Reactive oxygen species mediate cancer stem-like cells and determine bortezomib sensitivity via Mcl-1 and Zeb-1 in mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an aggressive, incurable non-Hodgkin B-cell lymphoma with good initial response to therapy then subsequently relapse. Cancer stem cells (CSCs) are considered to be an underlying cause of these inevitable drug resistance and tumor regrowth, but how CSCs are regulated is largely unknown. We demonstrate here for the first time the existence of CSC-like subpopulations that are modulated by reactive oxygen species (ROS) in MCL cell lines and patient-derived primary cells in an inverse correlation with bortezomib (BTZ) sensitivity. Using various known donors and inhibitors of cellular superoxide (O), hydrogen peroxide (HO) and hydroxyl radical (OH), we unveil their distinct roles in the regulation of CSC-like subpopulations and thus MCL response to BTZ. O inhibits CSC-like cells and sensitizes BTZ-induced apoptosis, whereas HO conversely enriches CSC-like cells and protects against apoptosis and OH has minimal effects. We further observed that an anti-apoptotic Mcl-1 and a transcription factor Zeb-1 are favorable targets of O and HO, respectively. Using small molecule inhibition, ectopic expression and CRISPR/Cas9-mediated gene manipulation, we verified the roles of Mcl-1 and Zeb-1 in CSC and apoptosis regulation by O and HO. Our findings provide a novel mechanistic insight into the significance of redox status of MCL cells in determining their drug response via CSC-like subpopulations, which are imperative to a better understanding of therapeutic resistance and relapse.