A new 3D cell culture technique developed by Purdue University researchers could make it possible to personalise treatment by understanding the contributions of different cell types in a tumour to the cancer's behaviour. The Purdue team is the first to demonstrate a 3D cell culture from individually selected cells. The technique is described in the paper, ‘Deterministic culturing of single cells in 3D’, Scientific Reports, would allow scientists to more accurately know the impact of each cell on a tumour’s formation and behaviour.
"I see a future where a cancer patient gives a blood sample, we retrieve individual tumour cells from that blood sample, and from those cells create tumours in the lab and test drugs on them," said Cagri Savran, a Purdue professor of mechanical engineering. "These cells are particularly dangerous since they were able to leave the tumour site and resist the immune system."
Each cancer patient's tumours have cells that look and act differently, making it difficult for scientists to determine treatments based on tumours grown from generic cell cultures in the lab. Cell culture is a technique that biologists use to conduct research on normal tissue growth as well as on specific diseases. A 3D cell culture permits the formation of tumours from cancer cells that grow in three dimensions, meaning that the tumour is more like a three-dimensional potato than a two-dimensional leaf.
"To produce tissue samples that are close to what we have in the body, which allows us to do high-fidelity research in the laboratory, we need to place cells in an environment that mimics their natural milieu, allowing the cells to organize into recognizable structures like tissues in vivo," said Sophie Lelièvre, a professor of cancer pharmacology in Purdue's College of Veterinary Medicine.
Current 3D cell culture techniques have their limits, said Lelièvre, who studies 3D cell culture and helps design new cell culture methods in her role as scientific director of the 3D Cell Culture Core (3D3C) Facility at the Birck Nanotechnology Center of Purdue's Discovery Park.
Real tumours, for example, are made up of cells of various phenotypes or behaviours. How different these cells are from each other is described by the term heterogeneity. The cellular heterogeneity of real tumours is not fully understood.
"Within a tumour, most cells are cancerous, but they do not have the same phenotype," Lelièvre said. "It has been proposed that some tumours respond to chemotherapy, and some are resistant depending on the degree of heterogeneity of these phenotypes. It's difficult to pinpoint treatments based on tumours grown in the lab because every patient's tumours have different levels of heterogeneity."
A typical cell culture dish or device also has a large number of cells. Scientists have no control over which cells develop into tumours. To understand how the heterogeneity inside a tumour develops and drives resistance to treatment, scientists need to study the contribution of each cell phenotype to the tumour by selecting individual cells and studying their impact.
Savran had previously demonstrated a microfluidic device capable of isolating single cancer cells from a blood sample.
"These cells are extremely rare," added Savran. "With a sample with billions of cells, we may find just one or two tumour cells. But since we've figured out how to find them, we can now hand them off to people like Sophie to help study their heterogeneity."
Savran's team created a mechanical device that successfully extracted single tumour cells from existing cell lines of breast and colon cancers. They deposited each single cell onto a matrix gel island following Lelièvre's advice.
After several days, the team observed that many of the selected single cells had developed into tumours that displayed degrees of aggressiveness corresponding to the cancer subtype of origin. The cells also recreated phenotypic heterogeneity, as shown with an imaging-based quantitative approach used previously by the Lelièvre lab.
"What Cagri's technique did is really priceless," said Lelièvre. "By simply analysing the morphology of the tumours developed from individual cells, we could confirm that the degree of heterogeneity among tumours of the same cancer subtype increases with time without any other pressure or stimuli than those exerted by the growth of the tumour itself."
The researchers also demonstrated that the degree of phenotypic heterogeneity inside a tumour depends on the cell of origin and could be related to fast-growing tumours for a specific breast cancer subtype, bringing new directions of research to understand the underlying mechanisms of aggressiveness in cancers.
"Creating specific treatments that can address an individual patient's cancer is the Holy Grail of personalized therapy, and now we're one step closer," added Savran.
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