When researchers gave SARS-CoV-2 to two groups of mice—one treated with MB-32 and one untreated—every single treated mouse survived. In the control group, every mouse died. That stark contrast, documented in peer-reviewed research published in Nature Communications, captures the therapeutic promise of a new antiviral drug developed by a collaborative team from the University of Hong Kong and Tsinghua University. Called MB-32, it represents a fundamentally different approach to fighting coronaviruses: rather than attacking the virus itself, it protects the doorway the virus needs to enter human cells. The findings offer a glimmer of hope that the world might be better prepared for the next pandemic, whenever it arrives. Professor Chen Zhiwei, chair professor of immunology and immunotherapy at HKUMed who led the research, explained the strategy simply: by targeting the human receptor ACE2 instead of viral proteins, scientists can "bypass many of the constraints imposed by viral evolution and adopt a strategy of 'meeting changes with constancy.'" Unlike existing antivirals that target viral components like proteases or polymerases—parts of the virus that mutate rapidly, enabling drug resistance—ACE2 is a human protein that remains largely unchanged across coronavirus variants. The team screened more than 20,000 small-molecule compounds before identifying MB-32 as their lead candidate. Through medicinal chemistry optimization, they engineered a molecule that binds to a specific site on ACE2, inducing a structural change that prevents the coronavirus spike protein from gaining entry. "It is like changing the shape of a receptor's 'lockhole' so that the virus, acting as a 'key,' can no longer fit," said first author Dr. Liu Li. The drug proved effective against SARS-CoV-2 variants including Alpha, Delta, and several omicron sublineages, as well as the original 2003 SARS virus and related bat- and pangolin-derived coronaviruses. Crucially, it showed no effect on viruses that use different entry mechanisms, confirming its precise target. Perhaps equally important, MB-32 preserves ACE2's normal physiological functions—particularly its role in regulating blood pressure and maintaining cardiovascular health. Preliminary safety studies found no adverse effects on blood pressure, heart rate, or heart rhythm in animal models. Delivered via intranasal spray, the drug concentrates where coronaviruses first attack—the respiratory tract—while limiting exposure elsewhere in the body. In transmission models, MB-32 even blocked the virus from spreading between infected and uninfected animals, suggesting potential for interrupting chains of infection. While the research remains in the preclinical stage, the team is pursuing further development. Should MB-32 prove safe and effective in human trials, it could become a versatile tool in the antiviral arsenal—not just for COVID-19, but for any future coronavirus that relies on ACE2 to infect cells.