Cell Metab. https://doi.org/10.1016/j.cmet.2019.01.020 (2019)

Glutamate–cysteine ligase (GCL)-mediated production of glutathione (GSH) mitigates oxidative stress in cells. Blocking GSH production through use of l-buthionine sulfoximine (BSO), an inhibitor of the catalytic subunit of GCL (GCLC), has been proposed as a cancer therapy strategy. However, it is not clear whether this approach is applicable to all types of cancer cells. Harris et al. performed a systematic analysis of CRISPR–Cas9 screening data on 300 different cancer cell lines and found that GCLC did not score as a dependency in these cell lines. However, long-term treatment with BSO revealed clusters of highly sensitive and resistant cell lines. A CRISPR–Cas9 screen on a BSO-resistant cancer cell line combined with a small-molecule screen to identify modulators of BSO resistance revealed that inhibition of deubiquitinases (DUBs) sensitized cells to GSH depletion. Combined inhibition of DUBs and GSH increased proteotoxic and ER stress, resulting in cell death. Finally, an additional CRISPR–Cas9 screen to identify modifiers of BSO/DUB inhibitor treatment revealed the anti-apoptotic protein XIAP and mTOR signaling as regulators of sensitivity. Overall, the combination of DUB and GSH inhibition reveals a new mechanism of cancer vulnerability.