Dual targeting of BRAFV600E and ferroptosis results in synergistic anticancer activity via iron overload and enhanced oxidative stress

While combination BRAF and MEK inhibitor treatment in BRAFV600E-mutant cancers results in a response, treatment resistance and toxicity are common. Ferroptosis is an iron-dependent form of non-apoptotic cell death. BRAF inhibition has been associated with increased sensitivity to ferroptosis that is dependent on Glutathione Peroxidase 4 (GPX4). In vitro, ex vivo, and in vivo models of anaplastic thyroid cancer (ATC) were used to evaluate the anticancer activity of combination BRAF inhibition and ferroptosis induction. Targeting key regulators of ferroptosis—GPX4, using RSL3 and ML162, and system Xc−, using erastin—induced significant cell death in all ATC cell lines. Combination of dabrafenib and RSL3 synergistically increased cell death in BRAFV600E-mutant ATC cells, and significantly inhibited colony formation. Mechanistically, lipid peroxidation, reactive oxygen species levels, and intracellular Fe2+ increased significantly with combination treatment compared with each agent alone. Analysis of cell membrane iron importers and exporters showed significantly lower expression of ferroportin-1 (an iron exporter), suggesting the synergistic anticancer activity was due to increased iron accumulation and oxidative stress, leading to enhanced ferroptotic cell death. BRAFV600E-mutant ATC cell spheroids showed synergistic cell death with dabrafenib and RSL3 treatment. In vivo, combination dabrafenib and ferroptosis induction (by targeting GPX4 using C18, and system Xc− with IKE) significantly inhibited tumor growth in an orthotopic ATC mouse model. Additionally, dabrafenib-resistant BRAFV600E-mutant ATC cells were more sensitive to ferroptosis induction than parental cells. Dual targeting of BRAFV600E and ferroptosis results in synergistic anticancer activity and overcomes resistance to BRAF inhibition.