Cancer is a leading cause of death worldwide and has propensity for rapid mutation,which constantly challenges our ability to treat aggressive forms. There is an unmet need
for next generation cancer medicine capable of overcoming chemotherapeutic resistance
in cancer. Ferroptosis is a form of regulated cell death that is caused by the iron dependent
peroxidation of lipids1,2. The glutathione-dependent lipid hydroperoxidase
glutathione peroxidase 4 (GPX4) prevents ferroptosis by converting lipid hydroperoxides
into non-toxic lipid alcohols3,4. Ferroptosis has been implicated in the cell death that
underlies several degenerative conditions2, and induction of ferroptosis by inhibition of
GPX4 has emerged as a therapeutic strategy to trigger cancer cell death5. However,
sensitivity to GPX4 inhibitors varies greatly across cancer cell lines6, suggesting that
additional factors govern resistance to ferroptosis.
Here in this dissertation, we employ a synthetic lethal CRISPR/Cas9 screen, and we
identify ferroptosis suppressor protein 1 (FSP1) (previously known as apoptosis-inducing
factor mitochondrial 2 (AIFM2)) as a potent ferroptosis resistance factor. Our data indicate
that myristoylation recruits FSP1 to the plasma membrane where it functions as an
oxidoreductase that reduces coenzyme Q10 (CoQ), generating a lipophilic radical-trapping
antioxidant that halts the propagation of lipid peroxides. We further find that
FSP1 expression positively correlates with ferroptosis resistance across hundreds of
cancer cell lines, and that FSP1 mediates resistance to ferroptosis in lung cancer cells in
culture and in mouse tumor xenografts. Thus, our data identify FSP1 as a key component
of a non-mitochondrial CoQ antioxidant system that acts in parallel to the canonical
glutathione-based GPX4 pathway. These findings define a new ferroptosis suppression
pathway and indicate that pharmacological inhibition of FSP1 may provide an effective
strategy to sensitize cancer cells to ferroptosis-inducing chemotherapeutics.
In addition, we screened more than 120,000 compounds using an in vitro FSP1 activity
assay and identified 168 compounds that directly inhibit FSP1 oxidoreductase activity.
We further characterized 19 FSP1 inhibitors, belonging to 7 structurally distinct groups,
and find that these compounds exhibit synthetic lethality with loss of GPX4 in H460 lung
cancer cells. The most potent of these FSP1 inhibitors, ferroptosis sensitizer 1 (FSEN1),
acts specifically through inhibition of FSP1 to sensitize cancer cells of different tissueorigins to ferroptosis induced by multiple compounds targeting the GSH-GPX4 pathway.
Together, our results define several structurally unique FSP1 inhibitors that sensitize
cancer cells to ferroptosis, providing tools for the study of FSP1 biology and enabling
further exploration of the potential of FSP1 as a therapeutic target.