Testing Drugs Under Realistic Conditions Reveals Hidden Behaviors Scientists Missed

A drug once dismissed as ineffective suddenly worked when scientists tested it under more realistic conditions that mimic the human body. The finding, from Northwestern University researchers, reveals that a medicine's effectiveness can change dramatically depending on the conditions inside our cells, and that standard lab testing may be causing scientists to overlook viable drug candidates.

The study, published in Nature Structural & Molecular Biology, centers on two fundamental features of human biology: body temperature and intracellular calcium levels. When incorporated into experiments, these factors exposed drug activities that had previously gone undetected.

“Drugs don’t act in isolation,” said Wei Lü, who co-led the study with Juan Du. “They act within the physiological environment of the cell. By incorporating temperature and calcium into our experiments, we uncovered drug activities that were completely invisible before.”

In early drug evaluations, researchers commonly test compounds at room temperature in artificial chemical environments that don't reflect conditions inside the human body. But proteins, the molecules that most drugs target, are dynamic and shape-shifting. Their structure responds to temperature and chemical signals like calcium, meaning a drug’s ability to bind to a protein can change based on surroundings.

The Northwestern team focused on TRPM4, a protein channel involved in heart rhythm and immune responses. When they tested triphenylphosphine oxide (TPPO) under simplified lab conditions, the compound appeared inactive. But at body temperature and with realistic calcium levels, the same compound powerfully activated the TRPM4 channel.

“This completely overturned what we thought we knew,” said Du. “It shows that we may be overlooking important drug candidates simply because we are not testing them under the right conditions.”

A second experiment added another layer. A known TRPM4 activator called Necrocide-1 behaved as expected at low calcium levels—but largely lost its effect when calcium levels increased, as they often do in stressed or diseased cells. “This tells us drug behavior is not fixed,” Lü said. “The same molecule can behave very differently depending on the biological context.”

Using cryo-electron microscopy, the team found that TRPM4 contains a flexible drug-binding region that physically changes shape depending on temperature and calcium, directly determining how compounds interact with the protein.

The researchers describe their approach as “environment-aware pharmacology”—designing drugs that activate only under specific disease conditions, such as inside damaged cells where calcium is abnormally high. This could improve treatment precision and reduce side effects. The team also suggests these hidden environmental effects may extend well beyond TRPM4 to other drug targets.

“By bringing physiological conditions back into the picture, we can better understand how proteins function—and how to target them effectively,” Du added.