New ways to modulate cell activity remotely

Imagine being at a big marquee event at an arena, like the Super Bowl, with the roar of the crowd, the smell of hot dogs, and a sea of jerseys all merging into one chaotic blur. While the frenzied, exciting environment certainly enhances your viewing experience, it can also make it difficult to find the people you came with if you get separated. If you’re communicating by phone or waving from the stands, it can be an exhausting game of hide-and-seek amid the noise and commotion.

Now imagine if you had a way to remotely guide them to you with pinpoint precision—an app that highlighted their exact location and gently nudged them to move in the right direction. That, in essence, is what bioengineer Lukasz Bugaj and his team at the University of Pennsylvania have achieved—except the arena is the human body, and the people you are directing are engineered cells sent in to carry out specific tasks like killing cancer or repairing damaged tissue.

“There’s a lot going on in complex living systems, so when we send modified cells into the body to execute a particular function, like to go in and find pathogens or cancerous cells, wouldn’t it be great if we could communicate with them, guide them, make sure they’re going exactly where they need to go, at the right time, to do the right thing?” asks Bugaj.

In a new paper, the Bugaj Lab introduces tools that essentially, “remotely and non-invasively communicate with and control the activity of cells” once they’ve entered the arena. Published in Nature Methods, the paper focuses on a protein the team developed called Melt, which can be toggled by temperature.

From light to heat: developing Melt

Controlling cellular behavior with light—a field known as optogenetics—has been a game-changer in biology since its development almost two decades ago. It involves researchers using light-sensitive proteins to activate or deactivate specific pathways within cells. But there’s a catch, light doesn’t penetrate deeply into tissues, making it impractical for many therapeutic applications.

“We needed something that could go deeper,” says Bugaj. “That’s where temperature comes in. Heat is a more penetrant stimulus—it travels through tissues in ways visible light simply can’t.”

The breakthrough came from a surprising source, a fungus known as Botrytis cinerea, infamous for causing rot in strawberries and grapes. The fungus produces a protein called BcLOV4, which was initially studied for its light sensitivity, but when Bugaj’s lab introduced the protein into human cell lines, something unexpected happened.

“We noticed that the protein wasn’t just responding to light—it was responding to temperature,” says first author and former Ph.D. student in the Bugaj Lab, Will Benman. “That’s when we thought, ‘okay, that’s actually really, really exciting,’ because there are a lot of known proteins that respond to light, but not as many proteins that respond to temperature.”

The team wondered, could they engineer the protein to respond solely to temperature? And if so, could they use it to control cellular behavior in a non-invasive way? Over months of experiments, they modified BcLOV4 into a new protein that acts as a purely temperature-sensitive tool: Melt—short for Membrane Localization using Temperature.

“We broke its light sensitivity and tuned its temperature sensitivity to operate at human body temperatures,” says Pavan Iyengar, a former undergraduate researcher in the Bugaj Lab. “Now we have a switch that works like a dimmer—you raise the temperature, and it activates; lower it, and it deactivates.”

By fusing Melt to different cellular pathways, the team demonstrated precise control over processes like cell signaling, peptide breakdown, and even cell death. In one striking experiment, they showed that applying a device for topical cooling—a “glorified icepack”—to an animal model could trigger cancer cell death, without the systemic toxicity of traditional chemotherapy.

Melt in action

The team also explored Melt’s use in basic research, where controlling cellular pathways in real-time can reveal new insights into how cells function.

“It’s kind of a rare case where a protein can do so many different things,” says co-first author of the Melt paper and a Ph.D. student in the Bugaj Lab, Zikang (Dennis) Huang. “It can sense light, it can sense temperature, it can go to the membrane, and also has some other molecular functions as well, whereas most known natural proteins may have only one of these functions. Once we figure out how this works, we can potentially design more new proteins that have those integrated functions in just a single protein.”

In the near term, that the team believes Melt could aid in key discoveries in cancer therapies, enabling treatments that are more targeted and less toxic.

“This work was only possible because of funding from the federal government and also through pilot funds from the Center for Precision Engineering for Health at Penn. Building from this initial support and our early results, our lab recently won a large NIH grant to further develop and test the efficacy of temperature-controlled tumor cell ablation in physiological models of cancer,” says Bugaj. “Further down the line, these tools could pave the way for new types of cell therapies that respond to physiological cues like fever or inflammation.”

Lukasz Bugaj is an assistant professor in the Department of Bioengineering in the School of Engineering and Applied Science at the University of Pennsylvania.

William Benman recently completed his Ph.D. in bioengineering at Penn Engineering and is now a postdoctoral researcher at the California Institute of Technology.

Zikang (Dennis) Huang is a Ph.D. candidate at Penn Engineering.

Pavan Iyengar graduated from Penn’s College of Arts and Sciences and is now a medical student at the University of Florida.

Other authors include Thomas Mumford and Delaney Wilde, both Ph.D. students in Penn Engineering.

The research was supported by the National Institutes of Health (Grants R35GM138211 and S10 1S10OD026986); the National Science Foundation (Award 2145699); and the Penn Center for Precision Engineering for Health.