HCC70, HCC1143, HCC1187, HCC1937, HCC1954, HCC1806, AU565, BT474, MCF7, MDAMB231, MDAMB436 and BT549 cell lines were purchased directly from ATCC. The MB468 cell line was engineered to express luciferase and was obtained from Dr. A. Kung (Memorial Sloan Kettering Cancer Center). All cell lines were tested for Mycoplasma infection by PCR every 3 months. Only early-passage cell lines were used and cells were kept in culture no longer than 21 days. Cell lines were obtained in 2012 with the exception of MDAMB231 that was obtained in 2016. Cell lines were authenticated by short tandem repeat (STR) analysis. Bortezomib was purchased from LC Laboratories. E7107 (18 (link)) was kindly provided by H3 Biomedicine, Inc.