A current perspective on the oncopreventive and oncolytic properties of selective serotonin reuptake inhibitors

Current cancer research strongly focuses on identifying novel pathways that can be selectively exploited in the clinic and identifying drugs capable of exploiting cancer vulnerabilities. Occasionally, drugs identified to exploit a cancer-specific vulnerability are on the market for clinical indications in another disease area. Rebranding them as anti-cancer drugs is a process commonly referred to as drug repurposing and is typically a faster method than bringing a novel drug to market. Selective serotonin reuptake inhibitors (SSRIs) are primarily used for treating several types of depression, but over the past two decades mounting evidence suggests that drugs in this class have oncolytic properties and reduce the risk of certain cancers. In the current work, we discuss how the secondary mechanisms of action associated with these drugs mediate their oncolytic effect. In particular, sertraline limits tumor growth by abrogating the PI3K/akt signaling pathway, a growth pathway shown to be constitutively active in multiple cancers. Fluoxetine has been shown to activate the AMPA-type glutamate receptor, induce massive calcium influx and mitochondrial calcium overload and induce caspase-9-dependent apoptosis. This receptor being highly overexpressed in cancer stem cells may explain why SSRIs lower the risk of multiple types of cancer. Fluoxetine has also been shown to inhibit multidrug resistance pumps, increasing the efficacy of several standard chemotherapies. Given the vast potential of SSRIs in treating cancer, these drugs should be more heavily used not only in treating cancer-related depression, but in combating cancer and increasing the efficacy of standard of care chemotherapies.