A Penn-led team has revealed how hydralazine, one of the world’s oldest blood pressure drugs and a mainstay treatment for preeclampsia, works at the molecular level. In doing so, they made a surprising discovery—it can also halt the growth of aggressive brain tumors.

Over the last 70 years, hydralazine has been an indispensable tool in medicine—a front-line defense against life-threatening high blood pressure, especially during pregnancy. But despite its essential role, a fundamental mystery has persisted: No one knows its “mechanism of action”—essentially how it works at a molecular level, which allows for improved efficacy, safety, and what it can treat.

“Hydralazine is one of the earliest vasodilators ever developed, and it’s still a first-line treatment for preeclampsia—a hypertensive disorder that accounts for 5%–15% of maternal deaths worldwide,” says Kyosuke Shishikura, a physician-scientist at the University of Pennsylvania. “It came from a ‘pre-target’ era of drug discovery, when researchers relied on what they saw in patients first and only later tried to explain the biology behind it.”