Abstract 1981P
Background
Tamoxifen (Tam) resistance poses a significant challenge for successfully treating breast cancer (BCa). It has been shown to increase oxidative stress and induce cell death by regulation of reactive oxygen species (ROS) which accumulation leaded to the production of lipid hydroperoxides. Ferroptosis, a cell death process riven by the accumulation of iron-dependent lipid hydroperoxides, has been induced by inactivation/depletion of glutathione peroxidases (GPxs).
Methods
The RelB level were examined by IHC and western blot in BCa tumor tissues and cell lines. The cell viability were determined by colony survival and MTT. The ROS and oxygen consumption rates were measured using ROS detection probes and a Seahorse XF96 Analyzer. The lipid peroxidation level was analyzed by immunofluorescence assay. The morphological changes of mitochondria were observed by TEM. RelB binding to the NF-κB intronic enhancer region of the human GPx4 gene was determined using a ChIP assay. The effect of RelB on BCa Tam resistance was further validated using BCa mice xenograft models.
Results
RelB was uniquely expressed at the high level in Tam resistance BCa tissues and cell lines, and correlated to BCa progression and patient survival. Down-regulation of RelB remarkably sensitized resistance cells to Tam. The high level of ROS and declination of mitochondrial respiration which induced by Tam were inhibited in resistant cells. Tam enhanced lipid peroxidation with concomitant non-apoptotic cell death, which are negatively regulated by GPx4 activity. In addition to GPx4 knockdown, deferoxamine was able to rescue Tam-induced cell death at certain extent in breast cancer cells. Importantly, RelB upregulates GPx4 expression through binding to an NF-κB enhancer element located at the 5’-flanking region. Consistently, in vivo functional validation confirmed that RelB inhibition not only impairs tumor growth, but also inhibits Tam resistance in nude mice.
Conclusions
It's demonstrated that the RelB-based noncanonical NF-κB pathway plays a predominant role in mediating the sensitivity of Tam in BCa. RelB could inhibit ferroptosis which induced by hydroxyl radicals accumulation through upregulating GPx4 in BCa.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
The National Natural Science Foundation of China.
Disclosure
All authors have declared no conflicts of interest.