion.”

In the middle of the structure, which is only a few millimeters thick, the researchers place glioblastoma tumor stem cells. The cells are derived from brain tumor patients thanks to Hongyan Zou, a neurosurgeon and professor of neuroscience at Mount Sinai’s medical school and head of the Zou Lab at the Icahn School of Medicine.

“We can observe how the brain tumor cells aggressively invade, just like what we see in patients,” Dai went on. “They invade everywhere. We treated the tumor with the same kind of drug you give to a patient when they undergo chemotherapy. We monitored this chemotherapy over two months, and what we found was that the chemotherapy was not able to kill the tumor.”

To get an accurate picture of what’s happening inside the 3D model without disrupting it, Intes used a laser to scan the sample and quickly create a 3D snapshot of the cellular structure, an imaging technique developed in his lab. This combination of techniques allowed them to evaluate the effectiveness of a commonly used chemotherapy drug, temozolomide (TMZ). Initially, the tumor shrank in response to the drugs, but then it grew back swiftly and aggressively. This indicates that the drug did not work in the long term, which seems to line up with the experience of patients with glioblastoma.

The TMZ chemotherapy treatment traveled through the channels provided by the bioprinted blood vessels. The team claims that in the body, drug delivery to glioblastoma cells is especially complicated because of the blood-brain barrier, a wall of cells that blocks most substances from reaching the brain. It appears that the team’s method provides a more accurate evaluation of a drug’s effectiveness than directly injecting the therapy into the cells.

Moreover, Dai suggested that they need to develop and screen other chemotherapy drugs, and this model may be able to speed up that process, since this method could be used to weed out unsuccessful drugs early, ensuring that only the most promising ones move to animal, and eventually human, trials.

Dai considered that “you have a tremendous amount of time and cost associated with animal research,” but “with our 3D glioblastoma model and imaging platform, you can see how the cells respond to radiation or chemotherapy very quickly.”

GBM spheroids cultured with glial cells and endothelial cells within soft extracellular matrix (Image: Northeastern University)

They conclude that beyond the necessity to guide the development of new drugs, efficient model systems that enable fast and predictive evaluations of candidate drugs are a critical need. To provide biological relevant experimental settings in which drug efficacy can be assessed, a suitable tumor growth environment and long-term culture capabilities are required.

The publication offers a detailed recount of the new technique that according to Intes, could allow researchers to evaluate the effectiveness of multiple drugs at the same time. According to Rensselaer’s School of Engineering, Intes pointed out that it is not yet realistic though for studying the effectiveness of certain therapeutics on a person’s tumor because of the short time that clinicians often have to provide treatment.

“We developed a new technology that allows us to see, first, if the cells are growing, and then, if they respond to the drug,” conveyed Intes.

If glioblastomas are the most common malignant brain tumor and one of the hardest to treat, then this team is certainly moving in the right direction. Glioblastoma tumor growth is considered to almost always outpace chemotherapy and radiation treatments, so the remaining available treatments are primarily experimental. With so much uncertainty with regards to a successful treatment, new techniques, like this one, offer an encouraging message. Researchers are hurrying to mimic the conditions of tumors thanks to 3D bioprinting and the ability to generate bioinks out of patient-derived tumor cells. Moving from lab research to actual clinical trials might take a long time, but at least the technology is providing the strong foundations needed to understand the true nature of these malignant tumors.