1. Buck Institute for Age Research, 8001 Redwood Blvd., 94945, Novato, CA, USA
2. the Mass Spectrometry Facility, Department of Pharmaceutical Chemistry, University of California, 94143-0446, San Francisco, CA
3. the Comprehensive Cancer Center and Division of Oncology-Hematology, University of California, 94143-1770, San Francisco, CA