The ovarian cancer cell lines, SKOV3ip1 and HeyA8, were obtained from ATCC and were maintained in RPMI 1640 supplemented with 15% fetal bovine serum and 0.1% gentamicin sulfate (Gemini Bioproducts; Calabasas, CA)38 (link). SKOV3-TR and HeyA8-MDR were kind gifts from Dr. Isaiah Fidler, Department of Cancer Biology, University of Texas M. D. Anderson Cancer Center and Dr. Michael Seiden, Department of Medicine, Massachusetts General Hospital, respectively.