Breast Cancer Use Protrusions to Pass Through Membranes

Researchers in Finland have developed a method for 3D culture that accurately quantifies how cancer cells generate forces to spread within tissue, findings that could advance understanding of cancer and accelerate drug discovery.

Studies designed 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.

The team at Aalto University used the method to provide more accurate computational data on cellular forces during invasion by breast cancer cells. Currently, developing medication against breast cancer is costly, slow and often inefficient, since fewer than 5% of drug candidates that are selected using 2D cell cultures and animal experiments prove to be effective in human clinical trials.

In breast cancer, a primary tumor can form inside the breast’s mammary duct, where the cancerous cells are confined by 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,” Juho Pokki, a principal investigator at Aalto University who led the research.  The cancer cells then enter the surrounding tissue and may travel further to blood vessels to spread to the rest of the body. Blood vessels are also surrounded by a basement membrane, but breast cancer cells potentially use a similar mechanism to break through into those basement membranes. “Professor Ovijit Chaudhuri’s group at Stanford originally found this protrusion mechanism in 2018. Collaboration with his group has been the key for the physiological significance of this work,” says Pokki.

The Aalto study used 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,” Pokki says. “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.”

The study was published recently in Nano Letters.