1. Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
2. Biosciences Faculty, University of Heidelberg, 69120 Heidelberg, Germany
3. Cancer Drug Development Group, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
4. German Cancer Consortium (DKTK), 69120 Heidelberg, Germany