Tubacin mediates the synthetic lethality of cysteine in breast cancer independent on HDAC6

Triple-negative breast cancer (TNBC) has a highly aggressive nature and distinct molecular characteristics from other subtypes of breast cancer and lacks effective targeted therapy. The molecular and genetic basis of cysteine/cystine dependency in TNBC is complex. We found that cysteine addiction associates with the expression of a set of Claudin genes in TNBC. The Claudin-high TNBCs are independent on cystine, while the Claudin-low TNBCs undergo rapid ferroptosis upon cystine deprivation or inhibition of cystine transport by erastin. To overcome the resistance of Claudin-high TNBC and luminal breast cancer to the potential targeted cystine-addiction therapy, we explored the synthetic lethality of cysteine by an epigenetic compound library screen. Several potent HDAC6 inhibitors were identified and rendered the Claudin-high TNBCs and luminal cancer cells dependent on extracellular cystine and undergoing ferroptosis upon cystine deprivation. The transcriptomic profiling showed that the HDAC6 inhibitor tubacin in combination with erastin activates a synthetic-lethal transcriptional program. Together, we have identified the HDAC6 inhibitors as potent therapy-sensitizers to revive the targeted cysteine-addiction therapy for various subtypes of breast cancer, not limit in the Claudin-low TNBC. RNA was extracted by RNAeasy kits (Qiagen) from the HCC38 cells that were exposed to the control, 5 µM erastin, 5 µM tubacin, or the combination of erastin and tubacin for 18 hours (three replicates in each condition).