Cell death is crucial for normal development, homeostasis and the prevention of hyper-proliferative diseases such as cancer (Fuchs and Steller, 2011; Thompson, 1995). It was once thought that almost all regulated cell death in mammalian cells resulted from the activation of caspase-dependent apoptosis (Fuchs and Steller, 2011; Thompson, 1995). More recently this view has been challenged by the discovery of several regulated non-apoptotic cell death pathways activated in specific disease states, including poly(ADP-ribose) polymerase-1 (PARP-1) and apoptosis inducing factor 1 (AIF1)-dependent parthanatos, caspase-1-dependent pyroptosis and receptor interacting protein kinase 1 (RIPK1)-dependent necroptosis (Bergsbaken et al., 2009; Christofferson and Yuan, 2010; Wang et al., 2009). It is believed that additional regulated forms of non-apoptotic cell death likely remain to be discovered that mediate cell death in other developmental or pathological circumstances.
The RAS family small GTPases (HRAS, NRAS and KRAS) are mutated in about 30% of all cancers (Vigil et al., 2010). Finding compounds that are selectively lethal to RAS-mutant tumor cells is, therefore, a high priority. Two structurally unrelated small molecules, named erastin and RSL3, were previously identified. These molecules were selectively lethal to oncogenic RAS-mutant cell lines, and together, they were referred to as RAS-selective lethal (RSL) compounds (Dolma et al., 2003; Yang and Stockwell, 2008). Using affinity purification, voltage dependent anion channels 2 and 3 (VDAC2/3) were identified as direct targets of erastin (Yagoda et al., 2007), but not RSL3. ShRNA and cDNA overexpression studies demonstrated that VDAC2 and VDAC3 are necessary, but not sufficient, for erastin-induced death (Yagoda et al., 2007), indicating that additional unknown targets are required for this process.
The type of cell death activated by the RSLs has been enigmatic. Classic features of apoptosis, such as mitochondrial cytochrome c release, caspase activation and chromatin fragmentation, are not observed in RSL-treated cells (Dolma et al., 2003; Yagoda et al., 2007; Yang and Stockwell, 2008). RSL-induced death is, however, associated with increased levels of intracellular reactive oxygen species (ROS) and is prevented by iron chelation or genetic inhibition of cellular iron uptake (Yagoda et al., 2007; Yang and Stockwell, 2008). In a recent systematic study of various mechanistically unique lethal compounds, the prevention of cell death by iron chelation was a rare phenomenon (Wolpaw et al., 2011), suggesting that few triggers can access iron-dependent lethal mechanisms.
Accordingly, there is a need for the exploration of various pathways of regulated cell death, as well as for compositions and methods for preventing the occurrence of regulated cell death. This invention is directed to meeting these and other needs.