1. Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, 2A Nanwei Road, Xicheng District, Beijing 100050, P. R. China
2. Southern Research Institute, 431 Aviation Way, Frederick, Maryland 21701, United States
3. Tsinghua-Peking Center for Life Sciences and Department of Pharmacology and Pharmaceutical Sciences, School of Medicine, Tsinghua University, Haidian District, Beijing 100084, P. R. China