By using a new 3D culture method, researchers from Finland have discovered cancer cells can spread by rapidly applying forces to tissue material.
Research to understand how cancers grow and spread has conventionally been done on two-dimensional, flat cultures of cells, which is very different to the three-dimensional structure of cells in the body. 3D cell cultures that incorporate tissue material have been developed, but the methods to measure how cancer cells use forces to spread have been lacking.
Now, researchers have developed a new method for 3D culture to accurately quantify how cancer cells generate forces to spread within tissue.
Juho Pokki, a principal investigator at Aalto University, Finland, who led the research, said: “We have applied the method for investigation of early progression of breast cancer.”
A primary tumour can form inside the breast’s mammary duct, where the cancerous cells are confined by a special membrane, called a basement membrane. Breast cancer cells are larger than the pores in these membranes, so they must break through to spread to other tissues. Previously, researchers thought that cells use enzymes to dissolve membranes, but now it is understood that breast cancer cells use another mechanism involving cellular protrusions to pass through the membranes.
“In this mechanism, breast cancer cells use forces generated by the protrusions to open up channels within the membrane material,” Pokki added. “Then, the cancer cells enter the surrounding tissue and may travel further to blood vessels to spread to the rest of the body. In fact, the blood vessels are also surrounded by a basement membrane. Breast cancer cells potentially use a similar mechanism to break through into those basement membranes.”
The new study uses 3D cell cultures composed of breast cancer cells and standard basement membrane material. Within the 3D cultures, researchers embedded two types of biocompatible spheres: one type moved along with forces generated by cancer cells, and the other type measured force-constraining mechanics. A modified fluorescence microscope was used to take videos of these spheres and track them at nanoscales. This allowed the researchers to measure the force pulses coming from cancer cells.
“Previous studies had measured motion of cellular protrusions over longer periods of time, but our study showed that a lot can happen in just 15 minutes. We saw nanoscale movement and force pulses within a few seconds, which is startling. Further, these pulses accumulate, resulting in stronger forces applied on the membrane material.
Pokki concluded: “This is currently the most accurate method for measuring how cellular forces are generated in 3D culture.”
Breast cancer is the most common form of cancer for women globally. Every year, over 350,000 women are diagnosed with breast cancer in the European Union alone.
This study, a collaboration between scientists at Aalto University and Stanford University, was published in the journal Nano Letters.
Image: An illustrated microscope view of a 3D culture of cancer cells. A cancer cell generates forces (in red) moving the tissue material further. The new technique detects the material movement to compute cellular forces. © Linus Nolte/ Juho Pokki group/ Aalto University.