[1] Univ Marburg, Inst Physiol Chem, Dept Physiol Chem, D-35043 Marburg, Germany
[2] German Canc Res Ctr, D-6900 Heidelberg, Germany
[3] Univ Essen Gesamthsch, Dept Internal Med & Tumor Res, D-4300 Essen, Germany
[4] Univ Freiburg, Tumor Biol Ctr, Freiburg, Germany