1. Department
of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, United States
2. Laboratory
of Cancer Biology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, United States
3. Basic Science Program,
Leidos Biomedical Research, Inc., Chemical Biology Laboratory, Frederick National Laboratory for Cancer Research, Frederick, Maryland 21702, United States