Enzyme inhibitors block replication of SARS virus

Finding could help speed SARS drug discovery

The study was conducted by researchers from Scripps Research; the Genomics Research Center, Academia Sinica, Taiwan; and the National Taiwan University. It is being published today in the journal Chemistry and Biology (Vol. 13, No. 3).

Chi-Huey Wong is currently the Ernest W. Hahn Chair in Chemistry at the Skaggs Institute of Chemical Biology and directs the Scripps Research lab heading the study. He said the new finding is an important step in developing a possible drug treatment against SARS.

"We have been working on the problem of SARS since the epidemic started in 2003," Wong said. "This new class of inhibitors represents the most potent SARS virus protease inhibitors known today."

The path to today's research finding has taken several years. In 2002, Severe Acute Respiratory Syndrome (SARS) emerged in rural China and eventually spread to 32 countries, according to the World Health Organization. SARS is caused by a ring-shaped virus, known as a coronavirus. The SARS coronavirus is suspected of originating in animal populations before migrating to humans. Hardest-hit were six Asian nations. By the time the epidemic had been controlled in 2003, the disease infected more than 8,000 people, causing 800 deaths. There is no current effective treatment or vaccine.

Researchers have known since 2003 that a site on the virus is responsible for mediating proteases that allow the virus to replicate. Since then researchers have been testing protease inhibitors to lock up this site, known as SARS 3CLpro, and effectively stop the virus from infecting additional cells in the body.

In 2004, Wong's lab discovered that Lopinavir, a protease inhibitor of HIV also known as TL3, also served as weak inhibitor of the SARS 3CLpro site (PNAS, 101, 10012-10017). Since then, members of Wong's group further studied Lopinavir and are preparing it for clinical trials against SARS.

Researchers in Wong's lab at Scripps Research and in Taiwan have been looking at other Liponavir-related compounds for similar blocking effects. During these experiments, they found that a group of catalyzing agents used to help promote chemical reactions in the laboratory were actually more powerful in blocking the SARS protease than either the Lopinavir or any of the target compounds.

These organic compounds are called benzotriazole esters. The esters entered the SARS protease site, formed an intermediary compound, then inactivated the SARS enzyme. The findings were confirmed using mass spectrometry analysis of the enzyme intermediary.

"These benzotriazole esters are relatively stable and act as suicide inhibitors," Wong said. "They block the enzyme, are transformed through a co-valent bond, and are unable to get out."

Wong said the findings published today provide better insight into the mode of action of the enzyme, which may lead to development of a drug against SARS. The findings were made by using rapid drug discovery techniques developed in the Wong lab to screen large numbers of weak enzyme inhibitors, and then attaching additional compounds to look for stronger reactions.

Research Associate Chung-Yi Wu, a member of the Wong lab, is the paper's lead author. He said the finding was unexpected.

"We wanted to improve Liponavir activity," Wu said. "But we found this very surprising and serendipitous result."

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Other authors of the study include Ke-Yung King, Chih-Jun Kuo, Jim-Min Fang, Ying-Ta Wu, Ming-Yi Ho, Chung-Lin Liao, Jiun-Jie Shie and Po-Huang Liang of the Genomcs Research Center, Academia Sinica, Taiwan and National Taiwan University, Taipei, Taiwan. The study was supported by the National Science Council, Taiwan, and Genomics Research Center, Academia Sinica. The work is supported by the National Science Council, Taiwan and Genomics Research Center, Academia Sinica.

About The Scripps Research Institute
The Scripps Research Institute, headquartered in La Jolla, California, in 18 buildings on 40 acres overlooking the Pacific Ocean, is one of the world's largest independent, non-profit biomedical research organizations. It stands at the forefront of basic biomedical science that seeks to comprehend the most fundamental processes of life. Scripps Research is internationally recognized for its research into immunology, molecular and cellular biology, chemistry, neurosciences, autoimmune, cardiovascular, and infectious diseases, and synthetic vaccine development. Established in its current configuration in 1961, it employs approximately 3,000 scientists, postdoctoral fellows, scientific and other technicians, doctoral degree graduate students, and administrative and technical support personnel. Scripps Florida, a 364,000 square-foot, state-of-the-art biomedical research facility, will be built in Palm Beach County. The facility will focus on basic biomedical science, drug discovery, and technology development. Palm Beach County and the State of Florida have provided start-up economic packages for development, building, staffing, and equipping the campus. Scripps Florida now operates with approximately 160 scientists, technicians, and administrative staff at 40,000 square-foot lab facilities on the Florida Atlantic University campus in Jupiter.


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