1. Research Institute of Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Shinlim-Dong, Kwanak-Ku, Seoul 151-742, Korea, College of Pharmacy, Sookmyung Women's University, Seoul 140-742, Korea, AmorePacific R&D Center, Yongin-Si, Kyounggi-Do 449-900, Korea, Digital Biotech, Ansan, Kyounggi-Do 425-839, Korea, and Laboratory of Cellular Carcinogenesis and Tumor Promotion, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland 20892