Cytocentric Visionaries: Shannon Mumenthaler, University of Southern California
Part One: Context is Everything, for Cells and for Scientists
Dr. Shannon Mumenthaler is an Assistant Professor of Research Medicine and Lab Director of the Lawrence J. Ellison Institute for Transformative Medicine of USC. She works closely with a multidisciplinary team, including mathematicians for data analysis. Her group’s latest study published in Nature’s Scientific Reports  describes a unique technological combination of high-throughput cell imaging with physiologically relevant oxygen levels in a cytocentric barrier isolator.
In Part One of this two-part interview, we talk with Dr. Mumenthaler about her approach for acquiring a better understanding of the complex drug responses of tumors in their natural environment.
Alicia Henn: Congratulations on your recent publication! We see you as a Cytocentric Visionary because you take the cells’ point of view in the tumor microenvironment during drug treatment. We were happy to see our technology used in such an important study.
Shannon Mumenthaler: If we want to mimic what happens physiologically within a human body, it is essential to control the oxygen. I don’t feel like this is as well established within the field as it needs to be.
AH: What made you want to develop an image-based HCS system in physiologically relevant oxygen?
SM: It started with, “How are we going to get this data?”
We wanted to model the evolution of drug resistance in the context of environmental selective pressures. We decided to build a model from the ground up and included parameters which we felt needed consideration.
The Physical Sciences and Oncology Center was an NCI initiative to bring physical scientists, experimental biologists and oncologists together. We wanted to understand the dynamics of cell behavior in the presence and absence of drug. Interacting with mathematician Jasmine Foo, a co-author on this paper, we went through cell assays to get growth rate data in a quantitative manner.
I feel like that moment of interacting with this mathematician changed my whole investigative direction. I realized that the assays I had learned during my training were qualitative static end point readouts, giving us only a snapshot of what was going on. Here I had claimed I was a cell biologist for ten years, yet I had not watched how cells behaved and responded dynamically! I had been missing out on the underlying biology.
The information that cell growth is arrested, cells are dying, or some combination of both, is critical in understanding how to treat patients in the clinic. Turning that behavior into quantitative readouts was vital.
AH: So what do you think the connection is between oxygen and cell growth for drug-sensitive and resistant cells?
SM: One of the things we’re looking at is the metabolic adaptation of heterogeneous cell types within a tumor. Using this imaging platform, we can look at multiple cell types and distinguish how the stress or shock of oxygen might influence not only the tumor cells, but the host environment as well. Even when exposed to the same oxygen levels, they may respond in different ways with different signaling and metabolic pathways. Our focus now is on understanding how to target those metabolic dependencies in addition to your standard chemotherapy.
AH: What made you think that physiologically relevant oxygen is essential for predictive research?
SM: Initially, I was just thinking more about the biology. This was a while ago, when some of the early papers were starting to come out about tumor microenvironment. However, my interactions with physical scientists from different fields took me away from the very traditional training that I had, where “this is how you do cell culture,” and “these are the readouts you use,” MTS assay and flow cytometry.
I didn’t necessarily question it. Stepping out of that comfort zone of traditional cell biology made me realize how important context really is.
We did some initial studies with very simple chambers which can control oxygen for 72 hours. From those very early experiments, we noticed that growth rates were different between drug-sensitive and drug-resistant cells. We found that when you tuned oxygen levels, the sensitive cells responded to lower oxygen with slowed growth, whereas the resistant cells weren’t as affected. We realized that it’s not as simple as we thought; it’s a dynamic process. In heterogeneous gradients of oxygen, cells are going to behave differently. That was an important clue that we needed to capture.
Then we moved into the Xvivo hypoxia work station and repeated a lot of those studies, combining the hypoxia work station with quantitative imaging to get a more detailed understanding of the biology under this heterogeneous environment.
AH: Do you have any plans to go back to the stage when cells are first brought out of the body to take a look at their responses in vitro?
SM: We are working on this in our lab right now because that’s a crucial aspect to try to maintain. We’ve taken patient samples from colorectal surgeries and split the population in half. Some are placed under atmospheric oxygen, or traditional cell culture, and then others are going into more physiologically relevant conditions at 5% and 1% oxygen. We’re observing them in long-term culture from the time the tumor is removed from the body to see how oxygen changes not only the molecular makeup of the tumor, but also the phenotypic behavior of those tumor cells and the surrounding stroma.
As cell biologists, we were so concerned about how the tumor might behave that we forgot about the symbiotic relationship between the host and the tumor. Now we want to understand how the host cells are also responding and what signals they might be sending to the tumors under this environmental stress.
AH: What do you want our readership to understand about your experiences in conducting these studies?
SM: Context matters. That is a pivotal insight that I’ve learned.
Also, for me, the key is to stay open-minded as a scientist. When I have put myself in a position where I interact with people that are not necessarily like-minded or trained in a similar way to me, that’s when I have identified where holes might be in my training and in my general understanding of cell biology. That was an important lesson that I learned: Interactions with people outside my area of expertise make me think differently.
In Part Two, we talk with Dr. Mumenthaler about capturing the dimension of time in her studies of heterogeneous cellular responses.
1. Garvey, C.M., et al., A high-content image-based method for quantitatively studying context-dependent cell population dynamics. Scientific Reports, 2016. 6: p. 29752.