New Imaging Technique Distinguishes Cell Types in Breast Tumor Environment
It is a long-standing paradox in diagnosing and treating cancers: Visualizing tumors in their natural environment gives a clearer picture of the disease and which therapies to use, but the best images require chemicals and antibodies and genetic changes that are neither safe nor practical in the clinic.
Now, an imaging study from the University of Wisconsin Carbone Cancer Center shows that different types of cells in the breast tumor microenvironment can be identified without the use of any added chemicals. The technique, which looks at differences in fluorescence of naturally-occurring molecules in a live mouse model, could lead to improved diagnosis and monitoring of breast cancers.
"It is becoming increasingly appreciated that tumors are composed of more than just cancer cells, and include cells of the surrounding connective tissue and the infiltrating immune system," said Patricia Keely, PhD, professor of cell and regenerative biology at UW Carbone Cancer Center and senior author of the study. "It will be helpful if we can visualize and better understand all the cells that make up the tumor and its environment, and that is what this work has accomplished."
Macrophages represent one group of non-cancerous infiltrating immune system cells that is important to identify.
"Many studies, from our lab and others, have shown that the higher the number of macrophages that have infiltrated the tumor, the poorer the prognosis for a patient," said Joseph Szulczewski, a graduate student in Keely's lab and lead author of the study. "One of our collaborators has suggested that macrophages appear to help tumor cells enter the blood stream, allowing tumor cells to begin metastasizing.”
Keely, Szulczewski and colleagues did not initially seek to identify macrophages, however. They were instead trying to understand how changes in tumor cell metabolism plays a role in the growth and spread of cancer. Previous studies had shown that some cellular metabolites found in all cell types, known as FAD and NADH, naturally fluoresce depending on the metabolic state of the cell, so the researchers visualized those metabolites in mouse breast cancer tissue using a technique called multi-photon fluorescence microscopy.
Then, they found something a bit unexpected: The tumor cells nearly all had a high NADH fluorescence, and another unidentified group of cells nearly all had a high FAD fluorescence. Further experiments using antibodies which identify macrophages or genetically labeling macrophage cells confirmed the FAD-high cells were those potentially diagnostic immune cells.
"This is the first paper to use endogenous fluorescence to identify cell types and one of the first studies of metabolism in a live animal, keeping the natural environment intact and without the need to extract tissue," Szulczewski said. "Clinically this is important because if we're able to visualize live samples and identify cell types, in this context macrophage infiltration in tumors, it could aid in diagnosis and treatment."
The researchers next plan to characterize the fluorescent metabolic signatures of human breast tumor biopsies to verify that the fluorescent cellular signatures translate to humans. They will also investigate endogenous fluorescence in other tissue types, to see if the ability to distinguish cell types is useful beyond breast tumors. Lastly, they have confirmed they have a useful mouse model to track metabolic changes in tumor and surrounding cells and to learn how those changes affect tumor growth and metastatic.
This work was performed in collaboration with members of the UW Laboratory for Optical and Computational Instrumentation (LOCI), including UW Carbone Cancer Center faculty member Kevin Eliceiri, PhD, director of LOCI. It was published in the journal Scientific Reports and was supported in part by NIH grants U54 CA126511, R01 CA142833 and R01 CA114462.
Date Published: 06/10/2016